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EKELE, DAVID EJIGA
PG/M.Sc/13/65552
PHYSICOCHEMICAL, SENSORY AND MOISTURE SORPTION CHARACTERISTICS OF INTERMEDIATE
MOISTURE SMOKED MEAT PRODUCTS.
DEPARTMENT OF FOOD SCIENCE AND TECHNOLOGY
Ebere Omeje Digitally Signed by: Content manager’s Name
DN : CN = Webmaster’s name
O= University of Nigeria, Nsukka
OU = Innovation Centre
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PHYSICOCHEMICAL, SENSORY AND MOISTURE SORPTION
CHARACTERISTICS OF INTERMEDIATE MOISTURE
SMOKED MEAT PRODUCTS.
BY
EKELE, DAVID EJIGA
PG/M.Sc/13/65552
DEPARTMENT OF FOOD SCIENCE AND TECHNOLOGY
UNIVERSITY OF NIGERIA, NSUKKA
AUGUST, 2016
i
TITLE PAGE
PHYSICOCHEMICAL, SENSORY AND MOISTURE SORPTION CHARACTERISTICS
OF INTERMEDIATE MOISTURE SMOKED MEAT PRODUCTS
A PROJECT SUBMITTED TO THE DEPARTMENT OF FOOD SCIENCE AND
TECHNOLOGY, UNIVERSITY OF NIGERIA, NSUKKA, IN PARTIAL FULFILMENT
OF THE REQUIREMENTS FOR THE AWARD OF THE DEGREE OF MASTER OF
SCIENCE (M.Sc) IN FOOD SCIENCE AND TECHNOLOGY
BY
EKELE, DAVID EJIGA
PG/M.Sc/13/65552
DEPARTMENT OF FOOD SCIENCE AND TECHNOLOGY, UNIVERSITY OF
NIGERIA NSUKKA
AUGUST, 2016
ii
CERTIFICATION
Mr. Ekele, David Ejiga, a postgraduate student in the Department of Food Science and
Technology with registration number PG/M.Sc/13/65552, has satisfactorily completed the
requirements for the award of the Degree of Master of Science (M.Sc) in Food Science and
Technology. The work embodied in his project report is original and has not been submitted in
part or full for any other diploma or degree of this or any other university.
Prof. T. M. Okonkwo
Supervisor
Department of Food Science and Technology,
University of Nigeria, Nsukka.
Prof. T. M. Okonkwo
Head of Department,
Food Science and Technology,
University of Nigeria, Nsukka.
iii
ACKNOWLEDGEMENT
I wish to express my profound gratitude to God Almighty for his Grace and Faithfulness. I also
wish to express my sincere gratitude to my supervisor, Professor T. M. Okonkwo, for his fatherly
guidance throughout the duration of this work. He provides most of the materials/equipments and
laboratory chemicals for this research. Sir, I’m highly indebted to you. I’m very grateful to Prof.
Iro, Nkama for his advisory role and provision of relevant materials. My immense gratitude is
also due to Dr. C. O. Orishagbemi, for his moral support and encouragement. Many thanks also
go to Mr. Abel Maji, (The Chief Technologist, Department of Food, Nutrition and Home
Sciences, Kogi State University), for his unrelented effort to provide me with all laboratory
chemicals to get the best result and also his encouragement in the course of this study. This study
could not have been carried out satisfactorily without the corporation of my wife. It is, therefore,
a pleasure to thank my lovely wife, Mrs. Akwu, Susan for being there for me under the sun or in
the rain. Many thanks also go to the entire members of staff of the Department of Food Science
and Technology, University of Nigeria, Nsukka, for their moral support and assistance at various
stages of this study. Much gratitude goes to Mr. Amove, Julius for his assistance at various
stages of this study which included literature and interpretation of the results of this research.
Finally, I wish to express gratitude to my classmates among who were Ochimana, T. O., Ogbobe
Nkem, Inyama, C. R., Azuka, U. I., Azuka, Chinonye for their moral support.
iv
TABLE OF CONTENT
TITLE PAGE i
CERTIFICATION ii
ACKNOWLEDGMENT iii
TABLE OF CONTENT iv
LIST OF TABLES viii
LIST OF FIGURES ix
ABSTRACT x
CHAPTER ONE: INTRODUCTION
1.1 Statement of Problem 3
1.2 Justification 3
1.3 Broad objective 4
1.4 Significance of study 5
CHAPTER TWO: LITERATURE REVIEW
2.1 Intermediate Moisture Meats 6
2.1.1 Preparation of Intermediate Moisture Meats 6
2.1.1.1 Formulation 6
2.1.1.2 Method of Production 8
2.1.2 Storage Stability of Intermediate Moisture Meats 10
2.2 Water Sorption Phenomenon in Foods 10
2.2.1 Water Activity: Definition and Importance in Food Systems 12
2.2.2 Measurement of Water Activity 13
2.2.3 Controlled Water Activity Environments 14
2.3 Moisture Sorption Isotherms 16
2.3.1 Sorption Isotherm Hysteresis 21
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2.3.2 Effect of temperature on Sorption Isotherms 22
2.4 Influence of Moisture and Other Factors on Stored Products 24
2.5 Sorption Models 24
CHAPTER THREE: MATERIALS AND METHODS
3.1 Materials 30
3.2 Methods 30
3.2.1 Sample Preparation 30
3.2.2 Formulation of Infusing Solution 31
3.2.3 Cook-Soak Equilibration 31
3.2.4 Smoking 31
3.3 Physicochemical Characteristics 31
3.3.1 Moisture Determination 31
3.3.2 Fat Content 33
3.3.3 Protein Determination 33
3.3.4 Ash Content Determination 34
3.3.5 Hydrogen Ion Concentration (pH) 34
3.3.6 Thiobarbituric Acid (TBA) Test 34
3.3.7 Protein Solubility in SDS-β-Mercapto ethanol solution 35
3.3.8 Water Activity 36
3.4 Sensory Evaluation of Samples 36
3.5 Sorption Experiments 36
3.5.1 Experimental Temperature 36
3.5.2 Experimental Water Activities 38
3.5.3 Equilibrium Moisture Content (EMC) 40
3.5.4 Experimental Design 41
vi
3.5.5 Experimental Procedure 41
3.5.6 Sorption Data Analysis 43
3.6 Statistical Analysis 45
CHAPTER FOUR
4.1.1 Moisture Content 46
4.1.2 Fat Content 48
4.1.3 Crude Protein Content 48
4.1.4 Ash Content 49
4.1.5 pH of Samples 49
4.1.6 Thiobarbituric Acid Content 49
4.1.7 Protein Solubility 50
4.1.8 Water activity 50
4.2 Sensory Characteristics 51
4.2.1 Appearance 51
4.2.2 Texture 53
4.2.3 Flavour 53
4.2.4 Taste 53
4.2.5 General Acceptability 54
4.3 Moisture Sorption Studies 54
4.4 Sorption Data Analysis 55
4.4.1 Oswin Model 55
4.4.2 Henderson Model 59
4.4.3 Brunauer-Emmet-Teller (BET) Model 62
4.4.4 GAB Model 63
4.4.5 Goodness of Fit Models 66
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CHAPTER FIVE
5.0 CONCLUSION AND RECOMMENDATION 69
5.1 Conclusion 69
5.2 Recommendation 70
5.3 Contribution of the Research Work 70
5.3.1 The Consumers 70
5.3.2 The Academic Community 71
5.3.3 The Food Industry 71
REFERENCES 72
viii
LIST OF TABLES
Table 1 composition of infusing humectants 32
Table 2 Sensory evaluation and scoring description format 37
Table 3 Water activity of sulfuric acid solution at selected concentration and temperature 39
Table 4 Models fitted to the experimental data 42
Table 5 Physicochemical characteristics of intermediate moisture meat samples 47
Table 6 Sensory characteristics of intermediate moisture meat (IMM) samples 52
Table 7 Oswin regression parameters 60
Table 8 Henderson regression parameters 61
Table 9 BET regression parameters 64
Table 10 GAB isotherm regression parameter derivatives for IMSM 65
Table 11 % RMS of sorption isotherm models for intermediate moisture smoked meat samples at different temperatures 67 Table 12 Correlation coefficient of sorption isotherm models for intermediate moisture smoked meat samples at different temperatures 68
ix
LIST OF FIGURES
Figure 1 Adsorption and desorption isotherms showing hysteresis 17
Figure 2 Partition of moisture sorption isotherms 19
Figure 3 Sorption isotherms classification 20
Figure 4 Moisture sorption isotherms of intermediate moisture smoked meat containing 6 % glycerol + 18 h smoking at equilibrium moisture content at temperatures of 20 oC (A), 30 oC (B) and 40 oC (C) 56 Figure 5 Moisture sorption isotherms of intermediate moisture smoked meat containing 12 % glycerol + 18 h smoking at equilibrium moisture content at temperatures of 20 oC (A), 30 oC (B) and 40 oC (C) 57 Figure 6 Moisture sorption isotherms of intermediate moisture smoked meat containing 18 % glycerol + 18 h smoking at equilibrium moisture content at temperatures of 20 oC (A), 30 oC (B) and 40 oC (C) 58
x
ABSTRACT This research work was carried out to evaluate the physicochemical, sensory and moisture sorption characteristics of intermediate moisture smoked meat products (IMSM). The products were produced by cook-soak equilibration of meat pieces in solutions containing 6 %, 12 % and 18 % glycerol, in addition to salt (2.5), sodium nitrite (0.016 %) and the remainder was water. The 2 cm3 meat pieces were placed in the infusing solution at the rate of 180 g and ratio of 2: 3 (meat: solution) and cooked at 77 oC to an internal temperature of 70 oC for 15 minutes in a water bath, followed by equilibration at room temperature for 16 h. samples were either unsmoked or lightly smoked (4 h) or heavily smoked (18 h) at 60 oC ± 10 oC. A portion of the unsmoked, 4 h and 18 h smoked samples were subjected to physicochemical and sensory quality evaluation while the remainder were used for moisture sorption studies. Equilibrium moisture content was determined gravimetrically at 20 oC, 30 oC and 40 oC by exposing the samples to atmospheres of known relative humidities, using sulfuric acid solutions of 15, 20, 30, 40, 50 and 60 % to provide water activities of 0.15 to 0.96. The results showed that the raw meat moisture content to be 77 %. This reduced to 57-66 % on cooking/equilibration and intermediate moisture level of 18.5-24.5 % on 4h smoking and 17.66-18.5 % on 18 h smoking. Water activity followed similar trend (0.74-0.92 after cooking, 0.66-0.85 after 4 h smoking and 0.6-0.75 after 18 h smoking). Both proteins, fat and ash contents increased per unit weight on smoking due to concentration resulting from moisture loss. Protein solubility was high in all samples (76-87 %) while thiobarbituric acid number was low (0.28-0.49 mg malonaldehyde per kg sample) in the smoked samples. Samples smoked for 18 h were ‘moderately liked‘(7.4, 7.3 and 7.5 respectively for samples containing 6 %, 12 % and 18 % glycerol). Samples smoked for 4 h were slightly liked (6.2 and 6.9 respectively for samples containing 6 % and 18 % glycerol). The unsmoked samples were the least liked (5.2, 5.0 and 4.9 respectively for samples containing 6 %, 12 % and 18 % glycerol). The moisture sorption isotherms exhibited sigmoidal shaped curves and the differences between adsorption and desorption processing resulted to hysteresis. Of all models tested, Oswin gave the best fit in terms of percentage root mean square (% RMS) for adsorption and desorption (0.64-4.68 and 0.77-1.69 respectively) compared to Henderson (1.4-9.1 and 1.39-3.89 respectively), Guggenhein Anderson and de-Boar (GAB)(10.86-13.02 and 10.21-11.90 respectively) and Brunauer-Emmet-Teller (BET)(5.8-16.13 and 6.42-13.02 respectively). The
values of Mo ranged from 7.5 to 9.5 for adsorptive mode and from 10.9 to 19.6 for desorptive mode. Using Oswin model % RMS as a guide, it was observed that desorption processing was predicted to give better product stability (average % RMS= 1.19) compared to adsorption (average % RMS= 2.32). Also products were predicted to be more stable at 20 oC storage (average % RMS= 1.2) compared to 30 oC (average % RMS=1.84) and 40 oC (average % RMS= 2.22). Products containing 6 % glycerol would be more stable (average % RMS= 1.63) compared to products containing 12 % glycerol (average % RMS= 1.76) or 18 % glycerol (average % RMS= 1.88).
1
CHAPTER ONE
INTRODUCTION Meat is animal flesh that is eaten as food (Lawrie and Ledward, 2006). It is mainly composed of
water and protein and is usually eaten together with other foods. It also contains some vitamins,
minerals and calorie source. Adult mammalian muscle flesh consists of roughly 75 % water, 19
% protein, 2.5 % intramuscular fat, 1.2 % carbohydrate and 2.3 % other soluble non-protein
substances. These include nitrogenous compounds such as amino acids and inorganic substances
such as minerals (Lawrie and Ledward, 2006). Meat consumption varies worldwide, depending
on cultural or religious preferences, as well as economic conditions. Vegetarians choose not to
eat meat because of ethical, economic, environmental, and religious or health concerns that are
associated with meat production and consumption.
Traditionally, in Nigeria, fresh meat is pre-cooked in water without adding any ingredients,
spices or preservatives and hot smoked to yield hard, desiccated and sometimes brittle products.
Thus, the products are of low aesthetic and organoleptic quality (Okonkwo, 1987). The quality of
the products could probably be improved by intermediate moisture meat processing techniques.
Obanu (1981) observed that intermediate moisture meats (IMM) are shelf stable under the
tropical climate without refrigeration and may be eaten directly with or without rehydration.
Hollis et al. (1968) defined intermediate moisture meats (IMM) as products which are partially
dehydrated but contain enough solids to bind the remaining water and make it unavailable for
microbial growth and physico-chemical reactions. Ogunsola and Omojola (2008) stated that
intermediate moisture meat is used to describe meat products that have less than 30 % of
moisture. The term “intermediate moisture food” has been used to identify heterogeneous groups
of foods which resemble dry foods in that they are resistant to bacterial spoilage but contain too
2
much moisture (generally, 15-50 %) to be considered dry. Although intermediate moisture
products are microbiologically more stable than raw or cooked meat, they are still subject to
deterioration through chemical and physical processes including oxidation, protein degradation,
cross-linkages and browning which can reduce their nutritive value and eating quality (Obanu et
al., 1975a,b; Webster et al., 1986). It is possible that when meat is processed to intermediate
moisture levels, the incorporation of smoke components could further stabilize the products
during storage.
The stability and nutritive value of meat products may be affected by oxidation reactions such as
rancidity and decrease the biological value of proteins and destroys some vitamins. Although,
smoking originated without any concern for oxidation, it is interesting to note that smoked
products are known to have increased resistance to oxidative effects. Phenolic substances
available in wood smoke have been shown to exhibit antioxidant effects on smoked meat (Daun,
1969; Tilgner and Daun, 1970; Toth and Potthast 1984).
The smoking of meat implies the exposure of meat to the action of smoke components, heat and
flow of gases (Daun, 1975). Smoking is a well-established method of meat processing in Nigeria
and many other countries of the world. Though meat was originally smoked for the purpose of
preservation and flavor development, but the modern advancements in food preservation
techniques have made the emphasis on the preservative roles of smoking to decline. The result is
that meat is smoked for the purpose of development of desirable flavor, color, texture, protection
from oxidation and creation of new products. The development of improved smoking ovens or
kilns and new methods of making smoke and smoking have made this advancement possible.
3
Moisture sorption isotherms are important thermodynamic means for evaluating interactions of
water and food substances, and provide information to examine food processing operations such
as drying, mixing, packaging and storage (Hossain et al., 2001). The knowledge of the sorption
characteristics is essential to understanding the stability in storage and acceptability of these
intermediate moisture meats, modelling the drying process, designing and optimizing the drying
equipment, and calculating the moisture content changes which may occur during storage, and for
selecting appropriate packaging materials (Ngoddy and Bakker-Arkema, 1975; Samapundo et al,
2006).
1.1 Statement of the Problem
Meat is a highly perishable product and becomes unfit to eat due to microbial growth, chemical
changes and breakdown by endogenous enzymes. Meats are subject to diverse conditions during
processing and storage; changes that occur result from microbiological, physical and /or
biochemical processes (Labuza 1975). These physical and chemical changes therefore appear to
be the major deteriorative reactions in intermediate moisture meat. Poor processing, handling,
and packaging of intermediate moisture meats have contributed largely to the small amount of
acceptability and consumption, which subsequently affect the quality and shelf- life of the
product. Degradation, discoloration and loss of muscle pigments (myoglobin and haemoglobin)
also occur in intermediate moisture meats during storage.
1.2 Justification Smoked meat products are popular meat products in Nigeria and all over the world. Intermediate
moisture smoked meats are varieties of smoked meat products. The intermediate moisture
smoked meat products are more stable, softer in texture and more desirable to eat. Effective
processing and safe storage of this intermediate moisture smoke meat product remains a major
4
problem. High wastage could also occurs as a result of storage under Nigerian high temperature
and humidity, leading to short shelf-life and low aesthetic and organoleptic quality, making the
products less acceptable to the discriminating and well-to-do meat consumer (Okonkwo, 1987).
In order to fully realize the gains of the dual potentials offered by intermediate moisture smoked
meat products, effective and satisfactory processing and storage technologies must be developed
through the knowledge from their moisture sorption studies, to predict stability in storage,
acceptable high quality smoked meat product that would be moist, chewy and have good mouth
feel. Development and quality evaluation of intermediate moisture smoked meat products were
earlier studied by Okonkwo (2001). The study involved analysis of samples containing 0 % to 18
% glycerol but the moisture sorption isotherm of the product was not studied. Since the author
found 0 % glycerol unstable during storage and unacceptable by consumers, the present study
focused on the evaluation of moisture sorption isotherm of similar samples treated with glycerol.
1.3 Broad Objective:
The broad objective of this study was to determine the physicochemical, sensory and moisture
sorption characteristics of intermediate moisture smoke meat products.
The specific objectives were to:
1. Produce intermediate moisture smoked meat products using cook-soak-equilibration
techniques in solution of glycerol, salt and sodium nitrite.
2. Determine the physicochemical and sensory properties of intermediate moisture smoked
meat products.
3. Determine the moisture transfer characteristics of the intermediate moisture smoked meat
product as influenced by storage environments.
5
1.4 Significance of the study
The sorption isotherm describes the interaction between water and food product. Such
relationships are key to understanding the moisture sorption properties of food, being of
particular value when selecting suitable packaging materials, predicting stability and moisture
changes during storage, equipment design for drying and determination of critical moisture and
water for acceptability of products that deteriorate mainly by moisture gain. Sorption isotherms
are employed in process design and control, such as in predicting the end point of drying and
optimizing ingredient selection in food formulations.
6
CHAPTER TWO
LITERATURE REVIEW
2.1 Intermediate Moisture Meats
These are meat products, which contain too much water to be considered as dry meat but less
water to be considered as high moisture meat. Hollis et al. (1968) defined intermediate moisture
meat as meat products which are partially dehydrated but contain enough solids to bind the
remaining water and make it unavailable for microbial growth and physico-chemical reactions.
Intermediate moisture meats usually have moisture contents between 15 to 50 % and water
activity within 0.65 to 0.90. The products are therefore intermediate between fresh meats (with
moisture content above 50 % and water activity above 0.91) which spoil very rapidly and dried
meats (with moisture content below 15 % and water activity below 0.65) which although are
more shelf stable, have poor texture and are usually expensive. Intermediate moisture meat
requires no rehydration, has a soft plastic texture and is more shelf stable than high moisture
meat and can be formulated to meet specific nutrients needs. Other advantages of intermediate
moisture meats include low bulk and weight, addition of variety to existing types of processed
meats, convenient and ready-to-eat products, and safe for consumption, resistant to microbial
attack and is suitable for the preservation of meat in the developing countries, particularly in
Africa, where modern means of food preservation such as canning, freezing, refrigeration e.t.c
are limiting.
2.1.1 Preparation of Intermediate Moisture Meats
2.1.1.1 Formulation The infusing solution used in the preparation of intermediate moisture meats may consist of
single additive or a combination of additives. As discussed by Ledward (1981), such an infusing
solution should not have deleterious effects on the organoleptic quality of the final intermediate
7
moisture product. It should be highly soluble, stable, non volatile, edible in large quantities and
metabolizable without adverse effect. Although none of the compound used in producing
intermediate moisture meats has fully satisfied these ideal conditions, several compounds have
been tried and the list includes sodium chloride, sucrose, glucose, fructose, glycerol, propylene
glycol, corn starch, gelatin, protein hydrolysate, polyethylene glycol, serum albumin (Brockman,
1970; Pawsey and Davies, 1976; Chirife et al., 1980; Ledward, 1981; Vellejo-cordoba et al.,
1986). These are incorporated into the meats for the purpose of lowering the water activity of the
meat in order to increase its shelf-stability. Salt (sodium chloride) is the most effective in
reducing water activity and preventing microbial growth but the level at which it is effective
imparts undesirable salty flavor on the products (Ledward, 1981). High salt intake has some
adverse physiological effects and these discourage its use in large quantities to stabilize
intermediate moisture meats for human consumption. However, salt is still used in small
quantity, to the limit of normal seasoning. Also novel functional sodium chloride compositions
which contain sodium gluconate as a substitute for sodium chloride are being introduced
(Kakikuchi et al, 1998). These novel salts are prepared by adding 40 to 400 parts by weight of
sodium gluconate to 100 parts by weight of compounds containing 40 to 60 % by weight of
sodium chloride and 40 to 60 % by weight of potassium chloride. These compounds are useable
as table salts for seasoning foods or imparting the required saltiness to foods. Sugars are
popularly used but the levels at which they are effective impart excessive sweet sugary taste to
the products and therefore objectionable. Glycerol is mostly used because it is soluble, stable,
non volatile, odorless, colorless, has less flavor impart than salt and sugars, although it still gives
detectable sweet taste. Other polyhydric alcohols such as propylene glycol, 1,3-butylene glycol,
sorbitol e.t.c have been suggested as good alternative to glycerol but they appear to be less
8
effective than glycerol in reducing water activity. As noted by Troller and Christian(1981), the
production of intermediate moisture meats for human consumption has met with limited success
because of the adverse effects the various humectants have on the flavor of the intermediate
moisture meats, most often resulting to low acceptability and palatability. This has led Dymsza
and Silverman (1979) to apply the intermediate moisture desorption (IMD) technique, in which
the humectants used in the preparation of intermediate moisture meat are leached out just prior to
consumption. Products whose infusing humectants have been removed just prior to consumption
possess better acceptability and palatability than the original intermediate moisture meat.
Although almost all bacterial growth can be retarded at water activity of less than 0.85, many
fungi can still grow in foods with normal pH and such water activity (Scott, 1953; Jay, 1979).
More especially as the inhibition of bacteria eliminates competition. This is why most
intermediate moisture meats are formulated with antimycotics as part of the infusing ingredients.
Sorbic acid and its potassium salt appear to be the most popular and widely used. It is stable
(Boyd and Tarr, 1955, Doesburg, 1969) and is the only known antimycotic metabolized to
carbon dioxide and water (Borgstrom, 1968), effective in inhibition of yeasts, moulds and some
bacteria (Jay, 1979) at concentrations far below levels that would affect taste and odor (Ledward,
1981). It is effective at levels of 0.3 to 0.5% (Acott and Labuza, 1975). Some polyhydric
alcohols such as propylene glycol, 1,3-butylene glycol and several other diols also have weak
antimycotic activities (Piltman et al., 1973, Acott and Labuza, 1975).
2.1.1.2 Method of Production The ancient technique of producing intermediate moisture meat is through traditional processing.
Products such as Suya in Nigeria (West Africa) and various sausages have been produced. Suya
consist of pieces of boneless meat of beef or mutton or goat meat stacked on sticks, coated with
spiced groundnut powder, salted and oiled and roasted for 20-30 minutes by arranging the sticks
9
around the fire (Alonge and Hikko, 1981; Okonkwo, 1987). These traditional intermediate
moisture meats productions have challenges which may include poor shelf life, lack of suitable
solutes, dry and tough texture and poor palatability. Thus, in modern times, there are three main
methods of preparing intermediate moisture meats. These include blending, adsorption and
desorption.
In blending method, dry and wet components are blended together through combination so that
the wet components lose part of their moisture to the dry components and in the process both
establish equilibrium with regards to moisture and solid components. After blending, the
resulting product is pasteurized, cut as it leaves the extruder and may also be formed into chunks.
In adsorption processing, also known as dry infusion, the water activity of a dry product is raised
to the required level by controlled rehumidification. A high quality dried starting material which
is porous and adsorptive is used (Ledward, 1981). The products are usually prepared by blending
a freeze-dried product in a low speed mixer, followed by infusion with humectants solution
(Chirife et al., 1980). Another method for the production of intermediate moisture meat is
desorption processing also known as moist infusion or osmotic dehydration. This is the simplest
method of producing intermediate moisture meats. In this method, the solid pieces of meat is
soaked / cooked in an appropriate solution to result in a final product having desired water
activity (Brockman, 1970; Kaplow, 1970). The products are pasteurized in the infusing solution
to accelerate diffusion and equilibration, inactivate or minimize enzymes and microbial
activities, finally, the products are left to equilibrate at room temperature for about 12-24 hours.
10
2.1.2 Storage Stability of Intermediate Moisture Meats
Although intermediate moisture meats are more stable under storage than raw or ordinary
pasteurized meat, they are, like most food stuffs, subject to spoilage. These spoilages could be
due to microbial, chemical or physical changes (Labuza et al., 1972 a,b). Furthermore, because
the products are usually processed to water activity of 0.84 or less and with antimycotics,
microbial problems are also of minor importance unless serious consumer and storage abuses
occur, such as storing the products in high relative humidity environment. Physical and chemical
changes therefore appear to be the major deteriorative reactions in intermediate moisture meat.
One major deteriorative change in glycerol/salt desorbed intermediate moisture meats during
storage at 28 0C-38 0C is the breakdown of collagen of the connective tissue, yielding water
soluble hydroxylproline (Obanu et al., 1975 a,b; 1976). Thus, it appears that heat has some
influence on the stability of collagen. Collagen when heated to about 65 oC is denatured,
changing its conformation to become more soluble and susceptible to degradation (Lawrie,
1991). Degradation, discoloration and loss of muscle color pigments (myoglobin and
haemoglobin) also occur in intermediate moisture meats during storage. Under prolonged
storage, the colors of both the heated and unheated intermediate moisture meat darken as a result
of non-enzymatic (maillard) browning reaction (Obanu et al., 1975 b). During storage, the
reflectance spectra show progressive flattening of peaks, depicting loss of haemoprotein
characteristics of the pigments (Obanu et al., 1975b).
2.2 Water Sorption Phenomenon in Foods
The water sorption phenomenon, as applied to food materials, refers to the mass transfer of
moisture into or out a food material depending on the water content gradient between the food
and the environment in which the food exist (Mujumdar and Devahastin, 2001). If the food is
11
placed in an environment whose water content (relative humidity) is higher than the food, then
water driven by osmotic pressure difference and the hygroscopic nature of food materials will
move to the food materials until equilibrium state is established between the two. This is known
as adsorption. The reverse will occur when the water content of the food is higher than its
environment (desorption). These two processes are very important in food dehydration and food
storage because they control the mass movement of water into and out of the food system, which
in turn regulates the rate of chemical, biochemical, physicochemical and enzymic activity, all of
which are largely responsible for food degradation during storage (Fortes and Okos, 1980). A
number of relationships have been reported (Rockland and Nishi, 1980) to describe the
dependence of microbial growth on the moisture content of foods. In addition to possible
microbial spoilage, dehydrated foods represent a concentrated biochemical system, which during
moisture adsorption become prone to deterioration by several mechanisms (Troller, 1981). Apart
from its importance in packaging and storability of foods and hence their stability, the moisture
content of food materials is an index of sensory and process quality (Fisher and Bender, 1985;
Kyzlink, 1990). The textures, preservation and quality control of foods depend intimately on the
water content (Karmas, 1981). The relationship between food product and its water contents is of
great importance in predicting quality changes during storage. However, the equilibrium
moisture content (EMC) of a food is much more important in monitoring the behavior of food in
storage than the floating moisture content (Pixton and Warburton, 1970). The EMC of a food
material has considerable bearing on its vulnerability to microbial attack (Beuchat, 1981;
Brennan et al., 1990). When expressed as a fraction, the EMC is reported as water activity.
12
2.2.1 Water Activity: Definition and Importance in Food Systems
When considering the influence of moisture on the stability of foods, it is not just the total
moisture content that is of interest but the moisture which is available for chemical and microbial
activity (Brennan et al., 1990). This available component of the moisture is known, in practice,
as the water activity. There is considerable evidence that a proportion of the total moisture
present in a food is strongly bound on the solid component (Aqualab, 2002) and an additional
amount is less firmly bound, but is still not readily available as a solvent for various soluble
components. Therefore, in studying the availability of water in foods, the water activity,
determined as the ratio of water vapor pressure exerted by a solution or wet solid over the vapor
pressure exerted by pure water at the same temperature, is of utmost important (Rockland and
Stewart, 1981). Mathematically, this is expressed as:
aw= pv/pw = ERH/100 (1)
Where
aw = the water activity
pv = the vapor pressure of water in the food
pw = the vapor pressure of pure water
ERH = equilibrium relative humidity.
The importance of water activity in food storage lies in the fact that it is a measure of the extent
to which water present in a food can contribute to the rate of chemical reactions in which water
takes part or serves as a solvating medium, or in which it enables growth and proliferation of
microbial activities. There is usually no proliferation of micro-organisms in stored foods at ≤0.5
13
aw. However, yeast and moulds start to grow on foods in the aw range of 0.6 to 0.75 (Duckworth
and Troller, 1975). According to Troller (1980), most studies indicate that a food with aw below
0.60 is stable towards microbial growth, which are in most cases, the most frequently
encountered spoilage factors. Franks (1982) reported that too high a water activity favors the
viability of the micro-organism but reduces their resistance to low or high temperature
treatments. Chen et al. (1986) showed that mould count on retail peanut kernels was independent
of their moisture content but dependent on water activity of the outer layers of the kernels. These
authors also observed that at higher water activities, the reacting chemical species became
soluble and mobile in the solvent water and the oxidation rate increase. This makes moisture
control very critical during storage of foods (meat products).
2.2.2 Measurement of Water Activity
The measurement of water activity in foods has been the subject of many studies and variety of
methods have been used and reported in the literature (Troller and Christian, 1978; Gal, 1981;
Nunes et al., 1985). The most commonly used methods include:
Measurement based on psychometric (Riggle and Slack, 1980; Weibe et al., 1981; Stamp et al.,
1984).
Measurements based on colligative properties of water (Labuza et al., 1976; Lewickki et al.,
1978; Ferro-Fontan and Cherife, 1981; Lerici et al., 1983).
Measurement based on suction potential (Labuza and Lewiki, 1978).
Measurement based on isopiestic transfer (Fett, 1973; McCune et al., 1981; Northolt and
Heuvelman, 1982).
The last method has been shown to be more flexible and versatile in terms of applicability on
different food materials, and provides more reliable and reproducible results within the most
14
crucial spoilage water activity values (Nunes et al., 1985). In addition to this advantage, the
method is less sophisticated, less expensive, and quite suitable for routine laboratory
measurements. The method relies on the equilibration of the water activities in two materials in a
closed system either through direct contact of the materials, allowing for movement of the bulk
micro capillary gaseous water or by maintaining the two materials separately, thus allowing the
materials to have contact only through the vapor phase.
2.2.3 Controlled Water Activity Environments
In order to obtain sorption data, it is often necessary to adjust the water activity of food samples
to a range of values (Rivzi, 1986). The two principal techniques used for the adjustment of water
activity are the integral and the differential methods (Neuber, 1981).
The integral method involves placing several samples, each under controlled environments,
simultaneously and measuring the moisture content upon attainment of constant weight. The
differential method utilizes a single sample which is placed under successively increasing or
decreasing relative humidity environment; moisture content is measured after each equilibration.
The differential method has an advantage of using only a single sample hence, all sample
parameters are kept constant, and the only effect becomes that of the environment. The method
has the disadvantage of long time required to obtain a set of sorption data which promotes
various degenerative changes such as deactivation of the sorptive sites (Neuber, 1981). The
integral method avoid this problem because each sample is discarded after the appropriate
measurement is made, thus the time for major deteriorative changes to occur is limited. The
common substances used for generating environments of defined conditions for adjustment of
water activity of foods consist of solution of saturated salts, sulfuric acid and glycerol
15
(Greenspan, 1977). The water activity of most salt always decreases with an increase in
temperature. This is due to increased solubility of salts and their negative heats of solution
(Lerici et al., 1983). In addition, a survey by Resnick et al. (1984) indicated variations in ERH
values assigned to selected salt solutions at 25 oC by various laboratories. Labuza et al. (1985)
measured the water activity values of eight saturated salt solutions by vapor pressure movement
(VPM) method and found them to be significantly (p<0.05) different from the Greenspan (1977)
data. The deficient performance associated with the use of saturated salt solution make their
results difficult to reproduce.
Sulfuric acid solutions of varying concentrations in water are also used to obtain different
controlled humidity environments (Ruegg, 1980). Changes in the concentration of the solutions
and the corrosive nature of the acid require caution in their use. According to Ruegg (1980),
changing the acid solutions regularly during sorption experiments gives consistent and reliable
results. Chirife and Resnick (1984) have proposed the use of unsaturated sodium chloride
solution as isopiestic standards. However, this does not provide water activity lower than 0.7 and
as such may not be suitable for a comprehensive evaluation of the sorption behavior over a wide
range of water activities. The standard procedure for adjusting the water activity of food
materials require that test samples be allowed to equilibrate to the preselected relative humidity
environment in the head space, using either glass desiccators or air-tight plastic containers,
maintained at a constant temperature(Gal, 1981). The use of air-tight plastic containers has been
recommended (Bhandari, 1999) as a substitute for glass desiccators because they are cheap, easy
to handle, non-fragile and inert to saturated salts and acids up to temperatures of 70 oC. It has
been shown (Bhandari,1999) that in order to provide sufficient adsorption/desorption during
sorption experiments, a large air-space volume ratio (greater than 10:1) of solution surface to
16
sample surface must be maintained and a larger air space volume to sample volume ratio (greater
than 20:1) should be maintained. Similarly, Neuber (1981) and Rizvi (1986) have suggested that
in order to shorten the time required for attainment of equilibrium, the physical distance between
the solution and the sample must be reduced. Rizvi (1986) developed an accelerated method
which utilizes either pure water (100 % RH) or pure desiccant (0 % RH) to achieve fastest
adsorption and desorption, respectively.
2.3 Moisture Sorption Isotherms
Labuza et al. (1985) described moisture sorption isotherm of a food as a plot of the adsorbed or
desorbed (EMC) against the relative humidity or water activity of the vapor space surrounding
the food at a given temperature.
Isotherm may be prepared by adsorption, which is placing a dry material in contact with
atmospheres of increasing relative humidity or by desorption, which is placing a wet material in
contact with atmosphere of decreasing relative humidity (Brennan et al., 1990). Thus two
different curves may be obtained for the same material as shown in Fig.1.
The gap created by the difference between the adsorption and desorption curves is referred to as
hysteresis which is an important phenomenon in sorption energetic and is typical of many foods
as discussed in the following section. Moisture sorption isotherms of food are often divided into
three regions denoted as A, B and C in Fig. 2 (Brennan et al., 1990). In region, A, water
molecules are strongly bound to specific sites on the solid. Such sites may be hydroxyl groups in
polysaccharide, carbonyl and amino groups in proteins and others on which water is held by
hydrogen bonding, ion-dipole bonds or other strong interactions. According to Troller (1981) this
bound water is unavailable as a solvent and hence does not contribute to microbial or chemical
activity.
17
Figure 1: Adsorption and Desorption isotherms showing hysteresis.
18
It is often referred to as the monomolecular or monolayer moisture value and is found in the
water activity range of 0 to 0.25. Above region A, water may still be bound to the solid but less
strongly than in region A. It has been the practice to distinguish region B as consisting of a
multi-layers of adsorbed water and region C as one with lower water vapor pressure as a result of
structural and solution effects (Brennan et al., 1990).
The division of the sorption isotherm into three segments represents the water activity range in
which three principal types of water binding predominate (Labuza, 1975; Rockland Nishi, 1980).
The first region characterized by water activity of 0 – 0.25 is called the local isotherm I or ionic
region. It is believed that in this region, water bound by ionic groups predominate. Labuza
(1968) referred to this region as corresponding to the adsorption of monolayer film of water. The
second region, characterized by water activity values of 0.25 – 0.75 is called the local isotherm II
or The Covalent region. It defines the adsorption of additional layers over the monolayer. The
third region is called the free solute and capillary or local isotherm III. It lies between water
activity of 0.75 – 1.0 and is believed to represent water multi-layers on protein and carbohydrate
polymers.
In addition to water in which the vapor pressure is reduced by dissolved solutes such as free
amino acids, sugars, and/or capillary attraction in the micro structure, these respective sections
have specific influences on the storage stability of food materials which is affected by the water
activity within the environments of the regions. Because of the differences both in composition,
and in their response to varying humidities, different foods have been observed to give different
types of moisture sorption isotherms. Type I is the Langmuir and type II is the sigmoid or s-
shaped. No special name has been attached to the other three types observed (Rizvi, 1986).
Generally, the moisture sorption isotherms of most foods are non-linear and generally sigmoid in
19
Fig 2: partition of moisture sorption isotherms
Water activity
A B C
0
0.2 0.6 0.8 0.1
Mo
istu
re c
on
ten
ts
20
Type I Isotherm Type II Isotherm
Type III Isotherm Type IV Isotherm
Types V Isotherm
Figure 3. Sorption isotherms classification
Source: Braunauer et al. (1940).
21
shape. These have been classified (Braunauer et al. 1940; Gal, 1981; Rizvi, 1986) into five
general types depending on the curves observed as shown in Figure 3.
2.3.1. Sorption Isotherm Hysteresis
The discrepancy that is usually observed between the adsorption and the desorption arms of
sorption isotherm is called hysteresis. According to Labuza (1974), this condition may not be a
true equilibrium condition but with respect to the normal shelf-life of the food; it is real and has a
significant effect on food stability. The magnitude of the hysteresis effect is determined primarily
by the composition of the material, and also the temperature and pre-treatment given to food
material (Sopade Ajisegiri, 1994). Hence, due to hysteresis, the moisture content at any
temperature of a food material at a specific ERH may vary appreciably depending on its recent
sorption history. Kapsalis (1981) noted that although hysteresis signifies the absence of
thermodynamic equilibrium, it does not seriously affect the qualitative or rough quantitative
interpretation of sorption data. Many theories have been put forward to explain the sorption
hysteresis phenomenon. One of these is the Rao's ink bottle theory (Labuza, 1968; Ajisegiri,
1987) which links sorption sites in food materials to ink bottles. During adsorption and
desorption, the necks and bottoms of the hypothetical ink bottles exercise different effects on the
moisture intake and escape respectively. In his discussion of hysteresis, Hill (1949) stated that
for first order phase changes, the adsorption branch represents the true equilibrium up to a certain
point in isotherm, and that the desorption branch never represents true equilibrium. He also noted
that for ordinary porous materials such as foods, the region of the adsorption branch that
represents equilibrium is limited non-existent. In their study on the moisture sorption of sucrose-
starch mixture, Chinachoti and Steinberg (1986) reported a close linear correlation between
hysteresis and the amount of amorphous sucrose present in the sample. This agrees with the
22
suggestion by Sopade and Ajisegiri (1994) that the magnitude of hysteresis depends on the
composition of the material. Despite the numerous hypotheses in existence on hysteresis,
Rockland and Nishi (1980) noted that a definitive interpretation of the hysteresis loop and its
relationship to quality stability of foods remain to be resolved. However, profound differences in
the properties of foods at any given water activity may be expected depending upon whether the
equilibrium conditions were established from a lower or a higher total moisture content.
2.3.2 Effect of Temperature on Sorption Isotherms
Temperature has been shown (Brennan et al., 1990; Sopade and Ajisegiri, 1994; Sopade et al.,
1996) to affect the sorption behavior of foods. The amount of adsorbed water at any given water
activity decreases with increase in temperature (Labuza et al., 1985). The effect of temperature
on moisture sorption has been explained by Lang et al. (1981), Chirife and Resnick (1984) and
Rizvi (1986). The explanations were based on the well known thermodynamic relationship:
∆G*=∆H- T∆S (2)
Where:
G* = the Gibb's free energy
H = the enthalpy of the system
T = the absolute temperature of the system.
If sorption is to occur spontaneously, ∆G* must have a negative value. During adsorption, ∆S
will be negative because the adsorbate becomes orderly and loses degree of freedom for ∆G* to
be less than zero, ∆H will have to be negative and the adsorption is thus exothermic. Similarly,
desorption can be shown to be endothermic. Also, because ∆H decreases very slightly with
temperature, the higher temperature will cause a corresponding increase in ∆S, resulting in a
reduction in adsorbed molecules. In principle, therefore, it can be generally said that adsorption
23
decreases with increasing temperature. Although greater adsorption is found at lower
temperature, the differences are usually small, though these differences may be large at times.
Since there is no particular trend in these differences, caution is required when interpreting them,
as temperature changes can affect several factors at the same time (Van-den-Berg and Bruin,
1981). According to Rizvi (1986), an increase in temperature may increase the rates of
adsorption, hydrolysis, and recrystallization reactions. A change in temperature may also change
the dissociation of water and alter the potential of reference electrodes. This will have immediate
practical applications in defining water activity option for food products which are exposed to
varying temperatures during processing and storage. Foods rich in soluble solids exhibit
antithetical temperature effects at high water activity values because of their increased solubility
in water (Rizvi, 1986). The constants in the moisture sorption isotherms equations, which
represent either temperature or a function of temperature, are used to calculate the temperature
dependence of water activity (Labuza et al., 1985). Moisture sorption studies by Copper and
Noel (1966), Moschiar et al. (1984) on fish products and by Konstance et al. (1983) on bacon
slices indicated that the quantity of sorbed water at a given water activity increased as
temperature decreased. The temperature dependence of moisture sorption isotherms was
evaluated from experimentally determined moisture sorption isotherms of casein, wheat, starch,
potato starch, pectin and micro-crystalline cellulose (Bandyopadhyay et al., 1980) and of corn
meal and fish flour (Labuza et al., 1985). Studies by Ajibola (1986) on the desorption of plantain
at several temperatures, kiranoudis et al. (1993) on heat of desorption of some vegetables,
Diosady et al. (1996) on canola meals, Palou et al. (1997) on moisture sorption isotherms of
some cookies and corn snacks confirmed such similar temperature dependence. Dural and Hines
(1993) attributed the shift in sorption isotherms with increase in temperature to the fact that
24
physical adsorption is an exothermic process. Hence low temperature or negligible temperature
dependence of such results could probably indicate that the heat of dissolution and adsorption
were of similar magnitude. The implication of such negligible temperature dependence on
isotherms of food is that the quality and stability of such foods (with low temperature
dependence) may not be significantly influenced by temperature during storage.
2.4 Influence of Moisture and Other Factors on Stored Products
In order to maintain the quality of products over long-term storage, degradation processes
(mainly the breakdown of major components of the products-starch, protein, lipid, water) must
be slowed down or even stopped. Moisture and temperature are the determining factors in
accelerating or delaying the complex phenomena of biochemical transformations (AEDS, 2002).
Furthermore, they have a direct influence on the rate of development of micro-organisms
(moulds, yeasts and bacteria). Temperature depends not only on climatic conditions but also on
the biochemical changes that occur inside the food products thereby, provoking undesirable
natural heating of the stored products. Hence the moisture content of stored food product
depends on the relative humidity of the air.
2.5 Sorption Models
Various theoretical models have been proposed to describe the sorption phenomenon (Boquet et
al., 1980; Van-den-Berg and Bruin, 1981; Bizot, 1983). These are mainly two or three parameter
models. They are empirical, semi-empirical, or theoretical, based on the physical chemistry of
the surfaces. On the whole, there are over seventy equations (Van-den-Berg and Bruin, 1981).
None of these equations is applicable to all foods and not all the models are suitable over the
entire water activity range because of the existence of different association of water and food
25
matrix at different water activity regions. This situation could be due to the fact that foods
represent the integrated hygroscopic properties of numerous constituents whose sorption
properties may change as a consequence of physical and / or chemical interactions induced by
heating or other pre-treatments (Iglesias and Chirife, 1976). More so, the depression of water
activity in foods is due to a combination of factors each of which may be predominant in a given
range of water activity. When a food sorbs water, it undergoes changes of constitution,
dimension and phase transformation, the combined effects of which will be different for each
food material and for each water activity range, depending mostly on the predominant change
(Kapsalis, 1981; Jowitt et al., 1989). The usefulness of a particular sorption model depends on
the objective of the user (Labuza, 1968; 1975). For instance, an equation which fits as closely as
possible to an experimental data will be appropriate for the prediction of drying times and the
shelf-life of packaged dry foods. Simplicity and ease of evaluation of sorption model enhance
their usability. Since sorption isotherms of foods represent the integrated hygroscopic properties
of various foods constituent, therefore, in assessing the usability of these equations for different
foods, the foods need to be grouped according to their main constituents (water, carbohydrates,
fats, proteins) and the goodness of fit of these groups may be evaluated separately (Boquet et al.,
1978). Some of the moisture sorption isotherms are therefore, understandably and necessarily
described by semi-empirical equations with two or three fitting parameters (Iglesias and Chirife,
1976). The goodness of fit of a sorption model to experimental data shows only a mathematical
quality and not the nature of the sorption process. Many of the seemingly different models turn
out to be the same after some rearrangement (Boquet et al., 1980). In the evaluation of eight, two
parameter equations in describing moisture sorption isotherms for 39 food materials, Boquet et
al., (1978) found the Halsey (1948) and the Oswin (1946) equations to be the most versatile of
26
the large number of sorption models available in the literature, (Van-den-Berg Bruin, 1981), a
few that are commonly used (Rizvi, 1986) and six of which are chosen for application
assessment of their suitability for describing water sorption are discussed below.
Bradley model
This equation is based on the assumption that the sorptive surface is polar in nature, the first
layer of water vapor is sorbed because of strongly induced dipoles, and these dipoles, in turn
polarizes the next layer and so on. Hence the constants in the equation, which is of the form
(Bradley, 1936):
In aw = C (K)m (3)
Where C, K and m are constants, define the dipole movement of the sorbed vapor and sorptive
polar groups. C in the equation is a function of the dipole movement of sorbed vapor. Both
constants have been shown (Ajisigiri and Sopade, 1990) to be temperature dependent.
The Brunauer-Emmett- Teller (BET) model;
The BET equation is of the form: = + (4)
where:
Aw= water activity
M = the equilibrium moisture content
M0 = the monolayer moisture content
C = a constant.
The equation is the most widely used model and gives a good fit to data for a variety of foods
particularly at aw range not exceeding 0.5 (Chirife and Iglesias, 1978; Rizvi, 1986). The equation
is useful for calculating the monolayer moisture adsorbed on the surface, which corresponds to
moisture contents for chemical and physical stability of foods (Labuza, 1968; 1975). Although
27
the theory behind the BET equation has been faulted on many grounds, these arguments lack the
strength to invalidate results from the model, particularly at lower water activities (Hill and
Rizvi, 1982).
Hasley Model;
The Hasley equation (Hasley, 1948) developed to provide an expression for condensation of
monolayer at a relatively large distance from the surface is of the form:
(5)
Where:
aw = the water activity
A and K = constants
R and T = the universal gas constants and absolute temperature respectively.
The equation is based on the assumption that the potential energy of a molecule varies with the
Kth power of its distance from the surface. If K is large, the attraction of the solid to the vapor is
presumably specific and does not extend far from the surface. If K is small, the forces are more
typical vander waal’s and are able to act at a greater distance. The equation has been used to
successfully describe 220 experimental sorption isotherms of 69 different foods in the water
activity range of 0.1 to 0.8. Luck (1981) has shown that the sorption behaviors of protein and
lipid containing foods were well described by this equation.
Henderson Model;
This equation (Henderson, 1952) is one of the most widely used models relating water activity
and the amount of water sorbed. It is of the form:
28
(6)
Where:
aw = the water activity
M = the equilibrium moisture content
T = the absolute temperature of experimentation
A and B = constants.
The equation was observed to give a better fit to both adsorption and desorption data when
applied on some local varieties of millet in Nigeria (Ajisegiri Sopade, 1990) and was used by
Ezeike (1988) for describing the moisture sorption isotherm of melon seeds.
Oswin Model;
The Oswin model (Oswin, 1946) is based on the Pearson’s expansion for sigmoid shaped curves
and is applied to type II isotherms equations. The equation is of the form:
M = (aw/1-aw) B (7)
where:
A and B are constants,
aw = the water activity
M= the equilibrium moisture content.
29
Boquet et al. (1978) adjudged the Oswin model one of the most versatile in terms of applicability
foods, from eight models used for 39 different foods.
Caurie Model;
The caurie equation is of the form:
(8)
The equation was proposed by Caurie (1970) based on purely mathematical manipulations. It is
one model that has generated curious interest in sorption because of the desire to establish the
authenticity of models developed in this theoretical manner, on empirical data.
All the models chosen for this work are two parametric models. Choice of the two parametric
models was not only because of their simplicity and ease of evaluation but also because they
have a more common basis for comparison since they are all two-parameter based.
30
CHAPTER THREE
MATERIALS AND METHODS
3.1 Materials
Raw meat was obtained from Ogige main market, Nsukka, Enugu state. Low density
polyethylene (LDPE), high density polyethylene (HDPE), plastic containers (PC) and glass
bottles (GB) were purchased. The samples were kept under ambient conditions (30 oC;)
throughout the duration of the work. The materials/ equipment that were used for
physicochemical and sorption analysis include:
Micrometer screw gauge (Moore and Wright Ltd., 0.01mm-25mm).
A sensitive weighing balance (Metler Toledo)
Thermometers, graduated to 100 oC
A T-200 Thermo cool refrigerator
A drying oven (Memmert D-26; West Germany)
An incubator (Gallenkamp size 2)
A continuous Soxhlet fat extractor (Electrothermal)
A Kjeldahl protein determination unit (2006 Digestor, Foss Tecator)
A water activity analyzer (model 5308)
3.2 Methods
3.2.1 Sample Preparation
The raw meat obtained was trimmed of visible fat and connective tissues and the resulting lean
was cut into pieces of about 2 cm3. The meat pieces were divided into 3 sublets to correspond to
infusing humectants solutions used as treatments as shown in Table 1.
31
3.2.2 Formulation of Infusing Solution
The ingredients used in the formulation of the infusing solutions were glycerol, salt, sodium
nitrite and water. The composition of the various treatment solutions and concentration of the
ingredients used are shown in Table 1.
3.2.3 Cook-Soak Equilibration
The cook –soak- equilibration technique of Obanu and Ledward (1975) was used to process the
meat samples. The meat pieces (2 cm) were placed in containers at the rate of 180 g (with the
solution being 1.5 times the weight of meat). The meat pieces were cooked at 77 oC to an internal
temperature of 70 oC for 15 minutes. After cooking, the containers were removed from the water
bath and allowed to equilibrate at room temperature. After equilibration, the containers were
opened to allow the solution to drain.
3.2.4 Smoking
This was carried out using the method of Okonkwo et al. (1992). The equilibrated meat pieces
were divided into three (3). One part was not smoked. Of the remaining two parts, one part was
smoked for four hours (light smoking) and the other for 18 hours (heavy smoking) each at 60 ±
10 oC. After smoking, the samples were allowed to cool and some were withdrawn for analysis
of the physicochemical and sensory characteristics of the products before and after smoking. The
remaining samples were used for moisture sorption studies.
3.3 Physicochemical Characteristics
3.3.1 Moisture Determination
This was determined by the air- oven method of AOAC (2010). Empty crucible was placed in an
oven at 130 oC for about 30 minutes after which it was transferred into desiccators, allowed to
cool and then
32
Table 1: Composition of Infusing Humectants.
Ingredients Infusion Solutions
% A B C
Water 91.484 85.484 79.484
Glycerol 6 12 18
Salt 2.5 2.5 2.5
Sodium nitrite 0.016 0.016 0.016
Total 100 100 100
Source: Okonkwo, (2001).
33
weighed (W1). A sample (3.0 g) was weighed and transferred into the crucible and the weight of
both crucible and sample was taken (W2). The sample was dried in the oven for 2 hours at 105
oC. The crucible was removed, cooled in desiccators and re-weighed (W3). This process was
repeated until a constant value was obtained. The moisture was obtained from the following
calculation.
% Moisture = (9)
3.3.2 Fat Content
The Soxhlet solvent extraction method was used for fat content as outlined by AOAC, (2010).
The Soxhlet thimble which was used for extraction was cleaned by drying in an oven for 1 hour
and cooled to room temperature and weighed. The sample (3 g) was weighed into a Soxhlet
thimble and placed inside the Soxhlet extractor. Extraction was allowed to proceed for 10 hours.
Thereafter petroleum ether was recovered by evaporation on an electric bath and the remaining
fat in the flask was dried at 60 oC for 30 minutes in the oven. This was cooled and weighed.
% Fat = (10)
3.3.3 Protein determination
The Kjeldahl method described by AOAC (2010) was used for protein determination. The
sample (1.0 g) was weighed into a Kjeldahl digestion flask and about 20 ml of concentrated
sulphuric acid was added. A Kjeldahl tablet was also added to act as catalyst. The sample was
digested and allowed to cool, then about 75 ml distilled water was added and the tube was
allowed to cool. After cooling, the tube was placed in a Kjeldahl distillation unit, neutralized
with 40 % sodium hydroxide and the liberated nitrogen was collected in 25 ml of 4 % boric acid
34
indicator containing screened methyl red. The distillate was then titrated with 0.0 N
hydrochloric acid and quantity of nitrogen was calculated as:
% Nitrogen = Titre x normality (of HCL) x 0.014 x dilution factor/Weight of sample x 100 (11)
3.3.4 Ash Content determination
The ashing crucible was ignited in a furnace at 550 oC for some minutes, cooled in a desiccator
and weighed. The sample (3 g) was weighed into the crucible and dried in an oven at 120 oC for
1 hour. The sample was removed from the drying oven and carbonized by using blue flame of a
Bunsen burner after which the sample was placed in a muffle furnace at 550 oC until the residues
appear whitish grey. The crucible containing the ash was placed in a desiccator and allowed to
cool to room temperature and then weighed.
% Ash = (12)
3.3.5 Hydrogen Ion Concentration (pH)
The pH was determined by using laboratory digital pH meter (PTI-15). The meat sample (5.0 g)
was homogenized in 50 ml of distilled water and the pH was taken with the aid of combined
electrode after allowing 1-2 minutes for stabilization. The accuracy of the pH meter was checked
by using pH 7 and 4 buffer solutions.
3.3.6 Thiobarbituric Acid (TBA) Test
A portion of the meat sample (10 g) was dispersed in 99 ml of distilled water in a quick-fit 250
ml flask. Concentrated hydrochloric acid (1.0 ml) was added to bring the pH to about 1.5. Also
few drops of antifoam emulsions were added. The distillation apparatus was assembled and the
flask was heated with electric mantle at the maximum setting. Heating was continued until 50 ml
of the distillate was collected and was thoroughly mixed by shaking. The distillate was pipetted
35
in duplicate of 5 ml into test tubes and 5 ml of TBA reagent was added to each tube. The tubes
were stoppered, shaken and placed in boiling water bath for 35 minutes. A blank solution
containing 5 ml of distilled water and 5 ml of TBA reagent was treated similarly. After removing
from the water bath, the tubes were cooled and optical density of the solutions was determined
against the blank reference at a wavelength of 538 nm.
The TBA number (mg malonaldehyde/kg sample) was calculated as follows: TBA Number =
Optical density (OD) . (13)
3.3.7 Protein Solubility in SDS-β-Mercapto ethanol solution
The sample (0.5 g) of the meat was dispersed in 50 ml of SDS-mercaptoethanol solution. This
was allowed to stand at room temperature for 30 minutes. After 30 minutes, it was transferred to
a boiling water bath and heated for a further 30 minutes. The sample was then centrifuged while
still hot for 30 minutes at 30000 g and filtered using a filter paper, the residue being the insoluble
fraction while the filtrate comprised the soluble fraction and non protein nitrogen. Each of the
two fractions was put in to separate Kjeldahl flasks and catalyst mixture (96 % sodium suiphate,
3.5 % copper sulphate and 0.5 % selenium dioxide) was added. 25 ml of concentrated sulphuric
acid (H2SO4) and silicon antifoam or antibump, were added. The flask was heated gently at first
and heating was increased and continued until one and half hour when the solution was clear.
The flasks were allowed to cool before 100 ml of distilled water was added. After cooling, 50 %
NaOH was also added and distilled into 50 ml boric acid indicator in 100 ml conical flask. 250
ml distillate from each fraction was collected and titrated with N/10 HCl to purple end point.
Percentage soluble nitrogen was calculated as follows:
Solubility (%) = x 100 (14)
36
3.3.8 Water Activity
The water activity was determined by using water analyzer (model 5308). The instrument was
calibrated at 30 oC. The sample (5 g) was placed in the sample chamber, closed tightly and
allowed to attain a constant reading (about three hours). The reading in water activity was
obtained.
3.4 Sensory Evaluation of Samples
Intermediate moisture smoked meat products were presented for sensory evaluation as described
by Iwe (2002). The samples were administered to 15-man panel of judges, who tested for color,
texture, taste, flavor and acceptability using nine point Hedonic scales as shown in Table 2. All
test samples were coded to prevent bias judgment. An ideal dinning section was set up to
stimulate appetite. The samples were placed at fixed position on the table and the panelists
approached them. Each panelist was made to consume one sample at a time, after which he / she
rinsed his mouth with pure water before tasting another sample. The panelists were allowed
enough time and leisure to make their assessment.
3.5 Sorption Experiments
3.5.1 Experimental Temperature
The sorption experiment was carried out in three different temperature (20 oC, 30 oC and 40 oC),
using the refrigerator, ambient and incubator environments, respectively. The ambient
temperature represents the mean temperature for the entire period during which the sorption
experiment was carried out. The refrigerator and incubator temperature were thermostatically
controlled. Choice of these temperature ranges is meant to cover the entire range of temperature
variations within the country during the changing seasons (dry and rainy season) of the year. The
37
Table 2: Sensory evaluation scoring and description format
___________________________________________________________________________________
Hedonic Description
Scale
______________________________________________________________________
Colour Texture Flavor Overall acceptability
___________________________________________________________________________________
9 Extremely bright extremely hard extremely sweet extremely liked
8 Very bright very hard very sweet very much liked
7 Moderately bright moderately hard moderately sweet moderately liked
6 Slightly bright slightly hard slightly sweet slightly liked
5 Neither bright nor dark neither hard nor soft neither sweet nor salty neither liked nor disliked
4 Slightly dark slightly soft slightly salty slightly disliked
3 Moderately dark moderately soft moderately salty moderately disliked
2 Very dark very soft very salty very much disliked
1 Extremely dark extremely soft extremely salty extremely disliked
____________________________________________________________________________
38
choice also depends on the fact that above 40 oC and below 10 oC, there exists instability in the
water activity values of sulfuric acid solutions (Ruegg, 1980). Temperature in the oven and the
refrigerator was constantly regulated to remain steady at 40 oC and 20 oC respectively, while the
ambient temperature was monitored three times daily using mercury thermometers graduated to
100 oC, and the mean temperature for the period was calculated. A stand-by departmental electric
generator was available to ensure uninterrupted power supply during experimentation and
weighing.
3.5.2 Experimental Water Activities
Six water activities were chosen, and maintained using varying concentrations of sulfuric acid
(Ruegg, 1980; Rizvi, 1986). The preference of sulfuric acid solutions for creating the desired
water activity environments, over saturated salt solutions is as a result of its ability to produce
relatively stable water activity values than the salt solutions. Secondly, for sorption experiment
of this nature where so many samples and replicates are involved, it was easier and less tedious
to use a single reagent than handling so many reagents at the same time (as would be required, if
saturated salt solutions were to be used). Thirdly, some of the salts that would be needed to
produce the desired water activity environments are either not accessible or very expensive for
the quantities needed. Thus, the choice of sulfuric acid was unavoidably the best option available
particularly against the background that other workers (Andrieu et al., 1985) have equally used
sulfuric acid with good results. The water activity range chosen, covered, as much as possible,
the entire aw range of 0.15 to 0.96 as shown in Table 3
39
Table 3: Water activity of sulfuric acid solution at selected concentrations and
temperatures.
H2SO4 (% Conc) aw at 20 oC aw at 30 oC aw at 40 oC
15
20
30
40
50
60
0.9237
0.8796
0.7491
0.5599
0.3482
0.1573
0.9245
0.8814
0.7549
0.5711
0.3674
0.1677
0.9253
0.8831
0.7604
0.5816
0.3702
0.1781
Source: Ruegg, (1980); Rizvi, (1986).
40
3.5.3 Equilibrium moisture content (EMC)
Equilibrium moisture content was determined gravimetrically by exposing the samples to
atmosphere of known relative humidities following the method described by Ariahu et al (2006)
with some modifications. Sulfuric acid solutions of 15, 20, 30, 40, 50 and 60 % were used to
provide water activities ranging from 0.15 to 0.96 as described by Ruegg (1980). A
thermostatically controlled biochemical incubator and 500 ml plastic containers were used for
temperature and humidity, respectively. The solutions made from the acid (100 ml each) were
carefully introduced into the plastic containers. A screen made of wire gauze was forced into the
plastic containers to form support which suspended the samples above the solution.
For desorption studies, the dried product was rewetted by sprinkling with distilled water
followed by mixing with spatula. The rewetted samples were allowed to equilibrate overnight in
a refrigerator before use. Triplicate samples (0.5 g each) of dried and rewetted IMM was
weighed in crown corks and placed on the wire gauze above the solution for adsorption and
desorption. The containers were covered tightly and placed in the incubator at selected
temperatures of 20, 30 and 40 oC. Small glass bottles containing toluene were placed in the
plastic containers to prevent mould growth at relative humidities above 50 % (Mclaughlin and
Magee, 1998). The samples were removed and weighed every 2 days using electronic balance
until differences between consecutive readings for about 2-5 minutes became constant as
recommended by the cooperative project cost 90 (Gal, 1981). The equilibrium moisture content
was determined by material balance from the initial moisture content using following equation:
M / 100(W1) + (W3 – W2) = EMC / 100 [W1 + (W3 – W2)] (15)
M = initial moisture content of the sample
41
W1 = weight of sample used during sorption
W2 = initial weight of sample and crown cork
W3 = final weight of sample and crown cork at equilibrium
EMC = equilibrium moisture content
3.5.4. Experimental Design
The sorption experimental set-up was therefore designed in the form of 3 meaning
3 meat products, two forms (adsorption and desorption) in six water activity environments at
three temperatures. Sorption was carried out following the integral gravimetric method (Neuber,
1981), which involved placing several samples, each under the required controlled environment
simultaneously and measuring the moisture content upon attainment of constant weight.
3.5.5 Experimental Procedure
The prepared samples (0.5 g each) were taken in triplicate in wire gauze inside six (6) different
water activity containers, representing the chosen water activities for experimentation. Each
water activity container and its contents (0.5g of the samples in triplicate) represented one
sorption unit. Thus, for the meat sample, eighteen sorption units were required altogether for the
three temperatures chosen. For adsorption and desorption, thirty-six (36) sorption units were
required. In order to ensure that uniform temperature treatment was applied to all the samples,
the three temperature environments were each filled with the six sorption units from the meat
product at a time and monitored concurrently. In effect, there were six (6) sorption units in each
of the three temperature environments for each experimental batch. The sorption units were
clearly marked. They were weighed at regular daily intervals using a sensitive balance (Mettler
42
Table 4. Models fitted to the experimental data
Model Equation Linearized form of the equation
BET (aw/M(1 – aw) = 1 / Moc) + (c + I /Moc)aw aw/M(1-aw) = Baw + A
GAB M = MoABaw/(1-Aaw)(1-Aaw + ABaw) LnM = LnMoABaw – In((1 – Aaw)(1 – Aaw + ABaw))
Henderson M = -1/Ln (1-aw)B1 Ln M = Ln (AT) + B Ln(1-aw)
Oswin M = A(aw)n/1-aw Ln M = LnA + B Ln (aw/1-aw)
Where in BET, M = the EMC, Mo = the monolayer moisture contents, C = constant and aw = the
water activity. For Henderson, M = the EMC, T = the absolute temperature of experimentation,
aw = the water activity, A and B are constants. While in Oswin model, M = EMC, aw = water
activity, A and n are constants.
43
Toledo, 0.001 g) until equilibrium was reached (when subsequent measurements showed no
weight changes).
3.5.6 Sorption Data Analysis
The equilibrium moisture contents for the samples were calculated using Guggenhein-De Boer
(GAB), Brunauer-Emmett-Teller (BET), Henderson and Oswin models as shown in Table 4.
Linear regression analysis was used for the linearized form of the equations to calculate the
respective constants, percentage root mean square (% RMS) and correlation coefficient (r2) using
Microsoft excels computer software.
The percentage root mean square (% RMS) was calculated for each model using: % RMS =
x 100 (16)
Where:
Mexp = experimental EMC,
Mcal = calculated EMC,
n = number of water activity.
Results of each triplicate determination were unified by computing the arithmetic mean. The
mean equilibrium moisture content values were used for plotting sorption isotherms and for
verification of goodness of fit of the various models.
Subsequently, the equilibrium moisture content data were subjected to spreadsheet analysis in
accordance with the procedure outlined by Ayoade and Sanni (2002), to obtain the relationship
44
that best described the sorption behavior (ideal model) of intermediate moisture smoke meat
under varying experimental conditions, while the apparent surface area of sorption of the sorbent
was determined using the BET monolayer moisture content based on the relationship (Ariahu et
al., 2006);
(17)
Where No = Avagadro’s number (6.023 x 1023 molecule/mole)
A = apparent surface area of one water molecule = 1.05 x 10-19 (m2)
Ms = molar mass of water = 18
Mo = monolayer moisture content (gH2O/g solid).
So = apparent area of sorption
Plots of moisture sorption isotherms (MSI) showing hysteresis, and other plots of the linearized
forms of the chosen models were made. A computer software (Microsoft excel) was used on the
data to produce the appropriate charts under each of the chosen models as well as the trend line
and their correlation coefficients to measure the goodness of fit of the models to the applied data.
The percentage root mean square of error (% RMS) between the experimental data (Mexp) and
predicted (Mest) moisture contents was computed as described by Iglesias and Cherife (1976),
Mok and Hettiaracy (1990) and Wang and Brennan (1991).
The trend line equations and the correlation coefficients for all the chosen models on all the
applied data were compared and the best fitting models under each data was identified. The
sorption models chosen for data application were:
45
The BET model
The GAB model
The Henderson model
The Oswin model
The choice of these models is based on versatility, simplicity, ease of evaluation and
intimidating recommendations from earlier researchers (Sopade and Ajisegiri, 1994;
Bhandari, 1999; Mujumdar and Devahasting, 2001) in this research area.
The characteristics constants in the models (unified in most cases to A and B for ease of
comparison) were calculated from the trend line equations using algebraic approach, for all
samples at the designated experimental conditions. In the case of BET model, the monolayer
moisture content for the meat products under various experimental conditions was proffered.
3.6 Statistical Analysis
The experimental design was Completely Randomized Design (CRD). The data generated from
the physicochemical analysis and sensory were subjected to analysis of variance (ANOVA)
using the statistical package for social sciences. When treatments differences were found to be
significant (p 0.05), Duncan’s Multiple Range Test as described by Obi, (2001) used to
separate means.
46
CHAPTER FOUR
4.1 PHYSICOCHEMICAL CHARACTERISTICS OF INTERMEDIATE
MOISTURE SMOKED MEAT PRODUCTS.
The physicochemical compositions of intermediate moisture smoked meat treated with different
level of glycerol and smoking hours are shown in Table 5.
4.1.1 Moisture Content
The average moisture content of the samples are shown in Table 5 and it ranged from 17.66 ±
0.41 for sample containing 18 % glycerol +18 hours smoking to 66.20 ± 0.10 for sample
containing 6 % glycerol + no smoking. Due to different levels of glycerol in the infusing
solutions and different smoking regimes, there were significant differences among samples in
their moisture contents (p < 0.05). The average moisture content of the samples agreed with
earlier report by Okonkwo et al. (1991). After cooking and equilibration, it reduced to between
57 % and 66 % due to influence of infusing solution and effect of heat on water binding ability
of meat proteins. Among the samples cooked/ equilibrated in infusing solution, sample
containing 6 % glycerol had significantly (p < 0.05) highest moisture content (66.2 % ± 0.1)
compared to samples containing 12 % glycerol (57 % ± 1.0) and that containing 18 % glycerol
(58.2 % ± 0.2). Thus, glycerol contributed to depression of moisture content in the cooked/
equilibrated samples; the higher the glycerol content, in the infusing solution , the lower the
moisture content due to osmotic dehydration of the samples. On smoking for 4 hours, the
moisture content further reduced, attaining intermediate moisture level (Okonkwo et al., 1991).
This reduction on moisture content was attributed to effect of heat, smoke components and flow
of gases on the water holding capacity of meat proteins. Similar trend observed on
cooked/equilibrated samples was followed on smoking for 4 hours. Thus, sample containing 6 %
47
TABLE 5: Physicochemical characteristics of intermediate moisture meat samples
Parameters 6% glycerol
+no smoking
6 % glycerol
+4 h smoking
6 % glycerol
+18 h smoking
12% glycerol
+no smoking
12 % glycerol
+4 h smoking
12% glycerol
+18 h smoking
18% glycerol
+ no smoking
18 % glycerol
+4 h smoking
18% glycerol
+18 h smoking
Moisture content (%)
66.2a ± 0.1 24.50d ± 0.2 18.5f ± 0.1 57c ± 1.00 18.2fg ± 0.1 17.90fg ± 0.00 58.2b ± 0.2 23.0e ± 0.03 17.66g ± 0.41
Fat content (%)
4.47c ± 0.58 11.67b ± 5.20 20.00ab ± 9.01 6.97bc ± 1.36 13.33b ± 7.64 20.33ab ± 0.58 8.20bc ± 0.1 9.6bc ± 4.50 23.50a ± 13.9
Crude protein (%)
26.35e ± 2.54 43.30bc ± 4.62 54.37ab ± 2.16 25.00e ± 1.00 51bc ± 2.65 45.33d ± 2.08 24.33e ± 3.06 59.00a ± 1.00 48.33cd ± 5.51
Ash content (%)
1.60de ± 0.3 2.50cd ± 0.26 3.13b ± 0.29 1.23e ± 0.32 2.50cd ± 0.35 2.80bc ± 0.95 2.30cd ±0.56 3.47ab ±0.83 4.05a ± 0.60
pH 6.7a ± 0.27 6.2bc ± 0.0 6.07c ± 0.26 6.5ab ± 0.30 6.2bc ± 0.10 6.2bc ± 0.15 6.30bc ± 0.15 6.17bc ± 0.57 6.20bc ± 0.25
Soluble protein (%)
87.4a ±1.1 81.7b ± 1.6 75.56d ± 2.4 82.77b ± 1.09 78.75c ± 3.8 79.57c ± 4.2 76.87cd ±2.96 84.17ab ±6.43 78.29c ± 6.4
Thiobarbituric acid number(mg/kg)
0.61a ± 0.01 0.49b ± 0.15 0.44c ± 0.03 0.65a ± 0.02 0.31de ± 0.03 0.34d ± 0.02 0.63a ± 0.05 0.42c ±0.02 0.28e ± 0.04
Water activity (aw)
0.92a ± 0.02 0.85b ± 0.03 0.73cd ± 0.02 0.84b ± 0.04 0.71cd ± 0.01 0.64e ±0.02 0.74c ± 0.03 0.66de ± 0.02 0.60e ± 0.1
Sample means with different superscript in the same row are significantly different (p < 0.05), values are in mean ± standard deviation
48
glycerol had higher moisture content (24.50 % ± 0.2) compared to sample containing 12 %
glycerol (18.2 % ± 0.1) and sample containing 18 % glycerol (23 % ± 0.03). The moisture
contents were further reduced on smoking for 18 hours, but still within intermediate moisture
range. Similar trend as observed earlier was maintained on smoking for 18 hours; hence, sample
containing 6 % glycerol had the highest moisture content.
4.1.2 Fat content
Table 5 shows that fat content ranged from 4.47 ± 0.58 to 23.50 ± 13.9. The sample cured with
18 % glycerol + 18 hours smoking had the highest level of fat content. The increase in fat
content for sample cured with 18 % glycerol + 18 h smoking could probably be as a result of
concentrating effect of moisture loss during 18 hours of smoking and high percentage of
glycerol added. The low fat content for sample cured with 6 % glycerol + no smoking was due
to the fact that after cooking and equilibration, the sample was not smoked and the level of
glycerol used was low. There was an increase in trend following concentration of smoking
hours and level of glycerol used for other samples respectively.
4.1.3 Crude protein content
The result obtained for protein in Table 5 showed that protein value obtained after cook-soak-
equilibration + 4 hours smoking and 18 hours smoking was found to be higher than those
samples that were not smoked after cook-soak-equilibration. These increases could possibly be
as a result of concentrating effect of moisture loss. The mean value of crude protein content
agreed with report by Okonkwo, (2001), Facolade, (2012). Thus results of crude protein content
shown in Table 5 showed that there was actually significant difference (p < 0.05) among
samples. This was because all the samples were treated with different level of glycerol and
smoking hours.
49
4.1.4 Ash content
Table 5 shows that the ash content of the samples not smoked but contained 12 %, 6 % and 18
% glycerol were found to be 1.23 ± 0.32, 1.60 ± 0.3 and 2.30 ± 0.56, respectively. This was less
than that obtained for samples cured with 4 hours smoking and 18 hours smoking. The increase
in ash content for smoked samples may be as a result of heat application which increased the
concentration of ash per unit weight as moisture was lost. The ash content is a measure of the
mineral contents which are very important for proper functioning of the body (Eyo, 2001). Thus
sample containing 18 % glycerol + 18 hours smoking had the highest ash content of 4.05 ± 0.60
while sample containing 12 % glycerol + no smoking had the least ash content of 1.23 ± 0.32.
4.1.5 pH of samples
Table 5 shows that the pH of the samples ranged from 6.07 ± 0.15 to 6.7 ± 0.27. The results also
showed that samples cured with 6 % glycerol had higher pH compared to samples treated with
12 % glycerol and 18 % glycerol. This may be due to the moderating influence of glycerol
which reduced the extent of deleterious effect of heating and drying on free acidic groups in
samples cured with high level of glycerol. Another possible reason may be due to the fact that
smoking lowers or reduces the pH of meat products (Randall and Bratzler, 1970; and Kako
1968). From Table 5, pH, tends to decrease with increase in phenol concentration in the
samples.
4.1.6 Thiobarbituric Acid Number
The thiobarbituric acid numbers of samples are shown in Table 5 and it ranged from 0.28 ± 0.04
to 0.65 ± 0.02. The samples treated with smoke had lower (p < 0.05) TBA number compared to
samples that were not smoked. It was observed that TBA numbers obviously showed that
smoke in intermediate moisture meats samples exhibited antioxidant properties. TBA number
50
for sample cured with 18 %, 12 % and 6 % + no smoking had significantly (p < 0.05) higher
TBA number than sample treated with 6 %, 12 % and 18 % glycerol + 4 h smoking and those
treated with 6 %, 12 % and 18 % glycerol + 18 h smoking. The decrease in TBA numbers of
heavily (18 h) smoked products was due to the fact that they received the highest level of smoke
(heavy smoke) for 18 hours. Report also confirms that phenol and other phenolic compounds in
wood smoke are both antioxidants, which slows rancidity of animal fats (McGee, 2004).
4.1.7 Protein solubility
Table 5 shows that the protein solubility values of the intermediate moisture smoked meat
samples were high and ranged from 75.56 ± 2.4 to 87.4 ± 1.1. There were significant differences
among samples in their protein solubility (p < 0.05). It was observed from Table 5 that sample
treated with 6 % glycerol + no smoking had the highest value of protein solubility and there was
a decrease in trend following concentration of 4 hours smoke and 18 hours smoke. This showed
that some cross-linkage occurred during processing as a result of the reactions of heat and
phenol with proteins (Randall and Bratzler, 1970 a, b). During smoking, reduction in protein
solubility was due to direct reaction of smoked components with protein and amino acids; thus
the heavier the smoking the lower the protein solubility (Okonkwo, 2001).
4.1.8 Water activity
Table 5 shows that the water activity of the intermediate moisture meat samples ranged from
0.60 ± 0.1 to 0.92 ± 0.02. Sample containing 6 % glycerol + no smoking had the highest aw of
0.92 ± 0.02 after cooking and equilibration probably because it was cured with low percentage
of glycerol (6 %) and received no smoke. Sample cured with 18 % glycerol + 18 h smoking had
the lowest aw of 0.60 ± 0.1 when compared to other samples treated with smoke. This was
because this sample was cured with high level of glycerol (18 %) with the incorporation of
51
smoke components into the sample for 18 hours. Decrease in moisture content therefore brought
about lower aw in the samples since the two are closely related (Lawrie, 1981). Therefore, the
reduction of water activity from cooking and equilibration to 4 hours and 18 hours smoking was
due to moisture loss from the samples (Okonkwo, 2001). Glycerol used in this work actually
played a significant role as a result of its ability to bind water and reduce its availability for
chemical reactions and microbial growth (Okonkwo, 2001).
4.2 Sensory Characteristics
Table 6 shows the results obtained from sensory evaluation of the intermediate moisture meat
samples.
4.2.1 Appearance
Results in Table 6 showed that samples cured with 4 hours smoking were highly preferred by
panelists in terms of appearance. They were not significantly different (p > 0.05) and were
described as moderately attractive. Samples smoked for 18 hours were equally the next most
preferred and were described as “slightly attractive” while samples not smoked were least
preferred, though unsmoked samples containing 6 % and 12 % glycerol were still acceptable
and were described as slightly attractive. It was observed from Table 6 containing 18 % glycerol
+ no smoking, with mean score of 4.93 ± 1.22, was the least acceptable by panelist and was
described as ‘slightly unattractive’.
Thus it was observed that samples cured with 4 hours smoking and 18 hours were darker
compared to cook cured samples + no smoke. The dark colour was probably as a result of the
effect of smoke application. The pink red colour found among the unsmoked samples was due
to the reaction of nitrite from cured solution with myoglobin in the muscle (Cassens et al.,
1974).
52
Table 6: Sensory characteristics of intermediate moisture meat (IMM) samples
Samples Appearance Texture Flavour Taste General
acceptability
6 % glycerol
+ no smoking
6.60ab ± 1.55 5.73bc ± 2.28 4.33b ± 1.63 4.20e ± 1.37 5.20c ± 1.21
6 % glycerol
+ 4 h smoking
7.33a ± 0.98 7.00a ± 1.36 6.93a ± 0.59 5.40c ± 0.83 6.20b ± 0.56
6 % glycerol
+ 18 h smoking
6.80ab ± 1.32 6.33ab ± 1.22 6.87a ± 0.74 7.07ab ± 0.59 7.40a ± 0.74
12 % glycerol
+ no smoking
6.07b ± 1.71 4.86c ± 2.56 4.27b ± 1.75 4.47de ± 0.92 5.00c ± 1.51
12 % glycerol
+ 4 h smoking
7.47a ± 1.34 7.27a ± 1.03 6.53a ± 1.75 6.93ab ± 1.03 7.33a ± 0.90
12 % glycerol
+ 18 h smoking
6.67ab ± 1.84 6.33ab ± 1.34 6.93a ± 1.03 7.20ab ± 0.77 7.33a ± 0.49
18 % glycerol
+ no smoking
4.93c ± 1.22 4.60c ± 1.50 4.53b ± 1.36 4.93cd ± 1.22 4.93c ± 1.22
18 % glycerol
+ 4 h smoking
7.47a ± 1.06 7.13a ± 1.30 6.67a ± 0.62 6.60b ± 0.51 6.93a ± 0.80
18 % glycerol
+ 18 h smoking
7.00ab ± 36 6.73ab ± 1.03 6.53a ± 1.45 7.60a ± 0.63 7.53a ± 0.64
Sample means with the same superscript in the same column are not significantly different (p >
0.05); values are in mean ± standard deviation of 15-man panel.
53
4.2.2 Texture
Results in Table 6 showed that samples cured with 4 hours smoking were highly preferred by
panelist terms of tenderization. They were not significantly different (p > 0.05) and were
described as “moderately” tender. Samples smoked for 18 hours were equally the next most
preferred samples and were described as “slightly tender” while samples not smoked were the
least preferred samples. Sample containing 6 % glycerol + no smoking was described as
“neither tender nor tough” while samples containing 12 % and 18 % glycerol + no smoking
were described as “slightly tough”. The increase in toughness from cooking and equilibration to
4 hours and 18 hours smoking has been attributed to moisture loss and protein denaturation and
cross linkage during the smoking process (Okonkwo, 2001).
4.2.3 Flavour
Results obtained in Table 6 for flavor showed that all samples cured with smoke were more
preferred compared to samples that were not smoked after cooking and equilibration. It was
observed also that samples that were more preferred were not significantly different (p > 0.05)
and were described as “moderately pleasant” while samples containing 6 %, 12 % and 18 %
glycerol + no smoking were least preferred from the result and were described as ‘slightly
unpleasant’.
4.2.4 Taste
Results in Table 6 showed that samples cured with 4 hours smoking and 18 hours smoking were
acceptable by panelist and were described as “slightly sweet” while sample not containing
smoke were rejected and were described as “slightly sweet less” for sample containing 6 % and
12 % + no smoking and “neither sweet nor sweet less” for sample containing 6 % glycerol + 4 h
smoking.
54
4.2.5 General acceptability
Results obtained in Table 6 showed that samples smoked for 18 h were ‘moderately liked’ in
terms of general acceptability of the products while products containing 6 % and 18 % glycerol
+ 4 h smoking were slightly liked. Samples containing 6 % and 12 % + no smoking were
“neither liked nor disliked”. Sample containing 18 % glycerol + no smoking was “slightly
disliked” by the panelist.
4.3 Moisture sorption studies
Based on the superior physicochemical and sensory characteristics of 18 h smoked samples,
they were chosen for moisture sorption studies. The moisture sorption isotherm (MSI) plots of
intermediate moisture smoked meat samples containing 6 % glycerol + 18 h smoking; 12 %
glycerol + 18 h smoking and 18 % glycerol 18 h smoking are shown in figures 4 to 6. Figure 4
represents the isotherms for sample cured with 6 % glycerol + 18 h smoking while Figure 5
represents the isotherm for sample cured with 12 % glycerol + 18 h smoking and Figure 6
represents sample cured with 18 % glycerol + 18 h smoking. The adsorption and desorption
isotherms of selected intermediate moisture smoked meat (IMSM) samples shown in Figure 4-6
exhibited sigmoidal shaped curves and are of type II according to the Brunauer, Emmet and
Teller (BET). These shapes were expected because typeII (sigmoidal) isotherms are typical for
intermediate moisture products (Shrestha et al., 2007). For most biological materials, the
adsorption-desorption curves are sigmoidal (Labuza, 1968) as confirmed by Ajisegiri and
Chukwu (2004) and Chukwu and Ajisegiri (2006). It was observed that the curves also show
that for both adsorption and desorption, there was an increase in equilibrium moisture content
(EMC) as the water activity increased at constant temperature. These increases in EMC at
higher water activities were expected because the more the available water in the surrounding,
55
the higher the water vapor changes, thus the higher the EMC becomes. This observation agreed
with the report by Ariahu et al. (2006). It is evident from the moisture sorption isotherm plots
for selected samples that equilibrium moisture content is higher at a particular water activity for
desorption curve compared to that of adsorption. The adsorption and desorption isotherms of
most food materials generally do not coincide (Tsami et al., 1990). This phenomenon is referred
to as hysteresis. This hysteresis effect has not been fully understood, although there is a general
agreement that some thermodynamically irreversible processes must occur during desorption or
adsorption or both (McLaughlin and Magee, 1998). It has been stated that the extent of
hysteresis (the difference in aw versus EMC between desorption and adsorption) is related to the
nature and state of the components in a food, reflecting their potentials for structural and
conformational rearrangement which alter the accessibility of energetically favorable polar sites
(Yan et al., 2008).
4.4 Sorption data analysis
Based on the four sorption models used to predict the adsorptive and desorptive equilibrium
moisture content (EMC) at 20 oC, 30 oC and 40 oC, both the correlation coefficient (r2) and
percentage root mean square (% RMS) was used. These parameters were used in literature to
evaluate the goodness of fit of different mathematical models as applied to experimental data
(Ariahu, 2006).
4.4.1 Oswin model
The Oswin model was applied to sorption data of intermediate moisture smoked meat (IMSM)
samples selected. This is because Oswin is an empirical model that consists of a series of
expansion for sigmoid shaped curves and it was developed by Oswin (1946). Based on the
56
Fig 4: Moisture sorption isotherms of intermediate moisture smoked meat samples containing 6 % glycerol + 18 h smoking at equilibrium moisture contents at temperatures of 20 oC (A), 30 oC (B) and 40 oC (C) Ads = Adsorption
Des = desorption
Emc = Equilibrium moisture content
aw = water activity
A
B
C
57
A
B
Fig 5: moisture sorption isotherms of intermediate moisture smoked meat products containing 12 %
glycerol + 18 h smoking at equilibrium moisture contents at temperatures of 20 oC (A), 30
oC (B) and
40 oC (C)
Ads = Adsorption
Des = desorption
Emc = Equilibrium moisture content
aw = water activity
C
58
Fig 6 : moisture sorption isotherms of intermediate moisture smoked meat products containing 18 %
glycerol + 18 h smoking at equilibrium moisture contents at temperatures of 20 oC (A), 30
oC (B) and
40 oC (C)
Ads = Adsorption
Des = desorption
Emc = Equilibrium moisture content
aw = water activity
A
B
C
59
Oswin model used to predict the adsorptive and desorptive EMC at 20 oC, 30 oC and 40 oC, both
the correlation coefficient (r2) and percentage root mean square (% RMS) of the estimates and
Oswin constants are shown in Table 7. The correlation coefficient (r2) ranged from 0.58 to 0.96
for adsorption mode and 0.81 to 0.96 for desorption mode while the % RMS ranged from 0.64
to 4.68 for adsorptive mode and 0.77 to 1.69 for desorptive mode. The % RMS shows all values
for both adsorption and desorption to be less than 10. It was also observed that Oswin gave a
correlation coefficient of r2 > 0.58 for both adsorption and desorption in this study. The
predictive equation for desorptive mode gave better goodness of fit at all temperatures
compared to adsorptive mode. This agreed with Sopade et al. (1996) that the desorption mode is
closer to equilibrium than adsorptive mode of a sorption isotherm.
4.4.2 Henderson model
Henderson model was applied to sorption data of intermediate moisture smoked meat (IMSM)
sample selected. This was because Henderson is a commonly used model for predicting the
equilibrium moisture content (EMC) at a given water activity and temperature. This model is
very important probably because of its ability to determine the effects of temperature on
moisture sorption isotherm. Table 8 summarizes the Henderson regression analysis and
Henderson constants for intermediate moisture smoked meat (IMSM) samples selected
respectively. The correlation coefficient (r2) ranged from 0.79 to 0.99 for adsorptive mode and
0.84 to 0.98 for desorptive mode. The % RMS ranged from 1.4 to 9.1 for adsorptive mode and
1.4 to 3.9 for desorptive mode. % RMS value obtained for both adsorption and desorption,
using Henderson equation, fall within the range of 1 to 10. Meaning that Henderson equation
used predicted a good fit for intermediate moisture smoked meat with correlation coefficient (r2)
all greater than 0.79 (r2 > 0.79) for both adsorptive and desorptive mode. It was also observed
60
Table 7 : Oswin regression parameters
S/Mode Sample Temp.
(oC)
Predictive
Equation
r2 % RMS B A
Adsorption 6 %
glycerol
+ 18 h
smoking
20 0.097 x + 3.04 0.78 3.03 0.097 3.04
30 0.087 x + 3.03 0.95 1.11 0.087 3.03
40 0.058 x + 2.97 0.65 2.42 0.058 2.97
12 %
glycerol
+ 18 h
smoking
20 0.032 x + 2.95 0.90 0.64 0.032 2.95
30 0.075 x + 2.99 0.58 3.64 0.075 2.99
40 0.067 x + 2.95 0.73 2.31 0.067 2.95
18 %
glycerol
+ 18 h
smoking
20 0.081 x + 3.07 0.96 1.01 0.081 3.07
30 0.057 x + 3.01 0.73 2.03 0.057 3.01
40 0.131 x + 3.02 0.71 4.68 0.131 3.02
Desorption 6 %
glycerol
+ 18 h
smoking
20 0.058 x + 3.79 0.95 0.81 0.058 3.79
30 0.055 x + 3.65 0.90 1.08 0.055 3.65
40 0.053 x + 3.74 0.84 1.32 0.053 3.74
12 %
glycerol
+ 18 h
smoking
20 0.0 75 x + 3.39 0.96 0.95 0.075 3.39
30 0.071 x + 3.36 0.89 1.48 0.071 3.36
40 0.062 x + 3.29 0.85 1.52 0.062 3.29
18 %
glycerol
+ 18 h
smoking
20 0.061 x + 3.64 0.96 0.77 0.061 3.64
30 0.06 x + 3.48 0.81 1.69 0.06 3.48
40 0.075 x + 3.47 0.94 1.11 0.075 3.47
61
Table 8: Henderson regression parameters
S/mode Sample Temp
. (oC)
Predictive equation R2 %
RMS
A B
Adsorption 6 %
glycerol
+ 18 h
smoking
20 Y = – 0.172 x +2.88 0.89 5.34 0.061 -0.172
30 Y = – 0.145 x + 2.90 0.99 1.40 0.060 -0.145
40 Y = – 0.104 x + 2.87 0.79 4.71 0.057 -0.104
12 %
glycerol
+ 18 h
smoking
20 Y = – 0.054 x + 2.90 0.91 1.54 0.062 -0.054
30 Y = – 0.132 x + 2.88 0.67 8.16 0.059 -0.132
40 Y = – 0.116 x + 2.84 0.83 4.55 0.055 -0.116
18 %
glycerol
+ 18 h
smoking
20 Y = – 0.132 x + 2.95 0.92 3.38 0.065 -0.132
30 Y = – 0.098 x + 2.92 0.79 4.47 0.061 -0.098
40 Y= – 0.23 x + 2.82 0.83 9.1 0.054 -0.23
Desorption 6 %
glycerol
+ 18 h
smoking
20 Y = – 0.092 x + 3.71 0.87 3.08 0.139 -0.092
30 Y = – 0.093 x + 3.57 0.97 1.54 0.117 -0.093
40 Y = – 0.090 x + 3.65 0.92 2.30 0.123 -0.090
12 %
glycerol
+ 18 h
smoking
20 Y = – 0.122 x + 3.29 0.93 3.06 0.092 -0.122
30 Y = – 0.117 x + 3.25 0.90 3.39 0.085 -0.117
40 Y = – 0.100 x + 3.20 0.84 3.89 0.078 -0.100
18 %
glycerol
+ 18 h
smoking
20 Y = – 0.102 x + 3.55 0.98 1.39 0.119 -0.102
30 Y = – 0.101 x + 3.39 0.86 3.6 0.098 -0.101
40 Y = – 0.123 x + 3.3 0.96 2.2 0.093 -0.123
62
from table 8 that the predictive equation for desorptive mode gave better goodness of fit
compared to adsorptive mode.
4.4.3 Brunauer-Emmet-Teller (BET) model
The BET model was applied to sorption data of intermediate moisture smoked meat (IMSM)
samples selected. This was because BET is the most widely used model in food systems and
represents a fundamental milestone in the interpretation of multi-layer sorption isotherms
particularly the type II and III. It is also an effective method for estimating the amount of bound
water in specific polar sites of dehydrated food systems (Timmermann, 1989). The linear zed
form of the BET model: aw/M(1-aw) = Baw + A derived from the original equation: aw/M(1-aw) =
1/MoC + C-1 x aw/MoC where Mo is the monolayer moisture content, which represents the
moisture content beyond which the water attached to each polar and ionic groups starts to
behave as liquid-like phase. aw is the water activity, M is the equilibrium moisture content, B
and A are slopes and intercepts respectively. BET model was used for sorption data of IMSM
that falls within the lower water activity range of (0.1573 to 0.5816). This is because the BET
model is known to fit sorption data in the water activity range of 0.05 to 0.45 (Brennan et al.,
1990; Aguerre et al., 1989). It was evident from Table 9 that the model fits all the samples as
pointed out by the correlation coefficient ranging from 0.97 to 0.98, although it was also
observed that half of its % RMS values were higher than 10, ranging from 5.79 to 16.13. The
BET constant (C) and the monolayer moisture values (Mo) shown in Table 9 were calculated
from the slope and intercept of the BET plot (aw/M(1-aw) against aw. It was observed from Table
9 that the values of Mo ranged from 7.5 to 9.5 for adsorptive mode and from 10.9 to 19.6 for
desorptive mode. It was also evident from Table 9 that the desorptive mode had higher Mo
values than adsorption mode. This agreed with report of McLaughlin and Magee (1998) that
63
some thermodynamically irreversible processes must occur during desorption or adsorption or
both. The BET constant (C) ranged from -11.7 to -7.0 for adsorption and -10.2 to -7.6 for
desorption.
The BET monolayer moisture content was used to calculate the apparent sorbate surface area of
sorption (So). Table 9 shows the apparent sorbate surface areas sorption (m2/g solid) for the
intermediate moisture smoked meat samples and were estimated using the Cadden, (1988)
equation which states that So = (1/Ms)NoAM o in (m2/g solid). Where So is the apparent sorbate
area for monolayer sorption, Ms is the molecular weight of water (18), Nois the Avagadro’s
constant (6.023 x 1023 molecules/mol.) and A is the apparent surface area of one molecule of
water (1.10 x 10-19m2).
4.4.4 Guggenhein Anderson and de-Boar (GAB) model
The GAB model was also applied to sorption data of intermediate moisture smoked meat
(IMSM) samples selected. This was because the model has advantages over the others, such as
having a viable theoretical background since it is a refinement of Langmuir and BET theories of
physical adsorption (Ricardo et al., 2011). The three parameters (Alpha, Beta and Gamma)
gotten from the polynomial plot of aw/M versus aw2 were used to estimate the values of K, C and
Mo. where K and C are the GAB constants and Mo is the GAB monolayer. Table 10 summarizes
regression analysis for intermediate moisture smoked meat samples selected. The correlation
coefficient (r2) ranged from 0.94 to 0.99 for adsorptive mode and from 0.98 to 0.99 for
desorptive mode. The % RMS ranged from 10.9 to 13.0 for adsorptive mode and 10.2 to 11.9
for desorptive mode.
64
Table 9: BET regression parameters
S/mode Sample Temp.(oC) Predictive equation R2 % RMS
Mo C So (m2/g solid)
Adsorption 6 %
glycerol
+ 18 h
smoking
20 Y = 0.131 x - 0.013 0.97 11.66 8.47 -9.08 297.7
30 Y = 0.130 x - 0.013 0.97 9.2 8.55 -9.00 300.3
40 Y = 0.153 x - 0.019 0.97 14.4 7.46 -7.05 262.2
12 %
glycerol
+ 18 h
smoking
20 Y = 0.141 x - 0.015 0.97 15.65 7.94 -8.4 278.8
30 Y = 0.139 x - 0.015 0.97 12.01 8.06 -8.27 283.3
40 Y = 0.153 x – 0.015 0.97 16.13 7.46 -7.05 262.2
18 %
glycerol
+ 18 h
smoking
20 Y = 0.114 x – 0.009 0.98 5.79 9.52 -11.7 334.6
30 Y = 0.134 x – 0.014 0.97 10.42 8.33 -8.57 292.8
40 Y = 0.143 x – 0.016 0.97 9.8 7.87 -7.94 276.6
Desorption 6 %
glycerol
+ 18 h
smoking
20 Y = 0.056 x – 0.005 0.98 8.35 19.6 -10.2 688.9
30 Y = 0.072 x – 0.008 0.97 13.03 15.6 -8 548.9
40 Y = 0.069 x – 0.008 0.97 10.00 16.4 -7.63 575.9
`12 %
glycerol
+ 18 h
smoking
20 Y = 0.086 x – 0.008 0.97 10.40 12.8 -9.75 450.4
30 Y = 0.092 x – 0.009 0.98 6.42 12.0 -9.22 423.3
40 Y = 0.102 x – 0.011 0.97 9.91 10.9 -8.3 386.1
18 %
glycerol
+ 18 h
smoking
20 Y = 0.069 x – 0.006 0.97 7.2 15.9 -10.5 557.7
30 Y = 0.083 x – 0.008 0.97 7.19 13.3 -9.38 468.5
40 Y = 0.085 x – 0.009 0.98 8.93 13.2 -8.44 462.3
65
Table 10: GAB isotherm regression parameters derivatives for IMSM
S/Mode Samples Temp.
(oC)
Predictive Equation R2 %
RMS
K C Mo
Adsorption 6 %
glycerol
+ 18 h
smoking
20 Y = -0.074x2 + 0.093x + 0.006 0.98 12.44 0.76 22.43 9.79
30 Y = -0.056x2 + 0.079x + 0.007 0.99 10.98 0.67 18.86 11.3
40 Y = -0.69x2 + 0.096x + 0.006 0.99 11.93 0.69 25.22 9.59
12 %
glycerol
+ 18 h
smoking
20 Y = -0.048x2 + 0.83x + 0.007 0.99 11.90 0.55 23.46 11.0
30 Y = -0.071x 2+ 0.096x + 0.006 0.94 12.60 0.71 24.59 9.57
40 Y = -0.066x2 + 0.094x + 0.007 0.98 11.79 0.67 22.09 9.67
18 %
glycerol
+ 18 h
smoking
20 Y = -0.045x2 + 0.070x + 0.007 0.99 10.86 0.61 18.50 12.7
30 Y = -0.056x2 + 0.084x + 0.007 0.98 12.02 0.63 20.95 10.8
40 Y = -0.090x2 + 0.104x + 0.006 0.96 11.79 0.83 22.98 8.78
Desorption 6 %
glycerol
+ 18 h
smoking
20 Y = -0.018x2 + 0.032x + 0.003 0.99 10.21 0.54 21.92 28.40
30 Y = -0.027x2 + 0.042x + 0.003 0.99 10.65 0.62 24.74 21.88
40 Y = -0.025x2 + 0.039x + 0.003 0.99 10.89 0.61 23.24 23.43
12 %
glycerol
+ 18 h
smoking
20 Y = -0.032x2 + 0.050x + 0.005 0.99 10.85 0.60 18.57 17.85
30 Y = -0.035x2 + 0.054x + 0.005 0.98 10.84 0.61 19.61 16.63
40 Y = -0.036x2 + 0.058x + 0.005 0.99 10.64 0.59 21.63 15.65
18 %
glycerol
+ 18 h
smoking
20 Y = -0.027x2 + 0.042x + 0.004 0.99 11.90 0.61 19.28 21.34
30 Y = -0.034x2 + 0.051x + 0.004 0.98 11.28 0.64 22.08 17.83
40 Y = -0.031x2 + 0.047x + 0.005 0.99 10.72 0.62 17.19 18.80
66
It was observed from Table 10 that there was no significant difference (p < 0.05) between
desorptive and adsorptive mode for correlation coefficient (r2) results gotten.
It also showed that GAB yielded a very good fit for all samples in terms of their R2 but a high
% RMS compared to Henderson and Oswin models. From Table 10, it was observed that Mo
values obtained for intermediate moisture smoked meat using the GAB equation were higher
than those obtained with BET model in Table 9.
4.4.5. Goodness of fit of models
To evaluate the goodness of fit each model % RMS and r2 were used (Aguerre et al., 1989).
Table 11 shows the percentage root mean square (% RMS) of the models used in this study for
both adsorption and desorption. The four models yielded different %RMS for adsorption and
desorption mode. Generally Oswin equation predicted the isotherms with the smallest % RMS.
therefore this model gave better fit for both adsorption and desorption. The validity of Oswin
equation was tested and the equation found to be applicable to a series of experimental data.
Henderson equation equally was the next smallest % RMS predicted. The % RMS for the
adsorption mode ranged from 0.64 to 4.68 (Oswin), 1.4 to 9.1 (Henderson), 10.86 to 13.02
(GAB) and 5.8 to 16.13 (BET). For desorption mode, the % RMS ranged from 0.77 to 1.69
(Oswin), 1.39 to 3.89 (Henderson), 10.21 to 11.90 (GAB) and 6.42 to 13.03 (BET). It can be
summarized from table 11 that Oswin model gave the best fit in terms of % RMS (generally
lower than 10 for sorption experiment).
67
Table 11: % RMS of sorption isotherm models for intermediate moisture smoked meat
samples at different temperature
% RMS
S/Mode Sample Temp.(oC) GAB BET Henderson Oswin
Adsorption 6 % glycerol
+ 18 h
smoking
20 12.44 11.66 5.37 3.03
30 10.98 9.20 1.40 1.11
40 11.93 14.40 4.71 2.42
12 %
glycerol
+ 18 h
smoking
20 11.90 15.65 1.54 0.64
30 12.60 12.01 8.16 3.64
40 11.79 16.13 4.55 2.31
18 %
glycerol
+ 18 h
smoking
20 10.86 5.79 3.38 1.01
30 12.02 10.42 4.47 2.03
40 13.02 9.80 9.10 4.68
Desorption 6 % glycerol
+ 18 h
smoking
20 10.21 8.35 3.08 0.81
30 10.65 13.03 1.54 1.08
40 10.89 10.00 2.30 1.32
12 %
glycerol
+ 18 h
smoking
20 10.85 10.40 3.06 0.95
30 10.84 6.42 3.39 1.48
40 10.64 9.91 3.89 1.52
18 %
glycerol
+ 18 h
smoking
20 11.90 7.20 1.39 0.77
30 11.28 7.19 3.6 1.69
40 10.72 8.93 2.2 1.11
68
Table 12: Correlation coefficient of sorption isotherm models for intermediate moisture
smoked meat samples at different temperature
r2
S/Mode Sample Temp.(oC) BET GAB Henderson Oswin
Adsorption 6 % glycerol
+ 18 h
smoking
20 0.97 0.98 0.89 0.78
30 0.97 0.99 0.99 0.95
40 0.97 0.98 0.79 0.65
12 % glycerol
+ 18 h
smoking
20 0.97 0.99 0.90 0.90
30 0.97 0.94 0.67 0.58
40 0.97 0.98 0.83 0.73
18 % glycerol
+ 18 h
smoking
20 0.98 0.99 0.92 0.96
30 0.97 0.98 0.79 0.73
40 0.97 0.96 0.83 0.71
Desorption 6 % glycerol
+ 18 h
smoking
20 0.98 0.99 0.87 0.95
30 0.97 0.99 0.97 0.90
40 0.97 0.99 0.92 0.84
12 % glycerol
+ 18 h
smoking
20 0.98 0.99 0.93 0.96
30 0.98 0.98 0.90 0.89
40 0.97 0.99 0.84 0.85
18 % glycerol
+ 18 h
smoking
20 0.97 0.99 0.98 0.96
30 0.97 0.98 0.87 0.81
40 0.98 0.99 0.96 0.94
69
CHAPTER FIVE
5.0. CONCLUSION AND RECOMMENDATION
5.1. CONCLUSION
The study showed that intermediate moisture meat (IMM) products through the use of glycerol,
sodium nitrite and application of smoke (4 hours and 18 hours), moisture content and water
activities were reduced. The moisture content were reduced to a mean value of 57.00 ± 1.00 to
66.2 ± 0.10 for 0 hour smoking, 18.20 ± 0.10 to 24.5 ± 0.20 for 4 hours smoking and 17.66 ±
0.41 to 18.5 ± 0.10 for 18 hours smoking. The water activities were reduced to 0.74 ± 0.03 to
0.92 ± 0.02 for the 0 hour smoking, 0.66 ± 0.02 to 0.85 ± 0.03 for 4 hours smoking and 0.60 ±
0.1 to 0.73 ± 0.02 for 18 hours smoking. The analysis of IMM products also revealed reduction
in lipid oxidation and increase in the fat content of samples. The study also revealed that
samples cured with 4 hours smoking and 18 hours smoking were moderately and slightly
acceptable by the panelist while samples not cured with smoke were neither acceptable nor
rejected or slightly rejected by panelist. It would therefore be suggested that intermediate
moisture meat (IMM) be cured with smoking to increase the level of acceptability of the
product by consumers and also to extend their shelf life. This is because products cured with
glycerol, sodium nitrite and smoke will enhance eating quality and stay longer than those cured
with glycerol and sodium nitrite alone.
From the study, moisture sorption isotherms were obtained for sample 6 % + 18 hours smoking,
12 % glycerol + 18 hours smoking and 18 % 18 hours smoking. The moisture adsorption and
desorption isotherms of the intermediate moisture smoked meat samples exhibited a sigmoidal
shaped curve which are generally typical for intermediate moisture products. The Brunauer-
Emmet-teller (BET), GAB (Guggenheim,Anderson and deBoer), Henderson and Oswin
equilibrium moisture isotherm equations were used to predict the goodness of fit to
experimental data but the Oswin and Henderson model were found to give better prediction as
70
shown by the % RMS and correlation coefficient (r2). The monolayer moisture content (Mo), the
safest value of moisture for storage, of intermediate moisture smoked meat (IMSM) samples
selected for sorption experiment was determined using BET and GAB models. The BET
monolayer was used to estimate the apparent sorbate surface areas of sorption. The constants
obtained from all the sorption models used would permit adequate prediction of the
characteristics of intermediate moisture meat products during processing, packaging, storage
and other procedures.
5.2 Recommendations
Based on the findings from this work and at commercial level of production of IMM cured with
smoke (4 hours and 18 hours), the following should be considered:
1. Further research work should be carried out on appropriate materials for packaging
intermediate moisture smoked meat (IMSM) using the Oswin model which consist of a series
expansion for sigmoidal shaped curves.
2. Airtight sealing and inert gas inclusion of IMSM might be necessary for longer storage under
room temperature.
3. The use of other models like Double log polynomial (DLP) in analysis of sorption data for
intermediate moisture smoked meat. This is also important for wider knowledge of the products.
4. The use of clausius-clayperon equation to obtain the water activity at different temperature
provided that the heat of sorption (Qs) is known.
5.3 contribution of the research work
5.3.1 The consumers
This research work will create awareness in the mind of the consumers about existing product
such as the intermediate moisture smoked meat which has been improved through moisture
sorption studies.
71
5.3.2 The academic community
This work would provide adequate information which would act as a means of strengthening
further research and development on intermediate moisture meat (IMM) cured with smoke.
5.3.3 The food industry
The constants obtained from all the sorption models used in this work should allow adequate
prediction of the characteristics of intermediate moisture smoked meat during processing,
packaging, storage and other procedures.
72
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