13
15 Smoke flavourings in processed meats' 1 J. ROZUM 15.1 Introduction For centuries, people have been searching for ways to preserve their hunt to ensure a food supply that would last them through the leaner times of the year. Possibly the first method used to preserve foodstuffs was smoking. Not only did it provide a cooked product with a different aroma, flavour and colour, it also prevented the product from spoiling as fast. Whether this was an accidental discovery or a thought-out process will never be known, but it changed the way people lived and ate. Wood smoke is composed of numerous chemical compounds and the possibilities of their reactions with food components are almost infinite. Over the course of the past 30 years or so, a great deal of research has been done to divide the components of smoke into major classes. Each class is considered the primary source for given functions in the smoking of foods. The major classes include acidic compounds which contribute to flavour and skin formation, phenolic compounds which provide flavour and preservation capabilities, and the carbonyls which react with proteins and other nitrogenous sources to give food a smoke colour. A fourth group, the polycyclic aromatic hydrocarbons (PAH), are undesirable frac- tion of smoke as they are known to be carcinogenic. The differences in natural vaporous and liquid smoke PAH content will be discussed later. In early modern times researchers (Ostertag and Young, 1934) believed that the preservation of food by smoking was caused by the shrinkage of the muscle fibres and widening of the interstitial spaces. Other early inves- tigators believed that the glossy appearance of meats after smoking meant that the proper resins, phenols and aldehydes were deposited onto the meat surface. The deposition of these compounds was termed the residual antiseptic effect in smoked meats. During the pyrolysis of wood to produce smoke, there are many variables which complicate any generalization as to the source of the important components of wood smoke. However, it is generally assumed that cellu- lose and hemicellulose form the carbonyl and acid fractions and lignin forms the phenolic fractions. It is then the make-up and amount of these com- ponents in wood which lead to the various flavours from different *This chapter is dedicated to the memory of Dr C.M. Hollenbeck.

Flavor of Meat, Meat Products and Seafoods 018

Embed Size (px)

Citation preview

Page 1: Flavor of Meat, Meat Products and Seafoods 018

15 Smoke flavourings in processed meats'1

J. ROZUM

15.1 Introduction

For centuries, people have been searching for ways to preserve their huntto ensure a food supply that would last them through the leaner times ofthe year. Possibly the first method used to preserve foodstuffs wassmoking. Not only did it provide a cooked product with a different aroma,flavour and colour, it also prevented the product from spoiling as fast.Whether this was an accidental discovery or a thought-out process willnever be known, but it changed the way people lived and ate.

Wood smoke is composed of numerous chemical compounds and thepossibilities of their reactions with food components are almost infinite.Over the course of the past 30 years or so, a great deal of research hasbeen done to divide the components of smoke into major classes. Eachclass is considered the primary source for given functions in the smokingof foods. The major classes include acidic compounds which contribute toflavour and skin formation, phenolic compounds which provide flavourand preservation capabilities, and the carbonyls which react with proteinsand other nitrogenous sources to give food a smoke colour. A fourthgroup, the poly cyclic aromatic hydrocarbons (PAH), are undesirable frac-tion of smoke as they are known to be carcinogenic. The differences innatural vaporous and liquid smoke PAH content will be discussed later.

In early modern times researchers (Ostertag and Young, 1934) believedthat the preservation of food by smoking was caused by the shrinkage ofthe muscle fibres and widening of the interstitial spaces. Other early inves-tigators believed that the glossy appearance of meats after smoking meantthat the proper resins, phenols and aldehydes were deposited onto themeat surface. The deposition of these compounds was termed the residualantiseptic effect in smoked meats.

During the pyrolysis of wood to produce smoke, there are many variableswhich complicate any generalization as to the source of the importantcomponents of wood smoke. However, it is generally assumed that cellu-lose and hemicellulose form the carbonyl and acid fractions and lignin formsthe phenolic fractions. It is then the make-up and amount of these com-ponents in wood which lead to the various flavours from different

*This chapter is dedicated to the memory of Dr C.M. Hollenbeck.

Page 2: Flavor of Meat, Meat Products and Seafoods 018

wood species. Knowledge of the wood and smoke chemistry allowsresearchers to take the smoking process a step further than the ancient cave-man. They are now able to control the pyrolysis and products of thepyrolysis of wood to provide a broad spectrum of flavours and colours tothe food industry.

A look at the structure of these wood components, and some of theresearch that has been done on their breakdown products, seems to verifythese generalizations (Maga, 1988). The chemical structures of the threemajor components of wood are shown in Figure 15.1. Some of the productsand their possible pathways for formation during pyrolysis are discussedin the following sections.

15.2 Pyrolysis of cellulose

Cellulose is the major component of most wood species. The number ofproducts produced by the pyrolysis of the cellulose component is large and

(a)

(b)

(C)

Figure 15.1 Structural inter-relationships of the three major components of wood: (a) cellu-lose; (b) hemicellulose; (c) lignin.

Page 3: Flavor of Meat, Meat Products and Seafoods 018

variable. The type and quantity of products are determined by the type ofcellulose source and conditions of the pyrolysis performed. Shafizadeh(1984) has provided a list of some of the major products of cellulosepyrolysis at 60O0C (Table 15.1). The aliphatic acids and the aldehydes arethe important compounds contained in smoke flavourings produced by thebreakdown of cellulose.

A series of pathways were proposed by Byrne et al. (1966) for the break-down of cellulose to lower molecular weight aldehydes (Figure 15.2). Itis these aldehydes which are responsible for the smoke colour formationin processed meats, including fish meat, and other foods.

15.3 Pyrolysis of hemicellulose

Hemicellulose does not represent only one compound but encompasses amixture of various polysaccharides. It represents about 20-35% of themass of wood. It is the first component to undergo thermal decomposi-tion in pyrolysis.

Fengel and Wegener (1984) proposed some pathways for the decom-position of hemicellulose (Figure 15.3). The major degradation productsare furan and its derivatives and a series of aliphatic carboxylic acids.These compounds contribute to the overall flavour and chemical proper-ties of smoke but the exact reactions involved cannot be easily identified.

Compound

AcetaldehydeFuranAcetone/propionaldehydePropanalMethanol2,3-Butanedione1 -Hydroxy-2-propanoneGlyoxalAcetic acid2-FuraldehydeFormic acid5-Methyl-2-furaldehyde2-Furfuryl alcoholCarbon dioxideWaterCharTar

Relative %

2.31.61.53.22.12.02.12.26.71.10.90.70.5

12.018.015.028.0

Table 15.1 Pyrolysis products of cellulose at 60O0C

Page 4: Flavor of Meat, Meat Products and Seafoods 018

Glycollaldehyde Furan Glyoxal Acrolein Hydroxypyruv-aldehyde

Figure 15.2 Mechanisms of the formation of carbonyl compounds.

Acetyl groups O-Methyl groups

J .1Furfural and Hydroxymethylfurfural Mucic acid

1 / \ /Levulinic acid Pyromucic acid

i JV-Hydroxyvaleric acid Furan

iK -Valerolactone

Figure 15.3 Thermal degradation products from hemicellulose.

Page 5: Flavor of Meat, Meat Products and Seafoods 018

15.4 Pyrolysis of lignin

Mature hardwoods contain 20-25% lignin. The pyrolysis of lignin producesmainly phenolic compounds. A pathway for the production of phenolicsfrom lignin has been proposed by Gilbert and Knowles (1975) as depictedin Figure 15.4. Syringol, 2,6-dimethoxyphenol, is the phenol that isproduced in the greatest quantity. Syringol, and other phenolics, play thegreatest role in providing the 'smoked' flavour to smoked foods. Otherphenols, contributing to the flavour of foods, found in large quantities inliquid smoke are eugenol, isoeugenol, guaiacol, phenol and cresols.

15.5 Formation of colour in smoked foods

The main colour-forming reaction in foods caused by smoke is the reactionof aldehydes with amino groups. This reaction, known as the Maillard reac-tion, and pathways involved have been described by Namiki and Hayashi(1983) as shown in Figure 15.5. Their pathway depicts the formation of apyrazine polymer in the sugar-amino acid compound by way of a hydroxy-acetaldehyde intermediate. Hydroxyacetaldehyde is the most activebrowning agent found in smoke. In the production of liquid smoke flavour-ings, every effort is made to maintain conditions for optimal aldehydeformation. This usually requires rapid quenching of the pyrolysis productsto prevent their reaction with other smoke components. A recent trend in

Lignin

IFerulic acid

14-Methylguaiacol -« 4-Vinylguaiacol >• Acetovanillone

4-Ethylguaiacol '̂ """̂

r

Vanillin

IVanillic acid

IGuaiacol

Figure 15.4 Thermal degradation products of ferulic acid.

Page 6: Flavor of Meat, Meat Products and Seafoods 018

Schiff base Amadori product Dialkylpyrazine cation radical

Figure 15.5 Two possible pathways for radical formation in the reaction of sugars with aminocompounds.

liquid smoke production is in the development of a very rapid pyrolysisprocess to reduce the amount of time the smoke stays in the pyrolysis zone(Underwood and Graham, 1989). Current technology allows pyrolysisto occur in milliseconds instead of several seconds in older processes.Figure 15.6 shows how a reduced pyrolysis time affects the yield of hydroxy-acetaldehyde.

Table 15.2 shows the relative colour-forming potential of selected purecarbonyls when measured in three different ways. The browning indexis a procedure used by Red Arrow Products Co. (Manitowoc, WI) indetermining the amount of brown colour formation potential that iscontained in their products. A glycine paper spot test involves coating afilter paper with a 1% glycine solution and allowing it to dry. A drop ofthe test solution is then dropped onto the glycine-coated filter paper. Thefilter paper is placed in an oven set at 200-30O0F (93-1490C) for approx-imately 1.5 min or until dry. This will give a colour which is subjectivelycompared to other tests. Weiner dip tests are done to determine thecarbonyls' reaction potential on a meat system. Normal weiners are stuffedand dipped for a certain time in a carbonyl solution, and then processed.Colour formation on the weiners is then compared. Rozum (1994) hasindicated that various individual carbonyls provide colour to slow-cookedpork fat even though the nitrogen level is fairly low in fat cells. The study

Page 7: Flavor of Meat, Meat Products and Seafoods 018

also found that none of the major phenolic compounds found in smokecoloured the pork fat.

In general, the reactions that occur to give the brown colour in smokedfoods are time and temperature dependent. At higher temperatures thereactions tend to be fast, whereas at low temperatures the reactions tendto take longer. As an example, the glycine paper test takes about 1 minat 30O0F (1490C) in the oven to form complete colour, but takes over ayear at O0F (-180C) to form any colour.

TIME (ms)

Colourintensity

Darkest

Lightest

Browning index(pure carbonyls)3

Glycoaldehyde(18.9)

Pyruvaldehyde(14.8)

Glyoxal(6.4)

Diacetyl(5.3)

Furfural(4.9)

Acetol(O)

Formaldehyde(O)

Glycine paper(pure carbonyls)b

Glyoxal

Pyruvaldehyde

Glycoaldehyde

Diacetyl

Acetol

Furfural

3-Hydroxy-2-butanone

Wiener dips(pure carbonyls)b

Glycoaldehyde

Glyoxal

Formaldehyde

Pyruvaldehyde

Acetol

3-Hydroxy-2-butanone

Furfural

a!0% solutions.bGlycoaldehyde 0-3% solution; all others 5%.

Figure 15.6 Fast pyrolysis of wood (hydroxyacetaldehyde versus residence time).

Table 15.2 Colour forming potential of selected carbonyls

HYD

RO

XAC

ETAL

DEH

YDE

YIE

LD

(*)

Page 8: Flavor of Meat, Meat Products and Seafoods 018

15.6 Smoke flavour in processed meats

The flavour produced by smoking foods is a combination of unreactedsmoke components and reacted smoke-protein components. The phenoliccompounds are the major unreacted smoke components that contributesmokiness to the flavour. The unreacted and reacted acids, esters, lactonesand carbonyls also contribute to the flavour. The flavour of the carbonylscomes from the Maillard reaction products. The flavour of individualsmoke phenolics have been described by Kim (1974), as shown in Table15.3. The profile of the phenolic components in a smoke can vary fromone type of wood to another. The major independent wood sources arehickory and mesquite. To obtain a non-specific flavour a combination ofhardwoods can be utilized.

15.7 Natural vaporous versus liquid smoke

The origin of smoke flavouring can be from two sources, the burning ofwood in a smokehouse or from liquid smoke flavourings. Both provideall the necessary compounds needed to flavour and colour meats and otherfoods. In natural vaporous smokehouses, all compounds formed from the

Table 15.3 Flavour descriptions of various phenols isolated from wood smoke

Compound

Phenolo-Cresolm- and /?-Cresol2,3-Xylenol2,4-Xylenol2,6-Xylenol3,4-Xylenol3,5-Xylenol2-Ethyl-5-methylphenol3-Ethyl-5-methylphenol2,3,5 -Trime thy !phenolGuaiacol3-Methylguaiacol4-Methylguaiacol4-Ethylguaiacol4-Allyguaiacol2,6-Dimethoxyphenol2,6-Dimethoxy-4-methylphenol2,6-Dimethoxy-4-ethylphenol2,6-Dimethoxy-4-propylphenol2,6-Dimethoxy-4-propenylphenolPyrocatechol3-Methylpyrocatechol4-Methylpyrocatecol4-Ethylpyrocatechol

Description

PungentPungentPungentPungentPungentCresolicCresolicCresolicCresolicCresolicCresolicSweet, smoky, somewhat pungentWeak, phenolicSweet, smokySweet, smokyWoodySmokyMild, heavy, burntMild, heavy, burntMild, heavy, burntMild, heavy, burntHeavy, sweet, burntHeavy, sweet, burntHeavy, sweet, burntHeavy, sweet, burnt

Page 9: Flavor of Meat, Meat Products and Seafoods 018

burning of wood are deposited on the surface of the meat and the inte-rior of the smokehouse. This includes all the wanted flavour and colouringcomponents as well as the tars, volatile light organics and the carcino-genic PAH. It is these last three components that have caused manyprocessors to go from the traditional natural vaporous smokehouse toliquid smoke. In the production of liquid smoke, the water insolubles(tars), light organics and PAHs are significantly reduced. This reduces theamount of time needed for clean-up (limited tar deposits), lowers lightorganic emissions, and lowers PAH levels in the final meat and fish prod-ucts. The PAH levels may even be further reduced in some smokes byusing resins to remove the PAH. Table 15.4 shows the reduction of PAHlevel in smoke over a period of time (Underwood and Rozum, 1995).

15.8 Evolution of smoke flavourings

The evolution of liquid smoke products has also allowed processors toobtain various flavours and colours that were not available to them beforethrough natural vaporous smoking. They also allow the processor to addsmoke flavourings to various recipes at a variety of steps in the processing.

Most liquid smoke flavourings originate from one main starting ingre-dient, a 10% acid liquid smoke produced by a smoke generator. Fromthis product a wide variety of acid levels, additions and deletions can bemade to the smoke to produce several products. One of the first derivedflavours was an oil-based smoke flavouring developed by Hpllenbeck(1969). This product is produced by extracting aqueous smoke flavouringwith a vegetable oil. The oil extracts mainly phenols from the liquid toprovide a flavouring agent with no colour forming properties. This product

Table 15.4 The removal of phenols from a 10% acid liquid smoke (Charsol C-10a) by adsorp-tion on a resin column

Treated volume(gal)

Starting feed102030405065758595

105

Phenols(mg/ml)

17.01.32.44.86.37.9

12.514.315.317.016.8

Carbonyls(%)

12.411.311.111.511.512.211.8na

11.3na

12.6

Browningindex

9.99.6

10.110.610.410.39.5na9.5na9.3

Brix

25.919.221.022.623.223.424.424.624.625.426.0

na = not analysed.aRed Arrow Products Co., Maintowoc, WI.

Page 10: Flavor of Meat, Meat Products and Seafoods 018

is widely used in processed meats and is added into the emulsion priorto stuffing.

The next major development came 12 years later in the developmentof a brine-soluble flavouring. Underwood and Wendorff (1981) found thatwhen a smoked oil was extracted with polysorbate 80, the phenoliccompounds transferred into the polysorbate and became water soluble.This product is used as a smoke flavouring agent in almost all of the baconcurrently produced in the USA, is used in other smoked meats, and isbeing added as a component of the pumping pickle.

When the polysorbate 80 product is used internally, processors wouldsometimes still smoke the outside of the bacon to provide the browncolour. Seeing the need for a smoke that colours but provides low flavour,Underwood (1990) developed an aqueous product that produced colourbut possessed very little flavour. This was accomplished by treating theaqueous smoke flavour with a non-ionic resin adsorption Column whichremoves a large portion of the phenolics from the smoke. Table 15.5 showsthe removal of phenols by the resin without affecting the level of colour-forming carbonyls in a 10% acid liquid smoke solution (Underwood,1990).

The low-flavour browning agent was then taken a step further toproduce a product with no flavour with a high level of browning poten-tial. This product developed by Underwood (1991) is used on a varietyof products where only a minimum amount of smoke flavour is desiredbut a dark brown colour is wanted.

The production of liquid smoke produces two main by-products, bothof which can be used in other applications. One, the ash, can be used asa fuel source or can be further processed to produce briquets. The otheris tar, which is the insoluble fraction that remains after the liquid smokeproduction. Tar is a good fuel source and can be utilized as such. It canalso be processed into food additives itself. The first use of tar as a foodingredient was proposed by Miler (1969) who used various extractions toproduce a product for flavouring sausages. Another important discovery

Table 15.5 Antibacterial properties of smoke flavourings in culture media

Smoke flavouring

Charsol C-6a (0.25% v/v, pH 2.4)Charsol C-6a (0.25% v/v, pH5.0)Charsol C-6a (0.25% v/v, pH 7.0)Acetic acid, 6.5% (0.25% v/v)Chardex3 (0.1% w/v)Aro-Smoke P-50* (0.25% w/v)CharoiP (0.25% v/v)

% inhibition

E. coli

33113

25O

20O

S. aureus

72312552776055

P. aeruginosa

52515429466252

L. viridescens

99971599211085

aRed Arrow Products Co., Manitowoc, WI.

Page 11: Flavor of Meat, Meat Products and Seafoods 018

was by Dainius el al (1979) who used a distillation process to produce alow carcinogenic product for use in meats and pet food applications.

15.9 Food preservation with smoke

Not only does smoking provide flavour, colour and other sensory effectsto foods, it also affects preservation of foods. Smoke flavourings arepotential effective antibacterial and antifungal agents. Varying degrees ofinhibition by different smoke types against several organism types havebeen found (Sofos et al., 1988). The study showed that certain smoke vari-eties worked better than others against the same organisms. Wendorff(1981) measured the bacteriostatic and fungistatic activities of some smokeflavourings against some of the common food bacteria and fungi. Datafrom these tests are shown in Tables 15.6 and 15.7. It is believed thatthe acids and phenolics of smoke contribute to the inhibition of growthof both bacteria and fungi. However, Rozum (1995) found that when apolysorbate 80 smoke flavouring was used in cooked chicken, the pheno-lics were not able to control bacterial growth. It was hypothesized that

Table 15.6 Antifungal properties of smoke flavourings

Smoke flavouring

Charsol C-6a (0.25% v/v, pH 2.5)Charsol C-6a (0.25% v/v, pH 5.0)Charsol C-6a (0.25% v/v, pH 7.0)Acetic acid, 6.5% (0.25% v/v)Chardex3 (0.1% w/v)Aro-Smoke P-50a (0.25% w/v)

Zones of inhibition (mm2)

Penicillium sp.

21191716129

A. niger

1816121299

A. flavus

1413111388

aRed Arrow Products Co., Manitowoc, WI.

Antioxidant

Untreated controlCharoil3 (0.4%)Charoil3 (0.2%)Aro-Smoke P-50a (0.04%)Aro-Smoke P-50a (0.02%)BHA (0.02%)BHT (0.02%)Propyl gallate (0.02%)

Peroxide value (meq/kg fat)

Initial

0.80.80.80.80.80.80.80.8

Week 1

3.51.21.31.21.41.41.31.4

Week 2

8.52.02.12.02.12.11.92.1

Week 4

18.42.43.02.22.93.32.83.0

Week 26

43.13.74.63.44.9

12.54.85.8

BHA = butylated hydroxyanisole; BHT = butylated hydroxytoluene.aRed Arrow Products Co., Manitowoc, WI.

Table 15.7 Antioxidant properties of natural smoke flavourings

Page 12: Flavor of Meat, Meat Products and Seafoods 018

when confronted with multiple organisms, the effectiveness of the anti-bacterial benefits is reduced.

The phenolics in oil and polysorbate 80 smoke flavourings tend tobehave as strong antioxidants as shown by Wendorff (1981) with pork fat.Previous research and casual observations show that smoke-processedmeats do not develop rancidity as rapidly as cured, unsmoked meats.

15.10 Summary

The pyrolysis of cellulose, hemicellulose and lignin is known to provideflavour and colour to smoked meats. The aldehydes produce the colourby reacting with nitrogenous compounds in meat, while flavour is mainlyprovided by the phenolics that are deposited on the meat surface.

Through years of research, several new and innovative ways have beendeveloped to provide a wider range of smoke flavours to the meat andfood industry. The flavours range from a basic liquid smoke to smokedoils to smoked emulsifiers plus a wide variety of liquids that have beentreated to remove or add certain properties. What has already been devel-oped will definitely not be the end of new smoke flavourings, but only astep towards future flavour development.

References

Byrne, G.A., Gardener, D. and Holmes, F.H. (1966). The pyrolysis of cellulose and theaction of flame retardants. J. Appi Chem., 16, 81-87.

Dainius, B., Dame, C. and O'Hara, J. (1979). Method of producing from wood tar a liquidsmoke for use in food processing, and product of said method. US Patent 4 154 866.

Fengel, D. and Weener, F. (1984). Wood: Chemistry Ultrastructure, Reactions. Walter deGruyter, Berlin, Chapter 12.

Gilbert, J. and Knowles, M.E. (1975). The chemistry of smoked foods. /. Food TechnoL, 10,245-251.

Hollenbeck, C.M. (1969). Preparation and use of a smoke of a smoke flavoured edible oil.US Patent 3 480 446.

Kim, K., Kurata, T. and Fujimaki, M. (1974). Identification of flavour constituents incarbonyl, non-carbonyl, neutral and basic fractions of aqueous smoke condensates. Agric.Bioi Chem., 38(1), 53-63.

Maga, J.A. (1988). Smoke in Food Processing. CRC Press, Boca Raton, FL.Miler, K. (1969). Method of producing a smoke preparation. US Patent 3 445 248.Namiki, M. and Hay asm', T. (1983). A new mechanism of the Maillard reaction involving

sugar fragmentation and free radical formation. In The Maillard Reaction in Foods andNutrition, eds. G.R. Waller and M.S. Feather. ACS Symposium Series, American ChemicalSociety, Washington, DC, p. 45.

Ostertag, J.L. and Young, T.D. (1934). Textbook of Meat Inspection. Alexander Eger,Chicago, IL, pp. 529-530.

Rozum, JJ. (1994). Effects of various carbonyls and phenols on the colour of cooked porkfat. Unpublished work. Red Arrow Products Co., Manitowoc, WI.

Rozum, JJ. (1995). Microbiological quality of cooked chicken breasts containing commer-cially available shelf-life extenders. M.Sc. Thesis, University of Wisconsin.

Page 13: Flavor of Meat, Meat Products and Seafoods 018

Shafizadeh, F. (1984). The chemistry of pyrolysis and combustion. In The Chemistry of SolidWood, ed. R. Rowell. American Chemical Society, Washington, DC, Chapter 13.

Sofos, J.N., Maga, J.A. and Boyle, D.L. (1988). Effect of ether extracts from condensedwood smokes on the growth of Aeromonas hydrophila and Staphylococcus aureus. J. FoodScL, 53, 1840-1843.

Underwood, G.L. (1990). Process making liquid smoke compositions and resin treated liquidsmoke compositions. US Patent 4 959 232.

Underwood, G.L. (1991). High browning liquid smoke composition and method of makinga high browning liquid smoke composition. US Patent 5 039 537.

Underwood, G.L. and Wendorff, W.L. (1981). Smoke flavoured hydrophilic liquid concen-trate and process of producing same. US Patent 4 250 199.

Underwood, G.L. and Graham, R.G. (1989). Method of using fast pyrolysis liquids as liquidsmoke. US Patent 4 876 108.

Underwood, G.L. and Rozum, JJ. (1995). Method of removing hydrocarbons from liquidsmoke and flavouring compositions. US Patent pending 8 536 948.

Wendorff, W.L. (1981). Antioxidant and bacteriostatic properties of liquid smoke. InProceedings of Smoke Symposium, Red Arrow Products Co., Manitowoc, WI, pp. 73-87.