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Chapter-5 74
PET FOOD FORMULATIONS AND
STABILITY
Chapter-5 75
1. INTRODUCTION
There are a number of important considerations in the formulations of pet food and
proper nutrition of dogs. Any formulation development is a multi step process' as shown in
Fig. 1. where ideas are converted into concepts which ultimately take the shape of product.
The product that meets the quality requirements is marketed and finally reaches the end user.
In its crude sense, product formulation development is the process of meeting the needs of
end user expectations.
Need k
Ideas ^ Concept Product w Marketing Customers Need w Ideas w Concept w Product ^ Marketing w Customers
Fig 1: The process of product formulation development
The new product formulation development is an extremely complex process, which demands
the need and role of equipments in process operations, ingredients quality and quantity,
process conditions and particle size, etc.,. Formulated extruded pet food products are the
result of the interaction of the extrusion process and various ingredients of the pet food
formula. That means qualitative and quantitative selection of the raw materials, particle size
distribution of these materials in the formulation are important factors in achieving desired
product qualities and extruder performance.
The introduction of extrusion technology (chapter-02 and 03) has allowed the
formulators to put forward the innovative ideas with wide range of applications including
shaped and texturized products. As" discussed by Harper^ and Rosen^, the extruder
applications for various ingredients include different types of materials like, extruded snack
products, dry cereals, texturized plant proteins, forming pastas and pet foods. With the help
of extrusion technology, the antinutritinal and undesirable factors in soybean are inactivated
Chapter-5 76
(chapter-04) for pet food applications. With this background, the following point is focused
for discussions on pet food formulations and its stability.
I. The discussion about nutritional criteria of ingredients for product
development.
II. Formulations and manufacturing of pet food.
III. Pet food stability studies with raw and extruded soybean
IV. Effect of extrusion on nutrients.
I. NUTRITIONAL CRITERIA OF INGREDIENTS FOR PRODUCT
DEVELOPMENT.
When the right quality ingredients are mixed in selective proportion, the desired end
product can be achieved with expected and enhanced quality parameters. The enhanced
quality effect of the ingredients would result in a better value added product. The nutritive
feeding value of the ingredients can be improved by extrusion cooking which contributes to
optimum utilization of nutrients in formulations. Since the anti-nutritive factors of soybean
are inactivated by extrusion as discussed in chapter-04, the extruded soybean was included in
pet food formulations. The studies were focused on selection of the quality ingredients based
on the following nutrient profile for pet food formulations.
A. Proteins:
Protein is an essential component of dog diet, providing amino acids for the
physiological states of maintenance, growth, lactation and gestation"*. The raw materials are
selected from different sources for pet food manufacturing. Many of the plant and animal
sources provide required ingredients to Pet food. Since dogs are carnivores, by-product
meals, meat and poultry meals, and meat-and-bone meal are commonly used as proteinacious
ingredients in pet food formulations. These sources are used as animal proteins. Quality of
the animal protein sources can vary from batch to batch and hence quality of these materials
was tested before utilization in pet food formulations.
Chapter-5 77
Most dry foods contain a large amount of cereal grain such as com gluten
meal/soybean meal which are used to boost protein percentages without expensive animal
source. Generally, these meals are produced by heat treatment and their production methods
involve either over, moderate or under heating. However, as discussed in. chapter-04, the
extrusion cooking inactivated the antinutritive factors and therefore the extruded soybean
was used in pet food formulations after confirming the inactivation levels.
B. Fat
The Fat used in pet food come from different sources of plant and animals. In general,
vegetable fat from soybean, flaxseed and sun flower and animal fat from chicken, fish and
mutton are used in Pet food formulations. Fat is included in Pet food formulations as an
energy supplement as well as palatability enhancer. However, during extrusion of Pet food
and subsequent storage the fat is susceptible to oxidation resulting in poor palatability. The
deterioration of lipids can be attributed to both hydrolytic and oxidative rancidity^'^. The
factors affecting the rate of lipid oxidation can be linked to heating^
In addition to the ingredients the porous nature, pH and heating affect the quality of
the pet food as they may cause them to be more susceptible to oxidation during storage. This
oxidation gets accelerated if the free fatty acids released by soybean lipase present are in the
sample. As discussed in chapter-04, the soybean lipase activity gets inactivated due to
extrusion process and hence does not contribute to the production of free fatty acids. In
addition to the soybean extrusion antioxidants were added and optimum pet food extrusion
conditions were maintained during pet food extrusion.
C. Carbohydrate
Once considered filler by the pet food industry cereal and grain products now replace
a considerable proportion of the meat that was used in the first commercial pet foods. The
amount and type of carbohydrate in pet food determines the amount of nutrient value the
animal actually gets. Dogs and cats can almost completely absorb carbohydrates from some
grains such as wheat and rice. In 1995^ a pet food company 'Nature's Recipe' pulled
Chapter-5 78
thousands of tons of dog food off the shelf after consumers complained that their dogs were
vomiting and losing their appetite. Nature's Recipe's loss amounted to USD 20 million. The
problem was a fungus that produced vomitoxin (a mycotoxin) a toxic substance produced by
mold. Ingredients that are most likely to be contaminated with mycotoxins are grains such as
corn, cottonseed meal, peanut meal, wheat and fishmeal. To avoid contaminations in pet
food maximum residual limits as per USFDA are tested in the ingredients used for pet food
formulations
D. Additives and Preservatives
Many chemicals are added to commercial pet foods to improve the taste, stability,
characteristics or appearance of the food. Additives provide no nutritional value. Additives
include
Emulsifiers to prevent water and fat from separating,
Preservatives to retain freshness and appeal to the customers.
Artificial colors and flavors to make the product more attractive to consumers and
more palatable to their companion animals.
Fats used in pet foods are preserved with either synthetic or natural preservatives.
Synthetic preservatives include butylated hydroxyanisole (BHA) and butylated
hydroxytoluene (BHT), propyl gallate, propylene glycol and ethoxyquin. Natural
preservatives include Vitamin C (ascorbate), Vitamin E (mixed tocopherols), and oils of
rosemary, clove or other spices. Synthetic preservatives such as BHA and ethoxyquin are
used in the present study of pet food formulations.
Chapter-5 79
11. THE PET FOOD FORMULATIONS AND MANUFACTURING PROCESS
During formulations, product development and manufacturing, pet food is subjected
to palatability studies (chapter-07). Most of the dry food is made with the extruder as
explained in chapter- 3.
Ingredients* which are used in pet food are almost all similar for wet, dry and semi-
moist foods, although the ratios of protein, fat and fiber may change. The main difference
between the types of food is the water content. It is difficult to compare directly the label
claims from different kinds of food unless it is converted and equated to "dry matter basis".
Q
A typical pet food formula consists of the following specifications and ingredients .
A. Pet food Specifications:
Table-01 : Maintenance diet specifications for adult dog
Constituent % Specification Constituent % BIS AAFCO
Moisture 10.00 10.00 Crude protein 24.00 22.00 Crude fat 05.00 08.00 Crude fibre 05.00 04.00
Table-02 Pet food specification for different growth stages^. Species and Growth Stage Recommended Protein
% Recommended Fat
% Puppy 28% 17%
Adult dog 18% 9-15%
Performance dog 25% 20%
Racing sled dog 35% 50%
Lactating dog 28% 17%
Chapter-5 80
B. Ingredients for pet food :
i. Grain Byproducts ii. Animal products: iii. Plant products (other than cereal based) iv. Industrial byproducts V. Other ingredients
Different pet food formulations were done using the various combinations of
ingredients as per the details given in 2.2. In addition to the combinations of above
ingredients, the raw and extruded soybean was also used in the pet food formulations as o
indicated in table-03. The pet food formula RS was done as per the BIS specifications
indicated in table-01 to assess the effect of raw soybean on pet food palatability (chapter-07)
and stability. The other pet food formulations ES-01 to ES 03 were done with extruded
soybean as per the specifications indicated in table-02 to study the implications on
nutritional, palatability and stability parameters of pet food after soybean extrusion.
Ingredients such as extruded soybean, ground wheat, rice powder, rice bran, com
gluten meal, vegetable fat, vitamin, mineral and salt mix were used for the test formula 'ES'.
The control formula 'RS' was done with the raw soybean, ground wheat, rice powder, rice
bran, poultry by product meal, com gluten meal, vegetable fat, vitamin, mineral and salt mix.
Ground wheat and rice were incorporated as starch additives, rice bran as source of fibre,
soybean, poultry byproduct meal and corn gluten meal as protein sources and fat as energy
and for palatability. Mixing was done in a mixer separately for all the formulations by
transferring all the relevant ingredients into the paddle mixer.
The formulated mix was extruded as pellets as discussed in chapter-03. During
extmsion, similar process conditions were maintained for all pet food formulations
containing raw soybean and extruded soybean. Though raw soybean was co-extruded with
other ingredients, the inactivation will not be effective as the friction, pressure and
temperature generated may not rupture the cells of soybean particles during extrusion due to
interference from the other ingredients present in the pet food formula.
Chapter-5 81
Table-03: Pet food formulations
SI. No. Ingredients
Quantity % SI. No. Ingredients RS ES-01 ES-02 ES-03
1. Soybean seeds 15.00 00.00 00.00 00.00
2. Extruded soybean 00.00 15.00 30.00 30.00
3. Ground wheat 39.00 39.00 28.00 26.00
4. Ground rice 10.00 10.00 06.00 05.00
5. Rice bran 02.00 02.00 02.00 02.00
6. Poultry by product meal 08.00 08.00 08.00 20.00
7. Com gluten meal 15.00 15.00 15.00 05.00
8. Fat 06.50 06.50 06.50 07.50
9. Additives 00.50 00.50 00.50 00.50
10. Vitamins, Minerals and salt mix. 04.00 04.00 04.00 04.00
III. PET FOOD STABILITY STUDIES:
A. Stability protocol:
Pet food with extruded Soybean 'E-Ol' and Pet food with raw soybean 'RS' were
subjected to product stability studies"^. Stability studies were planned for determining the
stability of the Pet foods kept at atmospheric conditions 25 to 35°C temperature and 55 to
65%_RH and at accelerated conditions ie., 40°C + 1°C temperature and 60%+ 1% RH.
Analysis was carried out for Peroxide value and acid value'' which was used as the criteria to
find out the activity of lipase for determining the shelf life of the pet foods.
B. Results:
Stability studies of Pet food ES-01 resulted in Peroxide values of 4.9 meq kg~l after 365 days
at atmospheric conditions, 3.96 meq kg~l after 90 days at accelerated conditions. Whereas
pet food RS resulted in peroxide values of 37.5 and 35.25 meq kg"l at same atmospheric
and accelerated conditions respectively.
Chapter-5 82
TabIe-04: Peroxide and acid values for Pet food samples at atmospheric Conditions.
No. of days
Peroxide value meq/kg of the pet food
FFA as oleic acid %
ES-01 RS ES-01 RS 1 1.1 0.80 0.49 0.72 15 1.05 2.50 0.51 0.69 30 1.41 3.00 0.50 0.69 45 1.50 3.50 0.67 0.90 60 1.9 4.1 0.68 1.01 75 2.1 14 0.75 1.9 90 2.6 16.09 0.91 2.00 120 2.91 17.2 1.21 2.1 240 3.85 22.4 1.51 4.2 365 4.9 37.5 1.91 6.9-
Table-05: Peroxide and acid values for Pet food samples at accelerated conditions
No. of days
Peroxide value meq/kg of the pet food
FFA as oleic acid %
ES-01 RS ES-01 RS 1 0.90 01.01 0.42 0.69 15 1.10 12.18 0.51 1.21 30 1.20 15.60 0.68 1.80 45 1.38 16.19 0.87 2.1 60 2.6 18.32 0.99 3.19 75 2.79 29.10 1.26 4.10 90 3.96 35.25 1.70 6.10
The free fatty acid values for Pet food ES-01 were in 1.91 and 1.7% at
ambient (365 days) and accelerated conditions (90 days) respectively Whereas pet food RS
resulted in free fatty acid values of 6.9 and 6.1% at same ambient and accelerated conditions
respectively.
Chapter-5 83
C. Discussion
From the Stability studies data for test ES-01 and RS samples over a period of time the
increase in peroxide values are considerably reduced for Pet food test 'ES-Ol' samples
compared to test 'RS' samples. The peroxide results for test 'ES-Ol' samples kept at
atmospheric and accelerated conditions as per the table-04 and table-05, indicated that the
values increased from 0.9 and l.lmeq kg"' to 3.96 and 4.9 meq kg"' respectively
propounding almost to 4 times increase in peroxide levels. The results for test RS samples
kept at accelerated and ambient conditions indicated that the peroxide levels increased from
1.01 and 0.8 meq kg"' to 35.25 to 37.50 meq kg" respectively resulting almost 35 to 40 times
increase in peroxide value. The peroxide values of test 'ES-Ol' and 'RS' pointed out that
there is almost 10 times increase in the peroxide levels for test 'RS' samples compared to test
'ES-Ol' samples emphasizing the advantages of extrusion. The free fatty acid content which
was calculated as oleic acid showed that for test 'ES-Ol' samples which were kept at
accelerated and ambient conditions, the free fatty acid content increased from 0.42 and 0.49
% to 1.7 to 1.91 % respectively resulting almost to four times increase in free fatty acid
content. Where as, for the test 'RS' samples which were kept at accelerated and ambient
conditions, the free fatty acid content increased from 0.69 and 0.72 % to 6.10 to 6.90 %
respectively leading almost to nine times increase in free fatty acid content. Results also
indicated that increase in free fatty acid content for sample 'ES-Ol' reduced by five times
when compared to test 'RS' samples.
Test sample ES-Ol was stable atleast for 365 days at ambient conditions and 90 days at
accelerated conditions indicating relatively less oxidation of pet food samples produced using
extruded soybean in the formulations. These observations as indicated by the data in the
Table-2 where the peroxide level in test 'RS' for 60"̂ day samples kept at atmospheric
conditions are 4.1 meq kg"' which is comparatively equal to 365 days test 'ES-Ol' samples
with the peroxide values of 4.9 meq kg" . It was also noticed that peroxide values further
increased after 90 days indicating the instability of test 'RS' sample due to presence of lipase
in raw soybeans. This instability was not observed in test 'ES-Ol' samples, where extruded
soybean was included in the pet food formulations. The marginal increase in free fatty acid
and peroxide values may be attributed to auto oxidation. This consistency in stability may be
Chapter-5 84
due to inactivation of lipase during extrusion of steam-conditioned material. This inactivation
(chapter-04) of lipase resulted in low free fatty acid content and hence decrease in peroxide
value when extruded soybean was incorporated in pet food formulations. The sudden
increase of peroxide and free fatty acid values clearly indicated that lipase is active in raw
soyabean contributing to the production of free fatty acids, which further resulted in increase
in peroxide value due to oxidation. With this examination, utilization of raw soybeans in pet
food formulations is not ideal to picturize as the quality ingredient. These observations
emphasize the importance of steam conditioning and extrusion of soybeans at optimum
process conditions. These extrusion conditions aid the inactivation of antinutritional factors
in soybean and thereby suggesting extruded soybean for pet food applications and finally for
the pet food product stability.
IV. EFFECT OF EXTRUSION ON NUTRIENTS:
To study the effect of extrusion on nutrients, the studies were planned to determine
the proximate nutrient values. The nutrient analysis of crude protein, crude fat, crude fibre,
calcium and phosphorous was done for raw soybean samples, extruded soybean samples and
extruded pet food.
4.1 Results:
Table-03: Proximate value for soybean
Parameter %
Before extrusion %
After extrusion %
Crude protein 38.5 38.71 +0.21
Crude fat 17.81 18.12 + 0.31
Crude fibre 05.01 04.31 ± 0.70
Calcium 0.26 0.28 + 0.02
Phosphorous 0.61 0.62 ± 0.01
Chapter-5 85
Table-4: Proximate analysis of Pet food with extruded soyabean (ES-01) during stability studies
Parameter %
Initial Values
Accelerated conditions
Atmospheric conditions Parameter %
Initial Values
60" day 90'" day 120'" day 365'May Variation Crude protein 24.99 24.55 25.01 24.61 5.12 ±0.44
Crude fat 11.10 10.90 10.70 11.30 10.61 ±0.59
Crude fibre 02.90 02.99 3.20 02.89 03.10 ±0.30
Calcium 01.65 01.69 1.60 01.65 01.70 ±0.30
Phosphorous 01.10 01.05 1.20 01.13 01.12 ±0.10
The results as indicated in table-03 that the proximate nutrient analysis values of
soybean showed maximum variation of + 0.70 for crude fibre and minimum variation of +
0.01 for phosphorous. The analysis variation for crude protein, crude fat and calcium are +
0.21,+ 0.31 and± 0.02 respectively.
For pet food with extruded soybean, the proximate value variations indicated for
crude protein, crude fat, crude fibre, and calcium and phosphorous are ±0.44, ±0.59, ±0.30, ±
0.30 and ±0.10 respectively.
4.2 DISCUSSION:
Further more as indicated in table-3, proximate analysis values for the test ES-01 pet
food samples specifies that extrusion of soybean between 120°C and 140°C temperatures
does not hamper the important major chemical nutrients, but improves the nutritional value
of soybean by inactivation of antinutritional factors. Heating, cooking, rendering, freezing,
dehydrating, canning, extruding, pelleting and baking are so common in place that they are
simply thought of as synonymous with food itself'^. He observed that processing of meat
and by-products, which are used in pet food could greatly diminish their nutritional value but
cooking/extrusion increases the digestibility of cereal grains. The data as indicated in table-3
and table -04 and digestibility studies (chapter-07) supported their observation that proximate
nutrient analysis values are not affected by extrusion. Nutrient analysis after stability studies
at atmospheric and accelerated conditions showed maximum variation of ±0.59 and
minimum of ±0.10 for crude and phosphorous respectively.
Chapter-5 86
2. CONCLUSION:
As discussed in chapter-04, the high temperature and pressure destroys anti-
nutritional factors and ruptures oil bearing cells in short duration thus prevents untoward
effects and improves the quality and stability of the extruded soybean and soybean products
These data on pet product stability, unchanged chemical nutrients after steam conditioning
and extrusion indicates that extruded soybean is a viable ingredient for pet food
formulations'^. In fact, extruded soybean is an economical nutrient source compared to
animal proteins and soy protein hydrolysate which is an expensive ingredient. Since
extruded soybean (extruded at 120-140°C temperature) has got good quality protein and fat,
it can be used for Pet food formulations in addition to other animal sources compared to Soy
protein hydrolysate (concentrate) which is an expensive ingredient.
Chapter-5 87
3. References:
1. Hrushikesh B, Agashe and Jain N.K., 2006, Pharmaceutical Product Development,
First Edition
2. Harper J.M., Food Extrusion, Critical Reviews in Food Science and Nutrition,
1979,1 l:155-215,Feb.
3. Rossen J.L., and R.C Miller., Food extrusion. Food Technology, 1973,27 (8) 46.
4. Fahey, G.C. Jr. and Hussein. H.S., The nutritional value of alternative raw materials
used in pet foods. Proc. Pet food Forum 1997, Watt Publishing Cp., Mt Morris, IL,
pp. 12-14.
5. Camire, M.E., Camire, A., Krumhar, K. Chemical and nutritional changes in food
during extrusion. CRC Crit.Rev.Food Sci. 1990, Nutr. 29, 35-57.
6. Bjorck, I., Asp, N,-G., The effects of extrusion cooking on nutritional value- a
literature review. J. Food Eng. 1983, 2, 281-308.
7. Becker, Ross. "Is your dog's food safe?" Good Dog!, November/December 1995.
8. BIS (Bureau of Indian Standards), Indian standard Specification for Dog feeds, IS
11968-1986, page 4-5, Appendix-A, Clause 2.4.
9. Drs. Foster & Smith, Inc. 2007, Protein Requirements for Good Nutrition, (AAFCO
nutrient profile) Veterinary & Aquatic Services Department,
10. Kenneth A Connors, Gordon L. Amidon, Valentino J. Stextla, 1986, Chemical
stability of pharmaceuticals, 2"'' edition, page 26.
11. AAFCO: Association of American Feed Control Officials Incorporated. Official
Publication 2001. Atlanta:
12. Wysong, R. L. Rationale for Animal Nutrition. Midland: Inquiry Press, 1993.
13. Morris, James G., and Quinton R. Rogers. "Assessment of the Nutritional Adequacy
of Pet Foods Through the Life Cycle." Journal of Nutrition, 124 1994: 2520S-2533S.