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.

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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.

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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%

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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.

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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.