Page 175 - Small Animal Clinical Nutrition 5th Edition

Commercial Pet Foods 177

inhibit bacterial putrefaction, mold formation or both. confinement units. Saponins or other active compounds in the
VetBooks.ir Examples include acids, propylene glycol and propionate and extract appear to reduce levels of free ammonia by binding
ammonia or converting ammonia to other products. Some
sorbate salts.
Humectants yucca extracts may also inhibit urease enzymes. Whether bind-
ing or preventing free ammonia is an effective way of reducing
Humectants reduce water activity and prevent loss of water pet fecal odor has not been proved. Yucca extract is not official-
after processing. See the soft-moist manufacturing section in ly approved for odor reduction use in pet food, although it is
this chapter for more details. approved as a flavoring agent for pet and human foods.

Coloring Agents/Preservatives Palatability Enhancers
Natural and synthetic colors are often added to pet food prod- Pet food companies have done a great deal of work in the area
ucts to enhance consumer appeal. Examples of natural colors of palatability enhancement. In general, dogs like fats, sugars,
include the carotenoids. Synthetic colors used in pet foods meat ingredients and digests, which are animal tissues that have
include iron oxide; coal tar derivatives (azo dyes) such as tar- been chemically or enzymatically altered. The digestion process
trazine (Food, Drug & Cosmetic [FD&C] yellow No. 5), sun- from which digests are made releases amino acids,such as lysine,
set yellow (FD&C yellow No.6) and allura red (FD&C red dye and dipeptide combinations that enhance palatability for dogs.
No. 40) and none-azo dyes such as brilliant blue (FD&C blue Cats strongly prefer meat ingredients and inorganic acids such
No. 1) and indigotin (FD&C blue No. 2). An artificial color as phosphoric acid to fats and sweet ingredients such as whey
may only be used in a pet food in the United States if it is list- and sugar. Cats also strongly prefer the amino acids cystine and
ed as safe in the United States Food and Drug Regulations (21 glycine. Feline digests generally have a low pH, which also aids
CFR 73 and 74).Several additives are not colors themselves but in preservation. Digests are available in dry and liquid forms to
are used to prevent discoloration of products. Examples of color best accommodate the manufacturer’s application process.
enhancers or preservatives are the nitrites and bisulfites. Formulating dry pet foods with wet meat ingredients com-
bined with fat (up to about 25% of the product) also improves
Emulsifying Agents and Stabilizers/Thickeners palatability (Box 8-6). In this process, a liquid mixture of meat,
Gums (hydrocolloids), glycerin, glycerides and modified starch water and fat is pumped into the extruder raising the overall
are used to prevent separation of ingredients and create the moisture, which is then driven off during the drying process.
gravy, sauce or jelly portion of moist pet foods. These additives The palatability of the finished product is enhanced because the
allow manufacture of high-moisture foods that are highly wet meat ingredient is cooked once in the extruder, as opposed
palatable to pets, but that do not have an excess of free water. to meat meals, which are rendered first then extruded.
Gums are long-chain,high molecular weight polysaccharides Palatability enhancers are less effective in a canned matrix
that dissolve or disperse in water to build viscosity in or thick- because of the high-moisture environment and deactivation
en products. Gums also are used for secondary effects that from high processing temperatures. Therefore, meat selection
include stabilization of emulsions, suspension of particulates, becomes the most important factor in improving the palata-
inhibition of syneresis (release of water from fabricated foods) bility of a moist product. In addition, a higher moisture con-
and formation of films or gels. Gums frequently used in pet tent can increase the palatability of moist foods. Table 8-9
foods include seaweed extracts such as alginates (brown sea- lists some palatability enhancers commonly used in the pet
weed) and carrageenan (red seaweed), seed gums such a guar food industry.
gum (ground endosperm of guar plants), microbial gums such
as xanthan gum (bacteria originally isolated from the rutabaga COMMERCIAL PET FOOD
plant cultured on carbohydrate media) and chemically modified MANUFACTURING
plant materials such as sodium carboxymethylcellulose (cellu-
lose chemically modified to become water soluble). Modified Principles of Extrusion/Dry Manufacturing
celluloses and vegetable gums are frequently sprayed on the sur- Most commercially prepared dry pet food is manufactured
face of commercial dry foods with digests. Water mixed with using a batch system (Figure 8-12). This system grinds and
these dry foods creates a gravy. blends raw ingredients in predetermined amounts ranging from
1,000 to 5,000 kg, depending on capacity, then transports the
Miscellaneous Additives resulting matrix to an extruder where it is cooked and formed
Polyphosphates are frequently used as additives in baked treats into kibbles. After extrusion, the kibbles are transported to a
and moist pet foods.These additives serve as dough condition- dryer where they are dried to target moisture, and then trans-
ers and help to improve texture, retain natural moisture and ported again by air or vibratory or conveyor belts to sites where
protein in meat ingredients, reduce oxidation and allow better fat and flavor enhancers are sprayed or dusted on the surface.
color development. The kibbles may or may not be sent through a cooler. The fin-
Extracts of Yucca schidigera are marketed in pet foods as a ished product is then transported to packaging machines that
means of reducing fecal odor. Yucca extracts, in higher concen- place it in containers for shipment and distribution. The entire
trations, reduce atmospheric ammonia in livestock and poultry process is usually automated and computer controlled.