Overview
The use of antioxidants in dry foods is essential. Without them, all fats, oils, and fat soluble micro-nutrients would rapidly deteriorate and the food would become rancid. This degradation of fatty acids involves the addition of free radicals (usually oxygen) to form fatty acid radicals, which in turn further react with oxygen and negatively affect the odor, taste, and nutrient value of the food, as well as produces harmful byproducts.
The use of antioxidants slows this process. The success of antioxidants in slowing the fat deterioration will vary both with the type of antioxidant, as well as the stage in the manufacturing process at which it is added. Generally, the earlier in the production process the antioxidant is utilized, the more effective it is in enhancing shelf life of the product.
Types of Antioxidants
Antioxidants are categorized as synthetic or natural, with the former being the most common due to its effectiveness and low cost. The most common synthetic antioxidants used in pet foods are ethoxyquin, butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT)
BHA and BHT
BHA and BHT tend to be more effective in preventing oxidation of animal fats than of vegetable oils. Like many antioxidants, they work together with one another. However, they are less effective than ethoxyquin and are used more in food packaging than in food. Their safety has come under closer scrutiny with some pressure being made to have them removed from the U.S. Food and Drug Administration’s so-called "GRAS" (Generally Recognized As Safe) listing of food additives.
Ethoxyquin
Ethoxyquin is, in many respects, an ideal antioxidant, since it has the greatest ability to maintain its antioxidant properties throughout a pet food manufacturing process. It also appears to be the most effective, protecting both animal fats and vegetable oils. Ethoxyquin has been used in pet foods for over 20 years and presently has no known side effects at recommended levels.
Naturally Occurring Antioxidants
Of the naturally occurring antioxidants, Vitamin E (of which there are seven different tocopherols; alpha, delta, gamma, etc.) is the most common with ascorbic acid used in some cases to act as a complementary antioxidant with vitamin E. Although alpha-tocopherol has the greatest physiological value for the animal, delta and gamma have the greatest value as antioxidants in pet food. The difficulties with delta and gamma tocopherols are their relatively high cost, weaker carry-through compared to the synthetic antioxidants and their own tendency to become oxidized. Such difficulties can significantly limit shelf life.
Consumer Concerns about the Safety of Synthetic Antioxidants
Recent consumer concerns over the safety of the synthetic antioxidants have resulted in a large increase in manufacturers claiming to produce an "all-natural" pet food. Veterinarians, like pet owners, must be cautious of such statements as they are very often false. In the U.S., FDA and USDA regulations require that antioxidants be indicated on the label, regardless of where in the process they were added. In Canada, labeling laws allow manufacturers to avoid this requirement. If ethoxyquin was in the feed that was fed to the chicken, then there will be ethoxyquin in the chicken meal used to formulate the pet food. If ethoxyquin was added to the vitamin-mineral premix before it was sent to the manufacturer, it will be found in the food. Under neither circumstance was it added directly by the manufacturer and hence need not be indicated on the label. Some major manufacturers have the capability to control the pet food production from the growing of the grain to the final steps in manufacturing. Under these circumstances, the manufacturers’ claim of "no ethoxyquin" may well be valid. Such control, however, is very uncommon.
Storing Pet Food
As the deterioration process is enhanced by both heat and light, storing dry foods in a cool, dark location is advised. When storing dry food in metal containers, it is advisable to keep the food in its original packaging inside the container, as the packaging material itself may also contain antioxidants. Direct contact of the food with certain heavy metals may accelerate the degradation process. Finally, keeping opened bags tightly sealed between use will minimize contact with air, the primary source of free radicals.