Written by Dr. Jill Cline, Ph.D.
Preservatives are components included in pet foods to protect nutrients from oxidative or microbial damage and to ensure that the food provides safe and wholesome nutrition throughout its shelf life.
Why are Preservatives Needed?
Pet food manufacturers must provide products that are both nutritious and safe for consumption by companion animals throughout the shelf life of the product. Preservatives are included in foods to prevent microbial contamination and the production of harmful toxins and to protect the food from degradation and loss of nutrients during storage.
Preservatives protect foods from microbial contamination: Food processing methods and preservatives work together to prevent microbial contamination in commercial foods. The low moisture content of dry pet foods inhibits the growth of most microbes and the high heat during cooking and the use of sealed cans preserves canned foods. Semi-moist pet foods often have a low pH and contain humectants that bind water in the product, making it unavailable for use by invading bacteria or fungi. Potassium sorbate is included as an additive in some foods to prevent growth of molds and yeasts.
Preservatives protect foods from nutrient loss: Foods that are formulated for dogs and cats contain animal fats, vegetable oils and the fat soluble vitamins A, D, E, and K. Because of their chemical structures, these nutrients are more susceptible to oxidative degradation that can lead to spoilage. Oxidative degradation refers to the destruction of nutrients as a result of exposure to oxygen and heat. It results in a loss of the food’s essential nutrients and calories and the production of toxic compounds, called peroxides, which can be harmful to the health of companion animals. Pet food that has sustained even low levels of oxidative damage may change in texture and develop an offensive odor and taste. Antioxidants are a specific type of preservative that are included in pet foods to protect fat and fat-soluble nutrients from oxidative damage.
Types of Antioxidants in Pet Foods
Antioxidants function to retard the oxidative process and prevent the destruction of the food’s fat and fat-soluble nutrients. Protecting fats from oxidation maintains the food’s flavor, odor, and texture, and prevents rancidity and accumulation of toxic end-products of lipid degradation. Similar to human foods, both synthetic (manufactured) and natural preservatives are used in commercial pet foods. Commonly used natural antioxidants are mixed tocopherols (vitamin E), ascorbic acid (vitamin C), citric acid, and rosemary. The most common synthetic antioxidants are butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), and ethoxyquin.
Mixed tocopherols (Vitamin E): Vitamin E, or alpha-tocopherol, is the most widely used naturally-derived antioxidant. Physiologically, vitamin E functions as an antioxidant in body tissues and also functions to protect fats in the diet from oxidative destruction. However, Vitamin E is just one of several types of tocopherols. Although the other forms are not essential vitamins, they are very effective as feed antioxidants. For this reason, mixed-tocopherols are often used as preservatives because they provide the highest level of antioxidant protection to foods. One disadvantage of this group of compounds is that the tocopherols are rapidly decomposed as they protect fat from oxidation, leading to a shorter shelf-life of foods that are stabilized with tocopherols alone. However, when formulating foods, manufacturers account for this by using a combination of antioxidant compounds and by declaring appropriate and safe shelf lives on their products.
Ascorbic acid (Vitamin C): Ascorbic acid functions naturally as an antioxidant but has limited value as a food preservative because it is a water soluble compound and is not easily solubilized with the lipid fraction of foods. However, Vitamin C does demonstrate additive protective benefit to foods when included with other antioxidants such as BHT and the mixed tocopherols. For this reason, it is used to complement the protective effects of the mixed tocopherols in foods that contain only natural preservatives.
Rosemary extract and citric acid: Rosemary is obtained from the dried leaves of an evergreen shrub, Rosemarinus officinalis and citric acid is found in citrus fruits such as oranges and lemons. These two naturally-occurring antioxidants are often included in combination with other antioxidants in pet foods to add supplemental protection.
BHT and BHA: BHA and BHT are synthetic products similar in structure to vitamin E and are common preservatives used in many human and pet foods. These compounds are highly effective in protecting animal fat, but are slightly less effective when used to protect vegetable oils.
Ethoxyquin: As an antioxidant, ethoxyquin is more efficient than BHA or BHT, which allows lower concentrations to be included in foods. Ethoxyquin is especially effective in the protection of polyunsaturated fatty acids, found in certain fish and vegetable oils. The maximum concentration of ethoxyquin allowed in animal feeds is 150 mg/kg. However, in response to consumer concerns about the use of ethoxyquin, the FDA requested that pet food companies voluntarily limit ethoxyquin in pet foods to 75 ppm. The pet food industry has complied with this request and is conducting additional studies of the effectiveness of ethoxyquin at even lower levels.
Pet Food Shelf Life
The term “shelf life” refers to the length of time, usually measured in months, that a pet food maintains its freshness and can be fed without a loss of nutrients or flavor. Dry pet foods have shelf lives between 6 to 16 months, while canned products typically have a 24-month shelf life. Here are some tips for making sure that you are feeding fresh food and getting the most out of the foods that you purchase for your dog or cat:
• Always check the ‘best if used by‘ date on the bag of food at the time of purchase to ensure that the product is well within its shelf life. Manufacturers of high quality foods include this information in a format that is easy to read and understand. Make sure that the food you are buying is within its recommended use date and avoid purchasing more food that your pet will consume within the shelf life of the product.
• Proper pet food storage helps to maintain the food’s nutritional integrity and prevents contamination and loss of nutrients due to moisture or excessive heat exposure. Store unopened foods in a cool, dry place, with the bag raised off of the floor. Opened bags of dry food should be stored in clean, dry containers with sealable lids. Opened cans of food should be sealed with a lid and stored in the refrigerator, and can be fed for up to three days after opening.
• Pet owners who wish to select foods that include a particular type or group of preservatives can find this information on the pet food label or by contacting the pet food manufacturer directly.