The main energy sources in pet foods are carbohydrates, proteins, and fats. All of these ingredients must be preserved against spoilage from organisms such as bacteria and molds, and from spoilage by exposure to air, which causes oxidation. Cooking the food helps kill any bacteria or mold that is present in the raw ingredients.
Proper packaging helps prevent recontamination by these organisms and seals out air to minimize spoilage due to oxidation. However, it only makes sense that some form of preservative is added to the food to maintain its quality and wholesomeness, no matter how it is prepared. The amount and type of preservative that is necessary depends on the formulation of the food. If no preservatives were added, the shelf life of dry or semi-moist food would be extremely short.
Of the 3 common formulations of pet food (canned, semi-moist, and dry), canned food usually contains the least amount of preservatives. This is because the canning process itself, followed by sealing in air-tight containers, destroys bacterial contaminants and prevents oxidation until the can is opened.
Dry formulations require a higher level of added preservatives to stabilize the fats and proteins, although the removal of moisture in the product serves to inhibit the growth of bacteria and molds, especially while they are still sealed in the original bag.
As a rule, semi-moist formulations require the most added preservatives because of their higher moisture content and soft texture.
Most pet food preservatives are anti-oxidants, which may be ‘natural’ or ‘synthetic’. In recent years, the majority of pet foods are preserved with natural preservatives such as tocopherols, Vitamin C and rosemary extract. Although Vitamin E is a tocopherol, it is not as good an antioxidant as other tocopherols. Thus, most manufacturers add ‘mixed tocopherols’ to the food, giving it better stability against oxidative spoilage when compared to Vitamin E alone.
Vitamin C is not a good antioxidant by itself, but works together with the tocopherols. Rosemary has a strong taste and smell, so when it is used as an antioxidant it is added as an extract rather than in its ‘natural’ state.
The main synthetic antioxidants are BHA, BHT and ethoxyquin, all of which have been used as preservatives for many decades. The first two are approved for use in human foods, while ethoxyquin is approved for use in animal feeds.
Synthetic preservatives tend to provide a longer ‘shelf-life’ to food products and the current trend towards the use of natural preservatives has lead to shorter expiration dates for pet food products.
You should be aware that suppliers of the individual ingredients of a pet food may add preservatives to the ‘raw material’ in order to stabilize it before shipping to the pet food manufacturer. The manufacturer will formulate the diet from all of the raw ingredients and add in further preservatives as necessary.
The ingredient list that is written on the product label will include the various food sources used to make up the diet, such as “poultry by-product meal”, and the various preservatives added by the manufacturer, but will not usually list anything that was added by the original supplier. Thus, just because a label says “no preservatives added”, it does not guarantee that the product does not contain preservatives – it only means that the manufacturer did not add any preservatives during the manufacturing process.
Reputable pet food manufacturers ensure that their suppliers use preservatives that are compatible with their product labeling claims.
Once you open a package of pet food, the product will become exposed to air and can potentially become contaminated with bacteria, fungi, and molds. The speed at which a product will go bad depends on the environmental temperature and the formulation of the food.
Canned food can turn rancid within a few hours on a hot summer day, while dry food is usually safe to be left out in a bowl or dish for 24 hours as long as it is protected from contamination by flies or other insects.
To protect the quality of the remainder of the package of food, you should tightly reseal the bag to prevent exposure to air, or immediately cover and refrigerate any unused portions of canned food. If the food bag cannot be resealed, or if the contents of the bag will last your pet a few weeks, it would be a good idea to transfer the food into one or more sealable plastic containers.
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Caution: These news items, written by Lifelearn Inc., are licensed to this practice for the personal use of our clients. Any copying, printing or further distribution is prohibited without the express written permission of Lifelearn Inc. Please note that the news information presented here is NOT a substitute for a proper consultation and/or clinical examination of your pet by our clinic veterinarian.