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Pet Food and Rancidity: More than Meets the Palate

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Pet Food and Rancidity: More than Meets the Palate?

Here we are in the third post of a six-post series focusing on pet food, pet treat, and pet supplement testing considerations. We have explored guaranteed analysis and other testing considerations such as shelf life and microbes. This time around I’ll expand on a topic that people often view as less a food safety issue and more of a palatability issue: Rancidity.

What is Rancidity?

Have you ever added butter to your food and wound up with an entree that tastes like dish soap? It’s possible that your container had some soap remnants, but more likely it’s rancidity at work. Rancidity occurs when fats and oils, i.e. lipids, begin to oxidize. Rancidity can be observed as an off odor or foul taste, such as a “soapy” or bitter flavor, in ingredients and finished products. Exposure to light, heat, microbial enzymes, and oxygen can all result in lipids oxidizing and turning rancid.

Rancidity and Ingredient Use

Many manufacturers of pet consumables are using ingredients with a significant amount of fat somewhere along their process. If you use ingredients that contain anything more than 2-5% fat such as oils, tallows, raw meats, flax, etc., your ingredients are at risk of turning rancid. Items that contain unsaturated oils are known for going “bad” more quickly than others; examples include canola or vegetable oil. Including ingredients that are on the brink of oxidizing or have already oxidized will cause the finished product to have the same issues. Verifying ingredients or ingredient suppliers is one way to avoid pitching a lot of finished product due to oxidation.

Rancidity and Final Products/Shelf Life

As oxidation happens over time, the shelf life determination of products should take rancidity into consideration. A product may be fit for consumption from a microbial, textural, and visual aspect, but if the flavor or odor is off, a pet will likely refuse to eat the product. As many of us know or acknowledge, animals tend to have a much more sensitive palate and sense of smell. We may not notice a product is rancid, whereas our pets will turn it down. To avoid releasing products with undesirable organoleptic traits, there are several options to assay the product before release. The same tests can be done to aid in evaluation of new product’s shelf life. For shelf life specifically, we tend to recommend using a primary indicator and a secondary indicator because rancidity occurs in stages.

Initial Indicator: Peroxide Value – This analysis, often referred to as “PV” for short, is indicative of the number of peroxides in the lipids.

Secondary Indicator: p-Anisidine Value – Also referred to as pAV, this assay quantifies the aldehydes in the material. As peroxides continue to degrade, they produce aldehydes. At low levels, aldehydes can produce very strong odors and less than desirable flavors.

The addition of antioxidant treatments and careful consideration/evaluation of ingredients can help hold off oxidation and prevent rancidity over time.

The above tests are two of many available. To learn more about the other tests offered to evaluate rancidity, read Eurofins’ Services page “Rancidity.”

Rancidity as a Food Safety Concern

As I mentioned, people often view rancidity, in the short term, as a palatability issue. However, rancid products can cause upset stomach leading to nausea, vomiting, or diarrhea. Longer term, free radicals are a concern. Free radicals, in layperson’s terms, are atoms that have unpaired electrons. These atoms look to find electrons to pair with and often damage key pieces of ours and our pets’ bodies such as proteins, DNA, cells, etc. In studies with humans, free radicals and oxidative stress have been linked to certain cancers, neurological disorders, and cardiovascular diseases such as heart disease.

In Summary

It is important to know your product and understand the risks associated with materials containing anything more than 2-5% fat. Releasing a rancid product into the marketplace causes negative customer experiences and brand damage. Testing your incoming ingredients and finished products can help you manage the quality your product. 


The Author

Kari Nichols, Senior Project Manager - Pet Nutrition

Eurofins Nutrition Analysis Center (Des Moines, IA)