Changes in markers of lipid oxidation and thermal treatment in feed-grade fats and oils

Authors: Moser, Jill; Hwang, Hong-Sik; Kerr, Brian

Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2020
Publication Date: 3/2/2020
Citation: Winkler-Moser, J.K., Hwang, H.-S., Kerr, B.J. 2020. Changes in markers of lipid oxidation and thermal treatment in feed-grade fats and oils. Journal of the Science of Food and Agriculture. 100(8):3328-3340. https://doi.org/10.1002/jsfa.10364.
DOI: https://doi.org/10.1002/jsfa.10364

Interpretive Summary: Fats and oils used in feeds for animal production can come from a variety of sources and may not be as highly refined as oils for human consumption, and can include, for example, used frying oils. Degradation compounds that form when feed oils oxidize are known to have detrimental effects on animal growth and metabolism, but the exact compounds responsible for these effects are unknown. There is also very little information on the levels of lipid oxidation products that are present or that form in feed-grade oils when obtained and during storage and use on a farm. The objectives of this study were to determine the types of lipid oxidation products that form in a variety of feed-grade oils when oxidized at different temperatures that mimic the storage and processing conditions. In agreement with the literature on lipid oxidation, oils with higher levels of polyunsaturated fatty acids oxidized most rapidly. However, depending on the temperature, lightly refined oils such as feed-grade tallow, can also rapidly oxidize despite having low levels of polyunsaturated fatty acids. These results will be used to design future studies to gain a better understanding of the types and levels of lipid oxidation products that have detrimental impact on animal health and production.

Technical Abstract: Oxidized feed lipids have been shown to have detrimental effects on food animal growth and metabolism, but it is unknown which lipid oxidation product(s) (LOP) are responsible for the effects. In addition, little is known about the types of LOP that are present in feed oils or that may form during storage at the farm level. Therefore, the objective of this study was to determine the evolution of different classes of LOP in feed-grade oils and fats at different temperatures (22.5 °C, 45 °C, 90 °C, and 180 °C) representing production and storage conditions. The evolution of primary and secondary LOP at each temperature depended on the oil type and was mainly influenced by the fatty acid compositions but was also likely influenced by the potential presence of prooxidant compounds as well as antioxidants. Fish oil, which had the highest ratio of unsaturated/saturated fatty acids, was the most unstable oil and formed high levels of primary and secondary LOP. Despite having a low unsaturated/saturated fatty acid ratio, tallow formed substantial levels of lipid hydroperoxides at 22.5 °C, but not at 45 °C, indicating that it likely contained either moisture or prooxidants that promoted oxidation at lower temperatures, but which were either destroyed or stripped off at the higher temperatures. Measuring both primary and secondary LOP will provide better information about the oxidative status of feel oils. Measures of % total polar materials or % polymerized triacylglycerols are good indicators of thermal abuse, but knowledge of the oil history, composition, and maintaining low temperatures will help prevent oxidation of oils.