Determination of oxidized fatty acids (OFA) of different feeding fats obtained from waste or by-products of the food chain

Over the past few years, there has been a growing attention on the presence of contaminants and degradation compounds in fats and oils used in animal feedings, due to the recent events concerning animal breeding. The aim of this study was to quantify and characterize the oxidized fatty acids (OFA) present in 123 feeding fats obtained from waste or by-products from the food chain; this determination was only focused on OFA generated from the unsaturated C18 series. Fat samples were classified in 9 categories, according to the origin of the raw material and/or the technology used for their production (acid oils from chemical refining, acid oils from physical refining, lecithins, recycled oils, animal fats, oils recovered from exhausted bleaching earths, fish oils, hydrogenated by-products and miscellaneous). Fats were first methylated with diazomethane, then converted to benzyl ester-derivatives and finally analyzed by RP-HPLC-UV/DAD. The OFA identification was confirmed by RP-HPLC-MS. The maximum OFA content found was about 17.4% of total fatty acids. The level of OFA significantly varied among the feeding fat categories, which mainly depended on the nature and quality of raw materials, as well as on the technology and processing conditions used for their production. The fatty acid oxidation degree of the analyzed fats was related to the fatty acid unsaturation level, especially to the unsaturated C18 series.