Epoxy and hydroxy fatty acids as non-volatile lipid oxidation products in oat.

The aim of the study was to investigate the occurrence and formation of peroxygenase catalysed non-volatile oxidised fatty acids (NVOFAs), especially epoxy and hydroxy fatty acids, which potentially provide off-flavours in oat. A method based on extraction of NVOFAs using accelerated solvent extraction and analysis by UHPLC-ELSD/MS was developed. Hydroxy and epoxy fatty acids from oleic and linoleic acids were present as major NVOFAs in non-heat treated (NHT) oat products, and the contents increased markedly during storage. In a controlled storage experiment, NVOFA contents in NHT oat flours increased to 1700-2000 µg/g, whereas in heat-treated samples, only to 200-400 µg/g. Epoxy fatty acids seemed to be the first products that occurred, followed by hydroxy fatty acids and minor NVOFAs. The formation of NVOFAs was related to lipase catalysed lipid hydrolysis and the formation of volatile lipid oxidation products. Inactivation of lipid degrading enzymes is crucial to producing stable oat products.