Formation of lipid-derived volatile products through lipoxygenase (LOX)- and hydroperoxide lyase (HPL)- mediated pathway in oat, barley and soy bean

The aim of this study was to explore the formation of volatile lipid oxidation products by the lipoxygenase (LOX)-hydroperoxide lyase (HPL)-mediated pathway in oat, barley and soy bean. LOX activity was found only in barley and soy bean samples, but the lipase and HPL activity was detected in all samples. HPL showed particularly high activity with 13-hydroperoxides, while the activity was quite low when using 9-hydroperoxides, especially in the oat and barley. The optimum pH for HPL in different samples was similar, i.e., pH 6-7. In this condition, the volatile compounds formed dramatically with aldehydes and furans as the dominant products. Furthermore, a remarkable enzymatic degradation of lipids occurred during the preparation of food models with highly refined rapeseed oil (RO) and rapeseed oil fatty acid (ROFA) emulsions, where the ROFAs were more prone to oxidation than RO. This study shows the significance of lipid-degrading enzymes in plant-food flavour formation.