Effect of post-milling process on the oxidation of the rice bran

The rancidity of rice bran is predominantly triggered by lipophilic enzyme activities. Bran stabilisation and defatting are the typical processes to inactivate the processes that cause rancidity. However, little is known about how this impacts the development of volatile compounds related to odour in the rice bran. The effects of the postmilling process on the development of secondary volatile oxidation compounds in the rice bran during storage were investigated. Based on the identified metabolites, there were three possible major pathways in the formation of off-odour and key aroma degradation of the stabilised rice bran during storage, including lipid oxidation, the Maillard reaction, and Strecker degradation. Butanal-2 methyl and furan compounds contributed to the cocoa, nutty, and malty aroma and were considered the important key aroma in the defatted stabilised bran. By contrast, butanal, hexanal, 2-hexenal, butanoic acid, hexanoic acid, pentanoic acid, and heptanoic acid were the discriminant volatile compounds in the non-defatted bran, and they were considered as the markers of rancidity of non-defatted stabilised rice. It can thus be suggested that the defatting process positively contributed to the low abundance of volatile oxidation products that are responsible for bran rancidity by slowing down the formation of lipid-derived oxidation products.