A Holistic View of the Genetic Factors Involved in Triggering Hydrolytic and Oxidative Rancidity of Rice Bran Lipids

The bran fraction of rice grains is used for extracting nutritious edible oil known as rice bran oil (RBO). In spite of its nutritional quality, bran lipids have a lower shelf-life due to the hydrolytic and oxidative rancidity. During the rice grain milling, endogenous lipases come in contact with storage lipids or triacylglycerols (TAGs) in the ruptured bran layers. The fatty acid ester bonds in the TAGs are hydrolyzed by the lipases causing the release of free fatty acids (FFAs) and glycerol. Further oxidation of these FFAs, especially the linoleic acid (18:2), are further oxidized by the action of lipoxygenases (LOXs). This reaction produces conjugated hydroperoxides of 18:2, which decompose and form secondary oxidation products responsible for the strong undesirable stale off-flavors. The outcome is a deterioration of bran lipids and significant loss of TAGs during RBO refining process. Therefore, this review aims to provide a holistic view on the current understanding of the catalog of genes and the underlying molecular mechanisms involved in triggering bran lipid rancidity. Generated knowledge about the individual genes will be crucial for developing advanced genome editing strategies to regulate rice bran lipid quality and stability.