Enzyme-catalyzed hydrolysis of γ-oryzanol

The hydrolysis of γ-oryzanol, a cholesterol-lowering and antioxidative mixture of steryl ferulates (mainly 24-methylenecycloartanyl ferulate 1, cycloartenyl ferulate 2, campesteryl ferulate 3, and β-sitosteryl ferulate 4) occurring in rice, by commercially available enzyme preparations was investigated. Lipase preparations from different sources did not accept γ-oryzanol as substrate. Cholesterol esterases, however, catalyzed a sterol-specific reaction, i.e., β-sitosterol and campesterol were liberated from 3 and 4, whereas 1 and 2 remained unhydrolyzed. The same specificity profile was observed for hydrolysis of γ-oryzanol in artificial pancreatic juice and in reactions catalyzed by pancreatic acetone powders. The data indicate that pancreatic cholesterol esterase is involved in the hydrolysis of γ-oryzanol in vivo. They also provide a perspective for tailoring the composition of steryl ferulate mixtures on a large scale.