Enzymatic hydrolysis of steryl ferulates and steryl glycosides

Steryl ferulates (SF) and steryl glycosides (SG) are phytosterol conjugates found characteristically in cereals. Currently, little is known about their properties with respect to enzymatic hydrolysis. SF and SG were extracted and purified from rye and wheat bran. Their percentages of hydrolysis with different enzymes were studied using normal phase HPLC with UV detection for steryl ferulates and evaporative light scattering detection for steryl glycosides. Steryl ferulates were hydrolysed by mammalian digestive steryl esterases. It was further demonstrated that a mixture of steryl ferulates from rye and wheat was hydrolysed much more effectively than a steryl ferulate mixture from rice (commonly known as gamma-oryzanol), suggesting greater bioavailability in non-rice steryl ferulates. Steryl glycosides were hydrolysed by a commercial microbial beta-glucosidase preparation (cellobiase), but were not effectively hydrolysed by two other highly purified beta-glucosidases. These results demonstrate for the first time the potential use of enzymes as a replacement for acid hydrolysis in analytical procedures for SG and also provide insights about the potential bioavailability of these sterol derivatives in human digestive systems.