Enzymatic hydrolysis of steryl ferulates and steryl glycosides
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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 γ-oryzanol), suggesting greater bioavailability in non-rice steryl ferulates. Steryl glycosides were hydrolysed by a commercial microbial β-glucosidase preparation (cellobiase), but were not effectively hydrolysed by two other highly purified β-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.
KeywordsSteryl ferulate Steryl glycoside Enzymatic hydrolysis Plant sterol γ-Oryzanol
Laura Huikko, Tanja Nurmi and Mike Powell are thanked for technical assistance. The study was funded by the University of Helsinki and The Finnish Graduate School of Applied Bioscience (ABS). L. Nyström´s research grants from the University of Helsinki Jubilee Fund and Raisio Research Foundation are gratefully acknowledged. We would like to thank the Eastern Regional Research Center, Agricultural Research Service, United States Department of Agriculture, for hosting L. Nyström as a visiting scientist, during which time part of the studies herein reported were conducted.
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