Submitted to: Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/25/2014
Publication Date: 8/4/2014
Publication URL: http://handle.nal.usda.gov/10113/60394
Citation: Winkler-Moser, J.K., Hwang, H.-S., Bakota, E.L., Palmquist, D.A. 2015. Synthesis of steryl ferulates with various sterol structures and comparison of their antioxidant activity. Food Chemistry. 169:92-101.
Interpretive Summary: Steryl ferulates are natural antioxidants found in cereal grains such as corn, rice, wheat, rye and triticale. Steryl ferulates from corn have previously been shown to protect frying oils from degradation, and they may have commercial potential as frying oil antioxidants and as a functional food ingredient for oils if they can be produced in a cost effective manner. From previous frying studies, questions were raised as to why corn steryl ferulates had much better activity compared to steryl ferulates from rice. In order to better understand how structural features impacts the antioxidant activity, steryl ferulates with various structural features were synthesized and their antioxidant activity was compared. We discovered that a dimethyl group at the C4 position of the sterol, as well as the cyclopropane group at the C9,C19 position, negatively affects antioxidant activity during frying. These structural features are typical of the sterols that make up the majority of rice steryl ferulates. Steryl ferulates with a saturated (i.e. no double bond) phytosterol group, such as those found in corn steryl ferulates, as well as sterols with one double bond at C5, which are typical of most common plant phytosterols, had much better antioxidant activity during frying. This information may be used by food technologists to design steryl ferulates for use as frying oil antioxidants.
Technical Abstract: Steryl ferulates extracted from corn and rice differ in the structures of the phytosterol head groups, which had a significant impact on their activity as antioxidants in soybean oil used for frying. An improved method was used to synthesize steryl ferulates from commercial sterols to better understand how structural features affect antioxidant activity in vitro, by oxidative stability index (OSI) of soybean oil, and by analysis of antioxidant activity during frying. Synthetic steryl ferulates and oryzanol did not differ much in antioxidant activity in vitro or by OSI. However, in their evaluation as frying oil antioxidants, steryl ferulates with a saturated sterol group had the best antioxidant activity, followed by sterols with one double bond in the C5 position. The results indicate that a dimethyl group at C4 as well as a C9, C19 cyclopropane group, as found in rice steryl ferulates, negatively affects antioxidant activity in frying oils.