Activity-guided fractionation of different wheat grain varieties

Abstract

Since observational studies have consistently shown an inverse relationship of whole grain consumption and risks for chronic diseases, the 2010 US dietary guidelines recommend the daily consumption of at least three whole grain servings. It is assumed that that both dietary fiber and, potentially even more important, whole grain phytochemicals contribute to the exerted health benefits. Because little is known about the contribution of individual phytochemicals to whole grain bioactivities, the aim of this thesis was to use activity-guided fractionation to identify major contributors of wheat to select in vitro bioactivities. Three wheat varieties (BacUp, blue wheat and Wheaton) were screened for in vitro antioxidant activity and blue wheat was additionally screened for starch digestion inhibitory compounds. Overall, the profiles of the dominant antioxidants in the three wheat varieties were very similar, with the exception of anthocyanins, which are only present in the pigmented blue wheat. One novel compound, beta-D-glucopyranosyl-(1->6)-beta-D-glucopyranosyl-(1->6)-(4-hydroxy-3-methoxy-phenyl)-beta-D-glucopyranoside, with potent in vitro antioxidant activity was identified in all varieties. A minor constituent of blue wheat, 1-(3,5-dihydroxyphenyl)heneicosan-2-one, was shown to substantially reduce the in vitro activity of α-amylase. In addition, certain fatty acids were demonstrated to reduce in vitro amylose digestion by α-amylase; however, this effect is most likely due to the formation of starch-fatty acids clathrates and not to an inhibition of the enzyme.