Access Type

Open Access Dissertation

Date of Award

January 2014

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Nutrition and Food Science

First Advisor

Kequan (Kevin) Zhou

Abstract

Background: Diabetes is currently a global public health problem affecting people at all ages. Dietary antioxidants have been associated with a reduced risk of type 2 diabetes. Grape pomace contains considerable amounts of polyphenols and it has been reported to exhibit an inhibitory activity against alpha- glucosidases. Alpha-glucosidases, in turn, play a major role in controlling starch digestion and therefore postprandial blood glucose, a target for diabetes management.

Objective: This study aims to investigate the anti-diabetes potential of a selection of six grape pomaces and prepare and purify active components in the active variety that specifically inhibit intestinal alpha-glucosidases. The study was also designed to evaluate the applicability of the isolated active components as natural inhibitors of alpha-glucosidases.

Methods: Chambourcin, Merlot, Norton, Petit Verdot, Syrah and Tinta Cao red wine grape pomace extracts were assessed for their rat intestinal alpha-glucosidase inhibiting activity and antioxidant properties via biochemical assays and UV detection. Then, the grape pomace variety shown to potently inhibit the enzyme was subjected to bioactivity-guided fractionation and the isolated active component was identified via analytical chemistry techniques. The characterized compound was then tested for functional food applicability via stability, enzyme specificity and cytotoxicity testing.

Results: Tinta Cao grape pomace extract was the most potent alpha-glucosidase inhibiting variety and possessed a remarkable antioxidant activity, both properties of which appeared to be correlated. HPLC analysis did not yield an antioxidant responsible for the observed trend. Hence, bioactivity-guided fractionation of the extract was pursued, yielding a pure active compound that was determined to be D-Glucopyranose 6-{(2E)-3-(4-Hydroxyphenyl)prop-2-enoate}, which also exhibited a strong antioxidant activity. Further testing indicated that the compound inhibits alpha-glucosidase and not alpha-amylase, and specifically inhibits the maltase and isomaltase moieties of alpha-glucosidase, in a dose-dependent fashion. The compound was fairly stable under different environmental and storage conditions, and it was also not cytotoxic to animal cells.

Conclusion: Red grape pomace, namely Tinta Cao, is a promising bioresource for the future development of a food-derived antidiabetic agent. At least one component, D-Glucopyranose 6-{(2E)-3-(4-Hydroxyphenyl)prop-2-enoate}, isolated from Tinta Cao grape pomace appears to potently and specifically inhibit mammalian intestinal alpha-glucosidases while exhibiting a notable ability to quench free radicals. It may thus represent an alternative future strategy for diabetes management and a novel antioxidant compound. Pre-clinical and clinical testing will validate the obtained results in vivo.

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