| Muscadine grape (Vitis rotundifolia) has potential health-promoting benefits and antioxidant properties from characteristic phytochemicals such as ellagic acid, ellagic acid glycosides, and ellagitannins. To provide fundamental information on ellagic acid derivatives in this commodity, typical polyphenolic compounds were characterized in eight cultivars. All polyphenolics generally increased as fruit ripened and the highest concentrations were located in the skins. Hot-pressed juices contained considerably lower polyphenolic concentrations than were present in whole grapes with actual recovery varying widely among cultivars. Antioxidant capacity was appreciably influenced by cultivar, maturity, and location in the fruit with good correlations to soluble phenolics found in both methanolic and ethyl acetate extracts (r = 0.83 and 0.92, respectively). Glycosidic forms of ellagic acid and major flavonoids were isolated by a series of solid-phase extractions. By using HPLC-MS/PDA, chemical identities were elucidated as ellagic acid xyloside, ellagic acid rhamnoside, myricetin rhamnoside, quercetin rhamnoside and kaempferol rhamnoside. Ellagitannins, a major source for hydrolytic free ellagic acid, were present in the C18 non retained fraction and their molecular weights having never been reported were determined.; Because of the lack of data on hydrolytic properties of ellagic acid precursors, central composite design was applied to demonstrate the evolution of hydrolytic ellagic acid depending on various time-temperature combinations in response surface methodology. Hydrolysis of ellagic acid precursors would be more temperature-dependent than time-dependent, and the resultant additional free ellagic acid showed good correlation to antioxidant capacity (r = 0.83). Using enzymes, beta-glucosidase (E.C. 3.2.1.21) or tannase (E.C. 3.1.1.20) is an alternative application to hydrolyze ellagic acid precursors, beta-glucosidase showed better reactivity on ellagic acid derivatives compare to tannase.; During storage, ellagic acid glycosides were relatively stable with ellagitannin hydrolysis the major source for evolution of free ellagic acid in a juice system. Free ellagic acid is partially responsible for the formation of insoluble sediments in addition to other juice constituents such as metal ions or insoluble pectins. Ascorbic acid fortification and air sparging did not significantly affect concentrations of ellagic acid derivatives in stored juices. However, a mild heat treatment influenced ellagitannin hydrolysis and was likely associated with activation of natural enzymes present in the juice.; Results provided by these studies suggest beneficial reasons to consume muscadine grapes leading to improve the market value of this crop not only as fresh grapes, juice or wine but also as health promoting components in various types of processed food. |
