Stilbene Levels in the Tissue and Juice of Muscadine Grapes (Vitis rotundifolia Michx.)

Abstract

Stilbenes are secondary metabolites of a class of non-flavanoid phenolics found in certain species of Vitis. This class of compounds includes resveratrol and a resveratrol glucoside called piceid that exists in trans and cis forms. This study was undertaken to determine the cis and trans forms of both resveratrol and piceid in the skin, pulp, seeds, and juice of nine cultivars of muscadine grapes and three cultivars of Vitis labruscana. Juice samples of the muscadine cultivars ‘Fry’, ‘Hunt’, ‘Magnolia’, ‘Watergate’, ‘Carlos’, ‘Noble’, and ‘Sweet Jenny’, and the V. labruscana cultivars ‘Albermarle’, ‘Miss Blanc’, ‘MidSouth’ and ‘Miss Blue’ were harvested at the full ripe stage and divided into two sub-samples. One subsample was used to extract juice and the other was divided into skins, pulp, and seeds. Sample analysis was performed using HPLC with a UV detector. Sample chromatagrams were compared with those of known standards for quantification. ‘Carlos’ and ‘Magnolia’ had the greatest total stilbene concentration in skin tissue and had bronze skin containing higher concentrations of total stilbenes than any of the black-skinned cultivars tested. Only one bronze skin cultivar, ‘Sweet Jenny’, had lower stilbenes than the dark skin cultivars. Piceid, cis piceid and resveratrol were found in the skins of all cultivars. ‘Carlos’ ‘Magnolia’, ‘Fry’ and ‘Albermarle’ muscadines contained cis resveratrol in the skins of the fruit. ‘Watergate’ was the only cultivar in which resveratrol was detected in seed tissue. ‘Sweet Jenny’ had the highest levels of cis piceid in seed tissue. ‘Albermarle’, ‘Carlos’ and ‘Sweet Jenny’ had significantly greater levels of cis picied in pulp tissue than all other cultivars.