A limited metabolomics analysis validates sonication-assisted extraction of Ice Wine grape pomace polyphenols and demonstrates their seasonal variation

Plant polyphenols have received a great deal of attention for their putative health-promoting effects. Grapes are a dietary source of polyphenols such as resveratrol, quercetin, catechin, and delphinidin. These compounds are particularly plentiful in the skins and seeds pomace) of grape berries. The levels of some polyphenols, like resveratrol, have been reported to increase in late fall and early winter. Here we developed a rapid and simple bath sonication-based method for extracting polyphenols from the pomace of Vidal and Cabernet Franc grapes into a 1.5% aqueous solution of beta-cyclodextrin (BCD). BCD is an inexpensive and generally recognized as safe food additive that is widely used in food manufacturing. Using a limited metabolomics approach, the levels of 28 individual polyphenols in these extracts were determined. We demonstrate a yield of 1.30-3.18 mu g resveratrol per mg lyophilized extract from Cabernet Franc berries harvested between November and January. In addition, the extraction protocol developed yields measurable levels of polydatin, quercetin, catechin, delphinidin, and other polyphenols. The levels of many of these polyphenols vary significantly between November, December, and January based on data from 2015, 2016, and 2017. In summary, we demonstrate an efficacious method for extracting polyphenols from waste winter grape pomace that yields a wide range of polyphenols in an edible extract form and show how the levels of these polyphenols varies from November to January.