Properties of Wine Pomace Flours from Koshu and Cabernet Sauvign on Grapes Grown in Japan

Wine pomace is a solid byproduct of winemaking and is often destined for waste. Wine pomace can be an upcycle resource because it contains compounds with properties functional for human health. Characteristics of pomace from Japanese Koshu grapes (for white wine) and macerated Cabernet Sauvignon red grapes were compared by evaluating the levels of various phenols, antioxidant activity, inhibitory effects on angiotensin-converting enzyme, heat tolerance, and resistanceto in vitro gastrointestinal digestion. In addition, the stability of pomace resveratrol in cookies stored for a year was investigated. Cabernet Sauvignon pomace was superior in the levels of total polyphenols, resveratrol, and proanthocyanidins compared with Koshu pomace. There was no significant difference in γ-aminobutyric acid levels between Koshu and Cabernet Sauvignon pomace extracts. Antioxidant activity and the inhibitory effect on angiotensin-converting enzyme were higher in Cabernet Sauvignon pomace extracts than in Koshu extracts. Heating reduced the levels of components, but the total polyphenols content of Koshu pomace was the least affected by heating. Correspondingly, there was no decrease in the antioxidant activity of Koshu pomace extract after heating. In vitro small intestine digestion decreased the levels of total polyphenols and proanthocyanidins, but not resveratrol levels. Resveratrol levels in cookies containing pomace flour and stored dry at ambient temperature were stable for at least a year. Overall, Cabernet Sauvignon pomace would be more useful as an upcycled resource based on the levels of useful ingredients, in comparison with Koshu pomace.