Abstract: In this paper, the effects of oak extracts on grape berry quality were studied, with the aim to make full use of oak waste. Cabernet Sauvignon and Chardonnay grapes were used as research materials. Oak extracts were sprayed onto grape berries at the early stage of veraison and the contents of tannins and polyphenols and anthocyanins in ripe grapes were determined with a spectrophotometer. Besides, the contents of monosaccharides and organic acid monomers were determined by high performance liquid chromatography (HPLC) and volatile aroma compounds were analyzed by gas chromatography-mass spectrometry (GC-MS). The results showed that oak extracts had no significant effect on physical and chemical properties but increased the total phenols and tannin contents of Chardonnay berries. Among the extracts evaluated, 25% American oak extract could result in a 33.2% increase in tannin content when compared with the control group. The oak extract could increase the contents of tannin and total anthocyanin of Cabernet Sauvignon berris, 25% American oak extract could result in a 40.7% increase in tannin content when compared with the control group, and pure American oak extract increased the anthocyanin content by 10.7%. Pure oak extracts elevated the fructose content in both varieties. Moreover, oak extracts resulted in increased glucose contents in the two varieties. Oak extracts had a significant impact on fruit aroma components in Chardonnay and Cabernet Sauvignon. The contents and types of aroma components especially esters, aldehydes and alcohols were increased after treatment. For instance, 25% American oak extract increased the concentration of 6-methoxy eugenol by 9 folds. In conclusion, exogenous oak extract could improve grape fruit quality. These results will provide a theoretical basis for the development and utilization of grape industrial processing wastes.

Key words: oak extracts, wine grape, volatile aroma, phenolic, monosaccharides, organic acid