Characterisation of Extracts Obtained from Unripe Grapes and Evaluation of Their Potential Protective Effects against Oxidation of Wine Colour in Comparison with Different Oenological Products

Abstract

Unripe grapes (UGs) are a waste product of vine cultivation rich in natural antioxidants. These antioxidants could be used in winemaking as alternatives to SO2. Three extracts were obtained by maceration from Viognier, Merlot and Sangiovese UGs. The composition and antioxidant activity of the UG extracts were studied in model solutions at different pH levels. The capacity of the UG extracts to protect wine colour was evaluated in accelerated oxidation tests and small-scale trials on both red and white wines during ageing in comparison with sulphur dioxide, ascorbic acid and commercial tannins. The Viognier and Merlot extracts were rich in phenolic acids while the Sangiovese extract was rich in flavonoids. The antioxidant activity of the extracts and commercial tannins was influenced by the pH. In the oxidation tests, the extracts and commercial products showed different wine colour protection capacities in function of the type of wine. During ageing, the white wine with the added Viognier UG extract showed the lowest level of colour oxidation. The colour of the red wine with the UG extract evolved similarly to wine with SO2 and commercial tannins. The obtained results indicated that natural and healthy UG extracts could be an interesting substitute for SO2 during wine ageing.

Comprehensive Utilization of Thinned Unripe Fruits from Horticultural Crops

“…This technique also takes advantage of the grapes removed by cluster thinning [114]. In addition to reducing alcohol content, Fia et al [115] also found that the addition of unripe grape fruit extracts to wine could play a role in protecting wine color during aging, and could be an interesting substitute for SO 2 during wine ageing. Considering that unripe fruits lack phenolic maturity, and bring an excess of astringency and herbaceous aromas, Junior et al [116] found that S. bacillaris can be used to increase glycerol content and malic acid degradation, thereby balancing the lack of palate fullness caused by low alcohol content and masking 'vegetative' odors.…”