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.
Highlights
Sulphur dioxide (SO2) is a chemical additive widely and traditionally used to preserve wine from oxidation and microbiological spoilage
The phenolic composition of the Unripe grapes (UGs) extracts was similar while the concentration of the different compounds and the total amount of the different phenol classes varied according to the type of extract
The Sangiovese extract had the highest concentration of flavan-3-ols, procyanidins and flavonols, while the Merlot and Viognier extracts had the highest concentration of phenolic acids
Summary
Sulphur dioxide (SO2) is a chemical additive widely and traditionally used to preserve wine from oxidation and microbiological spoilage. SO2 in food and beverages is associated with several human health risks including dermatitis, urticaria, abdominal pain, bronchoconstriction and anaphylaxis [1]. Other preservatives, such as ascorbic acid and potassium sorbate, can be used in association with SO2 to preserve wine from oxidation or to prevent fermentation of wines with residual sugars. Consumers’ increasing demands for “natural” and “healthy” wines has induced winemakers to lower the amount of SO2 in wine or to find alternative solutions to sulphur dioxide [3]. In 2011 the European Community established that a SO2 content of more than 10 mg/L should be declared on the wine label
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