Effects of glutathione and ascorbic acid addition on the CIELab chromatic characteristics of Muscat Ottonel wines

Glutathione (GSH) and ascorbic acid (AA) are often added as antioxidants in wines for a better preservation of aroma. However, depending on the dosage of these substances, changes in colour may occur in the wines. The paper presents the effect of the addition of glutathione, with or without ascorbic acid, on the colour of Muscat Ottonel wines after 4 months of ageing in bottles. The dosage of ascorbic acid varied between 30 and 70 mg/l and that of glutathione between 10 and 100 mg/l, while in the samples where both glutathione and ascorbic acid were added the latter was kept constant at 30 mg/l. An wines contained the same amount of sulphur dioxide at the moment of addition, namely 80 mg/l total and 42 mg/l free, respectively. The analysis took into account 3 groups of samples: only with glutathione, only with ascorbic acid and with combination of glutathione and ascorbic acid. The CIELab colour parameters were determined and the colour components compared for the three groups and the control. The results showed that during storage the colour of wines evolved, parameter a showing in most samples a shift toward more red component. The most significant colour change was recorded for the samples treated only with glutathione, while the presence of ascorbic acid, with or without glutathione, lowered the value of parameter a. A synergistic effect in lowering the values of both parameter a and b was observed in the samples treated with combinations of ascorbic acid and glutathione at higher concentrations. The results suggest that a combination of glutathione and ascorbic acid may confer better stability of colour of white wines during storage. (C) 2016 The Authors. Published by Elsevier B.V.