Effect of SO₂, glutathione and gallotannins on the shelf-life of a Cortese white wine bottled with different oxygen intakes

The work aimed to study the effect of adding reduced glutathione (GSH) and/or gallotannins at bottling on the shelf-life of a Cortese white wine to limit the use of SO2. The experimental trial was carried out following a full factorial plan consisting of 8 experimental trials that differed for the content of free SO2 (2 levels: 20 and 40 mg/L), the absence/presence of gallotannins (0 and 40 mg/L) and GSH (0 and 20 mg/L). The wines of the eight trials were oxygenated respectively at 5.5 ppm and 4.0 ppm of O2. The wines oxygenated at 5.5 ppm were bottled in 135 mL bottles and monitored during 12 months of storage (colour, polyphenolic composition, GSH, free and total SO2); the wines oxygenated at 4.0 ppm of O2 were bottled in 750 mL bottles, then analysed and tasted after 15 months. The oxygen consumption rate (OCR) was measured with a luminescence-based technology. The OCR followed a first-order kinetic in all the wines, and a significant OCR acceleration was observed when increasing the concentration of free SO2. A significant increase in OCR was also observed in the samples with GSH, albeit to a lesser extent than with SO2, while the addition of gallotannins caused a decrease in the OCR. It is possible that similar mechanisms are at the basis of the acceleration of OCR observed with GSH and SO2. However, unlike SO2, GSH showed poor antioxidant efficacy in the protection of both the colour and the aromatic component, probably also due to its lower molar concentration. The presence of GSH limited the oxidative losses of SO2, mostly in wines with higher SO2 levels. However, the effect of GSH decreased over time, since after 8 months, GSH was only present in traces. The resistance to oxidative browning of wines during bottle storage depends on the concentration of free SO2 present in the medium (> 10 mg/L), therefore, higher GSH intakes, such as to ensure sufficient preservation of the free SO2 content during storage, will have to be tested to evaluate the possibility of prolonging the shelf-life of wines.