Impact of SO2 addition before alcoholic fermentation on the oxidative stability of Chardonnay white wines

Abstract

Sulfites (SO2) addition during winemaking is a widespread practice worldwide. This addition is realized at different steps of the winemaking due to the antimicrobial and antioxidant capacity of SO2. In a context of understanding white wines oxidative stability, knowledge about the impact of SO2 on the wine molecular diversity, especially compounds involved in the antioxidant capacity of wine, appears to be very important. In recent years, some studies have shown that SO2 can react with a large number of wine compounds resulting in the formation of numerous adducts. The diversity of compounds involved is important including in particular pyruvic acid, 2-keto-glutaric acid, glyceraldehyde, sugar, phenolics compounds but also amino acids or peptides. Moreover Roullier-Gall et al. have shown using FT-ICR-MS analysis that the molecular composition of wines remains impacted by addition of SO2 to the must (0, 4 and 8 g/hL SO2), several years after winemaking. Indeed, wines made from protected must (8g/hL SO2) contain a larger diversity of CHOS and CHONS compounds than wines made from unprotected must (0 g/hL SO2). The study of the impact of glutathione addition on the sensory oxidative stability has further shown that CHOS and CHONS compounds (amino acids, aromatic compounds and peptides) are markers of the antioxidant metabolome of white wines. This suggests that CHOS and CHONS compounds arise from SO2 adducts formation but also from a protecting effect of SO2 on the antioxidant metabolome of white wines.

In this context, the aim of the present study was to compare the impact of SO2 addition and hyperoxygenation on the oxidative stability of wines, through complementary antioxidant capacity (DPPH) measurements and molecular diversity determined by targeted and untargeted analysis. 4 modalities were analyzed for two vintages (2017, 2018). Wines were analyzed during first months of barrel aging and several years after bottling (minimal aging of 3 years). Results showed that regardless of the vintage, wines from musts protected by 8 g/hL had a better antioxidant capacity compared to wines from hyperoxygenated must. Wines from protected must were also richer in phenolic compounds compared to the hyperoxygenated modality. Metabolomics analysis (LC-QToF-MS) confirmed that wines from protected must contained a diversity of peptides containing the Cysteine amino acid in their sequence, which can be involved in the antioxidant capacity of wines.