Maturation under different SO₂ environments: the impact on amino acid and volatile profile for two white wines

Abstract

EU countries are in the top 16 of the world’s wine producers. To respond to a public health concern, caused by SO2 excessive exposure, EU has required a warning in the products indicating that sulphites are present if concentrations are higher than 10mg/L and its reduction or replacement whenever possible. This additive is used as a preservative agent in the winemaking process, due to its antioxidative and antimicrobial properties[3]. Wine aroma depends on many factors, being grape variety and winemaking process that most contributes to volatile organic composition (VOC) found in wines where amino acid composition, due to their biosynthetic products play an important role. Also, during wine ageing VOCs can change depending on many factors such as temperature, pH or oxidation process[4]. In this work, the impact of different doses of SO2 (added after alcoholic fermentation) was evaluated on wine VOCs over time and amino acids content after 3 months over lees.

HS-SPME-GC/MS was used to identify and semi-quantify VOCs, and HPLC-DAD was used for amino acids quantification. Two white wines were studied: one varietal (Antão Vaz; AV) and one blend (BL) of Portuguese varieties. After being kept for 3 months over lees, wines were bottled and VOCs and amino acids were analysed after 3 and 6 months.

A total of 83 compounds were tentatively identified,70 compounds in monovarietal wine and 73 in the blend wine. The chemical functional groups observed were esters, alcohols, carboxylic acids, aldehydes and 12 miscellaneous compounds. When a Principal Component Analysis (PCA) was performed on VOCs semi-quantification of each wine it is observed that PCA plots present different trends throughout the factors under study. In Antão Vaz was attain lower samples distinction for different SO2 doses on sample with 3 and 12 months. However, for the evolution time of 6 months, samples were well separated. In this case, both factors seem to influence the distribution of samples with a similar weight. For the blend wine, a worse distribution of the samples was observed for evolution time of 3 and 6 months. This indicates that they might be more sensitive to SO2 doses and evolution time when compared with Antão Vaz wines. Regarding amino acids profile it was observed that maturation on lees lead to an increasing concentration of AA. However, Antão Vaz was more influenced by the SO2 doses applied.