Tracking of sulfonated flavanol formation in a model wine during storage

Abstract

AIM: The aim of this work was to determine the reaction products of bisulfite with grape seed flavanols and changes therein over different storage conditions in a model wine in order to gain knowledge of the formation of these compounds which could be markers of aging in wines stored under inappropriate conditions [1].

METHODS: A model wine solution (10% ethanol, 5 g tartaric acid, pH=3.6) with 15 g of commercial grape seed extract (tannin concentration, 6 g/L) and 5 g of Na2S2O5 was subjected to different storage conditions (temperatures 20, 37 and 60 ºC, during 3 months). Monomeric and dimeric flavanols and their sulfonated derivatives were analysed by HPLC-ESI-QTOF-MS/MS.

RESULTS: The sulfonation reaction gave rise to several non-galloylated and galloylated flavanol sulfonates, mainly products of (epi)catechin which were found at higher concentrations in the grape seed extract. Storage time led to the formation of these compounds, even though it was observed greater sulfonated flavanol concentrations at higher temperatures, increasing reaction speed. At 60 ºC, dimeric flavanols were quickly degraded, being a further factor for the sulfonated monomeric product rise in the same way as (epi)catechin concentrations from condensed tannins. 

CONCLUSIONS

Temperature contributed to the sulfonation reaction in a model wine, favouring the formation of sulphonared flavan-3-ols derivatives and tannin depolymerization. Our findings based on the study of sulfonated flavanols could be useful for better understanding the chemical changes during wine ageing.