Reactivity of volatile thiols with polyphenols in a wine-model medium: impact of oxygen, iron, and sulfur dioxide

As volatile thiols are nucleophiles, they are capable of additional reactions with electrophiles. In enology, this concerns reactions between volatile or non-volatile thiols and oxidized phenolic compounds. Initial studies concerning the reactivity of volatile thiols with polyphenols showed that (+)-catechin played a detrimental role in the level of 3-sulfanylhexan-1-ol (3SH), in the absence of sulfur dioxide. Our experiment revealed that (-)-epicatechin was more reactive with volatile thiols than (+)-catechin. Furthermore, Fe (III) was shown to play a crucial role in catalyzing polyphenol oxidation reactions, by affecting the direct reaction of phenolic compounds with oxygen. It was noted that, even if the volatile thiols studied were members of the same chemical family, they exhibited a different behavior pattern under oxidation conditions. 2-furanmethanethiol (2FMT) was more reactive than 3-sulfanylhexan-1-ol with both (+)-catechin and (-)-epicatechin. In contrast, 4-methyl-4-sulfanylpentan-2-one (4MSP) was less reactive with these phenolics. Additionally, the vital role of sulfur dioxide in protecting 3-sulfanylhexan-1-ol, 2-furanmethanethiol, and 4-methyl-4-sulfanylpentan-2-one was demonstrated in the model medium.