Origin of fresh mushroom off-flavor in grape must and wine: from linoleic acid breakdown to glycosylated compounds biosynthesis

Abstract

Fresh-Mushroom Off-Flavour (FMOff) is a recurrent wine defect associated with fungal alteration of grapes 1-3. Recent studies have identified 1-hydroxyoctan-3-one (HDY) and octane-1,3-diol as analytical markers of this taint 4, 5, with HDY also being confirmed as a sensory marker in wines 5. Its content appeared to be modulated by fermentation 6. These compounds are detected in free form in grape must and in wines but their origin and biosynthetic pathways remain poorly understood. This study aimed to elucidate the origin of these FMOff markers by (i) investigating the role of linoleic acid and glycosylated precursors and (ii) assessing the influence of environmental parameters on their biosynthesis. The catalytic breakdown of linoleic acid into C8 compounds was studied in synthetic must at two stages: the pre-fermentative stage, involving grapevine fungi and alcoholic fermentation (AF), involving yeast. A full factorial design was used to evaluate environmental effects on the production of free and glycosylated compounds. Both Penicillium crocicola and Botrytis cinerea were able to synthetize HDY and octane-1,3-diol but they secreted these compounds into the growing medium only under hypoxic conditions. These compounds were produced from linoleic acid with significant genus-specific differences. B. cinerea was also able to glycosylate these compounds, and glycosylated forms were detected for the first time in must from grapes naturally infected with grey mold. Linoleic acid concentration and pH significantly affected FMOff compounds biosynthesis, with contrasting responses between the two fungi. In contrast, the yeast studied did not produce these compounds from linoleic acid during AF, suggesting that fermentation is not a critical step for FMOff formation under our conditions. Overall, this work highlights two potential reservoirs of FMOff markers in contaminated matrices: free linoleic acid and its glycosylated derivatives.

References

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