Impact of noble rot on the aroma precursor of 3-sulfanylhexanol content in Vitis vinifera L. cv Sauvignon blanc and Semillon grape juice

The most famous sweet wine in France is made from botrytised grapes in the Sauternes region. Its distinctive, complex aromas are undoubtedly due to noble rot as a result of Botrytis cinerea development on perfectly ripe Sauvignon blanc and Semillon grapes. The contribution of volatile thiols in botrytised wine aroma was recently reported. The objective of this work was to investigate the impact of B. cinerea development on the aromatic potential of grape juice. The level of S-3-(hexan-1-ol)cysteine (P-3SH), the cysteinylated precursor of the most abundant volatile thiol in wine (3-sulfanylhexanol, 3SH), was determined during grape botrytisation and several grape overripening processes. Production was considerably amplified when B. cinerea had developed on the grapes in both on- and off-vine experiments. The P-3SH levels were increased about 100-fold between the healthy and botrytised stages in one week. We demonstrated that the grape metabolism produced aroma precursor under post-harvest conditions. When grapes were left to overrippen, the vine also produced P-3SH, but levels increased more moderately (about 10-fold). Moreover, a determination of P-3SH distribution demonstrated that B. cinerea was not directly responsible for precursor formation but probably stimulated the grape metabolic pathway involved in this formation.