Investigation into mousy off-flavor in wine using gas chromatography-mass spectrometry with stir bar sorptive extraction.

Three major compounds, 2-acetyl-1-pyrroline (APY), 2-acetyltetrahydropyridine (ATHP) and 2-ethyltetrahydropyridine (ETHP), have been identified as responsible for the mousy off-flavor in wines, although to date quantification data reported in the literature are limited. A simple method for simultaneous quantitation, by SBSE-GC-MS, of these N-heterocyclic compounds was developed. Both previously reported tautomers of ATHP, 2-acetyl-1,4,5,6-tetrahydropyridine and 2-acetyl-3,4,5,6-tetrahydropyridine were identified. The limits of detection and quantification of the method were determined in white, rosé and red wines and are lower than previously published concentrations in spoiled wine. ETHP was detected in almost all wines produced with limited use of SO2. ATHP was detected in almost all wines suspected of mousiness whereas APY was only detected in few cases. This method will provide a support for further studies aimed at understanding the phenomena that influence the occurrence of mousy off-flavor and the oenological parameters that modulate its expression.

Impact of Lactobacillus plantarum on thiol precursor biotransformation leading to production of 3-sulfanylhexan-1-ol.

3-Sulfanylhexan-1-ol (3SH) is an important contributor to the fruity notes of wine. 3SH exists as odorless precursors in grape and its release from the precursors is generally mediated by yeast during alcoholic fermentation. Here, the impact of lactic acid bacteria on 3SH production was investigated. Among the species tested, only Lactobacillus plantarum released 3SH from S-3-(hexan-1-ol)-l-cysteine (3SH-S-cys) and S-3-(hexan-1-ol)-l-cysteinylglycine (3SH-S-cysgly) in the whole-cell biotransformation assay. The conversion yields of 3SH from 3SH-S-cysgly by L. plantarum were always higher than those from 3SH-S-cys, suggesting that the direct cleavage of 3SH-S-cysgly to yield 3SH predominantly occurred. L. plantarum biotransformed the 3SH precursors, including 3SH-S-glut, to release 3SH in fermented grape juice. The results indicate that L. plantarum induces the release of 3SH from the 3SH precursors. To the best of our knowledge, this is the first study showing the impact of L. plantarum on thiol precursor biotransformation.