The impact of some clarifying agents on the precursors of the varietal thiols in juice

3-S-cysteinyl hexan-1-ol (Cys-3MH), 3-S-glutathionyl hexan-1-ol (GSH-3MH) and 4-S-cysteinyl-4-methylpentan-2-one (Cys-4MMP) are precursors of the so-called varietal thiols responsible for the tropical fruity notes produced during fermentation by some yeast strains having lyase activity. A very important step for saving/producing a remarkable level of precursors are grape and juice processing conditions (Larcher et al. 2013). In regards to this, the effects of the main clarifying agents on the content of the quoted precursors are not known up to day. For this reason, 19 juices were produced by direct pressing of white and red grapes according to protocols and with supplements (grape tannin having 224.2 mg/kg GSH-3MH and 25.5 mg/kg Cys-3MH) useful to reach in juice a remarkable level of precursors. These spiked juices, previously cold stabilised and with NTU <20, were treated with high doses (100 g /hL) of bentonite or PVPP or charcoal and cold settled (4°C x 48h), and compared with not spiked juices. Precursors were analysed in the juices using a UHPLC-MS/MS; accurate quantification was guaranteed by deuterated internal standards. Only charcoal caused statistically significant depletion; nevertheless, the changes in percentage terms were limited even with the high dose applied, being roughly 20% for GSH-3MH and 10% for Cys-3MH. No significant differences were found for Cys-4MMP, with a mean depletion due to the clarifying agents < 2% compared to the control treatment