Evidence of the Possible Interaction between Ultrasound and Thiol Precursors

Abstract

The effect of ultrasound (20 kHz, 153 μm) on the prefermentation extraction mechanisms in Sauvignon Blanc grapes was studied, focusing on 3-mercaptohexan-1-ol (3MH) and 4-mercapto-4-methyl-pentan-2-one (4MMP) precursors linked to glutathione (GSH) and cysteine (Cys). The treatment determined a positive extraction trend between the duration (untreated, 3 and 5 min) and the conductivity or the concentration of catechins and total phenols, significantly differentiated after 5 min. Nevertheless, the concentration of the thiol precursors in grape juice not only remained undifferentiated, but that of 3-S-glutathionyl mercaptohexan-1-ol showed a negative trend with the treatment time applied (168 ± 43, 156 ± 36, and 149 ± 32 μg/L, respectively, for control, 3 and 5 min). The divergence on the effect between families of compounds suggests an interaction between the sonication treatment and thiol precursor molecules. In order to evaluate the possible degradation properly, ultrasound was applied in a model solution spiked with 3MH and 4MMP precursors, reproducing the conditions of grapes. Except for Cys-3MH, the mean concentration (n = 5) for the rest of the precursors was significantly lower in treated samples, predominantly in those linked to glutathione (~−22% and ~18% for GSH-3MH and GSH-4MMP) rather than to cysteine (~−6%~−8% for Cys-3MH and Cys-4MMP). The degradation of precursors was associated with a significant increase of 3MH and 4MMP. The formation of volatile thiols following sonication is interesting from a technological point of view, as they are key aroma compounds of wine and potentially exploitable in the wine industry through specific vinification protocols.

Effect of Power Ultrasound Treatment on Free and Glycosidically-Bound Volatile Compounds and the Sensorial Profile of Red Wines

“…Just some individual bound compounds (4-vinyl- guaiacol, vanillin and ethyl vanillate) increased in the wines made from sonicated grapes at 28 kHz and 72 h of maceration. This fact supports the hypothesis of the possible release of aglycones from their precursors due to sonication [ 33 ].…”

“…Studies carried out on the use of US in grape maceration and its effect on the volatile fraction are focused on wines, so there are few references on its effect on musts. The only work in which the effect of US treatment on aroma precursors in musts has been studied is that carried out by Roman et al [ 33 ]. These authors did not observe a positive effect on the extraction of thiols precursors in Sauvignon Blanc grapes treated with an ultrasound probe at 20 kHz.…”

“…Its application to crushed grapes increased tannin and anthocyanin concentration in wines, the results being frequency-dependent [ 25 ], however the effect on must and wine volatile compounds was not studied. On the other hand, just one study has been found regarding the use of US to the extraction of grape precursors, specifically in the extraction of thiols precursors of Sauvignon Blanc grapes [ 33 ]. Therefore, the aim of this study was to evaluate for the first time the effect of the ultrasound treatment of crushed grapes, at winery scale and at two different frequencies (20 and 28 kHz), on the free and glycosidically-bound volatile compounds and aroma profile of musts and their resulting red wines.…”

Effect of Microwave Maceration and SO2 Free Vinification on Volatile Composition of Red Wines

“…Other authors have observed an increase in the free and bound fraction of must volatiles applying various techniques in the grape maceration step as ultrasounds and pulsed electric fields [ 8 , 16 , 31 ].…”

A New Approach to the Reduction of Alcohol Content in Red Wines: The Use of High-Power Ultrasounds

“…Bautista-Ortin et al [ 25 ] studied the application of HPUS to crushed grapes, looking for a reduction on the maceration time needed for the extraction of phenolic and volatile compounds, and they found only small differences in the wine volatile composition. Roman et al [ 58 ] applied ultrasounds to Sauvignon Blanc crushed grapes, and found an increase in thiol compounds, key aroma compounds for Sauvignon Blanc wines. Zhang et al [ 59 ] also studied the effect of ultrasounds on higher alcohol content in wine, reporting a decrease in these compounds, although they applied the HPUs treatment to finished wines to study their evolution during aging and not to crushed grapes.…”