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Grape berries were classified according to diameter and total soluble solids (TSS) to study the effect of light and temperature on methoxypyrazines (MPs), glutathione (GSH), and hydroxycinnamates (HCAs) during the ripening of Sauvignon blanc. The light exposure of the fruiting zone was modified within leaf and lateral removal at the phenological stage berry of peppercorn size and no removal (control). In comparison to the control, the concentration of 3-isobutyl-2-methoxypyrazine (IBMP) was below the limit of detection in leaf removal 2 weeks before harvest. Leaf removal had no significant influence on GSH and HCAs in the grape juice at harvest. Berry diameter significantly influenced the concentration of IBMP in the grape juice and did not influence the concentration of GSH and HCAs. At harvest, the concentrations of IBMP in grape juices of similar TSS in the control were 12.6 and 5.2 ng/L in 15.5 and 13.5 mm berry diameter classes, respectively. Furthermore, the study showed that berries of the same diameter were not at the same physiological ripening level (not the same TSS).

<p style="text-align: justify;"><strong>Aim</strong>: To investigate the effect of reducing leaf area by shoot hedging in combination with bunch thinning on metabolite concentration and sensorial quality of Sauvignon blanc grapes and wines.</p><p style="text-align: justify;"><strong>Methods and results</strong>: Four vine treatments were conducted: shoot hedging/bunch thinning (SH/BT), shoot hedging/no bunch thinning (SH/NBT), full canopy/bunch thinning (FC/BT) and full canopy/no bunch thinning (FC/NBT). Shoot hedging delayed total soluble solids accumulation at the beginning of the grape maturation in SH/BT and SH/NBT treatments. At harvest there were no significant differences in the concentration of hydroxycinnamoyl tartaric acids, glutathione, total soluble solids, titratable acidity and pH value in grape juice between all treatments and methoxypyrazines were below the limit of detection. Lutein concentration in grape berry was higher in treatments without bunch thinning, while there was no significant difference in the concentration of β-carotene and neoxanthin. The highest leaf area to yield ratio (FC/BT) resulted in higher concentration of glutathione in must and higher concentration of thiols in Sauvignon blanc wines. Upon sensory evaluation, the FC/BT wine was best scored for overall quality and heavier tropical aroma, whereas the FC/NBT wine was best scored for fresh tropical aroma and second best for overall quality.</p><p style="text-align: justify;"><strong>Conclusion</strong>: Leaf area to yield ratio impacted berry ripening kinetics, grape and wine metabolite composition, and sensorial properties of Sauvignon blanc wine.</p><p style="text-align: justify;"><strong>Significance and impact of the study</strong>: The study showed that the highest leaf area to yield ratio resulted in the best overall sensorial quality of wine.</p>

Varietal thiol precursors in grapes are subject to metabolic changes during post-harvest treatments. Metabolic activity should therefore be limited after sampling to understand their biosynthesis in the berry and genetic regulation. In this study, berries were frozen in liquid nitrogen immediately after harvesting, transported in dry ice, stored briefly at −80 °C, cryo-milled and extracted without being thawed in cold methanol in a ratio of 1:4 (w/v). A UHPLC-MS/MS method for quantitative determination of the thiol precursors 3-S-glutathionylhexan-1-ol (G3MH), 3-S-cysteinylhexan-1-ol (Cys3MH), 4-S-glutathionyl-4-methylpentan-2-one (G4MMP) and 4-S-cysteinyl-4-methylpentan-2-one (Cys4MMP), glutathione, oxidized glutathione and L-methionine in grapes was developed. Reference material was provided through synthesis of precursors and their deuterium labelled analogues. The average thiol precursor content in grapes in 2013–15 was in the range 8–16 μg kg−1 for G3MH, 1–6 μg kg−1 for Cys3MH, 1–4 μg kg−1 for Cys4MMP and 0.3 μg kg−1 for G4MMP. In 2013 and 2014, the highest precursor content in mature Sauvignon Blanc grapes from vineyards located in Italy regarded G3MH, followed by Cys3MH, Cys4MMP and G4MMP. In 2015, G3MH was again the most abundant precursor, but followed by Cys4MMP, Cys3MH and G4MMP.