| Abstract |
- New research has identified flavonols as a class of phenolic compounds which can be manipulated by both vineyard and winery practices. These phenolic compounds are key quality components of wine, affecting sensory characteristics, wine color, and wine stability. Modification of the phenolic precursors in grapes occur during fermentation and aging by oxidation, hydrolysis and polymerization. The solubility of these compounds varies substantially and their interactions with each other and with the changing solvent properties of must and wine contribute to final phenolic composition of wine. Phenolics, in general, are known to be responsible for much of the astringency, bitterness and 'length' of flavor impression on the palate. However, little is known of the effect of specific phenolic compounds, such as quercetin, on the sensory characteristics of wine. In order to investigate the effect of various phenolics on the solubility of quercetin aglycone, concentrations of quercetin aglycone (0, 5, 10, 20, 30, 40, 50, 60 mg L⁻¹) were added to a model wine system containing one of each of the following phenolic compounds: gallic acid, caffeic acid, (+) catechin, quercetin 3-[subscript L]-rhamnoside, grape seed tannin and malvidin 3,5-diglucoside. Gallic acid, caffeic acid, (+) catechin had no significant effect on the solubility of quercetin aglycone. The effect of quercetin 3-[subscript L]-rhamnoside was dependant on concentration of added quercetin aglycone. The grape seed tannin and malvidin 3,5- diglucoside significantly increased the solubility of quercetin aglycone in all added quercetin concentrations, with the malvidin 3,5-diglucoside resulting in the largest increase. Increasing concentrations of malvidin 3,5-diglucoside resulted in increased levels of stable quercetin in solution. Samples with malvidin 3,5-diglucoside and quercetin aglycone showed increases in absorbance (520 nm) of up to 20%. The anthocyanin-flavonol interaction that resulted in an increase in 520 nm absorbance (copigmentation) also appears to be responsible for the increased solubility of the quercetin aglycone. These results suggest that anthocyanins in wine influence the wine's final flavonol composition. The technique of free choice profiling was used to characterize the sensory attributes of 3 concentrations of quercetin aglycone (5, 10, 20 ppm) when added to a model wine and a chardonnay. Based on the consensus area of model wine data, there was no significant separation of the samples. Analysis of the chardonnay data resulted in significant separation of the samples on PA 1 and PA 2. On PA 1, the control and 5 ppm samples were described as higher in overall flavor intensity, sourness and burn/hot and less watery. On PA 2, the samples with quercetin (5, 10 and 20 ppm) were described as higher in sweetness, bitterness, numbness and fruitiness while having a less intense overall aroma. In both studies, panelist replication patterns were extremely varied which was reflected in the high V[subscript within] across PA's, samples and panelists.
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