Measurement of the interaction between mucin and oenological tannins by Surface Plasmon Resonance (SPR); relationship with astringency.

The interaction between stomach porcine mucin and 3 oenological tannins (extract of ellagitannins from oak, extract of gallotannins from gall nuts and extract of proanthocyanidins from grape seeds) was measured by Surface Plasmon Resonance (SPR). These tannins were analysed and their astringency was determined using the Astringency Index method and by tasting. The interaction constants were determined using a Biacore SPR device (1:1 Langmuir binding model). The results indicate that the ellagitannins are more astringent than gallotannins and those, in turn, are more astringent than seed proanthocyanidins if the richness of the commercial extracts is considered. The astringency index of these tannins had high correlation and regression coefficients with their kinetic and thermodynamic dissociation constants. This data support a hypothesis that astringency depends not only on the thermodynamic tendency to form the complex between tannins and salivary proteins but also probably on the time required to dissociate the complex.

Phenylalanine and urea foliar applications to grapevine: effect on wine phenolic content.

Phenolic compounds play a key role in the organoleptic properties of wines. Viticultural practices may influence grape and wine phenolic content, thus determining their quality. The objective of this study was to evaluate the effect of foliar applications of phenylalanine and urea, at two different doses, on wine phenolic composition. Grapes were harvested at their optimal technological maturity and their respective wines were elaborated at small scale. Wine detailed phenolic composition was determined. Results revealed that the content of several anthocyanins and flavonols was enhanced by the application of both phenylalanine doses and by the application of the low dose of urea. In contrast, flavanols and non-flavonoid compounds were less affected by the foliar treatments. The findings seem to be related to the time of application, since anthocyanins and flavonols are accumulated after veraison. In conclusion, nitrogen foliar fertilization increased the phenolic content of Tempranillo wines. This could be of interest since anthocyanins and flavonols are associated with wine quality, especially with its color.

Effect of two different treatments for reducing grape yield in Vitis vinifera cv Syrah on wine composition and quality: berry thinning versus cluster thinning.

The influence of two treatments for reducing grape yield, cluster thinning and berry thinning, on red wine composition and quality were studied in a Vitis vinifera cv Syrah vineyard in AOC Penedès (Spain). Cluster thinning reduced grape yield per vine by around 40% whereas berry thinning only reduced it by around 20%. Cluster thinning grapes had higher soluble solids content than control grapes, and their resultant wines have greater anthocyanin and polysaccharide concentrations than the control wine. Wine obtained from berry thinning grapes had a higher total phenolic index, greater flavonol, proanthocyanidin, and polysaccharide concentrations, and lower titratable acidity than the control wine. Wines obtained from both treatments were sufficiently different from the control wine to be significantly distinguished by a trained panel in a triangular test. Even though both treatments seem to be effective at improving the quality of wine, berry thinning has the advantage because it has less impact on crop yield reduction.

Effect of freeze-drying and oven-drying on volatiles and phenolics composition of grape skin.

Grape skins are the part of the fruit with the highest amount of volatile and polyphenolic compounds. Volatile compounds give the fruit and other grape derivatives their flavour. Polyphenolic compounds are responsible for the colour of the fruit, juice and wine, and also act as very important natural antioxidant compounds. Dehydration is a method used to prevent the damage of these compounds over time. Nevertheless, in the case of volatile compounds, removing water can cause compound degradation or the evaporation of such compounds. This work studied two drying methods, freeze-drying and oven-drying, at 60 degrees C, as skin preservation methods. The skins from two grape varieties, Carménère and Cabernet Sauvignon, were dried. Many volatile compounds, which are of interest in the aroma profile, were identified in both varieties as terpenes (linalool, etc.), sesquiterpenes (farnesol), norisoprenoids (vitispirane, etc.), C(6) alcohols (1-hexanol, etc.), etc., and their amount decreased significantly with the oven-drying method, in contrast to the freeze-drying method. Both phenolic compounds, anthocyanins and flavonols, were identified in fresh and dehydrated samples, thus resulting in the freeze-drying method being less aggressive than oven-drying methods.