Relationship between red wine grades and phenolics. 1. Tannin and total phenolics concentrations

Phenolic compositions of grapes and wines from cultivar cAbernet Sauvignon produced in Chile and their relationship to commercial value

The phenolic composition of wine depends on, among other factors, the grapes used to make it. In this sense, knowledge of the chemical composition of grapes and its association with the resulting wines is an important tool to determine if there is a relationship between the phenolic composition of grapes and the price that these wines obtain in the market. For this purpose, grape skins and seeds from the cultivar Cabernet Sauvignon from the central region of Chile, in 2009 and 2010 vintages from two ripening points, were subjected to chemical and phenolic analyses, as were the wines made from these grapes. Grapes and the corresponding wines from three retail price wine categories, U.S. $6-8, U.S. $28-30, and U.S. $150-160, were evaluated. No differences were found across the price categories in the chemical analysis of grapes. Berry skins and wines from the higher price categories presented a higher concentration only of total tannins, and the differences in their concentrations were only among the different fractions of proanthocyanidins in the skins, seeds, and wines; there were no differences in their proportions. A seasonal effect influenced the concentrations of certain compounds in grapes and led to a decrease in the concentration of total phenols, total tannins, and total anthocyanins between sampling dates as harvesting moved toward the common commercial grape harvest in Chilean viticulture.

Assessment of some Australian red wines for price, phenolic content, antioxidant activity, and vintage in relation to functional food prospects

Twenty-three Cabernet Sauvignon wines from the Mudgee region and thirty-two Shiraz wines from the Hunter Valley region were analyzed for phenolic content and antioxidant activity. Concentrations of (+)-catechin, quercetin, and transresveratrol, total phenolic content, and DPPH antioxidant activity varied considerably, both within and between varieties. Individual phenols, total phenols, and antioxidant activity were correlated with price and vintage. Shiraz wines showed positive and significant correlations for catechin and quercetin concentrations with total phenols, antioxidant activity, and vintage; and for total phenols and antioxidant activity with vintage. Cabernet Sauvignon wines showed positive and significant correlations for quercetin concentration with total phenols and antioxidant activity. There was a negative and significant correlation found between price and antioxidant activity for Cabernet Sauvignon wines. Results are discussed in terms of the potential for wine to be considered a functional food.

PRACTICAL APPLICATION

We report on potential health benefits (antioxidant activity) of 55 wines typical of 2 geographically close, but distinct, wine regions of Australia. Our results highlight the variability in functional components as an issue that needs further research and consideration in relation to wine as a functional food. The price of studied wines is not reflective of their health functionality, based on antioxidant activities.

Improving grape phenolic content and wine chromatic characteristics through the use of two different elicitors: methyl jasmonate versus benzothiadiazole

Benzothiadiazole (BTH) and methyl jasmonate (MeJ) have been described as exogenous elicitors of some plant defense compounds, polyphenols among them. The objective of this study was to determine whether the application of BTH or MeJ to grape clusters at the beginning of the ripening process had any effect on the accumulation of the main flavonoid compounds in grapes (anthocyanins, flavonols, and flavanols) and the technological significance of these treatments in the resulting wines. The results obtained after a 2 year experiment indicated that both treatments increased the anthocyanin, flavonol, and proanthocyanidin content of grapes. The wines obtained from the treated grapes showed higher color intensity and total phenolic content than the wines made from control grapes. The exogenous application of these elicitors, as a complement to fungicide treatments, could be an interesting strategy for vine protection, increasing, at the same time, the phenolic content of the grapes and the resulting wines.

Relationship between red wine grade and phenolics. 2. Tannin composition and size

Commercial red wines ( Vitis vinifera L. cv. Shiraz) produced during the 2009 vintage underwent winemaker assessment for allocation grade soon after production. The wines were then subjected to phenolic analysis to measure wine color (total anthocyanin, SO(2) nonbleachable pigment, and wine color density) and tannins (concentration, composition, and average degree of polymerization). A positive relationship was found between wine phenolic concentration and projected bottle price. Tannin compositional analysis suggested that there was specifically a relationship between wine grade and skin-derived tannins. These results suggest that maximization of skin tannin concentration and/or proportion is related to an increase in projected wine bottle price.

Wine and grape tannin interactions with salivary proteins and their impact on astringency: a review of current research

Astringency is an important characteristic of red wine quality. The sensation is generally thought to be produced by the interaction of wine tannins with salivary proteins and the subsequent aggregation and precipitation of protein-tannin complexes. The importance of wine astringency for marketability has led to a wealth of research on the causes of astringency and how tannins impact the quality of the sensation, particularly with respect to tannin structure. Ultimately, the understanding of how tannin structure impacts astringency will allow the controlled manipulation of tannins via such methods as micro-oxygenation or fining to improve the quality of wines.