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Effect of Different Enological Practices on Skin and Seed Proanthocyanidins in Three Varietal Wines

Proanthocyanidins are important for wine quality since they participate in astringency, bitterness and color. Given the localization of proanthocyanidins in the berry (skin and seeds), different methods have been developed that help to modulate the release of these phenolic compounds. In this study, the effect of two low prefermentative temperature techniques (cold soak and must freezing with dry ice) and the use of macerating enzymes has been studied during the vinification of three different varietal wines (Monastrell, Syrah and Cabernet Sauvignon) to assess their influence on wine proanthocyanidin concentration and composition. Syrah wines showed the lowest proanthocyanidin content, together with the lowest mDP and the highest percentage of galloylation in its proanthocyanidins. Monastrell and Cabernet Sauvignon wines showed similar proanthocyanidin concentration. The application of the low temperature prefermentative maceration (cold soak) was the most effective treatment, increasing the proanthocyanidin concentration in Monastrell and Cabernet Sauvignon wines although neither of the treatments had any effect on Syrah wines. As regards the effect of the different treatments on the proanthocyanidin composition, the results seem to indicate that the observed increases were mainly due to an increase in seed proanthocyanidins, even in the case of cold soak treatments, which occur in the absence of ethanol, suggesting that ethanol is not so crucial in the extraction of seed proanthocyanidins.

The extraction of anthocyanins and proanthocyanidins from grapes to wine during fermentative maceration is affected by the enological technique.

The effect of three enological techniques (low temperature prefermentative maceration, must freezing with dry ice, and the use of a maceration enzyme) on the extraction of anthocyanins and proanthocyanidins from must to wine during fermentative maceration was studied to determine the extent to which these compounds are extracted and to assess the changes on their qualitative composition due to enological technique applied. The results showed that the dry ice treatment led to wines with high color intensity and high anthocyanin content, the maximum rate of extraction being observed the first 6 days of fermentative maceration. Regarding the effect of the different techniques on the quantitative and qualitative composition of proanthocyanidins, only the dry ice treatment seemed to favor the extraction of high molecular weight skin proanthocyanidins. The low temperature prefermentative maceration treatment led to the highest concentration of proanthocyanidins at the moment of pressing; however, this treatment, contrary to expectations, led to wines with the highest content of seed-derived proanthocyanidins. The use of the maceration enzyme also increased the concentration of proanthocyanidins during all of the fermentative process, as compared to a control wine, although the increase was not only due to skin proanthocyanidins but also seed proanthocyanidins. We have demonstrated in this study that maceration enzymes also facilitate seed phenolic extraction.

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.

Effect of Micro-oxygenation on Color and Anthocyanin-Related Compounds of Wines with Different Phenolic Contents

Several factors may affect the results obtained when micro-oxygenation is applied to red wines, the most important being the moment of application, the doses of oxygen, and the wine phenolic characteristics. In this study, three red wines, made from Vitis vinifera var. Monastrell (2005 vintage) and with different phenolic characteristics, were micro-oxygenated to determine as to how this technique affected the formation of new pigments in the wines and their chromatic characteristics. The results indicated that the different wines were differently affected by micro-oxygenation. In general, the micro-oxygenated wines had a higher percentage of new anthocyanin-derived pigments, being that this formation is more favored in the wines with the highest total phenol content. These compounds, in turn, significantly increased the wine color intensity. The wine with the lowest phenolic content was less influenced by micro-oxygenation, and the observed evolution in the degree of polymerization of tannins suggested that it might have suffered overoxygenation.

Effect of Ethanol on Grape Seed Proanthocyanidin Extraction

Proanthocyanidins are found in the seeds and skins of winegrapes and are extracted into the must-wine during maceration. For seed proanthocyanidins, extraction is generally thought to be possible only in the presence of ethanol. This study examined the extraction of seed proanthocyanidins in model solutions with increasing concentrations of ethanol, from 0 to 15% v/v. Spectrophotometric and chromatographic results showed that ethanol was not required for proanthocyanidin extraction, although its presence increased the rate of extraction. Extraction dynamics indicated that alcohol increased the rate of proanthocyanidin extraction for the initial six days of maceration, after which, even in the absence of ethanol, the extraction rate was nearly identical for all treatments. These findings suggest that extraction time is an important consideration when managing techniques, such as cold soak, which are thought not to affect seed proanthocyanidin extraction.

Effect of Benzothiadiazole and Methyl Jasmonate on the Volatile Compound Composition of Vitis vinifera L. Monastrell Grapes and Wines

Benzothiadiazole and methyl jasmonate have been described as exogenous elicitors of some plant defence compounds. The objective of this study was to determine whether the application of benzothiadiazole and methyl jasmonate to Vitis vinifera L. Monastrell grape clusters at the beginning of the ripening process affects the synthesis of volatile compounds in grapes (as has been observed in other fruits) and whether this effect has a technological significance in the resulting wines. Results indicated that both treatments increased the levels of volatile compounds in grapes, especially terpenes and norisoprenoids in benzothiadiazole-treated grapes. The wines obtained from the treated grapes also showed higher levels of terpene and norisoprenoids. Wines from methyl jasmonate-treated grapes had levels of these volatile compounds almost two times higher than the wines made from control grapes. These differences in the volatile compound levels could be sensorially detected.

Interactions between grape skin cell wall material and commercial enological tannins. Practical implications.

Commercial enological tannins were used to investigate the role that cell wall material plays in proanthocyanidin adsorption. Insoluble cell wall material, prepared from the skin of Vitis vinifera L. cv. Monastrell berries, was combined with solutions containing six different commercial enological tannins (proanthocyanidin-type tannins). Analysis of the proanthocyanidins in the solution, after fining with cell wall material, using phloroglucinolysis and size exclusion chromatography, provided quantitative and qualitative information on the non-adsorbed compounds. Cell wall material showed strong affinity for the proanthocyanidins, one of the commercial tannins being bound up to 61% in the experiment. Comparison of the molecular mass distribution of the commercial enological tannins in solution, before and after fining, suggested that cell walls affinity for proanthocyanidins was more related with the proanthocyanidin molecular mass than with their percentage of galloylation. These interactions may have some enological implications, especially as regards the time of commercial tannins addition to the must/wine.

Effect of Wine Maceration Enzymes on the Extraction of Grape Seed Proanthocyanidins

Proanthocyanidins, which are located in the skins and seeds of grapes, are important for red wine quality since they participate in astringency, bitterness and colour stabilization. Maceration enzymes have long been used to improve the extraction of phenolic compounds from skins, but their role in seed degradation and the release of seed phenolic compounds is not well known. This contribution describes the effect of different pure enzyme activities (xylanase, cellulase, polygalacturonase and pectinmethylesterase) on the release of proanthocyanidins from seeds of Monastrell and Cabernet Sauvignon grapes. The results demonstrate that some enzymes, especially polygalacturonase and cellulase, favour the degradation of seed cell walls, promoting the diffusion of proanthocyanidins, although differences due to grape variety also exist.

Increasing Bioactive Phenolic Compounds in Grapes: Response of Six Monastrell Grape Clones to Benzothiadiazole and Methyl Jasmonate Treatments

The application of different elicitors to plants has proved a useful technique for the improvement of their phenolic content. However, studies have shown that the exact response of plants to elicitors depends both on variety and clone. In the present study, two elicitors (benzothiadiazole and methyl jasmonate) were applied in a vineyard where a collection of the six selected clones of Monastrell grape variety were planted to determine whether any observed effect was clone-dependent. The analysis of anthocyanins, flavonols, stilbenes, and seed and skin tannins showed that, in general, both elicitors increased the levels of phenolic compounds in the treated plants, although the extent of the response differed among different clones from the same variety. The positive effect of both benzothiadiazole and methyl jasmonate indicated that such treatments could be regarded as useful for improving grape and wine color while also increasing resistance to some pathogens. However, a preliminary exploratory field study should be carried out since differences in the response of the grapes to treatment might occur, depending on the clone.

Anthocyanins influence tannin-cell wall interactions.

The rate of tannin extraction was studied in a vinification of red grapes and the results compared with another vinification made with white grapes fermented as for typical red wine, in the presence of skins and seeds. Even though the grapes presented a quite similar skin and seed tannin content, the differences in tannin concentration between both vinifications was very large, despite the fact that the only apparent difference between the phenolic composition of both wines was the anthocyanin content. This suggests that anthocyanins play an important role in tannin extractability, perhaps because they affect the extent of the tannin-cell wall interaction, a factor that largely controls the resulting quantity of tannins in wines. To confirm this observation, the effect of anthocyanins on the tannin extractability from grape seeds and skin and on the interaction between tannins and grape cell walls suspended in model solutions were studied. The results indicated that anthocyanins favored skin and seed tannin extraction and that there is a competition for the adsorption sites between anthocyanins and tannins that increases the tannin content when anthocyanins are present.