Yolanda Ruiz-García

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.

Selective extraction of polysaccharide affects the adsorption of proanthocyanidin by grape cell walls

Cell wall material was isolated from two Vitis vinifera grape varieties, Cabernet Sauvignon and Shiraz, following a buffered phenol extraction method. Using sequential fractionation in chelating agent, then increasing the molarity of aqueous potassium hydroxide, polysaccharide classes were selectively extracted from cell walls to produce fractions of defined polysaccharide composition. Following the application of phloroglucinolysis and a modified HCl-butanol colourimetric assay to cell wall fractions, more than 54% of cell wall-bound proanthocyanidin was localised within the chelator-soluble (pectic) fraction. Model adsorption experiments with a purified skin proanthocyanidin confirmed that the removal of pectic polysaccharides by chelator most significantly reduced the adsorption of proanthocyanidin by cell walls. Nevertheless, cell wall hemicellulosic fractions retained a high binding capacity for proanthocyanidin, although lower than that observed when pectin was present. Following removal of hemicelluloses by fractionation, the primarily lignocellulosic residue had a significantly reduced affinity for proanthocyanidin. With the exception of lignocellulose, a greater selectivity of adsorption for higher molecular mass proanthocyanidins was observed by the respective cell wall fractions.

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.

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.

Remarkable proanthocyanidin adsorption properties of monastrell pomace cell wall material highlight its potential use as an alternative fining agent in red wine production.

The existence of interactions between the polysaccharides of vegetal cell walls and proanthocyanins makes this cell wall material an interesting option for its use as a fining agent to reduce the level of proanthocyanins in wines. Pomace wastes from the winery are widely available and a source of cell wall material, and the identification of varieties whose pomace cell walls present high proanthocyanin binding capacity and of processing methods that could enhance their adsorption properties could be of great interest. This study compared the proanthocyanin adsorption properties of pomace cell wall material from three different grape varieties (Monastrell, Cabernet Sauvignon, and Syrah), and the results were compared with those obtained using fresh grape cell walls. Also, the effect of the vinification method has been studied. Analysis of the proanthocyanidins in the solution after reaction with the cell wall material, using phloroglucinolysis and size exclusion chromatography, provided quantitative and qualitative information on the adsorbed and nonadsorbed compounds. A highlight of this study was the observation that Monastrell pomace cell wall material showed a strong affinity for proanthocyanidins, with values similar to that obtained for fresh grapes cell walls, and a preferential binding of high molecular mass proanthocyanidins, so these pomace cell walls could be used in wines to reduce astringency. The use of maceration enzymes during vinification had little effect on the retention capacity of the pomace cell walls obtained from this vinification, although an increase in the retention of low molecular mass proanthocyanidins was observed, and this might have implications for wine sensory properties.

Increasing the phenolic compound content of grapes by preharvest application of abcisic acid and a combination of methyl jasmonate and benzothiadiazole.

Benzothiadiazole (BTH) and methyl jasmonate (MeJ) have been described as exogenous elicitors of some plant defense compounds, polyphenols among them. Given that they activate different arrays of biochemical reactions to induce resistance, the objective of this study was to determine whether the joint application of BTH and MeJ to grape clusters affects the level of the main flavonoid compounds in grapes and in the resulting wines. The results are compared with those obtained when abscisic acid (ABA), a plant growth regulator involved in several physiological processes, was sprayed in the same vineyard. The results obtained indicated that, although the application of ABA increased the content of skin anthocyanins and tannins, these positive effects were not reflected in the wines made from these grapes. BTH+MeJ-treated grapes also presented higher anthocyanin and flavonol contents, and in this case, their wines presented better chromatic characteristics that the wine made from control grapes.

Evaluating the Polyphenol Profile in Three Segregating Grape (Vitis vinifera L.) Populations

This paper explores the characteristics of the anthocyanin and flavonol composition and content in grapes from plants resulting from intraspecific crosses of Vitis vinifera varieties Monastrell × Cabernet Sauvignon, Monastrell × Syrah, and Monastrell × Barbera, in order to acquire information for future breeding programs. The anthocyanin and flavonol compositions of twenty-seven hybrids bearing red grapes and 15 hybrids bearing white grapes from Monastrell × Syrah, 32 red and 6 white from Monastrell × Cabernet Sauvignon, and 13 red from Monastrell × Barbera have been studied. Among the intraspecific crosses, plants with grapes presenting very high concentrations of anthocyanins and flavonols were found, indicating a transgressive segregation for this character, and this could lead to highly colored wines with an increased benefits for human health. As regards the qualitative composition of anthocyanins and flavonols, the hydroxylation pattern of the hybrids that also may influence wine color hue and stability presented intermediate values to those of the parentals, indicating that values higher than that showed by the best parental in this respect will be difficult to obtain. The results presented here can be helpful to acquire information for future breeding efforts, aimed at improving fruit quality through the effects of flavonoids.

Effect of Combined Use of Benzothiadiazole and Methyl Jasmonate on Volatile Compounds of Monastrell Wine

One effect of applying elicitors to plants is an increase in phenolic and volatile compound content. In this study, grapes treated at veraison with a combination of benzothiadiazole (BTH) and methyl jasmonate (MeJA) were vinified and the volatile composition of the resulting wines was analyzed. Results indicate that the combined application of BTH and MeJA to the grapes led to wines with a similar composition in higher alcohols and esters as wines made with untreated grapes. Treated grapes led to wines with a significantly higher concentration of terpenes, with some of the terpenes only detected in wines from treated grapes. A descriptive sensory analysis indicated that these differences in volatile composition could be detected in wines, with wines made from treated grapes having significantly greater fruity notes, aroma, and mouthfeel quality.