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Changes in pathogenesis-related proteins and phenolics in Vitis vinifera L. cv. ‘Sauvignon Blanc’ grape skin and pulp during ripening

Tian, Bin, Harrison, Roland, Morton, James, Jaspers, Marlene
Scientia horticulturae 2019 v.243 pp. 78-83
Vitis vinifera, grapes, juices, pathogenesis-related proteins, phenolic compounds, pulp, ripening, total soluble solids, white wines
Grape proteins, particularly pathogenesis-related (PR) proteins, are responsible for white wine haze formation which is of great concern to winemakers. Phenolic substances in grapes have also been reported with involvement in protein haze formation by interaction with proteins. The protein and phenolic substances in grapes are important in determining their concentrations in juice and resultant wine, and thus consequent wine protein stability. This study investigated the changes in these haze formation related components in ‘Sauvignon Blanc’ grape skin and pulp during ripening. The phenolic content on per berry basis generally increased in grape skin and pulp, but the phenolic concentration on per gram of berry basis showed a decreasing trend in grape skin, suggesting the accumulation effect of phenolics in skin is less than the dilution effect caused by berry growth. Tannin was only detected in grape skin but not in the pulp and the changes in tannin were similar to total phenolics. PR proteins were synthesized and accumulated along with the increase of total soluble solids (TSS) in both skin and pulp from véraison until harvest during ripening. The increase of PR proteins in grapes during ripening was also reflected in corresponding juice. The results suggested most of PR proteins in juice is likely extracted from grape pulp, and the riper the grapes the more PR proteins may be extracted into juice. The higher level of phenolics in riper grapes could increase the extraction of phenolics into juice and thus decrease the final concentration of PR proteins.