Use of a recombinant protein (Harpin αβ) as a tool to improve phenolic composition in wines

Abstract

Climate change is modifying environmental conditions in all wine-growing areas of the world. High temperatures are the cause of an increased imbalance between industrial maturity and phenolic maturity, resulting in berries with high sugar levels, low concentration in organic acids and reduced concentrations in aromas and phenolic compounds. These grapes produce wines with high alcohol content and lack freshness, color intensity, and aromatic complexity. Viticultural strategies have been developed in recent years in order to maintain the quality of red wines, with a two-fold objective: improve the phenolic composition of wines and reduce their alcoholic content. Harpin αβ is a recombinant protein and elicitor of hypersensitive responses. When Harpin αβ is applied to crops, the expression of growth and defense genes is stimulated. These genes are generally associated with metabolic signals and pathways related to functions of protein and sugar transport and vegetative development. The objective of this work has been to apply Harpin αβ to the vines after veraison in order to advance harvest for reducing the alcohol content of the final wines while maintaining or improving their phenolic composition compared to full maturity grapes. This experiment was carried out in a commercial vineyard sited in Jumilla (Spain). Three treatments were applied; i) Control: untreated application of Harpin harvested at 15º Baume, ii) 2T: grapes treated twice with Harpin, at the time of veraison and 15 days later and harvested at 13º Baume and iii) 3T: an extra application of the compound made 15 days after the second treatment and grapes were also harvested at 13º Baume. In each treatment, the dose of Harpin αβ applied was 150 g/ha. All treatments were vinified in the same way. Once the wines were bottled, the physicochemical and chromatic parameters were analyzed. Wines from grapes of 2T treatments harvested at 13º Baume decrease significantly the pH, color intensity and total phenolic index of the wines. No significant difference was observed in the total acidity parameter. On the other hand, 3T treatmen increased significantly total anthocyanins compare to control wines. Moreover, this treatment obtained the highest concentration of tannins, although these differences were not significant compared to the control treatment. It is clear that the 3T treatment was much more effective in improving the phenolic concentration of the wines than the 2T treatment. These results showed that the Harpin application in the vineyard (3T) produced wines with similar phenolic content that the wines produced from fully ripe grapes but with 20% less alcohol. This makes the use of Harpin αβ an interesting strategy for winemakers seeking a natural reduction of alcoholic content in their wines without losing quality.