In this study, researchers wanted to evaluate the effect of pre-harvest application of elicitors such as methyl jasmonate (MeJ) and benzothiodiazole (BTH) on the composition and structure of grape berry skin cell walls. The extractability of the phenolic compounds during winemaking was also investigated to determine if wine quality was improved.
The trial was conducted over two consecutive seasons in Spain.
- Merlot, Cabernet Sauvignon and Monastrell were used in the trial.
- All treatments were performed in triplicate.
- There were three treatments namely control, MeJ application and BTH application.
- Treatments were applied twice, first at veraison and then one week later.
- Grapes were harvested at optimum maturity, some berries kept for analysis and from the rest of the grapes, wine was made according to a standard winemaking protocol.
The treatments delayed the maturation process in all varieties when rainfall was low.
- Application of MeJ and BTH during veraison significantly changed the phenolic compounds, proteins and structural sugars in berry skin cell walls. The effects however varied in different proportions depending on the variety and year, indicating that the responses are very much varietal and weather dependant.
- An increase in proteins and phenols were observed in the skin cell walls of Monastrell and Cabernet Sauvignon, improving the berry structure and resistance to fungal pathogens, as well as improving the phenolic profile.
- In Merlot, treatments decreased protein, phenol and cellulose content in cell walls, affecting the structural integrity of the berries.
- MeJ and BTH applications increased total anthocyanin content significantly in Monastrell and Merlot grapes in 2016, but it seemed like the changes in the cell wall structure hindered the extraction of anthocyanins during winemaking.
SIGNIFICANCE OF THE STUDY:
Increased berry phenolic content has benefits, especially in red wine production. Thus practices that increase phenolics can be useful for wine producers. The results from this study indicated that a more exhaustive study of the total phenolic compounds of fresh grape skins is necessary in order to determine the real increase achieved by the use of MeJ and BTH.
Image copyright: Kevin Crause