Training System and Methyl Jasmonate Application: A Tool to Improve Major Polyphenol Consumed by the Brazilian Population in Grape Juice

In this research, the effects of foliar methyl jasmonate (MJ) were evaluated on the phenolic composition of five grape varieties cultivated using a Pergola and Vertical Shoot Position (VSP). Their grape juice was investigated using UPLC-QTOF analysis over two seasons. Caffeic acid derivatives, such as caftaric acid and caffeic acid glucoside, were the most responsive hydroxycinnamates in the study. MJ significantly increased the anthocyanin content in the "Isabel" juices from a high-productivity training system ("Pergola"). The juice from treated grapes of 'Isabel Precoce' variety yielded promising results, as the total soluble solids content was higher during the experiment. The VSP system also yielded a positive reaction after MJ treatment for anthocyanins and hydroxycinnamates in 'Ives' variety. In conclusion, the integrated approach of varieties and training system enhances the MJ treatment efficacy, enabling the preparation of blends of grape juice, leading to improvements on quality and phenolic composition.