Induced Changes in Phenolic Composition of Wines After Foliar Application of Eugenol and Guaiacol Solutions to Grapevines

Due to the beneficial properties of polyphenols in wines and the effect of external factors on them, this work evaluates the effect of the foliar application of eugenol and guaiacol on grapevines on the phenolic composition of wines elaborated from such grapes. Three different treatments were carried out on cv. ‘Monastrell’ at veraison time- eugenol, guaiacol and eugenol + guaiacol. Several families of phenolic compounds were studied in wines at three different sampling times, including phenolic acids, stilbenes, flavanols, flavonols and anthocyanins, which were analysed by HPLC-DAD-MS. Eugenol treatment enhanced the concentration of the studied compounds, guaiacol produced changes in the compounds related to primary metabolism, such as sugar and acids, as well in some polyphenols, but when eugenol and guaiacol were applied altogether similar changes to eugenol alone were observed, such as an increase in the content of anthocyanins and stilbenes among other phenolic compounds. Results suggest that foliar applications of eugenol on Monastrell grapevines (alone or together with guaiacol) could be considered as an important stimulant for production of grape polyphenols, implicated in quality color, as well as in beneficial properties on human health.