Phenolic composition and chromatic characteristics of the epidermis of ‘Merlot’ grapes and wines treated in pre-harvest with plant regulator and biostimulants

Abstract

The development of new sustainable technologies to improve the quality of wine grapes can contribute to the advancement of the wine industry from an economic and environmental point of view. Thus, the objective of this work was to evaluate the effect of the application of abscisic acid (S-ABA), Ascophyllum nodosum (AN) seaweed extract and Aloe vera (AV) gel from the ‘Merlot’ vine on the phenolic characteristics of ‘Merlot’ grapes. The treatments were as follows: 1) control (water); 2) S-ABA 400 mg L^-1; 3) S-ABA 600 mg L^-1; 4) AV 200 mL L^-1; 5) AV 400 ml L^-1; 6) AN 0.2 ml L^-1 and 7) AN 0.4 ml L^-1. Applications were carried out at the stage, when the berries reached 50% color. In the epidermis, the following characteristics were evaluated: the contents of anthocyanins and total polyphenols, and the activity of the enzymes phenylalanine ammonia-lyase (PAL), polyphenoloxidase (PPO) and peroxidase (POD). In wine, total anthocyanins and polyphenols, monomeric anthocyanins, color index and antioxidant activity (DPPH) were evaluated. S-ABA applications increased the content of total anthocyanins and polyphenols and FAL activity in the epidermis of grapes, also increasing the monomeric anthocyanins in the wine. AV at 400 mg L^-1 had a positive effect on the increase of total polyphenol contents and on PPO enzyme activity. For the analysis of wine, AV gel and AN extract increased the content of total anthocyanins and DPPH.