Use of growth regulators on the total phenolic content and the antioxidant capacity of "Red Globe" grape

Table grape is one of the most consumed fruits in the world and it is one of the main sources of phenolic compounds and antioxidants. Plant growth regulators (PGR) are used in grapes to increase their size, improve their quality, and anticipate the harvesting period. The objective of this work was to determine the effect of the use of plant growth regulators on the total phenolic content (TPC) and the antioxidant capacity (AC) of the "Red Globe" grape. For this experiment a completely random block design was used, with 3 treatments (Ethrel®, Maxi-grow®, Ethrel® + Maxi-Grow®) and a control, with 5 blocks; thus, each sample would represent 1/60 experimental units. Significant differences (p≤0.05) were observed in soluble solids, titratable acidity, total phenolic content and antioxidant capacity with 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS · ₊) methods as a function of growth regulators. Significant differences (p≤0.05) were also found between blocks for the same treatment in the analyzed parameters, except for the water content. The highest average value for total phenolic content was found with the use of Ethrel® (124.5 mg of gallic acid equivalents 100 g^-1), while the control yielded the highest antioxidant capacity (63.8 and 22.2 mmol of Trolox equivalent antioxidant capacity 100 g^-1 with the ABTS+ and DPPH assay, respectively).