Quality, antioxidant compounds, antioxidant capacity and enzymes activity of ‘El-Bayadi’ table grapes at harvest as affected by preharvest salicylic acid and gibberellic acid spray

Abstract

Berry quality, antioxidant compounds, antioxidant capacity and enzymes activity of ‘El-Bayadi’ table grapes cultivar at harvest as affected by preharvest spray of salicylic acid (SA, 4.0mM) and gibberellic acid (GA3, 30mg/L) were evaluated during 2014 and 2015 seasons. GA3 spray increased berry weight, length and width compared to SA and control treatments. SA spray decreased berry length and width compared to control. Both cluster weight and length increased by SA and GA3 compared to control. TSS content was not affected by treatments, but was higher in 2015 than 2014 season. Titratable acidity was higher at GA3 and SA treatments than control and was higher in 2014 than 2015 season. TSS/acid ratio was lower at SA than GA3 and control treatments. Berry firmness was lower at SA than GA3 and control treatments and was higher in 2014 than 2015 season. Total phenols and flavonoids concentrations were higher at SA and GA3 treatments than control. trans-resveratrol concentration increased, while trans-piceid decreased by SA spray compared to GA3 and control treatments. Total phenols concentration was higher in 2015 than 2014 season, in contrast to total flavonoids and trans-resveratrol. Vitamin C concentration increased by GA3 spray compared to SA and control and was higher in 2015 season than 2014. Peroxidase (POD) polyphenoloxidase (PPO), polygalacturonase (PG) and xylanase activities increased by GA3 spray compared to SA and control. While, SA spray decreased both POD and PPO activities compared to control. Both SA and GA3 spray lowered antioxidant capacity (higher DPPH IC50 values) than control. Nitrogen, phosphorus and potassium, and protein concentrations were higher at SA and GA3 treatments than control. In conclusion, preharvest spray of SA and GA3 could be used to improve the overall quality ‘El-Bayadi’ table grapes.