Impact of preharvest salicylic acid treatment on phenolic content and antioxidant activity of grape berries

Grape berries contain high contents of phenolics, which are known to possess health promoting properties. Exogenous application of phytoregulators, mainly methyl jasmonate and abscisic acid, to grapevines to enhance fruit phenolic content has been reported. However, these phytohormones possess some drawbacks that can be overcome by using other phytoregulators as an alternative. In this work the effect of an additional phytohormone, salicylic acid, to grapevines on the phenolics and antioxidant activity of grape berries was investigated. To our knowledge, salicylic acid has been earlier applied to grapevines to affect fruit ripening and quality. However, this is the first time it is applied to increase the total phenolic content in grape berries. As a result of our study, total phenol content and the free radical scavenging activity increased with 100 mg L^‑1 of salicylic acid in grape berries. In particular, the total phenol content increased from 768.3 to 1843.5 mg 100 g^‑1 and the IC₅₀ values decreased from 45.2 to 13.2 mg mL^‑1 in grape berries. Also, the contents of individual phenolics mostly increased significantly with 100 mg L^‑1 of salicylic acid in grape berries, except anthocyanins. Higher concentrations of salicylic acid (i.e., 500 vs. 100 mg L^‑1) did not result in higher contents of phenolics in grape berries. Therefore, 100 mg L^‑1 was selected as the best salicylic acid concentration to be used in the treatment. The application of exogenous salicylic acid to grapevines is an interesting agronomic practice to obtain fruits with improved health-promoting properties.