Effects of defoliation and water restriction on total phenols and antioxidant activities in grapes during ripening

Aim: To compare the effect of water restriction and defoliation on the phenol contents and oxidant and antioxidant activities of Tempranillo grapes grown in the region of Extremadura, Spain. Methods and results: The results showed that at harvest, the water restriction treatment altered total foliar area, pH, and total soluble solid (TSS) and phenol contents but not polyphenol oxidase (PPO) and superoxide dismutase (SOD) activities. By contrast, the defoliation treatment did not affect TSS and pH, however, titratable acidity and phenol compounds were enhanced and PPO and SOD activities were decreased. Moreover, defoliation resulted in advanced grape ripening and reduced total foliar area.  Conclusion: At harvest, water restriction led to alterations in the levels of peroxidation and peroxidase (POX) activity, without any effect on the other parameters. Defoliation induced a lowering of PPO and SOD activities and an increase in phenol content. Significance and impact of the study: Given the environmental characteristics of the Extremadura region, defoliation may be suitable and efficient for regulating Tempranillo grape PPO activity, which is œnologically relevant since it could lead to lower levels of phenol oxidation and hence prevent wine discolouration