Pre-harvest drought stress treatment improves antioxidant activity and sugar accumulation of sugar apple at harvest and during storage

Physico-chemical and quality changes in 72 sugar apple (Annona squamosa Linn.) fruits subjected to pre-harvest drought stress were analyzed at harvest and during storage at 10 °C or 15 °C, with 90-95% relative humidity. At harvest, the ascorbic acid, sugar and endogenous abscisic acid concentrations increased while the concentration of the substrate indicating a 50% loss in 2,2-diphenyl-2-picrylhydrazyl scavenging activity (DPPH EC50) decreased in fruit from drought-treated trees compared with fruit from well-watered trees (control). The fresh weight loss of fruit stored at 15 °C was higher than at 10 °C, with no significant effect of drought treatment. In contrast, fruit firmness was reduced by drought treatment compared with the control during storage at both temperatures. Respiration, ethylene production and the endogenous abscisic acid and total sugar concentrations were higher in fruit from the drought-treated trees kept at 15 °C. The total ascorbic acid concentration was higher in fruit from drought-stressed trees kept at 10 °C compared with other treatments. This was concomitant with the DPPH EC50 value, which was lowest in fruit from drought-stressed trees stored at 10 °C. These results implied that pre-harvest drought stress treatment activated antioxidant activity and increased sugar concentration in sugar apple fruit. In addition, pre-harvest drought stress hastened fruit ripening. Thus, based on the results, storage of sugar apple fruit at 10 °C is recommended as this induces antioxidant activity which delays chilling injury for 8 d.