Starch degradation in 'Kensington' mango fruit following heat treatments

Abstract

Changes in carbohydrate metabolism of ‘Kensington’ mango fruit from 2 major production regions in Queensland were measured after conditioning fruit with hot air at 40°C for 0, 2, 4, 8 and 16 h or at 22°C for 16 h (control) followed by hot-water treatment at either 45°C fruit-core temperature for 30 min or 47°C fruit-core temperature held for 15 min. Advancing physiological maturity of ‘Kensington’ mango fruit was correlated with increased starch concentration within the mesocarp. An α-amylase inhibitor was present in unripe ‘Kensington’ mesocarp. α-Amylase activity was promoted by conditioning fruit at 40°C for 8 h, and this enhanced enzyme activity persisted until the fruit were ripe. Consequently, starch degradation was accelerated and the concentration of total soluble solids was higher in fruit conditioned at 40°C for 8 h than in fruit left at the lower temperature of 22°C for 16 h or not conditioned. Immediately on removal of fruit from hot-water treatment, activities of α-amylase and phosphorylase were inhibited. This inhibition was correlated with higher starch concentration and starch layer and starch spot injuries in these fruit. A positive correlation was also found between increased sucrose concentration and greater starch loss in 40°C conditioned ‘Kensington’ fruit. It is proposed that increased sugar concentration in the mesocarp increased the level of fruit heat tolerance.