Sun exposure and high preharvest fruit temperatures increase antioxidants, heat shock proteins and thermotolerance of mango fruit ( Mangifera indica L. )

Preharvest sun-exposure can improve the tolerance of fruit during postharvest handling conditions and thus we examined the postharvest responses of mangos. Sun-exposed and shaded fruit of 'Keitt' and 'Reynal' mango were harvested and assessed for external and internal damage following postharvest hot water (HW 55°C/50min) and hot air (HA 47°C/20min; 49°C/90min) treatments used for fruit fly disinfestation. Heat shock proteins and antioxidant systems were examined as possible biochemical strategies for stress protection of fruit tissues. With maximum air temperatures <37°C, fruit exposed to direct sunlight reached temperatures up to 47°C. Following HW, sun-exposed 'Reynal' fruit had less external damage than shaded fruit, with damage mainly on the exposed surfaces. In contrast, sun-exposed and shaded 'Keitt' fruit had similar levels of damage following HW. For both cultivars, HA treatments of either sun-exposed or shaded fruit did not cause any significant external damage, but internal damage was observed. Both cultivars exhibited biochemical stress responses. Hsp17.4 in the flesh of sun-exposed 'Reynal' and 'Keitt' fruit were 2 and 6 times higher than in shaded fruit, respectively. Total polyphenols and anthocyanins were higher in tissues of sun-exposed than shaded fruit. Results are discussed in terms of the different biochemical defence strategies among these cultivars.