Postharvest damage and darkening in fresh fruit of Uapaca kirkiana (Muell. Arg.)

Uapaca kirkiana is an important indigenous fruit crop in southern Africa that loses quality partly due to skin darkening. To determine whether the darkening is related to fruit injury during harvest and postharvest handling, the effects of damage caused by cutting, peeling or slicing on darkening of skin and flesh over time of unripe green and brown skinned fruit has been investigated. Also, unwashed and washed ripe fruit were exposed to direct sunlight to mimic the conditions at roadside markets where the fruit are commonly sold, and then compared with fruit kept under shade. Incising green fruit accelerated skin darkening and loss of yellowness and greenness as indicated by decreases in chroma L* and b* values, and increasing a* values, respectively. Decreases in skin brightness and yellowness also occurred in the incised brown skinned fruit, but their greenness did not change significantly over time. Severity of darkening increased with increasing level of damage on the skin. Peeling and slicing of both green and brown skinned fruit resulted in loss of flesh brightness, and yellowness and greenness over time. Exposing ripe fruit to direct sunlight after harvest resulted in more skin darkening compared with keeping the fruit under shade. No significant differences in skin darkening were found between unwashed and washed fruit. The study has demonstrated the important contribution of fruit damage and exposure to direct sunlight towards postharvest fruit darkening.