Postharvest peel pitting at non-chilling temperatures in grapefruit is promoted by changes from low to high relative humidity during storage

'Marsh' white grapefruit are prone to develop postharvest peel pitting during storage at non-chilling temperatures. The disorder is characterized by sunken areas or 'pits' on the flavedo followed by browning and dryness of affected areas in severe stages. Despite its uncertain cause, coating fruit with commercial waxes coupled with warm-temperature storage has been reported to promote peel pitting. In this work, we examined the effect of changes in relative humidity (RH) and waxing at various times during storage on the incidence of postharvest peel pitting. Grapefruit stored at 20degreesC and constant low (30%) or high (90%) RH developed low levels of peel pitting, even if waxed immediately after harvest. In contrast, when fruit stored at 30% RH were transferred to 90% RH, the incidence of peel pitting markedly increased, while transferring from 90 to 30% RH did not lead to increased pitting. This effect was greater in fruit exposed to prolonged periods of dehydration at 30% RH. Removal or redistribution of natural surface fruit waxes by washing followed by storage at low RH had little effect on peel pitting, but the transfer of washed fruits from low to high RH markedly increased peel damage. Waxing fruit enhanced severity of the damage only if there was a previous dehydration period. Light microscopy of damaged peel revealed no difference in morphology of affected tissues whether fruit were transferred from low to high RH, or after waxing following dehydration. Taken together, the results suggest that in 'Marsh' grapefruit the alteration of water relations in peel is a key factor in the incidence of postharvest peel pitting, and that preservation of a constant water status prior to and during postharvest handling may have an important role in maintaining peel quality. (C) 2003 Elsevier B.V. All rights reserved.