Influence of postharvest hot-dip fungicide treatments on 'Redblush' grapefruit quality during long-term storage

The efficacy of postharvest hot-dip treatment on Redblush grapefruit was investigated by 3-min dips in water at 50°C and 20°C, with and without 1500 ppm imazalil (IMZ) or thiabendazole (TBZ). Fruits were stored for 16 weeks in cold rooms at 8°C and then held at 20°C for 1 week to simulate shelf life. IMZ and TBZ treatment at 20°C considerably reduced the incidence of chilling injury (by about 50-60%) and the percentage (by 20%) of fungal infections. The effectiveness of the two fungicides was found to be considerably increased at 50°C. However, the beneficial effect of hot-dip treatment was noted, whether or not associated with the use of fungicides. The chilling index was threefold lower in fruit dipped in water at 50°C. Similar results were obtained by IMZ treatment and mold decay was decreased by about 50%. IMZ treatment at 50°C proved to be phytotoxic, thus resulting in reddish peel pitting, starting on the fourth week of storage. No further detrimental heat-related effect was detected in the remaining cases. Fruit treated with the two fungicides exhibited no significant differences in respiration rate under cold storage, when compared to control. By contrast, by the end of shelf life, sharply increased values were found in fruit treated with IMZ at 20°C. Endogenous ethylene production and internal quality attributes (juice%, total soluble solid content, juice acidity, and ripening index) did not reveal important differences between treatments. Ethanol concentration in the juice was remarkably lower in fruit treated with the two fungicides, whereas differences due to dip temperature were negligible in most cases.