Effect of postharvest heat treatments on fruit quality, surface structure, and fungal disease in Valencia oranges

Abstract

The effect of prestorage heat treatments on the quality of Valencia oranges and on postharvest disease was investigated during a 6-week storage trial. Fruit receiving a hot water immersion regime (45¦C core temperature for 42 min) designed to disinfest against Queensland fruit fly lost significantly less moisture and remained firmer during storage than unheated control fruit. Disinfestation treatment also significantly reduced fruit acidity and number of viable spores of Colletotrichum gloeosporioides, Penicillium digitatum, and P. italicum. The gradual heating process involved with disinfestation was more successful in maintaining fruit quality than surface sterilisation by hot water immersion (12 min at 53¦C), or conditioning in air (24 h at 30¦C and 90% relative humidity). Heat-treated fruit showed enhanced colour development. Light and electron microscopy studies showed that heating had little effect on the structure of surface waxes; however, collapsed oil glands were observed after cool storage. Prestorage heat treatments could be a favourable alternative to chemicals for control of pests.