Chemical and quality traits of ‘Olinda’ and ‘Campbell’ oranges after heat treatment at 44 or 46 °C for fruit fly disinfestation

Abstract

The chemical and quality characteristics of ‘Olinda’ and ‘Campbell’ oranges (nucellar budlines from Valencia late cultivar) were evaluated after exposure to a fruit core temperature of 44°C and held at 44°C for 100min or 46°C and held at 46°C for 50min, subsequent storage at 6°C for 2 weeks and an additional week of simulated marketing period (SMP) at 20°C. Exposure to either heat treatment caused neither visible damage nor fruit softening. Fruit weight loss rate in ‘Olinda’ oranges was unaffected by treatment but was higher than control fruit in heat exposed ‘Campbell’ oranges after storage, though at the end of SMP differences between treated and untreated fruit were non-significant. While neither heat treatment affected decay incidence in ‘Olinda’ oranges, significantly less decay was found in heat treated ‘Campbell’ fruit compared to control fruit both during storage and SMP.The chemical analyses of flavedo tissue of ‘Olinda’ oranges revealed that there were no treatment differences in neutral sugars, soluble and insoluble pectins and calcium bound to insoluble pectin fraction. The calcium content bound to soluble pectin fractions increased following heat treatments. At the end of SMP there was a significant decrease of soluble pectin and a significant increase of calcium bound to insoluble pectins in flavedo from oranges of the 46 and 44°C treatments.Following treatment at 46°C ‘Olinda’ fruit had a significantly lower content of soluble solids concentration. However, differences in soluble solids concentration between treated and control fruit after storage and SMP were not significant.Post-treatment levels of ethanol in both cultivars were significantly higher than in non-treated fruit. During storage and SMP, significant increases of ethanol were detected in control fruits with respect to their initial levels, whereas a reverse trend occurred in fruit subjected to heat treatment. Upon termination of the heat treatment at 44 or 46°C, mean taste scores of ‘Olinda’ oranges were lower than those of untreated fruit, while the taste of ‘Campbell’ oranges was adversely affected only by the 46°C treatment. After storage and SMP, taste differences between treated and control fruit were not significant. Flavour scores were unaffected by the treatment at 44°C. Following treatment at 46°C flavour rating in ‘Olinda’ fruit was significantly lower than control fruit while after storage and SMP the differences in flavour scores between treated and untreated fruit were non significant. Heat treatment to a fruit core temperature of 44°C for 100min or 46°C for 50min can thus have important commercial applications as an alternative to toxic chemical fumigants or to longer and more expensive disinfestation treatments such as cold quarantine.