Postharvest ethylene conditioning as a tool to reduce quality loss of stored mature sweet oranges

Abstract

Ethylene is related to senescence but also induces protective mechanisms against stress in plants. The citrus industry only applies the hormone to induce fruit degreening. The aim of this work was to determine the effect of ethylene on the quality of colored citrus fruit stored under commercial conditions to extend postharvest life, since it protects them from stress causing postharvest disorders such as chilling injury (CI) and non-chilling peel pitting (NCPP). The effect of conditioning mature Navelate and Lane Late sweet oranges (Citrus sinensis L. Osbeck) for 4 days with 2μLL−1 ethylene at 12°C, rather than at higher temperatures used for degreening, on the quality of fruit stored at 2 or 12°C, was examined. The ethylene conditioning (EC) treatment did not increase color but reduced calyx abscission and NCPP in fruit of both cultivars stored at 12°C, and also CI in Navelate fruit at 2°C. Lane Late fruit did not develop CI but showed a new disorder in EC fruit held at 2°C. This disorder began as scalded areas around the fruit stem end and extended over the fruit surface during storage. EC had no deleterious effect on the quality of Navelate oranges stored at either 2 or 12°C. Similar results were found in Lane Late fruit although EC slightly increased off-flavor perception at 2°C and the maturity index at 2 and 12°C. Moreover, EC slightly increased the content of bioactive flavonoids in the pulp of Navelate fruit but significant differences between control and EC fruit were only found after prolonged storage at 2°C. In Lane Late fruit, EC avoided the initial decrease in flavonoid content found in control samples. Results show, therefore, that EC at 12°C may be a tool to extend postharvest life of NCPP and CI-sensitive oranges, and that the tolerance of citrus cultivars to the combined effect of EC and non-freezing low temperature (2°C) should be tested to select the proper storage temperature.