Effects of harvest date and low-temperature conditioning on chilling tolerance of ‘Wonderful’ pomegranate fruit

• Early-season fruits are very chilling-susceptible; late-season ones are relatively tolerant.
• A 10-day prestorage treatment at 15 °C enhanced ‘Wonderful’ pomegranate chilling tolerance.
• Low-temperature-conditioning fortified fruits tolerance against cold-quarantine treatments.

The optimal storage temperatures for ‘Wonderful’ pomegranates are between 5 and 7.5 °C. However, application of a cold-quarantine disinfestation treatment against the Mediterranean fruit fly (Ceratitus capitate) requires exposure to a much lower temperature – below 1 °C – for at least 14 days; conditions that often cause chilling injury (CI) symptoms, manifested in surface pitting and internal browning of the white spongy tissue and inner membranes. We demonstrated that harvest time had a remarkable effect on fruit chilling tolerance: early-harvested fruits were very susceptible to CI and were severely damaged after 4 weeks of exposure to 1 °C followed by an additional week at a shelf-life temperature of 20 °C, whereas late-harvested fruits were rather chilling tolerant and showed hardly any CI symptoms after similar exposure. In addition, we developed a postharvest low-temperature-conditioning (LTC) treatment for ‘Wonderful’ pomegranate fruits; it involves exposure to a moderate temperature of 15 °C for 10 days before transfer to the cold-quarantine treatment. When this proposed LTC treatment was applied to mid-season fruits, it entirely prevented the appearance of CI symptoms after 4 weeks storage at 1 °C followed by one additional week at 20 °C, without impairment of fruit-quality parameters, as manifested in loss of weight, flavor, juice total soluble solids and acid contents, and total antioxidant activity. Overall, these findings demonstrate that harvesting mid- and, preferably, late-season fruits, and applying a pre-storage LTC treatment at 15 °C for 10 days, enables export of ‘Wonderful’ pomegranates to new markets that require cold-quarantine disinfestation treatments against the Mediterranean fruit fly.

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