Impact of postharvest hot water and calcium treatments on fruit quality and decay incidence of ‘Topaz’ apple under various storage conditions

Organic grown 'Topaz' apple has a high prevalence of Neofabraea spp. rot during storage. Previous research has shown that postharvest hot water (HW) dipping and calcium (Ca) treatments can effectively reduce fungal rot during the storage of apples. However, there is little information on the effectiveness of combining both treatments in reducing storage rot. Therefore, we examined the efficacy of HW in combination with CaCl2 dipping on reducing the incidence of fungal rot and maintaining the fruit quality of 'Topaz' apples during regular air (RA) and controlled atmosphere (CA) storage. Fruit were treated with HW (53 degrees C for 2 min) or no HW (control) combined with 0, 4, 8 and 12% CaCl2 and stored under RA or CA (1 kPa O2 plus 2.5 kPa CO2) at 1 degrees C. HW dipping reduced the incidence of rot and stalk pit browning under RA and CA. In the control, damaged fruit percentage was higher in fruit treated with 12% CaCl2 than 0%. In the HW treated fruit, decay percentage was highest at 12% CaCl2. The high percentage of damaged fruit was due to a higher incidence of decay and stalk pit browning for CA- and RA-stored apples, respectively. Fruit quality was better maintained under CA than RA, whereas the HW treatment did not affect the quality traits. In CA-storage, the control (0% CaCl2) maintained a better overall fruit quality compared to the 8 and 12% CaCl2 treatments. In contrast, CaCl2 application in RA-stored fruit maintained higher firmness compared to the control. Increasing the CaCl2 concentration decreased the K:Ca ratio, and the K:Ca ratio was found to be positively correlated with healthy fruit (r=0.76, p<0.01). Thus, increasing the CaCl2 increased 'Topaz' susceptibility to decay during CA-storage and was associated with excessive CaCl2.