Development of Superficial Scald in 'Washington Spur' Apples Grown Under Anti-Hail Nets and Stored Using Conventional Cold Storage Method

Abstract

Apple production plays an important part in the worldwide deciduous fruit industry, as both local and export markets require high-quality fruit throughout the year. Unfortunately, long-term storage of apples can result in the occurrence of physiological disorders such as internal browning (IB). The effect of different cooling treatments over 49 d before CA storage commenced on IB development were evaluated for the 2021 and 2022 season after controlled atmosphere (CA) (4 and 6 months at 0.5 kPa CO2 and 1.5 kPa O2 with room cooling at 0.5 °C and stepdown-1 and stepdown-2 at 1 °C) storage, after 6 weeks simulated shipping and handling at 0 °C under regular atmosphere (RA) and after 7 d simulated shelf-life at 20 °C under RA. Cooling treatments entailed room cooling at 0.5 °C, stepdown-1 cooling from 4 °C to 1 °C and stepdown-2 cooling from 3 °C to 1 °C in 14 d under RA before CA storage commenced. The evaluations involved determining the external and internal defects, maturity, changes in biochemical content, and other quality indices. The type of IB that manifested were found to be CO2 injury. In 2021, fruit were harvested closer to optimum maturity and no IB was found while bitter pit manifested in fruit that received stepdown cooling and was stored under CA for 4 months. However, in 2022, fruit were harvested at a more post-optimum maturity and CO2 injury was found while no bitter pit occurred in any of the treatments. The study found that when Fuji was harvested closer to optimum maturity, room cooling may have caused fruit to be slightly less firm compared to stepdown cooled fruit after storage. However, when fruit was harvested at a more post-optimum maturity, stepdown cooling caused fruit to have a lower TA and firmness compared to room cooled fruit. The results of the study suggest that Fuji should be harvested closer to optimum maturity and be room cooled under RA for 49 d at 0.5 °C inmediately after harvest and be stored under CA (0.5 kPa CO2 and 1.5 kPa O2 at 0.5 °C) for longer than 4 months to prevent CO2 injury and bitter pit development. Fruit harvested closer to optimum maturity, was less susceptible to CO2 injury development, and room cooling for 49 d resulted in low internal ethylene concentrations (IEC) after cooling and, together with a longer CA storage duration, caused the fruit to be less sensitive to ethylene action that prevent bitter pit development.