ASHS 2024 Conference

There has been a surge in demand for organic apples in the U.S. in the last decade. Washington State supplies more than 90% of them because of the ideal climate and soil conditions that favor production. Thermotherapy methods are widely used in Europe to reduce postharvest rots, but they have not been adopted in the U.S. because of their potential detrimental effects on fruit quality. The objective of this research was to evaluate the impact of hot water treatments at harvest on fruit quality during long-term storage. ‘Royal Gala’ and ‘Honeycrisp’ apples were immersed at 49 °C or 52 °C for 2 minutes in a controlled hot water bath immediately after harvest. After fruits were dried at 20 °C, they were placed in controlled atmosphere (CA; 2 kPa O2, 0.5 kPa CO2, 1°C-‘Royal Gala’, 3oC-‘Honeycrisp’) and air (RA; 1°C-‘Royal Gala’, 3oC-‘Honeycrisp’) storage for up to 9 months. Fruit quality (firmness and titratable acidity), defects, and physiological disorders were evaluated 1 and 7 days at 20 °C. In general, ‘Royal Gala’ apples immersed at 49 °C and stored in CA had no decay after 3 and 6 months of storage, but it was the highest (around 9%) in ‘Honeycrisp’ in both CA and RA. Peel damage was less at 49 °C for both ‘Royal Gala’ (RA-1.3%; CA-5%) and ‘Honeycrisp’ (RA-7.4%; CA-2.8%) compared to 52 °C after 3 months. Fruit firmness and titratable acidity were statistically different (p≤0.05) at 49 °C compared to 52 °C after 3 months. Although the hot water treatment in ‘Royal Gala’ apples was effective in reducing decay incidence without compromising fruit quality, the opposite was found in ‘Honeycrisp’; therefore, further research is needed to confirm these results and understand the variety-dependent effect.