Effects of storage temperature, harvest date and fruit origin on post-harvest physiology and the severity of mesocarp discolouration in ‘Pinkerton’ avocado (Persea americana Mill.)

Abstract

SummaryThe severity of mesocarp discolouration in ‘Pinkerton’ avocados, a disorder previously suspected to be chilling injury, was found to be decreased by storing fruit below the recommended temperature of 5.5°C. Furthermore, discolouration was intensified by storage at temperatures above normal (viz. 8°C), which coincided with higher electrolyte leakage and was used as a measure of membrane integrity. The disorder was therefore not ascribed to being the result of too low storage temperatures. Fruit firmness and carbon dioxide (CO2) production rates, monitored daily following storage, showed that fruit harvested later in the season had a slightly higher CO2 production rate than fruit picked earlier in the season. Throughout the study, the severity of mesocarp discolouration was affected by fruit origin. The potential for mesocarp discolouration appeared, therefore, to be initiated by pre-harvest factors, although its severity could be modified by storage at 2°C. At 2°C, the total content of phenolics was found to be significantly (P < 0.001) lower and soluble polyphenol oxidase (PPO) activity was similar to that in control fruit. Fruit also remained firm during storage at 2°C and electrolyte leakage remained similar to unstored fruit, indicating that membrane integrity was better preserved at this temperature. The role of membrane integrity became more important as the season progressed, as the total phenolics content increased and as total PPO activity decreased.