Heat-induced tolerance to internal browning of pineapple (Ananas comosuscv. ‘Mauritius’) under cold storage

SummaryPineapple (cv. ‘Mauritius’) fruit, under low temperature (10°C) and 85% RH storage, develops internal browning symptoms. Fruit acidity, polyphenol oxidase (PPO) and peroxidase (POD) enzyme activities increased sharply, and phenylalanine ammonia-lyase (PAL) activity increased slightly during low temperature storage, concurrent with the development of internal browning. Harvesting fruit early reduced both the incidence and severity of internal browning. Post-harvest heat-treatment, in the form of a hot water dip, induced pineapple fruit tolerance to cold injury and, in turn, reduced internal browning during prolonged low temperature storage. Several temperature-time combinations were effective, but the best was 38°C for 60 min. Pineapple fruits treated at 38°C for 60 min developed 70% and 45% less browning than untreated controls in the flesh and core regions, respectively. The results also indicate that an internal tissue temperature of 37°C is a prerequisite for the induction of cold tolerance. Heat treatment, however, slowed down fruit ripening and increased water loss. Wrapping heat-treated fruits in polythene, exposing only the crown, prior to cold-storage reduced internal browning by a further 10% and water loss by 8.5%, giving fruit a better appearance.