Biochemical changes associated with chilling in pineapple fruit

Pineapple (Ananas comosus [L.] Merr.) fruit of variable cultivar ('Smooth Cayenne' and PRI hybrid '73-50') and maturity were stored at chilling temperatures to investigate the mechanism for blackheart inducement and development. When chilled for three weeks at 13°C followed by 7 days storage at 25°C, fruit of both cultivars developed significantly increased polyphenol oxidase (PPO) activities concurrently with blackheart symptoms. Fruit stored continuously at 25°C developed no blackheart. There was no correlation between peroxidase activity (POD) and blackheart development for either cultivar. The influence of fruit maturity on blackheart development was also investigated, by storing 'Smooth Cayenne' fruit of six maturity ranges for 3 weeks at 10°C, or for 3 weeks at 10°C followed by 7 days at 25°C. Immature fruit developed negligible blackheart, while fruit of mid-range maturity were susceptible, the latter also developed increased PPO activity after 4 weeks. Over mature fruit developed a translucent breakdown of the pulp, rather than blackheart. Differences in subsequent fruit susceptibility to blackheart were not consistent with PPO activities at harvest. Total phenol concentration increased with fruit maturity, but high phenol concentration was not consistent with increased blackheart incidence. There was no significant difference in ascorbic acid levels at harvest between the maturity ranges. The suggestion in the literature that ascorbic acid level at harvest indicates susceptibility to blackheart is not support by our data