Blackheart development following chilling in fruit of susceptible and resistant pineapple cultivars

Smooth Cayenne, a widely grown commercial cultivar of pineapple (Ananas comosus L. Merr.), is susceptible to the internal browning disorder known as blackheart (also referred to as endogenous brown spot or internal browning). This disorder is induced by chilling and results in browning of the flesh and core of the fruit due to the oxidation of phenolic substances by the enzyme polyphenol oxidase. The hybrid pineapple cultivar Hawaiian Gold (53-116) is reported to be resistant to blackheart. Fruit of both Hawaiian Gold and Smooth Cayenne were stored for 14 days at 0, 2, 4, 6, 10 and 23degrees C, followed by 7 days at 23degrees C. Blackheart symptoms were observed in the flesh of Smooth Cayenne fruit chilled at 10degrees C and they were progressively less severe at lower chilling temperatures, with no symptoms observed in the flesh of fruit chilled at 0degrees C. Increased blackheart symptoms were observed in the core of the fruit at temperatures below 6degrees C. Blackheart symptoms were not observed in the flesh of Hawaiian Gold fruit chilled at any of the temperatures tested, but some symptoms were observed in the core tissue at temperatures between 0 and 6degrees C. Increased polyphenol oxidase activity was induced by chilling in the flesh of Smooth Cayenne fruit but not in the flesh of Hawaiian Gold. The levels of phenolics and juice pH were similar in the 2 cultivars. The results indicate that Hawaiian Gold fruit are resistant to blackheart in the flesh, at chilling temperatures of between 0 and 23degrees C. The unexpected observation that blackheart symptoms were restricted to the core of both Smooth Cayenne and Hawaiian Gold fruit following chilling at 0degrees C may have useful implications for the pineapple-processing industry.