Effects of Fruit Temperature, Calcium, Crown and Sugar Metabolizing Enzymes on the Occurrence of Pineapple Fruit Translucency

Chen, Ching-Cheng
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The role of preharvest fruit temperature, calcium, crown and sugar metabolizing enzymes in the occurrence of pineapple fruit translucency was studied. In Hawai‘i, pineapple fruit translucency began to appear 4 to 2 weeks before commercial harvest. Pineapple fruit flesh became very susceptible to high temperature 6 to 4 weeks before harvest as flesh cell electrolyte leakage increased. High fruit temperature during the last stage of pineapple fruit development decreased titratable acidity and increased translucency. The calcium concentration in pineapple fruit flesh declined with fruit development, possibly due to a decrease in the proportion of water imported via the xylem compared to the phloem. Mature fruit flesh tissue had a significantly reduced ability to bind divalent cations. Spraying calcium during pineapple fruit development decreased translucency occurrence at harvest. Removing the crown either at an early or late stage of pineapple fruit development did not cause any significant effect on the fruit weight and translucency, suggesting that the crown did not play a significant role in pineapple fruit development and translucency occurrence. Defoliation conducted 4 or 3 weeks before harvest did not significantly reduce the pineapple fruit weight, but did significantly reduce the total soluble solids and fruit translucency, suggesting that the photoassimilate partitioning during the last stage of fruit development played an essential role in the occurrence of translucency. Sucrose began to accumulate rapidly in pineapple fruit flesh 6 weeks before harvest, while the activities of three invertases and sucrose synthase were low. The activity of celliv wall invertase (CWI) increased in the fruit flesh again 4 weeks before harvest, followed by the occurrence of translucency. There was a positive correlation between the CWI activity and translucency severity in pineapple fruit flesh, suggesting that the high CWI activity, that favored apoplastic phloem unloading, may be one of the causes inducing pineapple fruit translucency.
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