Activities of several membrane and cell-wall hydrolases, ethylene biosynthetic enzymes, and cell wall polyuronide degradation during low-temperature storage of intact and fresh-cut papaya (Carica papaya) fruit

Fresh-cut fruit tissue deteriorates more rapidly than its intact counterpart. A study was conducted to determine changes in firmness, cell-wall polyuronides, and the activities of cell-wall and membrane hydrolases and ethylene biosynthetic enzymes in intact and fresh-cut papaya fruit during storage at 5 degreesC. Processing of papaya fruit was performed under sanitized conditions at 5 degreesC, and fruit pieces were stored for 8 days at 5 degreesC. Levels of total and CDTA-soluble polyuronides in intact fruit did not change during storage, but water-soluble polyuronides increased significantly by day 8 (15%). In contrast, total polyuronide content of fresh-cut papaya decreased (9.5%), whereas levels of CDTA- and water-soluble polyuronides increased 45 and 30%, respectively. Firmness and mol mass of polyuronides decreased more rapidly in fresh-cut fruit than in intact fruit. The activities of polygalacturonase (EC 3.2.1.15), alpha(EC 3.2.1.22) and beta-galactosidases (EC 3.2.1.23), lipoxygenase (EC 1.13.11.12), phospholipase D (EC 3.1.4.4), and ACC synthase (EC 4.4.1.14) and ACC oxidase increased within 24 h in fresh-cut fruit, and remained significantly higher compared with levels in intact fruit throughout the storage period. Pectin methyl esterase (EC 3.2.1.11), and phospholipase C (EC 3.1.4.3) activities showed no consistent differences between fresh-cut and intact fruit. The data suggest that a wound-induced increase in enzymes targeting cell walls and membranes contributes to the rapid deterioration of fresh-cut fruit. The significantly less pronounced changes observed for intact fruit stored under identical conditions indicate that the enhanced deterioration of fresh-cut fruit does not reflect low-temperature injury. (C) 2002 Elsevier Science B.V. All rights reserved.