Reduced degradation of the cell wall polysaccharides maintains higher tissue integrity of papaya (Carica papaya L.) during chilling storage

Abstract

Papaya (Carica papaya L.) fruit are vulnerable to chilling injury (CI), and the symptoms of CI develop more intensively when the fruit are stored at 6 ℃ rather than 1 ℃. This is considered to be abnormal CI behavior of papaya fruit, a phenomenon that is unclear but thought to be related to cell wall metabolism. Thus, this study examined the relationship between the development of CI and alterations of the cell wall metabolism in papaya fruit stored at 1 ºC and 6 ℃. The 1 ℃-storage maintained the integrity of the papaya exocarp and alleviated the development of CI and the loss of free moisture. Ultrastructural observations demonstrated that the middle lamellae were denser in papaya fruit stored at 1 ℃ than those in 6 ℃-storage, which alleviated the disintegration of cell wall at 1 ℃-storage. Compared with 6 ℃-storage, 1 ℃-storage inhibited the degradation of Na2CO3-soluble pectin, CDTA-soluble pectin, and cellulose. The 1 ℃-storage also delayed the solubilization of water-soluble pectin and the transformation of 24% KOH-soluble fraction to the 4% KOH-soluble fraction. Lower activities of cell wall-modifying enzymes, including pectin methylesterase, polygalacturonase, pectate lyase, β-galactosidase, xyloglucan endotransglycosylase, and cellulase, were observed in papaya fruit stored at 1 ℃. These results suggest that alleviating the degradation of cell wall polysaccharides maintains higher tissue integrity in papaya fruit during chilling storage.