Effect of low temperatures on chilling injury in relation to energy status in papaya fruit during storage

Papaya (Carica papaya L.), a typical tropical fruit, is susceptible to chilling injury (CI). In the present study, CI index, energy level, and energy metabolism-related enzymes activity in papaya fruit stored at 16, 11, 6, and 1 °C were investigated to evaluate the relationship between CI and energy metabolism of papaya fruit during cold storage. Results showed that there were no symptoms of CI in papaya fruit stored at 16 °C, while some typical CI symptoms including skin pitting, scald and flesh water soaking were appeared in papaya fruit stored 11 °C and 6 °C. Furthermore, we observed that papaya fruit did not appear obvious symptoms of CI during most duration of storage at 1 °C with the exception of slight CI at end of storage. ATP, ADP and the total content of AXP (=ATP + ADP + AMP) contents, EC and energy metabolism-related enzymes activity (H+-ATPase, Ca2+-ATPase, succinic dehydrogenase (SDH), and cytochrome c oxidase (CCO)) in papaya fruit stored at 1 °C were higher than those in fruit stored at 11 and 6 °C. The results suggest that higher energy status in papaya fruit during cold storage could contribute to the alleviation of CI.