| Summary: | 博士 === 國立中興大學 === 園藝學系所 === 105 === The purpose of this research was to study the characteristics changes and chilling development, quality changes and the activity of the related enzyme as well as the correlation between ethylene and the chilling damage on the jicama tuberous root during storage under chilling or non-chilling temperatures. The roots stored at 6ºC as chilling condition, and at 20ºC as non-chilling condition, for 30 days. Characteristics of chilling injury were induced by chilling condition, included external decay, internal browning, decreasing of interior tissue lightness (L*) value and total phenolic compound (TPC), and loss of root firmness. The chilling temperature induced membrane damage includes increasing of membrane ion leakage (%), malondialdehyde (MDA) and hydrogen peroxide (H2O2) content. There were significantly increased of phenylalanine ammonium-lyase (PAL), polyphenol oxidase (PPO) and peroxidase (POD) specific activities in severe symptoms of chilling injury. The increasing of external decay and internal browning were highly correlated with increasing of membrane ion leakage (%), MDA content, PAL specific activity, PPO specific activity and decreasing of TPC. For the root stored at 6ºC, 9 days after storing then transferred to higher temperature for another 3 days (15ºC, 20ºC, 25ºC or continuously at 6ºC). The severe symptoms were found in the roots which were transferred to higher temperature, whereas the ethylene production and respiration rates can reduce by low-temperature conditions. Nonlinear Arrhenius plots of respiration were found in the roots stored at various temperatures (1ºC, 3ºC, 6ºC, 9ºC, 12ºC, 15ºC, and 20ºC). The slope of the plot from root and tissue discs decreased with lower temperatures with breaks points at about 9ºC in root and at 7ºC in tissue discs.
For the evaluation of ethylene production and respiration rates, roots storing at 6ºC for 12 days. Every 3 days, roots were transferred to 25ºC for evaluation at every 3 hours for 24 or 36 hours. Ethylene production and respiration rate rapidly increased after the root were transferred to higher temperature and tended to decrease afterward. For intermittent warming treatment (IW), jicama tuberous roots were stored at 6ºC for 12.5 days. Continuously, every 2 days, roots were transferred to ambient temperature for 12 hours (after 12 hours, the roots were returned to 6ºC). Intermittent warming treatment reduced ion leakage (%), internal browning, maintained the interior tissue L* value, and showed a good appearance after storage for 12.5 days but did not maintain firmness and reduced external decay. Roots treated with IW showed significant lower in ethylene production and respiration rate than roots storing at 6ºC but these rates were not consistent with the increasing of external decay, internal browning, and membrane ion leakage (%). 1-MCP treatment reduced ethylene production and respiration but increased chilling injury symptoms, such as external decay, internal browning, decreasing of interior tissue L* value, loss of firmness, and decreasing of membrane integrity. These results indicated that ethylene probably does not directly involved in chilling injury symptom development of jicama tuberous root.
Hot water treatment (HWT, 50ºC, 53ºC, and 55ºC) suppressed external decay and internal browning development, but none of them could completely prevent all the symptoms. Firmness, lightness value, and H2O2 content were not affected by the HWT. Root treated with 55ºC hot water was lower in ion leakage percentage and malondialdehyde. Nonetheless, statistics showed that there has no significant difference as compared to control. Hot water treatment can also maintain higher level of total phenolic compound. After transferring to ambient temperature rate of ethylene production was significantly reduced by the HWT, but rate of respiration was reduced only in 55ºC HWT. PAL, PPO, and POD specific activity were significantly reduced by the 53ºC HWT. Ferric reducing ability of plasma was maintained by the 55ºC HWT. Superoxide dismutase and catalase specific activity were not affected by any treatment of the HWT. Lastly, the 50ºC HWT maintained high level of ascorbate peroxidase specific activity. Low O2 treatments can reduce browning discoloration, maintain interior tissue L* value and delay weight loss of root but did not affect the root firmness. The best browning prevention was found in root treated with 0% O2, nevertheless, high decay was also found in this treatment. Moreover, 0% O2 treatment damaged the root cell membranes, which give the rise of ion leakage (%) and decay.
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