Study On Mechanism Of Reducing Chilling Injury By Prestorage Hot Water Treatment In Tomato Fruit Following Chilling Storage

Heat treatment has been used for increasing the resistance of the fruit to chilling injury (CI),and also for improving storability. The mechanisms involved in the beneficial effects of heat treatment and the physiological basis associated with CI, however, still remain unclear. The objectives of this study were to evaluate the effectiveness of prestorage hot water, treatment to reduce CI and postharvest physiology, and whether these effects were related to changes in antioxidantion and contents of various types of polyamines (PAs). The effect of hot water treatment on chilling index, ripening index, electrolyte leakage, activities of SOD, CAT, APX, POD, ACS and PG, firmness, respiratory rate, ACC, ethylene, polyamines and so on in mature-green tomato fruits (Lycopersicu esculentum var. cerasifome) stored at 1C, 85%-90% RH before ripening at 20C were evaluated.1. Mature-green tomato were treated in water at 30-48 C for 10-60 min, and then ripened at 20C or stored at 1+1C for 14 days before ripening at 20C. It is found suitable hot water (30-38C) significantly reduced chilling injury and decay, whereas high temperature (42-48 C) increased decay. The treatment which tomato were treated at 38C for 60 minutes is the most effective one on reducing chilling injury.2. Mature-green tomato were treated in water at 38 C for Ihour, and then stored at 1+1C for 37 days before ripening at 20 C. Prestorage hot water treatment enhanced ACS activity, ACC, ethylene production and respiratory rate significantly. 68.2% control tomatoes didn' t ripen normally after cold storage, whereas 90. 0% heated tomatoes ripened normally by increasing ethylene production.3. Prestorage hot water treatment increased the activities of SOD, CAT, and APX (P<0.05) but could not raise POD, and persisted high activities of CAT and APX during long chilling storage. These results indicated prestoragehot water treatment might keep membrane permeability by improving the activities of antioxidant enzymes.4. In order to investigate the relationship between polyamines and CI, free, conjugated and bounded polyamine levels (putrescine(Put), spermidine(Spd), and spermine(Spm)) were analyzed by high-performance liquid chromatography (HPLC). The most contents of polyamine in tomato fruit was free polyamine, and the lest one was bound polyamine.In the tomato fruit stored at 1 C, free polyamine (f-PAs) level increased, conjugated polyamine (c-PAs) level stablized, and bound polyamine (b~PAs) increased in 1 month then decreased. Heat treatment increased the level of Spd and Spm and c-PAs levels. Exogenous polyamine treatment increased f-PAs , c-PAs levels, but no effect on b-PAs levels. Put and Spm treatment inhibited membrane electrolyte leakage increase and reduced CI. These results implied that the increase in Spm and Put levels in response to chilling exposure might serve as a defense mechanism against CI, and the effectiveness of Spm was more resistance to CI than that of Put. MGBG treatment increased f-PAs level, decreased c-PAs level. 0-phenanthro treatment increased c-PAs level in first few days, and then reduced c-PAs level in late days, inhibited the increase of b~PAs seriously . MGBG and 0-phenanthro aggravated membrane electrolyte leakage and CI.These results indicated that bound polyamine level was the premise factors against chilling injury, and increase in Spd, Spm and conjugated polyamine levels in response to chilling exposure might reduc chilling injury of tomato fruit. And hot water treatment might delay chilling injury and decay of tomato fruit through a mechanism that involved Spd, Spm and conjugated polyamine levels.