Lychee (litchi Chinensis Sonn.) Chilling Injury Physiological And Ice Temperature Storage Technology

Litchi (Litchi chinensis Sonn.) is one of the most competitive fruits in domesticand international markets. It is an important way to exploit wider overseas marketsto keep the bright future of litchi industry. Low-temperature storage andtransportation is the most effective technologies to prolong the postharvest life oflitchi fruit. A cold chain and film packaging could extend fruit storage life up to onemonth with shelf life 1~2 days. But litchi is susceptible to chilling injury andpericarp may brown uniformly and quickly at below 3℃, followed by rapidbreakdown of the fruit when returned to room temperature, resulting in reducingcommercial value.In this study, the physiological and chemical reactions of litchi pericarp andpulp under chilling temperature were studied respectively; the application ofchemical treatments for inducing cold tolerance was assessed as well. Finally, thetechnologies of pericarp colour retention combined with ice-temperature storagewere investigated in detail.The storage effect of litchi fruits under low temperature varied with geneticdifference between cultivars. During chilling injury at 0℃, pericarp gradually gotdark and the colour index(a, L, C) continuously decreased. At the same time,anthocyanin concentration of pericarp quick descented, and anthocyanin of the 21stday was only 37.3% as much as that of 3℃. The content of phenols and flavonoidsdecreased as well. As the browning induced by chilling injury was worsening, waterloss leaded to the disruption of structure of pericarp cells, resulting in the rapidincrease in cell membrane permeability and pH value. The respiration rate andethylene releasing rate were inhibited strongly by 0℃, endogenous polyaminescontent accumulated markedly with an increase in putrescine and spermidine and adecrease in spermine. The relationship between chilling injury and enzymatic activities in pericarpwas investigated. PPO, POD, anthocyanase and LOX activities tended to increasewhen stored at 0℃for 7~21 days. SOD, CAT activities of fruit at 0℃were lowerthan those at 3℃, which accumulated free radical and enhanced lipid peroxidation,as a result, MDA content went up and the browning was even severe. 'Nuomici', more sensitive to chilling injury, stored at 0℃for 14 days, began tobrown on the protuberances of the pericarp; when stored for 21 days, slight uniformwater-spots in the epicarp were developed. Apparent chilling injury was irreversibleafter 28 days. The symptoms of chilling injury were skin browning and water-spots.As for 'Guiwei'fruit, which is less susceptible to pericarp browning, the extent ofphysiological and chemical changes was lower than 'Nuomici'. Some physiological and chemical changes of naked pulp and whole fruit of'Baila'stored at 3℃and -1℃respectively were studied to explore the criticalchilling-injury temperature of pulp. During storage at -1 ℃, water loss andmembrane leakage rate of pulp increased slowly, 3 polyamines content rose as well.SOD, CAT and AsA-POD activities decreased to some extent. The delay insenescence of naked pulp at -1℃was due to alleviation of lipid peroxidation. Butthese changes were not significant difference as compare to those of 3℃. The thickpericarp safeguarded pulp ,but during the later storage period of 3℃, the fungalcontamination in pericarp could accelerated the breakdown of pulp. Neverthelesswhole fruits stored over 60 days at -1℃had been brown seriously , but the pulpsfrom them were not injury on flavor and structure. It appeared that the criticalchilling-injury temperature of litchi pulp was much lower than that of pericarp. The effect of exogenous ABA, Spd,1-MCP, CaCl2, Ca( Ac)2 on chilling injuryresponses in 'Guiwei'fruit stored at 0℃was evaluated. The result showed thatfruits infiltrated vacuums with Spd,1-MCP, CaCl2 were alleviate the chilling injurysymptoms for the first 14 days. But when the storage time extended, the protectiveeffect was disappeared. ABA exerted less effect on lighting the injury degree.Interestingly, Ca(Ac)2 enhanced the pericarp browning. When the tolerance to coldwas induced, the activities of enzymes related with pericarp browning were inhibitedwhile enzymes of cleaning free radical were increased. The endogenous polyaminesincreased sharply while treated by Spd and then decreased quickly. Those have beensuggested that chemical treatments could induced the tolerance to cold for the timebeing, however, the practical effect of them on retarding pericarp browning oflong-term storage and transportation was not ideal. Hot water dipping or acid dipping alone inhibited or enhanced enzymaticactivities and could not control effectively the pericarp browning for a relative longtime. And hot water treatment combined with acid dipping not only inhibited theactivities of PPO, POD, anthocyanase and LOX, but also maintained the red colourof pericarp. The fruits did not exhibit the appearance of chilling injury symptomswhen stored for over 35 days at 0℃. According to our experiments, the pH value ofpericarp was the key factor for the colour retention of litchi fruit. Penicillium oflitchi became the main postharvest disease after treated with acid dipping and thefungal grew vigorous at medium of pH3.5. Sportak, a fungicide, could dissolve...