Effect Of Colletotrichum Gloeosporioides And Polyphenol Oxidase On Litchi Preservation At Normal Temperature

Litchi, a famous and precious fruit in the subtropical zone , was not easy to be preserved. In this thesis preserving litchi at normal temperature wasstudied , basing on two key processes------the enzymatic catalyzing oxidationreaction and the damage induced by pathogen ,which result in browning of litchi pericarp.Colletotrichum gloeosporioides Penz, a major pathogen of litchi , was isolated from litchi chinesis Sonn. Wuye cultivar , and then biologically characterized . The study showed that the fungus had a strong pathogenicity to litchi fruit, the temperature and pH value suitable for its growth were 19*C ~31 "C and 5~7 , red light could stimulate its growth , but blue light depressed its growth . Tests in vitro indicated that the growth of this fungus was strongly suppressed by Sportak or Tecto .Polyphenol oxidase was separated and partially purified from litchi pericarp . Experiments showed that PPO could effectively catalyze phenol changing into quenol ,which further congregated into brown substance , the processes caused browning on litchi pericarp . Enzymatic study indicates that suitable pH value to PPO was 7.0?.9 , and the PPO's ability resist to heat was weak , with waterheated at 80 癈 for 30 minutes , its activity was lost completely .Tests in vitro elicited : 25mM ascorbic acid , ruduced glutathion, sodium bisulfite could inhibit PPO's activity at 100% , sodiumdiethyldithiocarbamate trihydrate , polyvinylpyrrolidone , 3,5-dinitrosalicylic acid also had highly inhibiting effect on PPO.To study litchi preservation at normal temperature . This experiment controlled rotting and browning of litchi by dipping the fruit in reagents then packing it in plastic bags . Effective antiseptics and PPO s inhibitors were choosed for the test .Experiments showed that 0.75% chitosan +1% sodium diethyldithiocarbamate trihydrate + 0.5% polyvinylpyrrolidone + l%ascorbic acid + 0.2% 3,5-dinitrosalicylic acid +0.5% citric acid + 200ppm giberellin + 300ppm Sportak + 600ppm Tecto achieved an efficiency at 32.81% of preventing browning in 10 day preservation.