Effect Of Chitosan Treantment For Increasing Storability Of Harvested Carambola Fruits And Its Action Mechanism

Carambola(Averrhoa carambola L.)is a major cultivated subtropical fruit in the south of China which has high nutritional and commercial value.However,because of the characteristics of carambola fruits that are thin,brttle and others,damage easily affected by the extrusion force during the process of picking and transportion,and other phenomena such as shrinkage,colour change and pathogen infection that was easy to happen during the storage,they were greatly influenced postharvest quality,transportation and consumption.XiangMi carambola fruit,the major cultural variety in Fujian Province,was used as testing materials.Fresh-keeping effect of the different concentration chitosan treatment on harvested carambola fruits was studied to select the best concentration.The further research about effect of the best concentration chitosan treatment on postharvest physiology,storage quality and storability was studied,elaborating effect of the best concentration chitosan treatment on storability of harvested carambola fruits and its action mechanism from cell wall metabolism,reactive oxygen species metabolism,membrane lipid metabolism,energy and respiratory metabolism,antifungal substances metabolism.The main research results were shown below:1.The effect of the different concentration chitosan treatment on fresh-keeping effect of harvested carambola fruits was studied.Compared with control fruit,different concentrations chitosan treatment(diluted 100,300,600 and 900 times)could decrease respiratory rate and permeability of cell membrane of carambola fruits,delay the decline to content of pericarp pigments of carambola fruits,keep higher contents of TSS,TA,total sugar,sucrose sugar,reducing sugar and vitamin C of carambola fruits,delay the change of pericarp surface color of carambola fruits,decrease fruit decay index of carambola fruits,and maintain higher fruit hardness,commodity rate and lower water loss percentage of carambola fruits.Chitosan diluted 100 times was the best among the different concentrations.Therefore,chitosan diluted 100 times could be used as the best concentration during the postharvest storage at(15±0.5)℃.2.The effect of the best concentration chitosan treatment(diluted 100 times)on postharvest physiology,storage quality and storability of harvested carambola fruits was studied.Compared with control fruit,the best concentration chitosan treatment could decrease respiratory rate and permeability of cell membrane of carambola fruits,delay the decline to content of pericarp pigments of carambola fruits,keep higher contents of TSS,TA,total sugar,sucrose sugar,reducing sugar and vitamin C of carambola fruits of carambola fruits,delay the change of pericarp surface color of carambola fruits,decrease fruit decay index of carambola fruits,and maintain higher fruit hardness,commodity rate and lower water loss percentage of carambola fruits.According to result,chitosan treatment(diluted 100 times)could strengthen storability of harvested carambola fruits and keep better storage quality of carambola fruits.3.The relationship between effect of the best concentration chitosan treatment(diluted 100 times)on softening of harvested carambola fruits and cell wall metabolism was studied.Compared with control,the results showed that the best concentration chitosan treatment could keep higher firmness and contents of cell wall material,pectin,cellulose and hemicelluloses,lower contents of soluable pectin and activities of cell wall-degrading enzymes such as pectinmethylesterase(PME),polygalacturonase(PG),cellulae(Cx)and β-Galactosidase(P-Gal).According to result,chitosan treatment(diluted 100 times)could be better to maintain the integrity of the cell wall structure of harvested carambola fruits by reducing activity of cell wall material degradation enzyme activity,leading to effectively delay softening of harvested carambola fruits,improve storability of harvested carambola fruits and better keep storage quality of carambola friits.4.The effect of the best concentration chitosan treatment(diluted 100 times)on ROS metabolism of harvested carambola fruits was studied.The results showed that,compared with control,the best concentration chitosan treatment could effectively reduce super oxygen anion(02-.)producing rate and malondialdehyde(MDA)content,inhance activities of scavenging enzyme for active oxygen such as superoxide dismutase(SOD),catalase(CAT)and ascorbic acid peroxidase(APX),delay the decline to contents of ascorbic acid(AsA)and reduced glutathione(GSH),and keep higher DPPH scavenging activity and reducing power.According to result,chitosan treatment(diluted 100 times)could reduce ROS accumulation by maintaining higher ROS scavenging ability of carambola fruits,leading to reduce membrane lipid peroxidation of carambola fruits,better keep the integrity of the cell membrane structure,improve storability of harvested carambola fruits and better keep storage quality of carambola fruits.5.The effect of the best concentration chitosan treatment(diluted 100 times)on membrane lipid metabolism of harvested carambola fruits was studied.Compared with control,the results showed that the best concentration chitosan treatment could decrease permeability of cell membrane,inhibit activities of membrane lipid-degrading enzymes such as lipoxygenase(LOX),lipase and phospolipase D(PLD),keep higher contents of phosphatidyl choline(PC),phosphatidyl inositol(PI)and lower content of phosphatidic acid(PA),maintain higher relative contents of unsaturated fatty acids and lower relative content of saturated fatty acids,hold higher index of unsaturated fatty acids(IUFA)and the ratio of unsaturated fatty acids to saturated fatty acids(U/S)of carambola fruits.According to result,chitosan treatment(diluted 100 times)could reduce the membrane lipid degradation by inhabit activities of membrane lipid-degrading enzymes of carambola fruits,leading to better keep the integrity of the cell membrane structure,improve storability of harvested carambola fruits and better keep storage quality of carambola fruits.6.The effect of the best concentration chitosan treatment(diluted 100 times)on energy and respiratory metabolism of harvested carambola fruits was studied.The results showed that,compared with control fruit,the best concentration chitosan treatment could keep higher ATP,ADP content and energy charge level,improve activities of H+-ATPase,Ca2+-ATPase,Mg2+-ATPase and NAD kinase,and inhibit activities of cytochrome c oxidase(CCO)、ascorbic acid oxidase(AAO)and the contents of NAD and NADH,and maintain higher contents of NADP and NADPH.According to this,chitosan treatment(diluted 100 times)could maintain balance of Ca2+、Mg2+、H+ and osmotic pressure inside and outside the cell membrane by maintaining energy charge level and activity of ATP,leading to better keep the integrity of the cell membrane structure and function,improve storability of harvested carambola fruits and better keep storage quality of carambola fruits.In addition,storability of harvested carambola fruits could be inhanced relating to changes of activity of breathing terminal oxidase and respiratory metabolism pathway.7.The effect of the best concentration chitosan treatment(diluted 100 times)on antifungal substances metabolism of harvested carambola fruits was studied.The results showed that the best concentration chitosan treatment could improve activities of disease resistance-related enzymes such as polyphenoloxidase(PPO),peroxidease(POD),phenylalanine ammonialyase(PAL),β-1,3-gulcanase(GLU)and chitinase(CHI),and increase contents of antifungal substances such as lignin and total phenols.According to result,chitosan treatment(diluted 100 times)could inhance durability and disease resistance of harvested carambola fruits by maintaining higher contents of antifungal substances such as lignin and total phenols,and higher activities of disease resistance-related enzymes,leading to reduce the occurrence of postharvest diseases of harvested carambola fruits.