Effects Of Pre-storage Treatment On Postharvest Physiological Changes Of Litchi Fruit Under Modified Atmosphere Packaging

Litchi（Litchi chinensis Sonn.）fruit can’t be stored long after harvest,seriously affect the development of Chinese litchi industry.At present,although modified atmosphere packaging（MAP）combined with cold storage has been identified as a major measure of storage and transportation of harvested litchi fruit,no work has documented the effect of pre-storage on litchi fruit MAP storage.In this study,mature fruit of litchi（cv.‘Yuanhong’）was used as experimental material and and three different MAP treatments were set up for cold storage（MAP1:packed with 0.03 mm PE film;MAP2:packed with 0.1 mm PE film;MAP3:0.03 mm PE film was used for pre-storage for 10 d and then replaced with 0.1 mm PE film）.To investigate the effects of pre-storage treatment on gas concentration,appearance quality,sugar and acid content,glycolysis,fermentation metabolism and pericarp browning-related enzymes,and pericarp polyphenolic substances of litchi fruit during cold storge,in order to providing theoretical references for further improve of postharvest commercial storage and transportation technology of litchi fruit.The main findings are as follows:（1）Effects of pre-storge treatments on the gas inside the package and the appearance quality of litchi fruitDuring MAP cold storage,the O₂ and CO₂ concentrations were maintained between 18.6%～19.47%and 0.73%～1.17%in the package of MAP1 treatment,respectively.In 2 days of storage,the O₂ concentration in the package of MAP2 treatment decreased significantly due to the additional O₂ absorber,while that of CO₂ increased sharply,from 10 to 40days of storage,the O₂ and CO₂ concentrations in this package were equilibrated,ranging 4.2%～7.57%and 2.50～3.37%,respectively.When the MAP3 treatment were pre-stored in the 0.03 mm PE bag for 10 days,and then were changed the package of 0.1 mm PE,the O₂ and CO₂concentrations inside the bag from 20 to 40 days of storage demonstrated the similarity to those in the aforementioned MAP2 treatment.Pericarp color value A*and moisture content were significantly lower in the MAP2treatment during cold storage,and fruit decay at 40 d.In contrast,Pericarp color value A*and moisture content were substantially higher in the 0.03mm PE treatment,but fruit decay at 30 d.After pre-storage MAP3treatment prevented the decline of pericarp color values A*and moisture content,and there was no decay occurred during whole storage period.（2）Effects of pre-storage treatments on sugar and acid content and key enzymes of glycolysis and fermentation metabolism in litchi fruitUPLC was used to quantify the soluble sugar and organic acid components of litchi fruit,and the results showed that the soluble sugar components of litchi fruit included fructose,glucose and sucrose.The organic acid components of fruit pericarp included shikimic acid and malic acid,quinic acid and citric acid,and the organic acid components of aril included malic acid and citric acid.The citric acid content of the pericarp and the sucrose and malic acid content of the aril in MAP2 treatment were significantly lower than those in MAP1 treatment during cold storage,while the MAP3 treatment of after pre-storage delayed this change after pre-storage.The key enzymes for glycolysis and fermentation metabolism of the litchi fruit were measured,and the results showed that fructose-1-phosphate kinase（FPK）,pyruvate decarboxylase（PDC）,and lactate dehydrogenase（LDH）activities were significantly higher than those in MAP1 treatment,while the MAP3 of after pre-storage treatment preserved similar low level as the MAP1 treatment during storage.This indicates that the aril reaction is more intense after the rapid entry into the low oxygen environment,and the pre-storage treatment can delay this change,so that the litchi fruit solids maintain a high level of sugar and acid content during storage.This indicates that the rapid entry into the low oxygen environment after harvesting significantly promoted the glycolysis and fermentation metabolic processes in the fruit,especially in the aril;while the pre-storage treatment significantly delayed these changes,allowing the litchi fruit to maintain a higher level of sugar and acid content content during storage.（3）Effects of pre-storage treatments on pericarp browning-related enzymes and phenolic substances components and contentDuring cold storage,MAP3 treatments inhibited effectively the increase of relative leakage rate of litchi pericarp by pre-storage.The results of pericarp PPO,SPOD and BPOD enzyme activities showed that there was no significant difference in pericarp PPO and SPOD activities among different MAP treatments.The pericarp BPOD activity of MAP2treatment fluctuated drastically during storage,while the pericarp BPOD activity of after pre-storage MAP3 treatment remained stable during 20d～40 d of storage after pre-storage and was similar to that of MAP1treatment.UPLC-MS was used to quantify the polyphenolic substances components and content of litchi pericarp,and the results showed that the polyphenolic substances components of litchi pericarp included（-）-epicatechin,（+）-catechin,procyanidin B2,procyanidin A2,rutin,and centaureidin-3-O-rutinoside.The polyphenolic substances content of the pericarp in MAP2 treatment were significantly lower than those in MAP1treatment during cold storage,while the MAP3 of after pre-storage treatment delayed this change after pre-storage,implyed that it was beneficial in maintained the pericarp polyphenolic substances content.In conclusion,after pre-storage MAP3 treatment could effectively inhibit of harvested litchi fruit decay and the decline of pericarp color values A*and moisture content by pre-storage,and inhibit the increase of aril FPK,PDC and LDH activity,which glycolysis,fermentation metabolic rate decreased,thus the fruit sugar and acid content maintained higher level.It’s also effectively delay the decline in peel phenolic content.Within 40 d of storage,the litchi fruit could maintain the appearance and internal quality of fruits.