Effects Of Different MA Packaging On Postharvest Storage Physiology Of Litchi

In this experiment,ripe litchi fruits such as‘Wuye’and‘Yuanhong’were used as materials,0.035mm PE,0.1mm PE and0.1mm PA films were selected for modified atmosphere storage（MA）,O₂ absorber and CO₂absorber were used as assistance,MA was used to form different controlled atmosphere environments,and the dynamic changes of O₂ and CO₂ in different MA packaging were observed and compared.The effects of different MA packaging and storage treatments on postharvest quality index and some postharvest physiology and biochemistry of litchi were studied.The main results are as follows:1.The results of gas analysis showed that:with the extension of storage time,the O₂concentration in MA packaging gradually decreased,0.035mm PE>0.1mm PE>0.1mm PA,while CO ₂showed an upward trend,0.035mm PE<0.1mm PE<0.1mm PA.Under the treatment of PA film packaging,the concentration of CO₂ in‘Wuye’fruit was as high as 50.4%after 30 days of postharvest.CO₂absorbent helps to control the stability of CO ₂concentration in the bag.After adding CO ₂ absorbent,the PA package was packed at 10-30 days after harvest,and the CO ₂ in the bag was maintained between 2.8-3.4%,while the CO₂ in the0.1mm PE bag was 2.3-3.6%,respectively.O₂ absorbent treatment can significantly accelerate the reduction of O ₂ in the bag.The results showed that when the precooled fruits were packaged with three different films,the differ ence of O₂ concentration in the bag was small within 5 days after harvest,and the difference began to increase significantly at 10 days after harvest,and the O₂concentration of 0.1mm PE and 0.1mm PA packaging could be reduced rapidly within 5 days after postharvest treatment.After the above optimization,under the 0.035mm PE treatment,the O₂concentration of‘Yuanhong’litchi was 14.7%～16.4%,the CO₂concentration was 1.1%～1.7%;Under the 0.1mm PE treatment,the O₂ concentration was maintained 4.9%～5.1%,and the CO₂concentration was maintained at 3.3%～3.6%;while the O₂concentration of the 0.1mm PA treatment was 4.7%-6.6%,and the CO₂ concentration was 2.9%-3.2%.2.A method for the determination of soluble sugars and organic acids in litchi pericarp and aril by UPLC was established to determine the sugar and acid components of litchi pericarp and aril,and to explore the changes of sugar and acid components in litchi pericarp and aril under different MA storage after postharvest.The main soluble sugar components of litchi fruit were determined by UPLC-ELSD,including fructose,glucose and sucrose,and the organic acids of litchi pericarp mainly included shikimic acid and quinic acid,followed by malic acid,fumaric acid,citric acid,tartaric acid and succinic acid.At the same time,it was also determined that the organic acid of mature pulp mainly contained malic acid and fumaric acid,and the content of oxalic acid was low.3.The results of the determination of pericarp relative leakage rate showed that,the pericarp relative leakage rate increased significantly under bulk storage,while the pericarp relative leakage rate was significantly inhibited by packaging storage.There were significant differences in pericarp relative leakage rate among different MA packaging treatments at low temperature.The pericarp relative leakage rate of litchi fruits treated with PE increased slowly,and when a large amount of mildew,the relative leakage rate increased significantly,while the fruits treated with PA,whether treated with CO ₂ absorbent or not,showed a significant increase in relative leakage rate from 10 days after harvest.The results showed that the membrane system integrity of pericarp cells was significantly damaged by PA treatment up to 10 days after harvest.4.The physiological and biochemical results of postharvest peel are as follows.（1）The determination results o f postharvest quality indexes showed that the postharvest quality indexes changed significantly under bulk storage.Under packaging and storage,the postharvest quality indexes were significantly inhibited.There was no significant difference in water cont ent,weight loss rate and soluble solids under packaging treatment.The browning index,fruit decay rate and aril sugar acid components were significantly different under different MA treatments.Under 0.035mm PE treatment,fruit browning index,decate rate and aril sugar acid components were better than 0.1mm PE.Although there was no mildew fruit during the whole storage period,the fruit browning index reached grade 5 at 20 days after harvest,and a large amount of lactic acid was detected in ar il during storage.It is suggested that the accumulation of lactic acid is related to the fermentation metabolism of fruits under hypoxic conditions.（2）The results of enzyme activity determination showed that browning related enzymes changed significantl y under bulk storage.The browning-related enzymes were significantly inhibited at 25℃,while the enzyme activity was significantly inhibited at 4±1℃,and the enzyme activities were significantly different among different treatments.After PE treatment,the activities of pericarp browning related enzymes remained stable within 10-30 days after harvest,among which 0.035mm PE treatment had the best effect.However,the browning-related enzymes under PA treatment were significantly different from those under PE treatment at 10 days after harvest,and there were also significant differences among varieties.PPO and SPOD of‘Wuye’litchi increased significantly under PA treatment,while BPOD fluctuated violently,while PPO,SPOD and BPOD of‘Yuanhong’litchi decreased significantly under PA treatment.It was preliminarily considered that due to the difference of O ₂down-regulation rate among different varieties in PA group,‘Wuye’litchi with slow O₂ down-regulation rate in bag was able to respond to stress,resulting in significant differences in browning-related enzymes among varieties.The results showed that PA treatment was not suitable for the storage of litchi.With regard to ADH enzyme,the ADH activity of pericarp increased when stored at 25℃.Under 4±1℃storage,ADH activity of PE group maintained in a certain range during 30 days after harvest,while PA treatment decreased significantly during the whole storage period.Therefore,we speculated that the activity of ADH enzyme under PA treatment was related to the accumulation of acetaldehyde in the bag.However,a large amount of lactic acid was also detected in the pericarp treated with PA.Whether anaerobic respiration in postharvest litchi is through lactic acid metabolism or ethanol metabolism,or both,remains to be confirmed by further study.（3）Seventeen components of polyphenols in litchi pericarp were determined by UPLC-MS,including flavane-3-ol monomer,（+）-catechin and（-）-epicatechin,four procyanidins dimers in flavane-3-ol units,including procyanidin A2,procyanidin B1,procyanidin B2 and procyanidin B4,7 pr ocyanidin trimers,Cya-3-O-rut and rutin.The quantitative results show ed that,under the postharvest bulk treatment,the polyphenols in the pericarp were consumed rapidly,and the degradation of phenols in the pericarp was significantly inhibited by packaging and storage,and there were significant differences among the trea tments at 4±1℃.EC,as the direct substrate of browning,and Cya-3-O-rut,the most important anthocyanin substance in litchi pericarp,showed the highest in0.035mm PE and the lowest in 0.1mm PA in both varieties.The synthesis of anthocyanins may be relat ed to the increase of total organic acids in pericarp.（4）The soluble sugar components in pericarp were analyzed for the first time.The results showed that the reducing sugar components in PA group were significantly higher than those in PE group,while the sucrose components in PE group were significantly higher than those in PA group.The results showed that the reducing sugar of PE packaging treatment was used as the direct substrate of respiration,so it was lower than that of PA treatment,while the sucrose transformation of fruit of PA treatment was significantly faster than that of PE treatment.The results showed that PA treatment was not conducive to the maintenance of soluble sugar,in contrast,0.035mm PE was more suitable.（5）The organic acid components in pericarp were analyzed for the first time.The results showed that the total acid content of pericarp was 0.035mm PE>0.1mm PE>0.1mm PA under different MA storage.The components of organic acids changed differently during postharvest storage,which showed that due to the lag of glycolysis,the respiratory quotient of fruit increased and the tricarboxylic acid cycle was disordered.0.035mm PE can carry out normal physiological metabolism for a long time under the condition of low temperature storage because its controlled atmosphere environment is close to the atmosphere,while the hypoxia condition in 0.1mm PE and 0.1mm PA bags aggravates the disorder of tricarboxylic acid cycle.The results showed that0.035mm PE was more beneficial to t he maintenance of organic acids in pericarp.