Study On CO₂ And 1-MCP Treatment To Delay Chlorophyll Degradation Characteristics Of 'Granny Smith' Apple Fruits

After harvesting,green horticultural products will undergo chlorophyll degradation and yellowing due to the mature and aging process,which greatly reduces the quality and value.High CO₂ and 1-MCP treatment can effectively delay the degradation of chlorophyll,maintain the appearance color of the fruit,and prolong the storage time.To clarify the regulatory effect of CO₂ and 1-MCP treatment on chlorophyll degradation and metabolism,the experiment was conducted to study the effects of 2%CO₂,5%CO₂ and 1?L·L^-11-MCP1-MCP on the physiological changes and quality of‘Granny Smith'with a green peel and rich chlorophyll content.The chlorophyll degradation metabolites of‘Granny Smith'fruits were determined by high performance liquid chromatography,and combined with q RT-PCR analysis to clarify the regulation effect of CO₂ and 1-MCP treatment on chlorophyll degradation metabolism.1.The treatment of CO₂ and 1-MCP significantly inhibited the degradation of chlorophyll in‘Granny Smith'fruits.From the storage of‘Granny Smith'until the 80th day,the peel began to yellow.At 100d,the yellowing was obvious.At the end of storage stage,the CO₂ and 1-MCP treatment fruits no yellowing was observed.The CO₂ and1-MCP treatments inhibited the increase of the color difference L*,a*,and b*values,and delayed h value decrease;the greenness preservation effect of the 2%CO₂ and 5%CO₂treatments is better than that of the 1-MCP treatment.5%CO₂ can better maintain chlorophyll a,b content and total chlorophyll content.HPLC analysis found that the contents of chlorophyll a,chlorophyll b and pheophorbide a in the peel of‘Granny Smith'showed a gradual downward trend,and the content of pheophytin a showed an increasing trend after each treatment.The content of chlorophyll a and b in in the peel of‘Granny Smith'in the CO₂ and 1-MCP groups was significantly higher than that in the CK group.The content of pheophytin a degraded chlorophyll a in the middle and late storage period was significantly higher in the 5%CO₂treatment group than in the CK group.At the end of storage,the content of pheophytin a in the treatment group was higher than that in the control group.Compared with other chlorophyll degradation metabolites,pheophorbide a was the lowest in each treatment group and showed a downward trend,but the differences between the treatments were not significant.2.The CO₂ and 1-MCP treatments significantly inhibited the expression of genes related to the chlorophyll degradation pathway of the‘Granny Smith'fruits after harvest.The chlorophyll degradation pathway relational genes are expressed in different stages of‘Granny Smith'peel.The expression patterns of the genes Md SGR,Md NYC1 and Md PPH in the CK group were similar,and they all peaked at 60d and then decreased.CO₂ and1-MCP treatment inhibited or delayed the expression of genes Md SGR,Md NYC1 and Md PPH to a certain extent.The expression level of gene Md NOL in each treatment group was relatively low in the period from 0 to 80d,and the expression level was high at 100d.At 100d,the Md NOL gene expression in the peel of the CK group was 7.67 times and 3.83times that of the 2%CO₂ and 1-MCP treatment groups.CO₂ and 1-MCP treatment significantly inhibited the expression of the key gene Md PAO in the chlorophyll degradation pathway.During the entire storage period,the expression of Md PAO in the1-MCP and 5%CO₂ treatment groups was significantly lower than that in the CK group.CO₂ and 1-MCP treatment significantly decreased the relative expression level of the gene Md RCCR.At 80d,the expression levels of Md RCCR and Md HCAR in the 2%CO₂treatment group were significantly higher than those in other treatment groups.3.Correlation analysis showed that Md PPH and Md NOL were positively correlated L*value,Md PAO was negatively correlated with L*value;h value was negatively correlated with Md PPH and positively correlated with Md PAO.The correlation between Md PPH and color difference in the 2%CO₂ group was significant.Md PAO was positively correlated with chlorophyll a,chlorophyll b,and pheophorbide a,and negatively correlated with pheophytin a.Md SGR,Md PPH was negatively correlated with chlorophyll and its degradation products,Md PAO was a key regulatory gene for chlorophyll degradation pathway.4.CO₂ and 1-MCP significantly inhibited the deterioration of the quality of‘Granny Smith'apple fruits.After harvested,the firmness of the‘Granny Smith'fruits decreased slowly,1-MCP preserved the fruit firmness,and the firmness decreased rapidly during the later storage of CO₂ treatment.Compared with the control group,CO₂ and 1-MCP treatment can significantly reduce fruits weight loss,maintain fruit water,and 5%CO₂ treatment fruits weight loss rate was the smallest.The titratable acid content of 2%CO₂,5%CO₂ and1-MCP treatment was higher than that of the CK group,maintained the fruit‘Granny Smith'fruits acid flavor.1-MCP treatment delayed the appearance of ethylene peaks and reduced the rate of ethylene production and respiration in the fruit;the respiration rate of the two CO₂ groups was at a relatively high level during the entire storage period.CO₂ and1-MCP treatment improved the antioxidant capacity of the fruit,delayed the senescence and quality loss of the fruit.CO₂and 1-MCP treatment significantly droped the accumulation of MDA,maintained SOD,CAT,POD activity,and defered the elevated of PPO activity.Compared with CO₂ treatment,1-MCP improves fruit antioxidant capacity better.