Effect And Mechanism Of Temperature On The Quality And Ripening Of ‘‘Xiahui 8’’ Peach Fruits During Storage

Peach fruit is one of the most valuable fruit products in the world.Honey peaches from Jiangsu and Zhejiang provinces in southern China have good taste and high nutritional values.However,they are not resistant to storage.They age rapidly within 2-3 days after harvest,which seriously affects the circulation and supply scope of high-quality peach fruits.At present,low temperature storage is one of the most economical and effective methods to prolong the storage period of peach fruits.Therefore,the research on the mechanism of ripening and senescence of peach fruits under low temperature conditions and related technologies has been widely concerned.In this study,’Xiahui 8’ peach was taken as the research object.Firstly,the preservation effects of peach fruit under different storage temperatures（4℃ and 25℃）were studied.Proteomics technology was used to identify the differentially expressed proteins at different temperatures,and the effects on related metabolic pathways were analyzed.Then,combined with proteomics data and transcriptome data,the effects of different storage temperatures on peach fruit preservation were analyzed.At last,the preservation effects of low temperature combined with chitosan coating on ’Xiahui 8’ peach fruit were studied.The main research results are as follows:The results showed that the weight loss rate,decay rate and firmness of ’Xiahui 8’fruits stored at 4℃ for 20 days were 1.96%,6.24%and 28.42N,which were significantly lower than those stored at 25℃ for 8 days.The decay rate and firmness of ’Xiahui 8’fruits stored at 4℃ for 8 days were 35.62%and 19.84 N,respectively,which effectively prolonged the storage period of peach fruits.The VC content of fruits stored at 4℃ for 20 days still reached 5.97 mg/100g FW,which was slightly higher than that of fruits stored at 25℃ for 8 days（5.97 mg/100 g FW）.The results showed that low temperature could effectively reduce the loss of Vc in peach fruit;reducing sugar content,soluble solids,titratable acid,fruit pH and other indicators showed similar dynamic trends in samples stored at different temperatures,and the above indicators changed gently at low temperature.At 4℃,the respiration rate of ’Xiahui 8’ peach fruit was lower than the initial intensity before the 10th day of storage.At room temperature,the respiration peak value of fruit samples was 44.70±0.35 mg·kg·s^-1 on the 8th day.When stored at 4℃,the respiration reached the highest on the 20th day,and the low temperature storage effectively delayed the peak of respiration.In addition,low temperature reduced the contents of malondialdehyde（MDA）,superoxide anion（O2·-）and the increasing rate of electrical conductivity.Low temperature delayed the peak of PPO activity,indicated that the defense function of peach fruit was affected.2.ITRAQ technology was used to analyze the protein expression of ’Xiahui 8’fruit under two storage temperatures（4℃ and 25℃）,and 303 differentially expressed proteins（DEPs）were identified.At 4℃ for 20 days,152 DEPs were detected.In the samples stored at 4℃ for 10 days and 20 days,the down-regulated DEPs were mainly related to the formation of fruit color and flavor,the slow degradation of cell wall and the decrease of energy metabolism;the up-regulated DEPs were mainly reflected in fruit coloring,starch hydrolysis,sugar transport and generation,cell wall expansion,stress resistance and the process of fruit cell decay.According to the results of this study and previous studies,the main functional DEPs that may participate in delaying peach fruit ripening and senescence and related to fruit preservation at 4℃ temp erature were preliminarily summarized.25 DEPs（including 10 up-regulated and 15 down-regulated）could participate in delaying peach fruit ripening and senescence,which was related to fruit preservation at low temperature.3.Compared with the room temperature（25℃）,the apoptosis process of ’Xiahui 8’peach fruit was effectively inhibited under low temperature（4℃）By comparing the transcriptome sequencing and iTRAQ data of samples stored at 25℃ and 4 ℃,17 differentially expressed genes were identified,including 6 serine carboxypeptidase genes（ppa005420m,ppa005420m、ppa004656m、ppa005192m、ppa000419m、ppa005264m）,2 LOX genes（ppa001216m、ppa001016m）,7 POD genes（ppa010771m,ppa012416m,ppa009960m,ppa009582m,ppa007748m,ppa012407m,ppa008008m）and 2 CAT genes（ppa004763m,ppa004776m）.These results showed that low storage temperature could reduce the content of free radicals in peach fruit cells and inhibit the process of cell apoptosis,thus delaying the fruit ripening and senescence.The data provided in this paper may help to enrich the mechanism of fruit ripening and senescence,and to improve the storage technology of fruits.4.The effects of low temperature（4℃）combined with chitosan and gallic acid grafted chitosan coating on fruit quality and physiological indexes of ’Xiahui 8’ peach were studied.The results showed that the decrease rate of firmness and weight loss rate of peach fruit treated with chitosan and gallic acid grafted chitosan were lower than that of the control group under low temperature,especially gallic acid grafted chitosan coating treatment showed the best effects in inhibiting the decay rate of peach fruit.Coating treatment could effectively reduce the loss of Vc in peach fruit and sugar content in peach fruit.The content of reducing sugar,soluble solids,titratable acid and fruit pH changed more slowly in the coated fruits.After coating treatment,the respiratory intensity of peach fruits decreased,and the increase rate of malondialdehyde（MDA）and superoxide anion（O2·-）and electrical conductivity further slowed down.The changes of phenylalanine ammonia lyase（PAL）of coated samples were slow,and the antioxidant enzymes of peach fruit were increased.The results of flow cytometry showed that the apoptotic rates of chitosan coated samples at 10 days（10-F-CMCS）and 20 days（20-F-CMCS）were 24.4%and 8.5%that lower than those of uncoated samples,respectively.While the apoptotic rates of the samples coated with gallic acid grated chitosan derivative at 10 days（10-F-CMCSGA）and 20 days（20-F-CMCS-GA）were 26.9%and 15.6%lower than those of uncoated samples,respectively.These results indicated that low temperature（4℃）combined with coating technology could further delay the senescence process and prolong the shelf life of peach fruit.