Effects Of Harvest Time And Postharvest Treatments On Quality Changes Of "Cuiguan" Pear Fruit During Shelf Life At Room Temperature

‘Cuiguan' Pear,also known as "Honey Pear" and "June Snow",is a genus of the genus Rosaceae,which is the main cultivar of early-maturing pears in southern China.It has many advantages,including thin and juicy fruit,Sweet,tender and so on.However,‘Cuiguan' pear fruit ripening period is mid-July,is in the high temperature and humidity environment in summer,and is prone to fruit aging,decay and deterioration during shelf life.Therefore,this paper uses ‘Cuiguan' pear fruit as research material.The weight loss rate,decay rate,respiratory intensity,hardness,soluble sugar content(TSC),titratable acid content(TA),vitamin C content(Vc),color,browning degree,membrane relative permeability,malondialdehyde(MDA)content and peroxide dismutase(SOD),catalase(CAT),peroxidase(POD)and polyphenol oxidase(PPO)activity of ‘Cuiguan'pear fruit were determined during shelf life at room temperature.The effects of different harvesting periods,different concentrations of chitosan coating,different post-harvest treatments and different refrigerated time transfer shelves on the shelf life quality of‘Cuiguan' pear fruits at room temperature were studied.The main results are as follows:1.Early harvesting could reduce the respiration intensity and fruit weight loss of‘Cuiguan' Pear during shelf life,and delay the accumulation of MDA and the decrease of PPO activity during shelf life.During the middle and late shelf life(9 d-21 d of shelf life),the respiration intensity,weight loss rate and MDA content of fruits in harvesting period I were significantly lower than those in harvesting period II and III,and PPO activity was significantly higher than those in harvesting period II and III.However,the content of Vc and TSC in early harvested fruits was low,and the quality of fruits was poor.After harvesting too late,the respiration intensity and decay rate of ‘Cuiguan' pear fruit were too high,the water loss was faster and the weight loss rate was larger.At the same time,TSC degradation,MDA accumulation and skin color browning were too fast,which made the quality of fruit deteriorated rapidly during shelf life.Comprehensive analysis showed that harvesting period II could be used as the optimum harvesting period for‘Cuiguan' pear shelf at room temperature.Its fruit had good quality at the beginning of shelf,and maintained high quality at the middle and later stages of shelf.2.Compared with the control,the weight loss rate,decay rate and respiratory intensity of chitosan coated fruits decreased,fruit firmness and nutritional quality improved,while fruit browning,relative membrane permeability,MDA content and PPO activity growth rate slowed down,and the activities of antioxidant enzymes CAT,SOD and POD maintained a higher level.The results showed that all three chitosan coating treatments could improve the fruit resistance of ‘ Cuiguan ' Pear during shelf life at room temperature and delay the occurrence of browning.Among them,1.5% chitosan coating had the best effect in inhibiting the relative permeability of fruit film and the increase ofMDA content,delaying the decrease of resistance enzyme activity and inhibiting the occurrence of peel browning.Principal component analysis(PCA)showed that 1.5%chitosan coating had the best effect on the shelf life of‘Cuiguan'pear,followed by 2.0%chitosan coating and 1.0% chitosan coating.3.0.25 ?L/L 1-MCP treatment,2.0 % calcium chloride treatment and 1.5 % chitosan coating treatment could significantly reduce the rot rate and weight loss rate of ‘Cuiguan'pear fruit during shelf life,delay the emergence of peak respiration,and maintain higher fruit firmness,TSC,TA and Vc.At the same time,the three treatments could effectively inhibit the increase of relative membrane permeability and MDA content of pericarp browning,and delay the decrease of SOD,CAT and POD activities.Principal Component Analysis(PCA)showed that the shelf life of'Cuiguan'pear was 1.5% chitosan coating treatment,0.25 ml/L 1-MCP treatment and 2.0% calcium chloride treatment..4.Respiratory strength,hardness and nutritional quality of ‘Cuiguan' pear fruit decreased gradually during shelf life at room temperature,weight loss rate and decay rate increased gradually,and color became worse.Meanwhile,with the extension of shelf life,fruit browning degree and relative membrane permeability increased gradually,MDA accumulated gradually,SOD,CAT and POD activities decreased gradually,and fruit quality decreased.Compared with 0 d of cold storage,the weight loss and rot rate of the fruit on the shelf increased,the hardness and nutritional quality of the fruit decreased rapidly,and the deterioration rate of the fruit was aggravated.By comparing the quality changes of three refrigerated fruits during the shelf life at room temperature,it was found that the longer the refrigeration time was,the faster the quality of ‘Cuiguan' pear fruit declined in the later shelf life,and the easier the fruit deteriorated.Principal Component Analysis(PCA)showed that fruits of 30 d and 0 d of refrigeration began to deteriorate in 9d-12 d,fruits of 40 d of refrigeration on shelf deteriorated in 3 d-6 d,fruits of 50 d of refrigeration on shelf of Cuiguan pear deteriorated fastest in shelf life at room temperature,and fruits of 30 d of refrigeration on shelf could maintain a high level of fruit quality while delaying fruit listing.