| Strawberry is tender and juicy,with a sweet and sour taste.It is a fruit loved by consumers and has great market value in China.Fresh strawberry is not easy to store after harvest,and often cause economic losses due to improper storage methods.Therefore,exploring a suitable method for preservation of postharvest strawberry to extend its shelf life is currently the focus of strawberry research.In this paper,nano-SiO2 were added to chitosan coating solution to enhance their mechanical properties,and then to improve the preservation performance of the film.Fresh strawberry were used as material,by comparing the effects of single and combined treatment of 1-MCP and chitosan/nano-SiO2 composite film on the quality of postharvest strawberry,then a new and efficient preservation method of strawberry was explored.The main results are as follow(1)The amount of chitosan,nano-SiO2 and monoglyceride in chitosan composite fil m was optimized by response surface methodology.The regression equation with CO2 pe rmeability coefficient of composite film as response value was obtained as:Y=0.24+0.021 A-0.019B-0.017C-0.01AB+0.038AC+0.022BC+0.21A2+0.17B2+0.13C2.According to the ma thematical model established by response surface analysis,the optimum formulation and p rocess conditions of chitosan/nano-SiO2 composite film were obtained as follows:1.18 g of chitosan,0.08 g of nano-SiO2 and 0.05 g of monoglyceride.The mechanical propertie s of the optimized membranes were significantly improved,and the exchange of carbon dioxide inside and outside the membranes was better inhibited,thus improving its preserv ation performance.Strawberry were treated with chitosan film and optimized film,and th e quality of strawberries treated was compared with that of control material.It was foun d that both chitosan and optimized film treatment could effectively alleviate the decline O f strawberry quality during storage,and the effect of optimized film treatment was better.Optimized film treatment can significantly inhibit the increase of weight loss and color difference,and the decrease of firmness,soluble solids,titratable acid and Vc content.(2)The effects of single and combined treatment of 1-MCP and chitosan/nano-SiO2 composite film on the quality of strawberry under cold storage were compared.The results showed that compared with the control group,each treatment group could effectively inhibit the respiratory intensity,delay the color change,inhibit the decrease of firmness and soluble solids,Vc,titratable acid,reducing sugar,soluble protein content and the increase of weightloss and relative conductivity,thus delay the senesence of strawberry.Among treatments,1-MCP and chitosan/nano-SiO2 composite film were treated separately and there was little difference in the effect,and the combination of the two treatments had the best preservation effect.(3)The effects of single and combined treatment of 1-MCP and chitosan/nano-SiO2 composite film on the active oxygen metabolism of strawberry under cold storage were compared.The results showed that both 1-MCP and chitosan/nano-SiO2 composite film could inhibit the accumulation of superoxide anion and hydrogen peroxide in strawberry compared with the control group,but the effect was not as significant as the combined treatment.The combination of 1-MCP and chitosan/nano-SiO2 composite film treatment can significantly inhibit the damage of reactive oxygen species to strawberry under cold storage.Compared with the control group,the combination treatment can significantly improve the activities of SOD,CAT,POD and APX enzymes in strawberry,thereby improving the strawberry's ability to directly remove reactive oxygen species.At the same time,the combination treatment can reduce the loss of AS A and GSH by increasing the activities of DHAR,MDHAR and GR,thus maintain the antioxidant level of strawberry cells.(4)The effects of single and combined treatment of 1-MCP and chitosan/nano-SiO2 composite film on the cell wall metabolism of strawberry under cold storage were compared.The results showed that both 1-MCP and chitosan/nano-SiO2 composite film could effectively alleviate the degradation of cell wall substances such as pectin,cellulose and hemicellulose in strawberry under cold storage,and maintain the stability of cell wall,and the combined treatment of 1-MCP and chitosan/nano-SiO2 composite film had even better effect,which was confirmed by the observation of electron microscopy of cell wall.The activity of PME,PG,Cx and ?-glucosidase could be effectively maintained by the both treatment of 1-MCP and chitosan/nano-SiO2 composite film,and then the cellulose-hemicellulose-pectin structure of strawberry cell wall could be maintained and the softening of strawberry could be delayed.The combination of the 1-MCP and chitosan/nano-SiO2 composite film has better effect.Single treatment of 1-MCP and chitosan/nano-SiO2 composite film can improve the antimicrobial activity of strawberry by increasing the activity of chitinase and ?-1,3-glucanase,and the combination of the two treatments was better.(5)In conclusion,the single treatment of 1-MCP and chitosan/nano-SiO2 composite film can effectively alleviate strawberry senescence and prolong shelf life,and the combination of the two treatments is more significant. |
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