| This paper was the part work of two foundations:Ministry of Education Scientific Research Foundation for returning overseas reserchers "Selection permeability of chitosan coating and its preservation effect of blueberry", and Jilin Province Science and Technology Development Fundation "Postharvest physiology of blueberries and chitosan coating preservation mechanism (201201128)".The work was that:(1) Tween 20 was added to chitosan-methoxyl pectin composite coating as surfactant to improve the wettability on the slide with wax. With the concentration of Tween 20 increased to 0.75%, the contact angle decreased to 72.90°;after 30s, the contact angle decreased to 59.7°with good wettability on the waxed slide.(2) Adding the surfactant increased the degree of crosslinking and compactness, as well as strengthened the molecular interaction, and enhanced the interaction between polymer chains investigated by AFM. The property of chitosan-methoxyl pectin composite film showed that:adding 0.75% Tween 20 as surfactant could improve the thermal stability and mechanical properties including tensile strength (TS) and elongation (E) of chitosan-methoxyl pectin film, as well as the barrier properties including oxygen permeability (Po2), carbon dioxide permeability (Pco2) and water vapor transmission (WVT).(3) Chitosan-methoxy pectin coating and cold storage (4℃) were combined to keep fresh of grapes, and then investigated the physiological metabolism. Kyoho Grapes were coated with/without complex chitosan coating and stored at room temperature or 4℃ up to 30d for physicochemical quality evaluation. The results showed that complex chitosan-methoxy pectin coating at room temperature and cold storage without coating had same effects on the physiological characteristics of grapes. Complex coating combined with cold storage could inhibite the respiration intensity to 7.1 (CO2 mg·Kg-1·h-1), delay repening time, decrease fruit decay rate, maintain higher Vc content, increase the brightness and stabilize SSC content. Besides, the glass transition temperature of grapes coated with chitosan coating increased 9.75℃ which could benefit grape frozen preservation.(4) Chitosan-methoxy pectin coating and cold storage (4℃) were combined to keep fresh and physiological metabolism of blueberries. The results showed that the difference on physiological indexes of control and coating ones were not significant at the beginning of storage. After storaged for 10-15d, chitosan-methoxy pectin coating reduced the decay rate and weight loss of blueberries, and delayed blueberry soften significantly. Vc content of control ones decreased 12.92%, but of coating ones decreased 8.04%. Coating storage maintained growth with respiration intensity 8.75 (CO2 mg·Kg-1·h-1) and high CAT and POD activity at later storage, which reduced the accumlation of MDA and cell damage. The result was that chitosan-methoxy pectin coating maintained the nutritional content.(5) The glass transition temperature of blueberry with chitosan coating increased from-33.83℃ to -26℃, which could benefit glass transition preservation for blueberry. In this theoretical basis, at -26℃～-28℃, blueberries with glass transition storage had the same trends in the indexes with cold storage, especially drip loss of frozen blueberries without coating was significantly reduced compared to ones with coating.(6) The preservation mechanism of chitosan-methoxy pectin composite coating for grapes and blueberries were discussed. Chitosan-methoxy pectin composite coating regulated the gas storage tune the environment, so that the respiration intensity of grapes and blueberries was inhibied, as well as water reduced rate, to prevent being infected and ensure its storage quality. |
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