Quality Coparison Between Dried And Fresh Walnuts And Study On Effect Of Ethylene On Postharvest Ripening Of Fresh Walnut

This thesis compared the sensory qualities, nutrients contents, and oil qualities of ‘Qingxiang’ walnuts(Juglans regia L.) under 5 conditions:(1) peeled, and dried by oven;(2)peeled, and dried by air;(3) peeled, and stored freshly;(4) in-husk, and stored freshly;(5) in-husk, and stored with Modified Atmosphere Packaging(MAP), to screen out the optimized method of walnut drying and preservation, and to provide theoretical basis for the selection of walnut consumption pattern. Besides, the thesis also studied the physiological properties and green husk cell wall-degrading enzymes of ‘Qingxiang’ walnuts treated by exo-propylene(used as an analogue of ethylene) in different concentrations and 1-MCP(competitive inhibitor of ethylene), to throw light on walnut green husk peeling technology. The following results were obtained:(1) Compared to fresh walnuts, dried walnut kernels possessed higher total phenols contents and lower acid value; Fresh walnut kernels possessed higher contents of oil and soluble protein and lower peroxide value, and performed better in sensory evaluation. Overall, fresh walnut kernels possessed better nutritional quality. The contents of unsaturated fatty acids in the oil of dried and fresh walnuts were both over 90% and there was no significant difference between them, so walnut kernel, no matter dried or fresh, could serve as a good source of unsaturated fatty acids.(2) Compared to peeled walnuts, in-husk walnuts obtained higher contents of total amino acids and soluble sugar. Thus green husk has some positive effect on maintaining of kernel quality in postharvest walnuts.(3) postharvest treatment of 5000μl/L propylene inhibited respiration and ethylene releasing rate of walnut fruits, and enhanced the activity of polygalacturonase(PG) and cellulose(Cx) in green husk on the whole, performing the effect of enhancing green husk soften and cracking. For walnuts after 30-day cold storage, 5000μl/L propylene also performed the same effect. When the concentration became higher, a stronger effect was shown. Postharvest 1-MCP treatment delayed the decrease of hardness, enhanced ethylene releasing rate, and inhibited the activity of pectin methylesterase(PME).The results revealed that fresh walnut obtained higher nutritional value and it is a potential way of consumption; Fresh in-husk storage is an ideal method of walnut preservation. The results also revealed the regulation effect of ethylene on postharvest ripening of fresh walnut, bringing new insights that exo-ethylene treatment could solve the problem of green husk-isolating on stored walnuts.