Theoretical And Experimental Study On Temperature Shock Treatments Of Postharvest Fruits And Vegetables

China, as a primary agricultural country, the yields of fruits and vegetables have ranked the first throughout the world in recent years, however, because of the morbid cold chain, postharvest losses of fruits and vegetables are serious, and the direct economic loss reaches one hundred billion yuan every year. In addition, with the issues related human health and food safety being concerned, chemical preservative method is fully questionable, and thus green environmental protected physical method exploration for fruits and vegetables postharvest preservation has become important task. Based on multi-subject approaches, cold storage and pre-storage temperature shock treatment for fruits and vegetables were theoretically and experimentally researched in present dissertation, and the main contents are as following:(1) The intelligent control, defrosting method and airflow organization of cold storage for fruits and vegetables preservation were studied. A novel cold storage defrosting method was proposed for the first time, and its technical characteristics were experimentally researched. With the CFD numerical simulation method, the key components affecting cold storage airflow distribution were analyzed. (2) The universal heat transfer model for columnar and spherical fruits and vegetables was established and numerical calculated with Taylor series expansion finite difference method. The results showed that the established models could accurately predict the temperature changes of fruits and vegetables in different shapes. Heat transfer characteristics of products subjected to different temperature shock treatment were compared and studied. The effects of fruit size, packing, medium velocity, treatment temperature and relative humidity on heat transfer and tissue weight loss were investigated. (3) With cucumber as test materials, the effects of cucumbers preservation subjected to different strength of cold and heat shock treatment were comparatively studied by method of heat transfer analysis combined with physicochemical indexes testing, and entropy weight of fuzzy comprehensive evaluation method for fruits and vegetables fresh-keeping effect evaluation was proposed. (4) Taking total color difference, hue angle, lightness, firmness, rot index of fruit as response parameters, heat shock treatment technique for cucumber was optimized with response surface methodology (RSM). The optimizing experiment scheme was central composite designed, and the quadratic models for quality parameters of cucumber were obtained. Furthermore, evaluation function for optimization was established through liner weighting method, in which the weight vector was determined by principal component analysis method. (5) The physical method for fruits and vegetables color measurement was introduced, and the best indexes for cucumber color evaluation were experimentally determined. Color of cucumber subjected to refrigerating, heat shock treatment + refrigerating, cold shock treatment + refrigerating, modified atmosphere package + refrigerating respectively were chemical kinetics studied, and the reaction orders, reaction rate constants and apparent activation energies of cucumber lightness and total color difference were obtained. The conclusions obtained can provide references for preservation method selection and treatment parameter determination of postharvest fruits and vegetables, meanwhile, it also has an important significance for cold storage system optimization.