Explosion Puffing Drying Technology For Papaya At Variable Temperature And Pressure Difference

Papaya was chosen as the raw material to study, in order to provide a theoretical basis for industrial application of hot air drying for papaya, the paper discusses drying characteristics in hot air drying at different temperatures and thicknesses and vacuum freeze drying; The process of combined hot air and vacuum freeze drying with explosion puffing drying of papaya optimized by the central composite design response surface method, the effect of pre-drying time, puffing temperature and vacuum drying time on product quality including moisture content, hardness, crispness, color and rehydration ratio was studied. In the final experiment, the suitable parameters was obtained by comprehensive score with identifying the factor analysis five index weigh; Effects of different drying methods (hot air drying, freeze drying, hot air-explosion puffing drying, vacuum freeze-explosion puffing drying) on quality of papaya chips were studies in this paper. The work is aiming at providing theory basis and technical support for papaya dehydration industry development.Through the explosion puffing drying for papaya at various temperatures and pressures of research, the conclusions are as follow:1. Hot air drying of papaya chips mainly occurs in the falling rate drying period. The effective diffusion coefficient increased with the increase of film thickness and air temperature; The Page model could properly describe the hot air drying behavior of papaya chips. By regression analysis, the expression of the relationship among the temperature, thickness and the effective moisture diffusion coefficient were achieved, Deff=-27.70041+2.05536T0.37418+39.034122L0.13871.2. Pre-drying time, puffing temperature and vacuum drying time had a great impact on the moisture content, hardness, friability, color and rehydration rate of dehydrated products, and the influence of interactions of three factors on the quality of dried papaya was significant(p<0.05). The best drying condition of hot air combined with explosion puffing drying for papaya was showed as follows:pre-drying time of 4.96-6.00 h, puffing temperature of 80.00～97.23 ℃, vacuum drying time of 2.02～3.00 h.3. Three factors that are puffing temperature, vacuum drying temperature and vacuum drying time had a significant impact on the moisture content, hardness, crispness, color and rehydration ratio, and the interactions of three factors are significant(p<0.05). The optimal technical parameter of vacuum freeze combined with explosion puffing drying papaya were obtain as follows:puffing temperature 87.46～100.00 ℃, vacuum drying temperature 72.42～80.00 ℃, vacuum drying time 3.64-4.00 h.4. The drying time of hot air combined with explosion puffing drying was shortest,446 min; the shrinkage of two combination drying with explosion puffing drying were smaller than that of others dehydration methods, the value of hot air and vacuum freeze combined with explosion puffing drying was 0.61 and 0.33, respectively; the best texture of dried products was obtained by vacuum freeze combined with explosion puffing drying, the hardness was 2677.77 g and the crispness was 51; the effect of vacuum drying on color of samples was smallest, the total color change was 9.74; the dehydrated papaya slices shown better rehydration, the maximum rehydration ratio was 5.58 g/g, after hot air combined explosion puffing drying; the retention content of ascorbic acid was higher in vacuum freeze drying and vacuum freeze combined explosion puffing drying, and was 68.45% and 63.06%, respectively; the micro structure of dried papaya slices was better in vacuum freeze combined with explosion puffing drying, vacuum freeze drying and hot air combined explosion puffing drying. Therefore, the better quality of papaya products was got in hot air combined explosion puffing and vacuum freeze combined explosion puffing drying.