| Chinese yam is widely planted in China, but the fine-processing proportion is very limited, resulting in many Chinese yam were wasted or rotted. The quality of drying for Chinese yam after harvesting has a direct impact on the quality of Chinese yam. In recent years, drying methods of Chinese yam after harvest start to turn from the original and natural drying methods to the more scientific and convenient methods.In order to improve the quality of Chinese yam, ensure the high-yield harvest of farmers, and promote the development of Chinese yam industry. Drying characteristics of Chinese yam was explored by combination drying with microwave and vacuum in this paper. Main contents and conclusions are as follows:1.Polyphenol oxidase activitie of fresh Chinese yam was spectrophoto-metrically determined at 408 nm. The results showed that the optimum pH and temperature for PPO activity was 6.0 and 30℃respectively, thermal stability of polyphenol oxidase activity could be enhanced with raising substrate concentration and grew sharply with enzyme concentration increasing. The results of orthogonal experiment showed that the optimal antibrowning without sulphite composition of Chinese yam was L-cystenine 0.02%, citric acid 1.4%, VC 0.016%, NaCl 2.5% and steeping time 3 h.2.The drying characteristics of Chinese yam were investigated by using hot-air, microwave and vacuum drying respectively. The results indicated drying rates of the three drying methods were different significantly, the microwave drying spent shorter time than methods, and the vacuum drying brought the best sensory quality. The highest rehydration rate and polysaccharide yield derived from the microwave drying among the three drying method.3.Experimental models of drying for Chinese yam were investigated in this paper. Three experiential thin-layer drying models were analyzed, the results revealed that Page equation was more suitable to express Chinese yam drying than monomial proliferation model and the exponential model. At the same time, coefficients of the Page equation were obtained, and analyses of variance were significant.4.Through regression experiment of the second general rotation design, combination drying with microwave and vacuum tests of Chinese yam was studied, and regression equation of polysaccharides rate and drying time were established, then significant test was carried out. Results of validation test showed that predicted value was very close to the experimental value, and then the optimum parameters were obtained as following:(1) The polysaccharides yield was the highest (0.1054) when the vacuum pressure, microwave power and slice thickness were 0.062 Mpa, 11.092 W/g and 2 mm respectively.(2) The drying time was shortest (14.685 min) when the vacuum pressure, microwave power and slice thickness were 0.03 Mpa, 13.62 W/g and 2 mm respectively. |
