Study On The Technology And Equipment Of Litchi Drying

on the short maturation period of fresh litchi. Besides, mature period of litchi is in the season of high temperature and high moisture. Surprisingly, the highest moisture content of different kinds of fresh litchi reaches up to 82% and the sugar content of different varieties of fresh litchi is between 22% and 60%. There are litchi cultivations in Guangdong, Guangxi, Hainan, Fujian, Sichuan, Yunnan and Taiwan in present-day China, from about 18 degrees north latitude and 28 degrees north latitude. Many countries have grown litchi outside of China, near the most Southeast Asian countries, such as Vietnam, Thailand, far to the United States, Florida and California, and Queens all have set up litchi production. In addition, Australia has also introduced litchi planting. Without the preservative treatment, litchi have characteristics of two variable three smell, taste, color and flavor as much as four days to nothing.The research of fresh litchi in hot constant temperature drying box, the air speed is1.0,2.0,3.0 m/s, hot air temperature is 60, 70 and 80 centigrade degrees of the drying quality and drying mathematical model. As litchi is granular fruit, in order to discuss its water ratio and show a reasonable analysis, by hot air drying derived data as the basis, according to the Fick's second law formula, of litchi whole fruit drying mathematical model and using SAS software calculated litchi drying mathematical model.In this article, drying device made by laboratory their own was adopted to study the characteristics of coupled hot-air and microwave drying design experiments. In the experiment, drying time and sensory evaluation value are taken as response value to optimize the drying process with the method of Box-Benhnken central composite experimental design and response surface analysis. Drying process depends on different air temperatures (60, 70, 80 centigrade degrees), different wind speeds (0.5, 1.0, 1.5 m/s) and different microwave power densities (2.0, 2.2, 2.4 W/g). Then regression equations were drawn by means of SAS software procedure and response surface and contour analysis were given by response surface regression REREG procedures of ORIGIN 8.0.Experimental results show that: the relationship between hot-air temperature, hot-air velocity, microwave power density and drying time and sensory evaluation is not a simple linear relationship. Results microwave power density, hot-air temperature hot air velocity were the factors which influence the drying time and sensory evaluation value, among them microwave power density was the most significant factor, hot-air temperature is next and hot air velocity is the last. When the hot air temperature is 78.46 centigrade degree, wind speed is 1.99 m/s, the microwave power density is 2.37 W/g, then drying time is 67.19min, sensory evaluation value is 87.86. It can concluded that coupled hot-air drying and microwave is a relatively reasonable drying method than single because coupled hot-air drying and microwave drying combines all of the advantages of the hot air drying and microwave drying, effectively reduce the shortcomings of both.In addition, this article also focus on the drying process of peeling litchi, such as vacuum microwave drying, hot air drying, coupled hot-air and microwave drying and vacuum freeze-drying. The optimum drying process of four drying methods were taken out respectively to compare their protein content, reducing sugar and the values of L, a, b respectively which are: 0.4103 g/100g, 0.2739 g/100g, 0.2176 g/100g, 0.1837 g/100g, 0.2241g/100g and 6.9 g/100g, 5.64 g/100g, 6.14 g/100g, 5.24 g/100g, 5.09 g/100g and 42.99, 9.84, 16.79; 40.79, 10.05, 17.18; 26.48, 13.31, 13.27; 59.99, 11.12, 23.08; 22.72, 13.59, 10.72. In the sample drying process, litchi polyphenol oxidize readily reacts with oxygen, the drying time is longer, the more thoroughly the browning reaction, the more obvious. With the hot-air, microwave vacuum freeze-drying, hot air microwave, four methods of dry litchi a have varying degrees of the larger, made of fresh litchi value a from 9.84 increased to 10.05 ~ 13.31.