Studies On Technology Of Hot-air Combined Microwave Vacuum Drying Of Taro Slices

Taro(Colocasia esculenta(L.)Schott)is a kind of premium vegetables with high starch content,special flavor,rich nutrition,various healthy and medical values.In China,It is mainly produce in Fujian,Ningbo,Guangxi,Jiangxi,Hunan and other provinces.At present,the major research of taro in China is fresh-cut preservation.There is extensive processing problem in the processing industry of taro,that is,the processing is simple and primitive,short in science and technology investment,development and utilization of deep processing shortage.Therefore,the development of new processed taro products has important implications for the processing industry.In this study,combined hot-air and microwave vacuum drying technology was firstly introduced for the drying of taro slices.Using dipping treatment to determine the optimal impregnation process and improve the brittleness of taro slices.The hot-air drying characteristics and dynamic models of taro slices were stud-ied as well as the microwave vacuum drying,optimized the hot-air combined with microwave vacuum drying process,finally got the HACCP system in order to guide the processing and production of taro slices.In order to to improve the brittleness,reduce the difficult to chew and ameliorate product quality,the three factors with four levels for L16(45)orthogonal experiment were carried out to investigate the effects of different concentrations of ?-Cyclodextrin,soak time and soak temperature on the brittleness and expansion rate.The results showed the optimum parameters for dipping process is mass fraction of 6%?-Cyclodextrin,soak time 1.5 h,soaking temperature of 40?,under this test condition the product can get optimum brittleness and expansion rate.The hot-air drying characteristics and dynamic models of taro slices under different hot-air temperature,hot-air velocity,and loading capacity were investigated.It had only decelerated drying period,without accelerated drying and constant drying.Moisture changing of taro hot-air drying process could be described by Modified Henderson and Pabis equation.Effects of pressure,thickness,microwave power and on/off ratio on microwave vacuum drying rate were studied,and the moisture content of taro slices could be predicted by establishing the mathematical model.Constant drying and decelerated drying period were found in microwave vacuum drying scallop,and a accelerated period showed obviously in the drying curve under different on/off ratio.The experimental drying data of taro slices were used to fit twelve thin layer-drying mathematical models.It showed that Modified Henderson and Pabis model could exactly describe and predict the moisture changing of taro slices during micro-wave vacuum drying process.A L16(45)orthogonal experimental study was carried out to investigate the effects of hot-air temperature,conversion moisture,microwave power and pressure on brittleness,expansion ratios,sensory value,starch content,energy consumption.Through a comprehensive evaluation of the test results,the optimal level of experimental parameters is A2B1C4D1,that is,hot-air temperature was 60?,conversion moisture was 60%,microwave power was 25 w/g,pressure was 46 KPa.Products under the optimal parameters obtained brittleness of 12.47 N,expansion ratios was 95%,sensory value of 9 point,the starch content of 52.28%,energy consumption was 0.9 Kw/h.By analyzing the possible hazards during taro slices processing,seven critical control points were established:acceptance of the raw materials,dipping,steaming,drying,product grade,Packaging and storage.A HACCP system was established to eliminate or reduce safety hazards during processing,to ensure product quality stability and to improve the quality.