Studies On Technologies Of Hot-air Combined Microwave Vacuum Drying Of Chinese Yam Slices

Chinese yam(Dioscorea opposite Thunb)is an important Chinese medicine as well as common vegetable.As one of the traditional resources of medicinal and edible food in our country,it is widely planted in Fujian,Guangdong,Taiwan and other provinces.But Chinese yam is hard to be long-time storage and long-distance transmission,for it decay rapidly after harvest.Therefore,adopting the advanced processing technology to process Chinese yam into dried products,which can reduce postharvest loss,extend the storage period,balance the relationship between supply and demand in different season and area,improve the economic value,has significant and realistic meanings.this thesis adopted the hot air combined microwave vacuum drying for Chinese yam,which were purchased from AnXi ShanGe,to develop new kind of Chinese yam processed products,studied the drying mechanisms and dynamic models systematically,applied the response surface methodology to optimiz the hot air and microwave vacuum combination drying process,investigated the law of adsorption isotherms,and fianlly applied the HACCP syetems to guide the practical processing to ensure the quality.The main results are as follows:1.The process of hot air drying and microwave vacuum drying was studied respectively on this thesis.In the hot air drying period,drying rate was significantly affected by hot air temperature,hot air velocity,thickness and loading capacity.With only down-speed period during the drying process,there were no obvious up-speed and constant-speed time.Modified Henderson and Pabis model is the most suitable one to describe the moisture changing of Chinese yam slices during hot air drying process.In the microwave vacuum drying period,pressure,microwave power levels and loading capacity have significant effects in drying rate.The process composed of increasing drying,constant drying and decelerated drying.While entering the constant drying period,there appears apparent puffing phenomenon.Modified Henderson and Pabis model is the most suitable one to describe the moisture changing of Chinese yam slices microwave vacuum drying process.2.Taking the L*value of Chinese yam slices,energy consumption,sensory value,starch content and brittleness as evaluation indexes,adopting the response surface methodology to explore the effect of hot air temperature,conversed moisture content and microwave power levels on the quality of Chinese yam slices.Through comprehensive evaluation of the test results,the optimal condition is:hot air temperature was 72.81?,conversion moisture was 41.37%,microwave power level was 9.84 W/g.Under the optimal parameters obtained L*value of Chinese yam slices is 88.29,energy consumption is 1.64 Kw/h,sensory value of 8.27 point,the starch content of 54.68%and the value of brittleness was 17.71 N.3.The moisture absorption characteristic of Chinese yam slices was affected by the temperature and water activity,The value of equilibrium moisture is more obviously affected by water activity than temperature.The value of equilibrium moisture content of hot air combined microwave vacuum drying of Chinese yam slices decreased with increasing temperature at the same water activity.While raising water activity,the value of equilibrium moisture content of hot air combined microwave vacuum drying of Chinese yam slices rised at the same temperature.Through the simulation research on adsorption isotherms of Chinese yam slices shows that Peleg model could describe the adsorption characteristic more accurately.4.Analysis on possible hazards in each process of combined drying and to establish five key control points:acceptance of raw fruit,steaming,combined drying,packing and storage contion.On this basis,HACCP plan table was developed to improve the quality stability of Chinese yam slices.