Study On The Freeze Drying Characteristics And Drying Technology Optimization Of Pinang-taro

Pinang taro is an endangered perennial herb belonging to t infecting Araceae plants.which has rich nutrition.What's more,the deep processing gets extensive attention dut to the taro's rapid development and increasing outputs that is about 5300～5800 thousands tons every year. .Eutectic temperature and Crystallizing temperature were measured in the study.And then,The indexs were determined which include freeze drying rate,shrinkage and hydration value before the parameters were studied which contain vacuum pressure,heating temperature and material thickness. Finally,freeze drying kinetic model was established as optimum technology of the taro's freeze dryig was determined which provide important theoretical references for the taro's deep proceesing.First of all,material parameters was studied.it showed that the Crystallizing temperature was -28℃and Eutectic temperature was -23℃so that prefreezing temperature was -40℃due to the loss of temperature in the experiment while material temperature was less than -23℃in the sublimation. Because freeze drying equipment is batch type,temperature successive approximation was adopted for judging the final point of drying time which avoides the interruption and loss of material in the freeze drying compared to traditional weighing.And frzze dying curve shows that sublimation interface temperature was controlled to close to and less than the Eutectic temperature in the sublimation while temperature was highten as far as possible in the desorption drying but not higher than highest temperature 80℃. Secondly ,processing parameters was studied in the pinang taro freeze drying which shows that significant effect was found on vacuum pressure,sublimation temperature and material thickness by the indexs that include freeze drying rate,shrinkage and hydration value but the desorption temperature.Desorption temperature was made to 60℃.And then, According to the quadratic general rotary unitized design the regression models of vacuum pressure(x1),sublimation temperature(x2),material thickness(x3)and freeze drying rate(y1),shrinkage(y2),hydration value(y3)were set up and parameters were optimized。As follows:Meanwhile,whenprocess optimization based on freeze drying rate as index,optimum parameters was that vacuum pressure was 110 Pa,sublimation temperature was 37.5℃and material thickness was 3 mm;when process optimization based on shrinkage as index,optimum parameters was that vacuum pressure was 10 Pa,sublimation temperature was 15℃and material thickness was 3 mm.when process optimization based on rehydration value as index,optimum parameters was that vacuum pressure was 105 Pa,sublimation,temperature was 34℃and material thickness was 5.5 mm.Finally, Classic diffusion model,Index model and Page equation was studied which shows that R2 valuves of both the curve of t—-ln(MR)and lnt—ln(-lnMR)are approach to 1 .that is to say , the curves-fitting are accuracy.however,the R2 valuve of lnt—ln(-lnMR)are closest to 1 that means Page equation is the best model as pinang taro freeze drying kinetic study; At last,The freeze drying dynamic model ,2.429 0.051 0.228 2, 0.317 0.104 0.2012is the MR = e ? rt Nofwhich r = e ? + x ?xN = + x ?x。It was proved that the model can be used to describe and predict the moisture change in the taro's freeze drying.