Apple Chips Dried By Microwave Vacuum Freeze-drying And Comparison Tests

Apple is one of the most popular nutrient-rich fruits all over the world. Apple chips is a kind of deep-processed product and it has become a popular snaked food because of its good characteristics of crisp taste, rich nutrient, easy to carry, long shelf life and so on. In the tradition processing frying with the oil was used to dehydration and drying. With this method the product could have the unique taste, but it will lead to high level of residual oil and a serious loss of nutrients of the product. Vacuum drying method could solve the above problems radically and retain the original nutrients and flavor as maximum as possible. According to the different pre-treatments and the difference in heating mode, vacuum drying methods are divided into vacuum drying, microwave-vacuum drying, vacuum freeze-drying and microwave vacuum freeze-drying method. The microwave freeze drying is a novel drying technology which has the advantages of high product quality and low energy consumption. From the literatures there were lots of documents on the apple chips with the drying method of vacuum drying, microwave vacuum drying and freeze-drying, while there were few reports on the study of apple chips dried by microwave freeze-drying.In this study the orthogonal rotatable central composite design was adopted and the optimization processing parameters of microwave vacuum freeze-drying method of apple chip were determined by response surface methodology of software SAS6.0 firstly. And then the single-factor test of product characteristics and energy consumption were completed to compare the effection on the product quality of four different drying methods vacuum drying, microwave vacuum drying, vacuum freeze-drying and microwave vacuum freeze-drying. Finally the optimal drying technology was determined and theoretical instructions were provided fro the industry production of apple chip.The results showed that the optimal parameters of microwave freeze-drying process were as follows: when the thickness of apple slices is 8mm, the pre-freeze temperature will be -30.09℃, the microwave power will be 108.44W, and the vacuum level will be 60Pa. Compared with the other three vacuum drying methods, the apple chips dried by microwave freeze-drying will have the best product quality. The energy consumption of microwave freeze-drying was 59.02% lower than that of freeze-drying.