Analysis of Micro wave Freeze-drying Characteristics and Quality of Blueberry
In order to investigate the microwave freeze-drying characteristics and quality changes of blueberries,this pa-per explores the effects of different microwave power(300,400,500,600 W),vacuum degree(50,100,150,200 Pa)and material loading(60,120,180,240 g)on the drying characteristics of blueberries and their quality.A Box-Behnken central combination experimental design was carried out on the basis of a one-way experiment,and the com-prehensive scores of drying rate,color difference,shrinkage,rehydration ratio,Vitamin C preservation rate,and antho-cyanin retention rate of blueberries were used as evaluation indexes.The results showed that:the drying rate of blueber-ries in the pre-drying period was larger and became larger with the increase of microwave power,the R2 of Page model were all greater than 0.95,which could better predict the moisture changes in the drying process of blueberries,and the effective moisture diffusion coefficient of blueberries ranged from 3.341×10 8 to 5.110×108 m2/s,and was significantly af-fected by the microwave power and loading capacity(P＜0.05).The chromatic aberration △E increased with the increase of microwave power and decreased with the increase of vacuum.The microwave power and vacuum degree had a greater in-fluence on the rehydration performance,the VC retention rate decreased rapidly with the increase of microwave power,and increased slowly with the increase of vacuum degree and loading capacity,and had a maximum value at 400 W;whereas the anthocyanin content showed an overall rapid decreasing trend with the increase of microwave power and vac-uum degree.According to the results of the response surface test,the contribution of each factor to the overall score of blueberry drying was:microwave power＞vacuum degree＞loading capacity.When the drying parameters of dried blue-berry products were microwave power of 400 W,vacuum degree of 100 Pa,and loading capacity of 120g,the microwave freeze-drying effect of blueberries was the best,at which time the blueberry color and luster,rehydration ratio,textural characteristics,vitamin C and anthocyanin content and internal pore distribution were relatively the best,and the quality was the best.
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