Research on characteristics of combined microwave-hot air drying of burdock based on temperature control

The temperature and moisture content change of combined microwave-hot air drying were studied using burdock as the raw material. The results of microwave drying with temperature control showed a shortening of drying time and reduction of deviation of the sample 's internal temperature by selecting appropriate microwave power density and the set value of sample's internal temperature. Response surface methodology was used to optimize the drying technology and the mathematical model was built to describe the reservation rate of carotene. The optimal drying conditions were as follow :microwave density 8.4 W/g,the set value of sample's internal temperature 72.2 ℃ and the temperature of hot air 73.2 ℃,the predicted value of reservation rate of carotene was 60.6%.