Optimization of Microwave-Hot Air Dehydration Process and Quality Evaluation of Frozen Tofu by Response Surface Methodology

In order to solve the problems of high storage and transportation cost and high energy consumption of frozen tofu, microwave and hot air drying were used to prepare dehydrated frozen tofu. The drying sequence of microwave followed by hot air (M-H) was determined by investigating the moisture content and rehydration rate. Taking drying rate, rehydration rate and color difference as the indexes, the single factor and response surface methodology experiments were carried out to optimize the process conditions. The microwave power was 516 W, and the hot air drying was carried out when the moisture content of the conversion point was 37%. The hot air drying temperature was 68 ℃. After rehydration, the elasticity, chewiness and cohesiveness of dehydrated frozen tofu were 0.963 mm⁻¹, 5810 g and 0.79, respectively. The rehydration rate reached 531.97%, and the color became dark. SEM characterization and section structure results showed that the dried freeze-dried tofu gel network was more compact and the pores became more uniform.