Abstract:In this study, ultrasonic pretreatment of cauliflower was used before drying, and the effects of different levels of ultrasonic pretreatment conditions on the quality of dried cauliflower products were explored. Meantime, the moisture status and distribution of cauliflower during hot air drying were analyzed. Based on single-factor experiments, taking color, rehydration ratio, vitamin C content and DPPH free radical scavenging capacity as response values, ultrasonic time, ultrasonic frequency and ultrasonic power density were selected to perform a three-factor three-level response surface center combination design experiment. And the ultrasonic conditions with better quality of dried cauliflower products were obtained. The results showed that the optimal process for ultrasonic pretreatment of cauliflower was ultrasonic time 6.00 min, ultrasonic frequency 80 kHz, ultrasonic power density 0.22 W/cm2. Under these conditions, the b* value of the dried cauliflower product was 30.58, the rehydration ratio was 2.97, the Vc content was 311.78 mg/100 g, and the DPPH free radical scavenging ability was 7.20 μmol Trolox/g. The results of low-field nuclear magnetic resonance found that free water was firstly removed during the process of hot air drying of cauliflower, followed by semi-bound water and partially bound water. After ultrasonic pretreatment, the degree of freedom of hydrogen protons in cauliflower was increased, so the water removal rate could be accelerated during the drying process. Therefore, to improve the quality of dried cauliflower products and reduce drying time, the response surface center combined design experiment and LF-NMR technology can be used to optimize the pretreatment process of dried cauliflower products and analyze the moisture changes during drying.
