Effect of Ultrasound and Ultrahigh Pressure Pretreatment on Quality of Freeze-dried Strawberry Slices

In order to explore the effect of ultrasonic combined with ultra-high pressure pretreatment on water migration and color of strawberry slices. After ultrasonic combined with ultra-high pressure pretreatment, vacuum freeze-drying was carried out. The moisture characteristics, color (a^*), anthocyanin contents and pigment distribution of strawberry slices before and after pretreatment were determined. The mechanism of ultrasonic combined with ultra-high pressure pretreatment on moisture and color of strawberry slices was analyzed. The results showed that the color (a^* value) and anthocyanin contents of strawberry slices could be improved by ultrasonic combined with ultra-high pressure pretreatment, the distribution of pigment body in the center of strawberry slices was more, the color was uniform, the relaxation time of free water of strawberry slices decreased, and the free water content increased significantly, especially in the pretreatment condition of ultrasonic-200 MPa ultra-high pressure treatment group, the initial water content of strawberry slices decreased by 2.41%, and a^* value of the center epidermis was 2.60 and 8.68, and the anthocyanin contents was 0.36% and 0.55%, respectively. In conclusion, the application of ultrasound combined with ultrahigh pressure pretreatment could significantly improve the quality of freeze-dried strawberry slices, which has a certain value in the production of fruits and vegetables freeze-drying.