Effect of ultrasound immersion pretreatment combined magnetic field assisted freezing on the quality of frozen blueberries

This study investigated the effect of ultrasound combined with static magnetic field freezing on the freezing process and quality changes of blueberries. The aim is to provide a reference for the study of magnetic fields in food. The freezing parameters, quality, and microstructural structure were examined. The results showed that the effect of ultrasound-assisted static magnetic field freezing (U-MF) was better, which significantly shorted the freezing time of the sample. In comparison to −20 °C control frozen (CF), the degree of supercooling increased by 50.08%, freezing time shorted by 16.36%, drip loss decreased by 28.28%, respectively, and the water distribution state was closer to that of fresh fruits. Microstructural analysis indicated that the sample structure of U-MF treated blueberries was better approximated by the fresh sample. Moreover, overall sensory scores for blueberries showed that U-MF treated blueberries presented positive sensory evaluation. In conclusion, ultrasound and static magnetic field play a synergistic effect in assisting freezing, and the combined effect is better than that of ultrasound or static magnetic field alone. • Ultrasonic assisted magnetic field (U-MF) improved the quality of frozen blueberry. • The subcooling degree of U-MF treated blueberries was increased by 50.08% as compared to control. • U-MF treated blueberry presented excellent sensory evaluation.