Moisture migration and rheological properties of dual-frequency ultrasound combined vacuum drying on <i>Pangasius bocourti</i> surimi

Abstract To explore the effect of dual-frequency ultrasound combined vacuum drying (DUVD) on non-Newtonian fluid food, the experiments of DUVD on Pangasius bocourti surimi (PBS) were carried out, and the dehydration, water migration, microstructure and rheological properties of PBS were studied under different ultrasonic powers and frequency combinations. The results showed that the drying times were shortened by 43.48 %–86.97 % with applying dual-frequency ultrasound in vacuum drying process. The low-field nuclear magnetic resonance results illustrated that the content of free water decreased continuously during drying, and higher ultrasonic power could cause faster free water reduction rate, while semi-bound water content increased first and then decreased. The scanning electron microscope results demonstrated that increasing ultrasonic power was beneficial to the formation of dense micropores and the reduction of mass transfer resistance. The rheological properties examinations revealed that PBS remained the characteristics of pseudoplastic fluid and elastic fluid after DUVD treatment, the shear stress and apparent viscosity, energy storage modulus and loss modulus of the composites were increased at different degrees. The study clarified that DUVD technology could achieve faster and better drying of PBS.