Rheological properties and microstructure of spotted catfish surimi during ultrasound enhanced far-infrared radiation combined vacuum drying

To investigate the structural and rheological evolution of surimi during ultrasound enhanced far-infrared radiation combined vacuum drying (CUFIR-VD), spotted catfish surimi was used to analyze the effects of ultrasonic power on drying characteristics, water migration, rheology and microstructure. Increasing ultrasonic power shortened drying time by 20–60 min and enhanced water mobility. Rheological analysis revealed that the apparent viscosity at 30 and 60 W improved by 6.18 and 34.53%, respectively, compared with that without ultrasound at the same drying time. The storage modulus and loss modulus increased significantly with water removal, which reflected the continuous enhancement of viscoelasticity. Under large strain conditions, the sample exhibited obvious nonlinear viscoelastic behavior. With the rise of ultrasonic power, the expansion of Lissajous curve and the enhancement of stress response indicated that ultrasound promoted the formation of protein network and accelerated the transition from fluid state to solid-like state. LF-NMR results showed that free water first increased slightly and then decreased until complete removal, while semi-bound water reduced initially and then stabilized, and bound water remained nearly unchanged. SEM observations demonstrated that ultrasound facilitated the formation of internal microporous structures and increased pore size, thereby reducing mass transfer resistance. Micro-CT analysis further confirmed that pore structures gradually developed during drying, with porosity first increasing and then decreasing. In summary, CUFIR-VD not only accelerates moisture migration but also regulates the structural evolution of surimi, providing a theoretical basis for optimizing drying processes of surimi and related aquatic products.