Correlation of Viscoelastic Properties with Water Status of Scallop Adductors During Heat Pump Drying: Effects of Ultrasound Pretreatment and Drying Conditions

The effects of ultrasound (US) pretreatment, heat pump drying temperature and drying time on the water status and viscoelastic properties as well as the correlation between them of scallop adductors were investigated. As drying progressed, the transverse relaxation time (T₂) of tightly and loosely bound water maintained a relatively stable state, while the T₂ of free and immobilized water shifted leftwards with US pretreatment and increasing drying temperature. The creep compliance was increased, but the relaxation modulus decreased with US pretreatment and an increase in drying temperature. However, the creep compliance exhibited a decreasing trend, but the relaxation modulus showed an increase tendency as drying proceeded, viz., decreasing moisture content. Burger’s model and the three-element generalized Maxwell model achieved the best fit to describe the creep behavior and stress relaxation, respectively. The storage modulus (G′) and loss modulus (G″) were decreased with US pretreatment, increasing the drying temperature and moisture content. The T₂ of all water components and peak area fraction of immobilized water were positively correlated with the creep compliance but significantly negatively correlated with the stress relaxation modulus, G′ and G″. Low-field nuclear magnetic resonance provided reliable viscoelastic properties of scallop adductors by monitoring the water status during the drying process, which can be used to accurately control the final product quality.