Title: Study on physical and sensory properties of heat pump dried fish fillets and shrimps

Peeled, headed and whole shrimp as well as fish cake of 50 mm (diameter) × (7-9) mm (thickness) and 50 mm × (14-18) mm were dried in a heat pump dryer at -2~0°C and 20°C. Physical and sensory properties as well as the stability of the dried products were evaluated. The desorption isotherms of shrimp and the adsorption isotherms of shrimp and fish cake were investigated. The results show that the drying time decreased greatly and the degree of shrinkage became higher as drying temperature increased from -2~0°C to 20°C. Higher shear force was required to cut the dried shrimp samples when the drying temperature was increased. Drying temperature (-2~0°C or 20°C) has no measurable effect on the sorption isotherms of the headed and whole shrimp and has little influence on peeled shrimp, but it affects significantly the adsorption characteristic of fish cake. The drying and drying rate curves display that the drying process of shrimp and fish cake could be well described by the diffusion model (MR = A exp(-kt)). The results demonstrate that the Oswin model (X = a [aw/(1-aw)]n ) is suitable for predicting the desorption isotherms of shrimp and the adsorption isotherms of shrimp and fish cake. The hysteresis phenomenon between desorption isotherms and adsorption isotherms of frozen peeled shrimp has been observed in the range of aw>0.85 and aw = 0.75-0.88 when dried at -2~0°C and 20°C, respectively. A strong hysteresis existed in thawed peeled shrimp at aw>0.65. Frozen headed shrimp dried at 20°C (B-2) had the best synthetic performance compared with all the shrimp samples, and thin fish cake dried at -2~0°C (D-1) is the best of the fish cake samples.