Desorption isotherms and drying characteristics of shrimp in superheated steam and hot air

Desorption isotherms for shrimp were determined at the temperatures of 50, 60, 70 and 80degreesC. Amongst the moisture equilibrium predictions between the BET and GAB models, the latter has a better predictable capability. The GAB parameters are correlated with the temperatures by the Arrhenius expression. Drying characteristics of shrimp in drying media at the temperature range of 120-180degreesC for superheated steam and of 70-140degreesC for hot air have been examined. Drying rate and effective diffusion coefficient are used to quantify quantitatively the difference between the superheated steam and the hot air dryings. The temperature is more important effect on drying rate and effective diffusion coefficient in the superheated steam than in the hot air. Inversion temperature exists between 140 and 150degreesC. Comparing to the hot air, the shrimp dried by the superheated steam shows a lower degree of shrimp shrinkage. In addition, product colours are slightly different to those from the commercial sources.