Evaluation of desorption isotherms, drying characteristics and rehydration properties of crab stick by-product

Abstract : Crab stick by-product is the underspecification product from crab stick production. The by-product contains high moisture content inducing a short shelf life. Therefore, drying is considered as a food preservation technique to extend its shelf life. This study is focused on an investigation of desorption isotherms, drying characteristics and rehydration properties of crab stick by-product. Desorption isotherms were determined at three different temperatures (20, 35 and 50 degrees C). The experimental data obtained were modeled by fourteen sorption isotherm models for water activity ranging from 0.36 to 0.99 and Double Log Polynomial model was found to be the best-describing model. The net isosteric heat of desorption increased continuously with decreasing of equilibrium moisture content. The crab stick by-products were dried at 50, 60 and 70 degrees C with a constant air velocity of 1 m/s. The drying data were fitted with five thin layer drying models and Approximation of diffusion model was the best-describing model. Drying curves showed only falling rate period. Moisture diffusivities (D-eff) of the by-product drying were ranging from 8.87 x 10(-10) to 1.47 x 10(-9) m(2)/s and increasing drying air temperature led to an increment of D-eff. Rehydration properties including weight gain (%), rehydration ratio and co-efficient of reconstitution of dried sample at 60 and 70 degrees C were higher than the drying at 50 degrees C. Peleg model was the best fit with rehydration data. The D-eff of moisture absorption was in the range from 6.49 x 10(-9) to 7.31 x 10(-9) m(2)/s.