Desorption isotherms and drying characteristics of Nile tilapia fish sheet
2017
Rojanakorn, T. | Ponwiboon, N.
This study aimed to investigate desorption isotherm properties and drying behavior of fish sheets prepared from minced Nile tilapia at various conditions. Desorption isotherms of fish sheet samples were determined at 25ºC, 35ºC and 50ºC over a water activity (aw) range of0.33-0.96. Five sorption isotherm equations including the Modified Halsey, Modified Oswin, Modified Henderson, Modified Chung-Pfost and Mujica model were fitted to the experimental desorption data. In convection drying experiments, fish sheet samples were dried in a single layer at 50ºC, 60ºC and 70ºC with a constant air velocity of 0.5 m/s. The experimental drying data were then fitted to the Newton, Page, Henderson and Pabis and Two-term exponential models. Desorption isotherms of Nile tilapia fish sheet behaved like a type II in the BET classification and had a sigmoid form. At any given moisture content, an aw of the sample increased with increasing temperature. The Modified Oswin gave the best fit to the experimentaldesorption data. The total heat of desorption of water decreased continuously with increasing equilibrium moisture content. Drying chiefly occurred in the falling rate period and the dryingrate increased with temperature. The Page’s equation gave the best fit to the experimental drying data over the respective range of temperatures studied, with corresponding R2 , SEE and RMSE varying from 0.995 to 0.997, 0.012 to 0.015, and 0.011 to 0.014 respectively. The moisture diffusivity increased from 1.108x10-11 m2/s at 50ºC to 1.752x10-11 m2 /s at 70ºC. The temperature dependence of moisture diffusivity was successfully described by the Arrheniustype equation.
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