真鲷水分脱湿等温曲线和热力学性质的研究

Study on moisture desorption isotherm and thermophysical property for Red sea bream Chrysophrys major Temminck et Schlegel

研究了真鲷水分脱湿(解吸附)等温曲线的动力学特性、不冻结水和冻结点之间的关系以及热力学性质。研究采用水蒸汽压法和差示扫描量热法测定了真鲷各个处理条件下的水分活度、熔融热和冰点。实验通过GAB(Guggenheim-Anderson-de Boer)模型和BET(Brunauer-Emmett-Teller)模型对真鲷的水分解吸附等温曲线进行了拟合,确定了各参数间的拟合方程。实验发现,真鲷的水分解吸附等温曲线为Ⅱ型(S形),GAB模型和BET模型均具有较好的拟合度,R2分别为0.9915(GAB模型,aw:0.13～0.98)和0.9825(BET模型,aw<0.90)。由拟合方程计算得真鲷的单分子层饱和水分含量分别为0.0820g/g干基(GAB模型)和0.0781g/g干基(BET模型)。实验发现,真鲷中可冻结水含量与熔融热存在线性关系(R2=0.9996),并计算得当熔融热(ΔHf)为0时,真鲷的不可冻结水水分含量为0.2912g/g干基。

This paper aimed at the kinetic character of moisture desorption isotherms, the relationships between unfrozen water and freezing point and thermodynamic of red sea bream Chrysophrys major Temminck et Schlegel. Differential scanning calorimeter （DSC） and water vapor pressure capacitance manometer were applied to study the water activity （aw）, enthalpy of water fusion （△Hf） and freezing point. Experimental data were modeled by the Guggenheim Anderson de Boer （GAB） and the Brunauer, Emmett and Teller （BET）. Moisture desorption isotherms of red sea bream exhibited the sigmoid （Type Ⅱ） shape. The GAB model gave the better fit （R^2 =0. 991 5） to the experimental sorption data for a wide range of water activity （0.13 -0.98） while the BET model gave the worse fit （R^2 =0. 982 5） for a water activity range of less than 0.90. Monolayer moisture content was computated through the two models, which was 0. 082 0 g/g dried base （GAB model） and 0. 078 1 g/g dried base （BET model）. Liner equation about △Hf and frozen water content were applied（R^2 = 0. 999 6） for red sea bream. And from the equation, the unfrozen water content were calculated to be 0. 291 2 g/g dried base, at the time of △Hf=0.