采用动态水分吸附法研究不同孔隙率和脂肪含量的发酵饼干在25℃下的水分吸附动力学特性,基于GAB模型和无限大平板模型确定其等温吸湿曲线和有效水分扩散系数。结果表明:孔隙率对饼干平衡水分含量几乎没有影响,而随着脂肪含量的增加,饼干的平衡水分含量逐渐下降。GAB模型能成功拟合饼干的等温吸湿数据。饼干的有效水分扩散系数随含水量变化先增大而后逐渐减小,有效水分扩散系数在水分含量为10 g/100 g(干基)左右时达到最大值。初始孔隙率87%、76%和68%的最大有效水分扩散系数分别为7.8×10-10m2/s、5.6×10-10和3.4×10-10m2/s,这与水分扩散机理从以气态传输为主向以液态传输为主的转变有关。增加脂肪含量会显著降低水分扩散系数,有效水分扩散系数从最大值5.6×10-10m2/s下降到2.3×10-10m2/s。

The water sorption kinetics of fermented biscuits with different porosity and fat content were determined using dynamic moisture adsorption methods at 25℃. The moisture sorption isothermal and effective moisture diffusion coefficient were obtained based on GAB model and infinite slab model. The results showed that the porosity had almost no effect on equilibrium moisture content of biscuits,while as the fat content increased,the equilibrium water content gradually decreased. GAB model was suitable for fitting the sorption data of biscuits. Effective moisture diffusion coefficient reached a maximum with water content increasing and then decreased to a constant value. The maximum of effective diffusion coefficient was reached at the moisture content of 10 g /100 g dry basis. The maximum of effective moisture diffusion coefficients of fermented biscuits with porosity of 87%,76% and 68% were 7. 8 × 10- 10m2/ s,5. 6 × 10- 10m2/ s and 3. 4 × 10- 10m2/ s respectively,which were mainly related to the mechanism of moisture diffusion,i. e. vapor water diffusion in pores was changed to liquid water diffusion in the solid matrix. Increasing fat content significantly decreased moisture diffusion coefficient. Results showed that the effective diffusion coefficient decreased from the maximum value of 5. 6 × 10- 10m2/ s to 2. 3 × 10- 10m2/ s.