Arnaud J P, Lacroix C, Castaigne F
Centre de Recherche STELA, Université Laval, Quebec, Canada.
Enzyme Microb Technol. 1992 Sep;14(9):715-24. doi: 10.1016/0141-0229(92)90111-z.
The effective diffusion coefficient (De) and equilibrium partition factor (Kp) for lactose and lactic acid in k-carrageenan (2.75% w/w)/locust bean gum (0.25% w/w) (LBG) gel beads (1.5-2.0 mm diameter), with or without entrapped Lactobacillus casei subsp. casei (L. casei), were determined at 40 degrees C. Results were obtained from transient concentration changes in well-stirred solutions of finite volume in which the beads were suspended. Mathematical models of unsteady-state diffusion into and/or from a sphere and appropriate boundary conditions were used to calculate effective diffusion coefficients of lactose and lactic acid from the best fit of the experimental solute concentration changes. The effective diffusivities of lactose and lactic acid were 5.73 x 10(-10) and 9.96 x 10(-10) m2 s-1, respectively. Furthermore, lactic acid was found to modify gel structure since lactose diffusion characteristics (De and Kp) differed significantly from an earlier study and in the literature. In gel beads heavily colonized with L. casei, the effective diffusion coefficients of lactose and lactic acid were respectively 17% and 24% lower than for cell-free beads. Partition coefficients also confirmed the obstruction effect due to the cells, and decreased from 0.89 to 0.79, and from 0.98 to 0.87, for lactose and lactic acid, respectively. External mass transfer was estimated by an unsteady-state model in infinite volume using the Biot number. The effect of external mass transfer resistance on De results and the data reported in the literature are discussed.
在40摄氏度下，测定了乳糖和乳酸在κ-卡拉胶（2.75% w/w）/刺槐豆胶（0.25% w/w）（LBG）凝胶珠（直径1.5 - 2.0毫米）中的有效扩散系数（De）和平衡分配系数（Kp），凝胶珠中有或没有包埋干酪乳杆菌干酪亚种（L. casei）。结果来自于悬浮有凝胶珠的有限体积充分搅拌溶液中的瞬态浓度变化。利用非稳态扩散进入和/或离开球体的数学模型以及适当的边界条件，通过对实验溶质浓度变化的最佳拟合来计算乳糖和乳酸的有效扩散系数。乳糖和乳酸的有效扩散率分别为5.73×10⁻¹⁰和9.96×10⁻¹⁰平方米每秒。此外，发现乳酸会改变凝胶结构，因为乳糖的扩散特性（De和Kp）与早期研究及文献中的显著不同。在被L. casei大量定殖的凝胶珠中，乳糖和乳酸的有效扩散系数分别比无细胞的凝胶珠低17%和24%。分配系数也证实了细胞造成的阻碍作用，乳糖和乳酸的分配系数分别从0.89降至0.79，从0.98降至0.87。使用毕奥数通过无限体积的非稳态模型估算外部传质。讨论了外部传质阻力对De结果的影响以及文献中报道的数据。
