Matrix Effects on the Kinetics of Lactose Hydrolysis in Fermented and Acidified Milk Products

J. Wilde, C. Baumgartner, B. Fertsch and J. Hinrichs

Abstract
Diffusion may limit the homogeneous hydrolysis of the lactose when adding the hydrolyzing enzyme, lactase, to a fermented pasty milk product. The diffusion of lactose in soft cheese (quark) and acid milk gels (obtained by Glucono-δ-lacton) was determined in experiments. By variating amount of dry matter it was possible to study matrix effects on the diffusion rate. The model of one-dimensional infinite media with a constant cross-section based on Fick´s second law of diffusion for time-dependent diffusion processes was verified concerning the diffusibility of lactose in viscose milk products. It appeared that the apparent diffusion coefficient “Dapp” showed a linear decline as the dry matter of the product increased. Concerning the kinetics of lactose hydrolysis, no significant limitation was caused by the diffusion resistance of the matrix of fermented or acidified milk products.

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Keywords
Milk products, lactose, lactase, diffusion, hydrolysis