The mathematical formulation of mass transfer in food processes is often based on the diffusion equation with the diffusion coefficients considered as effective parameters. In some cases. more than one specie can be simultaneously diffusing in opposite directions. Therefore, the movement of one component could affect the movement of the remaining components. The aim of this work is to describe a mathematical procedure to obtain the diffusion coefficients of different species that simultaneously diffuse in such a situation that each mass flux is affected by the existence of the others. The correspondent microscopic mass balances combined with Fick's law were simultaneously solved using a numerical finite difference method.