Determination of effective diffusion coefficients in calcium alginate gel plates with varying yeast cell content

Effective diffusion coefficients (De) have been determined for lactose, glucose, galactose, and ethanol in calcium alginate gel with varying yeast cell concentration. The measurements have been performed in a diffusion cell, and the results evaluated with the quasisteady-state method. An ultrasonic meter was used for gel thickness determination with an accuracy of 1.5% and a new method for the reproducible preparation of gel plates was developed. It was found thatD e in pure alginate gel decreased to about 90% of the diffusivity in water and did not vary with alginate concentration.D e decreased considerably with increasing yeast cell concentration. For the solutes studied, the effective diffusion coefficient can be estimated according to the equationD e =D eo (1 - ϕ)/[1+(ϕ/2)], whereD eo is the effective diffusivity in pure gel and ϕ is the volume fraction of yeast cells.