Sorption and Permeation of Gases in the Powdered Foodstuffs

I. Permeation of Water Vapor through the Layer of Skim-milk Powder

Abstract

We observed various cases of one-dimensional diffusion phenomenon of water vapor passed through the layer of skim-milk powder. The assembly employed consists of three cylindrical dishes, one of which includes salt solution which maintains a dish at a constant humidity and the other contains absorbent and powder respectively. When a steady state is reached in the layer of powder, moisture content of powder becomes a equilibrium value. From these results, we can calculate the diffusion constant by two ways.
The values of D obtained from sorption rate in powder and apparent Dd* from time lag of permeation is 4.37×10-6 (cm2/sec) and 3.50×10-4 (cm2/sec), respectively.
Thus, the fact that Da* is larger than D may be due to the capillary flow of water vapor;i.e., at the initial stage of sorption, water vapor passes through pores between the powders as capillary flow and at the final stage, after moisture contents of the powder reached a steady state, diffusion also occurs as capillary flow.