Modelling the Milk Powder Equilibrium Moisture Content under Storing Conditions

Abstract

Equilibrium moisture content data for adsorption and desorption from skimmed milk powder were investigated at temperatures in the range of 10 - 30°C. The experimental procedure used was a gravimetric dynamic method with continuous registration of sample weight changes. Four mathematical models of sorption isotherms (Chung-Pfost, Halsey, Henderson, and Oswin) were evaluated to determine the best fit for the experimental data. The modified Oswin equation was a good model for moisture adsorption and desorption of skimmed milk powder. Water sorption capacity decreases as temperature increases. The critical value (average between water adsorption and desorption) of equilibrium moisture content of milk powder tested, corresponding to the water activity equal 0.6, was 10.3, 10.9, 11.5, 12.0, and 12.5 % (wet basis) at the temperature 10, 15, 20, 25, and 30°C respectively.