Modelling the water sorption isotherms of yoghurt powder spray Original Research Article

Moisture sorption isotherms of yoghurt powder spray were determined using a gravimetric dynamic method with continuous recording of changes in sample weight. Equilibrium data for adsorption and desorption of water from yoghurt powder spray were investigated at ambient temperatures in the range of 20–40 °C and water activity ranging from 0.40 to 0.99. Sorption capacity decreased as temperature increased. Four models available in the literature (Chung-Pfost, Halsey, Henderson and Oswin) were evaluated by determining the best fit to the experimental data. The modified Chung-Pfost equation was found to be a good model for moisture adsorption and desorption of yoghurt powder spray. The critical value of equilibrium moisture content (EMC) of samples tested, corresponding to the water activity equal 0.6, was 8.1–8.9% (wet basis, w.b.) at the temperature of 20 °C.