Moisture adsorption and desorption isotherms of powdered infant formula milk with different compositions

Abstract.

This research explored the constant temperature and humidity chamber method as an alternative of saturated salt solution method in establishing adsorption and desorption isotherms. Adsorption and desorption isotherms were established for powdered infant formula milk with different compositions at 20°C. Adsorption isotherms of powdered infant formula milk revealed as type II, with a glass transition relative humidity of around 43% due to the presence of lactose. Water activities decreased with the increase of protein and lactose contents at constant equilibrium moisture content. Equilibrium moisture content of powdered infant formula milk decreased with increasing fat content during adsorption procedure, while increased during desorption procedure at constant water activity. Despite of the variation of protein, fat and sugar contents, the glass transition relative humidity kept constant. Five mathematical models were employed to fit the experimental data, among which GAB model was the best to fit all the adsorption isotherms, while all GAB, Smith and Halsey models agreed well with desorption isotherms.