Characterisation of aged infant formulas and physicochemical changes.

Three different infant formulas (P1, P2 and P3) were characterised, and changes in their physicochemical properties under three different ageing conditions (i.e. 25°C, 45°C and 60°C) were established. At 60°C, all of the three powders exhibited increased moisture content, which was consistent with an increase in water activity. The GAB sorption model fitted for P1 while P2 and P3 did not follow the same sorption isotherm pattern. The glass transition temperature (Tg) for all of the powders significantly decreased at 45°C and 60°C. Confocal analysis revealed that all three powders had different concentrations of surface fat, and fat globules migrated from within the powders to the powder surface during storage under the conditions described. XRD analysis of the aged powders showed no occurrence of lactose crystallisation.