Physicochemical properties and surface composition of infant formula powders

Compositional difference in infant formula (IF) tends to influence its functionality and storage behaviour. The aim was to study the composition and physico-chemical properties of different stages of two commercial IF (A and B). Lactose crystallization measured by X-ray diffraction ranged between 2 and 32 % and was observed to decrease with increasing IF stages, which directly correlates with their composition. Scanning electron microscopy confirmed the presence of crystalline lactose which significantly (p < 0.05) increased the powder particle size. On the contrary, a negative correlation was observed between surface fat and lactose crystallization in all samples. Bulk and surface-free fat composition was significantly (p < 0.05) different for all samples. Surface free-fat analysis showed restricted presence (5-10% of surface fat) of unsaturated fatty acids (C18:1 and C18:2) in IF with higher crystalline lactose as opposed to >40% in others, suggesting a possible role of lactose crystallization in preferential migration of triglycerides to particle surface.