Physicochemical Properties and Surface Composition of Infant Formula Powders Made from Different Milks

This study was conducted in order to explore the influence of different milks on the stability of infant formula milk powder. The physicochemical properties of infant formula milk powders made from goat milk and cow milk such as moisture content, water activity (aw), glass transition temperature (Tg), lactose crystallinity, solubility, color, protein composition, total fatty acid and the composition of surface free fatty acids were analyzed. The surface components were determined by X-ray photoelectron spectroscopy (XPS), and the surface morphology was observed by scanning electron microscopy (SEM). The results showed that goat milk infant formula powder had good physicochemical properties. Compared with cow milk infant formula powder, goat milk infant formula powder had lower moisture content, aw, chroma and Tg, but similar crystallinity and solubility. Fatty acid composition analysis by gas chromatography-mass spectrometry (GC-MS) showed that in both infant formula powders, unsaturated fatty acids accounted for a higher percentage of the total fatty acids, while saturated fatty acids accounted for a higher percentage of the surface free fatty acids. The results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that the content of β-casein in goat milk infant formula powder was higher, and the difference in casein content affected the surface components of milk powder. Consistently, the XPS results showed that goat milk infant formula had a relatively low fat content and a relatively high protein content in the surface composition, which could explain the more agglomerated and denser particles of cow milk infant formula powder observed by SEM. The above results indicated that the physicochemical properties and surface composition of infant formula powders made from different milks are different due to the difference in casein composition, affecting the stability of infant formula powder.