Component distribution and interactions in powdered infant formula

A 600 kg batch of experimental milk-based infant formula mix (40:60 casein to whey protein ratio) was processed in a pilot plant and samples were taken immediately before processing and immediately after HTST pasteurization, homogenization, condensing and spray drying. In electron microscopy observations, fat globules and casein micelles appeared as well-defined discrete spheres before processing. After pasteurization, casein micelles displayed rough irregular surfaces, presumably due to casein-whey protein interactions, and confirmed by an increase in sedimentable N from 45% of total N before pasteurization to 55% after pasteurization. After homogenization, casein-whey protein aggregates appeared to be attached to the surfaces of fat globules. Nitrogen content of the fat fraction increased from 2% of total N before homogenization to 30% after homogenization, confirming high levels of protein-lipid interactions. SDS-PAGE showed high levels of caseins and whey proteins in the fat fraction. Minerals that are strongly associated with casein micelles (Ca, P, Mg and Zn) increased dramatically in the fat fraction, suggesting that casein-bound minerals were associated with fat phase as a result of casein-lipid interactions on homogenization. Protein-lipid interactions were evidenced by both the presence of high protein level in the fat fraction and the presence of fat globules in the pellet on centrifugation. There was little change in microstructure, N, and mineral distribution after condensing and spray drying. (C) 1998 Elsevier Science Ltd. All rights reserved.