Protein-Lipid Interactions in Concentrated Infant Formula

Abstract

Radiolabeled milk proteins ([carbon-14] β-lactoglobulin or [carbon-14] κ-casein) were added to raw skim milk used to prepare concentrated humanized infant formula. Ultracentrifugation of the sterilized product allowed separation of three fractions: lipids and the proteins associated with them; free casein micelles and other dense particles; and the fluid phase. Distribution of radiolabeled tracer proteins or of protein measured by chemical methods among these three phases varied significantly with differences in processing conditions (time and temperature of sterilization) or amount of certain additives (potassium hydroxide or urea). In the range of 0 to 8 meq/L of potassium hydroxide added to the formula after homogenization but before sterilization, the lipid layer content of carbon-14 from [carbon-14] κ-casein in the sterilized product decreased by 4.7% for each 1 meq/L of added potassium hydroxide. Lipid layer content of protein decreased by 2g/L (of a total of 32g/L) for each 1 meq/L potassium hydroxide. Such differences in the structure of the product, related to interactions of protein with lipid, protein, or calcium phosphate, may correlate with physical properties and stability of milk-based lipid-rich products.