Formation of casein micelles simulating human milk casein composition from bovine caseins: Micellar structure and in vitro infant gastrointestinal digestion

Abstract

Bovine casein micelles in infant formula differ from human micelles in composition, structure and digestion. Preparation conditions, micellar structure and in vitro gastrointestinal digestion under infant of casein micelles formed from bovine caseins but simulating human micelles were investigated. Bovine caseins were fractionated and formulated based on the composition of human caseins, i.e., at a ratio of 68:20:12 for β-, κ- and αs1-caseins. Citrate (Cit), calcium (Ca), and inorganic phosphate (Pi) were added into casein dispersions (0.4% caseins, w/v) to obtain casein micelles. Optical absorbances showed that the optimal conditions of formation were mineral addition in the order of Cit → Ca → Pi over three cycles and final concentrations of 2.1–2.8 mM Cit, 6.1–7.1 mM Ca and 1.5–3.0 mM Pi. For micelles formed using 2.3 mM Cit, 7.1 mM Ca, and 2.8 mM Pi (the average concentrations in human milk), the particle size, micellar hydration, internal structure and morphology were similar to those of human micelles, while the percentage of serum caseins was lower and the molar ratio of Ca:casein was higher. During the gastrointestinal digestion, the gastric flocs, free amino groups and molecular weight distribution of peptides were close to those of human micelles, with casein degradation rate being lower, while the flocs were smaller and the free amino groups and casein degradation rate were higher compared to bovine micelles. These results suggested a potential to form micelles with composition, structure and digestion close to human micelles for use in infant formula.