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

Abstract

This study investigated the micellar structure and in vitro infant gastrointestinal digestion of formed casein micelles simulating human casein composition and phosphorylation patterns. Caseins were fractionated from bovine caseins and formulated according to human casein composition, i.e., β-, κ- and αs1-caseins with a ratio of 68:20:12. The formulated caseins were dephosphorylated for different times and were mixed to obtain mixed phosphorylation patterns (FC-MP) for β-casein, showing 0–5 phosphate groups comparable to human β-casein. The formulated caseins without dephosphorylation and with high dephosphorylation, showing 5 phosphate groups and 0–2 phosphate groups for β-casein, respectively, were categorized as high (FC-HP) and low phosphorylated (FC-LP). With the average mineral concentrations found in human milk, CaCl2, MgCl2, citrate and inorganic phosphate were added into the different formulated casein dispersions to obtain casein micelles (FM-HP, FM-MP and FM-LP). Compared to FM-HP, FM-MP was closer to human micelles in relation to particle size, micellar hydration, molar ratio of Ca:casein, morphology and internal structure, whereas FM-LP showed did not show a characteristic micellar structure and had a larger size and lower molar ratio of Ca:casein. For gastrointestinal digestion, FM-MP was closer to human micelles in terms of the gastric flocs, casein degradation rate, free amino groups, and molecular weight distribution of peptides compared to FM-HP, whereas FM-LP showed larger flocs and lower casein degradation rate. These results show the significance of post-translational phosphorylation in facilitating the assembly of caseins into micellar structures, indicating the potential to form human-like micelles for application in infant formulae.