Kappa-casein interactions in the suspension of the two major calcium-sensitive human beta-caseins

Structure And Biological Functions Of Milk Caseins

Caseins, which are contained in milk, play a significant role in the development of clinical symptoms of allergic reactions in adults and children. To date, the properties of caseins have been studied, their primary structure has been identified. However, despite available scientific reviews and original articles, an issue of the structural organization of milk casein micelles and their biological functions is still very controversial. In this regard, the proposed review is relevant, since it most fully reflects current information about various types of caseins, their physicochemical and immunobiological properties, and analyzes in detail the existing theories on the structural organization of casein micelles. Of particular interest in our review are the data on the comparative analysis of the structure and properties of caseins in both human breast milk and cow’s milk, as well as the section dealing with the allergenic activity of cow’s milk caseins and their cross-reactivity with milk proteins of other mammalian species. The objective of this review is to summarize current data on the structure and properties of casein proteins, and to determine their role in the formation of sensitization to dairy products.

Formulation of infant formula with different casein fractions and their effects on physical properties and digestion characteristics

This study investigated whether casein (CN) fractions exhibit better physical properties and digestibility than native casein micelles presently used in the production of infant formula. The structural performance of native casein micelles (micellar casein concentrates, MCC), β-CN, κ-CN and β + κ-CN were explored, and physical properties and digestion characteristics (i.e., digestibility, particle size, zeta potential and microscopic morphology) of the infant formula with MCC, β-CN, κ-CN or β + κ-CN were determined to elucidate the applicability of these casein types in infant formula. Results indicated that the β + κ-CN infant formula solution had the largest particle size with the most unstable potential. Moreover, both β-CN and κ-CN infant formula showed high solubility, while κ-CN displayed the lowest foaming capacity and high foaming stability. β-CN infant formula expressed an effective digestibility property, however, it possessed the largest particle size after gastrointestinal digestion. Therefore, β-CN fraction infant formula showed better digestibility than casein infant formula, and thus this work provides a theoretical basis for the development of infant formula.

Temperature-dependent dissociation of human micellar β-casein: Implications of its phosphorylation degrees and casein micelle structures

Temperature-dependent dissociation of human micellar β-casein regarding its phosphorylation degrees and micelle structures were studied. Human milk was fractionated at 25 °C into soluble (S-25 °C) and micellar (M-25 °C) fractions, and the latter was fractionated at 4 °C into soluble (S-4 °C) and micellar (M-4 °C) fractions. β-casein ratios among S-25 °C, S-4 °C and M-4 °C were 19%, 59% and 22%. β-casein isoforms were predominated by 0-P, 1-P and 2-P in S-25 °C, by 0-P, 1-P, 2-P and 4-P in S-4 °C, and by 0-P in M-4 °C. For micelles remained after dissociation of β-casein and calcium, the size increased, molar mass decreased, morphologies were maintained, and internal protein inhomogeneities disappeared, compared with micelles in M-25 °C. β-casein isoforms with lower phosphorylation degrees may form a frame mainly through hydrophobic interactions, attached with more highly phosphorylated isoforms and colloidal calcium phosphate via calcium bridges for forming human micelle.

Reconstituted Micelle Formation Using Reduced, Carboxymethylated Bovine κ-Casein and Human β-Casein

In milk, kappa-casein, a mixture of disulfide-bonded polymers, stabilizes and regulates the size of the unique colloidal complex of protein, Ca2+ and inorganic phosphate (Pi) termed the casein (CN) micelle. However, reduced, carboxymethylated bovine kappa-CN (RCM-kappa) forms fibrils at 37 degrees C and its micelle-forming ability is in question. Here, the doubly- and quadruply-phosphorylated human beta-CN forms and 1:1 (wt:wt) mixtures were combined with RCM-kappa at different beta/kappa weight ratios. Turbidity (OD(400 nm)) and a lack of precipitation up to 37 degrees C were used as an index of micelle formation. Studies were with 0, 5 and 10 mM Ca2+ and 4 and 8 mM Pi. The RCM-kappa does form concentration-dependent micelles. Also, beta-CN phosphorylation level influences micelle formation. Complexes were low-temperature reversible and RCM-kappa fibrils were seen. There appears to be equilibrium between fibrillar and soluble forms since the solution still stabilized after fibril removal. The RCM-kappa stabilized better than native bovine kappa-CN.

The Formation of Casein Micelles Reconstituted with Ca+2 and Added Inorganic Phosphate is Influenced by the Non-phosphorylated Form of Human β-Casein

The beta-casein (CN) human milk fraction is comprised of a single protein phosphorylated at levels from 0 to 5. Component interactions are dependent on the phosphorylation level. Here, 3 mg/ml of beta-CN-0P, beta-CN-2P, beta-CN-4P, a 2P/4P 1:1 (wt:wt) mixture, or a mixture of all six forms in the ratio in human milk, were mixed with bovine kappa-CN at a kappa/beta molar ratio of 0.33. Measurements were with 0, 5 and 10 mM Ca+2 and 4 and 8 mM added inorganic phosphate (Pi). The turbidity (OD400 nm) and a lack of precipitation as T increased from 4 to 37 degrees C was an index of micelle formation. The results indicate: (1) while micelles will form with Ca+2 alone, added Pi has a significant enhancing effect on micelle formation; (2) the patterns of micelle formation as a function of T are influenced by the beta-CN-0P and beta-CN-1P forms of beta-CN to an unexpected extent.