Suspension of the calcium-sensitive human beta-caseins by human kappa-casein

Which is the optimal choice for neonates' formula or breast milk?

The incidence of prematurity has been increasing since the twenty-first century. Premature neonates are extremely vulnerable and require a rich supply of nutrients, including carbohydrates, proteins, docosahexaenoic acid (DHA), arachidonic acid (ARA) and others. Typical breast milk serves as the primary source for infants under six months old to provide these nutrients. However, depending on the individual needs of preterm infants, a more diverse and intricate range of nutrients may be necessary. This paper provides a comprehensive review of the current research progress on the physical and chemical properties, biological activity, function, and structure of breast milk, as well as explores the relationship between the main components of milk globular membrane and infant growth. Additionally, compare the nutritional composition of milk from different mammals and newborn milk powder, providing a comprehensive understanding of the differences in milk composition and detailed reference for meeting daily nutritional needs during lactation.

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.

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

The possible effects of both the beta-casein (beta-CN) phosphorylation level and the kappa-CN glycosylation level on micelle formation were studied using the doubly-phosphorylated form (beta-CN-2P) and the quadruply-phosphorylated form (beta-CN-4P) of human beta-CN, along with bovine kappa-CN to compare with previous studies using the more highly glycosylated human kappa-CN. Addition of bovine kappa-CN to human beta-CN-2P, beta-CN-4P, or a 1/1 (wt/wt) mixture of the two was at kappa/beta molar ratios from 0.0 to approximately 0.6 and micelles were reconstituted by addition of Ca+2 either directly at 37 degrees C for determination of the fraction suspended or at an initial temperature of 4 degrees that was gradually increased to 37 degrees C with the change in particle size monitored by turbidity measurements. Analysis of the data indicates that the 4P form requires more kappa-CN for stabilization than the 2P form but that the mixture of the two is more like the 4P form in that lateral kappa-kappa interactions may enhance beta-kappa interactions and micelle formation. Above a kappa/beta molar ratio of about 0.2, the caseins were fully suspended into reconstituted micelles. However, micelle size decreased at a higher ratio, indicating that the kappa-CN probably occupies a surface position and may regulate micelle size by its relative abundance. A comparison with published results suggests that the higher glycosylation level of human kappa-CN may protect a larger surface area and result in smaller micelles. Changes in reconstituted micelle size with pH indicate that positively charged groups in the kappa-CN may interact with the negatively charged phosphate esters in the beta-CN moieties in addition to kappa-beta hydrophobic interactions.