The association of low-molecular-weight hydrophobic compounds with native casein micelles in bovine milk

Abstract

The agreed biological function of the casein micelles in milk is to carry minerals (calcium, magnesium, and phosphorus) from mother to young along with amino acids for growth and development. Recently, native and modified casein micelles were used as encapsulating and delivery agents for various hydrophobic low-molecular-weight probes. The ability of modified casein micelles to bind certain probes may derive from the binding affinity of native casein micelles. Hence, a study with milk from single cows was conducted to further elucidate the association of hydrophobic molecules into native casein micelles and further understand their biological function. Hydrophobic and hydrophilic extraction followed by ultraperformance liquid chromatography-high resolution mass spectrometry analysis were performed over protein fractions obtained from size exclusion fractionation of raw skim milk. Hydrophobic compounds, including phosphatidylcholine, lyso-phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin, showed strong association exclusively to casein micelles as compared with whey proteins, whereas hydrophilic compounds did not display any preference for their association among milk proteins. Further analysis using liquid chromatography-tandem mass spectrometry detected 42 compounds associated solely with the casein-micelles fraction. Mass fragments in tandem mass spectrometry identified 4 of these compounds as phosphatidylcholine with fatty acid composition of 16:0/18:1, 14:0/16:0, 16:0/16:0, and 18:1/18:0. These results support that transporting low-molecular-weight hydrophobic molecules is also a biological function of the casein micelles in milk.

Nature-Assembled Structures for Delivery of Bioactive Compounds and Their Potential in Functional Foods

“…The formation of the complex between casein micelles and curcumin was attributed to hydrophobic interactions. Mohan et al ( 2013 ) showed that natural casein micelles have the ability to associate with hydrophobic vitamin A. Cheema et al ( 2015 ) reported that native casein micelles isolated from raw milk exhibited a stronger binding affinity toward hydrophobic compounds, including sphingomyelins, phosphatidylcholines, and phosphatidylethanolamines. Clearly, a further understanding of the ability and the mechanism of the binding of hydrophobic molecules within casein micelles would allow us to create novel nanometer-scale structures that would be suitable for the delivery of bioactive compounds.…”

Production of Liquid Milk Protein Concentrate with Antioxidant Capacity, Angiotensin Converting Enzyme Inhibitory Activity, Antibacterial Activity, and Hypoallergenic Property by Membrane Filtration and Enzymatic Modification of Proteins

“…α-casein was hydrolyzed at more than 99% with 0.064 g•L −1 of trypsin. This can be justified by the fact that α-casein might has less chance to participate in enzymatic reaction because in the interior part of casein micelle, calcium phosphate clusters bind with the phosphoseryl residues of α s -casein and β-casein, whereas κ-casein was present in the periphery of casein micelle and received chance to participate in enzymatic reaction [111]. Due to partial hydrolysis of β-casein with 0.008 g•L −1 of trypsin, some peptone and γ-casein with molecular weight~22 kDa might produce and they were hydrolyzed when milk with concentrated proteins was treated with 0.032 g•L −1 of trypsin.…”

Challenges and opportunities of bovine milk analysis by mass spectrometry

“…In addition, to maximize protein identifications and expand the analysis of the milk proteome, multiple analytical approaches including fractionation techniques have been adopted. For example, casein which makes up 80 % of overall milk protein content was extracted using hydrophobic and hydrophilic procedures followed by size exclusion fractionation to identify low molecular weight molecules [ 33 ]. Similarly, enhanced identification of whey proteins was reported after precipitation of casein [ 34 , 35 ].…”