title: 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.
authors.affiliation: Department of Food Science, Pennsylvania State University, University Park 16802.
authors.forename: M
authors.initials: M
authors.lastname: Cheema
authors.affiliation: Department of Food Science, Pennsylvania State University, University Park 16802.
authors.forename: M S
authors.initials: MS
authors.lastname: Mohan
authors.affiliation: Department of Chemistry, University of Tennessee, Knoxville 37996.
authors.forename: S R
authors.initials: SR
authors.lastname: Campagna
authors.affiliation: Department of Entomology and Plant Pathology, University of Tennessee, Knoxville 37996.
authors.forename: J L
authors.initials: JL
authors.lastname: Jurat-Fuentes
authors.affiliation: Department of Food Science, Pennsylvania State University, University Park 16802. Electronic address: fede@psu.edu.
authors.forename: F M
authors.initials: FM
authors.lastname: Harte
mesh_terms: D000818:Animals; D002364:Caseins / Q000032:analysis / Q000378:metabolism*; D002853:Chromatography, Liquid; D057927:Hydrophobic and Hydrophilic Interactions; D013058:Mass Spectrometry; D008823:Micelles; D008892:Milk / Q000737:chemistry*; D008894:Milk Proteins / Q000032:analysis*; D008970:Molecular Weight; D010743:Phospholipids / Q000032:analysis*
chemical_list: D002364:Caseins; D008823:Micelles; D008894:Milk Proteins; D010743:Phospholipids
keywords: binding; casein micelle; hydrophobicity; liquid chromatography-mass spectrometry; sphingomyelin