High pressure effects on the structure of casein micelles in milk as studied by cryo-transmission electron microscopy

Processing of phosphocasein dispersions by dynamic high pressure: Effects on the dispersion physico-chemical characteristics and the binding of α-tocopherol acetate to casein micelles

“…Depending on the protein structural characteristics (globular structure for whey proteins or self-assembly for caseins), homogenisation at ≥200 MPa can induce some reduction in average casein micelle size (Hayes & Kelly, 2003b) or formation of whey protein aggregates of controlled-size (Grácia-Juliá et al, 2008). In opposite, more data are available concerning the effects of isostatic high-pressure on casein micelles, that is useful to consider in the present study to explain pressure-induced phenomena: isostatic pressurisation of bovine milk or phosphocasein dispersions up to 300 MPa at 9-20°C caused dissociation of native casein micelles into sub-units (or neomicelles) smaller than the native ones as observed after pressure release by PCS measurements, atomic force or cryo-transmission microscopy (Gebhardt, Doster, Friedrich, & Kulozik, 2006;Knudsen & Skibsted, 2010;Regnault, Thiebaud, Dumay, & Cheftel, 2004). The pressureinduced dissociation of casein micelles in the range 100-300 MPa was assigned to the weakening of interactions between hydrophobic areas, the weakening of electrostatic interactions between the charged groups of caseins and the potential disruption of ionic bonds between caseins and colloidal calcium phosphate (Dumay, Picart, Regnault, & Thiebaud, 2006).…”

The pressure-induced, lactose-dependent changes in the composition and size of casein micelles

“…The samples for the cryo-transmission electron microscopy (cryo-TEM) technique were created based on the method of Knudsen and Skibsted (2010). The samples (3.5 ll) were deposited on lacey carbon membranes (Lot BZ110223a, Zhongjing Keyi, Beijing, China) supported by a copper grid.…”

Alpha-Casein as a Molecular Chaperone

“…Further evidence for the localisation of -casein at the surface of the micelle forming a diffuse outer region [20] was provided by the discovery that in the formation of cheese, the more hydrophilic C-terminal portion is the one cleaved by the action of rennet [2]. Recent Cryo-TEM and TEM studies have shown that the small electron-dense regions consistent with calcium phosphate nanoclusters are evenly distributed throughout the micellar structure rather than being sequestered within the core of the micelle [21][22][23][24] and that these structures, linked together by chains of caseins, were continuous throughout the entire micelle [25]. The sequestration of calcium phosphate, which accounts for 7% of the solute mass of bovine casein micelles, within a phosphoprotein matrix in this way is critical to maintaining the stability of these potentially very insoluble minerals in milk which would otherwise precipitate, compromising lactation [19].…”