Structure of casein micelles studied by small-angle neutron scattering

Abstract

The structure of casein micelles has been studied by small-angle neutron scattering and static light scattering. Alterations in structure upon variation of pH and scattering contrast, as well as after addition of chymosin, were investigated. The experimental data were analyzed by a model in which the casein micelle consists of spherical submicelles. This model gave good agreement with the data and gave an average micellar radius of about 100-120 nm and a submicellar radius of about 7 nm both with a polydispersity of about 40-50%. The contrast variation indicated that the scattering length density of the submicelles was largest at the center of the submicelles. The submicelles were found to be closely packed, the volume fraction varying slightly with pH. Upon addition of chymosin the submicellar structure remained unchanged within the experimental accuracy.

Casein micelle structure: Models and muddles

“…Holt's suggestion that the micellar calcium phosphate particle is equal in all respects to their nanocluster is based on the prediction that 800 such clusters, acting as scattering points in an average micelle of radius 100 nm, give a value of 18 nm for their mean spacing or correlation length, just as measured experimentally by neutron or X-ray scattering [42,3]. The network arises because the multi-functional caseins, a S1 -and a S2 -casein, can cross-link the nanoclusters, as in Fig.…”

Invited review: Caseins and the casein micelle: Their biological functions, structures, and behavior in foods

“…By contrast, crosslinking with transglutaminase appears not to affect casein micelle size or substructure, as measured by a range of scattering methods, and produces particles that are resistant to drastic changes in solvent quality (de Kruif et al, 2012). In protein submicellar models of casein micelle structure, the average separation of the dense substructures, about 18 nm, has been interpreted as the diameter of the submicelles (Stothart and Cebula, 1982;Stothart, 1989;Hansen et al, 1996;Farrell et al, 2006a). Notwithstanding the many difficulties of sample preparation, a number of recent electron microscopical methods have yielded images of casein micelles that do not support any submicelle model but are consistent with nanocluster models (Holt et al, 1978;McMahon and McManus 1998;Marchin et al, 2007;Trejo et al, 2011).…”

Characterisation of fractionated skim milk with small-angle X-ray scattering

“…The experimental SAXS data were analysed according to a new model based on the original casein micellar model of Hansen et al (1996) and the more recent extended version of Keerl, Pedersen, and Richtering (2009). The proposed casein model is thereby based on a set of smaller substructures collected into the larger spherical object, describing the overall casein micelle.…”