Molecular Weight of Bovine Milk Casein Micelles From Diffusion and Viscosity Measurements

Abstract

We have measured the average molecular weight of casein micelles in skimmilk by combining diffusion and intrinsic viscosity results. The diffusion coefficients and hydrodynamic radius were measured by inelastic laser light scattering spectroscopy. The results in simulated milk ultrafiltrate buffer at 25 C were diffusion coefficient D = 2.18 × 10-8 cm2/sec, hydrodynamic radius Rh = 941 A, intrinsic viscosity [ђ] = .1011 100 ml/g, and molecular weight M = 5.20 × 108. This value for the molecular weight, obtained entirely by measurements in solution and not depending on assumptions about the voluminosity of the micelles, is about half that obtained by Nitschmann from electron microscopy. The average micelle molecular weight by these measurements is approximately weight average. © 1973, American Dairy Science Association. All rights reserved.