A versatile viscometric method for the study of dissolved proteins, exemplified for casein micelles in ammoniacal solutions

摘要

Viscosities of casein solutions were measured within the dilute range in ammoniacal water and in saline solvents containing different amounts and different kinds of salt. All these data are modeled quantitatively by means of an approach accounting for the polyelectrolyte character of casein micelles. Two parameters are required: The intrinsic viscosity [eta] and a viscometric interaction parameter beta. The behavior of casein is compared with that of chain-like polyelectrolytes. For both polymers one observes a pronounced reduction of [eta] with increasing salt concentration. However, for casein the decline of [eta] is less pronounced by more than an order of magnitude and depends on the chemical nature of the salt. In the case of low solvent salinities, the beta values are in both cases positive (less than exponential increase of the viscosity with rising solute concentration). However, for casein beta changes from positive to negative (more than exponential increase) with rising salt concentration. Reasons for the dissimilarities between the two types of polyelectrolytes are discussed. (C) 2017 Elsevier Ltd. All rights reserved.