Structure of protein solutions. Part 1. Investigation and interpretation of viscosity anomalies

Abstract

The state of proteins in water-protein systems was investigated qualitatively using viscosimetric technique and preparative ultracentrifugation. In the case of cooperative processes, 4 concentration intervals bounded by three critical concentrations have been found for each protein.The first value of critical concentration is bound up with the initiation of supermolecular formations (herein also referred to as associates) due to self-association of polypeptide chains. The second critical concentration is observed when the weight fraction of associate becomes predominant (80-85 %) and when the change of secondary and tertiary structures is completed.The third critical concentration is connected with the change in the nature of supermolecular formations. The thermodynamic stability of the water-protein system varies when the critical concentrations are passed through. The system is stable and, apparently, close to the true solution over the first concentration interval. As soon as the first critical concentration is reached, colloid particles appear in the system and become predominant after the second critical concentration is passed, and the solution should be considered as a colloid one.According to the generally accepted definition the solution is a uniphase system consisting of at least two components [I]. As far as water-protein mixtures are concerned, the term "solutions" is applied to systems which entirely differ in phase state and structure. Such is the case with slurries and dilute enzyme solutions, the latter being close to the true solutions.The purpose of our experimentation is to particularize the physical sense of the term "solutions" in application to water-protein systems and generalize the structural features and characteristics of water-soluble proteins in a wide range of temperatures and concentrations. The present paper is the first report on a series of our experiments wherein the relation between the volumetric processes in the system and the observed viscosity anomalies is discussed in the light of data obtained by other methods. Materials and methods Materials

Properties of Sodium Caseinate Film-Forming Dispersions and Films

“…The viscosity of the solution increases with glycerol content (Figure 4), which can be attributed to the decrease in the free solvent volume as glycerol molecules interact with the NaCAS chain. Similar behavior has also been observed by Soloshenko et al (1984) and Siew et al (1999). Siew et al (1999) attribute the viscosity increase with glycerol content to the formation of larger NaCAS-glycerol aggregates as glycerol molecules interact with the NaCAS chain.…”

Solution and Film Properties of Sodium Caseinate/Glycerol and Sodium Caseinate/Polyethylene Glycol Edible Coating Systems

“…The regions near the turning points are probably connected with variations in the three-dimensional structure of the system as the NaCAS/glycerol particles form larger aggregates. This process is expected to be accompanied by a sharp decrease in the volume of the free solvent and observed as an increase in the system viscosity (Soloshenko et al, 1984) (see regions DE and FG of the viscosity graph in Figure 2).…”

“…Solution Systems. Although the viscosity of casein and caseinate solutions has been studied previously (Konstance and Strange, 1991;Soloshenko et al, 1984), there appears to be a paucity of data for caseinate/ plasticizer systems. The effects of glycerol and PEG on the viscosity of aqueous NaCAS was investigated in this study over a wide concentration range.…”