Showing papers by "Ganesan Narsimhan published in 1991"

A surface equation of state for globular proteins at the air-water interface

Abstract: A surface equation of state for globular proteins at the air-water interface accounting for the structure of the protein molecule, its degree of unfolding, and segment-segment, segment-solvent, and electrostatic interactions is proposed. The proposed lattice model employs the simplifying assumption that all the adsorbed segments are present in the form of trains. Results obtained by fitting the equation of state to the experimental data indicate that the average degree of unfolding of bovine serum albumin (BSA) is greater than that of lysozyme. The number of segments adsorbed per molecule of BSA is found to vary linearly with the surface concentration, whereas the segments of lysozyme adsorbed at the interface are fairly independent of surface concentration. The segment-solvent interactions of the adsorbed segments of BSA and lysozyme are found to be unfavorable (χ > 0.5) due to the exposure of hydrophobic functional groups resulting from unfolding. The maximum surface pressure and surface concentration for monolayer coverage are highest at pI and their predicted variation with pH is in good agreement with the experimental data.

Solubility of Globular Proteins in Polysaccharide Solutions

Abstract: A statistical thermodynamic model based on the lattice model proposed by Baskir et al. (1987) was employed to predict the solubilities of globular proteins such as ovalbumin and lysozyme at their isoelectric points in dextran solutions of different molecular weights. The model accounted for protein-polysaccharide and polysaccharide-solvent interactions as well as entropy of mixing, and it employed simplifying assumptions such as a linear homogeneous polysaccharide molecule and a spherical globular protein molecule of uniform surface properties. The protein-polysaccharide interaction parameter χs, obtained by fitting the model to experimental data for one molecular weight of dextran, was found to be 0.132 and 0.115 for ovalbumin and lysozyme, respectively. Solubilities of ovalbumin and lysozyme in dextran solutions of different molecular weights exhibited a shallow maximum at intermediate dextran concentrations and compared well with model predictions. Protein solubility was found to be very sensitive to protein-polysaccharide interactions and increase with more favorable protein-polysaccharide interactions (larger χs), less favorable polysaccharide-solvent interactions (larger χ), smaller size protein molecule, and lower molecular weight polysaccharide.

On Static Drainage of Protein-Stabilized Foams

Abstract: Publisher Summary Foam stability is intricately related to the kinetics of liquid drainage. Fundamental understanding of foam drainage is, therefore, important in order to characterize its stability. Foam ability and foam stability are important functional properties of proteins essential in many food formulations. Foam ability of protein solutions has been inferred through the experimental measurement of over-run. Bubbling, whipping, and shaking are the three different methods employed for foam formation. It is customary to infer the stability of foam from the transients of drainage and collapse. Several experimental techniques, such as static drainage, surface decay, half-life of foam, and half-life of drainage have been developed for this purpose. Extensive experimental investigations on the effect of different variables on the drainage and stability of protein-stabilized foams have been undertaken. Despite the considerable volume of work elucidating the qualitative effects of different variables, both on the formation and stability of foams, studies on quantitative prediction of foam drainage are limited. This chapter makes an effort to understand the static drainage of protein-stabilized foams.