Showing papers by "Ganesan Narsimhan published in 2007"
TL;DR: In this paper, low-field NMR spin-spin relaxation (T2) measurements were used to study the denaturation and aggregation of β-lactoglobulin (β-LG) solutions of varying concentrations (1−80 g L−1) as they were heated at temperatures ranging from ambient up to 90 °C.
Abstract: Low-field nuclear magnetic resonance (NMR) spin–spin relaxation (T2) measurements were used to study the denaturation and aggregation of β-lactoglobulin (β-LG) solutions of varying concentrations (1–80 g L−1) as they were heated at temperatures ranging from ambient up to 90 °C. For concentrations of 1–10 g L−1, the T2 of β-LG solutions did not change, even after heating to 90 °C. A decrease in T2 was only observed when solutions having higher concentrations (20–80 g L−1) were heated. Circular dichroism (CD) spectroscopy and fluorescence tests using the dye 1-anilino-8-naphthalene sulfonate (ANS) on 0.2 and 1 g L−1 solutions, respectively, indicated there were changes in the protein's secondary and tertiary conformations when the β-LG solutions reached 70 °C and above. In addition, dynamic light scattering (DLS) showed that protein aggregation occurred only at concentrations above 10 g L−1 and for heating at 70 °C and above. The hydrodynamic radius increased as T2 decreased. When excess 2-mercaptoethanol was added, the changes in both T2 and the hydrodynamic radius followed the same trend for all β-LG protein concentrations between 1 and 40 g L−1. These observations led to the conclusion that the changes in T2 were due to protein aggregation, not protein unfolding. Copyright © 2007 Society of Chemical Industry
30 citations
TL;DR: Steam sterilization of xanthan gum solutions at 121°C caused a decrease in the helix conformation as well as the molecular weight distribution with a corresponding increase in the coil structure, suggesting a two-step mechanism of disentanglement followed by degradation with the first step being predominant at higher concentrations.
Abstract: Steam sterilization of xanthan gum solutions at 121 degrees C caused a decrease in the helix conformation as well as the molecular weight distribution with a corresponding increase in the coil structure. The effect was directly related to the exposure time and inversely to the xanthan gum concentration, thus suggesting a two-step mechanism of disentanglement followed by degradation with the first step being predominant at higher concentrations. Mark-Houwink exponent of 0.9002 for the intrinsic viscosity of xanthan gum compared favorably with reported values in the literature. The model for intrinsic viscosity of a free draining coil yielded an expansion coefficient of 1.2 (independent of molecular weight) and a root mean square radius of unperturbed chain in the range of 189.5-368 nm. The root mean square unperturbed chain length increased with molecular weight without reaching an asymptotic value, thus indicating that the xanthan molecule behaved as a stiff chain.
7 citations
TL;DR: A generalized formalism for the rupture of a draining foam film due to imposed random pressure fluctuations, modeled as a Gaussian white noise, is presented and it is shown that a composite rupture time distribution combining short time simulation results with equilibrium distribution is a good approximation.
Abstract: A generalized formalism for the rupture of a draining foam film due to imposed random pressure fluctuations, modeled as a Gaussian white noise, is presented in which the flow inside the film is decomposed into a flow due to film drainage and a flow due to imposed perturbation. The evolution of the amplitude of perturbation is described by a stochastic differential equation. The rupture time distribution is calculated from the sample paths of perturbation amplitude as the time for this amplitude to equal one-half the film thickness and is calculated for different amplitudes of imposed perturbations, film thicknesses, electrostatic interactions, viscosities, and interfacial mobilities. The probability of film rupture is high for thicker films, especially at smaller times, as a result of faster growth of perturbations in a thick film due to a smaller disjoining pressure gradient. Larger viscosity, larger surface viscosity, higher Marangoni number, and smaller imposed pressure fluctuation result in slower growth of perturbation of a draining film, thus leading to larger rupture time. It is shown that a composite rupture time distribution combining short time simulation results with equilibrium distribution is a good approximation.
5 citations