Showing papers by "Ganesan Narsimhan published in 2013"

Effect of thermal behavior of β-lactoglobulin on the oxidative stability of menhaden oil-in-water emulsions.

Abstract: This study reports how emulsion oxidative stability was affected by the interfacial structure of β-lactoglobulin due to different heat treatments. Four percent (v/v) menhaden oil-in-water emulsions, stabilized by 1% (w/v) β-lactoglobulin at pH 7, were prepared by homogenization under different thermal conditions. Oxidative stability was monitored by the ferric thiocyanate peroxide value assay. Higher oxidative stability was attained by β-lactoglobulin in the molten globule state than in the native or denatured state. From atomic force microscopy of β-lactoglobulin adsorbed onto highly ordered pyrolytic graphite in buffer, native β-lactoglobulin formed a relatively smooth interfacial layer of 1.2 GPa in Young's modulus, whereas additional aggregates of similar stiffness were found when β-lactoglobulin was preheated to the molten globule state. For denatured β-lactoglobulin, although aggregates were also observed, they were larger and softer (Young's modulus = 0.45 GPa), suggesting increased porosity and thus an offset in the advantage of increased layer coverage on oxidative stability.

Effect of interaction with coesite silica on the conformation of Cecropin P1 using explicit solvent molecular dynamics simulation

Abstract: Explicit solvent molecular dynamics (MD) simulation was carried out for the antimicrobial peptides (i) Cecropin P1 and C-terminus cysteine modified Cecropin P1 (Cecropin P1 C) in solution, (ii) Cecropin P1 and Cecropin P1 C adsorbed onto coesite −Si − O − and Si − O − H surfaces, and (iii) Cecropin P1 C tethered to coesite −Si − O − surface with either (PEO)3 or (PEO)6 linker. Low energy structures for Cecropin P1 and Cecropin P1 C in solution consists of two regions of high α helix probability with a sharp bend, consistent with the available structures of other antimicrobial peptides. The structure of Cecropin P1 C at low ionic strength of 0.02 M exhibits two regions of high α helix probability (residues AKKLEN and EGI) whereas at higher ionic strength of 0.12 M, the molecule was more compact and had three regions of higher α helix probability (residues TAKKLENSA, ISE, and AIQG) with an increase in α helical content from 15.6% to 18.7% as a result of shielding of electrostatic interactions. In the presence of Cecropin P1 C in the vicinity of −Si − O − surface, there is a shift in the location of two peaks in H − O − H density profile to larger distances (2.95 A and 7.38 A compared to 2.82 A and 4.88 A in the absence of peptide) with attenuated peak intensity. This attenuation is found to be more pronounced for the first peak. H-bond density profile in the vicinity of −Si − O − surface exhibited a single peak in the presence of Cecropin P1 C (at 2.9 A) which was only slightly different from the profile in the absence of polypeptide (2.82 A) thus indicating that Cecropin P1 C is not able to break the H-bond formed by the silica surface. The α helix probability for different residues of adsorbed Cecropin P1 C on −Si − O − surface is not significantly different from that of Cecropin P1 C in solution at low ionic strength of 0.02 M whereas there is a decrease in the probability in the second (residues ISE) and third (residues AIQG) α helical regions at higher ionic strength of 0.12 M. Though the total α helical content of adsorbed and tethered Cecropin P1 C was lower for hydrophilic Si − O − H surface compared to hydrophobic −Si − O −, hydrophobicity of the surface did not significantly affect the α helix probability of different residues. The conformation of Cecropin P1 C in solution is closer to that of tethered to −Si − O − with (PEO)6 than that tethered with (PEO)3 as a result of less surface interaction of tethered polypeptide with a longer linker. At low ionic strength of 0.02 M, tethered Cecropin P1 C to −Si − O − is found to exhibit lower α helix (13.0%) compared to adsorbed (15.6%) for (PEO)3 linker with this difference being insignificant for larger (PEO)6 linker molecule. Experimental values of % α helix inferred from circular dichroism spectra of Cecropin P1 in solution as well as in adsorbed state on silica surface compared well with the corresponding values obtained from MD simulation thereby validating the simulation procedure.

A mechanistic model for baking of unleavened aerated food

Abstract: A mechanistic model for baking of unleavened aerated food is proposed. The aerated food was assumed to consist initially of uniformly distributed same sized bubbles. The liquid medium was assumed to be Newtonian. Bubble coalescence, nucleation of bubbles and formation of interconnected channels were neglected. Unsteady state heat conduction and moisture diffusion equations were solved to obtain the evolution of temperature, moisture and air volume fraction profiles as well as cake rise. Consistent with experimental observations reported in the literature, the height of aerated food was found to increase with time, reach a maximum and decreased at longer times. The cake rise was found to be faster and larger at higher oven temperatures and for aerated food of higher initial air fraction and larger sugar content. The model predictions of cake rise agreed fairly well with the experimental data of Pernell, Luck, Foegeding, & Daubert, 2002 for fitted initial air volume fractions with the agreement being better at longer times for decreasing air volume fractions. The calculated air volume fraction profiles indicated an expanded inner region of more or less uniform density and a denser surface crust region whose thickness increased with baking time.