Showing papers by "Ganesan Narsimhan published in 2008"

Characterization of secondary and tertiary conformational changes of beta-lactoglobulin adsorbed on silica nanoparticle surfaces.

Abstract: Nanoparticles possess unique properties as a result of their large surface area per unit volume and therefore can be functionalized by the immobilization of enzymes for a variety of biosensing applications. Changes in the tertiary conformation of beta-lactoglobulin adsorbed on 90 nm silica nanoparticles with time were inferred using tryptophan fluorescence and Fourier transform infrared spectroscopy (FTIR) for different surface concentrations, temperature, pH, ionic strength, and 2,2,2-trifluoroethanol (TFE) and dithiothreitol (DTT) concentrations. Rapid initial unfolding followed by a much slower rate at longer times was observed, with the extent of unfolding being higher at lower surface concentrations, higher ionic strengths, higher temperature, higher TFE and DTT concentrations, and pI. The effect of temperature on the unfolding of adsorbed protein on the nanoparticle surface was similar to that in the bulk even though the extent of unfolding was higher for adsorbed protein molecules. The results of the extent of change in tertiary conformation using FTIR as indicated by the change in the ratio of amide II'/amide I were consistent with those obtained by tryptophan fluorescence whereas the rates of conformational changes given by FTIR were found to be much faster. Circular dichroism (CD) spectra showed that altering the surface concentration by itself did not change the secondary structure of beta-lactoglobulin on the surface. TFE was found to increase the alpha helix content at the expense of the fraction of the beta sheet, whereas the beta sheet was converted to an unordered conformation in the presence of DTT.

Guidelines for Processing Emulsion-Based Foods

Abstract: Emulsions are dispersions of one liquid into the second immiscible liquid in the form of fine droplets. Emulsions can be classified as either oil-in-water or water-in-oil emulsions depending on whether oil or water is the dispersed phase. Milk, cream and sauces are some examples of oil-in-water emulsions whereas butter and margarine are examples of water-in-oil emulsions. This chapter discusses the physical principles that are involved in the formation and stability of food emulsions. Prediction of droplet size distribution for food emulsions that are formed in colloid mill (predominantly by shear) and high pressure homogenizer (predominantly by turbulence) in terms of operating conditions in these equipments is discussed. The fluid mechanics of droplet breakage and coalescence in shear and turbulence are discussed and applied to the formation of food emulsions and to the prediction of drop size. The role of proteins and surfactants on the stability of emulsions is discussed. The effect of interfacial dilatational and shear elasticity on thin film stability and drop coalescence is described. Some recent results of a new technique, layer by layer deposition, to improve the shelf life of emulsions by using alternate layers of proteins and polysaccharides is presented. Thermodynamics and phase behavior of microemulsions and its application to food is discussed.

Characterization of the effect of food emulsifiers on contact angle and dispersibility of lipid coated neutrally buoyant particles

Abstract: To investigate the dispersibility of lipid coated particles in food suspensions, contact angle of lipid surface at different pH, salt concentration, protein concentration, surfactant type and concentration was measured. Contact angle decreased with an increase in the emulsifier conecentration when the concentration was low, and reached a fairly constant value at higher concentrations. Whey protein was more efficient compared to other emulsifiers and decreased the contact angle from 100° to 40° at a concentration of 0.5 g/L or higher in water. Tween 20 was more efficient than other tween emulsifiers and it decreased the contact angle from 100° to 67° at a concentration of 1 g/L. Surface pressure area isotherm of 150-80SV soybean oil coated particles at an air–water interface was obtained using Langmuir trough. Contact angle of the particles at the air–liquid interface, inferred from the critical surface pressure in the isotherm, agreed well with the contact angle of planar surface obtained using goniometer. Dispersibility of 150-80SV soybean oil coated particles in aqueous solution was characterized by measuring the bulk particle concentration upon suspension. At pH 2.5, 5 g/L whey protein in the presence of 0.5 mol/L NaCl in 50 g/L citrate buffer showed highest dispersibility.