Solvation Of Micelles Research Articles

Reconstituted skim milk: effect of re-dilution after heating concentrated milk at different pH and temperatures

The change in particle size in milk is dependent on the concentration, pH and the temperature of heating. Many of the changes are attributed to a partial aggregation of the casein micelles during heating. κ-Casein dissociation and serum-phase whey protein levels increased with increasing milk concentration at each pH and temperature, whereas αS-casein/β-casein dissociation increased to a maximum at intermediate temperatures before decreasing and then increasing again. Small changes in non-sedimentable calcium and phosphate were observed. Casein micelle solvation decreased with increasing pH and milk concentration at temperatures above 80 °C. This decrease is related to the pH-dependent dissociation of κ-casein from the casein micelles and the extent of denatured whey protein in the serum phase. It is likely that the properties of milk could be manipulated by choosing appropriate milk concentrations pH and/or and heating conditions, even if the milk is subsequently diluted.

Contrasting effect of 1-butanol and 1,4-butanediol on the triggered micellar self-assemblies of C16-type cationic surfactants.

The self-assembly in aqueous solutions of three quaternary salt-based C16-type cationic surfactants with different polar head groups and identical carbon alkyl chain viz., cetylpyridinium bromide (CPB), cetyltrimethylammonium tosylate (CTAT), and cetyltriphenylphosphonium bromide (CTPPB) in the presence of 1-butanol (BuOH) and 1,4-butanediol (BTD) was investigated using tensiometry, 2D-nuclear Overhauser enhancement spectroscopy (2D-NOESY) and small angle neutron scattering (SANS) techniques. The adsorption parameters and micellar characteristics evaluated at 303.15 K distinctly showed that BuOH promotes the mixed micelle formation while BTD interfered with the micellization phenomenon. The SANS data fitted using an ellipsoid (as derived by Hayter and Penfold using the Ornstein-Zernike equation and the mean spherical approximation) and wormlike micellar models offered an insight into the micelle size/shape and aggregation number (Nagg) in the examined systems. The evaluated descriptors presented a clear indication of the morphology transition in cationic micelles as induced by the addition of the two alcohols. We also offer an investigation into the acceptable molecular interactions governing the differences in micelle morphologies, using the non-invasive 2D-NOESY technique and molecular modeling. The experimental observations elucidated from computational simulation add novelty to this work. Giving an account to the structural complexity in the three cationic surfactants, the molecular dynamics (MD) simulation was performed for CPB micelles in an aqueous solution of alcohols that highlighted the micelle solvation and structural transition, which is further complemented in terms of critical packing parameter (PP) for the examined systems.

Structure and solvation thermodynamics of asymmetric poly (acrylic acid)-b-polystyrene polyelectrolyte block copolymer micelle in water: Effect of charge density and chemical composition

Molecular structure and thermodynamic behavior of micelles formed by polyelectrolyte-neutral block copolymer chains, in particular polystyrene-b-poly(acrylic acid) (PS-b-PAA), in salt-free aqueous solution was studied via detailed explicit atomistic molecular dynamics simulations as a function of the copolymer composition (XPS) and the fractional charge (f) of ionizable PAA blocks. Micelle formation occurs via self-aggregation of PS-b-PAA copolymer chains with formation of PS core and PAA corona. The size of the PS core shows power-law dependence with respect to number of PS units per chain with an exponent 0.56 in agreement with scaling relations and experimental observations. The overall size of the micelle increases linearly with XPS. Increase in XPS results in a linear increase in micelle size and change in shape from spherical to prolate. The number of hydrogen bonds, pair correlation functions and various interatomic pair-wise energetic contributions to solvation enthalpy indicate favorable copolymer-water interaction. Micelle solvation is significantly influenced by hydrogen bonding interactions of carboxylic hydrogen atoms with water oxygens. Atom density profiles, solvation enthalpy and correlation functions of copolymer-Na+ ion pairs confirm the existence of micelle in osmotic regime, in agreement with mean-field theory.

Hydrophobicity enhancement in micelles of Triton X-165 by the presence of the cosolvent 2,2,2 trifluoroethanol (TFE)

This work focuses on the effect of 2,2,2-trifluoroethanol (TFE) on certain micellar properties of Triton X-165 (TX-165) in aqueous solutions. The results obtained from various experimental techniques are used to interpret the interactions in the systems studied. The added TFE has strong effect on lowering the cloud point (CP) in the solutions of TX-165. This effect is consistent with partial dehydration of the oxyethylene groups in the micelle. The decrease of both the critical micelle concentration (CMC) and the CP with the increase of TFE concentration is justified by the interaction between TFE molecule and the oxyethylene group of TX-165, by the low hydrogen bond ability of the hydroxyl oxygen atom of TFE and by the water structure maker effect of TFE. The micelle aggregation number determined by fluorescence decreases initially with the increase of TFE concentration and then increases for the highest TFE concentrations. Fluorescence quenching data indicate that about 45% of pyrene probe is accessible to the quencher (TFE). The results of viscosity are consistent with ellipsoidal shape of TX-165 micelles. The changes in the intrinsic viscosity with increasing TFE concentration may reflect changes in the solvation of micelles and conformational changes in the polar head groups in the micelle. These factors affect the packing of the monomers and the micelle aggregation number. The TFE cosolvent confers hydrophobicity to the micelles of TX-165.

Cloud-point extraction of bismuth (III) with nonionic surfactants in aqueous solutions

Two-aqueous phase extraction of bismuth (III) as a solute from its aqueous solutions was investigated using polyethoxylated alcohols (CiEj) as a biodegradable non-ionic surfactant. Cloud points of these surfactants were found to be functions of their concentrations and concentrations of additives. The concentration effect of non-ionic surfactants on the cloud point was determined when the phase diagrams of water-surfactant binary systems (C13E10 and C12E10) were being traced. According to the given surfactant concentration, the extracted solute at pH = 3 arrived at 86% and 45% for C12E10 and C13E10, respectively, in one step. Addition of inorganic salts can either increase or decrease the cloud points. For example, the addition of sodium chloride lowers the cloud points of surfactants. According to the optimal extraction conditions, the extraction mechanism is based on bismuth species – CiEj non-anionic surfactant micelle solvation.

Diffusion of an Ionic Drug in Micellar Aqueous Solutions

Supramolecular carriers such as micelles can be used to noncovalently bind drug molecules for pharmaceutical applications. However, these carriers can fundamentally affect diffusion-based drug transport due to host-guest coupled diffusion. We report a ternary interdiffusion study on an ionic drug in aqueous micellar solutions. Specifically, high-precision Rayleigh interferometry was used to determine the four multicomponent diffusion coefficients for the potassium naproxenate-tyloxapol-water ternary system at 25 degrees C and pH 7. In addition, we have measured drug solubility as a function of tyloxapol concentration. These measurements were used to characterize drug-surfactant thermodynamic interactions using the two-phase partitioning model. Furthermore, we propose a novel model on host-guest coupled diffusion that includes counterions. We show that quantitative agreement between model and experimental diffusion results can be achieved if the effect of micelle solvation on transport parameters is included in the model. This work represents an essential addition to our previous diffusion study on a nonionic drug and provides guidance for the development of accurate models of drug diffusion-based controlled release in the presence of nanocarriers.

Preliminary observations on the effects of milk fortification and heating on microstructure and physical properties of stirred yogurt

The aim of this work was to study how milk fortification and heating affect yogurt microstructure (micellar characteristics, protein network) and physical properties (viscosity, water-holding capacity (WHC), and graininess). Milk was fortified with skim milk powder (control), whey protein concentrate (WPC), caseinate, or a mixture of caseinate and whey protein. Two heat treatments were applied, giving average whey protein denaturation levels of 58% and 77%. For caseinate-enriched yogurts, the heating effect was negligible. When milk was enriched with WPC, heating led to a high level of cross-linking within the gel network. Heating increased yogurt viscosity and WHC, but also graininess. When milk was fortified with a blend of WPC and caseinate giving a whey protein-to-casein ratio of 0.20, the yogurt viscosity was greatly improved, while graininess was kept low. The results show a relationship between micelle solvation and yogurt microstructure, as well as micelle size in milk base and yogurt graininess.

Photophysical and light scattering studies on the aggregation behaviour of Triton X-100 in formamide—water mixed solvents

Micelle formation and structure of the non-ionic surfactant p-tert-octyl-phenoxy (9.5) polyethylene ether (Triton X-100) in mixed solvents consisting of water and formamide have been investigated. Changes in the critical micelle concentration of the surfactant upon the addition of formamide were examined by using the pyrene 1:3 ratio method. The observed increase in the critical micelle concentration was attributed to a rise in the solubility of the surfactant as the formamide content increased in the solvent system. Micelle structure parameters were obtained as a function of the co-solvent concentration by using combined static and dynamic light scattering measurements. It was found that the decrease in the micelle size, produced by the addition of formamide, is mainly due to a reduction in the mean aggregation number rather than to changes in the magnitude of the whole solvation of micelles. This fact was also supported by the observed trend in the partial specific volume of the TX-100 micelles, obtained by complementary density measurements. However, the postulated changes in the composition of the solvation layer of micelles were supported by the rise in both the surface area per head group and the cloud point of the surfactant. From the photophysical response of different fluorescent probes incorporated in the micellar phase, we obtained information on the changes in the microstructure of Triton X-100 micelles upon the addition of formamide. The pyrene 1:3 ratio index revealed an increasing micropolarity as the formamide content increases in the solvent system. On the other hand, studies based on both fluorescence polarization of coumarin 6 and intermolecular pyrene excimer formation have shown that the microviscosity of Triton X-100 decreases with the presence of co-solvent. These results were interpreted on the basis of considerable contact of the co-solvent with the inner region of the micelles.

Effect of SDS on Casein Micelles: SDS‐Induced Milk Gel Formation

ABSTRACT: The addition of sodium dodecyl sulfate (SDS) during skim‐milk reconstitution contributed to a modification of hydrophobic interactions and, consequently, to change in the micellar structure. SDS‐induced modifications in casein micelles were investigated by biochemical measurements (soluble mineral and protein analyses, granulometric and electrokinetic potential measurements, and casein micelle solvation). SDS induced micellar κ‐casein dissociation and caused a decrease in steric, hydration, and electrostatic repulsive forces between casein micelles and as a result altered micellar stability. Consequently, SDS‐modified micelle aggregation occurred. Mineral analysis indicated that Ca, PO43‐ and Mg partitioning between aqueous phase and curd is similar, suggesting a possible bridging mechanism via minerals and SDS molecules.

Hydratation des micelles de caséine et structure fractale des agrégats et des gels de lait

Casein micelle solvation and fractal structure of milk aggregates and gels. Milk gela- tion by combined action of acidification and rennetting constitutes the first stage of cheese making. The effects of pH on rennetting milk are studied in natural milk, pH 6.58 (the initial pH) to pH 5.60. The methodology used to study the structure of aggregates and gels is based upon the fractal theory. A relationship is observed between the hydration of casein particles, the structure of milk aggre- gates and gels, and the rheological properties of gels. casein / fractal / gelation / milk / solvation

Effect of the A and B variants of both alpha s1- and kappa-casein on bovine casein micelle solvation and kappa-casein content.

Casein micelle solvation, a micelle characteristic that is sensitive to many factors, has been measured by a centrifugation technique at 30 degrees C for a series of uncooled fresh skim milks at pH 6.3, 6.6, 6.9 and 7.1. The relative alpha s-(alpha s1-plus alpha s2-), beta- and kappa-casein contents of all centrifuge pellets and supernatants were determined by a standardized electrophoretic method. The calcium and phosphate contents of a number of the pellets and milk samples were also determined. Solvation of micelles from milks with various genetic variants of beta-lactoglobulin (A and B), alpha s1-casein (A and B) and kappa-casein (A and B) was often found to be lower for milks containing either the B variant of alpha s1-casein or the A variant of kappa-casein. It was also found that these two variant caseins were associated with a lower kappa-casein. It was also found that these two variant caseins were associated with a lower kappa-casein content of the milks and the micelles, which is consistent with the lower solvation as kappa-casein is associated with smaller micelle size and greater solvation. The solvations also seemed to increase during the lactation period. It is possible that some of the other features of milk and its products that have been ascribed to the differences in functional character between the A and B variants of alpha s1-casein may be partly caused by the increased level of kappa-casein. The reason for the association of the A variant of alpha s1-casein with higher concentrations of kappa-casein (and micelle solvation) is not obvious but possibly the haplotype alpha s1-casein A, beta-casein A1, kappa-casein A contains a controlling sequence in the chromosomal DNA that enhances expression of the kappa-casein gene.

Beneficial and Adverse Effects of Water-Protein Interactions in Selected Dairy Products

Water-protein interaction is an important factor in the dehydration, rehydration, solubility, viscosity, gelation, heat stability, browning reaction, and other important properties of dairy products over a wide range of water activities. The ability of the major milk proteins, e.g., casein micelles and whey proteins, to interact with and immobilize water in dehydrated, solution, and gelled milk product systems is largely dependent upon their physicochemical state. This latter phenomenon is largely a function of pH; temperature; protein concentration: total solids concentration; ionic composition; addition of Ca-chelating compounds, stabilizer gums and sugars; and by thermal processing treatments that promote whey protein denaturation, aggregation, and interaction with casein micelles. Examples of the role of water and protein interactions in dairy products are illustrated by casein micelle solvation and voluminosity; whey protein aggregation in heated whey systems; casein micelle aggregation and syneresis in cheese manufacture; viscosity and gelation of sterile milk concentrates; rehydration, solvation, solubility, and functionality of casein, caseinate, whey protein concentrate, and milk powder in formulated food products; viscosity, body, and texture of ice cream and frozen desserts; and viscosity and gelation of cultured dairy products.

Size Distribution and Solvation of Casein Micelles in Milk Containing αs1-Casein A

We compared the size distribution and solvation of micelles in skim milk from a cow homozygous for αs1-casein A with the properties of micelles from pooled skim milk. Hydrodynamic radii of the micelles were measured by inelastic laser light scattering, and a cumulative distribution curve of the weight fraction of micelles with radii less than or equal to a given value was constructed. Micelle solvations were measured from voluminosities measured viscometrically. The distribution of micelle sizes is strikingly different in αs1-casein A milk and in pooled milk, with the former having both much larger micelles and a greater proportion of small micelles. We found no significant differences in solvation of micelles from αs1-casein A or pooled skim milks.