Maria G. Semenova

Salt stability of casein emulsions

We present a comparison of the salt stability of oil-in-water emulsions prepared separately with αauthor-casein, β-casein and sodium caseinate at low protein/oil ratios. Measurements have been made of changes in average droplet sizes, creaming rates, and bulk and interfacial rheology over the pH range 5.5–7.0 and ionic strength range 0.01–0.20 M. Static light-scattering has also been used to determine second virial coefficients in dilute casein solutions under similar conditions of pH and ionic strength. It has been demonstrated that αauthor-casein emulsions become flocculated at ionic strengths of 0.1 M and above, whereas emulsions made with β- casein or sodium caseinate remain stable. The emulsion stability behaviour is interpreted in terms of (i) recent theoretical calcula- tions of interactions between adsorbed casein layers and (ii) the experimentally determined thermodynamic interaction parameters of the caseins in bulk solution

Effect of sucrose on molecular and interaction parameters of sodium caseinate in aqueous solution: relationship to protein gelation

Abstract The effect of sucrose on molecular and interaction parameters of sodium caseinate in aqueous medium has been investigated using static and dynamic multi-angle laser light scattering over a wide range of sucrose concentration (from 10 to 78 w/v%) and pH values (from 7.0 to 3.5). Measurements have been made of the molar mass, the radius of gyration, the hydrodynamic radius, and the second virial coefficient of sodium caseinate in aqueous solution. Pronounced dissociation of sodium caseinate sub-micelles 1 was found in the presence of sucrose at a pH above the proteins isoelectric point. The effect of sucrose at a pH near the isoelectric point is very different. This is reflected in the pronounced increase in molar mass, radius of gyration, and the difference between the radius of gyration and the hydrodynamic radius. It was found that the extent of the protein association, caused by the presence of sucrose, is a key factor contributing to the hydrophobic–hydrophilic balance of the protein surface, and hence to the thermodynamic affinity of the caseinate sub-micelles for the aqueous medium and for each other. Analysis of light-scattering data using structure-sensitive plots shows a clear transition from Gaussian to wormlike chain/rod behaviour for sodium caseinate on pH lowering. Apparent relationships between the effects of sucrose on the self-association of sodium caseinate and a marked enhancement of the viscoelasticity of acid-induced casein gels have been revealed. Moreover, the dissociation of sodium caseinate sub-micelles is in excellent agreement with the more homogeneous microstructure of acid-induced protein gels in the presence of sucrose as detected by confocal laser scanning microscopy. We discuss likely molecular mechanisms underlying the observed effects of sucrose on the interactions and rheology in acidified caseinate systems.

The effect of sucrose on the thermodynamic properties of ovalbumin and sodium caseinate in bulk solution and at air–water interface

Abstract This paper presents a study of the effect of sucrose on the molecular parameters and thermodynamic properties in a bulk aqueous medium and at the air–water interface for two proteins differing both in nature and structure, that is Na-caseinate and ovalbumin. To get more insight into the molecular nature of the effect of sucrose, mixing calorimetry, light scattering and tensiometry measurements have been made under different pHs (7.0 and 5.5) and temperatures (20–55°C) at an ionic strength of 0.005 mol dm −3 . Combined temperature dependencies of light scattering and mixing calorimetry testify to hydrogen bonding (sucrose-protein and/or sucrose-water) as being the primary basis of the effect of sucrose on the molecular and thermodynamic properties of the proteins in the bulk and at interface of an aqueous medium. At pH 7.0, in the case of ovalbumin, the interaction with sucrose causes an increase in the protein hydrophilicity in the bulk aqueous medium followed by a decrease in the protein surface activity, whilst for Na-caseinate, there is an increase in the protein hydrophobicity due to Na-caseinate micelle dissociation and, consequently, to an increase in the protein surface activity. Lowering the pH to 5.5, accompanied by a strengthening of the competition between less charged proteins and sucrose for water molecules, induces a rise in the protein hydrophobic aggregation in the bulk. The special features of the latter process are probably mainly responsible for the changes in the surface activity of the proteins under influence of sucrose at pH 5.5.

Food protein interactions in sugar solutions

Over the past few years a growing interest has occurred in the effect of small molecules, specifically sugars, on protein structural functionality in compositionally complex food systems. A number of surprising phenomena, requiring further systematic investigations, have been revealed in protein/sugar systems. By now, the attempts, deserving of consideration, are being made in more penetrating understanding the molecular mechanisms, underlying a marked change in thermal stability, conformation, self association, surface activity and bulk network formation of food proteins in sugar solutions. These insights have important implications for creation of the desirable structure and physicochemical properties of sweetened food products.

On relationships between molecular structure, interaction and surface behavior in mixture: small-molecule surfactant+protein

We report on the effect of distinct in nature small-molecule surfactants (model, a sodium salt of capric acid, Na-caprate; and commercially important, a citric acid ester of monoglyceride, CITREM; a sodium salt of stearol-lactoyl lactic acid, SSL (Na(+)); polyglycerol ester, PGE (080)) on molecular properties in a bulk and at the air-water interface of globular legumin and random-coiled micellar sodium caseinate. The role of the structure of both proteins and small-molecule surfactants in the effect studied has been elucidated by measurements in a bulk aqueous medium of the enthalpy of their interaction from mixing calorimetry, the change in value of weight average molecular weight of the proteins and the thermodynamics of the pair protein-protein interactions from laser static light scattering as well as, in addition, by measurements of the change in hydrodynamic radius for micellar sodium caseinate from laser dynamic light scattering. The effect of the small-molecule surfactants on the thermodynamics of the protein heat denaturation and thereby on the protein conformational stability has been studied by differential scanning calorimetry in the case of globular legumin. The interrelation between the effects of the small-molecule surfactants on the properties of the proteins in a bulk and at the planar air-water interface has been elucidated by tensiometry. The combined data of mixing calorimetry, differential scanning calorimetry and laser light scattering suggest some complex formation between the small-molecule surfactants and the proteins in a bulk aqueous medium. Predominantly hydrophobic interaction along with electrostatic and hydrogen bonding form the basis of the complex formation. The found effect of the small-molecule surfactants on the surface activity of their mixtures with proteins is governed primarily by both the extent of the protein association, resulting in specific hydrophobicity/hydrophilicity of the surface of the protein associates, and the specific protein conformational stability, for the globular protein, produced by the interaction between the proteins and the small-molecule surfactants.

The influence of dextran on the interfacial pressure of adsorbing layers of 11S globulin vicia faba at the planar n-decane/aqueous solution interface

Abstract The influence of dextran on the interfacial pressure of adsorbing layers of legumin (11S globulin vicia faba ) at the planar n-decane/aqueous solution interface was studied under conditions of thermodynamic compatibility and incompatibility between these biopolymers. The thermodynamic incompatibility of legumin with dextran in the bulk aqueous solution leads to an increase in the interfacial pressure of the adsorbing layers of legumin. This effect may be caused by the excluded volume effect between molecules of the biopolymers in the bulk aqueous solution. Opposite effects are observed under conditions of thermodynamic compatibility between these biopolymers. In the latter case they may be related to the intensification of thermodynamically favourable interactions of legumin with dextran molecules in the bulk aqueous solution.

The influence of incompatibility on the formation of adsorbing layers and dispersion of n-decane emulsion droplets in aqueous solution containing a mixture of 11S globulin from Vicia faba and dextran

Abstract The interfacial surface area and the degree of protein adsorption has been compared after 24 h of emulsion storage for an emulsion of decane in an aqueous medium containing 11S globulin from Vicia faba (legumin) alone and a mixture of this protein with dextran. The investigation has been carried out both under the conditions of biopolymer thermodynamic incompatibility in 0.1 mol/dm 3 NaCl, pH 7.8 and 25°C and thermodynamic compatibility in 0.01 mol/dm 3 NaCl, pH 7.8, 25°C. We have found significant differences between the studied emulsion characteristics for emulsions containing protein alone and mixtures of protein and dextran in the case of biopolymer thermodynamic incompatibility. These differences are found to be highly dependent on the phase state and quantitative composition of the biopolymer mixture in the aqueous continuous phase.

INFLUENCE OF MALTODEXTRINS WITH DIFFERENT DEXTROSE EQUIVALENT ON THE THERMODYNAMIC PROPERTIES OF LEGUMIN IN A BULK AND AT THE AIR-WATER INTERFACE

Abstract This paper presents the influence of the potato maltodextrins with different dextrose equivalent (DE 2, 6 and 10) on the legumin thermodynamic properties in the bulk aqueous medium and at the air–water interface both in the simple mixed solutions and under the covalent complex (conjugate) formation (by the Maillard reaction), at pH 7.0 and ionic strength of 0.05 mol dm−3. The weak net attractive interaction between legumin and maltodextrin has been found in an aqueous medium by both the light scattering and the mixing calorimetry methods. On the basis of both the mixing and differential scanning calorimetry data a hydrogen bonding is supposed to be fundamental for this interaction. It was found that these attractive interactions produced an increase in the protein hydrophilicity and consequently a decrease in the protein surface activity. The effect was more pronounced for the maltodextrin with the largest dextrose equivalent (DE 10). The covalent complexation between legumin and maltodextrin induced the change of the fine hydrophobic–hydrophilic balance in the protein globule due to both addition of the hydrophilicity of the covalently attached polysaccharide and the partial protein unfolding as a result of the such kind of attachment. The combined data of tensiometry, light scattering, mixing and differential scanning calorimetry demonstrated the importance of the maltodextrin polymerization (DE) in controlling both the protein hydrophilicity (thermodynamic affinity for the aqueous phase) and surface activity.

Light scattering and thermodynamic phase behavior of the system 11S globulin-κ-carrageenan-water

Abstract The thermodynamic incompatibility of 11S globulin ( Vicia faba ) and the sodium form of k-carrageenan has been studied by measurements of the phase behavior at moderate to high concentrations and by light scattering on dilute solutions below the separation threshold. The two approaches provide consistent information. The second virial coefficient obtained by light scattering for the different types of pair interactions between macromolecules [protein-protein ( A 22 ), polysaccharide-polysaccharide ( A 44 ) and protein-polysaccharide ( A 24 )] indicates the possibility of phase separation ( A 24 ) due to mutual exclusion forces which exist in the solution for these biopolymer pairs. The nature (but not magnitude) of these forces is independent of the conformation of κ-carrageenan. The temperature dependence of A 24 suggests entropie and enthalpic contributions of comparable magnitude. The general character of the water distribution between coexisting phases in this system is consistent with the relative hydrophilicities of the two polymers. Helical conformations of κ-carrageenan give rise to increased thermodynamic incompatibility presumably because of increased excluded volume effects.

Effect of maltodextrins on the surface activity of small-molecule surfactants

We report on the effect of commercially important polysaccharides (maltodextrins with variable dextrose equivalent (Paselli SA-2, MD-6 and MD-10) on the surface activity at the air–water interface of small-molecule surfactants (sms), possessing different hydrophobic–lipophilic balance ((SSL (Na+), the main component is a sodium salt of stearol–lactoyl lactic acid, and PGE (080), polyglycerol ester of C18 fatty acid), and widely used in food products. A marked change of the surface activity of sms was found in the presence of maltodextrins by tensiometry. The combined data of laser multiangle light scattering and mixing calorimetry have suggested that this result is governed by specific complex formation between maltodextrins and sms in aqueous medium. Measurements have been made of the molar mass, the second virial coefficient and the enthalpy of intermolecular interactions in aqueous solutions. The implication of a degree of polymerization of maltodextrins in this phenomenon was shown. The interrelation between the molecular parameters of the formed complexes and their surface activity at the air–water interface has been revealed and discussed.