Anna S. Antipova

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.

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.

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.

Surface activity at the planar interface in relation to the thermodynamics of intermolecular interactions in the ternary system: maltodextrin–small-molecule surfactant-legumin

We report on the effect of potato maltodextrins with variable dextrose equivalent (Paselli SA-2, SA-6 and SA-10) on the surface behavior at the air-water interface of the mixture: legumin+small-molecule surfactant. Distinct in nature small-molecule surfactants (model: sodium salt of capric acid, Na-caprate; and commercially important: a citric acid ester of monoglyceride, CITREM) have been under our consideration. The role of the structure of both of the maltodextrins and the 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, value of weight average molecular weight of the maltodextrins and the thermodynamics of the pair maltodextrin-solvent and maltodextrin-protein interactions from laser static light scattering. The combined data of mixing calorimetry and light scattering suggest some complex formation between the small-molecule surfactants and the maltodextrins. Predominantly hydrophobic interactions along with hydrogen bonding form the basis of the complexes. The effect of the maltodextrins on the thermodynamics of the protein heat denaturation and thereby on the protein conformational stability in the presence of the small-molecule surfactants has been studied by differential scanning calorimetry. The interrelation between the thermodynamics of intermolecular interactions in a bulk and the surface behavior at the planar air-water interface of the ternary systems (maltodextrin+legumin+small-molecule surfactant) has been elucidated by tensiometry. The effect of the maltodextrins on the surface activity of mixtures of legumin with the small-molecule surfactants is governed by the competitive in relation to the protein interactions with the small-molecule surfactants and a subsequent change in the thermodynamic properties of the both biopolymers, which are favorable to the ternary complex formation.

On the effect of calcium ions on the sticking behaviour of casein-coated particles in shear flow

Abstract The use of the particle scattering apparatus has been extended to investigate the effects of calcium ion addition on the aggregation of individual pairs of particles in a laminar shear field at a wall. In this case the particles are oil droplets in the size range 5–6 μm, stabilized by sodium caseinate in a buffers of ionic strength 0.05 mol dm−3 and pH 5–7, with Ca2+ concentrations varied between 0 and 20 mM. The aggregation, or sticking, of mobile droplets with one already irreversibly stuck to the wall was investigated over shear rates ranging from 0.25 to 12 s−1. The percentage of particle collisions that lead to sticking is reproducibly seen to increase as the pH is reduced from 7 to 5, in accordance with decreasing net charge on the molecules of caseinate, which when adsorbed presumably leads to reduced net electrostatic repulsion between droplets. Surprisingly, beyond Ca2+ concentrations of 5mM, the percentage of sticking does not markedly increase further (but even decreased, in some instances), in the pH range studied. However, this behaviour can be rationalized in terms of the competing effects of Ca2+ and pH on electrostatic and steric mechanisms of colloid stabilization, via changes in the aggregation of the caseinate and the probable changes in the thickness and stickiness of the adsorbed protein film.

Biopolymer nanovehicles for essential polyunsaturated fatty acids: Structure–functionality relationships

Design of stimuli-sensitive (i.e., smart) nano-sized delivery systems for nutraceuticals, having both a nutritional and pharmaceutical value, is very important for the formulation of novel functional food. Omega-3 and omega-6 polyunsaturated fatty acids (PUFAs) are among the most needed nutraceuticals for the maintenance of good health. It is medically proven that in order to get the best effect on the human health the weight ratio of ω-6/ω-3 PUFAs should be within the range between 1/1 and 5/1. Thus, our work was focused on the molecular design of the delivery systems based on the nano-sized complexes formed between covalent conjugate (sodium caseinate+maltodextrin (a dextrose equivalent=2)) and the combinations of polyunsaturated lipids, which are mutually complementary in the ω-6 and ω-3 PUFAs content: α-linolenic (ALA)+linoleic (LA) acids; liposomes of soy phosphatidylcholine (PC)+ALA; and micelles of soy lysophosphatidylcholine (LPC)+ALA. For such complex particles the high extent (>95%) of encapsulation of these all combinations of lipids by the conjugate was found along with both the high protection of the lipids against oxidation and their high solubility in an aqueous medium. To gain a better insight into such functionality of the complex particles a number of their structural (the weight-averaged molar weight, Mw; the radius of gyration, RG; the hydrodynamic radius, Rh; the architecture; the volume; the density; the ζ-potential; the microviscosity of both the bilayers of PC liposomes and LPC micelles), and thermodynamic (the osmotic second virial coefficient, A2, reflecting the nature and intensity of both the complex-complex and complex-solvent pair interactions) parameters were measured by a combination of such basic physico-chemical methods as static and dynamic multiangle laser light scattering, particle electrophoresis, atomic-force microscopy and electron spin resonance spectroscopy.