Interfacial composition and stability of emulsions made with mixtures of commercial sodium caseinate and whey protein concentrate

The interfacial composition and the stability of oil-in-water emulsion droplets (30% soya oil, pH 7.0) made with mixtures of sodium caseinate and whey protein concentrate (WPC) (1:1 by protein weight) at various total protein concentrations were examined. The average volume-surface diameter (d₃₂) and the total surface protein concentration of emulsion droplets were similar to those of emulsions made with both sodium caseinate alone and WPC alone. Whey proteins were adsorbed in preference to caseins at low protein concentrations (<3%), whereas caseins were adsorbed in preference to whey proteins at high protein concentrations. The creaming stability of the emulsions decreased markedly as the total protein concentration of the system was increased above 2% (sodium caseinate >1%). This was attributed to depletion flocculation caused by the sodium caseinate in these emulsions. Whey proteins did not retard this instability in the emulsions made with mixtures of sodium caseinate and WPC.     

Influence of κ-carrageenan on the properties of a protein-stabilized emulsion

We report on the influence of κ-carrageenan (κ-CAR) on the surface activity of bovine serum albumin (BSA) and on the properties of BSA-stabilized oil-in-water emulsions. Surface tension data at low ionic strength indicate an electrostatic interaction at neutral pH which becomes much stronger at pH 6. The effect of the attractive BSA–κ-CAR interaction on the state of aggregation and creaming stability of protein-stabilized emulsions (20 vol% n-tetradecane, 1.7 wt% BSA, 5 mM) has been investigated at three pH values. At pH 6 the system behaviour is interpreted in terms of bridging flocculation leading to an emulsion droplet gel network over a certain limited polysaccharide concentration range. While the trend of behaviour is qualitatively similar to that reported recently for equivalent BSA+ι-carrageenan (ι-CAR) solutions and emulsions, the BSA–κ-CAR interaction is clearly weaker than the BSA–ι-CAR interaction under similar pH and ionic strength conditions. This means that a higher polysaccharide content is required to induce flocculation in systems containing κ-CAR, and also that the resulting emulsion gel network is weaker. The behaviour is consistent with the lower density of charged sulfate groups on the κ-CAR as compared with the ι-CAR.     

Thermoreversible gelation of caseinate-stabilized emulsions at around body temperature

We have formulated food-grade protein-stabilized emulsions (30 vol% vegetable oil, 4 wt% sodium caseinate) which exhibit heat-induced gelation at around body temperature. Prior to emulsification, these systems have the continuous phase pH adjusted to between 6.8 and 5.3 and various concentrations of calcium chloride added. The minimum CaCl₂ content required to cause gelation on heating decreases with decreasing pH, and the gelation temperature also decreases with decreasing pH. Under certain conditions the small-deformation rheological change associated with the heat-induced gelation has been found to be reversible on back-cooling to ambient. The systems have also been studied with regards to viscometry and phase separation. Emulsion compositions associated with depletion flocculation by excess non-adsorbed protein are shown to be sensitive to both the ionic calcium content and the pH.     

Neutron reflectivity study of the competitive adsorption of β-casein and water—soluble surfactant at the planar air-water interface

Application of the technique of specular neutron reflection to the study of adsorbed layer structure is illustrated for the case of β-casein at the air—water interface in the presence and absence of nonionic water—soluble surfactant C₁₂E₆. Guinier analysis of reflectivity data for a 5 × 10⁻³ wt% solution of pure β-casein in air-contrast-matched water (8 vol% D₂O) at pH 7.0 gives a time-independent adsorbed amount of 2.05 ± 0.10 mg/m2 and an adsorbed layer thickness of 1.65 ± 0.07 nm; these values are found to increase quite substantially as the pH is reduced towards the protein's isoelectric point. In the presence of surfactant the loss of reflectivity is a direct measure of protein displacement from the interface because the hydrogenated surfactant is almost contrast matched to the aqueous phase. At a C₁₂E₆ concentration in the range 2–2.5 × 10⁻⁴ wt% (surfactant: protein molar ratio, R ≈ 2.2), there is roughly half the protein lost from the interface but little change in adsorbed layer thickness as inferred from the slopes of the Guinier plots. Protein is effectively completely removed from the surface for R 10. These results are in semi-quantitative agreement with complementary competitive adsorption data for β-casein in soya oil-in-water emulsions.     

Improvement of stability of oil-in-water emulsions containing caseinate-coated droplets by addition of sodium alginate

ABSTRACT:  The potential of sodium alginate for improving the stability of emulsions containing caseinate-coated droplets was investigated. One wt% corn oil-in-water emulsions containing anionic caseinate-coated droplets (0.15 wt% sodium caseinate) and anionic sodium alginate (0 to 1 wt%) were prepared at pH 7. The pH of these emulsions was then adjusted to 3.5, so that the anionic alginate molecules adsorbed to the cationic caseinate-coated droplets. Extensive droplet aggregation occurred when there was insufficient alginate to completely saturate the droplet surfaces due to bridging flocculation, and when the nonadsorbed alginate concentration was high enough to induce depletion flocculation. Emulsions with relatively small particle sizes could be formed over a range of alginate concentrations (0.1 to 0.4 wt%). The influence of pHs (3 to 7) and sodium chloride (0 to 500 mM) on the properties of primary (0 wt% alginate) and secondary (0.15 wt% alginate) emulsions was studied. Alginate adsorbed to the droplet surfaces at pHs 3, 4, and 5, but not at pHs 6 and 7, due to electrostatic attraction between anionic groups on the alginate and cationic groups on the adsorbed caseinate. Secondary emulsions had better stability than primary emulsions at pH values near caseinate's isoelectric point (pHs 4 and 5). In addition, secondary emulsions were stable up to higher ionic strengths (< 300 mM) than primary emulsions (<50 mM). The controlled electrostatic deposition method utilized in this study could be used to extend the range of application of dairy protein emulsifiers in the food industry.     

Effect of Aqueous Phase Composition on Stability of Sodium Caseinate/Sunflower oil Emulsions

The aim of the present work was to investigate the effect of aqueous phase composition on the stability of emulsions formulated with 10 wt% sunflower oil as fat phase. Aqueous phase was formulated with 0.5, 2, or 5 wt% sodium caseinate, or sodium caseinate with the addition of two different hydrocolloids, xanthan gum or locust bean gum, both at 0.3 or 0.5 wt% level or sodium caseinate or with addition of 20 wt% sucrose. Emulsions were processed by Ultra-Turrax and then further homogenized by ultrasound. Creaming and flocculation kinetics were quantified by analyzing the samples with a Turbiscan MA 2000. Emulsions were also analyzed for particle size distribution, microstructure, viscosity, and dynamic surface properties. The most stable systems of all selected in the present work were the 0.3 or 0.5 wt% XG or 0.5 wt% LBG/0.5 wt% NaCas coarse emulsion and the 20 wt% sucrose/5 wt% NaCas fine emulsion. Surprisingly, coarse emulsions with the lower concentration of NaCas, which had greater D _4,3, were more stable than fine emulsions when the aqueous phase contained XG or LBG. In these conditions, the overall effect was less negative bulk interactions between hydrocolloids and sodium caseinate, which led to stability. Sugar interacted in a positive way, both in bulk and at the interface sites, producing more stable systems for small-droplet high-protein-concentration emulsions. This study shows the relevance of components interactions in microstructure and stability of caseinate emulsions.     

黄原胶对酪蛋白酸钠乳状液稳定性的影响

研究了一定pH条件下,黄原胶浓度及剪切稀化效应对酪蛋白酸钠乳状液稳定性的影响。结果表明,在酸性条件下,黄原胶无法抑制酪蛋白的变性沉淀,乳液在制备之初,即产生严重絮凝。在中性和弱碱性条件下,黄原胶在一定浓度范围内,诱发了乳状液的排斥絮凝;体系的pH显著影响了乳状液的稳定性,pH6条件下,较低的黄原胶浓度(0.2wt%)便可赋予乳状液良好的稳定性。均质过程大大降低了黄原胶的粘度,导致乳状液的稳定性下降,与添加未经均质处理的黄原胶相比,添加量增大近一倍,才能获得稳定的乳状液。     

Transglutaminase cross-linking kinetics of sodium caseinate is changed after emulsification

Enzymatic cross-linking is an important method of modifying the structure of food products to control their texture and stability. In this paper we look at the effect that adsorption to the oil–water interface of triglyceride oil-in-water emulsion has on rates of cross-linking of sodium caseinate by microbial transglutaminase. The kinetics of cross-linking has also been assessed for the individual casein proteins within the caseinate. In solution the rates were α_s2-casein > β-casein > α_s1-casein > κ-casein. This order is not as expected given the rheomorphic nature of the proteins and the number of glutamine and lysine residues in each protein. In particular, the α_s1-casein was cross-linked much more slowly than expected. When sodium caseinate was adsorbed to an emulsion the rates for all constituent caseins were decreased but the cross-linking rate for α_s1-casein was markedly reduced, indicating the most significant change in accessibility following adsorption. This knowledge will facilitate optimal production of cross-linked emulsions for use in future studies aimed at engineering emulsions with improved nutritional quality.     

Characterisation of sodium caseinate as a function of ionic strength, pH and temperature using static and dynamic light scattering

Extensive static and dynamic light scattering (DLS) measurements were done on sodium caseinate solutions as a function of the ionic strength (3–500 mM NaCl), pH (5–8) and temperature (10–70 °C). DLS results were analysed in terms of two populations: the caseinate and a small weight fraction of large particles with a hydrodynamic radius (R_h) of about 65 nm that was independent of the ionic strength, pH and temperature. Caseinate was present as individual molecules at low ionic strength (3 mM), but formed small aggregates (R_h=11 nm) at high ionic strength (>100 mM). The aggregation number (N_agg) increased weakly with decreasing pH between pH 8 and 6, but extensive acid-induced aggregation occurred below pH 5.4 at 250 mM and below pH 6.0 at 3 mM. N_agg increased reversibly with increasing temperature.     

Comparison of the Emulsifying Properties of Fish Gelatin and Commercial Milk Proteins

ABSTRACT: We have compared the flocculation, coalescence, and creaming properties of oil-in-water emulsions prepared with fish gelatin as sole emulsifying agent with those of emulsions prepared with sodium caseinate and whey protein. Two milk protein samples were selected from 9 commercial protein samples screened in a preliminary study. Emulsions of 20 vol% n -tetradecane or triglyceride oil were made at pH 6.8 and at different protein/oil ratios. Changes in droplet-size distribution were determined after storage and centrifugation and after treatment with excess surfactant. We have demonstrated the superior emulsifying properties of sodium caseinate, the susceptibility of whey protein emulsions to increasing flocculation on storage, and the coalescence of gelatin emulsions following centrifugation.     

Influence of xanthan gum on the formation and stability of sodium caseinate oil-in-water emulsions

Studies have been made of the changes in droplet sizes, surface coverage and creaming stability of emulsions formed with 30% (w/w) soya oil, and aqueous solution containing 1 or 3% (w/w) sodium caseinate and varying concentrations of xanthan gum. Addition of xanthan prior to homogenization had no significant effect on average emulsion droplet size and surface protein concentration in all emulsions studied. However, addition of low levels of xanthan (≤0.2 wt%) caused flocculation of droplets that resulted in a large decrease in creaming stability and visual phase separation. At higher xanthan concentrations, the creaming stability improved, apparently due to the formation of network of flocculated droplets. It was found that emulsions formed with 3% sodium caseinate in the absence of xanthan showed extensive flocculation that resulted in very low creaming stability. The presence of xanthan in these emulsions increased the creaming stability, although the emulsion droplets were still flocculated. It appears that creaming stability of emulsions made with mixtures of sodium caseinate and xanthan was more closely related to the structure and rheology of the emulsion itself rather than to the rheology of the aqueous phase.     

Factors influencing the production of o/w emulsions stabilized by β-lactoglobulin–pectin membranes

A primary emulsion was prepared by homogenizing 10 wt% corn oil with 90 wt% aqueous β-lactoglobulin solution (0.5 wt% β-lg, pH 3 or 7) using a two-stage high-pressure valve homogenizer. This emulsion was mixed with aqueous pectin (citrus, 59% DE) stock solution (2 wt%, pH 3 or 7) and NaCl solution to yield secondary emulsions with 5 wt% corn oil, 0.225 wt% β-lactoglobulin, 0.2 wt% pectin and 0 or 100 mM NaCl. The final pH of the emulsions was then adjusted (3–8). Primary and secondary emulsions were ultrasonically treated (30 s, 20 kHz, 40% amplitude) to disrupt any flocculated droplets. Secondary emulsions were more stable than primary emulsions at intermediate pHs. Secondary emulsions prepared at pH 7 had smaller particle diameters (0.35 to 6 μm) than those prepared at pH 3 (0.42 to 18 μm) across the whole pH range studied, and also had smaller diameters than the primary emulsions (0.35 to 14 μm). Ultrasound treatment reduced the particle diameter of both primary and secondary emulsions and lowered the rate of creaming. The presence of NaCl screened the charges and thus the electrostatic interaction between biopolymer molecules and primary emulsion droplets. Secondary emulsions were more stable to the presence of 100 mM NaCl at low pHs (3–4) than primary emulsions. This study shows that stable emulsions can be prepared by engineering their interfacial membranes using the electrostatic interaction of natural biopolymers, especially at intermediate pHs where proteins normally fail to function.     

Factors affecting the acid gelation of sodium caseinate

Acid gelation, turbidity and particle size development of dispersions of sodium caseinate and other protein fractions were studied. Sodium caseinate dispersions became particulate prior to the onset of gelation. Casein particles had enhanced stability to gelation in the presence of sodium chloride. Removal of the hydrophilic part of the κ-casein molecule through renneting and acidification of the soluble sodium para-caseinate resulted in increased gelation pH. Removal of most of the κ-casein through ethanol fractionation of sodium caseinate resulted in an α_s1-β-fraction, which was markedly destabilised at higher pH values during acidification in the presence of sodium chloride. Preheated β-lactoglobulin/sodium caseinate dispersions had similar acid gelation profiles in the presence of sodium chloride with or without N-ethylmaleimide, suggesting that secondary thiol-disulphide interchange reactions between κ-casein and pre-heated β-lactoglobulin aggregates did not effect the gel point and final storage modulus in the short time-frame (120 min) of acidification. It was found that κ-casein and sodium chloride played a significant role in both particle development and subsequent stability of sodium caseinate dispersions on acidification.     

Polymerization of β-lactoglobulin and bovine serum albumin at oil-water interfaces in emulsions by transglutaminase

Polymerization of β-lactoglobulin and bovine serum albumin at the oil—water interfaces in n-tetradecane-in-water emulsions induced by the transglutaminase reaction was studied. The emulsions were incubated with transglutaminase for various times, and adsorbed and unadsorbed protein fractions at the oil—water interfaces were analyzed by sodium dodecyl sulfate—polyacrylamide gel electrophoresis. While only monomers were detected in the unadsorbed fractions, polymers were observed in the adsorbed fractions of the both proteins. The sizes and amounts of the polymers increased with incubation time. The incubation with transglutaminase caused much flocculation of the emulsion stabilized by β-lactoglobulin. An increase in viscosity was also observed with the flocculation. The flocculation was probably initiated by the formation of ε-(γ-glutamyl)-lysyl isopeptide bonds between β-lactoglobulin molecules adsorbed on different oil droplets. In the case of the emulsion stabilized by bovine serum albumin, however, the flocculation and the increase in viscosity occurred to only limited extents by the transglutaminase reaction. This suggests that ε-(γ-glutamyl)-lysyl isopeptide bonds induced by the transglutaminase reaction were formed only between neighboring molecules of bovine serum albumin on the same droplet.     

Fabrication and characterization of filled hydrogel particles based on sequential segregative and aggregative biopolymer phase separation

In this study, filled hydrogel particles were created based on the ability of proteins and ionic polysaccharides to phase separate through both aggregative (complexation) and segregative (incompatibility) mechanisms. At pH 7, a mixture of 3% (w/w) high-methoxy pectin and 3% (w/w) sodium caseinate phase separated through a segregative mechanism. Following centrifugation, the phase separated system consisted of an upper pectin-rich phase and a lower casein-rich phase. Casein-coated lipid droplets added to the phase separated pectin/caseinate system partitioning into the lower casein-rich phase. This was attributed to a reduction in the unfavorable osmotic stress in this phase associated with biopolymer depletion. When shear was applied this system formed an oil-in-water-in-water (O/W₁/W₂) emulsion consisting of oil droplets (O) contained within a casein-rich watery dispersed phase (W₁) suspended in a pectin-rich watery continuous phase (W₂). Acidification of the O/W₁/W₂ system from pH 7–5 promoted adsorption of pectin around the casein-rich W₁ droplets, resulting in the formation of filled hydrogel particles (d = 3–4 μm) that remained stable to aggregation or dissociation when stored for 24 h at ambient temperature. These particles may be useful as encapsulation and delivery systems for lipophilic components in the food, cosmetics and pharmaceutical industries.     

Utilization of layer-by-layer interfacial deposition technique to improve freeze–thaw stability of oil-in-water emulsions

The freeze–thaw stability of 5 wt% hydrogenated palm oil-in-water emulsions (pH 3) containing droplets stabilized by sodium dodecyl sulfate (SDS)–chitosan–pectin membranes was studied. The multilayered interfacial membranes were created using an electrostatic layer-by-layer deposition method. The ζ-potential, mean particle diameter, fat destabilization, apparent viscosity and microstructure of the emulsions were used to examine the influence of freezing on their stability. Emulsions containing oil droplets stabilized only by SDS were highly unstable to droplet coalescence when either the oil phase became partially crystallized or the water phase crystallized. Emulsions containing oil droplets stabilized by SDS–chitosan membranes were stable to droplet coalescence, but unstable to droplet flocculation. Emulsions containing droplets stabilized by SDS–chitosan–pectin membranes were stable to both droplet coalescence and flocculation. The interfacial engineering technology utilized in this study could lead to the creation of food emulsions with improved stability to freeze–thaw cycling.     

Influence of high pressure on interactions of 11S globulin Vicia faba with ι-carrageenan in bulk solution and at interfaces

The influence of ι-carrageenan (ι-CAR) on the solution, interfacial and emulsifying properties of 11S globulin Vicia faba at low ionic strength and pH 8 has been investigated before and after high-pressure processing at 200 MPa for 20 min. The total calorimetric enthalpy (ΔH) and size exclusion chromatography studies for the pure 11S indicate that there is subunit dissociation and extensive aggregation of the protein during or following treatment. Under the same treatment conditions, 1-anilinonaphthalene-8-sulphonate (ANS) data has shown increased protein surface hydrophobicity. Pressure treatment of 11S gives much lower values of the surface tension, and apparent surface shear rheology experiments show that the molecules in the film adsorbed from the pressurised 11S are much more strongly interacting than those adsorbed from the native 11S. However, emulsions prepared with pressure processed 11S give substantially bigger droplets than those made with the untreated pure protein. Addition of ι-CAR to 11S reduces the denaturation temperature (T_m), the ΔH value, and protein surface hydrophobicity. Size exclusion chromatography at low ionic strength is indicative of complex formation. Tension measurements at the air–water interface are also consistent with the presence of a complex. Emulsions made with the simple 1:0.33 mixture of 11S+ι-CAR give emulsions with smaller droplets and pressure processing of the biopolymer mixture leads to emulsions with even smaller droplets. The presence of ι-CAR at low ionic strength appears to protect the globulin against pressure-induced aggregation.     

Interfacial Composition of Sodium Caseinate Emulsions

Oil-in-water emulsions stabilized by sodium caseinate were prepared and diluted with water or solutions of α_sl- or β-casein. The emulsions were aged for 24 hr and the composition of the aqueous phase (and hence of the surface) was determined using Fast Protein Liquid Chromatography. There was no distinct preference for either α_sl- or β-casein at the surface during homogenization, but on aging, β-casein replaced some, but not all, of the surface α_sl-casein. The exchange was stoichiometric, unless the initial surface concentration was low, in which case extra adsorption occurred to achieve a protein load of - 1.2 mg m^-2. Build up of multilayers was not observed.     

Improvement of emulsifying properties of milk proteins with κ or λ carrageenan: effect of pH and ionic strength

The objective of this work was to determine the effect of λ‐carrageenan or κ‐carrageenan on the emulsion capacity, emulsion work and emulsion stability of milk proteins concentrate (MP) or sodium caseinate (SC) emulsions at different levels of pH and ionic strength. Incorporation of carrageenans to proteins emulsions resulted in an improvement of emulsifying properties at pH 6.0 and low ionic strength (0.2 m NaCl). Although emulsion capacity was high in MP than for SC, irrespectively of carrageenan employed, addition of λ‐carrageenan increased twofold emulsion work values (15 327 Ω s^?1 for MP and 11 455 Ω s^?1 for SC; around 6000 Ω s^?1 in the other treatments). Emulsion stability was high with λ‐carrageenan (9.8 s) than MP‐κ‐carrageenan or MP (7.45 and 7.40 s, respectively). Carrageenan improving of emulsion properties was because of the complex formation with MP, characteristic of this type of food system when pH was above of isoelectric point.     

Sodium caseinate/carboxymethylcellulose interactions at oil–water interface: Relationship to emulsion stability

The effect of carboxymethylcellulose (CMC) on the properties of oil-in-water emulsions prepared with sodium caseinate (CN) was studied at different pHs (4–7). At pH 7, the surface protein coverage increased gradually with increasing CMC concentration, followed by a preferential adsorption of β-casein. While at pH 4, a sharp decrease in surface protein coverage was noted between 0 and 0.3 wt.% CMC, and no obvious difference in protein composition was observed. ζ-Potential measurements indicated that CMC adsorbed onto the CN-coated droplets at pH 4–5, but not at pH 6–7. As a result, the excess of non-adsorbed CMC induced depletion flocculation in the neutral emulsions. However, the acidic emulsions containing high levels of CMC (>0.3 wt.%) remained stable after 60 days of storage due to the formation of multilayer structures. At pH 4, CMC desorbed from the droplet surfaces at high NaCl concentrations, leading to lower emulsion stability.