Prebiotic emulsions stabilised by whey protein and kefiran

The goal of this work has been to assess the influence of a health-promoting hydrocolloid, such as kefiran, in oil-in-water emulsions (O/W: 50/50) containing whey protein isolate (1.0% wt.). Different kefiran concentration levels (0%, 0.25%, 0.5%, 1% wt.) were studied, observing a shift from a fluid-like to a solid-like behaviour and higher viscosities when kefiran content increased. A pseudoplastic behaviour was detected for all systems studied. The observed evolution is attributed to the thickening effect exerted by kefiran, which promoted stability, in spite of observing a certain flocculation degree within the emulsion systems, demonstrated through the addition of sodium dodecyl sulphate (1% wt.). Furthermore, short-term stability of these pseudoplastic emulsions has been verified by laser-scattering techniques. Thus, a Sauter diameter around 1 µm remained unaltered up to 7 days since preparation. The addition of kefiran in the formulation would benefit from their well-known health-promoting effects.     

Improved emulsion stabilizing properties of whey protein isolate by conjugation with pectins

Functional properties of glyco-protein conjugates of the anionic polysaccharide pectin with whey protein isolate, obtained by dry heat treatment at 60 °C for 14 days, have been investigated in O/W emulsions containing 20% (w/w) soybean oil and 0.4% (w/w) protein both at pH 4.0 and 5.5. Emulsion stabilizing properties of mixtures and conjugates were compared at five protein to pectin weight ratios by determining changes in droplet size distribution and extent of serum separation with time. The results indicated that the dry heat-induced covalent binding of low methoxyl pectin to whey protein, as shown by SDS-PAGE, led to a substantial improvement in the emulsifying behaviour at pH 5.5, which is near the isoelectric pH of the main protein β-lactoglobulin. At pH 4.0, however, a deterioration of the emulsifying properties of whey protein was observed using either mixtures of protein and pectin or conjugates.The observed effects could be explained by protein solubility and electrophoretic mobility measurements. The protein solubility at pH 5.5 was hardly changed using mixtures of protein and low methoxyl pectin or conjugates, whereas at pH 4.0 it was decreased considerably. Electrophoretic mobility measurements at pH 5.5 revealed a much more pronounced negative charge on the emulsion droplets in the case of protein–pectin conjugates, which clearly indicated that conjugated pectin did adsorb at the interface even at pH conditions above the protein's iso-electric point. Hence, the improved emulsifying properties of whey protein isolate at pH 5.5 upon conjugation with low methoxyl pectin may be explained by enhanced electrosteric stabilization.Comparing two different commercial pectin samples, it was clearly shown that the dextrose content during dry heat treatment of protein–pectin mixtures should be as low as possible since protein–sugar conjugates not only resulted in increased brown colour development, but also gave raise to a largely decreased protein solubility which very badly affected the emulsifying properties.     

Comparing the heat stability of soya protein and milk whey protein emulsions

The heat stability of emulsions stabilized by WPC or SPI or mixtures of the two are compared by following the change in oil droplet number during heating, and applying kinetic rate equations to calculate the rate constant (k) for destabilization. SPI emulsions were found to be unstable to heat at pH around the pI, whilst being stable at pH further from the pI. This is related to the pH dependent solubility of soy proteins. This determined that a pH close to the pI (pH 4.5) be used for further studies so as to give a heat labile emulsion. Both WPC and SPI emulsions showed a weak dependence of k on protein concentration at pH 4.5, and an increasing k as the temperature increased. Arrhenius plots for emulsions made with WPC were bilinear, whilst those for SPI followed a single straight line. The change in slope of the Arrhenius plots for the WPC emulsions occurred around 70 °C, lower than would be expected from the denaturation temperature of β-lactoglobulin, the protein that dominates the thermal behaviour of WPC. The activation energies for WPC and SPI emulsions calculated from the slopes of the Arrhenius plots are slightly lower for WPC and considerably lower for SPI than the equivalent values in the literature for these proteins in solution. This, and the apparent lower denaturation temperature of β-lactoglobulin in emulsions, we explain by hypothesizing that the WPC and SPI proteins are already partially denatured by surface adsorption when they are heated, and thus require less energy to denature, and unfold at lower temperatures than native non-adsorbed proteins.     

Depletion flocculation and thermodynamic incompatibility in whey protein stabilised O/W emulsions

The stability of whey protein stabilised emulsions, containing methylcellulose added after emulsification in their bulk phase, was investigated. The phase diagram of the ternary system whey proteins/methylcellulose/water was first established and used to identify the conditions permitting polymer phase separation within the emulsion bulk phase. Emulsions containing a whey protein and methylcellulose concentration in the bulk phase below and above the phase separation threshold could therefore be prepared. Below the phase separation threshold, the creaming rate of the oil droplets was faster than the one predicted by the Stokes equation, due to methylcellulose-induced depletion flocculation. Above the phase separation threshold, the destabilisation of the emulsion involved different mechanisms, depending on the emulsifier adsorbed at the O/W interface. In the case of Tween 40 stabilised droplets, depletion flocculation led to a complete creaming of the fat globules while phase separation led to the formation of two polymer-rich phases, namely a protein-rich phase at the bottom of the tube and a methylcellulose-rich phase above. In the case of whey protein stabilised droplets, phase separation between bulk whey proteins and methylcellulose occurred, and the fat globules were entrapped in the protein-rich phase. These results permitted to describe the destabilisation mechanisms of both Tween 40 and whey protein stabilised emulsions in the presence of unadsorbed polysaccharide. They could be used to better understand the destabilisation processes arising in food emulsions, especially in those emulsions containing whey proteins, small surfactant molecules and polysaccharides.     

Ability of conventional and nutritionally-modified whey protein concentrates to stabilize oil-in-water emulsions

The ability of a modified whey protein concentrate (MWPC), which contains relatively high proportions of phospholipid and high molecular weight protein fractions, to form and stabilize 10 wt% corn oil-in-water emulsions (pH 7.0, 5 mM phosphate buffer) was compared with that of a conventional whey protein concentrate (CWPC). The MWPC stabilized emulsions required less protein to prepare stable emulsions with monomodal particle size distributions and small mean droplet diameters (d₄₃ ≈ 0.3 μm at [WPC] ⩾ 0.5 wt%) than CWPC stabilized emulsions (d₄₃ ≈ 0.4 μm at [WPC] ⩾ 0.9 wt%) under similar homogenization conditions (5 passes at 5000 psi). In addition, the emulsions stabilized by 0.9 wt% MWPC were more stable to high salt concentration (NaCl ⩽ 200 mM), thermal processing (30–90 °C for 30 min) and pH (3, 6 and 7) than those stabilized by the same concentration of CWPC, which was attributed to polymeric steric repulsion rather than electrostatic repulsion. This study has important implications for the wide application of WPC as a natural emulsifier in food products.     

Characterization of cold-set gels produced from heated emulsions stabilized by whey protein

This paper reports the cold gelation of preheated emulsions stabilized by whey protein, in contrast to, in previous reports, the cold gelation of emulsions formed with preheated whey protein polymers. Emulsions formed with different concentrations of whey protein isolate (WPI) and milk fat were heated at 90 °C for 30 min at low ionic strength and neutral pH. The stable preheated emulsions formed gels through acidification or the addition of CaCl₂ at room temperature. The storage modulus (G′) of the acid-induced gels increased with increasing preheat temperature, decreasing size of the emulsion droplets and increasing fat content. The adsorbed protein denatures and aggregates at the surface of the emulsion droplets during heat treatment, providing the initial step for subsequent formation of the cold-set emulsion gels, suggesting that these preheated emulsion droplets coated by whey protein constitute the structural units responsible for the three-dimensional gel network.     

Rheology and stability of whey protein stabilized emulsions with high CaCl2 concentrations

The influence of pH and CaC1₂ on the rheology and physical stability of emulsions stabilized by whey protein isolate (WPI) has been studied. The particle size, creaming index and shear viscosity of 10 wt% soy bean oil-in-water emulsions (d=0.55 μm) were measured with varying pH (3, 5 and 7) and CaC1₂ concentration (0–150 mM). In the absence of CaCl₂ extensive droplet aggregation occurred around the isoelectic point of the whey proteins (4<pH<6) because of their low electrical charge. In the presence of CaC1₂, extensive droplet aggregation, viscosity enhancement and creaming instability occurred at pH 7 for CaC1₂>3 mM. These effects were much less pronounced in emulsions at pH 3 even at 150 mM CaC1₂. Droplet aggregation, creaming and viscosity of emulsions at pH 5 were fairly independent of CaC1₂ concentration. Droplet aggregation was induced by CaC1₂ probably because of the reduction in electrostatic repulsion between droplets. Re-stabilization of oil-in-water emulsions at high CaC1₂ concentrations was not observed in this study.     

乳清分离蛋白-葡聚糖接枝物乳液冻融稳定性研究

研究冻融处理对乳清分离蛋白―葡聚糖接枝产物乳液稳定性的影响。颗粒尺寸数据结果表明,以接枝产物为基质的乳液冻融稳定性得到明显改善;表观形态和微观结构的测定进一步印证这一现象。ξ–电位的测定结果说明电荷不是决定接枝产物乳液体系稳定性的主要因素。这可能是由于接枝物在油滴表面形成的界面膜相对较厚,使得低温条件下的固体脂肪颗粒很难渗透和破坏界面膜,有效抑制低温状态下油滴之间的聚结和絮凝,从而改善乳液冻融稳定性。     

Rheological properties of whey protein isolate stabilized emulsions with pectin and guar gum

Dynamic oscillatory and steady-shear rheological tests were carried out to evaluate the rheological properties of whey protein isolate (WPI) stabilized emulsions with and without hydrocolloids (pectin and guar gum) at pH 7.0. Viscosity and also consistency index of emulsions increased with hydrocolloid concentration. At γ = 20 s⁻¹, the value of viscosity of the emulsion with 0.5% (w/v) pectin was about fivefold higher than that of the emulsion without pectin. Flow curves were analyzed using power law model through a fitting procedure. Flow behaviour index of all emulsions except for containing 0.5% (w/v) guar gum was approximately in the range of 0.9–1.0, which corresponds to near-Newtonian behaviour. The shear thinning behaviour of emulsions containing 0.5% (w/w) guar gum was confirmed by flow behaviour index, n, of 0.396. Both storage (G′) and loss modulus (G″) increased with an increase in frequency. Emulsions behaved like a liquid with G″ > G′ at lower frequencies; and like an elastic solid with G′ > G″ at higher frequencies. Effect of guar gum was more pronounced on dynamic properties. Phase angle values decreased from 89 to <10° with increasing frequency and indicated the viscoelasticity of WPI-stabilized emulsions with and without pectin/guar gum.     

Characterization and acid-induced gelation of butter oil emulsions produced from heated whey protein dispersions

Whey protein isolate was dispersed at 4% or 8% (w/v) and heated at neutral pH to produce protein polymers. Butter oil, up to 20%, was homogenized in heated whey protein dispersions at pressure ranging from 10 to 120 MPa. Emulsion gelation was induced by acidification with glucono-δ-lactone. Whey protein polymers produced finely dispersed emulsions with fat droplet diameter ranging from 340 to 900 nm. Homogenization pressure was the main factor influencing droplet size. At low fat volume fraction, the emulsions exhibited Newtonian behaviour. As fat content increased, shear thinning behaviour developed as a result of depletion flocculation. Emulsion consistency index increased with protein and fat concentrations. Increasing homogenization pressure had no effect on Newtonian emulsions but promoted flocculation and significantly increased the consistency of high fat emulsions. Protein concentration was the main factor explaining emulsion gel hardness and syneresis. Syneresis decreased with increasing fat content in the gel.     

Cold,gel-like whey protein emulsions by microfluidisation emulsification: Rheological properties and microstructures

Novel cold, gel-like whey protein concentrate (WPC) emulsions at various oil fractions (φ; 0.2–0.6) were formed through thermal pretreatment (at 70 °C for 30 min) and subsequent microfluidisation. The rheogical properties and microstructures, as well as emulsification mechanism of these emulsions were characterised. The rheological analyses indicated that the gel-like emulsions exhibited shear-thinning and predominantly elastic gel behaviours, and the apparent viscosities and the mechanical moduli of the emulsions remarkably and progressively increased with increasing the φ from 0.2 to 0.6. Confocal laser scanning microscopy analyses confirmed close relationships between rheological properties and gel network structures at various φ values. The formation of the gel-like network structure was closely related to the high emulsifying efficiency by microfluidisation. This kind of novel gel-like emulsion might exhibit great potential and be applicable in food formulations, e.g. as a kind of carrier for heat-labile and active ingredients.     

Differences in in vitro gastric behaviour between homogenized milk and emulsions stabilised by Tween 80, whey protein,or whey protein and caseinate

This study focuses on the behaviour of liquid food emulsion systems in the stomach. Gastric digestion was studied in vitro using a stomach model consisting of a thermostatted titration vessel to which solutions of HCl, pepsin and a lipase were simultaneously added slowly. Four systems were studied: a whey protein-stabilised emulsion, a whey protein-stabilised emulsion with additional sodium caseinate, a Tween 80 stabilised emulsion, and homogenized full fat milk. It is shown that the in vitro colloidal behaviour of the systems under simulated gastric conditions is influenced significantly by their composition. The Tween 80 stabilised emulsion did not show instabilities, whereas the two protein-stabilised emulsions and full fat milk showed extensive flocculation, which for the protein-stabilized emulsions led to creaming and for full fat milk led to sedimentation. The experimental results also show some coalescence in the Tween 80 and milk systems. The formation of free fatty acids did not vary much between the systems, showing that flocculation and coalescence did not strongly affect lipolysis. The possible physiological relevance of these different behaviours are discussed, suggesting differences in stomach emptying rate and feelings of fullness and satiety.     

Performance of whey protein hydrolysate–maltodextrin conjugates as emulsifiers in model infant formula emulsions

Model infant formula emulsions containing 15.5, 35.0 and 70.0 g L⁻¹ protein, soybean oil and maltodextrin (MD), respectively, were prepared. Emulsions were stabilised by whey protein hydrolysate (WPH) + CITREM (9 g L⁻¹), WPH + lecithin (9 g L⁻¹) or WPH conjugated with MD (WPH–MD). All emulsions had mono-modal oil droplet size distributions post-homogenisation with mean oil droplet diameters (D_4,3) of <1.0 μm. No changes in the D_4,3 were observed after heat treatment (95 °C, 15 min) of the emulsions. Accelerated storage (40 °C, 10 d) of unheated emulsions resulted in an increase in D_4,3 for CITREM (2.86 μm) and lecithin (5.36 μm) containing emulsions. Heated emulsions displayed better stability to accelerated storage with no increase in D_4,3 for CITREM and an increase in D_4,3 for lecithin (2.71 μm) containing emulsions. No increase in D_4,3 over storage was observed for unheated or heated WPH–MD emulsion, indicating its superior stability.     

Stability of oil‐in‐water emulsions as influenced by thermal treatment of whey protein dispersions or emulsions

Properties of whey protein concentrate stabilised emulsions were modified by protein and emulsion heat treatment (60–90 °C). All liquid emulsions were flocculated and the particle sizes showed bimodal size distributions. The state and surface properties of proteins and coexisting protein/aggregates in the system strongly determined the stability of heat‐modified whey protein concentrate stabilised emulsions. The whey protein particles of 122–342 nm that formed on protein heating enhanced the stability of highly concentrated emulsions. These particles stabilised protein‐heated emulsions in the way that is typical for Pickering emulsions. The emulsions heated at 80 and 90 °C gelled due to the aggregation of the protein‐coated oil droplets.     

Impact of whey protein isolates and concentrates on the formation of protein nanoparticles‐stabilised Pickering emulsions

Whey protein nanoparticles (NPs) were prepared by heat‐induced method. The influences of whey protein isolates (WPIs) and concentrates (WPCs) on the formation of NPs were first investigated. Then Pickering emulsions were produced by protein NPs and their properties were evaluated. After heat treatment, WPC NPs showed larger particle size, higher stability against NaCl, lower negative charge and contact angle between air and water. Dispersions of WPC NPs appeared as higher turbidity and viscosity than those of WPI NPs. The interfacial tension of WPC NPs (~7.9 mN/m at 3 wt% NPs) was greatly lower than that of WPI NPs (~12.1 mN/m at 3 wt% NPs). WPC NPs‐stabilised emulsions had smaller particle size and were more homogeneous than WPI NPs‐stabilised emulsions. WPC NPs‐stabilised emulsions had higher stability against NaCl, pH and coalescence during storage.     

Emulsification mechanisms and characterizations of cold, gel-like emulsions produced from texturized whey protein concentrate

A novel supercritical fluid extrusion (SCFX) process was used to successfully texturize whey protein concentrate (WPC) into a product with cold-setting gel characteristics that was stable over a wide range of temperature. It was further hypothesized that incorporation of texturized WPC (tWPC) within an aqueous phase could improve emulsion stability and enhance the rheological properties of cold, gel-like emulsions. The emulsifying activity and emulsion stability indices of tWPC and its ability to prevent coalescence of oil-in-water (o/w) emulsions were evaluated and compared with the commercial WPC80. The cold, gel-like emulsions were prepared at different oil fractions (φ = 0.20–0.80) by mixing oil with the 20% (w/w) tWPC dispersion at 25 °C and evaluated using a range of rheological techniques. Microscopic structure of cold, gel-like emulsions was also observed by Confocal Laser Scanning Microscope (CLSM). The results revealed that the tWPC showed excellent emulsifying properties compared to the commercial WPC in slowing down emulsion breaking mechanisms such as creaming and coalescence. Very stable with finely dispersed fat droplets, and homogeneous o/w gel-like emulsions could be produced. Steady shear viscosity and complex viscosity were well correlated using the generalized Cox–Merz rule. Emulsions with higher viscosity and elasticity were obtained by raising the oil fraction. Only 4% (w/w) tWPC was needed to emulsify 80% (w/w) oil with long-term storage stability. The emulsion products showed a higher thermal stability upon heating to 85 °C and could be used as an alternative to concentrated o/w emulsions and in food formulations containing heat-sensitive ingredients.     

Influence of pH and CaCl2 on the stability of dilute whey protein stabilized emulsions

The influence of pH and CaCl₂ on the physical stability of dilute oil-in-water emulsions stabilized by whey protein isolate has been studied. The particle size, zeta potential and creaming stability of 0.05 wt% soy bean oil-in-water emulsions (d ≈ 0.53 μm) were measured with varying pH (3 to 7) and CaCl₂ concentration (0 to 20 μM). In the absence of CaCl₂ extensive droplet aggregation occurred around the isoelectric point of the whey proteins (4 < pH < 6) because of their low electrical charge, which led to creaming instability. Droplet aggregation occurred at higher pH when CaCl₂ was added to the emulsions. The minimum concentration of CaCl₂ required to promote aggregation increased as the pH increased. Aggregation was induced in the presence of CaCl₂ probably because of the reduction in electrostatic repulsion between droplets, caused by binding of counter ions to droplet surfaces and electrostatic screening effects.     

Effect of heat treatment and droplet size on the oxidative stability of whey protein emulsions

The present paper examines whether certain processing factors may influence the oxidative stability of whey protein oil-in-water emulsions, which are structurally close to innovative industrial products (e.g. “fresh-cheese” and “non-dairy cream” types).