Physicochemical properties of whey protein isolate stabilized oil-in-water emulsions when mixed with flaxseed gum at neutral pH

Concentrations ranging from 0% to 0.33% (w/v) of gum (Emerson and McDuff) were added to the emulsions at pH 7. Particle size distribution, viscosity, ζ-potential, microstructure, and phase separation kinetics of the emulsions were observed. Both polysaccharides and protein coated droplets are negatively charged at this pH, as shown by ζ-potential measurements. At all the concentrations tested, the addition of gum did not affect significantly (p < 0.05) the apparent diameter of the emulsion droplets. At low concentrations (gum  0.075% (w/v)), no visual phase separation was observed and the emulsion showed a Newtonian behaviour. However, at concentrations above the critical concentration of gum, depletion flocculation occurred: when 0.1 flaxseed gum was present, there was visual phase separation over time and the emulsion exhibited shear-thinning behaviour. These results demonstrate that flaxseed gum is a non-interacting polysaccharide at neutral pH; it could then be employed to strengthen the nutritional value of some milk-based drinks, but at limited concentrations.     

Heat-induced changes in oil-in-water emulsions stabilized with soy protein isolate

The physicochemical properties of soy proteins stabilized oil-in-water emulsions were studied after heating at two different temperatures, 75 and 95 °C. The effect of changing the order of the process (heating the solution before emulsification, or heating the emulsion) was also studied. The heating temperatures were chosen as they are known to selectively cause denaturation of the two major proteins present in the soy protein isolate: β-conglycinin and glycinin. The thermal transitions observed for soy proteins adsorbed at the interface were different from those measured in protein solutions, suggesting that some changes occur in the structure of the soy proteins upon adsorption on the oil droplet. Heating induces aggregation of the oil droplets, as shown by an increase of the particle size and the bulk viscosity of the emulsions, with a more prominent effect after heating at 95 °C. Transmission electron microscopy observations clearly demonstrate that heating induces the formation of large protein aggregates at the interface. In addition, the composition of the protein present at the interface changes depending on the order of heating and homogenization. While heating the solutions before emulsification results in all the protein subunits to be present at the interface in an aggregated form, when heating is applied after emulsification, a portion of the α and the α′ subunit of β-conglycinin as well as the acidic subunits of glycinin remain unadsorbed.     

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.     

Antioxidant properties of caseins and whey proteins in model oil-in-water emulsions

The oxidative stabilities of both wheyproteinisolate (WPI)- and sodiumcaseinate-stabilized linoleic acid emulsions with different droplet sizes, protein concentrations and protein concentrations in the continuous phase were examined by determining lipid hydroperoxide and hexanal in the headspace. Emulsions with small droplet size had greater oxidative stability than emulsions with large droplet size in both WPI and sodiumcaseinate-stabilized emulsions. Lipid oxidation was in general lowered by an increase in the protein concentration. At high protein concentrations, the antioxidative effect of the protein in the emulsions appeared to offset the effects of emulsion droplet size and protein type. Replacing the unadsorbed protein in the continuous phase with water markedly decreased the oxidative stability of the emulsions. In contrast, the oxidative stability of the emulsions increased with increasing protein concentration in the continuous phase. This suggests that the antioxidative mechanism of protein in the interfacial region, such as binding trace metal ions from the lipid phase and free-radical-scavenging activity, may involve a dynamic exchange process with protein molecules from the continuous phase.     

Effects of protein concentration and oil-phase volume fraction on the stability and rheology of menhaden oil-in-water emulsions stabilized by whey protein isolate with xanthan gum

The influences of protein concentration (0.2, 1, 2 wt%) and oil-phase volume fraction (5%, 20%, 40% v/v) on emulsion stability and rheological properties were investigated in whey protein isolate (WPI)-stabilized oil-in-water emulsions containing 0.2 wt% xanthan gum (XG). The data of droplet size, surface charge, creaming index, oxidative stability, and emulsion rheology were obtained. The results showed that increasing WPI concentration significantly affected droplet size, surface charge, and oxidative stability, but had little effect on creaming stability and emulsion rheology. At 0.2 wt% WPI, increasing oil-phase volume fraction greatly increased droplet size but no significant effect on surface charge. At 1 or 2 wt% WPI, increasing oil-phase volume fraction had less influence on droplet size but led to surface charge more negative. Increasing oil-phase volume fraction facilitated the inhibition of lipid oxidation. Meanwhile, oil-phase volume fraction played a dominant role in creaming stability and emulsion viscosity. The rheological data indicated the emulsions may undergo a behavior transition from an entropic polymer gel to an enthalpic particle gel when oil-phase volume fraction increased from 20% to 40% v/v.     

The effect of chitosan on the properties of emulsions stabilized by whey proteins

The influence of the cationic amino polysaccharide chitosan content (0–0.5%) on particle size distribution, creaming stability, apparent viscosity, and microstructure of oil-in-water emulsions (40% of rapeseed oil) containing whey protein isolate (WPI) (4%) at pH 3 was investigated. The emulsifying properties, apparent viscosity and phase separation behaviour of aqueous WPI/chitosan mixture at pH 3 were also studied. The interface tension data showed that WPI/chitosan mixture had a slightly higher emulsifying activity than had whey protein alone. An increase in chitosan content resulted in a decreased average particle size, higher viscosity and increased creaming stability of emulsions. The microstructure analysis indicated that increasing concentration of chitosan resulted in the formation of a flocculated droplet network. This behaviour of acidic model emulsions containing WPI and chitosan was explained by a flocculation phenomenon.     

Influence of EDTA and citrate on thermal stability of whey protein stabilized oil-in-water emulsions containing calcium chloride

The influence of calcium ions and chelating agents on the thermal stability of model nutritional beverages was examined. Oil-in-water emulsions (6.94% (w/v) soybean oil, 0.35% (w/v) WPI, 0.02% (w/v) sodium azide, 20 mM Tris buffer, 0–10 mM CaCl₂, and 0–40 mM EDTA or citrate, pH 7.0) were stored at temperatures between 30 and 120 °C for 15 min. The particle size, particle charge, creaming stability, rheology, and free-calcium concentration of the emulsions were then measured. In the absence of chelating agents, appreciable droplet aggregation occurred in emulsions held at temperatures from 80 to 120 °C, which led to increased emulsion particle diameter, shear-thinning behavior, apparent viscosity, and creaming instability. Addition of chelating agents to the emulsions prior to heating decreased, but did not prevent, droplet aggregation in the emulsions. EDTA was more effective than citrate in decreasing droplet aggregation. Heat treatment increased the amount of chelating agents required to prevent droplet aggregation in the emulsions. Free-calcium concentration and droplet surface potential was independent of heat-treatment temperature, indicating that the performance of the chelating agents in binding calcium ions was not affected by the heat treatment. It was suggested that increased hydrophobic attractive interactions between the droplets occurred during heating, which induced droplet aggregation.     

豌豆分离蛋白/卡拉胶复合物乳液的性质研究

为改善豌豆分离蛋白(PPI)在酸性乳液体系中的乳化稳定性,将PPI与阴离子多糖卡拉胶(CG)在酸性条件下混合,制备可溶性静电复合物乳液。通过测定PPI乳液和PPI/CG复合物乳液在不同pH(4～7)下粒径、ζ-电位、显微结构以及乳析指数的变化,判断两种乳液的稳定性。结果表明：pH 4～5时,PPI乳液粒径达到35μm以上,而pH 4～7时PPI/CG复合物乳液粒径均小于18μm;储藏14 d时,PPI乳液和PPI/CG复合物乳液粒径均稍有增加;酸性条件下,PPI乳液的ζ-电位绝对值均小于30 mV,而PPI/CG复合物乳液的ζ-电位绝对值均大于40 mV;酸性条件下,PPI/CG复合物乳液较PPI乳液分散性有明显改善;在储藏14 d过程中,PPI乳液乳析指数随储藏时间的延长而逐渐增大,而PPI/CG复合物乳液乳析指数基本为0。综上,PPI/CG复合物可显著改善PPI在酸性条件下的乳化稳定性。     

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.     

大豆分离蛋白对大豆肽纳米颗粒Pickering乳液性能的影响

为提高大豆肽纳米颗粒(SPN)Pickering乳液稳定性,以大豆肽聚集体为原料,采用超声法制备SPN,对超声时间进行了优化;在SPN体系中引入大豆分离蛋白(SPI)构建复合乳化剂,研究不同乳化剂质量浓度下SPI对SPN界面活性和乳化稳定性的影响。结果表明：选取超声时间10 min制备SPN;随着乳化剂质量浓度的增大,乳液粒径逐渐减小,当乳化剂质量浓度较低(5 mg/mL)时,乳液出现桥联,乳化剂质量浓度过高(30 mg/mL)时则出现絮凝;界面蛋白吸附率随着乳化剂质量浓度的增加呈现先升高后降低的趋势。在相同乳化剂质量浓度下,添加SPI的SPN乳液(SPI-SPN乳液)的粒径分布峰左移,其粒径、界面蛋白吸附率显著小于SPN乳液的;在储存过程中,SPN乳液粒径逐渐增大,SPI-SPN乳液粒径没有显著变化;SPI-SPN乳液的乳析指数小于相同乳化剂质量浓度的SPN乳液,当乳化剂质量浓度为30 mg/mL时,储存15 d SPI-SPN乳液未出现分层现象。综上,SPI可以提高SPN的界面活性和SPN乳液储存过程中的絮凝稳定性和分层稳定性。     

Rheological properties of reduced-fat and low-fat ice cream containing whey protein isolate and inulin

Instrumental analyses were used to evaluate the rheological properties of regular (10%), reduced-fat (6%) and low-fat (3%) ice cream mixes and frozen ice creams stored at −18 °C. The reduced-fat and low-fat ice creams were prepared using 4% whey protein isolate (WPI) or 4% inulin as the fat replacement ingredient. The composition, colour, apparent viscosity, consistency coefficient, flow behaviour index, hardness and melting characteristics were measured. No effect of WPI or inulin was obtained on the colour values. Compared with regular ice cream, WPI changed rheological properties, resulting in significantly higher apparent viscosities, consistency indices and greater deviations from Newtonian flow. In addition, both hardness and melting resistance significantly increased by using WPI in reduced-fat and low-fat ice creams. Inulin also increased the hardness in comparison to regular ice cream, but the products made with inulin melted significantly faster than the other samples.     

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.     

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。     

Heat stability of oil-in-water emulsions formed with intact or hydrolysed whey proteins: influence of polysaccharides

The heat stability of emulsions (4 wt% corn oil) formed with whey protein isolate (WPI) or extensively hydrolysed whey protein (WPH) products and containing xanthan gum or guar gum was examined after a retort treatment at 121 °C for 16 min. At neutral pH and low ionic strength, emulsions stabilized with both 0.5 and 4 wt% WPI (intact whey protein) were stable against retorting. The amount of β-lactoglobulin (β-lg) at the droplet surface increased during retorting, especially in the emulsion containing 4 wt% protein, whereas the amount of adsorbed α-lactalbumin (α-la) decreased markedly. Addition of xanthan gum or guar gum caused depletion flocculation of the emulsion droplets, but this flocculation did not lead to their aggregation during heating. In contrast, the droplet size of emulsions formed with WPH increased during heat treatment, indicating that coalescence had occurred. The coalescence during heating was enhanced considerably with increasing concentration of polysaccharide in the emulsions, up to 0.12% and 0.2% for xanthan gum and guar gum, respectively; whey peptides in the WPH emulsions formed weaker and looser, mobile interfacial structures than those formed with intact whey proteins. Consequently, the lack of electrostatic and steric repulsion resulted in the coalescence of flocculated droplets during retort treatment. At higher levels of xanthan gum or guar gum addition, the extent of coalescence decreased gradually, apparently because of the high viscosity of the aqueous phase.     

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.     

Fat mimetic capacity of Chlorella vulgaris biomass in oil-in-water food emulsions stabilized by pea protein

Vegetable proteins proved to be good emulsifiers for food emulsions with dietetic advantages. The use of these emulsions as carriers for healthy ingredients, such as colourings, with antioxidant and other beneficial properties, is an interesting subject.In this work, the capacity of the biomass of the microalga Chlorella vulgaris (which has been widely used as a food supplement) as a fat mimetic, and its emulsifier ability, was evaluated. Pea protein emulsions with C. vulgaris addition (both green and orange – carotenogenic) were prepared at different protein and oil contents. The rheological properties of the respective food emulsions were measured in terms of the viscoelastic properties and steady state flow behaviour and texture properties. It was observed that the two microalgal forms evidenced a fat mimetic capacity in these emulsions, the performance of the green stage of this C. vulgaris organism was significantly (p < 0.05) better than the orange stage.     

Inhibition of droplet flocculation in globular-protein stabilized oil-in-water emulsions by polyols

The influence of neutral cosolvents (polyols) on the stability of hydrocarbon oil-in-water emulsions stabilized by a globular protein was investigated. Glycerol (0–40 wt%) and sorbitol (0–35 wt%) were added to n-hexadecane oil-in-water emulsions stabilized by β-lactoglobulin (β-lg, pH 7.0, 150 mM NaCl), either before or after incubation at 30 °C for 24 h. The stability of the emulsions to flocculation and creaming improved when neutral cosolvents were added, with the effectiveness of the cosolvents depending on their type, concentration and time of addition. Emulsion stability was better for sorbitol than glycerol, improved with increasing cosolvent concentration, and was better when the cosolvents were added immediately after homogenization than when they were added 24 h later. The influence of the cosolvents on emulsion stability is interpreted in terms of their effect on the conformation and interactions of the adsorbed proteins, as well as on the droplet–droplet collision frequency. This study has implications for the development of protein stabilized oil-in-water emulsions for utilization in industrial products.     

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.     

Physicochemical characteristics and stability of oil-in-water emulsions stabilized by OSA starch

Starch hydrophobically modified with octenyl succinic anhydride (OSA starch) has strong surface activity and capability to modify viscosity of continuous phase. The influences of OSA starch, used as emulsifier, on stability, disperse and rheological properties of oil-in-water emulsions were examined in this work. The oil content in emulsions varied from 5 to 60% and OSA starch concentrations were 8, 10, 12, 14 and 16% expressed relative to the water mass.