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.     

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.     

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.     

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.     

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。     

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.     

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.     

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.     

Infrared spectroscopic analysis of structural features and interactions in olive oil-in-water emulsions stabilized with soy protein

Lipid and protein structural characteristics of olive oil-in-water emulsions formulated with various stabilizer systems were investigated using Fourier transform infrared spectroscopy (FT-IR). Proximate composition, water binding and textural properties were also evaluated in these emulsions. Two different olive oil-in-water emulsions were studied: E/SPI prepared with soy protein isolate as a stabilizing system, and E/SPI + SC + MTG prepared with a combination of soy protein isolate, sodium caseinate and microbial transglutaminase as a stabilizing system. Results showed that textural properties (P < 0.05) were dependent on the stabilizing system. E/SPI + SC + MTG emulsion presented greater (P < 0.05) lipid chain disorder, more lipid-protein interactions, and more (P < 0.05) ??-helix and ??-sheet structures. A relationship between textural and structural properties was also observed as a function of the stabilizing system employed in the formulation of emulsions. A more thorough understanding of this connection could help improve the development of food products with appropriate physical properties.     

Influence of chitosan and NaCl on physicochemical properties of low-acid tuna oil-in-water emulsions stabilized by non-ionic surfactant

An influence of low molecular weight (LMW) chitosan on physicochemical properties and stability of low-acid (pH 6) tuna oil-in-water emulsion stabilized by non-ionic surfactant (Tween 80) was studied. The mean droplet diameter, droplet charge (ζ-potential), creaming stability and microstructure of emulsions (5 wt% oil) were evaluated. The added chitosan was adsorbed on the surface of oil droplets stabilized by Tween 80 through electrostatic interactions. Such addition of chitosan at different concentrations (0–10 wt%) to emulsions showed slight effect on the mean droplet diameter. However, the degree of flocculation was a function of chitosan concentration assessed by emulsions' microstructure and creaming index. The impact of chitosan on the strength of the colloidal interaction between the emulsion droplets increased with increasing chitosan concentration. The mean diameter of droplet in emulsions increased with increasing NaCl because of the electrostatic screening effect. The addition of LMW chitosan could be performed to create tuna oil emulsions with low-acid to neutral character, as well as various physicochemical and stability properties suitable for health food products.     

Physicochemical properties of lactoferrin stabilized oil-in-water emulsions: Effects of pH,salt and heating

Lactoferrin is a globular protein from bovine milk with an unusually high isoelectric point (pI > 8), which may lead to novel functional properties in foods and other products because it is cationic across a wide pH range. In this study, we investigated the influence of pH (2–9), NaCl addition (0–200 mM), CaCl₂ addition (0–200 mM), and thermal processing (30–90 °C, 20 min) on the stability of lactoferrin (LF) stabilized oil-in-water emulsions. At ambient temperature, the emulsions were stable to droplet aggregation at low pH (pH ≤ 6), but exhibited some aggregation at pH ≈ pI (pH 7–9). The thermal stability of the emulsions depended on pH, holding temperature, and thermal history. When LF-coated droplets were heated in distilled water, and then their pH was adjusted in the range 2–9, they were highly unstable to aggregation at pH 7 and 8. On the other hand, when the pH was altered in the range 2–9 first, and then they were heated, the LF-coated droplets were highly unstable to aggregation at pH ≥ 5 when heated above 50 °C. The stability of the emulsions to salt addition depended on pH and salt type, which was attributed to counter-ion binding and electrostatic screening effects. For NaCl, emulsions were stable from 0 to 200 mM at pH 3 and 9, but aggregated at ≥100 mM at pH 6. For CaCl₂, emulsions were stable from 0 to 200 mM at pH 3, but aggregated with ≥150 mM CaCl₂ at pH 6 and 9. These results have important implications for the formulation and production of emulsion-based products using lactoferrin as an emulsifier.     

自由基氧化引起乳清蛋白理化性质变化的研究

研究了在羟基自由基氧化体系中,不同H2O2浓度(1～20 mmol/L)及不同FeCl3浓度(0.1～2 mmol/L)对乳清蛋白羰基、巯基、二聚酪氨酸等理化性质的影响.每种氧化条件的氧化时间分别为1,3,5 h..结果表明:氧化显著地影响了乳清蛋白的理化性质,同未氧化的对照组乳清蛋白相比,经过5 h氧化,所有浓度的FeCl3体系中,羰基增加3倍以上;所有条件下的巯基损失均达40%以上;在浓度为20 mmol/L的H2O2或2 mmol/L的FeCl3中,二聚酪氨酸分别增加了5倍和7倍.并且发现,在不同的FeCl3条件下其变化趋势更为迅速.由此可知,氧化极大程度地改变了蛋白的理化性质,并可能导致蛋白结构的改变,进而可能影响其功能性质.     

Emulsifying properties of lactose-amines in oil-in-water emulsions

Lactose-amines were synthesized with hexadecyl-amide and lactose via the Maillard reaction and their emulsion stabilization properties were investigated. Lactose-amines were synthesized using two different constant heating (4 and 8 h) and two different heating/cooling cycles (12 and 24 h). Each lactose-amine sample was used as an emulsifier in 20:80 ratio oil-in-water emulsions at four different concentrations (0.01%, 0.05%, 0.1%, and 1%). Emulsion stability was monitored by measuring the oil droplet sizes and the extent of destabilization via clarification over 5 days. At 1% concentrations, emulsions prepared with lactose-amines synthesized for 4, 12, and 24 h were as stable as the whey protein positive control emulsion. The 8 h lactose-amine sample resulted in a less stable emulsion. We assume the difference is related to the amount of heat this sample was exposed to during synthesis, with extensive heat leading to advanced Maillard products, which possessed reduced emulsification properties.     

Influence of interfacial composition on oxidative stability of oil-in-water emulsions stabilized by biopolymer emulsifiers

The objective of this research was to evaluate the influence of storage pH (3 and 7) and biopolymer emulsifier type (Whey protein isolate (WPI), Modified starch (MS) and Gum arabic (GA)) on the physical and oxidative stability of rice bran oil-in-water emulsions. All three emulsifiers formed small emulsion droplets (d₃₂ < 0.5 μm) when used at sufficiently high levels: 0.45%, 1% and 10% for WPI, MS and GA, respectively. The droplets were relatively stable to droplet growth throughout storage (d₃₂ < 0.6 μm after 20 days), although there was some evidence of droplet aggregation particularly in the MS-stabilized emulsions. The electrical charge on the biopolymer-coated lipid droplets depended on pH and biopolymer type: −13 and −27 mV at pH 3 and 7 for GA; −2 and −3 mV at pH 3 and 7 for MS; +37 and −38 mV at pH 3 and 7 for WPI. The oxidative stability of the emulsions was monitored by measuring peroxide (primary products) and hexanal (secondary products) formation during storage at 37 °C, for up to 20 days, in the presence of a pro-oxidant (iron/EDTA). Rice bran oil emulsions containing MS- and WPI-coated lipid droplets were relatively stable to lipid oxidation, but those containing GA-coated droplets were highly unstable to oxidation at both pH 3 and 7. The results are interpreted in terms of the impact of the electrical characteristics of the biopolymers on the ability of cationic iron ions to interact with emulsified lipids. These results have important implications for utilizing rice bran oil, and other oxidatively unstable oils, in commercial food and beverage products.     

Antioxidant and emulsifying properties of potato protein hydrolysate in soybean oil-in-water emulsions

The efficacy of a previously developed antioxidative potato protein hydrolysate (PPH) for the stabilisation of oil droplets and inhibition of lipid oxidation in soybean oil-in-water (O/W) emulsions was investigated. Emulsions (10% lipid, pH 7.0) with PPH-coated oil droplets were less stable than those produced with Tween 20 (P < 0.05). However, the presence of PPH, whether added before or after homogenisation with Tween 20, retarded emulsion oxidation, showing reduced formation of peroxides up to 53.4% and malonaldehyde-equivalent substances up to 70.8% after 7-d storage at 37 °C (P < 0.05), when compared with PPH-free emulsions. In the emulsions stabilised by PPH + Tween 20, 8–15% of PPH was distributed at the interface. Adjustment of the pH from 3 to 7 markedly increased ζ-potential of such emulsions (P < 0.05). Inhibition of lipid oxidation by PPH in soybean O/W emulsions can be attributed to both chemical and physical (shielding) actions.