Influence of biopolymer emulsifier type on formation and stability of rice bran oil-in-water emulsions: whey protein, gum arabic, and modified starch

Rice bran oil (RBO) is used in foods, cosmetics, and pharmaceuticals due to its desirable health, flavor, and functional attributes. We investigated the effects of biopolymer emulsifier type and environmental stresses on the stability of RBO emulsions. Oil-in-water emulsions (5% RBO, 10 mM citrate buffer) stabilized by whey protein isolate (WPI), gum arabic (GA), or modified starch (MS) were prepared using high-pressure homogenization. The new MS used had a higher number of octenyl succinic anhydride (OSA) groups per starch molecule than conventional MS. The droplet diameters produced by WPI and MS were considerably smaller (d < 300 nm) than those produced by GA (d > 1000 nm). The influence of pH (3 to 8), ionic strength (0 to 500 mM NaCl), and thermal treatment (30 to 90 °C) on the physical stability of the emulsions was examined. Extensive droplet aggregation occurred in WPI-stabilized emulsions around their isoelectric point (4 < pH < 6), at high salt (> 200 mM, pH 7), and at high temperatures (>70 °C, pH 7, 150 mM NaCl), which was attributed to changes in electrostatic and hydrophobic interactions between droplets. There was little effect of pH, ionic strength, and temperature on emulsions stabilized by GA or MS, which was attributed to strong steric stabilization. In summary: WPI produced small droplets at low concentrations, but they had poor stability to environmental stress; GA produced large droplets and needed high concentrations, but they had good stability to stress; new MS produced small droplets at low concentrations, with good stability to stress. Practical Application: This study showed that stable rice bran oil-in-water emulsions can be formed using biopolymer emulsifiers. These emulsions could be used to incorporate RBO into a wide range of food products. We compared the relative performance of whey protein, GA, and a new MS at forming and stabilizing the emulsions. The new OSA MS was capable of forming small stable droplets at relatively low concentrations.     

Modifications in stability and structure of whey protein-coated o/w emulsions by interacting chitosan and gum arabic mixed dispersions

The influence of chitosan and gum arabic mixtures on the behaviour of o/w emulsions has been investigated at pH = 3.0. The emulsion behaviour, properties and microstructure were found to be greatly dependent on the precise gum arabic to chitosan ratio. Mixing of gum arabic with chitosan leads to the formation of coacervates of a size dependent on their ratio. Incorporation of low gum arabic to chitosan weight ratios into whey protein-coated emulsions causes depletion flocculation and gravity-induced phase separation. Increasing the polysaccharide weight ratio further, a droplet network with a rather high viscosity (at low shear stress) is generated, which prevents or even inhibits phase separation. At even higher gum arabic to chitosan ratios, the emulsion droplets were immobilised into clusters of an insoluble ternary matrix. Although the emulsion droplet charge had the same sign as that of the coacervates, clusters of oil droplets in a ternary matrix were generated. A mechanism to explain the behaviour of the whey protein-stabilised o/w emulsions is described on the basis of confocal and phase contrast microscopic observations, rheological data, zeta potential measurements, particle size analysis and visual assessment of the macroscopic phase separation events.     

Zeta potentials of gum arabic stabilised oil in water emulsions

The electrostatic contribution to the mechanism by which gum arabic stabilises oil in water has been investigated using laser Doppler electrophoresis. Electrophoretic mobilities of -limonene emulsion droplets measured in 10⁻³, 10⁻² and 10⁻¹ M NaCl over a pH range from 1 to 10, and 10⁻³–10⁻¹ M CaCl₂ in doubly distilled water, yielded relatively low potentials (less than 28 mV in magnitude). The interpreted zeta potentials are less than those required for electrostatic stabilisation alone. This data supports the postulated steric stabilisation mechanism with a finite electrostatic contribution. A model which suggests the arabino galacto proteins are adsorbed—via the proteins—to the interface with the polysaccharide moieties protruding into solution to give rise to a steric stabilising layer is supported by the data. No charge reversal is observed for the Ca solutions in contrast to the pH data indicating that some of the charge groups are inaccessible to the Ca ions.     

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.     

Stability and opacity of orange oil cloudy emulsions based on gum elemi and gum arabic

Orange oil cloudy emulsions based on naturally occurring oil-soluble gum elemi and naturally occurring water-soluble gum arabic have been prepared and evaluated. Cloud and emulsion stability, as well as the opacity of each emulsion, were recorded and compared. It was demonstrated that the emulsion stability is determined by the gum elemi/orange oil ratio, the orange oil content, and the gum arabic/orange oil ratio. The opacity is a function of the orange oil content and to a lesser extent also depends on the gum elemi/orange oil ratio. Since the gum elemi/orange oil ratio is a critical parameter affecting both opacity and stability it should be carefully chosen and controlled.
Gum arabic is not the sole emulsifier, as gum elemi also adsorbs on the oil droplets and plays a role in emulsion stability.     

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.     

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.     

Emulsifying properties of pea protein/guar gum conjugates and mayonnaise application

Modified plant protein may be used as a healthy and more functional emulsifier in food products. The objective of this study was to evaluate the emulsifying properties of functionally enhanced pea protein (i.e. pea protein conjugated with guar gum, G-PPI) and its potential application to mayonnaise, compared with unmodified pea protein. Emulsions containing G-PPI were prepared at different pH, salt concentrations, protein concentrations and oil/water ratios. Mayonnaise samples were prepared using the pea proteins or egg yolk powder. Various characteristics of the emulsions, including droplet size, apparent viscosity, viscoelasticity and microstructure, were analysed. The emulsions with G-PPI had significantly increased stability of up to 89.4% and apparent viscosity of up to 48.62 mPa.s. The G-PPI emulsion had a smaller average droplet size of 934.4 nm at pH 7 compared with the PPI emulsion (stability 62.7%, apparent viscosity 22.8 mPa.s and droplet size 1664.8 nm). The pH, NaCl concentration, protein concentration and oil/water ratio greatly affected the emulsifying properties. The G-PPI mayonnaise at higher protein concentrations (6 or 8%) exhibited excellent emulsifying and rheological properties. The modified pea protein through the green modification process with natural polysaccharides could be used as a safe and functional emulsifier in different emulsified foods.     

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。     

Flaxseed gums and their adsorption on whey protein-stabilized oil-in-water emulsions

The effect of the addition of flaxseed gum on the physicochemical properties of whey protein-stabilized (WPI) oil-in-water emulsions at pH 3.5 was investigated. Two different varieties (Emerson and McDuff) were tested at concentrations ranging from 0% to 0.33% (w/v), by measuring droplet size, ζ-potential, phase separation behavior, microstructure and apparent viscosity. With addition of flaxseed gum the ζ-potential of the droplets decreased from around +30 mV to a negative value (−10 mV) at concentrations >0.2%. These results indicated that the negatively charged polysaccharide fraction from flaxseed interacted with the protein adsorbed at the interface. An increase in apparent particle size was also noted with increasing flaxseed concentration, with destabilization becoming visually evident at concentrations higher than 0.1% (w/v). Microscopy, rheological data and size distribution analysis demonstrated for the first time that flaxseed gum interacts with protein-stabilized oil droplets at low pH, causing bridging flocculation. No significant differences were noted between flaxseed gums extracted from the Emerson and McDuff varieties. This research demonstrated that the electrostatic interactions between flaxseed gums and protein-stabilized emulsions need to be controlled when designing novel acidic beverages containing these polysaccharides.     

Influence of tragacanth gum exudates from specie of Astragalus gossypinus on rheological and physical properties of whey protein isolate stabilised emulsions

The aim of this work was to investigate the effects of Iranian tragacanth gum (Astragalus gossypinus) (0.5, 1 wt.%), Whey protein isolate (WPI) (2, 4 wt.%) and acid oleic‐phase volume fraction (5, 10% v/v) on droplet size distribution, creaming index and rheological properties of emulsions with various compositions. Rheological investigations showed that both loss and storage modules increased with gum and oil contents. However, the viscoelastic behaviour was mainly governed by the gum concentration. Delta degree (storage and loss modules ratio) increased with frequency indicated that liquid like viscose behaviour dominates over solid like elastic behaviour. The shear‐thinning behaviour of all dispersions was successfully modelled with power law and Ellis models and Ellis model was founded as the better model to describe the flow behaviour of dispersions. Droplet size distribution was measured by light scattering; microscopic observations revealed a flocculated system. Increase in gum, WPI and oil contents resulted in decrease in creaming index of emulsions with dominant effect of gum concentration.     

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.     

Effect of Lepidium perfoliatum seed gum addition on whey protein concentrate stabilized emulsions stored at cold and ambient temperature

In this study the effect of Lepidium perfoliatum seed gum on the properties of whey protein concentrate (WPC) stabilized corn oil-in-water emulsions at pH 7 was investigated. Various concentrations (0–0.6% w/v) of L. perfoliatum seed gum were used together with 2% (w/v) WPC to emulsify corn oil in water at a ratio of 1:5. Quality attributed such as particle size distribution, creaming profile and coalescence rate during storage at 4 and 25 °C; surface and interfacial tension; zeta potential and viscosity of the emulsions were determined. The results indicated that the addition of L. perfoliatum seed gum had no significant effect on zeta potential but the surface and interfacial tension increased with the rise of gum concentration. It was also found that the addition of L. perfoliatum seed gum to WPC emulsions at a critical concentration of 0.2% (w/v) caused flocculation of oil droplets, which resulted in marked increase in particle size and the creaming rate. However at higher gum concentrations beyond this value, the particle size remained constant, apparently because of the high viscosity of the aqueous phase. At all concentrations tested, emulsions stored at 4 °C were more stable except for those containing 0.2% L. perfoliatum seed gum.     

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.     

乳清蛋白的功能特性及应用

介绍了乳清蛋白的组成成分和功能特性；论述了乳清蛋白的生物利用价值及在运动营养、医疗保健和食品加工等方面的广阔应用前景。