Depletion Flocculation of Beverage Emulsions by Gum Arabic and Modified Starch

ABSTRACT: The creaming velocity, apparent viscosity, and ultrasonic attenuation spectra (1 to 50 MHz) of 5 wt% n hexadecane oil-in-water emulsions containing different droplet radii (r = 0.15 - 0.7 μm), biopolymer types (gum arabic or modified starch), and biopolymer concentrations (0 to 2.5 wt%) were measured. Depletion flocculation was observed in the emulsions when the nonabsorbed biopolymer concentration exceeded a critical concentration (CFC). The CFC increased with decreasing droplet radius for both biopolymers because the magnitude of the depletion attraction increases with droplet size. The CFC was lower for gum arabic than modified starch because it has a higher effective volume in solution. Depletion flocculation led to an increase in creaming instability and apparent viscosity of the emulsions. Flocculation could be nondestructively monitored by measuring the decrease in ultrasonic attenuation of the emulsions. These results show that depletion flocculation by gum arabic and modified starch can have an adverse effect on the stability of beverage emulsions.     

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.     

纳米SiO2改性4 种大分子材料的乳液制备及性质

为提高乳液稳定性,采用纳米SiO2改性明胶（gelatin,GE）、大豆分离蛋白、壳聚糖和阿拉伯胶（gum arabic,GA）制备茶油乳液。以乳化活性、乳化稳定性、离心稳定性、平均粒径、流变特性为考察指标,探究质量分数3.000%的纳米SiO2对4 种大分子材料复合乳液性质的影响,并对乳液的微观结构及油滴分布进行观察。结果表明,纳米SiO2能增强乳液稳定性,其中GE-纳米SiO2复合乳液综合性质最佳。添加纳米SiO2后乳化活性和乳化稳定性显著增加（P＜0.05）,离心稳定性降低68.444%。平均粒径为8.472 μm,乳液粒径最小且分布均匀,表面光滑呈球状。流变表现为典型的弱凝胶特性,稳定性良好。研究结果可为天然高分子和纳米SiO2乳液的制备和应用提供实践基础。     

不同黏度多糖阿拉伯胶和瓜尔胶对肌原纤维蛋白乳化性质的影响

选取两种分子质量相近、黏度相差较大的天然高分子多糖阿拉伯胶（arabic gum,AG）和瓜尔胶（guar gum,GG）分别与肌原纤维蛋白（myofibrillarprotein,MP）进行复合,研究不同多糖添加量（0.1%～0.5%）对MP-多糖复合物乳液性质的影响规律。结果表明,AG和GG均可以显著改善MP的乳化性质,其中AG对乳化活性的改善效果较好,而GG更有利于乳液的稳定性。随着多糖质量分数增加,乳化活性指数和稳定性指数均呈先升高后降低趋势,AG和GG添加量分别为0.3%和0.2%时,乳化活性指数和稳定性指数达到最大值。界面蛋白含量测定结果显示,AG和GG均会导致界面蛋白含量下降,尤其是GG的作用更明显。随着AG和GG添加量增加,乳液粒径逐渐减小,且尺寸分布更加均一,添加量超过0.3%后,GG组乳液出现少量絮凝现象。同一添加量下,GG组乳液粒径明显小于AG组。流变学分析证实,所有乳液均为假塑性流体,表现出弱凝胶性质。AG添加量较少（≤0.3%）时会降低乳液黏度,并明显提高乳液的储能模量,而GG的添加使乳液表观黏度和储能模量均显著提高,与AG相比,高黏度GG制备的乳液拥有更高的...     

Stability and Oil Migration of Oil‐in‐Water Emulsions Emulsified by Phase‐Separating Biopolymer Mixtures

Oil‐in‐water (O/W) emulsions with varying concentration of oil phase, medium‐chain triglyceride (MCT), were prepared using phase‐separating gum arabic (GA)/sugar beet pectin (SBP) mixture as an emulsifier. Stability of the emulsions including emulsion phase separation, droplet size change, and oil migration were investigated by means of visual observation, droplet size analysis, oil partition analysis, backscattering of light, and interfacial tension measurement. It was found that in the emulsions prepared with 4.0% GA/1.0% SBP, when the concentration of MCT was greater than 2.0%, emulsion phase separation was not observed and the emulsions were stable with droplet size unchanged during storage. This result proves the emulsification ability of phase‐separating biopolymer mixtures and their potential usage as emulsifiers to prepare O/W emulsion. However, when the concentration of MCT was equal or less than 2.0%, emulsion phase separation occurred after preparation resulting in an upper SBP‐rich phase and a lower GA‐rich phase. The droplet size increased in the upper phase whereas decreased slightly in the lower phase with time, compared to the freshly prepared emulsions. During storage, the oil droplets exhibited a complex migration process: first moving to the SBP‐rich phase, then to the GA‐rich phase and finally gathering at the interface between the two phases. The mechanisms of the emulsion stability and oil migration in the phase‐separated emulsions were discussed.     

In vitro study of intestinal lipolysis using pH-stat and gas chromatography

Developing healthy products requires in-depth knowledge of digestion. This study focuses on lipid digestion in relation to emulsion properties typically followed by pH-stat. Although this is a fast and easy method to follow the overall digestion, it provides no details on lipid digestion products. Thus, the aims of the present study were to use gas chromatography (GC) to determine all products present during lipolysis, i.e. monoglycerides (MG), diglycerides (DG) and triglycerides (TG), and to compare this method with the pH-stat method for free fatty acids (FFA). Fine, medium and coarse emulsions stabilized with two different emulsifiers (whey protein isolate (WPI) or gum arabic) were digested under in vitro intestinal conditions. Although the amount of FFA increased for both methods for WPI stabilized emulsions, the amount of FFA was 2-3 times higher when determined by GC compared with pH-stat. GC analysis showed decreasing amounts of MG and DG with increasing droplet size for both emulsions. Molar ratios of FFA/DG and MG/DG were twofold higher for WPI than for gum arabic stabilized emulsions. This indicates that the total production of lipolytic products (i.e. FFA + MG + DG) depends on the droplet size and the emulsifier but their proportions only depend on the emulsifier. Although pH-stat provides a fast measure of FFA release, it is influenced by the emulsifier type at the oil-water interface and therefore care should be taken when interpreting pH-stat results. We suggest combining this method with GC for accurate FFA determination and further evaluation of all lipolytic products.     

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.     

Physical and Oxidative Stabilities of O/W Emulsions Formed with Rice Dreg Protein Hydrolysate: Effect of Xanthan Gum Rheology

The shortening of shelf-life of food emulsions is frequently due to poor creaming and lipid oxidation stability. The lipid oxidation of O/W emulsions can be inhibited by rice dreg protein hydrolysate (RDPH); however, emulsions were stabilized by Tween-20. Polysaccharides can control the rheology and network structure of the aqueous continuous phase by increasing viscosity and yield stress, hence retarding phase separation and gravity-induced creaming, especially for xanthan gum. The objective of this research was to evaluate whether emulsions formed with 2 wt% RDPH and stabilized by xanthan gum (0–0.5 wt%) could produce 20 % (v/v) soybean oil-in-water emulsions that had good physical and oxidative stability. The degree of flocculation of droplets as a function of xanthan gum concentration was assessed by the microstructure, rheology, and the creaming index of emulsions. Addition of xanthan gum prior to homogenization had no significant effect on the mean droplet diameter in all emulsions studied. Increase in xanthan gum concentration led to the increase in creaming stability of emulsions, due to an increase in viscosity of the continuous phase and/or the formation of a droplet network with a yield stress, as well as the enhanced steric and electrostatic repulsion between the droplets. Lipid oxidation of the emulsions was significantly inhibited at xanthan gum concentrations of 0.12 wt% or above with RDPH, which could due to the fact that xanthan gum increases the viscosity of the aqueous phase and hindered the diffusion of oxidants to the oil droplet surface area, synergistic effect between RDPH and xanthan gum to suppress oil peroxidation, and metal ion chelation capability of xanthan gum. Thus, stable protein hydrolyzates-type emulsions could be obtained with increasing concentration of xanthan gum.     

Development of high internal phase Pickering emulsions stabilised by ovotransferrin–gum arabic particles as curcumin delivery vehicles

This study explored feasibility of preparing high internal phase Pickering emulsions (HIPEs) as curcumin delivery vehicles. Particles assembled from ovotransferrin (OVT) and gum arabic (GA) could stabilise HIPEs successfully, and OVT–GA particle-stabilised HIPEs with extremely high oil fraction of 0.90 were stable. Droplet size and rheological properties of OVT–GA particle-stabilised HIPEs were dependent on both particle concentration and oil fraction. Either increasing particle concentration or decreasing oil fraction resulted in a decrease of droplet size. Increase in storage modulus and viscosity of HIPEs could be achieved by increasing particle concentration or oil fraction. Food structures with controlled shape could be constructed by OVT–GA particle-stabilised HIPEs. When compared with bulk MCT oil, OVT–GA particle-stabilised HIPEs improved both extent of lipolysis and curcumin bioaccessibility significantly. These findings provided novel insight into potential application of HIPEs with extremely high oil fractions in nutraceutical delivery systems.     

壁材对方竹叶黄酮微胶囊结构及抗氧化性能的影响

本文以麦芽糊精、阿拉伯胶、明胶、大豆分离蛋白、月桂酸单甘酯为壁材,通过喷雾干燥制备方竹叶黄酮微胶囊,利用扫描电镜、激光粒度仪对其结构进行表征,并以理化性质及抗氧化活性为指标,对比5种壁材的包埋效果及微胶囊性能。结果表明:阿拉伯胶制备微胶囊的包埋率最高（91.23%±1.00%）,堆积密度最高（0.53±0.01 g/cm3）,休止角最小（33.27°±1.20°）,含水量最低（5.33%±0.28%）,并具有良好的流动性及储存性能;微胶囊粒径分布从大到小依次为:月桂酸单甘酯（22.87 μm）>大豆分离蛋白（15.65 μm）>麦芽糊精（14.26 μm）>明胶（8.95 μm）>阿拉伯胶（6.96 μm）;扫描电镜结果显示,阿拉伯胶制备的微胶囊呈球形且表面较为完整光滑;在体外抗氧化活性及还原性实验中,阿拉伯胶制备的微胶囊抗氧化活性及还原性较高,其清除DPPH自由基的IC₅₀为364.30 μg/mL。综上,阿拉伯胶制备的方竹叶黄酮微胶囊性质明显优于其他4种壁材微胶囊产品,为开发功能更加稳定的方竹叶黄酮产品提供技术支撑。     

不同乳化剂对油酸和亚油酸乳状液稳定性的影响

本文以粒径、稳定性和流变为考察指标,利用激光粒度仪、食品稳定性分析仪、流变仪等研究不同种类和添加量的食品乳化剂(阿拉伯胶、酪蛋白酸钠、吐温20)对不饱和脂肪酸(油酸和亚油酸)乳状液的制备及其稳定性的影响。结果表明,三种乳化剂均可制备出稳定性较好的乳状液,不同乳化剂的质量分数不同得到乳状液的稳定性不同。较高质量分数的阿拉伯胶(4%,w/v)乳状液,具有最低的澄清指数并且具有最大粘度(0.30~0.40 Pa·s)。当酪蛋白酸钠的质量分数为2%时,制备出的乳状液较稳定,但粒径较大,贮藏稳定性较差。较低质量分数的吐温20(1%,w/v)的乳状液具有最小粒径(0.20~0.21 μm),经过贮藏后变化程度也最小。本文研究了不同食品乳化剂制备的不饱和脂肪酸乳状液及其稳定性,可为不饱和脂肪酸乳状液的制备和应用提供参考。     

STABILITY OF CAPSICUM ANNUUM OLEORESIN-IN-WATER EMULSIONS CONTAINING PROSOPIS AND ACACIA GUMS

Chilli oleoresin-in-water emulsions were stabilized with very low concentrations of mesquite ( Prosopis juliflora ), arabic ( Acacia Senegal ) and acacia ( Acacia spp.) gums at different pH values in order to establish which polysaccharide had the best emulsifying capacity and provided the best stability against droplet coalescence and pigment degradation. Mesquite gum was the best emulsifying and stabilizing agent, followed by gum arabic and acacia gum. In all cases, pH had a dramatic effect on the emulsion stability against droplet coalescence and color degradation. The stabilizing mechanisms governing these two deteriorative processes were opposite. While coalescence kinetics was hindered at high pH values, color degradation kinetics took place at a higher rate, while the opposite effect occurred at lower pH values. A number of factors were important in determining the emulsifying capacity, the droplet coalescence stability and the color degradation stability of the gums among them, the protein content, the molecular weight, the surface charge and the steric configuration adopted at different pH values.     

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.     

阿拉伯树胶-肌原纤维蛋白共建乳状液体系的物理稳定性

研究不同质量分数阿拉伯树胶(arabic gum,AG)对肌原纤维蛋白(myofibrillar protein,MP)为乳化剂的乳化体系稳定性的影响。结果显示,乳化活性和乳化稳定性随着AG质量分数的增加呈先增加后降低的变化趋势。AG质量分数为0.3%时,MP-AG共建乳状液体系表现出最高的物理稳定性,显著地增加了ζ-电势,降低了粒径大小,表现出最低的乳析指数(P0.05)。激光共聚焦显微镜(confocal laser scanning microscopy,CLSM)观察结果表明,与单独以MP为乳化剂的样品相比,添加0.3%AG的乳状液样品液滴颗粒最小,这与粒径大小和分布的结果相一致。通过CLSM进一步观察MP在界面上的吸附行为,结果表明,与未添加AG的乳状液样品相比,添加0.3%AG的MP-AG共建乳状液体系所形成的界面膜更加坚固和致密。总之,AG可以促进蛋白质在油水界面上的吸附作用,提高MP乳化的水包油型乳状液的物理稳定性。     

COLOR DEGRADATION AND COALESCENCE KINETICS OF AZTEC MARIGOLD OLEORESIN-IN-WATER EMULSIONS STABILIZED BY MESQUITE OR ARABIC GUMS AND THEIR BLENDS

Aztec marigold oleoresin-in-water (O/W) emulsions were formulated with mesquite gum or gum arabic and their blends as emulsifying and protective agents, at pH values of 3, 5 and 7. Changes in the emulsions average particle size were determined by laser ray diffraction, in tinctorial power by visible spectrophotometry and in color by reflectance measurements. Both gums and their blends form highly stable O/W emulsions against drop coalescence and color loss. The emulsifying agent composition and pH have an important role in determining the degree of effectiveness of the emulsions against color loss and drop coalescence kinetics. Mesquite gum provided a better stability against drop coalescence than gum arabic, and furthermore their blends had a synergistic effect providing a higher stability     

Steady and Dynamic Shear Rheological Properties,and Stability of Non-Flocculated and Flocculated Beverage Cloud Emulsions

Rheological properties of single-phase, and emulsions containing modified starch and gum arabic as surface active hydrocolloids, as well as xanthan and tragacanth gums as stabilizers were evaluated under steady and dynamic shear testing conditions using a control stress rheometer. Emulsions were formed by 9% and 14% gum concentrations with oil concentration maintained at 9% thus giving a 1:1 and 1.5:1 surface active agent to oil ratio, respectively. The rates of droplet coalescence and creaming, for a total of 8 emulsions, as a function storage time before and after dilution in a simulated fruit beverage were then investigated. Steady shear (flow curve) were well described by the Carreau model at shear stress ranging from 0.01 to 100 Pa. All prepared water phases indicated a zero-shear viscosity plateau followed by shear thinning behavior with flow behavior index (n) ranging from 0.51 to 0.79 for 14% starch-0.3% xanthan and 14% gum arabic-0.8% tragacanth stabilized emulsions, respectively. The water phase flow property data were well fitted by the Einstein equation and its expansions. The dynamic rheological properties of water phase and emulsions were also evaluated for G′(ω) and G″(ω) from 1 to 50 rad/s. Similar curves were obtained with varying degrees of deviations (G′ from G″) for different emulsions. Starch-xanthan emulsion and associated water phase at 1.5/1 agent to oil ratio demonstrated viscoelastic behavior (G′ ≥ G″) with lower droplet coalescence and creaming rates. On the other hand, gum arabic-xanthan emulsion at 1:1 agent to oil ratio showed the highest rate of droplet coalescence and a greater degree of creaming. It was speculated that the lower stability of gum arabic-xanthan emulsion could be related to the denaturation of proteinaceous part in the gum and loss of emulsification capacity due to lower pH and pasteurization.     

Comparison of Gum Arabic, Modified Starch, and Whey Protein Isolate as Emulsifiers: Influence of pH, CaCl2 and Temperature

ABSTRACT: The particle size and zeta potential of model beverage emulsions (0.01 wt% soybean oil-in-water emulsions, d ≅ 1 mm) stabilized by gum arabic, modified starch, or whey protein isolate (WPI) were studied with varying pH (3 to 9), CaCl₂ concentration (0 to 25 mM), and temperature (30 °C to 90 °C). Temperature, pH, CaCl₂ strongly influenced emulsions stabilized by WPI because its stabilizing mechanism was mainly electrostatic repulsion, but not those stabilized by gum arabic or modified starch because their stabilizing modes of action were mainly steric repulsion. This study may have important implications for the application of WPI as an emulsifier in beverage emulsions.     

Effects of xanthan gum on physicochemical properties and stability of corn oil-in-water emulsions stabilized by polyoxyethylene (20) sorbitan monooleate

The influence of added xanthan gum on rheological and dispersion characteristics and stability of concentrated (50% w/w) corn oil-in-water emulsions, stabilized with 5% (percentage on oil amount) polyoxyethylene (20) sorbitan monooleate (Tween 80), have been investigated. Emulsion with no xanthan indicated coalescence and poor creaming stability. All emulsions, with and without xanthan, showed shear-thinning flow behavior. Addition of xanthan protected emulsions from coalescence during 15 days of storage. Increase in xanthan concentration led to decrease in droplet average radius and creaming index, and increase in elastic properties of emulsions. Decrease in the emulsions flow behavior indexes, which suggested the extent of non-Newtonian behavior of emulsions, was influenced by increase in xanthan concentration. Above 0.04% of xanthan concentration, G′ and G″ values indicated formation of weak gels. Gel structure existence arises from droplet network association, due to depletion flocculation. Standard deviation of emulsions droplet size mean diameter decreased while concentration of added xanthan increased.     

复合凝聚角鲨烯微胶囊的制备研究

为了提高角鲨烯的稳定性,以明胶和阿拉伯胶为壁材、角鲨烯为芯材、转谷氨酰胺酶为固化剂,采用复合凝聚法制备角鲨烯微胶囊。研究了壁材组成、芯壁比、壁材浓度、p H值、搅拌速度、乳化速度等单因素对微胶囊的包埋率、载药量以及粒径大小的影响,并通过正交试验优化了制备工艺。结果表明,角鲨烯微胶囊的最佳制备工艺:明胶:阿拉伯胶(w:w)为1.00:1.00,芯壁比为1:1,壁材浓度为2%,p H为3.6,搅拌速度为500 r/min,乳化速度10 000 r/min。该条件下,角鲨烯微胶囊的包埋率为(68.2±1.5)%,载药量为(40.8±1.2)%,粒径为(98.5±2.5)μm。     

Stabilization of olive oil – lemon juice emulsion with polysaccharides

An olive oil – lemon juice Greek salad dressing was developed employing xanthan gum as stabilizer and gum arabic or propylene glycol alginate as emulsifier in various combinations. In general, samples containing xanthan gum arabic were more stable against oil droplet coalescence and less stable against creaming. The use of propylene glycol alginate in the place of gum arabic, on the other hand, resulted in emulsions of higher creaming stability. Application of steady shear rheology and determination of rheological parameter values from the shearing stress-rate of shear curves, indicated that the rheological properties of the dressings were decreased with storage. Dressing texture assessment preference tests indicated that potential consumers of the product may opt for a medium viscosity product and this has to be taken into consideration when designing polysaccharide – stabilized dressings exhibiting a decrease in their textural characteristics with storage time.