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.     

Influence of chitosan on stability and lipase digestibility of lecithin-stabilized tuna oil-in-water emulsions

The influence of chitosan concentration (0–0.3 wt%) and molecular weight (120, 250 and 342.5 kDa) on the physical stability and lipase digestibility of lecithin-stabilized tuna oil-in-water emulsions was studied. The ζ-potential, droplet size, creaming stability, free fatty acids and glucosamine released was measured for the emulsions when they were subjected to an in vitro digestion model. The ζ-potential of the oil droplets in lecithin-chitosan stabilized emulsions changed from positive (≈+53 mV) to negative and the emulsions were unstable to droplet aggregation for all chitosan concentrations and molecular weights used after being subjected to the digestion model. The amount of free fatty acid and glucosamine released per unit amount of emulsion was higher when pancreatic lipase was included in the digestion model. These results suggest that lecithin-chitosan coated droplets can be degraded by lipase under simulated gastrointestinal conditions. Consequently, chitosan coated lipid droplets may serve as useful carriers for the delivery of bioactive lipophilic nutraceuticals.     

Effect of chitosan molecular weight on the stability and rheological properties of β-carotene emulsions stabilized by soybean soluble polysaccharides

In this study, β-carotene emulsions were prepared using a two-stage homogenization process and adsorption of chitosan to anionic droplets coated with soybean soluble polysaccharides (SSPS). Effects of the molecular weights of chitosan on the stability and rheological properties of β-carotene emulsions were investigated. Results demonstrated that the ζ-potential, particle size and rheological properties of emulsions were greatly dependent on the chitosan molecular weight. It was found that the particle size of SSPS-stabilized emulsions increased with the rise of chitosan molecular weight at higher chitosan concentrations (>0.2 wt%). Chitosan molecular weight had a significant impact on the heat and light stability of β-carotene in emulsions. SSPS-stabilized emulsion with the adsorption of medium molecular weight-chitosan (MM-chitosan) was more stable than those with the adsorption of low and high molecular weight-chitosan (LM-chitosan and HM-chitosan). Dynamic oscillatory shear tests indicated that the viscoelasticity could be enhanced by the adsorption of higher molecular weight of chitosan onto the SSPS-coated droplet surfaces.     

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.     

Effect of chitosan on the stability and properties of modified lecithin stabilized oil-in-water monodisperse emulsion prepared by microchannel emulsification

The effect of chitosan (CHI) on the stability of monodisperse modified lecithin (ML) stabilized soybean oil-in-water (O/W) emulsion was investigated. Monodisperse emulsion droplets with particle size of 24.4 ± 0.7 μm and coefficient of variation below 12% were prepared by microchannel (MC) emulsification using a hydrophilic asymmetric straight-through MC silicon 24 × 24 mm microchip consisting of 23,348 microchannels. The stability of the ML stabilized monodisperse emulsion droplets was investigated as a function of CHI addition at various concentration, pH, ionic strength, thermal treatment and freezing-thawing treatment by means of particle size and ζ-potential measurements as well as microscopic observation. The monodisperse O/W emulsions were diluted with CHI solution at various concentrations to a final droplet concentration of 1 wt% soybean oil, 0.25 wt% ML and 0–0.5 wt% CHI at pH 3. Pronounced droplet aggregation was observed when CHI was present at a concentration range of between 0.01 and 0.04 wt%. Above this concentration range, flocculations were less extensive, indicating some restabilization. ML stabilized emulsions were stable at a wide range of NaCl concentrations (0–1000 mM) and pH (3–8). On the contrary, in the presence of CHI, aggregation of the emulsion droplets was observed when NaCl concentration was above 200 mM and when the pH started to approach the pKa of CHI (i.e. ∼6.2–7.0). Emulsions containing CHI were found to have better stability at high temperature (>70 °C) in comparison to the emulsion stabilized only by ML. With sucrose/sorbitol as cryoprotectant aids, emulsions with the addition of CHI were found to be more resistant to droplet coalescence as compared to those without CHI after freezing at −20 °C for 22 h and thawing at 30 °C for 2 h. The use of CHI may potentially destabilize ML-stabilized O/W emulsions but its stability can be enhanced by selectively choosing the appropriate CHI concentrations and conditions of preparation.     

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。     

Effect of ultrasound on physicochemical properties of emulsion stabilized by fish myofibrillar protein and xanthan gum

To investigate the effects ultrasound (20 kHz, 150–600 W) on physicochemical properties of emulsion stabilized by myofibrillar protein (MP) and xanthan gum (XG), the emulsions were characterized by Fourier transform infrared (FT-IR) spectroscopy, ζ-potential, particle size, rheology, surface tension, and confocal laser scanning microscopy (CLSM). FT-IR spectra confirmed the complexation of MP and XG, and ultrasound did not change the functional groups in the complexes. The emulsion treated at 300 W showed the best stability, with the lowest particle size, the lowest surface tension (26.7 mNm⁻¹) and the largest ζ-potential absolute value (25.4 mV), that were confirmed in the CLSM photos. Ultrasound reduced the apparent viscosity of the MP-XG emulsions, and the changes of particle size were manifested in flow properties. Generally, ultrasound was successfully applied to improve the physical stability of MP-XG emulsion, which could be used as a novel delivery system for functional material.     

Crosslinking of interfacial layers in multilayered oil-in-water emulsions using laccase: Characterization and pH-stability

The enzymatic crosslinking of polymer layers adsorbed at the interface of oil-in-water emulsions was investigated. A sequential two step process, based on the electrostatic deposition of pectin onto a fish gelatin interfacial membrane was used to prepare emulsions containing oil droplets stabilized by fish gelatin-beet pectin membranes (citrate buffer, 10 mM, pH 3.5). First, a fine dispersed primary emulsion (5% soybean oil (w/v), 1% (w/w) gelatin solution) (citrate buffer, 10 mM, pH 3.5) was produced using a high pressure homogenizer. Second, a series of secondary emulsions were formed by diluting the primary emulsion into pectin solutions (0 - 0.4% (w/w)) to coat the droplets. Oil droplets of stable emulsions with different oil droplet concentrations (0.1%, 0.5%, 1.0% (w/v)) were subjected to enzymatic crosslinking. Laccase was added to the fish gelatin-beet pectin emulsions and emulsions were incubated for 15 min at room temperature. The pH- and storage stability of primary, secondary and secondary, laccase-treated emulsions was determined. Results indicated that crosslinking occurred exclusively in the layers and not between droplets, since no aggregates were formed. Droplet size increased from 350 to 400 nm regardless of oil droplet concentrations within a matter of minutes after addition of laccase suggesting formation of covalent bonds between pectin adsorbed at interfaces and pectin in the aqueous phase in the vicinity of droplets. During storage, size of enzymatically treated emulsions decreased, which was found to be due to enzymatic hydrolysis. Results suggest that biopolymer-crosslinking enzymes could be used to enhance stability of multilayered emulsions.     

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.     

豌豆分离蛋白-羧甲基纤维素纳静电复合物在乳液中的应用研究

为改善豌豆分离蛋白(PPI)在酸性乳液体系中的应用特性,采用阴离子多糖-羧甲基纤维素钠(CMC)与PPI在酸性条件下形成的静电复合物稳定O/W型乳液。首先研究了3% PPI溶液的溶解度、表面疏水性随CMC浓度(0~0.5%)的变化,在此基础上,分析了PPI-CMC静电复合物对乳液ζ-电位、粒径、粘度、乳析稳定性指数及微观结构的影响。结果表明:在pH4.5条件下,随着CMC浓度由0增加至0.5%,乳状液滴表面负电性不断增强,当CMC浓度≥0.4%时,PPI乳液稳定性明显提高,液滴分散均匀,絮凝程度明显降低,在4 ℃下存放一周,未发现明显分层。因此,通过调控PPI-CMC相互作用可有效改善PPI在酸性乳液体系中的应用特性,研究成果有望为高豌豆蛋白酸性乳品和饮料的开发提供参考。     

Sodium caseinate/carboxymethylcellulose interactions at oil–water interface: Relationship to emulsion stability

The effect of carboxymethylcellulose (CMC) on the properties of oil-in-water emulsions prepared with sodium caseinate (CN) was studied at different pHs (4–7). At pH 7, the surface protein coverage increased gradually with increasing CMC concentration, followed by a preferential adsorption of β-casein. While at pH 4, a sharp decrease in surface protein coverage was noted between 0 and 0.3 wt.% CMC, and no obvious difference in protein composition was observed. ζ-Potential measurements indicated that CMC adsorbed onto the CN-coated droplets at pH 4–5, but not at pH 6–7. As a result, the excess of non-adsorbed CMC induced depletion flocculation in the neutral emulsions. However, the acidic emulsions containing high levels of CMC (>0.3 wt.%) remained stable after 60 days of storage due to the formation of multilayer structures. At pH 4, CMC desorbed from the droplet surfaces at high NaCl concentrations, leading to lower emulsion stability.     

Interactions of milk protein-stabilized oil-in-water emulsions with bile salts in a simulated upper intestinal model

The behaviour of milk protein-stabilized emulsions (1.0 wt% protein) as influenced by the addition of bile salts was studied in simulated intestinal conditions (37 °C; pH 7.5; 39 mM K₂HPO₄, 150 mM NaCl, 30 mM CaCl₂; with continuous agitation at ～95 rpm for 2 h). Oil-in-water emulsions (20.0 wt% soy oil) stabilized by lactoferrin or β-lactoglobulin (β-lg) were prepared at pH 6.8 to produce cationic or anionic interfaces respectively. Varying physiological concentrations of bile salts (0.0–25.0 mg/ml) were added to each emulsion. The changes in droplet size, ζ-potential and confocal microstructures were monitored as a function of incubation time. Pre-heat treatment of simulated intestinal buffer containing bile salts was performed to eliminate any residual enzymatic activities.For β-lg-stabilized droplets, ζ-potential significantly changed from ?63.1 ± 0.5 mV to ?37.2 ± 0.3 mV in presence of bile salts due to competitive interfacial displacement of β-lg by bile salts as characterized by SDS-PAGE analysis of the continuous phase. On the other hand, lactoferrin-stabilized emulsion droplets showed considerable aggregation in presence of intestinal electrolytes alone at pH 7.5. The ζ-potential values of lactoferrin emulsion decreased gradually from +53.5 ± 0.6 mV to ?12.2 ± 0.2 mV in presence of bile salts due to certain electrostatic effects (e.g. pH shift towards the isoelectric point, binding of anionic bile salts to cationic interfacial lactoferrin layer) in comparison to the behaviour of β-lg-stabilized droplets.     

Emulsion properties of algae soluble protein isolate from Tetraselmis sp.

To study possible applications of microalgae proteins in foods, a colourless, protein-rich fraction was isolated from Tetraselmis sp. In the present study the emulsion properties of this algae soluble protein isolate (ASPI) were investigated. Droplet size and droplet aggregation of ASPI stabilized oil-in-water emulsions were studied as function of isolate concentration (1.25–10.00 mg/mL), pH (3–7), and ionic strength (NaCl 10–500 mM; CaCl₂ 0–50 mM). Whey protein isolate (WPI) and gum arabic (GA) were used as reference emulsifiers. The lowest isolate concentrations needed to reach d₃₂ ≤ 1 μm in 30% oil-in-water emulsions were comparable for ASPI (6 mg/mL) and WPI (4 mg/mL). In contrast to WPI stabilized emulsions ASPI stabilized emulsions were stable around pH 5 at low ionic strength (I = 10 mM). Flocculation only occurred around pH 3, the pH with the smallest net droplet ζ-potential. Due to the charge contribution of the anionic polysaccharide fraction present in ASPI its droplet ζ-potential remained negative over the whole pH range investigated. An increase in ionic strength (≥100 mM) led to a broadening of the pH range over which the ASPI stabilized emulsions were unstable. GA emulsions are not prone to droplet aggregation upon changes in pH or ionic strength, but much higher concentrations are needed to produce stable emulsions. Since ASPI allows the formation of stable emulsions in the pH range 5–7 at low protein concentrations, it can offer an efficient natural alternative to existing protein–polysaccharide complexes.     

Characterization of emulsion stabilization properties of quince seed extract as a new source of hydrocolloid

The capability of seed extracts in stabilizing emulsions has particularly received interest in recent years. Upon soaking quince seeds into water, biopolymers inside the seeds are extracted to water, forming mucilage. This study investigates the physical stability, rheology and microstructure of oil (sunflower oil) in water emulsions, stabilized by 2% (w/v) whey protein isolate with varying concentrations of xanthan and quince seed gum. Quince seed gum resulted in emulsions with smaller low-shear viscosities and shear thinning capabilities compared to the same concentrations of xanthan. Quince seed gum emulsions with concentrations ≤ 0.1 (w/v), displayed rapid creaming due to bridging flocculation. Despite the difference in apparent viscosities, for gum concentrations < 0.2 (w/v), both gums demonstrated comparable stability with xanthan gum in general yielding marginally more stable emulsions. Gum concentrations > 0.3 (w/v) resulted in physically stable emulsions even after 5 months. Overall, quince seed gum displayed significant emulsification and stabilization properties.     

Thermal treatment to form a complex surface layer of sodium caseinate and gum arabic on oil–water interfaces

This study reported an alternative approach to electrostatic interaction to generate a biopolymer complex surface layer on emulsion droplets. By increasing the temperature, a complex surface layer of sodium caseinate (CN) and gum arabic (GA) on emulsion droplets could be formed either through the adsorption of complexes formed in the solution or through direct complexation of CN and GA with the surface. Mixtures of CN and GA were heated at pH 7 and then used to form oil-in-water emulsions at high temperatures. Changes in the average particle size and the ζ-potential of the emulsions indicated that complexes of GA and CN adsorbed to the interface at temperatures above 60 °C. A thick complex surface layer was also observed using confocal laser scanning microscopy. The addition of GA or CN to emulsions made with CN or GA resulted in an apparent binding of GA or CN to the emulsion droplets that depended on the sequence of addition. This temperature-induced formation of a complex surface layer was considered to be due to hydrophobically driven complexation between CN and the protein fraction of GA. The formation of the complex surface layer was dependent on the concentration, the temperature, and the addition order of the second component. This finding may imply an alternative option for the formation of biopolymer multilayers or complex surface layers on colloidal particles.     

不同NaCl浓度条件下亚麻籽胶对肌原纤维蛋白凝胶作用力及乳化特性的影响

为改善低盐肉制品凝胶乳化品质的降低,明确亚麻籽胶（flaxseed gum,FG）添加对肉制品品质的影响,以肌原纤维蛋白（myofibrillar protein,MP）为研究对象,通过测定乳析指数、电位值、粒径、显微观察研究不同NaCl浓度条件下FG对MP乳液乳化稳定性的影响,而化学键的测定显示FG对MP凝胶化学作用力的影响。结果表明,形成MP凝胶及FG-MP凝胶体系的关键是二硫键和非二硫共价键的贡献;不同NaCl浓度对FG-MP乳液的乳析指数、ζ-电位、粒径的影响均不显著（P＞0.05）,而MP乳液随着NaCl浓度的提高,乳化稳定性、ζ-电位、粒径均显著变化（P＜0.05）。特别是在低浓度NaCl条件下,FG的加入可以显著提高MP乳液的稳定性（P＜0.05）。显微观察发现加入FG可以改善MP乳液液滴聚集的现象。因此,说明在低浓度NaCl条件下加入FG可以显著提高肌原纤维蛋白乳液的乳化稳定性,提高其抗盐能力,促进亚麻籽在肉制品中的应用。     

Rheological behavior and stability of d-limonene emulsions made by a novel hydrocolloid (Angum gum) compared with Arabic gum

Our goal was to evaluate emulsion stability, droplet size analysis and rheological behavior of the emulsions prepared by a native biopolymer namely Angum gum (An) compared with Arabic gum (Ar) stabilized emulsions. After gum extraction, gum dispersions with maltodextrin were prepared in water (in 1-5% concentrations) and emulsified with 5% and 10% d-limonene using high pressure homogenization. Statistical analysis revealed a significant influence of gum type and gum concentration on emulsion stability at α = 0.05. Flavor level was not important statistically in emulsion stability but it was the only factor with a significant influence (P < 0.05) on surface tension of the emulsions. The results showed that Angum gum was superior to Arabic gum in stabilizing emulsions during storage. Also, rheological data revealed that Angum gum-emulsions’ behavior was following the Herschel-Bulkley model with higher viscosities compared to Arabic gum emulsions, which could be the main reason of higher emulsion stabilities with this novel hydrocolloid.     

Hydrocolloids in emulsions: particle size distribution and interfacial activity

The emulsification properties of 14 hydrocolloid gums (propylene glycol alginate, gellan, carrageenan, pectin, methylcellulose, microcrystalline cellulose, gum arabic, locust bean gum, guar, xanthan, mustard, flaxseed, fenugreek, oat) were investigated. Gum dispersions were prepared in water (0.5%) and emulsified with 40% oil using a Polytron homogenizer. Emulsion stability was determined by centrifugation and storage time, surface and interfacial tension by Du Nouy ring, particle size by integrated light scattering and overall morphology by light microscopy. When compared to the other gums in this study, fenugreek produced a very stable emulsion. Fenugreek was more efficient than other gums in lowering the interfacial free energy, its emulsion was composed of very small oil droplets (70%<1 μm) and under the light microscope appeared as uniform droplets with a narrow size distribution.     

Emulsifying properties of sweet potato protein: Effect of protein concentration and oil volume fraction

The effect of protein concentrations (0.1, 0.25, 0.5, 1.0, 1.5 and 2.0% w/v) and oil volume fractions (5, 15, 25, 35 and 45% v/v) on properties of stabilized emulsions of sweet potato proteins (SPPs) were investigated by use of the emulsifying activity index (EAI), emulsifying stability index (ESI), droplet size, rheological properties, interfacial properties and optical microscopy measurements at neutral pH. The protein concentration or oil volume fraction significantly affected droplet size, interfacial protein concentration, emulsion apparent viscosity, EAI and ESI. Increasing of protein concentration greatly decreased droplet size, EAI and apparent viscosity of SPP emulsions; however, there was a pronounced increase in ESI and interfacial protein concentration (P < 0.05). In contrast, increasing of oil volume fraction greatly increased droplet size, EAI and emulsion apparent viscosity of SPP emulsions, but decreased ESI and interfacial protein concentration significantly (P < 0.05). The rheological curve suggested that SPP emulsions were shear-thinning non-Newtonian fluids. Optical microscopy clearly demonstrated that droplet aggregates were formed at a lower protein concentration of <0.5% (w/v) due to low interfacial protein concentration, while at higher oil volume fractions of >25% (v/v) there was obvious coalescence. In addition, the main components of adsorbed SPP at the oil–water interface were Sporamin A, Sporamin B and some high-molecular-weight aggregates formed by disulfide linkage.     

Flaxseed oil – Whey protein isolate emulsions: Effect of high pressure homogenization

The effect of high-pressure homogenization (20–100 MPa) and the number of homogenization cycles (1–7) on the stability of flaxseed oil - whey protein isolate emulsions was evaluated. All the emulsions were stable to creaming for at least 9 d of storage. An increase in homogenization pressure from 20 to 80 MPa and number of passes through the homogenizer up to 3, decreased the mean droplet size of the O/W emulsions despite the higher polydispersity. Emulsions homogenized at lower pressures (20 MPa) showed a monomodal distribution of the particles, whereas, an increase in pressure to 80 MPa led to a bimodal distribution, indicating droplets coalescence. High-pressure homogenization (80 MPa) and an increase in the number of homogenization cycles, led to the formation of high molecular weight aggregates (>200 kDa), which favored an increase in viscosity of the emulsions. The increase in homogenization pressure also increased the formation of primary oxidation products, which could be explained by the increase in temperature and in the surface area of the droplets.