Emulsifying properties of Ghanaian grewia gum

Grewia gums were extracted with phosphate (PB) and sodium metabisulphite buffers (SMB) and their emulsification properties in acidic oil-in-water emulsions on ageing were studied by means of droplet size distribution, ζ-potential measurements, interfacial composition analysis and viscometry. PB extracts showed smaller droplet sizes (~10 μm) than SMB isolates (>35 μm) and greater long-term stability. PB-stabilised emulsions also demonstrated the least polysaccharide (~0.6 mg m⁻²) and protein (~0.2 mg m⁻²) interfacial coverage compared with SMB counterparts (~1.5 mg m⁻² for polysaccharide and ~ 1 mg m⁻² for protein). ζ-Potential measurements revealed negative interfacial charge for all emulsions confirming the presence of polysaccharide-laden interfaces. Droplet size distribution also varied among emulsions during ageing indicating a complex relationship between interfacial composition and stability. The present work shows that different emulsifying properties may be obtained depending on the extraction technique employed that could be exploited in preparation of emulsions for flavour or bioactive-delivery applications.     

Potential of bagasse obtained using hydrothermal liquefaction pre-treatment as a natural emulsifier

Bagasse, a by-product from raw sugar factories, is conventionally burned for energy production. In this study, bagasse extracts from hydrothermal liquefaction (HTL) treatment (160 °C, 1 MPa and 30 min) with a carbohydrate content of 510.3 mg g⁻¹ and 0.5 mg g⁻¹ of total phenols were applied as emulsifiers in oil-in-water (O/W) emulsions. Bagasse extracts from HTL (0.5–4 wt%) lowered the interfacial tension between oil–water interphase from 19.8 to 14.0 mN m⁻¹, owing possibly to the surface-active hydrophilic carbohydrate-hydrophobic lignin complexes in the extracts (lignin content: 7.1% w/w). Emulsions stabilised by bagasse extracts from HTL with average droplet size, d_av of 0.79 μm were comparable with gum arabic (GA), d_av of 2.24 μm after 11 days at 25 °C. Bagasse extracts containing biopolymers have the potential for industrial applications involving emulsion systems; therefore, HTL treatment of bagasse without any solvents can be regarded as an effective tool for producing natural emulsifiers.     

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.     

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。     

Physical characteristics of submicron emulsions upon partial displacement of whey protein by a small molecular weight surfactant and pectin addition

O/W emulsions (6 wt.% olive oil) were prepared at pH 3.3 using different WPI:Tween 20 weight ratios (1:0, 3:1, 1:1, 1:3, 0:1) at 1 wt.% total concentration. The emulsion droplet size was found to decrease with an increase in Tween 20. A minimum droplet size of d_3,2 300 nm was found for Tween systems alone, similar to that found (360 nm) for a 1:1 WPI:Tween 20 combination (p < 0.05). This specific composition showed a value for the interfacial tension close to that of Tween 20 alone. However, the emulsions presented low stability regardless of the WPI:Tween 20 ratio. To increase their stability, pectin was added, in various concentrations (0.2, 0.4 and 0.6 wt.%), using the Layer by Layer technique. In the presence of pectin, the ζ-potential of the oil droplets became negative; indicating that negatively charged pectin was absorbed onto the positively-charged droplet surface forming a secondary layer. The additional layer resulted in a wide range of emulsion stability. For all pectin concentrations, the 1:1 ratio of WPI:Tween 20 showed the highest stability. In most emulsions, extensive aggregation of oil droplets was observed, and their viscosity increased. Insufficient amounts of pectin to form the secondary layers led to bridging flocculation phenomena of oppositely charged pectin and proteins, leading to aggregation of the oil droplets. The higher the concentration of pectin, the greater the stability of the emulsion due to higher viscosity. All in all, the addition of a second layer consisting of pectin can be used to increase the stability of an emulsion containing emulsion droplets in the sub-micron range.     

Steam-exploded camellia (Camellia oleifera Abel.) seed protein improves the stability of camellia seed oil emulsions

We aimed here to investigate the ability of steam-exploded camellia seed protein (SECSP) in stabilising steam-exploded camellia seed oil-in-water emulsion in comparison with soy protein isolate (SPI). Emulsions with different SECSP and SPI contents (0.5, 1, 1.5 and 2 g 100 mL⁻¹) were formulated and the effect of protein concentration on emulsion droplet size, zeta (ζ)-potential, physical stability and bioaccessibility was examined. The stability of emulsion increased with increasing protein concentration. SECSP emulsion was characterised by smaller droplet sizes, higher surface charge and better stability than SPI emulsion. Furthermore, SECSP emulsion exhibited good digestive stability. SECSP emulsion showed creaming only at protein concentrations above 0.5 g 100 mL⁻¹ after 28 days of storage, while SPI emulsion showed stratification and flocculation during the same storage period. Hence, steam explosion pretreatment physical modification of camellia seed protein (CSP) provides a novel approach of utilising proteins for emulsions stabilisation, and digestive stability improvement under gastrointestinal conditions.     

大豆分离蛋白与卵磷脂间相互作用对O/W型乳状液稳定性的影响

研究大豆分离蛋白与卵磷脂的复合比例及相互作用对乳化体系稳定性及功能性质的影响。结果显示:乳状液的乳化活性和粒径分布等性质受大豆分离蛋白与卵磷脂比例分配的影响较大。当大豆分离蛋白与卵磷脂间的质量比为10∶1时,复合体系的乳化活性较高(98.1 m~2/g),同时乳液的体积平均直径D_(4,3)最小(13.34μm),乳液双峰分布程度较低。乳化稳定性和ζ-电位测试结果显示,复合体系中大豆分离蛋白与卵磷脂比例为1∶1或100∶1都不利于体系稳定,此时激光共聚焦显微镜观测乳液出现相分离和不规则非球形液滴。这说明大豆分离蛋白与卵磷脂作为复合乳化剂具有最适配比,在该比例下大豆分离蛋白与卵磷脂间的相互作用对食品级水包油(oil-in-water,O/W)乳状液的稳定性是有利的。     

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。

     

NaCl浓度对蔗糖酯黄原胶乳浊液稳定性的影响

研究NaCl浓度对蔗糖酯-黄原胶溶液的水力学直径DH、ζ-电势和界面张力及乳浊液的粒径d4,3、ζ-电势、粘度和稳定性的影响。在此基础上,探讨蔗糖酯-黄原胶相互作用与乳浊液稳定性之间的联系。结果表明:随着NaCl浓度增加,由于静电屏蔽作用,蔗糖酯-黄原胶溶液的DH值、ζ-电势和界面张力均增大,导致乳浊液ζ-电势和d4,3也逐渐增大。NaCl浓度达到0.1mol/L时,由于蔗糖酯-黄原胶疏水作用增强,形成蔗糖酯-黄原胶复合物,提高液滴的空间位阻作用,使得复合乳浊液稳定性高于蔗糖酯乳浊液稳定性。      

Effects of residual phospholipids on surface properties of a soft-refined sunflower oil: Application to stabilization of sauce-types’ emulsions

Vinegar sauces’ type emulsions were prepared from water–alcohol mixture (90:10) and three different sunflower oil samples (Reference oil, SUN1 and SUN3) at 20 wt% with sunflower lecithin as O/W emulsifier. Besides the addition of lecithins at 0–2 wt%, the oil composition varied based on the minor components present in each oil due to the different crushing and refining process. Reference oil sample was nutrient-free while SUN oil contained nutrient component sterols, tocopherols, phosphorus and phenols. Interfacial tension of the different systems was monitored using an automated tensiometer. The vinegar sauces’ type oil-in-water emulsions were prepared by a two-step homogenization procedure (10,000 rpm for 10 min, followed by a passage through an homogenizer at 400 bar pressure), the lipid droplets’ stability against aggregation/coalescence was monitored using integrated light scattering (particle size distribution) and multiple light scattering (creaming) measurements for two-month storage at 4 °C. In the absence of added lecithins, SUN oil sample containing phospholipids presented lower interfacial tension values than the Reference oil. Equilibrium values obtained are ∼4.4 mN m⁻¹ for SUN3, ∼10.5 mN m⁻¹ for SUN1, instead of 13.7 mN m⁻¹ for Reference sample. Addition of phospholipids (lecithin) to the Reference sample led to a similar trend of adsorption kinetics observed in the SUN sample (nutrient rich oil). SUN3 showed the best ability to form elastic film and Reference oil showed lowest ability, which could be attributed to concentration and the composition of phospholipids.     

Utilization of layer-by-layer interfacial deposition technique to improve freeze–thaw stability of oil-in-water emulsions

The freeze–thaw stability of 5 wt% hydrogenated palm oil-in-water emulsions (pH 3) containing droplets stabilized by sodium dodecyl sulfate (SDS)–chitosan–pectin membranes was studied. The multilayered interfacial membranes were created using an electrostatic layer-by-layer deposition method. The ζ-potential, mean particle diameter, fat destabilization, apparent viscosity and microstructure of the emulsions were used to examine the influence of freezing on their stability. Emulsions containing oil droplets stabilized only by SDS were highly unstable to droplet coalescence when either the oil phase became partially crystallized or the water phase crystallized. Emulsions containing oil droplets stabilized by SDS–chitosan membranes were stable to droplet coalescence, but unstable to droplet flocculation. Emulsions containing droplets stabilized by SDS–chitosan–pectin membranes were stable to both droplet coalescence and flocculation. The interfacial engineering technology utilized in this study could lead to the creation of food emulsions with improved stability to freeze–thaw cycling.     

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.     

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 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.     

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.     

Effect of processing parameters on physicochemical characteristics of microfluidized lemongrass essential oil-alginate nanoemulsions

The purpose of this work was to study the effect of processing parameters (pressure and cycles) on the formation of microfluidized lemongrass oil-alginate nanoemulsions considering their average droplet size and size distribution, ζ-potential, viscosity and whiteness index. To confirm that nanoemulsions were in the nano-range, samples were also observed through transmission electron microscopy (TEM) and atomic force microscopy (AFM) techniques. Average droplet size, viscosity and whiteness index of nanoemulsions decreased by increasing the processing pressure and the cycles through the interaction chamber of the microfluidizer device. Nanoemulsions obtained at 150 MPa for 10 cycles exhibited a minimum average droplet size of 6 nm. Moreover, the droplet electrical charge of nanoemulsions ranged between −36.66 and −51.95 mV while it was −17.61 mV in the coarse emulsion. Furthermore, nanoemulsions obtained at 150 MPa for 3 times or more through the microfluidization system were almost transparent. Results obtained in the present study reveal that microfluidization is a potential technology to be used to produce nanoemulsions of essential oils. However, more information is needed about the influence of microfluidization conditions on the antimicrobial properties of essential oils dispersed in nano-sized emulsions.     

Interactions at the interface between hydrophobic and hydrophilic emulsifiers: Polyglycerol polyricinoleate (PGPR) and milk proteins,studied by drop shape tensiometry

The equilibrium interfacial tension and dilational elasticity at the soy oil–water interface were studied in the presence of a lipophilic emulsifier, polyglycerol polyricinoleate (PGPR), in the continuous oil phase, and dairy proteins, β-lactoglobulin (β-lg) or sodium caseinate, in the aqueous phase using drop shape tensiometry. The interfacial tension decreased with increasing PGPR concentration, and was <2 mN m⁻¹ at PGPR concentrations beyond 1%. The presence of proteins in the water phase, β-lg and sodium caseinate, further reduced the interfacial tension. Even at the low concentrations (0.008%) tested, PGPR dominated the interfacial elasticity, which was only slightly affected by the addition of elevated levels of protein. While in the presence of β-lg (0.1%) in isolation, the system showed a high interfacial elasticity, the addition of PGPR lowered the elasticity, suggesting that PGPR interfered with protein–protein interactions at the interface, or caused displacement of β-lg. Interfacial elasticity at the oil–water interface showed little dependence on dilation or frequency of the sinusoidal oscillation, when the interface was dominated by PGPR.     

Protection of Lactobacillus acidophilus from the low pH of a model gastric juice by incorporation in a W/O/W emulsion

The protective effect of a W/O/W emulsion for Lactobacillus acidophilus from a model gastric juice was investigated in order to develop a method for utilizing the advantages of the probiotics. The bacteria were included in the inner-phase solution of the W/O/W emulsion, and a method for counting the viable-bacteria included in the W/O/W emulsion was developed. The relative viability of the bacteria included in the W/O/W emulsion was 49% at 2 h in the model gastric juice, whereas the viability of the bacteria directly dispersed in the juice declined to 1.3% even at 0.67 h. The relative viabilities of the encapsulated bacteria in the model gastric juice at 2 h were 0.12 and 1.10 for the emulsions having the median diameters of 11.9 and 25.4 μm, prepared with inner-phase volume ratios at 0.03 and 0.45, respectively. The relative viabilities of the bacteria in the W/O/W emulsions with the median diameters of 11 and 27 μm, prepared at the homogenization speed of 2.2×10⁴ and 9.8×10³ rpm, were 0.4 and 0.8, respectively. These results suggested that both the inner-phase volume ratio and the median diameter of oil droplet affected the relative viability of the included bacteria.     

Combined effects of limited enzymatic hydrolysis and high hydrostatic pressure on the structural and emulsifying properties of rice proteins

The combined effects of limited enzymatic hydrolysis and high hydrostatic pressure (HHP) treatment on the structural and emulsifying properties of rice proteins (RPs) were investigated. Alcalase exhibited higher hydrolysis efficiency than papain. Through alcalase-catalyzed hydrolysis and HHP treatment, emulsifying activity index (EAI) and emulsifying stability index (ESI) of RPs were improved from 14.58 m²/g and 22.54 min to 29.93 m²/g and 43.35 min, respectively. The content of random coil in RPs increased, while the content of α-helix decreased. HHP at 300 MPa led to the highest surface hydrophobicity (H₀) and fluorescence intensity. The enzymatic hydrolysis-HHP (300 MPa) modified RPs could form an oil-in-water emulsion with a d_4,3 of 0.347 nm, ζ-potential of −36.4 mV, and creaming index of 10.5% after 7 days storage. This work sheds light on employing limited enzymatic hydrolysis and HHP to modify RPs for better application in emulsion-based food products.     

Pancreatin-induced coalescence of oil-in-water emulsions in an in vitro duodenal model

The behaviour of cationic lactoferrin-stabilized and anionic β-lactoglobulin (β-lg)-stabilized oil-in-water emulsions (20.0% (w/w) soy oil, 1.0% (w/w) protein) in the presence of simulated intestinal fluid (SIF) containing physiological concentrations of pancreatin (0.0–10.0 mg mL^?1) and/or bile salts (0.0–25.0 mg mL^?1) at 37 °C, pH 7.5 and inorganic salts (39 mm K₂HPO₄, 150 mm NaCl and 30 mm CaCl₂) was investigated. Both emulsions showed a significant degree of coalescence and fatty acid release on mixing with SIF. Appreciably negative ζ-potential values (≥?50 mV) for both types of emulsion droplet at the highest pancreatin/bile salts concentration could be attributed to displacement of and/or binding to the interfacial proteins by bile salts, together with interfacial proteolysis by pancreatin, which enhanced the potential for lipase to act on the hydrophobic lipid core, thus generating free fatty acids and possibly mono- and/or diglycerides at the droplet surface.