Effects of different dairy ingredients on the rheological behaviour and stability of hot cheese emulsions

The influence of sodium caseinate (SC), butter milk powder (BMP) and their combinations on particle size, rheological properties, emulsion stability and microstructure of hot cheese emulsions made from mixtures of Cheddar and soft white cheese was studied. All emulsions exhibited shear-thinning flow behaviour and increasing SC concentration (1–4%) led to an increase in particle size and a decrease in apparent viscosity. In contrast, increasing BMP concentration caused significant decrease in particle size and slightly reduced the apparent viscosity. Stability against creaming and precipitation increased with increasing concentration of SC, whereas BMP destabilised the emulsions resulting in extensive precipitation. Confocal laser scanning microscopy images showed that SC exerted markedly better emulsification ability than BMP. Emulsions containing equal amounts of SC and BMP presented better stability against creaming and precipitation and this could be developed into a novel strategy to replace emulsifying salts in production of cheese powder.     

Modulation of physicochemical properties of emulsified lipids by chitosan addition

Electrostatic interactions between polysaccharides and proteins at oil–water interfaces alter the physicochemical properties and stability of emulsions. In this research, we studied the influence of chitosan addition on the properties of oil-in-water emulsions containing whey protein-coated lipid droplets. Experiments were carried out under conditions where the protein and polysaccharide had similar charges (pH 3.0) or opposite charges (pH 6.5). At pH 3.0, chitosan addition (0–0.025%) had little influence on droplet charge, aggregation, creaming stability or shear viscosity of whey protein emulsions, which was attributed to the fact that the cationic chitosan molecules did not adsorb to the cationic droplet surfaces due to electrostatic repulsion. At pH 6.5, chitosan addition caused a decrease in particle negative charge, an increase in particle size, a decrease in creaming stability, and an increase in viscosity. These effects were attributed to droplet aggregation caused by charge neutralization and bridging resulting from attraction of cationic chitosan molecules to anionic patches on the protein-coated droplet surfaces. Addition of cationic polyelectrolytes to protein-stabilized emulsions may be utilized to control their physicochemical properties, stability and biological fate, which may be useful for developing commercial products with novel or improved functional properties.     

Impact of High Hydrostatic Pressure on the Emulsifying Properties of Whey Protein Isolate–Chitosan Mixtures

The influence of high hydrostatic pressure (HHP) on the emulsifying properties of whey protein isolate (WPI) and chitosan mixtures in sunflower oil-in-water emulsion has been investigated at pH 4.0. WPI and chitosan mixtures at various ratios were treated at pressure levels in the range of 0–600 MPa for 10–30 min. The emulsifying properties of the mixtures were analyzed by dynamic light scattering and a centrifugal sedimentation technique. HHP treatments of the mixtures resulted in improvement in their emulsifying properties, with the emulsions formed showing more than threefold reductions in droplet size, much more homogeneous droplet distribution, and better creaming stability. The higher the treatment pressure was, the smaller the droplet size and more stable the emulsions were, with those prepared with the mixtures treated at 600 MPa showing no noticeable creaming after 30 days of storage at ambient temperature. The ratio of WPI to chitosan and treatment time also affected the emulsification stability of the mixtures, with a WPI to chitosan ratio of 1:4 (w/w) and treatment time of 20 min found to be the optimum conditions. These results showed that HHP could be a useful method for enhancing the emulsifying properties of protein–polysaccharide mixtures.     

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.     

Physical Stability of Whey Protein-stabilized Oil-in-water Emulsions at pH 3: Potential ω-3 Fatty Acid Delivery Systems (Part A)

ABSTRACT: The oxidative stability of polyunsaturated lipids can be improved by incorporating them in oil droplets surrounded by positively charged whey protein isolate (WPI) membranes. This study dealt with the factors that influence the physical properties of WPI-stabilized oil-in-water emulsions at pH 3. Emulsions containing 5 to 50 wt% corn oil and 0.5 to 5.0 wt% WPI (protein-to-oil ratio of 1:10) were prepared at pH 3. The apparent viscosity of the emulsions increased appreciably at oil concentrations ≥ 35 wt%; however, the particle size was relatively independent of oil concentration. The influence of NaCl (0 to 250 m M ) on the physical properties of 28 wt% emulsions was examined. Significant increases in mean particle size, apparent viscosity, and creaming instability occurred at ≥150 m M NaCl, which were attributed to flocculation induced by screening of the electrostatic repulsion between droplets. The influence of heat treatment (30°C to 90°C for 30 min) on 28 wt% emulsions was examined in the absence and presence of salt, respectively. At 0 m M NaCl, heating had little effect on the physical properties of the emulsions, presumably because the electrostatic repulsion between the droplets prevented droplet aggregation. At 150 m M NaCl, the mean particle diameter, apparent viscosity, and creaming instability of the emulsions increased considerably when they were heated above a critical temperature, which was 70°C when salt was added before heating and 90°C when salt was added after heating. These results have important implications for the design of WPI-stabilized emulsions that could be used to incorporate functional lipids that are sensitive to oxidation, for example, ω-3 fatty acids.     

再生纤维素凝胶对乳清分离蛋白预乳化液稳定性的影响

利用再生纤维素（regenerated cellulose,RC）凝胶改善蛋白质预乳化液的乳化稳定性。考察添加量分别为0%、0.4%、0.8%、1.2%、1.6%的RC对乳清分离蛋白（whey protein isolate,WPI）-橄榄油预乳化液乳化稳定性、乳化活性、粒度大小、微观结构、流变特性的影响。结果表明,添加RC可以显著提高WPI预乳化液的乳化稳定性及乳化活性（P＜0.05）,RC添加量为0.8%时可以有效抑制乳化液的分层现象;随着RC添加量的增加,乳化液粒度大小及絮凝程度显著降低（P＜0.05）;乳化液流变学特性显示RC具有很好的增稠作用和凝胶性能。结果表明RC的添加对于WPI-预乳化液稳定性有很大影响,预乳化液中添加1.2% RC,可以有效增加乳化液黏度,获得较强的凝胶网络结构,显著降低粒度,改善乳化液稳定性。     

Manipulating oral behaviour of food emulsions using different emulsifiers

This study aims to investigate the assumption that the presence of α-amylase in the human saliva will interact instantly with starch and will lead to very different oral behaviour and enhanced flavour release. Hence, orange oil flavoured emulsion was prepared with whey protein isolates (WPI) and modified starch (MS). The stability and flavour release of emulsions were examined through in vitro and in vivo studies. MS emulsion mixed with artificial saliva containing α-amylase resulted in more pronounced changes in mean particle size from 0.185 to 2.35 μm and a significant increase in viscosity. Morphology and turbidity revealed strong flocculation, coalescence and creaming. However, WPI emulsion exhibited very little changes in stability and behaviour. Similar results were observed during oral digestion (in vivo) for both emulsion systems. Moreover, a higher intensity of flavour release (37%) was observed in MS emulsion than WPI. This work demonstrated that a starch-stabilised emulsion has a very different oral behaviour to that of a protein-stabilised emulsion.     

Assessing the potential of flaxseed protein as an emulsifier combined with whey protein isolate

The potential use of flaxseed protein isolate (FPI) as an emulsifying agent was studied in combination with whey protein isolate (WPI) or alone. All the FPI and WPI–FPI emulsions were kinetically unstable. The increase of FPI concentration (0.7% w/v) led to a higher creaming stability of the FPI emulsions due partly to a reduction in interfacial tension between aqueous and oil phases, but mainly to the gel network formation. However at this same high FPI concentration, WPI–FPI emulsions showed a decrease in droplet size and creaming stability, which could be due to the presence of flaxseed gum in the protein isolate enhancing depletion effects. A protein excess was verified in the mixed systems (0.14 or 0.7% (w/v) FPI) and the increase of FPI concentration led to an even greater surface protein content. Increasing homogenization conditions (pressure and number of passes), the creaming stability of the FPI systems increased, mainly at higher concentration (0.7% w/v). Meanwhile, in the mixed systems, the creaming stability of the emulsions containing 0.7% (w/v) FPI decreased even more, but was improved for the emulsions with 0.14% (w/v) FPI. Thus, it was observed that systems containing only FPI at higher concentration were stabilized by gel formation, while in WPI–FPI systems there was a competition by interface between biopolymers with a consequent depletion process. As a result, more stable systems were obtained with WPI addition at lower FPI concentration (0.14% w/v) and using higher homogenization pressure and number of passes (60 MPa, two passes).     

Physicochemical Properties of Whey Protein-Stabilized Emulsions as affected by Heating and Ionic Strength

Corn oil-in-water emulsions (19.6 wt%; d₃₂～ 0.6 μm) stabilized by 2 wt% whey protein isolate (WPI) were prepared with a range of pH (3–7) and salt concentrations (0–100 mM NaCl). These emulsions were heated between 30 and 90°C and their particle size distribution, rheological properties and susceptibility to creaming measured. Emulsions had a paste-like texture around the isoelectric point of WPI (～φ 5) at all temperatures, but tended to remain fluid-like at pH >6 or <4. Heating caused flocculation in pH 7 emulsions between 70 and 80°C (especially at high salt concentrations), but had little effect on pH 3 emulsions. Flocculation increased emulsion viscosity and creaming. Results were interpreted in terms of colloidal interactions between droplets.     

Rheology and stability of whey protein stabilized emulsions with high CaCl2 concentrations

The influence of pH and CaC1₂ on the rheology and physical stability of emulsions stabilized by whey protein isolate (WPI) has been studied. The particle size, creaming index and shear viscosity of 10 wt% soy bean oil-in-water emulsions (d=0.55 μm) were measured with varying pH (3, 5 and 7) and CaC1₂ concentration (0–150 mM). In the absence of CaCl₂ extensive droplet aggregation occurred around the isoelectic point of the whey proteins (4<pH<6) because of their low electrical charge. In the presence of CaC1₂, extensive droplet aggregation, viscosity enhancement and creaming instability occurred at pH 7 for CaC1₂>3 mM. These effects were much less pronounced in emulsions at pH 3 even at 150 mM CaC1₂. Droplet aggregation, creaming and viscosity of emulsions at pH 5 were fairly independent of CaC1₂ concentration. Droplet aggregation was induced by CaC1₂ probably because of the reduction in electrostatic repulsion between droplets. Re-stabilization of oil-in-water emulsions at high CaC1₂ concentrations was not observed in this study.     

Pilot-scale formation of whey protein aggregates determine the stability of heat-treated whey protein solutions—Effect of pH and protein concentration

Denaturation and consequent aggregation in whey protein solutions is critical to product functionality during processing. Solutions of whey protein isolate (WPI) prepared at 1, 4, 8, and 12% (wt/wt) and pH 6.2, 6.7, or 7.2 were subjected to heat treatment (85°C × 30 s) using a pilot-scale heat exchanger. The effects of heat treatment on whey protein denaturation and aggregation were determined by chromatography, particle size, turbidity, and rheological analyses. The influence of pH and WPI concentration during heat treatment on the thermal stability of the resulting dispersions was also investigated. Whey protein isolate solutions heated at pH 6.2 were more extensively denatured, had a greater proportion of insoluble aggregates, higher particle size and turbidity, and were significantly less heat-stable than equivalent samples prepared at pH 6.7 and 7.2. The effects of WPI concentration on denaturation/aggregation behavior were more apparent at higher pH where the stabilizing effects of charge repulsion became increasingly influential. Solutions containing 12% (wt/wt) WPI had significantly higher apparent viscosities, at each pH, compared with lower protein concentrations, with solutions prepared at pH 6.2 forming a gel. Smaller average particle size and a higher proportion of soluble aggregates in WPI solutions, pre-heated at pH 6.7 and 7.2, resulted in improved thermal stability on subsequent heating. Higher pH during secondary heating also increased thermal stability. This study offers insight into the interactive effects of pH and whey protein concentration during pilot-scale processing and demonstrates how protein functionality can be controlled through manipulation of these factors.     

乳清分离蛋白聚集体乳化性能及其Pickering乳液稳定性

以乳清分离蛋白（whey protein isolate,WPI）为原料,分别在pH 2.0和pH 7.0条件下,85 ℃加热12 h制备2 种不同形态的蛋白质聚集体,研究2 种聚集体微观形貌的特征以及不同pH值和盐离子浓度下的乳化性能;采用透射电镜、动态光散射、光学显微镜等技术手段,探究WPI与2 种聚集体稳定的Pickering乳液微观结构、盐离子稳定性和热稳定性。结果表明：WPI分别在pH 2.0和pH 7.0且高温加热条件制得2 种微观形貌截然不同的蛋白聚集体（纤维状聚集体和球状聚集体）,并且2 种蛋白聚集体相较于WPI等电点均发生偏移,在不同pH值或盐离子浓度环境下,乳化性能均提高。2 种聚集体所稳定的Pickering乳液对不同pH值、盐离子浓度环境下有更好的稳定性,球状聚集体所稳定的Pickering乳液具有更好的热稳定性。这也为WPI聚集体稳定的Pickering乳液在乳饮料中的应用奠定基础。     

Effect of CaCl2 and KCl on Physiochemical Properties of Model Nutritional Beverages Based on Whey Protein Stabilized Oil-in-Water Emulsions

ABSTRACT: Calcium chloride (0 to 10 mM) and potassium chloride (0 to 600 mM) were added into model nutritional beverage emulsions containing 7% (w/w) soybean oil droplets and 0.35% (w/w) whey protein isolate (pH 6.7). The particle size, surface charge, viscosity, and creaming stability of the emulsions then were measured. The surface charge decreased with increasing mineral ion concentration. The particle size, viscosity, and creaming instability of the emulsions increased appreciably above critical CaCl₂ (3 mM) and KCl (200 mM) concentrations because of droplet flocculation. The origin of this effect was attributed to reduction of the electrostatic repulsion between droplets due to electrostatic screening and ion binding. CaCl₂ promoted emulsion instability more efficiently than KCl because Ca²⁺ ions are more effective at reducing electrostatic repulsion than K⁺ ions.     

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.     

Impact of whey protein isolates and concentrates on the formation of protein nanoparticles‐stabilised Pickering emulsions

Whey protein nanoparticles (NPs) were prepared by heat‐induced method. The influences of whey protein isolates (WPIs) and concentrates (WPCs) on the formation of NPs were first investigated. Then Pickering emulsions were produced by protein NPs and their properties were evaluated. After heat treatment, WPC NPs showed larger particle size, higher stability against NaCl, lower negative charge and contact angle between air and water. Dispersions of WPC NPs appeared as higher turbidity and viscosity than those of WPI NPs. The interfacial tension of WPC NPs (~7.9 mN/m at 3 wt% NPs) was greatly lower than that of WPI NPs (~12.1 mN/m at 3 wt% NPs). WPC NPs‐stabilised emulsions had smaller particle size and were more homogeneous than WPI NPs‐stabilised emulsions. WPC NPs‐stabilised emulsions had higher stability against NaCl, pH and coalescence during storage.     

Interactions between Whey Protein Isolate and Soy Protein Fractions at Oil–Water Interfaces: Effects of Heat and Concentration of Protein in the Aqueous Phase

ABSTRACT:  The 2 main storage proteins of soy—glycinin (11S) and β-conglycinin (7S)—exhibit unique behaviors during processing, such as gelling, emulsifying, or foaming. The objective of this work was to observe the interactions between soy protein isolates enriched in 7S or 11S and whey protein isolate (WPI) in oil–water emulsion systems. Soy oil emulsion droplets were stabilized by either soy proteins (7S or 11S rich fractions) or whey proteins, and then whey proteins or soy proteins were added to the aqueous phase. Although the emulsifying behavior of these proteins has been studied separately, the effect of the presence of mixed protein systems at interfaces on the bulk properties of the emulsions has yet to be characterized. The particle size distribution and viscosity of the emulsions were measured before and after heating at 80 and 90 °C for 10 min. In addition, SDS-PAGE electrophoresis was carried out to determine if protein adsorption or exchanges at the interface occurred after heating. When WPI was added to soy protein emulsions, gelling occurred with heat treatment at WPI concentrations >2.5%. In addition, whey proteins were found adsorbed at the oil–water interface together with 7S or 11S proteins. When 7S or 11S fractions were added to WPI-stabilized emulsions, no gelation occurred at concentrations up to 2.5% soy protein. In this case also, 7S or 11S formed complexes at the interface with whey proteins during heating.     

乳清分离蛋白与壳聚糖美拉德反应初级阶段产物乳化性研究

采用干热美拉德反应制备乳清分离蛋白(WPI)-壳聚糖复合物,通过对复合物的乳液粒径及稳定性分析,研究反应温度、WPI与壳聚糖质量比及反应时间对复合物乳化性的影响。荧光光谱分析表明：WPI和壳聚糖在干热反应后发生共价交联并且结构发生了变化。WPI与壳聚糖在50℃、相对湿度79%干热条件下,反应1～4d的产物为Maillard反应初级阶段产物,该产物的乳化性质得到改善。其中,WPI与壳聚糖以质量比1:4混合,50℃反应1d的产物乳化稳定性是反应前的10倍。     

Physical and oxidative stability of whey protein oil-in-water emulsions produced by conventional and ultra high-pressure homogenization: Effects of pressure and protein concentration on emulsion characteristics

Oil-in-water pre-emulsions (15% sunflower + 5% olive oils) obtained by colloid mill homogenization (CM) at 5000 rpm using whey protein isolate at different levels (1, 2 and 4%) were stabilized by ultra high-pressure homogenization (UHPH, 100 and 200 MPa) and by conventional homogenization (CH, 15 MPa). Emulsions were characterized for their physical properties (droplet size distribution, microstructure, surface protein concentration, emulsifying stability against creaming and coalescence, and viscosity) and oxidative stability (hydroperoxide content and thiobarbituric acid reactive substances, TBARs) under light (2000 lux/m² for 10 days). UHPH produced emulsions with lipid droplets of small size in the sub-micron range (100–200 nm) and low surface protein with unimodal distribution when produced at 4% whey proteins and 200 MPa. All emulsions exhibited Newtonian behavior (n ≈ 1). Long term physical stability against creaming and coalescence was observed in UHPH-emulsions, compared to those obtained by CM and CH. However, CH emulsions were highly stable against creaming (days) in comparison to the CM emulsions (hours). UHPH resulted in emulsions highly stable to oxidation compared to CM and CH treatments, especially when 100 MPa treatment was applied.Industrial relevanceIn the food, cosmetic and pharmaceutical sectors, industrial operators are currently interested in developing encapsulating systems to delivery bioactive compounds, which are generally hydrophobic, unstable and sensitive to light, temperature or/and oxygen. Ultra high-pressure homogenization is capable of producing stable submicron emulsions (< 1 μm) with a narrow size distribution, inducing more significant changes in the interfacial protein layer thus preventing droplet coalescence and also inhibit lipid oxidation. The present study suggests that emulsions produced by whey protein (4%) treated by ultra high-pressure homogenization have a good physical stability to flocculation, coalescence and creaming and also high stability to lipid oxidation, opening a wide range of opportunities in the formulation of emulsions containing bioactive components with lipid nature.     

Physical Properties of Whey Protein Stabilized Emulsions as Related to pH and NaCl

Corn oil-in-water emulsions (20 wt%, d₃₂～ 0.6 μm) stabilized by 2 wt% whey protein isolate were prepared with a range of pH (3–7) and salt concentrations (0–100 mM NaCl), and particle size, rheology and creaming were measured at 30°C. Appreciable droplet flocculation occurred near the isoelectric point of whey protein (pH 4–6), especially at higher NaCl concentrations. Droplet flocculation increased emulsion viscosity and decreased stability to creaming. Results are related to the influence of environmental conditions on electrostatic and other interactions between droplets.     

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.