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.     

Viscosity change in oil/water food emulsions prepared using a membrane emulsification system

This paper reports viscosity measurements of oil/water (O/W) monodispersed emulsions of different droplet diameters obtained in a membrane emulsification system. Hydrophilic microporous glass membranes of different pore diameters were used to prepare O/W emulsions. The results showed that the droplet diameter of the emulsions varied with the average pore diameter of the membrane. The average droplet diameter was found to be about five times greater than the average membrane pore diameter. A correlation was found for the relationship between the average droplet diameter and the emulsion viscosity. As the dispersed droplet size became smaller, the total surface area of the droplets increased. Therefore, the emulsion viscosity and the relative viscosity increased. Few studies have reported the viscosity of O/W emulsions with droplet diameter of 5 μm or more and an oil phase concentration of 10 vol% or less. In the present study a correlation between the droplet diameter and the emulsion viscosity was statistically established. ©     

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.     

Droplet characterization and stability of soybean oil/palm kernel olein O/W emulsions with the presence of selected polysaccharides

Droplet characteristics, flow properties and stability of egg yolk-stabilized oil-in-water (O/W) emulsions as affected by the presence of xanthan gum (XG), carboxymethyl cellulose (CMC), guar gum (GG), locust bean gum (LBG) and gum Arabic (AG) were studied. The dispersed phase (40%) of the emulsions was based on soybean oil/palm kernel olein blend (70:30) that partially crystallized during extended storage at 5 °C. In freshly prepared emulsions, the presence of XG, CMC, GG and LBG had significantly decreased the droplet mean diameters. XG, LBG, GG and CMC emulsions exhibited a shear-thinning behavior but AG emulsion exhibited a Bingham plastic behavior and control (without gum) emulsion almost exhibited a Newtonian behavior. Both control and AG emulsions exhibited a severe phase separation after storage (30 days, 5 °C). The microstructure of stored XG emulsion showed the presence of partially coalesced droplets, explaining a large increase in its droplet mean diameters. Increases in droplet mean diameters and decreases in flow properties found for stored GG and LBG emulsions were attributed to droplet coalescence. Nevertheless, the occurrence of droplet coalescence in these emulsions was considered to be small as no free oil could be separated under centrifugation force. Increases in flow properties and excellent stability towards phase separation found for stored CMC emulsion suggested that CMC could retard partial coalescence. Thus, the results support the ability of CMC, GG and LBG in reducing partial coalescence either by providing a sufficiently thick continuous phase or by acting as a protective coating for oil droplets.     

Influence of Ultrasonication Parameters on Physical Characteristics of Olive Oil Model Emulsions Containing Xanthan

Ultrasonic emulsification of 20-wt.% o/w emulsions (pH 3.8) containing a food-grade emulsifier (whey protein isolate, WPI, 2.7 wt.%) and xanthan gum (XG, 0.25 wt.%) was performed. Time and amplitude of ultrasonic treatment changed in order to evaluate their influence on emulsion droplet size, viscosity, and stability (by multiple light scattering (MLS) profiles) during cold storage (10 days at 5 °C). Ultrasonic treatment duration changed from 1 to 4 min at constant amplitude of 70 %. Considering the amplitude, intervals of 40, 60, 80, and 100 % were chosen, for a constant time of 1 min. Similarly, time and amplitude conditions were used to treat solutions of XG of 1 wt.% and evaluate their influence on viscosity and how that was related to the stability of the emulsion. Increase in sonication time from 1 to 4 min led to a significant oil droplet size decrease from 1.14 to 0.89 μm (median droplet diameter). The viscosity of emulsions and XG solutions was highly influenced and considerably decreased with sonication time applied. At those conditions, an increase of backscattering was observed from 58.9 to 72.7 % after 10 days of storage, meaning that more stable emulsions, thinner and of smaller oil droplet size were produced. A similar trend was observed when the amplitude was increased, but droplet size and creaming were always greater than those noticed by changing the sonication time. However, the rate of viscosity, droplet size, and stability change was greater by increasing the amplitude rather than by changing the sonication time.     

Influence of xanthan gum on the formation and stability of sodium caseinate oil-in-water emulsions

Studies have been made of the changes in droplet sizes, surface coverage and creaming stability of emulsions formed with 30% (w/w) soya oil, and aqueous solution containing 1 or 3% (w/w) sodium caseinate and varying concentrations of xanthan gum. Addition of xanthan prior to homogenization had no significant effect on average emulsion droplet size and surface protein concentration in all emulsions studied. However, addition of low levels of xanthan (≤0.2 wt%) caused flocculation of droplets that resulted in a large decrease in creaming stability and visual phase separation. At higher xanthan concentrations, the creaming stability improved, apparently due to the formation of network of flocculated droplets. It was found that emulsions formed with 3% sodium caseinate in the absence of xanthan showed extensive flocculation that resulted in very low creaming stability. The presence of xanthan in these emulsions increased the creaming stability, although the emulsion droplets were still flocculated. It appears that creaming stability of emulsions made with mixtures of sodium caseinate and xanthan was more closely related to the structure and rheology of the emulsion itself rather than to the rheology of the aqueous phase.     

Influence of anionic dietary fibers (xanthan gum and pectin) on oxidative stability and lipid digestibility of wheat protein-stabilized fish oil-in-water emulsion

The influence of two anionic dietary fibers (xanthan gum and pectin) on the oxidative stability and lipid digestibility of fish oil emulsions stabilized by wheat protein (gliadin) was investigated. Lipid oxidation was determined by measuring lipid hydroperoxides and TBARS of the emulsions during storage, while protein oxidation was measured using fluorescence spectroscopy. Lipid and protein oxidation was faster at pH 3.5 than at pH 7, which may have been due to increased iron solubility under acidic conditions. Xanthan gum inhibited lipid and protein oxidation, which was attributed to its ability to bind iron ions. Conversely, pectin promoted oxidation, which was attributed to the presence of endogenous transition metals in the polysaccharide ingredient. In vitro digestion was carried out to evaluate the digestibility of oil droplets in emulsions with or without polysaccharides. Both xanthan gum and pectin significantly increased the rate of lipid digestion, which was attributed to their ability to inhibit droplet aggregation under gastrointestinal conditions. These results have important implications for designing emulsion-based functional foods with improved oxidative stability and lipid digestibility.     

Thermal behavior of concentrated oil-in-water emulsions based on soybean oil and palm kernel olein blends

Droplet size distribution and thermal behavior of concentrated oil-in-water emulsions based on soybean oil (SBO)/palm kernel olein (PKO) blends were investigated. The emulsions were prepared using 70% (wt./wt.) oil blends of SBO/PKO as dispersed phases and stabilized by egg yolk. An increase in PKO level (0–40% wt./wt.) in the oil dispersed phase volume fraction caused significant increases (p < 0.05) in volume-weighted mean diameter (d_4,3). The DSC data suggested that crystallization of the emulsions was induced by a ‘template effect’ of yolk constituents via a surface heterogeneous nucleation. Emulsions with 0–20% (wt./wt.) PKO levels in the dispersed phase demonstrated a good cool–heat stability even after three successive thermal cycles (from 50 °C to ?70 °C at 10 min/°C). After the first thermal cycle, emulsions with 30% and 40% PKO levels in the oil dispersed phase were destabilized due to strong coalescence and crystallized via volume-surface heterogeneous nucleation. The unstable emulsions were attributable to high level of saturated triacylglycerols from PKO, with high droplet size characteristic, causing them to be more prone to partial coalescence.     

Oil droplet release from emulsion-filled gels in relation to sensory perception

Oil droplet release upon shearing was studied in emulsion-filled gels containing oil droplets either bound or unbound to the gel matrix. At 20 °C no release was observed for gels containing droplets bound to the matrix, whereas the release measured for gels with unbound droplets related to the fat content and the size of the gel particles obtained after shearing. For gels with bound droplets and melting at the oral processing temperature, increasing the temperature of the determination to 37 °C resulted in an almost complete release of the oil droplets.An increase of the oil content induced an increase of the creaminess scores for all gels. These scores were somewhat higher for gels containing unbound droplets and gels melting at oral processing temperature. For these gels, the oil droplet release appears to correlate with creaminess. However, because a similar increase in creaminess at increasing oil concentration was also found for gels with oil droplets bound to the matrix, it is concluded that the release of oil droplets during oral processing is not the main mechanism causing creaminess perception in emulsion-filled gels.     

Evaluation of aging mechanisms of olive oil–lemon juice emulsion through digital image analysis

The aging mechanisms of olive oil–lemon juice emulsions were investigated. The emulsions were prepared with xanthan gum where different concentrations of modified starch or maltodextrin were added. Emulsions stability was followed through analysis of the evolution of mean droplet size measured by image analysis during 203 days. All the samples presented phase separation at the end of the studied storage period. The stability results indicate that large droplets mean diameter were obtained in samples where maltodextrin or only xanthan gum was used. The study of the evolution of the droplet mean diameter with time show that the studied salad dressing ages preferentially through coalescence, although in certain cases molecular diffusion may occur. The incorporation of xanthan gum in salad dressing emulsions has a large influence in their rheological behavior.     

Comparison of the Dispersed Phase Coalescence Mechanisms in Different Tablespreads

ABSTRACT:  Temperature-induced destabilization of the dispersed phase in butter and margarine was compared by following changes in droplet size ( d _3,3), solid fat content (SFC), and fat crystal spatial organization in the 28–34 °C range. At 28 °C, both butter and margarine were stable, with similar d _3,3 values (approximately 6 μm) and droplet size distributions. As the storage temperature was raised above 30 °C, notable droplet coalescence was observed (for example, at 32 °C d _3,3 values of approximately 10 μm for butter and approximately 12 μm for margarine were obtained). Dispersed phase coalescence in butter was dominated by coagulation, with the fat crystal network-limiting droplet–droplet contact until a minimum SFC was reached (approximately 2.5%). In margarine, the rate-limiting step for coalescence was the melting of Pickering crystals present around the dispersed aqueous droplets. Unlike butter, there was no sharp change in stability at a particular temperature or critical SFC. With these differences, coalescence in butter could be modeled as a 2nd-order process and as a 1st-order process in margarine. Overall, these results demonstrated that the kinetic stability of the dispersed aqueous phase in butter and margarine depends on SFC and the spatial distribution of fat crystals within the spreads.     

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.     

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.     

Formation of oil droplets in plasticized starch matrix in simple shear flow

This paper describes the effect of simple shear flow on the formation of triglyceride oil droplets in a plasticized starch matrix. An in-house developed shearing device was used that enabled the application of controlled shear flow and rheological characterization of the native maize starch–triglyceride blends at shear stresses of up to 37 kPa. Due to the high viscosity of starch matrix, the viscosity ratio of the continuous starch phase and the dispersed triglyceride phase varied between 10⁻⁷ and 10⁻⁵. It was possible to create small droplets with a droplet diameter of 2.1 μm using simple shear flow only. An increase in shear rate had no influence on droplet diameter. However, an increase in oil content led to a vast increase in droplet diameter indicating the occurrence of coalescence. The results further show that the maximum stable droplet size in plasticized starch is significantly smaller (up to 100 times) than the predicted values for a Newtonian matrix. The differences of plasticized starch to Newtonian matrices are discussed in detail.     

Gel‐like emulsions prepared with zein nanoparticles produced through phase separation from acetic acid solutions

In this article, we report the microstructure and rheological property of Pickering emulsions stabilised with zein nanoparticles prepared through phase separation from acetic acid solution. The fresh emulsions showed liquid‐like behaviour and reasonable small droplet size. Interestingly, after 3 days of storage at 25° C, the emulsions changed into solid‐like state. The viscosity remarkably increased, and the storage modulus was much larger than the loss modulus. These results indicate the formation of the gel‐like network in emulsions. The droplet size also showed an obvious increase, while the big droplets could be disrupted into small ones in the presence of sodium dodecyl sulphate. The particle network in the continuous phase was seen in the confocal laser scanning microscopy. Therefore, it is suggested that the gel‐like network is formed by the flocculation of oil droplets and particle network in continuous, mainly through the hydrophobic interactions between the particles.     

Properties and thermal stability of Pickering high internal phase emulsion prepared by TGase cross-linked collagen fibres

In this study, high internal phase emulsions (HIPEs) were prepared by algal oil and transglutaminase (TGase) cross-linked collagen fibres, and the properties and thermal stability (90 °C, 40 min) of HIPEs were also investigated. Under 1.0 wt % collagen fibres without TGase, the emulsion prepared by centrifugation could achieve an oil phase volume up to 60%, the non-centrifuged emulsion could only come up to 50% oil phase volume, however, with the addition of TGase, the HIPEs could be formed with 72% oil phase volume. The obtained HIPEs showed gel-like morphology. The droplets size of unheated HIPEs decreased as the TGase concentration increased, but the change was not significant when TGase was more than 20 U g⁻¹ collagen fibres. The droplets size of heated HIPEs increased, but it was almost the same as the unheated samples when TGase was more than 30 U g⁻¹ collagen fibres, suggesting good thermal stability.     

Disulfide-mediated Polymerization Reactions and Physical Properties of Heated WPI-stabilized Emulsions

Heating a 19 wt% corn oil-in-water emulsion stabilized by 1 wt% whey protein isolate from 30 to 70°C and then cooling to 25°C for at least 15 hr, brought about minimal changes in droplet aggregation, apparent viscosity and susceptibility to creaming. At 75°C, droplet aggregation occurred but this decreased on heating to 90°C. The apparent viscosity and susceptibility of droplets to creaming increased as the degree of droplet aggregation increased. Inclusion of the sulfhydryl blocking agent N-ethylmaleimide to inhibit thiol/disulfide interchange reactions did not affect droplet aggregation but resulted in higher apparent viscosity values and susceptibility to creaming at 85 and 90°C and not at lower temperatures. The results suggest that droplet aggregation results from noncovalent interactions between unfolded protein molecules adsorbed on different droplets and that the interactions are strengthened by disulfide bonds.     

Large microchannel emulsification device for producing monodisperse fine droplets

In this paper, we present a novel microchannel emulsification (MCE) system for mass-producing uniform fine droplets. A 60×60-mm MCE chip made of single-crystal silicon has 14 microchannel (MC) arrays and 1.2×10⁴ MCs, and each MC array consists of many parallel MCs and a terrace. A holder with two inlet through-holes and one outlet through-hole was also developed for simply infusing each liquid and collecting emulsion products. The MCE chip was sealed well by physically attaching it to a flat glass plate in the holder during emulsification. Uniform fine droplets of soybean oil with an average diameter of 10 μm were reliably generated from all the MC arrays. The size of the resultant fine droplets was almost independent of the dispersed-phase flow rate below a critical value. The continuous-phase flow rate was unimportant for both the droplet generation and the droplet size. The MCE chip enabled mass-producing uniform fine droplets at 1.5 mL h–1 and 1.9×10⁹ h^–1, which could be further increased using a dispersed phase of low viscosity.     

Utility of Blended Polymeric Formulations Containing Cellulose Nanofibrils for Encapsulation and Controlled Release of Sweet Orange Essential Oil

The characteristics and encapsulating potential of blended polymeric formulations containing gum arabic (GA), maltodextrin (MD), and cellulose nanofibrils (CNF) for microencapsulation of sweet orange essential oil were evaluated in this study. CNF acted as a thickener, increasing emulsion viscosity. The droplet size was affected by the partial replacement of GA in the formulations without CNF; however, the presence of CNF contributed to decreasing the droplet size. CNF-containing formulations had the best encapsulation efficiency. Images obtained by microscopy showed no cracks on the surface of the microparticles. CNF-containing formulations released more essential oil at 25 °C and presented different behaviors when compared to formulations without CNF at 45 °C. The presence of CNF in the wall material formulations was associated with higher encapsulation efficiency of the particles containing essential oil produced by the spray drying.