Influence of pH and iota-carrageenan concentration on physicochemical properties and stability of beta-lactoglobulin-stabilized oil-in-water emulsions

The influence of pH and iota-carrageenan concentration on the properties of beta-lactoglobulin (beta-Lg)-stabilized oil-in-water emulsions was investigated by measuring the particle charge, particle size distribution, and creaming stability. Emulsions containing droplets stabilized by beta-Lg were produced by homogenization, and then, iota-carrageenan was added. At pH 3, the droplet charge did not change for iota-carrageenan concentrations 相似文献   

Influence of calcium, magnesium, or potassium ions on the formation and stability of emulsions prepared using highly hydrolyzed whey proteins

Oil-in-water emulsions (4 wt % soy oil) containing 4 wt % whey protein hydrolysate (WPH) (27% degree of hydrolysis) and different levels of calcium, magnesium, or potassium chloride were prepared in a two-stage homogenizer. Other emulsions containing 4 wt % WPH but including 0.35 wt % hydroxylated lecithin and different levels of the above minerals were similarly prepared. The formation and stability of these emulsions were determined by measuring oil droplet size distributions using laser light scattering and by confocal scanning laser microscopy and a gravity creaming test. Both lecithin-free and lecithin-containing emulsions showed no change in droplet size distributions with increasing concentration of potassium in the range 0-37.5 mM. In contrast, the diameter of emulsion droplets increased with increasing calcium or magnesium concentration >12.5 mM. Emulsions containing hydroxylated lecithin were more sensitive to the addition of calcium or magnesium than the lecithin-free emulsions. Storage of emulsions at 20 degrees C for 24 h further increased the diameter of droplets and resulted in extensive creaming in emulsions containing >25 mM calcium or magnesium. It appears that both flocculation and coalescence processes were involved in the destabilization of emulsions induced by the addition of divalent cations.     

Impact of weighting agents and sucrose on gravitational separation of beverage emulsions

The influence of weighting agents and sucrose on gravitational separation in 1 wt % oil-in-water emulsions was studied by measuring changes in the intensity of backscattered light from the emulsions with height. Emulsions with different droplet densities were prepared by mixing weighting agents [brominated vegetable oil (BVO), ester gum (EG), damar gum (DG), or sucrose acetate isobutyrate (SAIB)] with soybean oil prior to homogenization. Sedimentation or creaming occurred when the droplet density was greater than or lower than the aqueous phase density, respectively. The weighting agent concentrations required to match the oil and aqueous phase densities were 25 wt % BVO, 55 wt % EG, 55 wt % DG, and 45 wt % SAIB. The efficiency of droplet reduction during homogenization also depended on weighting agent type (BVO > SAIB > DG, EG) due to differences in oil phase viscosity. The influence of sucrose (0-13 wt %) on the creaming stability of 1 wt % soybean oil-in-water emulsions was also examined. Sucrose increased the aqueous phase viscosity (retarding creaming) and increased the density contrast between droplets and aqueous phase (accelerating creaming). These two effects largely canceled one another so that the creaming stability was relatively insensitive to sucrose concentration.     

Lentil and chickpea protein-stabilized emulsions: optimization of emulsion formulation

Chickpea and lentil protein-stabilized emulsions were optimized with regard to pH (3.0-8.0), protein concentration (1.1-4.1% w/w), and oil content (20-40%) for their ability to form and stabilize oil-in-water emulsions using response surface methodology. Specifically, creaming stability, droplet size, and droplet charge were assessed. Optimum conditions for minimal creaming (no serum separation after 24 h), small droplet size (<2 μm), and high net droplet charge (absolute value of ZP > 40 mV) were identified as 4.1% protein, 40% oil, and pH 3.0 or 8.0, regardless of the plant protein used for emulsion preparation.     

Effect of arabic gum and xanthan gum on the stability of pesticide in water emulsion

The effect of arabic gum (AG) and xanthan gum (XG) on the physicochemical properties of 2% pesticide avermyctin in water emulsions was systematically investigated by measuring creaming stability, droplet size, zeta potential, and rheology. Addition of AG and XG had significant influence on the physicochemical properties of emulsions. Emulsions showed high stability throughout the storage time in the AG concentration range of 0-0.14%. In contrast, addition of XG induced the apparent creaming of emulsion as the XG concentration increased from 0.011 to 0.15%, which might be well explained by the depletion flocculation of droplets. The droplet diameter increased progressively with increasing AG concentration; however, it sharply grew initially with XG concentration and reached a maximum, followed by a gradual decrease. Zeta potential increased gradually as AG concentration was lower than 0.081%, followed by a slight decrease, whereas it reduced dramatically as XG concentration increased from 0.011 to 0.040% and then remained almost unchanged. In the AG concentration range of 0-0.14%, the emulsion exhibited typical Newtonian flow behavior and the viscosity decreased a little. The XG emulsion exhibited Newtonian flow behavior at low XG concentrations (≤0.019%), whereas, non-Newtonian flow behavior was displayed at relatively high XG concentrations (>0.019%), wherein viscosity value and yield value increased gradually as XG concentration increased. In addition, the curves of shear stress versus shear rate for XG emulsion and solution were well fitted by a power law model and the Herschel-Bulkley model; the Herschel-Bulkley model fitted much better. The present study would provide useful information for the reasonable application of AG and XG in making stable pesticide emulsion.     

Role of hydrocolloids in the creaming of oil in water emulsions

The influence of guar gum and xanthan gum on the creaming of 10% oil in water emulsions has been investigated. The presence of very low concentrations of the polysaccharides (typically < approximately 0.075%) was found to induce depletion flocculation of the emulsion droplets and increased the rate of creaming. However, at higher polysaccharide concentrations (typically > approximately 0.1%) the creaming rate was reduced due to the increased viscosity of the aqueous phase. For most systems a delay period was noted before creaming started, which was found to be dependent on the zero shear viscosity of the continuous phase and independent of polysaccharide type. The delay period increased significantly at zero shear viscosities approaching 1 Pa s. A mathematical model has been used to fit the creaming rate profiles and a simple exponential relationship obtained between delay time and polysaccharide concentration.     

Stabilization of oil-in-water emulsions by cod protein extracts

The ability of two protein fractions extracted from cod to form and stabilize oil-in-water emulsions was examined: a high salt extracted fraction (HSE protein) and a pH 3 acid extracted fraction (AE protein). Both fractions consisted of a complex mixture of different proteins, with the predominant one being myosin (200 kDa). The two protein fractions were used to prepare 5 wt % corn oil-in-water emulsions at ambient temperature (pH 3.0, 10 mM citrate-imidazole buffer). Emulsions with relatively small mean droplet diameters (d(3,2) < 1 microm) and good creaming stability (> 9 days) could be produced at protein concentrations > or =0.2 wt % for both fractions. The isoelectric point of droplets stabilized by both protein fractions was pH approximately 5. The emulsions were stable to droplet flocculation and creaming at relatively low pH (< or =4) and NaCl concentrations (< or =150 mM) when stored at room temperature. In the absence of salt, the emulsions were also stable to thermal treatment (30-90 degrees C for 30 min), but in the presence of 100 mM NaCl droplet flocculation and creaming were observed in some of the emulsions, particularly those stabilized by the AE fraction. The results suggest that protein fractions extracted from cod can be used as emulsifiers to form and stabilize food emulsions.     

Influence of polysaccharides on the rate of coalescence in oil-in-water emulsions formed with highly hydrolyzed whey proteins

The objective of this study was to examine the effects of added xanthan gum, guar gum, or kappa-carrageenan on the formation and properties of emulsions (4 wt % corn oil) formed with an extensively hydrolyzed commercial whey protein (WPH) product under a range of conditions. The rate of coalescence was calculated on the basis of the changes in the droplet size of emulsions during storage of the emulsions at 20 degrees C. Compared with the emulsion made without the addition of polysaccharides, the rate of creaming and coalescence in emulsions containing xanthan gum, guar gum, or kappa-carrageenan was markedly enhanced with increasing concentration of polysaccharides during storage for up to 7 days. At a given concentration, the rate of coalescence was highest in the emulsions containing guar gum, whereas it was lowest in the emulsions containing kappa-carrageenan. All emulsions containing xanthan gum, guar gum, or kappa-carrageenan showed flocculation of oil droplets by a depletion mechanism. This flocculation was considered to enhance the coalescence of oil droplets. The different rates of coalescence could be explained on the basis of the strength of the depletion potential, which was dependent on the molecular weight and the radius of gyration of the polysaccharides.     

Properties and stability of oil-in-water emulsions stabilized by coconut skim milk proteins

Protein fractions were isolated from coconut: coconut skim milk protein isolate (CSPI) and coconut skim milk protein concentrate (CSPC). The ability of these proteins to form and stabilize oil-in-water emulsions was compared with that of whey protein isolate (WPI). The solubility of the proteins in CSPI, CSPC, and WPI was determined in aqueous solutions containing 0, 100, and 200 mM NaCl from pH 3 to 8. In the absence of salt, the minimum protein solubility occurred between pH 4 and 5 for CSPI and CSPC and around pH 5 for WPI. In the presence of salt (100 and 200 mM NaCl), all proteins had a higher solubility than in distilled water. Corn oil-in-water emulsions (10 wt %) with relatively small droplet diameters (d32 approximately 0.46, 1.0, and 0.5 mum for CSPI, CSPC, and WPI, respectively) could be produced using 0.2 wt % protein fraction. Emulsions were prepared with different pH values (3-8), salt concentrations (0-500 mM NaCl), and thermal treatments (30-90 degrees C for 30 min), and the mean particle diameter, particle size distribution, zeta-potential, and creaming stability were measured. Considerable droplet flocculation occurred in the emulsions near the isoelectric point of the proteins: CSPI, pH approximately 4.0; CSPC, pH approximately 4.5; WPI, pH approximately 4.8. Emulsions with monomodal particle size distributions, small mean droplet diameters, and good creaming stability could be produced at pH 7 for CSPI and WPI, whereas CSPC produced bimodal distributions. The CSPI and WPI emulsions remained relatively stable to droplet aggregation and creaming at NaCl concentrations of < or =50 and < or =100 mM, respectively. In the absence salt, the CSPI and WPI emulsions were also stable to thermal treatments at < or =80 and < or =90 degrees C for 30 min, respectively. These results suggest that CSPI may be suitable for use as an emulsifier in the food industry.     

Emulsion properties of casein and whey protein hydrolysates and the relation with other hydrolysate characteristics

Casein and whey protein were hydrolyzed using 11 different commercially available enzyme preparations. Emulsion-forming ability and emulsion stability of the digests were measured as well as biochemical properties with the objective to study the relations between hydrolysate characteristics and emulsion properties. All whey protein hydrolysates formed emulsions with bimodal droplet size distributions, signifying poor emulsion-forming ability. Emulsion-forming ability of some casein hydrolysates was comparable to that of intact casein. Emulsion instability was caused by creaming and coalescence. Creaming occurred mainly in whey hydrolysate emulsions and in casein hydrolysate emulsions containing large emulsion droplets. Coalescence was dominant in casein emulsions with a broad particle size distribution. Emulsion instability due to coalescence was related to apparent molecular weight distribution of hydrolysates; a relative high amount of peptides larger than 2 kDa positively influences emulsion stability.     

Protein-stabilized nanoemulsions and emulsions: comparison of physicochemical stability, lipid oxidation, and lipase digestibility

The properties of whey protein isolate (WPI) stabilized oil-in-water (O/W) nanoemulsions (d(43) ≈ 66 nm; 0.5% oil, 0.9% WPI) and emulsions (d(43) ≈ 325 nm; 0.5% oil, 0.045% WPI) were compared. Emulsions were prepared by high-pressure homogenization, while nanoemulsions were prepared by high-pressure homogenization and solvent (ethyl acetate) evaporation. The effects of pH, ionic strength (0-500 mM NaCl), thermal treatment (30-90 °C), and freezing/thawing on the stability and properties of the nanoemulsions and emulsions were compared. In general, nanoemulsions had better stability to droplet aggregation and creaming than emulsions. The nanoemulsions were unstable to droplet flocculation near the isoelectric point of WPI but remained stable at higher or lower pH values. In addition, the nanoemulsions were stable to salt addition, thermal treatment, and freezing/thawing (pH 7). Lipid oxidation was faster in nanoemulsions than emulsions, which was attributed to the increased surface area. Lipase digestibility of lipids was slower in nanoemulsions than emulsions, which was attributed to changes in interfacial structure and protein content. These results have important consequences for the design and utilization of food-grade nanoemulsions.     

Effect of emulsifier on oxidation properties of fish oil-based structured lipid emulsions

The effects of the emulsifiers lecithin, Tween 20, whey protein isolate, mono-/diacylglycerols, and sucrose fatty acid ester on oxidation stability of a model oil-in-water emulsion prepared with enzymatically synthesized menhaden oil-caprylic acid structured lipid were evaluated. Oxidation was monitored by measuring lipid hydroperoxides, thiobarbituric acid reactive substances, and the ratio of combined docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) contents to palmitic acid in the emulsion. After high-pressure homogenization, all emulsions, except those prepared with lecithin, had similar droplet size distributions. All structured lipid emulsions, except for the lecithin-stabilized emulsions, were stable to creaming over the 48-day period studied. Emulsifier type and concentration affected oxidation rate, with 0.25% emulsifier concentration generally having a higher oxidation rate than 1% emulsifier concentration. Overall, oxidation did not progress significantly enough in 48 days of storage to affect DHA and EPA levels in the emulsion.     

Influence of EDTA and citrate on physicochemical properties of whey protein-stabilized oil-in-water emulsions containing CaCl2

The influence of chelating agents (disodium ethylenediaminetetraacetate (EDTA) and sodium citrate) on the physicochemical properties of whey protein isolate (WPI)-stabilized oil-in-water emulsions containing calcium chloride was determined. The calcium-binding characteristics of EDTA and citrate at 30 degrees C were characterized in aqueous solutions (20 mM Tris buffer, pH 7.0) by isothermal titration calorimetry (ITC). EDTA and citrate both bound calcium ions in a 1:1 ratio, but EDTA had a much higher binding constant. Oil-in-water emulsions (pH 7.0) were prepared containing 6.94% (w/v) soybean oil, 0.35% (w/v) WPI, 0.02% (w/v) sodium azide, 20 mM Tris buffer, 10 mM CaCl(2), and 0-40 mM chelating agent. The particle size, apparent viscosity, creaming stability, free calcium concentration, and particle surface potential of the emulsions were measured. The chelating agents reduced or prevented droplet aggregation in the emulsions. When they were present above a certain concentration (>3.5 mM EDTA or >5 mM citrate), droplet aggregation was prevented. The reduction of aggregation was indicated by decreases in particle size, shear-thinning behavior, apparent viscosity, and creaming. Emulsions containing chelating agents had lower free calcium concentrations and more negatively charged droplets, indicating that the chelating agents improved emulsion stability by binding calcium ions. EDTA could be used at lower concentrations than citrate because of its higher calcium ion binding constant.     

Stabilizing behavior of soy soluble polysaccharide or high methoxyl pectin in soy protein isolate emulsions at low pH

The stability of emulsions prepared with soy protein isolates was investigated as a function of pH in the presence of two negatively charged polysaccharides: high methoxyl pectin (HMP) and soy soluble polysaccharide (SSPS). Both polysaccharides are composed of a backbone which contains galacturonic acid but, when added to soy protein isolate-stabilized emulsions, SSPS showed a different behavior than that of HMP. At neutral pH and above a critical concentration of stabilizer (0.05%), HMP caused flocculation of the emulsion droplets via a depletion mechanism. On the other hand, the emulsions containing a similar amount of SSPS did not show creaming or flocculation. At acidic pH (<4.0) the addition of pectin caused extensive droplet aggregation, while no aggregation was observed with the addition of SSPS. The differences in the stabilization behavior between the two polysaccharides can be attributed to their differences in charge, neutral sugars side chains, and molecular weight.     

Production and characterization of O/W emulsions containing cationic droplets stabilized by lecithin-chitosan membranes

Oil-in-water emulsions containing cationic droplets stabilized by lecithin-chitosan membranes were produced using a two-stage process. A primary emulsion was prepared by homogenizing 5 wt % corn oil with 95 wt % aqueous solution (1 wt % lecithin, 100 mM acetic acid, pH 3.0) using a high-pressure valve homogenizer. This emulsion was diluted with aqueous chitosan solutions to form secondary emulsions with varying compositions: 1 wt % corn oil, 0.2 wt % lecithin, 100 mM acetic acid, and 0-0.04 wt % chitosan (pH 3.0). The particle size distribution, particle charge, and creaming stability of the primary and secondary emulsions were measured. The electrical charge on the droplets increased from -49 to +54 mV as the chitosan concentration was increased from 0 to 0.04 wt %, which indicated that chitosan adsorbed to the droplet surfaces. The mean particle diameter of the emulsions increased dramatically and the emulsions became unstable to creaming when the chitosan concentration exceeded 0.008 wt %, which was attributed to charge neutralization and bridging flocculation effects. Sonication, blending, or homogenization could be used to disrupt flocs formed in secondary emulsions containing droplets with high positive charges, leading to the production of emulsions with relatively small particle diameters (approximately 1 microm). These emulsions had good stability to droplet aggregation at low pH (< or =5) and ionic strengths (<500 mM). The interfacial engineering technology utilized in this study could lead to the creation of food emulsions with improved stability to environmental stresses.     

Effects of ultrasound pretreatment on the enzymatic hydrolysis of soy protein isolates and on the emulsifying properties of hydrolysates

Soy protein isolate (SPI) was modified by ultrasound pretreatment (200 W, 400 W, 600 W) and controlled papain hydrolysis, and the emulsifying properties of SPIH (SPI hydrolysates) and USPIH (ultrasound pretreated SPIH) were investigated. Analysis of mean droplet sizes and creaming indices of emulsions formed by SPIH and USPIH showed that some USPIH had markedly improved emulsifying capability and emulsion stabilization against creaming during quiescent storage. Compared with control SPI and SPIH-0.58% degree of hydrolysis (DH), USPIH-400W-1.25% (USPIH pretreated under 400W sonication and hydrolyzed to 1.25% DH) was capable of forming a stable fine emulsion (d43=1.79 μm) at a lower concentration (3.0% w/v). A variety of physicochemical and interfacial properties of USPIH-400W products have been investigated in relation to DH and emulsifying properties. SDS-PAGE showed that ultrasound pretreatment could significantly improve the accessibility of some subunits (α-7S and A-11S) in soy proteins to papain hydrolysis, resulting in changes in DH, protein solubility (PS), surface hydrophobicity (H0), and secondary structure for USPIH-400W. Compared with control SPI and SPIH-0.58%, USPIH-400W-1.25% had a higher protein adsorption fraction (Fads) and a lower saturation surface load (Γsat), which is mainly due to its higher PS and random coil content, and may explain its markedly improved emulsifying capability. This study demonstrated that combined ultrasound pretreatment and controlled enzymatic hydrolysis could be an effective method for the functionality modification of globular proteins.     

Impact of electrostatic interactions on formation and stability of emulsions containing oil droplets coated by beta-lactoglobulin-pectin complexes

Interfacial protein-polysaccharide complexes can be used to improve the physical stability of oil-in-water emulsions. The purpose of this study was to examine the impact of ionic strength on the formation and stability of oil-in-water emulsions containing polysaccharide-protein-coated droplets. Emulsions were prepared that contained 0.1 wt % corn oil, 0.05 wt % beta-lactoglobulin, and 0.02 wt % pectin at pH 7. The emulsions were then adjusted to pH 4 to promote electrostatic deposition of the pectin molecules onto the surfaces of the protein-coated droplets. The salt concentration of the aqueous phase (0 or 50 mM NaCl) was adjusted either before or after deposition of the pectin molecules onto the droplet surfaces. We found that stable emulsions containing polysaccharide-protein-coated droplets could be formed when the salt was added after pectin adsorption but not when it was added before pectin adsorption. This phenomenon was attributed to the ability of NaCl to promote droplet flocculation in the protein-coated droplets so that the pectin molecules adsorbed onto the surfaces of flocs rather than individual droplets when salt was added before pectin adsorption. We also found that polysaccharide-protein-coated droplets had a much improved stability to salt-induced flocculation than protein-coated droplets with the same droplet charge (zeta-potential). Theoretical predictions indicated that this was due to the ability of the adsorbed polysaccharide layer to strongly diminish the van der Waals attraction between the droplets.     

Preparation and Characterization of Starch Particles for Use in Pickering Emulsions

Particle‐stabilized emulsions, called Pickering emulsions, can be produced by using starch particles. In this work we studied how the properties of the starch particles affect the droplet size and creaming of such emulsions. In the study, various sizes of starch particles were generated by two different methods and used to stabilize Pickering emulsions. Sedimentation according to Stokes’ law was used to separate small and large starch granules. Acid hydrolysis was another method used to obtain smaller particles. All samples were modified with octenyl succinic anhydride (OSA) to increase their hydrophobicity with a level of OSA substitution between 1.8 and 3.1%. The size of starch particles was the main factor influencing emulsion droplet sizes. Furthermore, the droplet size decreased as the starch concentration increased. Using small starch particles with sizes <10 μm produced stable emulsions with smaller droplet size compared with larger sizes of starch particles, >10 μm. When subjected to acid hydrolysis, smaller starch particles were generally obtained, which could subsequently create smaller emulsion droplets. The emulsion index increased for the acid‐hydrolyzed starch owing to the size reduction of starch particles. The shape of the starch seemed to have a minor impact on the droplet size and the creaming of Pickering emulsions.     

Front-face fluorescence spectroscopy study of globular proteins in emulsions: influence of droplet flocculation

Measurement of the intensity (I(MAX)) and/or wavelength (lambda(MAX)) of the maximum in the tryptophan (TRP) emission spectrum using front-face fluorescence spectroscopy (FFFS) can be used to provide information about the molecular environment of proteins in nondiluted emulsions. Many protein-stabilized emulsions in the food industry are flocculated, and therefore, we examined the influence of droplet flocculation on FFFS. Stock oil-in-water emulsions stabilized by bovine serum albumin were prepared by high-pressure valve homogenization (30 wt % n-hexadecane, 0.35 wt % BSA, pH 7). These emulsions were used to create model systems with different degrees of droplet flocculation, either by changing the pH, adding surfactant, or adding xanthan. Emulsions (21 wt % n-hexadecane, 0.22 wt % BSA) with different pH (5 and 7) and molar ratios of Tween 20 to BSA (R = 0-131) were prepared by dilution of the stock emulsion. As the surfactant concentration was increased, the protein was displaced from the droplet surfaces, which caused an increase in both I(MAX) and lambda(MAX), because of the change in TRP environment. The dependence of I(MAX) and lambda(MAX) on surfactant concentration followed a similar pattern in emulsions that were initially flocculated (pH 5) and nonflocculated (pH 7). Relatively small changes in FFFS emission spectra were observed in emulsions (21 wt % n-hexadecane, 0.22 wt % BSA, pH 7) with different levels of depletion flocculation induced by adding xanthan. These results suggested that droplet flocculation did not have a major impact on FFFS. This study shows that FFFS is a powerful technique for nondestructively providing information about the molecular environment of proteins in concentrated and flocculated protein-stabilized emulsions. Nevertheless, in general the suitability of the technique may also depend on protein type and the nature of the physicochemical matrix surrounding the proteins.     

Stability of whey-protein-stabilized oil-in-water emulsions during chilled storage and temperature cycling

The stability of heat-treated and/or acidified, partly-crystalline-fat-based, whey-protein-stabilized oil-in-water (o/w) emulsions against partial coalescence was investigated during chilled storage (at 5 degrees C) and repeated temperature cycling (three times between 5 and 25 degrees C). Experiments focused on the evolution of firmness and droplet size (using pulsed field gradient NMR and scanning electron microscopy). Besides the effects of denaturation and/or acidification, the influence of the droplet size of the dispersed phase on emulsion stability was investigated also. It was found that heat treatment or acidification before emulsification led to unstable emulsions during temperature cycling, whereas heat treatment after acidification resulted in stable emulsions.