Emulsifying Properties of Whey Protein-Carboxymethylcellulose Complexes

ABSTRACT: Proteins/polysaccharides complexes could improve emulsifying properties of proteins by thickening the layer at the interface of the oil droplets. Emulsifying properties of whey protein-carboxymethylcellulose complexes (WPI/CMC) were compared with those of a whey protein isolate (WPI). Ingredients were incorporated into oilinwater emulsions with various protein and oil contents. Visual observations, protein load, protein distribution and rheological measurements were used to evaluate emulsion stability. Protein load up to 26.1 and 48.9 mg protein/g oil were obtained for WPI and WPI/CMC emulsions, respectively. The higher protein load of WPI/CMC emulsions and visual observations indicated that WPI/CMC complexes had greater emulsifying properties against coalescence than whey proteins. However, complexes enhanced flocculation of oil droplets.     

Creaming Stability of Oil-in-Water Emulsions Formed with Sodium and Calcium Caseinates

Creaming stability of emulsions formed with calcium caseinate, determined after storage of emulsions at 20 °C for 24 h, increased gradually with an increase in protein concentration from 0.5% to 2.0%; further increases in caseinate concentration had much less effect. In contrast, the creaming stability of sodium caseinate emulsions showed a decreased with an increase in protein concentration from 0.5% to 3.0%. Confocal laser micrographs of emulsions formed with >2% sodium caseinate showed extensive flocculation of oil droplets with the appearance of a network structure. However, emulsions formed with calcium caseinate or emulsions formed with low concentrations of sodium caseinate (0.5% and 1.0%) were homogenous with no sign of flocculation.     

Factors that influence the coalescence stability of protein-stabilised emulsions,estimated from the proportion of oil extracted by hexane

The coalescence stability of protein-stabilised emulsions was estimated by measuring the degree to which the oil content could be extracted by hexane. The hexane extraction method is an empirical one but it correlates well with both an absolute method, such as increase in droplet size, and with another ‘accelerating’ technique, oil separation by centrifugation. Moreover, the hexane extraction method is capable of measuring coalescence stability over a wide range of instability, whereas the centrifugation method only provides information about the final stages of emulsion instability. Among the proteins studied, caseinates were generally the best stabilisers, especially at pH 6. Soya proteins gave rise to emulsions of minimal stability, whereas whey protein concentrate and blood plasma resulted in emulsions of medium stability. The coalescence instability of the protein-stabilised emulsions, viewed overall, was significantly and positively related to the droplet size, the degree of flocculation and the amount of protein in the membrane. High values of these emulsion parameters were due mainly to frequent recoalescence and bridging during emulsification. To minimise these effects emulsifying conditions creating high protein: surface area ratios should be used, as well as proteins that quickly change their conformation at an interface and have low aggregation numbers in solution.     

Interfacial composition and stability of emulsions made with mixtures of commercial sodium caseinate and whey protein concentrate

The interfacial composition and the stability of oil-in-water emulsion droplets (30% soya oil, pH 7.0) made with mixtures of sodium caseinate and whey protein concentrate (WPC) (1:1 by protein weight) at various total protein concentrations were examined. The average volume-surface diameter (d₃₂) and the total surface protein concentration of emulsion droplets were similar to those of emulsions made with both sodium caseinate alone and WPC alone. Whey proteins were adsorbed in preference to caseins at low protein concentrations (<3%), whereas caseins were adsorbed in preference to whey proteins at high protein concentrations. The creaming stability of the emulsions decreased markedly as the total protein concentration of the system was increased above 2% (sodium caseinate >1%). This was attributed to depletion flocculation caused by the sodium caseinate in these emulsions. Whey proteins did not retard this instability in the emulsions made with mixtures of sodium caseinate and WPC.     

Ability of whey protein isolate and/or fish gelatin to inhibit physical separation and lipid oxidation in fish oil-in-water beverage emulsion

The effect of pH on the capability of whey protein isolate (WPI) and fish gelatin (FG), alone and in conjugation, to form and stabilize fish oil-in-water emulsions was examined. Using layer-by-layer interfacial deposition technique for WPI–FG conjugate, a total of 1% protein was used to prepare 10% fish oil emulsions. The droplets size distributions and electrical charge, surface protein concentration, flow and dynamic rheological properties and physiochemical stability of emulsions were characterize at two different pH of 3.4 and 6.8 which were selected based on the ranges of citrus and milk beverages pHs, respectively. Emulsions prepared with WPI–FG conjugate had superior physiochemical stability compare to the emulsions prepared with individual proteins. Higher rate of coalescence was associated with reduction in net charge and consequent decrease of the repulsion between coated oil droplets due to the proximity of pH to the isoelectric point of proteins. The noteworthy shear thinning viscosity, as an indication of flocculation onset, was associated with whey protein stabilized fish oil emulsion prepared at pH of 3.4 and gelatin stabilized fish oil emulsion made at pH of 6.8. At pH 3.4, it appeared that lower surface charge and higher surface area of WPI stabilized emulsions promoted lipid oxidation and production of hexanal.     

Effect of emulsifier type on sensory properties of oil-in-water emulsions

This work investigates the fundamental properties of emulsifiers that may contribute to the fat-associated sensory attributes of emulsions. Model oil-in-water emulsions were prepared with 0, 12, 24, 36 and 48% oil and emulsified with seven different emulsifiers; two proteins; sodium caseinate and whey protein, and five different sucrose esters. Emulsions were rated for perceived ‘fat content’, ‘creaminess’ and ‘thickness’ on nine-point category scales. Instrumental measurements of particle size, viscosity, thin film drainage, surface dilational modulus and interfacial tension were made. The sensory results indicate significant main and interactive effects of fat level and emulsifier type. At higher fat levels, emulsions prepared with sodium caseinate and whey protein emulsifiers had higher viscosities and higher sensory scores than those prepared with the sucrose esters. Results indicate that emulsifier type has a significant effect on the sensory properties of oil-in-water emulsions, and relationships between instrumental and sensory measures suggest that this may be due to the interfacial properties of emulsifiers at the oil–water interface. © 1998 SCI.     

Effect of high-methoxy pectin on properties of casein-stabilized emulsions

We report on the effect of high-methoxy pectin on the stability and rheological properties of fine sunflower oil-in-water emulsions prepared with α_s1-casein, β-casein or sodium caseinate. The aqueous phase was buffered at pH 7.0 or 5.5 and the ionic strength was adjusted with sodium chloride in the range 0.01–0.2 M. Average emulsion droplet sizes were found to be slightly larger at the lower pH and/or with pectin present during emulsification. Analysis of the serum phase after centrifugation indicated that some pectin becomes incorporated into the interfacial layer at pH 5.5 but not at pH 7.0. This was also supported by electrophoretic mobility measurements on protein-coated emulsion droplets and surface shear viscometry of adsorbed layers at the planar oil–water interface. A low pectin concentration (0.1 wt%) was found to give rapid serum separation of moderately dilute emulsions (11 vol% oil, 0.6 wt% protein) and highly pseudoplastic rheological behaviour of concentrated emulsions (40 vol% oil, 2 wt% protein). We attribute this to reversible depletion flocculation of protein-coated droplets by non-adsorbed pectin. At ionic strength below 0.1 M, the initial average droplet sizes, the creaming behaviour, and the rheology were found to be similar for emulsions made with either of the individual caseins (α_s1 and β) or with sodium caseinate. At higher ionic strength, however, whereas emulsions containing β-casein or sodium caseinate were stable, the corresponding α_s1-casein emulsions exhibited irreversible salt-induced flocculation which was not inhibited by the presence of the pectin.     

Emulsifying Effects of Food Macromolecules In Presence of Ethanol

The influence on droplet size of ethanol present during homogenization was investigated for emulsions stabilized by macromolecular emulsifiers: sodium caseinate, whey protein isolate, gelatin and gum arabic. Emulsions produced with polysaccharide gum arabic had increasing droplet size as ethanol concentration increased, in contrast to the protein-stabilized emulsions which had decreasing droplet size (up to 20 % ethanol for gelatin and 30 % ethanol for the milk proteins), followed by increasing droplet size with increasing ethanol concentration. Interfacial tension measurements indicated that the emulsifying property of the macromolecules depended on adsorption at the oil-water/alcohol interface during emulsification.     

The choice of homogenisation equipment affects lipid oxidation in emulsions

Milk proteins are often used by the food industry because of their good emulsifying properties. In addition, they can also provide oxidative stability to foods. However, different milk proteins or protein components have been shown to differ in their antioxidative properties, and their localisation in emulsions has been shown to be affected by the emulsification conditions. The objective of this study was to investigate the influence of homogenisation equipment (microfluidizer vs. two-stage valve homogeniser) on lipid oxidation in 10% fish oil-in-water emulsions prepared with two different milk proteins. Emulsions were prepared at pH 7 with similar droplet sizes. Results showed that the oxidative stability of emulsions prepared with sodium caseinate was not influenced by the type of homogeniser used. In contrast, the type of homogenisation equipment significantly influenced lipid oxidation when whey protein was used as emulsifier, with the microfluidizer resulting in lower levels of oxidation.     

EPA、DHA的微胶囊化:壁材的筛选

以产品的产率、效率和贮存稳定性 (包括产品的抗氧化性和心材的持留率 )为评定指标 ,选用多种蛋白质 ,如明胶 (GEL)、浓缩乳清蛋白 (WPC)、大豆分离蛋白 (SPI)、大豆水解蛋白 (SPH)和酪蛋白酸钠 (CAS)等 ,作为 EPA、DHA微胶囊化壁材 ,并进行了比较。结果表明 :SPI作为壁材制得的微胶囊产品具有较高的产率和效率 ,但其贮存稳定性很差 ;而 GEL、SPH(DH8)和 WPC 3种壁材制得的产品具有较好的贮存稳定性 ,其中又以 GEL为最佳。     

STABILITY OF OIL-IN-WATER EMULSIONS. 2. Effects of Oil Phase Volume, Stability Test, Viscosity, Type of Oil and Protein Additive

SUMMARY –Stability of oil-in-water emulsions stabilized in sodium caseinate, gelatin and soy sodium proteinate was found to be increased by either an increase in the aqueous phase protein concentration (0.5–2.5%) or oil phase volume (20–50%). Both factors were significantly interrelated. Emulsions stabilized by soy sodium proteinate were generally higher in stability as compared to those stabilized by gelatin or sodium caseinate. With emulsions containing gelatin, greater stability occurred when the stability testing temperature was increased from 37–70°C and when the time interval was decreased from 24 hr to 90 min. Maximum relative viscosities of emulsions stabilized by gelatin and sodium caseinate were 2.0 and 2.5, respectively. Emulsions stabilized by soy sodium proteinate were quite viscous, with relative viscosity from 1.5–30 depending on both protein concentration and oil phase volume. Interchanging the emulsified oil among corn, soybean, safflower and peanut oils did not alter emulsion stability when examined at three concentrations of soy sodium proteinate. Changing the oil to olive oil significantly increased emulsion stability at each soy sodium proteinate level with oil phase volumes of 30, 40 and 50%.     

Stability of Emulsions Containing Highly Hydrolyzed Whey Protein and Starch During Retort Treatments

ABSTRACT: The influence of added unmodified amylopectin starch and modified amylopectin starch on the stability of oil-in-water emulsions (4 wt% corn oil), formed with a highly hydrolyzed commercial whey protein (WPH) product, during retort treatment (121°C for 16 min), was examined. The creaming, coalescence, and flocculation of the emulsions were studied by determining changes in the droplet size and the micro structure of the emulsions after retorting. At a low starch concentration (≤ 1.5%), the extent of coalescence was higher in the emulsions containing modified amylopectin starch than in those containing unmodified amylopectin starch. All emulsions containing moderate levels of unmodified or modified amylopectin starch showed flocculation of oil droplets by a depletion mechanism. The degree of flocculation, which was dependent on the molecular weight and the radius of gyration of the amylopectin molecules, was considered to correlate with the extent of coalescence of the oil droplets in these emulsions. At high levels of added starch (>1.5%), the degree of coalescence decreased gradually, apparently because of the high viscosity of the aqueous phase.     

Stability of oil: Water emulsions of amaranth proteins. Effect of hydrolysis and pH

In this contribution we have determined the effect of limited enzymatic hydrolysis on the emulsifying capacity of amaranth proteins. The action of enzyme (alcalase and trypsin) and the pH of the continuous phase of the oil/water emulsion (pH 2.0, 6.3 and 8.0) were the variables analyzed. The results obtained show that amaranth protein isolates, AI, contain proteins species capable of forming and stabilizing emulsions, mainly at acidic pH (2.0) and to a lesser extent at pH 8.0. While the emulsions obtained are sensitive to creaming and flocculation, they do not undergo destabilization by coalescence. The emulsions prepared from proteins subjected to low grade trypsin hydrolysis (TH2.2) are sensitive to creaming - flocculation, whereas alcalase-hydrolyzed proteins (AH1.7 and AH9.5) exhibited a significant destabilization by creaming, flocculation and coalescence, mainly at pH 6.3. The effect of the pH of the aqueous phase was determining on the emulsion stability beside the structural and physicochemical characteristics of protein species utilized as tensioactive. At acidic pH (pH 2.0) the unfolding and charge of polypeptides and the capacity of form a viscoelastic film at the interface were essential while at alkaline pH (pH 8.0) the balance among high and low molecular mass protein species and flexibility of the molecule fixed the emulsions properties.     

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.     

Optimization of nano-emulsions production by microfluidization

The purpose of this study was to produce an oil-in-water nano-emulsion with different compositions of the continuous and dispersed phases through microfluidization. The aqueous phase was a solution of maltodextrin with five different emulsifying ingredients including modified starch (Capsul and Hi-Cap), sodium caseinate (SC), whey protein hydrolysate (WPH), or whey protein concentrate (WPC), while the oil phase consisted of d-limonene or fish oil. Results showed that micofluidizer was capable of producing nano-emulsions (D32 as small as 150 nm) with a narrow size distribution. Generally, moderate microfluidization pressures (42–63 MPa) and cycles (1–2) were the optimum conditions beyond which, there were adverse changes in the emulsion size. For the two oils tested as the dispersed phase, fish oil emulsions had lower Sauter mean diameters (D32) but with wider size distributions than d-limonene. When different emulsifying ingredients were compared, Hi-Cap produced nano-emulsions with the narrowest distribution but highest D32 (about 600 nm). Nano-emulsions with WPC had the smallest D32 (about 200 nm) but the widest size distribution. It was found that a d-limonene volume fraction of 0.10 was the optimum dispersed-phase concentration in terms of emulsion droplet size (D32). Also, adding a surfactant (Tween 20) helped to reduce the emulsion size significantly during microfluidization, but it lead to extensive flocculation of emulsion droplets because of surfactant–biopolymer interactions and emulsifier displacement.     

Freeze-thaw stability of oil-in-water emulsions prepared with native and thermally-denatured soybean isolates

Freeze-thaw stability of oil-in-water emulsions prepared with native or thermally-denatured soy isolates (NSI and DSI, respectively) as the sole emulsifier and sunflower oil (? = 0.25) has been examined at various protein concentrations (0.5, 1.0 and 2.0% w/v), comparatively with sodium caseinate (SC). The freeze-thaw stability was assessed by measurements of particle size, oiling off and gravitational separation after isothermal storage at −20 °C for 24 h and further thawing. The oil phase remained in liquid state and the amount of ice formed was similar (>97%) whatever the sample type and protein concentration. At 0.5%, NSI and DSI emulsions where highly unstable, exhibiting a coagulated cream layer with appreciable oiling off (>25%), whereas those prepared with SC were more stable, due to their initial lower flocculation degree (FD %) and particle size. For all emulsions, the increase of protein concentration (0.5–2.0% w/v) improves the freeze-thaw stability as a consequence of a decrease of initial FD %. At 2.0%, where is enough protein to cover the interface, a lower coalescence stability of NSI emulsion respect to those prepared with NSI was observed after freeze-thawing. This result can be attributed to the high tendency to aggregation of native soy globulins at subzero temperatures. Notwithstanding this, unlike the SC emulsions, the formation of new flocs in soy isolates-stabilized emulsions during freeze-thawing cannot be totally controlled.     

The effect of chitosan on the properties of emulsions stabilized by whey proteins

The influence of the cationic amino polysaccharide chitosan content (0–0.5%) on particle size distribution, creaming stability, apparent viscosity, and microstructure of oil-in-water emulsions (40% of rapeseed oil) containing whey protein isolate (WPI) (4%) at pH 3 was investigated. The emulsifying properties, apparent viscosity and phase separation behaviour of aqueous WPI/chitosan mixture at pH 3 were also studied. The interface tension data showed that WPI/chitosan mixture had a slightly higher emulsifying activity than had whey protein alone. An increase in chitosan content resulted in a decreased average particle size, higher viscosity and increased creaming stability of emulsions. The microstructure analysis indicated that increasing concentration of chitosan resulted in the formation of a flocculated droplet network. This behaviour of acidic model emulsions containing WPI and chitosan was explained by a flocculation phenomenon.     

Spray-dried whey protein/lactose/soybean oil emulsions. 1. Surface composition and particle structure

Emulsions made of whey protein, lactose and soybean oil were spray-dried and the chemical surface composition of the dried powders estimated by electron spectroscopy for chemical analysis. In particular, the ability of whey protein to encapsulate fat was highlighted. Additionally, the structure of the spray-dried powder particles was studied by scanning electron microscopy. The powders were examined after storage in both dry and humid atmospheres (relative humidity 75%, 4 days). It was found that the ability of whey protein to encapsulate soybean oil is rather low compared with sodium caseinate, with a large part of the powder surface covered by fat after spray-drying. After storage in humid atmosphere there is a release of encapsulated oil onto the powder surface in most cases, and an increase in fat coverage. The release offat onto the powder surfaces causes the particle structure to change dramatically for powders containing a critical amount of lactose. Such powders agglomerate and lose structure completely. In comparison, powders containing no lactose storage under humid conditions also cause a release of fat onto the powder; however, in this case particle structure remains intact. Powders containing only a small amount of lactose, up to ~25% of emulsion dry weight, do not exhibit the release of fat onto the powder surfaces after storage under humid conditions and the structure of these powder particles does not change. The presence of lactose in whey protein-stabilized emulsions, however, does not increase fat encapsulation by whey protein, as reported earlier for sodium caseinate-stabilized emulsions that were spray-dried. During spray-drying of whey protein/lactose solutions there is a strong overrepresentation of surface-active whey protein on the powder surface. Whey protein coverage increases even further when the powders are stored under humid conditions, also making them lose structure.     

Production and stabilization of a flaxseed oil multi-layer emulsion containing sodium caseinate and pectin

The purpose of this research is the evaluation of a flaxseed oil-in-water emulsion, stabilized by a multi-layer structure consisting of sodium caseinate (Na-caseinate) and pectin to provide a basis for the combination of these materials for future studies. In the first step, the o/w emulsion (10 g oil, 90 g aqueous phase, and a pH 6.8) with varying concentration of Na-caseinate was investigated. Second, the pectin solution (0.05–1.5 g/100 g solution) was added to the primary emulsions and the pH was adjusted to 3.0. The emulsions were characterized by mean particle size (dynamic light scattering and static light scattering techniques), ζ-potential, turbidity value, creaming index, and the visualization of the microstructure. A clear separation of the oil phase at low protein contents and destabilizing by depletion flocculation at high protein content were observed. Extensive droplet flocculation and coalescence were determined until the pectin concentration reached 0.5 g/100 g solution for the secondary emulsion. After 7 days of storage, a 1.5 g/100 g solution pectin content had good stability with a relatively small size distribution, high turbidity value, and no cream phase separation.     

pH-dependent emulsifying properties of pea [Pisum sativum (L.)] proteins

Emulsifying properties of two partially purified legumin and vicilin (PL and PV) and protein isolate (PPI) from dry pea seeds at various pH values (3.0, 5.0, 7.0 and 9.0) were investigated. The tested emulsion characteristics included droplet size, flocculation and coalescence indices (FI and CI), creaming index, as well as interfacial protein adsorption. Some physicochemical properties of these proteins, e.g., free sulfhydryl and disulfide bond contents, protein solubility (PS), surface hydrophobicity (H_o) and thermal stability (and denaturation), were also characterized. The results indicated that emulsifying ability and emulsion stability of various pea proteins considerably varied with the preparation process, protein composition and pH. Overall, all the pea proteins exhibited least emulsifying ability at pH 5.0 (around isoelectric point), and concomitantly, the resultant emulsions were most unstable against coalescence and creaming. The emulsifying ability of these proteins at pH 3.0 was generally better than that at neutral or alkali pH values, and among all the three proteins, PL exhibited highest emulsifying ability at this pH. The flocculated state and size of droplets in fresh emulsions did not directly affect stability of these emulsions against flocculation and coalescence (upon 24 h of storage), and even creaming (up to 7 days). Interestingly, the PL and PV exhibited much better creaming stability than PPI, at pH deviating from the pI. The emulsifying properties of these proteins were not only related to their PS and H_o, but also associated with the protein adsorption and nature (e.g., viscoelasticity) of interfacial protein films. These results can greatly extend the knowledge for understanding the emulsifying properties of pea proteins, especially the pH dependence of emulsion characteristics.