Structuring lipids by aggregation of acidic protein microspheres in W/O emulsions (original) (raw)
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Food Research International, 2012
Controlled aggregation of protein microspheres in water-in-oil (W/O) emulsions was used to form semi-solid lipid materials. The aqueous phase consisted of 10 wt% whey protein isolate (WPI) in buffer solution (pH 7.0, 100 mM NaCl). The oil phase consisted of a lipophilic nonionic surfactant (8 wt % polyglycerol polyricinoleate, PGPR) dispersed in a liquid oil (soybean oil). Lipid phases containing protein microspheres were formed by homogenization of the oil and aqueous phases to form a W/O emulsion followed by heating (90°C for 30 min) to promote gelation of the WPI in the aqueous phase. Temperature-scanning dynamic shear measurements showed that the W/O emulsions underwent an irreversible liquid-to-solid transition when heated above the thermal denaturation temperature of WPI, which was attributed to protein gelation and microsphere aggregation. Optical microscopy indicated that a three-dimensional network of aggregated protein microspheres was formed at high aqueous phase contents (>30 wt %). Shear rheology measurements (shear stress versus shear rate) indicated that these structured emulsions were non-ideal plastic-like materials. The apparent shear viscosity increased with thermal treatment, increasing aqueous phase content, and decreasing shear rate. The structured W/O emulsions developed in this study may be useful materials for the development of foods with highly viscous or gel-like lipid phases, but low saturated or trans-fat contents.
Journal of Food Engineering, 2013
The effect of heteroaggregation of oppositely charged protein microspheres dispersed within a liquid oil phase on the microstructure and rheological properties of water-in-oil (W/O) emulsions was evaluated. The aqueous phase of the initial W/O emulsions contained either 10% b-lactoglobulin or 10% lactoferrin (pH 7, 100 mM NaCl). At this pH, b-lactoglobulin (BLG) is negatively charged while lactoferrin (LF) is positively charged. The oil phase consisted of a lipophilic non-ionic surfactant (8% polyglycerol polyricinoleate, PGPR) dispersed within soybean oil. Three 40% W/O emulsions were formed containing different types of protein microspheres: (i) BLG: 100% BLG droplets; (ii) LF: 100% LF droplets; and (iii) Mixed: 50% BLG droplets and 50% LF droplets. Prior to heating, the mixed emulsions had a higher shear viscosity, yield stress, and shear modulus than the BLG or LF emulsions, which suggested that electrostatic attraction led to the formation of a three-dimensional network of aggregated droplets. All three W/O emulsions underwent an irreversible fluid-to-solid transition when they were heated above %70°C. This phenomenon was attributed to thermal denaturation of the globular BLG and LF molecules within the aqueous phase promoting aggregation and network formation of the protein microspheres. After heating, the mixed emulsions had a higher shear viscosity, yield stress and shear modulus than the BLG or LF emulsions, suggesting that a stronger droplet network was formed due to electrostatic attraction. Shear rheology measurements of the W/O emulsions showed that the lipid phases formed after heating were nonideal plastics characterized by a yield stress and shear thinning behavior. These results may facilitate the design of semi-solid or solid foods with reduced saturated-or trans-fat contents suitable for use in commercial products.
1999
Effects of small-molecule surfactants (emulsifiers) on the small-deformation viscoelastic properties of heat-set whey protein emulsion gels have been investigated using a controlled stress rheometer. The surfactants used in this investigation were the water-soluble diglycerol monolaurate (DGML) and diglycerol monooleate (DGMO), and the oil-soluble glycerol monooleate (GMO). The elastic modulus of the emulsion gel was found to decrease in the presence of a small amount of surfactant, but then to recover at higher surfactant concentrations. The initial reduction in modulus correlates with protein displacement from the oil droplet surface. The recovery of the storage and loss moduli at higher surfactant concentrations of DGML or DGMO may be due to the depletion flocculation of the emulsion prior to heat-treatment. However, for systems containing high content of GMO in the oil phase, the recovery of the moduli is probably owing mainly to the smaller average particle size. Effects of surface monolayer composition, droplet aggregation and average particle size were discussed. The behaviour obtained here was compared with results for previously investigated whey protein emulsion gel systems containing different emulsifiers.
International Dairy Journal, 2013
The effect of heat treatment on the physical stability of milk protein concentrate (MPC) stabilised emulsions was investigated; 3% (w/w) MPC dispersions were preheated at 90 C for 5 min at neutral pH prior to emulsification. Heat-treated (120 C, 10 min) emulsions stabilised by preheated MPC had slightly fewer dropletedroplet interactions than that stabilised by unheated MPC because the whey proteins were pre-denatured (w90% denaturation of the total whey proteins), which led to a reduction in subsequent heat-induced dropletedroplet and dropleteprotein interactions. Emulsions stabilised by calcium-depleted MPC were also investigated. The presence of some non-micellar casein fractions gave better emulsification and may have conferred a protective stabilising effect on whey protein aggregation, in both the dispersed phase and the continuous phase during the secondary heat treatment. It was concluded that calcium manipulation and thermal modification of MPC can be utilised to control the functionality in oil-in-water emulsions.
Food Hydrocolloids, 2017
Cinnamaldehyde (CA), a common hydrophobic flavor, was encapsulated in oil-in-water emulsions that were stabilized by whey protein isolate (WPI). The impact of CA content and pH on the physical stability and lipolysis of the emulsions was then investigated. The presence of CA gave the emulsions a creamy yellow color, which became darker during storage. Emulsions formed using only CA as the oil phase contained large droplets that were physically unstable to particle growth and phase separation. The addition of medium chain triglyceride oil (MCT) improved the stability of emulsions containing CA, which was attributed to inhibition of Ostwald ripening effects. Fluorescent microscopy indicated that the adsorption of the protein to the droplet surfaces led to a thicker adsorbed layer in the presence of CA. The stability of the emulsions to droplet flocculation and coalescence depended on the CA level in the oil phase and the pH of the aqueous phase. An in vitro model was used to assess the impact of oil phase composition and pH on lipid hydrolysis and emulsion microstructure under simulated gastrointestinal tract conditions. The rate of lipid hydrolysis was highly dependent on CA level and pH. These results may facilitate the fabrication of emulsions with controlled GIT fate that are suitable for use in functional foods and beverages.
Characterization of cold-set gels produced from heated emulsions stabilized by whey protein
International Dairy Journal, 2009
This paper reports the cold gelation of preheated emulsions stabilized by whey protein, in contrast to, in previous reports, the cold gelation of emulsions formed with preheated whey protein polymers. Emulsions formed with different concentrations of whey protein isolate (WPI) and milk fat were heated at 90 C for 30 min at low ionic strength and neutral pH. The stable preheated emulsions formed gels through acidification or the addition of CaCl 2 at room temperature. The storage modulus (G 0) of the acidinduced gels increased with increasing preheat temperature, decreasing size of the emulsion droplets and increasing fat content. The adsorbed protein denatures and aggregates at the surface of the emulsion droplets during heat treatment, providing the initial step for subsequent formation of the cold-set emulsion gels, suggesting that these preheated emulsion droplets coated by whey protein constitute the structural units responsible for the three-dimensional gel network.
VISCOELASTIC PROPERTIES OF HEAT-SET WHEY PROTEIN EMULSION GELS
Journal of Texture Studies, 1998
The viscoelastic properties of heat-set whey protein gels and whey protein-stabilized emulsion gels have been studied using the dynamic oscillatory rheometry technique. The storage modulus was monirored and analysed for pure protein gels and emulsion gels over a wide range of protein concentrations. The dependence of storage modulus on protein concentration is different for gels of low and high modulus. At low protein concentrations, the increase of storage modulus is much more sensitive to the increase of protein concentration. The protein-coated oil droplets behave as active jiller particles and dramatically enhance the gel strength. The effect of the oil volume fraction on the rheology has been investigated for emulsion gels containing 11 vol. %, 20 vol. % and 45 vol. % Trisun oil. The formula of van der Poel fails to describe the experimental results. l l i s is attributed to the strongly flocculated state of the emulsion system.
Effects of whey protein aggregation on fat globule microstructure in whipped-frozen emulsions
Food Hydrocolloids, 2006
Four oil-in-water emulsions, stabilized by native or pre-denatured whey proteins in the absence or presence of casein, were whipped at À5 1C and stored at À30 1C for several weeks. The microstructure of these whipped-frozen emulsions, which differed by their protein content, were observed by low-temperature scanning electron microscopy (LT-SEM), and transmission electron microscopy (TEM) following freeze-substitution and low-temperature embedding. Fat globule aggregation and adsorbed protein content in whipped-frozen emulsions were determined after application of thawing, dilution or centrifugation. Micrographs indicated that in aerated products, partial replacement of native whey proteins by pre-denatured whey proteins or casein introduced (i) more homogeneity in air bubble size, (ii) more attachment of fat globules to their air-serum interface, and (iii) fat globules in the continuous matrix that were in closer contact with each other. These differences in the microstructures of whipped-frozen emulsions were attributed to differing surface heterogeneity of adsorbed protein particles to fat globule interfaces. r
Food Hydrocolloids, 2002
The kinetics of heat-induced destabilization of whey protein emulsions was studied in the presence of varied concentrations of the polysacchride stabilizer xanthan, carrageenan or propylene glycol alginate (PGA). Both xanthan and carrageenan increased the rate of emulsion droplet aggregation in heated whey protein emulsions, whilst PGA had no observable effect. The maximum effect for xanthan was a 3.5-fold increase in the rate of destabilization for concentrations of 0.05 wt% and above. For carrageenan the increase in aggregation rate was smaller, with a 2.7 times increase observed at a carrageenan concentration of 0.1 wt%. For xanthan gum the decrease in heat stability was explained in terms of the known tendency for xanthan to cause depletion¯occulation in emulsions. For carrageenan the effect was related to evidence that the polysaccharide can interact with denatured whey protein, but not with the native molecule.