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.     

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.     

Flocculation of Whey Protein Stabilized Emulsions as Influenced by Dextran Sulfate and Electrolyte

The creaming stability and viscosity of oil-in-water emulsions stabilized by whey protein isolate were monitored as functions of dextran sulfate (DS) and electrolyte (NaCl) concentration. At a specific DS concentration (the critical flocculation concentration, CFC), the droplets became flocculated, which promoted creaming. Addition of electrolyte caused an increase in CFC. At NaCl concentrations <0.5 wt%, addition of electrolyte decreased emulsion viscosity, but at concentrations >0.5 wt% it caused an increase in viscosity due to increased flocculation. The results were due to the influence of electrostatic screening on the effective volume of DS molecules and colloidal interactions between droplets.     

Viscoelastic Properties of Heat-Set Whey Protein-Stabilized Emulsion Gels with Added Lecithin

Our objective was to determine how lecithin affects the small-deformation shear rheology of heat-set emulsion gels made from whey protein concentrate (WPC). Fine oil-in-water emulsions were prepared with WPC, lecithin or WPC + lecithin present during homogenization. Storage and loss moduli were measured in situ during thermal processing at temperatures up to 90°C and afterwards at 30°C. The positive influence of pure egg lecithin added after emulsification on the elastic modulus of the WPC emulsion gel was attributed to lecithin-protein complexation. Crude egg lecithin gave a broadly similar increase in gel strength, but pure soybean lecithin was not so effective in reinforcing the network, and crude soybean lecithin was ineffective. Using lecithin as sole emulsifier, with WPC added after homogenization, gave a lower modulus for the heat-set WPC emulsion gel. With protein + lecithin present during emulsification, the considerable loss of gel strength was attributable to some WPC displacement from the emulsion droplet surface.     

离子强度和温度对乳清蛋白凝胶的影响

本实验主要研究凝胶温度和CaCl2 浓度对乳清蛋白冷凝胶的影响。结果表明：较低的凝胶温度和增加CaCl2浓度能够致使乳清蛋白形成清亮的凝胶;在0、10、20℃凝胶温度条件下,增加CaCl2 浓度使得凝胶硬度有所增加;乳清蛋白凝胶的持水性在凝胶温度为0、10℃,CaCl2 浓度为20、40mmol/L 时受到影响;除了0℃ 和20mmol/LCaCl2 条件下,低温能够使乳清蛋白形成较高的凝胶硬度和持水性。凝胶温度和CaCl2 浓度是影响乳清蛋白冷凝胶的关键因素。     

Kinetics for Describing the Creaming of Protein-Stabilized O/W Emulsions by Multiple Light Scattering

In the present work, new kinetics to describe the creaming stability of oil-in-water emulsions determined by backscattering measurements （BS） is proposed. The emulsions assayed exhibited a different backscattering profiles regarding creaming destabilization hyperbolic and sigmoid one. Hyperbolic behavior can be described by a second order kinetics, where k_h could be equaled to a rate constant that describes the creaming process and its values would indicate the stability of emulsions. While for the sigmoid BS pattern, kinetics with two terms, is adequate to describe the creaming process in contrast to kinetics previously reported in the literature. The kh value has the same meaning as before, and ks indicates the delaying effect on the creaming rate.     

乳铁蛋白-乳清分离蛋白乳状液微聚集体构建与酶交联对其流变学特性的影响

以乳清分离蛋白（whey protein isolate,WPI）与乳铁蛋白（lactoferrin,LF）乳状液形成微聚集体与转谷氨酰胺酶酶促交联微聚集体,以期提高体系流变特性。通过微射流分别制备WPI和LF乳状液,二者混合后,乳状液微滴之间发生异型聚集效应,通过转谷氨酰胺酶交联结合形成具有特定三维空间网络结构的微聚集体。研究结果表明：WPI与LF乳状液发生异型聚集,最大程度的聚集和最高物理稳定性体系发生在50% LF-50% WPI微滴形成的微聚集体。异型聚集效应改变了乳状液的流变特性,与单一WPI和LF乳状液相比,50% LF-50% WPI微聚集体流变学特性黏度值分别为单一乳状液的3.72?倍和2.2?倍,通过转谷氨酰胺酶交联,乳状液微聚集体的黏度值为原来的11.4?倍。因此,基于异型聚集效应结合酶促交联,可提高食品体系的流变特性,为开发食品脂质替代物提供了一定的理论支持。     

Foaming and Interfacial Properties of Polymerized Whey Protein Isolate

ABSTRACT: Yield stresses (τ) of whipped foams prepared from various ratios of native whey protein isolate (WPI) and polymerized whey protein isolate (pWPI) were characterized by means of vane rheometry Yield stress displayed a parabolic response to increasing concentrations of pWPI, peaking at 50%. Foam air phase volume steadily decreased with increasing pWPI content, whereas equilibrium surface tension steadily increased. Dynamic surface tension measurements revealed that native WPI adsorbed much more rapidly than pWPI, presumably because of the latter's larger size. Interfacial dilatational elasticity (E') displayed a parabolic trend with increasing pWPI content, peaking at 50%. This suggested that pWPI coadsorbs with native WPI, bolstering E' of native WPI interfaces. However, too much pWPI caused a weakening of the network. A positive, curvilinear relationship between E' and τ was observed, consistent with a previous observation for WPI foams formed at various pH levels and salt concentrations, further suggesting a general link between these parameters.     

离子强度对乌鳢胶原蛋白短肽聚集结构及理化特性的作用

为了研究乌鳢胶原肽在6种不同离子强度诱导下聚集的结构与特性的变化规律,对聚集体变化过程中的内源荧光、浊度、微观结构、粒径、黏度及其二级结构进行测定。结果表明,在0～500 mM的Na Cl范围内,离子强度具有促进胶原蛋白肽自组装聚集的效果,且聚集速率随离子强度的增大而增加。在0～150 mM范围内,胶原蛋白肽聚集的三维网络紧密性增加,聚集体平均粒径增大74.42%,最大剪切黏度增加487.67%。当离子强度在150～500 mM范围时,胶原蛋白肽三维网络紧密性降低,聚集体平均粒径下降,最大剪切黏度降低21.39%。胶原蛋白肽聚集体的二级结构并没有随离子强度变化而发生明显变化。因此,适度的增大样品离子强度可促进胶原肽的自组装聚集,改善其凝胶的三维网络结构和理化特性,为胶原蛋白肽进一步应用于制备药物载体的研究提供参考。     

Physical Properties of Extruded Products as Affected by Cheese Whey

Corn, rice and potato flour were extruded with sweet whey solids (SWS) or whey protein concentrate (WPC) using low and high shear extrusion processing conditions. WPC added at product content of 25% had minimal effect on the texture of extruded products. Expansion and breaking strength were improved in some processes through changes in extrusion shear and moisture. Whey product incorporation resulted in reduced specific mechanical energy input to the process. Increasing whey product concentration beyond 25% reduced expansion and water absorption indices significantly, affecting textural hardness. Product quality characteristics were directly related to the whey product content.     

Disulfide Bond Formation Affects Stability of Whey Protein Isolate Emulsions

The viscosity and degree of flocculation of 20 wt% n-hexadecane oil-in-water emulsions stabilized by whey protein isolate (1 wt% WPI in 0.05M phosphate buffer, pH 7.0) increased as the emulsions aged. These effects were reduced when N-ethylmaleimide, a sulfhydryl blocking agent, was added to the emulsions immediately after homogenization, but were not completely eliminated. Gel electrophoresis (SDS-PAGE) showed an increase in the extent of intermolecular disulfide bond formation between proteins absorbed at the droplet interface with time. Floes were probably formed initially by noncovalent bonding or bridging flocculation, and then stabilized by disulfide bonds between proteins absorbed to different droplets.     

Isostrength Comparison of Large-Strain (Fracture) Rheological Properties of Egg White and Whey Protein Gels

The effects of protein concentration and heating conditions on the physical properties of whey protein isolate (WPI) (in 50 mM NaCl, pH 7) and egg white (pH 9) gels were examined. Egg white and WPI gels had similar values for shear stress at fracture (i.e., isostrength), while trends for shear strain at fracture were protein-type specific. The rigidity ratio (R_0.3), ratio of the rigidity at fracture (G_f) to the rigidity at 30% of fracture strain, measured departure from the stress-strain relationship of an ideal Hookean solid. All gels fit master curves of G_f vs R_0.3, which were described by a power law model of R_0.3=A(G_f)-°19, where "A" showed protein type-specific characteristics.     

Gel Point of Whey and Egg Proteins Using Dynamic Rheological Data

The gel point temperatures of coagulation type proteins and gelation type proteins were determined by extrapolating the rapidly rising phase of the storage modulus G’back to the temperature axis. The gelation onset. temperatures of the concentration-independent proteins oval-bumin, ovotransferrin, and BSA were 81°C, 62°C, and 75°, respectively, Gelation of whey protein isolate and egg white gels, both concentration-dependent, was presumably due to disulfide bonds formed by the interactions of the concentration-independent proteins: α-lac-talbumin and β-lactoglobulin, and ovalbumin and ovotransferrin, respectively. Moreover, the incipient gel temperature of whey proteins decreased when the concentration of whey proteins increased.     

Gel Properties of Whey Protein Concentrates as Influenced by Ionized Calcium

Ionic calcium in four whey protein concentrates (WPC) was decreased using sodium tripolyphosphate (NaTPP) or ethylenediamine tetraacetic acid (EDTA) and effects on gel properties were determined. Total calcium ranged from 0.22–0.41 g/100g WPC and ionic calcium 2.98–47.25 mg/100g protein. Hardness was maximized and expressible moisture (EM) minimized in three WPC gels with 10 mM NaTPP. EDTA had a similar effect on one WPC gel. Addition of 10 mM NaTPP decreased ionic calcium to 5.23–10.31 mg/100g protein. NaTPP or CaCl₂ did not improve hardness or EM of one WPC gel which contained the lowest total and ionized calcium. Chelating agents were effective in improving gel properties of WPC containing higher than optimal calcium.     

Factors Affecting the Functional Properties of Whey Protein Products: A Review

Numerous why protein products (WPP) have been developed as excellent food ingredients with unique functional properties. However, the functional properties of WPP are affected by several compositional and processing factors. Recently, novel processing technologies such as high hydrostatic pressure, ultrasound, extrusion and tribomechanical activation have been used to modify the functional properties of WPP. Also, WPP have been used as delivery systems for functional ingredients and in edible films. The present paper reviews the latest developments in the role of different factors on the functional properties of WPP with emphasis on novel processing technologies, and interaction with other food ingredients     

Microencapsulating Properties of Whey Protein Concentrate 75

ABSTRACT Emulsions containing various levels of soya oil dispersed in solutions of whey protein concentrate (WPC) 75 (5% w/v) were spray-dried to yield powders with oil contents ranging from 20% to 75% (w/w). The effect of homogenizing pressure and oil/protein ratio on oil globule size distributions and protein load of the emulsions and the microencapsulation efficiency (ME) and redispersion behavior of the powders were examined. Emulsion oil droplet size decreased with increasing homogenization pressure but was not affected by oil/protein ratio. Emulsion protein load and ME of the powders were negatively correlated with increasing oil/protein ratio. Powders with an oil/protein ratio < 0.75 were least susceptible to destabilization during spray-drying.     

Structure-Mechanical Properties of Heat-Induced Whey Protein/Cassava Starch Gels

Structure-mechanical properties of heat-induced whey protein isolate/cassava starch (WPI/CS) gels were studied by hot-stage video microscopy (HSVM) and axial compression testing (ACT). Elastic moduli (or compression stress) of pure WPI and CS gels followed a power dependence with concentration. ACT confirmed that reinforcement occurred when CS was added at 10–25% of total solids. HSVM revealed that CS granules swelled first, removed water from the system and concentrated the WPI solution that gelled later. Reinforced gels had a continuous WPI phase filled with swollen CS granules. A modified Takayanagi model accounting for water redistribution during gelatinization accurately fitted the mechanical properties of these gels.     

Compressive Properties of Whey Protein Composite Gels Containing Fractionated Milkfat

Compressive properties of composite gels consisting of 13% whey protein isolate (WPI) and 10% to 30% selected milkfat fractions were investigated at different temperatures. Compressive properties of gels were significantly affected by melting properties of the filler. Maximum compressive strength of composite gels was proportional to filler load and proportion of solid lipids. Compressive strength of composite gels was higher than that of WPI-only gels, and the relative increase in hardness ranged from about 5% to 91%. Results indicated that compressive properties of gels were affected by a combined effect of filler load and temperaturedependent influence on compressive properties of matrix, interface, and filler particles.     

不同pH条件下乳清蛋白-桑椹多酚复合营养粉的制备及其理化性质

近年来,蛋白质与多酚类物质的相互作用是食品领域的研究热点之一,两者的结合受到多种因素的影响,其中pH值是重要的影响因子。该文研究了不同pH值条件下桑椹多酚(Mulberry Polyphenols,MP)对乳清蛋白(Whey Protein,WP)理化性质和功能特性的影响。结果表明,桑椹多酚改变了复合蛋白粉的色泽、粒径大小和Zeta电位。同时,还提高了乳清蛋白的溶解性、乳化性能,在pH值3.0时乳清蛋白的乳化能力和乳化稳定性分别达到7.23 m²/g prot和89.56%,较对照组分别提高了2.66%和1.21%。通过高效液相色谱法对桑椹多酚-乳清蛋白粉中的单体酚类进行定量分析,在pH值5.0和7.0条件下结合的单体酚含量比pH值1.0和3.0高。此外,较空白对照组而言,添加桑椹多酚提高了乳清蛋白的DPPH自由基清除率、ABTS⁺自由基清除能力和FRAP还原能力,最高分别达到89.28%、81.70%和530.95μmol/g prot。综上所述,利用动物蛋白结合植物多酚是创新功能食品组分的手段,反应体系的pH值对结合效率有重要影响,为今后...