Reducing the stiffness of concentrated whey protein isolate (WPI) gels by using WPI microparticles

Concentrated protein gels were prepared using native whey protein isolate (WPI) and WPI based microparticles. WPI microparticles were produced by making gel pieces from a concentrated WPI suspension (40% w/w), which were dried and milled. The protein within the microparticles was denatured and the protein concentration after drying was similar to the native WPI powder. WPI microparticles had irregular shape with an average size of about 70 μm. They absorbed water when dispersed in water, but the dispersion did not gel upon heating. Replacing part of the native WPI powder with WPI microparticles in the protein gel resulted in lower gel stiffness compared with a gel with the same overall protein concentration but without microparticles. However, microparticles also strengthened the continuous phase because they take up water from this phase. This might increase gel stiffness more than would be expected from an inert particle/filler. There was also good bonding between the microparticles and the WPI continuous phase in the gel, which contributed to gel stiffness.     

Stability and mechanism of whey protein soluble aggregates thermally treated with salts

The formation of whey protein aggregates, often termed soluble aggregates, with specific physicochemical properties has been shown to result in improved functionality in gels, foams, emulsions, encapsulation, films and coatings. This work evaluated the potential of whey protein soluble aggregates to improve thermal stability in the presence of salts and determine the mechanism of improved thermal stability. Solutions of whey protein isolate (WPI) or β-lactoglobulin (β-lg) (7% w/w, pH 6.8) were heated for 10 min at 90 °C to form soluble aggregates. Native proteins and soluble aggregates were diluted to 3% w/w in solutions containing 0–108 mM NaCl and thermally treated (90 °C, 5 min). Turbidity, solubility, and viscosity were evaluated, in addition to ζ-potential and S_o (surface hydrophobicity). Size exclusion chromatography coupled with multi-angle laser light scattering (SEC-MALLS) and dynamic light scattering were used to determine aggregate size and transmission electron microscopy (TEM) was used to evaluate aggregate shape. Use of soluble aggregates improved thermal stability due to their altered aggregate shape and higher charge, and resulted in final aggregates that were smaller and less dense, leading to reduced viscosity and turbidity, and increased solubility compared to native proteins. It is concluded that soluble aggregates formed under the appropriate conditions to produce the desirable physicochemical properties can be used to improve whey protein thermal stability with a possible application in beverages.     

Pilot-scale formation of whey protein aggregates determine the stability of heat-treated whey protein solutions—Effect of pH and protein concentration

Denaturation and consequent aggregation in whey protein solutions is critical to product functionality during processing. Solutions of whey protein isolate (WPI) prepared at 1, 4, 8, and 12% (wt/wt) and pH 6.2, 6.7, or 7.2 were subjected to heat treatment (85°C × 30 s) using a pilot-scale heat exchanger. The effects of heat treatment on whey protein denaturation and aggregation were determined by chromatography, particle size, turbidity, and rheological analyses. The influence of pH and WPI concentration during heat treatment on the thermal stability of the resulting dispersions was also investigated. Whey protein isolate solutions heated at pH 6.2 were more extensively denatured, had a greater proportion of insoluble aggregates, higher particle size and turbidity, and were significantly less heat-stable than equivalent samples prepared at pH 6.7 and 7.2. The effects of WPI concentration on denaturation/aggregation behavior were more apparent at higher pH where the stabilizing effects of charge repulsion became increasingly influential. Solutions containing 12% (wt/wt) WPI had significantly higher apparent viscosities, at each pH, compared with lower protein concentrations, with solutions prepared at pH 6.2 forming a gel. Smaller average particle size and a higher proportion of soluble aggregates in WPI solutions, pre-heated at pH 6.7 and 7.2, resulted in improved thermal stability on subsequent heating. Higher pH during secondary heating also increased thermal stability. This study offers insight into the interactive effects of pH and whey protein concentration during pilot-scale processing and demonstrates how protein functionality can be controlled through manipulation of these factors.     

Characterisation of soluble aggregates from commercial whey protein concentrate suspensions: Effect of protein concentration,pH, and heat treatment conditions

Soluble aggregates obtained from heat‐treated suspensions of commercial whey protein concentrate with 74.4% w/w protein were characterised. The effect of protein concentration (7 and 8% w/w), pH (7.0, 7.5 and 8.0), and heating time (0, 5, 10, 15, 20 and 30 min) at 80 °C were evaluated. Whey protein concentrate suspensions with the highest protein concentration (8% w/w) and the lowest pH (pH 7.0) had the highest steady shear viscosity and absorbance values, indicating the effect of the soluble aggregate content (high concentration) and the aggregate size (at lower pH values). According to principal component analysis, samples with 8% w/w and pH 7.0 were grouped in a plot region that confirmed the behaviour observed by confocal microscopy. Those whey protein concentrate suspensions could have soluble aggregates with a strong probability of interacting with cations (in cold gelation applications such as microencapsulation) and with each other (in film‐formation during coating).     

Structure-forming processes in Ca-induced whey protein isolate cold gelation

The structure-forming process of Ca²⁺-induced whey protein isolate (WPI) gels was studied, at 24°C, in the presence of 10 and 120 m CaCl₂. Pre-heating WPI suspensions (10% protein) at 90°C dramatically increased specific viscosity, but did not change the number of accessible sulfhydryl groups, compared to pre-heating at 70°C. The most important factor governing the process appeared to be CaCl₂ concentration, rather than the reactive sulfhydryl groups. At 10 m CaCl₂, the increase in aggregate size and network connectivity over time was achieved by clustering of adjacent aggregates. At 120 m CaCl₂, the increase in aggregate size and connectivity was by enlargement of the aggregates which formed connected paths and filled up interstitial spaces.     

Physical properties of whey protein coating solutions and films containing antioxidants

ABSTRACT:  Antioxidants (ascorbyl palmitate and α-tocopherol) were incorporated into 10% (w/w) whey protein isolate (WPI) coating solution containing 6.67% (w/w) glycerol (WPI:glycerol = 6:4). Before incorporation, the antioxidants were mixed using either powder blending (Process 1) or ethanol solvent-mixing (Process 2). After the antioxidant mixtures were incorporated into heat-denatured WPI solution, viscosity and turbidity of the WPI solutions were determined. The WPI solutions were dried on a flat surface to produce WPI films. The WPI films were examined to determine transparency and oxygen-barrier properties (permeability, diffusivity, and solubility). WPI solution containing antioxidants produced by Process 1 and Process 2 did not show any difference in viscosity and turbidity, but viscosity was greater for the WPI solution with rather than without antioxidants. WPI films produced by Process 2 were more transparent than the films produced by Process 1. Oxygen permeability of Process 1 film was lower than Process 2 film. However, both the diffusivity and solubility of oxygen were statistically the same in Process 1 and Process 2 films. Both control WPI films and antioxidant-containing WPI films had very low oxygen solubility, comparable to polyethylene terephthalate films. Permeability of antioxidant-incorporated films was not enhanced compared to control WPI films.     

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.     

Controlled whey protein aggregates to modulate the texture of fat-free set-type yoghurts

The impact of nanoparticulated whey protein aggregates on the texture of fat-free set-type yoghurts was investigated. Monodisperse (MFA) and polydisperse (PFA) fractal aggregates obtained from heated whey protein isolate (WPI) were added to skimmed milk for yoghurt manufacture at four different concentrations (0.2%–1.5%, w/w). The impact of the concentration and the polydispersity of the aggregates on fat-free set-type yoghurts were studied by instrumental measurements (rheology, penetrometry, syneresis and microscopy) and sensory analysis. Yoghurt gel strength and firmness increased with the concentration of WPI, MFA and PFA. However, yoghurts enriched with PFA clearly differed from the yoghurts enriched with WPI. Indeed, yoghurts enriched with PFA were characterised by a weak gel, a low firmness and a low-density of the protein network. Sensory analysis confirmed the results obtained by instrumental measurements. The whey protein aggregates studied are thus promising tools to modulate fat-free yoghurt texture while using milk-derived ingredients.     

Heat-induced aggregation of whey proteins in the presence of κ-casein or sodium caseinate

Aggregates were formed by heating mixtures of whey protein isolate (WPI) and pure κ-casein or sodium caseinate at pH 7 and 0.1 M NaCl. The aggregates were characterized by static and dynamic light scattering and size exclusion chromatography. After extensive heat-treatment at 80 °C for 24 h, almost all whey proteins and κ-casein formed mixed aggregates, but a large proportion of the sodium caseinate did not aggregate. At a given WPI concentration the size of the aggregates decreased with increasing κ-casein or sodium caseinate concentration, but the overall self-similar structure of the aggregates was the same. The presence of κ-casein or caseinate therefore inhibited growth of the heat-induced whey protein aggregates. The results were discussed relative to the reported chaperone-like activity of casein molecules towards heat aggregation of globular proteins.     

Rheology of whey protein isolate-xanthan mixed solutions and gels. Effect of pH and xanthan concentration

Flow properties at pH 5.5-7.5 of whey protein isolate (WPI)-xanthan solutions containing 0-0.5 w/w% xanthan were studied by viscosimetry, although rigidity and fracture properties of the corresponding heat-set gels (90°C, 30 min) were determined by uniaxial compression. All the studied solutions displayed generalized shearthinning flow behaviour. Synergistic WPI-xanthan interactions has been revealed by observing that rheological parameters [σ_msf, K, n, η (γ)] characterizing blends were larger than those calculated from the two separated solutions. Such a behaviour was attributed to segregative phase separation of whey proteins and xanthan. Effects of xanthan on WPI-xanthan gel properties both depended on pH and xanthan concentration. Simultaneous increased xanthan concentration and decreased pH inhibited gelation of WPI-xanthan blends. Regarding gel strength, synergistic WPI-xanthan interactions were observed at pH >7.0 and low xanthan concentration (0.05 or 0.1 w/w%). Antagonism between the two macromolecules occurred at low xanthan concentration and pH ≤6.5, and high xanthan concentration (0.2 or 0.5 w/w%) at all pH tested. Low xanthan concentration rendered mixed gels more brittle than protein gels, and high xanthan concentration decreased pH effects on gel stress-strain relationships. The balance between strong thermal aggregation of concentrated whey proteins - in presence of incompatible xanthan -, high viscosity of blends and repulsive surface forces of protein molecules was thought to be at the origin of WPI-xanthan gel mechanical properties.     

Effect of dynamic heat treatment on the physical properties of whey protein foams

The influence of dynamically heat-induced aggregates on whey protein foams was investigated as a function of the thermal treatment applied with the aim of determining the optimal temperature for the production of heat-induced aggregates dedicated to foaming. The native protein solutions (2% w/v WPI; 50 mM NaCl) at neutral pH were heat-treated using a tubular heat exchanger between 70 °C and 100 °C. Protein denaturation and aggregation were followed by micro-differential scanning calorimetry, size exclusion chromatography, laser diffraction and dynamic light scattering. The protein solutions were whipped using a kitchen mixer to produce foams. Foam overrun, stability against drainage, texture and bubble size distribution were measured.     

Rheology and microstructure of cross-linked waxy maize starch/whey protein suspensions

The objective of the present work was to investigate the effect of the heating process on the structural and rheological properties of whey protein isolate/cross-linked waxy maize starch (WPI/CWMS) blends depending upon the concentration and the starch/whey protein ratio. Starch concentration ranged from 3 to 4% (w/w) and the protein content was of 0.5, 1 and 1.5% (w/w). The blend (pH 7, 100 mM ionic strength) was heated using a jacketed vessel at two pasting temperatures: 90 and 110 °C. The particle size distribution of the WPI suspension (1.5%) displayed three distinct classes of aggregates (0.3, 65 and 220 μm), whereas the size of swollen starch granules varied from 48 to 56 μm according to the pasting temperature. When the two components were mixed together, the peak attributed to swollen starch granules was attenuated and broadened towards higher values (up to 88 μm) due to protein aggregates (260–410 μm). This effect was more pronounced as the protein concentration increased. When compared to starch alone, the rheology of the mixed system was dramatically modified for the flow behaviour as well as for the viscoelastic properties which changed from a solid-like (3–4% starch) to a liquid-like behaviour (3–4% starch/1.5% protein). Microscopic observations showed aggregated proteins located in the continuous phase and swollen starch granules as the dispersed phase. Protein aggregates were of different sizes, part of them appeared adsorbed onto swollen starch granules while another part was unevenly distributed in the continuous phase, yielding discontinuous network which could explain the peculiar viscoelastic behaviour of such suspensions.     

Whey protein aggregate formation during heating in the presence of κ-carrageenan

The effect of a negatively charged polymer, κ-carrageenan, on the aggregation behaviour of whey proteins during heating was studied. Aqueous solutions of whey protein isolate (WPI) at 0.5% were heated in the presence of κ-carrageenan (0.1%) at pH 7.0. This concentration was chosen as optimal in the detection of the intermediate aggregates during chromatographic analysis. The residual unaggregated protein, the intermediate aggregates and the soluble aggregates were all examined as a function of heating time and temperature, using size-exclusion chromatography coupled with light scattering detection. The presence of κ-carrageenan did not affect the aggregation of whey proteins heated at 75 °C; however, a change in the mechanism of aggregation seemed to occur at higher temperatures, and intermediates with higher molecular mass formed at 85 °C. At 90 °C, in the presence of κ-carrageenan, the extent of WPI aggregation was much larger, as soluble aggregates were no longer present and less residual protein was recovered in the unaggregated peak.     

COLD GELATION OF WHEY PROTEIN EMULSIONS

Stable and homogeneous emulsion‐filled gels were prepared by cold gelation of whey protein isolate (WPI) emulsions. A suspension of heat‐denatured WPI (soluble WPI aggregates) was mixed with a 40% (w/w) oil‐in‐water emulsion to obtain gels with varying concentrations of WPI aggregates and oil. For emulsions stabilized with native WPI, creaming was observed upon mixing of the emulsion with a suspension of WPI aggregates, likely as a result of depletion flocculation induced by the differences in size between the droplets and aggregates. For emulsions stabilized with soluble WPI aggregates, the obtained filled suspension was stable against creaming, and homogeneous emulsion‐filled gels with varying protein and oil concentrations were obtained. Large deformation properties of the emulsion‐filled cold‐set WPI gels were determined by uniaxial compression. With increasing oil concentration, the fracture stress increases slightly, whereas the fracture strain decreases slightly. Small deformation properties were determined by oscillatory rheology. The storage modulus after 16 h of acidification was taken as a measure of the gel stiffness. Experimental results were in good agreement with predictions according to van der Poel's theory for the effect of oil concentration on the stiffness of filled gels. Especially, the influence of the modulus of the matrix on the effect of the oil droplets was in good agreement with van der Poel's theory.     

Coating of Peanuts with Edible Whey Protein Film Containing α‐Tocopherol and Ascorbyl Palmitate

ABSTRACT: Physical properties of whey protein isolate (WPI) coating solution incorporating ascorbic palmitate (AP) and α‐tocopherol (tocopherol) were characterized, and the antioxidant activity of dried WPI coatings against lipid oxidation in roasted peanuts were investigated. The AP and tocopherol were mixed into a 10% (w/w) WPI solution containing 6.7% glycerol. Process 1 (P1) blended an AP and tocopherol mixture directly into the WPI solution using a high‐speed homogenizer. Process 2 (P2) used ethanol as a solvent for dissolving AP and tocopherol into the WPI solution. The viscosity and turbidity of the WPI coating solution showed the Newtonian fluid behavior, and 0.25% of critical concentration of AP in WPI solution rheology. After peanuts were coated with WPI solutions, color changes of peanuts were measured during 16 wk of storage at 25 °C, and the oxidation of peanuts was determined by hexanal analysis using solid‐phase micro‐extraction samplers and GC‐MS. Regardless of the presence of antioxidants in the coating layer, the formation of hexanal from the oxidation of peanut lipids was reduced by WPI coatings, which indicates WPI coatings protected the peanuts from oxygen permeation and oxidation. However, the incorporation of antioxidants in the WPI coating layer did not show a significant difference in hexanal production from that of WPI coating treatment without incorporation of antioxidants.     

Impact of Residual Lactose on Dry Heat-Induced Pre-texturization of Whey Proteins

Controlling denaturation/aggregation of whey proteins during their pre-texturization is highly critical to avoid variability in their functional properties. We investigated how the dry heat-induced (16 h at 100 °C and a_w?=?0.23) pre-texturization of whey protein isolate (WPI) is affected by traces of remaining lactose (0.3–2.0%) and how it influences its subsequent gelling properties. Lactose even in trace quantities developed intense browning of WPI. Dry-heating conditions used in this study mainly developed soluble aggregates stabilized by covalent crosslinks other than disulfide bonds. The extent of aggregation and size of aggregates were drastically increased with increasing lactose. Intermediate quantity (39–46%) of soluble aggregates improved the gel strength, while excessive aggregation (>?50%) resulted in loss of gel strength. Elasticity of gels was also increased by increasing protein aggregates. This study suggests that the traces of lactose that remain in WPI are critical for controlling its pre-texturization by dry heating and its subsequent gelling properties.     

Comparative effect of thermal treatment on the physicochemical properties of whey and egg white protein foams

The optimization of the functionalities of commercial protein ingredients still constitutes a key objective of the food industry. Our aim was therefore to compare the effect of thermal treatments applied in typical industrial conditions on the foaming properties of whey protein isolate (WPI) and egg white proteins (EWP): EWP was pasteurized in dry state from 1 to 5 days and from 60 °C to 80 °C, while WPI was heat-treated between 80 °C and 100 °C under dynamic conditions using a tubular heat exchanger. Typical protein concentrations of the food industry were also used, 2% (w/v) WPI and 10% (w/v) EWP at pH 7, which provided solutions of similar viscosity. Consequently, WPI exhibited a higher foamability than EWP. For WPI, heat treatment induced a slight decrease of overrun when temperature was above 90 °C, i.e. when aggregation reduced too considerably the amount of monomers that played the key role on foam formation; conversely, it increased foamability for EWP due to the lower aggregation degree resulting from dry heating compared to heat-treated WPI solutions. As expected, thermal treatments improved significantly the stability of WPI and EWP foams, but stability always passed through a maximum as a function of the intensity of heat treatment. In both cases, optimum conditions for foam stability that did not impair foamability corresponded to about 20% soluble protein aggregates. A key discrepancy was finally that the dry heat treatment of EWP provided softer foams, despite more rigid than the WPI-based foams, whereas dynamically heat-treated WPI gave firmer foams than native proteins.     

Assessing the potential of flaxseed protein as an emulsifier combined with whey protein isolate

The potential use of flaxseed protein isolate (FPI) as an emulsifying agent was studied in combination with whey protein isolate (WPI) or alone. All the FPI and WPI–FPI emulsions were kinetically unstable. The increase of FPI concentration (0.7% w/v) led to a higher creaming stability of the FPI emulsions due partly to a reduction in interfacial tension between aqueous and oil phases, but mainly to the gel network formation. However at this same high FPI concentration, WPI–FPI emulsions showed a decrease in droplet size and creaming stability, which could be due to the presence of flaxseed gum in the protein isolate enhancing depletion effects. A protein excess was verified in the mixed systems (0.14 or 0.7% (w/v) FPI) and the increase of FPI concentration led to an even greater surface protein content. Increasing homogenization conditions (pressure and number of passes), the creaming stability of the FPI systems increased, mainly at higher concentration (0.7% w/v). Meanwhile, in the mixed systems, the creaming stability of the emulsions containing 0.7% (w/v) FPI decreased even more, but was improved for the emulsions with 0.14% (w/v) FPI. Thus, it was observed that systems containing only FPI at higher concentration were stabilized by gel formation, while in WPI–FPI systems there was a competition by interface between biopolymers with a consequent depletion process. As a result, more stable systems were obtained with WPI addition at lower FPI concentration (0.14% w/v) and using higher homogenization pressure and number of passes (60 MPa, two passes).     

Effects of sucrose on egg white protein and whey protein isolate foams: Factors determining properties of wet and dry foams (cakes)

The effects of sucrose on the physical properties of foams (foam overrun and drainage ½ life), air/water interfaces (interfacial dilational elastic modulus and interfacial pressure) and angel food cakes (cake volume and cake structure) of egg white protein (EWP) and whey protein isolate (WPI) was investigated for solutions containing 10% (w/v) protein. Increasing sucrose concentration (0–63.6 g/100 mL) gradually increased solution viscosity and decreased foam overrun. Two negative linear relationships were established between foam overrun and solution viscosity on a log–log scale for EWP and WPI respectively; while the foam overrun of EWP decreased in a faster rate than WPI with increasing solution viscosity (altered by sucrose). Addition of sucrose enhanced the interfacial dilational elastic modulus (E′) of EWP but reduced E′ of WPI, possibly due to different interfacial pressures. The foam drainage ½ life was proportionally correlated to the bulk phase viscosity and the interfacial elasticity regardless of protein type, suggesting that the foam destabilization changes can be slowed by a viscous continuous phase and elastic interfaces. Incorporation of sucrose altered the volume of angel food cakes prepared from WPI foams but showed no improvement on the coarse structure. In conclusion, sucrose can modify bulk phase viscosity and interfacial rheology and therefore improve the stability of wet foams. However, the poor stability of whey proteins in the conversion from a wet to a dry foam (angel food cake) cannot be changed with addition of sucrose.     

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。