Whey Protein Isolate Solutions Research Articles

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.

Impact of MG2+ and Tara Gum Concentrations on Flow and Textural Properties of WPI Solutions and Cold-Set Gels

Cold-set gels of whey protein isolate (WPI) and of WPI plus tara gum (TG) were produced through the addition of magnesium chloride to heat-denatured (HD) WPI and WPI+TG solutions. The flow behaviour of the WPI, TG, and WPI+TG samples was analyzed: WPI solutions exhibit Newtonian behavior while the behavior of the TG and WPI+TG solutions can be described through the Cross and Carreau models. The mechanical characterization of the cold-set gels was done through puncture tests, and the Young's modulus for each cold-set gel was obtained. Statistical analysis of the mechanical data was made according to the Marquadt-Levenberg algorithm.

Effects of the free and pre-encapsulated calcium ions on the physical properties of whey protein edible film

Summary Effects of the free and the pre-encapsulated calcium ions on the physical properties of the whey protein isolate film were studied for improving calcium content in the edible films. At pH 8, the film-forming process was hindered by serious protein aggregation and gelation caused by 0.5% (w/w) free calcium ions added in an 8% whey protein isolate solution. If the calcium ions were pre-encapsulated in the protein microparticles (contained 17% Ca2+) using spray drying method, and then added in the film-forming solution prepared using the same protein, the calcium content could be doubled (1%, w/w) without significant effects on the physical properties of the film. The calcium release ability (55% at pH 1.2, 32% at pH 7.4 and more than 75% with the enzymes) of the film was also investigated.

Liquid and vapour water transfer through whey protein/lipid emulsion films

Edible films and coatings based on protein/lipid combinations are among the new products being developed in order to reduce the use of plastic packaging polymers for food applications. This study was conducted to determine the effect of rapeseed oil on selected physicochemical properties of cast whey protein films. Films were cast from heated (80 degrees C for 30 min) aqueous solutions of whey protein isolate (WPI, 100 g kg(-1) of water) containing glycerol (50 g kg(-1) of WPI) as a plasticiser and different levels of added rapeseed oil (0, 1, 2, 3 and 4% w/w of WPI). Measurements of film microstructure, laser light-scattering granulometry, differential scanning calorimetry, wetting properties and water vapour permeability (WVP) were made. The emulsion structure in the film suspension changed significantly during drying, with oil creaming and coalescence occurring. Increasing oil concentration led to a 2.5-fold increase in surface hydrophobicity and decreases in WVP and denaturation temperature (T(max)). Film structure and surface properties explain the moisture absorption and film swelling as a function of moisture level and time and consequently the WVP behaviour. Small amounts of rapeseed oil favourably affect the WVP of WPI films, particularly at higher humidities.

Spray-freeze-drying of whey proteins at sub-atmospheric pressures

Spray-freeze-drying (SFD) involves spraying a solution into a cold medium, and freeze-drying the resultant frozen particles, which can be performed by contacting the particles with a cold, dry gas stream in a fluidized bed, typically at atmospheric pressure. This enables much faster drying rates than are usually possible by conventional freeze-drying, due to the small particle sizes involved. However, the quantities of gas required for atmospheric fluidized bed freeze-drying are prohibitively expensive. This has led to a process modification whereby fluidization is performed at sub-atmospheric pressures, which still allows rapid freeze-drying, but using much less gas. This study demonstrates the fluidized bed SFD technique at sub-atmospheric pressures (0.1 bar) using whey protein isolate solution (20% w/w solids) at gas inlet drying temperatures ranging from −10 °C to −30 °C. The process yields a powder consisting of highly porous particles and shows little loss of solubility for β-lactoglobulin and α-lactalbumin, the principal proteins in the isolate. A wet basis moisture content of 8.1% was achieved after freeze-drying at −10 °C for only 1 h, while at 30 °C a longer drying time (100 min) produced a wetter product (14% w.b.).

Kinetics of microstructure formation of high-pressure induced gel from a whey protein isolate

The kinetic process of pressure-induced gelation of whey protein isolate (WPI) solutions was studied using in situ light scattering. The relationship of the logarithm of scattered light intensity (I) versus time (t) was linear after the induced time and could be described by the Cahn-Hilliard linear theory. With increasing time, the scattered intensity deviated from the exponential relationship, and the time evolution of the scattered light intensity maximum Im and the corresponding wavenumber qm could be described in terms of the power-law relationship as Im~fβ and qm~f−α, respectively. These results indicated that phase separation occurred during the gelation of WPI solutions under high pressure.

냉각유도젤화에 의한 엽산 함유 분리유청단백 나노담체의 제조

냉각유도젤화(cold-induced gelation) 기술을 이용하여 제조한 엽산 함유 유청단백질 나노담체에 대하여 실험적 변수, 즉, 고분자의 종류, 분리유청단백 용액의 농도 및 pH, 수용액층(aqueous phase)과 유기용매층(organic phase)의 비율, 분리유청단백 용액의 열처리 온도 등에 따른 입도 및 용출 양상의 변화를 고찰하였다. 고분자의 경우 알긴산을 이용하였을 때 가장 작은 입도를 나타내었으며, kcarrageenan의 경우 가장 큰 입도를 나타내었다. 수용액층과 유기용매층의 비율의 경우 그 값이 감소할수록 낮은 평균입도를 나타내었다. 분리유청단백 용액의 농도는 1%, pH는 8.0, 열처리 온도는 <TEX>$80^{\circ}C$</TEX>일 때 가장 작은 입자경 (<330 nm)을 나타내었다. 용출시험 결과, pH 7.4에서 2시간 이내에 대부분의 포집된 엽산이 용출된 반면, pH 1.2에서는 6시간 이상 용출이 지연되는 것을 확인하였다. 이와 같은 결과는 냉각유도젤화에 의해 나노담체를 제조하는 경우 실험적 변수들이 나노담체의 특성에 큰 영향을 미치는 것을 의미한다. Folate loaded WPI (whey protein isolate) nanoparticles were prepared using the cold-induced gelation process. The aim of this work was to investigate the effects of process parameters, such as the concentration of the WPI solution, pH, temperature, etc, on the properties of nanoparticles. The results show that the smallest nanoparticles were obtained when a WPI concentration of 1% was used at a pH of 8.0 (<330 nm). In the case of the concentration of <TEX>$CaCO_3$</TEX>, the smallest particles were obtained at a concentration of 5 mM. Alginate produced the smallest mean size with the narrowest particle size distribution, while the largest particles were prepared with k-carrageenan. As the w:o ratio increased, the mean particle size also increased. When the release profile was analyzed, the particles were shown to be stable for more than 6 h at a pH of 1.2, where almost all of the folic acid was released within 2 h in the dissolution media of PBS at a pH of 7.4. Thus, the process parameters appear to be important factors that affect the properties of nanoparticles.

Separation of transforming growth factor-beta2 (TGF-β2) from whey protein isolates by crossflow microfiltration in the presence of a ligand

The effects of pH adjustment, ionic strength and adding lambda-carrageenan (λ-CG) to whey protein isolate (WPI) solutions on the transmission of transforming growth factor-beta2 (TGF-β2) through a 0.8 μm pore size microfiltration (MF) membrane were investigated. Increasing pH (7–9) or adding NaCl (0.1 M) increased both the transmission of proteins and TGF-β2. Adding 0.01% λ-CG to WPI solutions decreased both the transmission of proteins and TGF-β2 and increased membrane fouling. The highest membrane selectivity (0.28) and concentration factor (1.67) for TGF-β2 were obtained at neutral pH conditions without NaCl or λ-CG. The addition of λ-CG allowed the preparation of a retentate slightly enriched in TGF-β2 but also in immunoglobulins.

Water vapour permeability, thermal and wetting properties of whey protein isolate based edible films

This study deals with the effect of whey protein isolate (WPI) and glycerol (GLY) used as a plasticizer on some physical properties of cast whey protein isolate (WPI) films. Films were prepared from heated (80 °C for 30 min) aqueous solutions of WPI at 7, 8, 9 and 10% (w/w), GLY (40%, w/w, of WPI) and WPI at 8% (w/w), GLY (30, 40, and 60%, w/w, of WPI). For all types of films, water vapour permeability for four relative humidity differentials (30–100%, 30–84%, 30–75%, and 30–53%), surface and thermal properties were measured. Varying the proportion of WPI and GLY in edible films had some effect on water vapour permeability, wetting and thermal properties of WPI films. A cumulative effect of both glycerol and protein content was observed on the water vapour permeability increase. Indeed film barrier properties are much better for the lowest WPI (7%) and GLY (40%) contents. GLY increases the degradation temperature and favours film surface wettability whereas protein content did not affects thermal properties of films.

Whey protein isolate–chitosan interactions: A calorimetric and spectroscopy study

Isothermal titration calorimetry (ITC) measurements were performed using solutions of whey protein isolate (WPI) and chitosan with different deacetylation degrees (DD), in acetate buffer solutions, pH 3–6. Turbidity measurements were performed in parallel in order to follow the changes in aggregation, so as to get deeper insight on the interaction mechanism. The viscosity–average molar mass of chitosan was obtained from intrinsic viscosity measurements, and the interaction enthalpies were derived at the studied pH values. Further, the denaturation process of α-lactalbumin and β-lactoglobulin within WPI was characterized by differential scanning calorimetry (DSC). At pH 3, where both chitosan and the proteins are positively charged, a weak carbohydrate–protein interaction is observed. When the pH is raised to 6, where the protein charge is expected to be negative, a much stronger interaction takes place. The results are discussed with special emphasis on the effect of pH on the interactions observed in this complex system.

Foams Prepared from Whey Protein Isolate and Egg White Protein: 2. Changes Associated with Angel Food Cake Functionality

The effects of sucrose on the physical properties and thermal stability of foams prepared from 10% (w/v) protein solutions of whey protein isolate (WPI), egg white protein (EWP), and their combinations (WPI/EWP) were investigated in wet foams and angel food cakes. Incorporation of 12.8 (w/v) sucrose increased EWP foam stability (drainage 1/2 life) but had little effect on the stability of WPI and WPI/EWP foams. Increased stability was not due to viscosity alone. Sucrose increased interfacial elasticity (E ') of EWP and decreased E' of WPI and WPI/EWP combinations, suggesting that altered interfacial properties increased stability in EWP foams. Although 25% WPI/75% EWP cakes had similar volumes as EWP cakes, cakes containing WPI had larger air cells. Changes during heating showed that EWP foams had network formation starting at 45 degrees C, which was not observed in WPI and WPI/EWP foams. Moreover, in batters, which are foams with additional sugar and flour, a stable foam network was observed from 25 to 85 degrees C for batters made from EWP foams. Batters containing WPI or WPI/EWP mixtures showed signs of destabilization starting at 25 degrees C. These results show that sucrose greatly improved the stability of wet EWP foams and that EWP foams form network structures that remain stable during heating. In contrast, sucrose had minimal effects on stability of WPI and WPI/EWP wet foams, and batters containing these foams showed destabilization prior to heating. Therefore, destabilization processes occurring in the wet foams and during baking account for differences in angel food cake quality.

Alkali Cold Gelation of Whey Proteins. Part I: Sol−Gel−Sol(−Gel) Transitions

The cold gelation of preheated whey protein isolate (WPI) solutions at alkaline conditions (pH>10) has been studied to better understand the effect of NaOH in the formation and destruction of whey protein aggregates and gels. Oscillatory rheology has been used to follow the gelation process, resulting in novel and different gelation profiles with the gelation pH. At low alkaline pH, typical sol-gel transitions are observed, as in many other biopolymers. At pH>11.5, the system gels quickly, after approximately 300 s, followed by a slow degelation step that transforms the gel to a viscous solution. Finally, there is a second gelation step. This results in a surprising sol-gel-sol-gel transition in time at constant gelation conditions. At very high pH (>12.5), the degelation step is very severe, and the second gelation step is not observed, resulting in a sol-gel-sol transition. The first quick gelation step is related to the quick swelling of the WPI aggregates in alkali, as observed from light scattering, which enables the formation of new noncovalent interactions to form a gel network. These interactions are argued to be destroyed in the subsequent degelation step. Disulfide cross-linking is observed only in the second gelation step, not in the first step.

Properties of biopolymers produced by transglutaminase treatment of whey protein isolate and gelatin

Byproduct utilization is an important consideration in the development of sustainable processes. Whey protein isolate (WPI), a byproduct of the cheese industry, and gelatin, a byproduct of the leather industry, were reacted individually and in blends with microbial transglutaminase (mTGase) at pH 7.5 and 45 °C. When a WPI (10% w/w) solution was treated with mTGase (10 U/g) under reducing conditions, the viscosity increased four-fold and the storage modulus (G′) from 0 to 300 Pa over 20 h. Similar treatment of dilute gelatin solutions (0.5–3%) had little effect. Addition of gelatin to 10% WPI caused a synergistic increase in both viscosity and G′, with the formation of gels at concentrations greater than 1.5% added gelatin. These results suggest that new biopolymers, with improved functionality, could be developed by mTGase treatment of protein blends containing small amounts of gelatin with the less expensive whey protein.

Kinetics of phase separation during pressure-induced gelation of a whey protein isolate

The kinetic process of pressure-induced gelation of whey protein isolate (WPI) solutions (20–28%, w/v) was studied using in situ light scattering. The gelation of WPI solutions could be induced by pressurization at 250 MPa, a pressure lower than that reported in other studies. The gelation time decreased with increasing WPI concentration and followed an exponential rule. The relationship of the logarithm of scattered light intensity ( I) versus time ( t) was linear after the induced time and could be described by the Cahn–Hilliard linear theory. With increasing time, the scattered intensity deviated from the exponential relationship, and the time evolution of the scattered light intensity maximum I m and the corresponding wavenumber q m could be described in terms of the power-law relationship as I m ∼ t β and q m ∼ t − α , respectively. These results indicated that phase separation occurred during the gelation of WPI solutions under high pressure.

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.

Reduction of Oil Absorption in Deep‐Fried, Battered, and Breaded Chicken Patties Using Whey Protein Isolate as a Postbreading Dip: Effect on Flavor, Color, and Texture

The effect of the application of whey protein isolate (WPI) solution as a postbreading dip to reduce oil absorption in deep-fried, battered, and breaded chicken patties on sensory properties was investigated. Chicken patties were battered, breaded with either crackermeal (CMP) or Japanese breadcrumbs (JBP), and dipped into WPI solutions at varying protein concentrations (0%, 2.5%, 5%, and 10%[w/w] WPI) and pH levels (pH 2, 3, and 8). A trained descriptive sensory panel evaluated the patties for 16 attributes relating to appearance, texture, and flavor. Instrumental analysis on the color and texture of the patties was also performed. The only perceivable changes in treated patties were related to color, hardness, and crunchiness. Increasing WPI concentration caused darkening of JBP but made CMP lighter. Patties treated at pH 8 were significantly darker across all WPI concentrations. The presence of WPI increased hardness and crust fracture for CMP but not JBP. Variations in pH levels did not affect texture. Thus, JBP that showed the highest lipid reduction (10% WPI at pH 2) were observed to be darker, less yellow, but did not produce any perceivable changes in hardness or crunchiness, while CMP with the lowest lipid content (5% WPI at pH 2) were lighter, more yellow, harder, and crunchier.

Influence of spelt bran on the physical properties of WPI composite films

In this study, the properties of whey protein isolate (WPI)-based films with different levels of glycerol and spelt bran were investigated using response surface methodology. Tests were carried out to determine to what extent the water vapor permeability (WVP) of the films can be improved by adding the bran. Moreover, the mechanical and dynamical properties, colour of the films and the rheological properties of the film-forming solutions were also investigated. Results highlighted that the WVP was significantly affected by the spelt bran concentration: increasing the spelt bran concentration led to decrease in water vapor permeability, whereas the glycerol concentration incremented the WVP values of the films. The elastic modulus ( E C) and complex modulus ( E *) of the composite films increased with the decrease of the glycerol content and the increase of the bran concentration. Glycerol addition, acting as a plasticizer, led to more flexible films. Regarding the rheological characteristics, the WPI solutions with the lower bran concentration behaved as Newtonian fluid. As the bran concentration increased the solutions demonstrated a non-Newtonian behaviour. Colour results highlighted that yellow index (YI), a and b parameter of Hunter scale increased with the bran concentration increase; on the contrary, L parameter decreased with the bran concentration increase.

Whey Protein/Arabic Gum Gels Formed by Chemical or Physical Gelation Process

Whey proteins (WP) gelation process with addition of Arabic gum (AG) was studied. Two different driving processes were employed to induce gelation: (1) heating of 12% whey protein isolate (WPI) solutions (w/w) or (2) acidification of previous thermal denatured WPI solutions (5% w/w) with glucono-δ-lactone (GDL). Protein concentrations were different because they were minimal to form gel in these two processes, but denaturation conditions were the same (90 °C/30 min). Water-holding capacity and mechanical properties of the gels were evaluated. The BST equation was used to evaluate the nonlinear part of the stress–strain data. Cold-set gels were weaker than heat-set gels at the pH range near the isoelectric point (pI) of the main whey proteins, but heated gels were more deformable (did not exhibit rupture point) and showed greater elasticity modulus. However, gels formed by heating far from the pI (pH 6.7 or 3.5) showed more fragile structure, indicating that, in these mixed gels, there are prevailing biopolymers interactions. Cold-set and heat-set gels at pH near or below the WP pI showed strain-weakening behavior, but heated gels at neutral pH showed strong strain-hardening behavior. Such results suggest that differences in stress–strain curve at the nonlinear part of the data could be correlated to structure particularities obtained from different gelation processes.

On the confocal images and the rheology of whey protein isolated and modified pectins associated complex

The conditions necessary to form an associated complex between whey protein isolate (WPI) and enzymatically modified pectin in water, at pH values above the isoelectric point of the protein, have been documented. The existence of the complex is not easily verified and its characterization in solution is even more complicated, since the structure is an intermediate entity between the non-interacting, incompatible aqueous soluble mixture of the biopolymers, and a strongly interacting coacervated precipitating complex. Evidence for the formation of this associated complex is provided from confocal laser scanning microscope images and rheological behavior of the aqueous mixtures. The associated complex is characterized by small fluorescent “patches” interpreted as small aggregates. The viscosity of this solution is greater than that of its individual biopolymer constituents, indicating a synergy of attractive interactions that occurs in the solution. While individually, the pectin and the WPI solutions at the studied range of concentrations exhibit moderately non-Newtonian behavior, at specific weight ratios, mixtures of the two behave either as highly entangled polymeric structures or as weak gels. The values of the storage modulus G′ are equal to or greater than those of the loss modulus G″. We conclude that the associated complexes are formed at pH 6, and at 4 wt% WPI with a pectin concentration ranging from 0.1 to 0.75 wt%. The influence of the charge distribution (degree of order of the carboxylic groups) of pectin on the associated complex was also investigated, and it was found that the more “ordered” pectin (U63) favors the formation of the associated soluble complex.

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

Physical properties of whey protein isolate (WPI) coating solution incorporating ascorbic palmitate (AP) and alpha-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 degrees 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.