Stability Of Whey Protein Isolate Research Articles

Prevention of thermal gelation in concentrated whey protein isolate dispersions by using H2O2 and SHMP

In the present study, the effect of hydrogen peroxide (H2O2) and sodium hexametaphosphate (SHMP) on the thermal (121.5 °C for 15 min) stability of aqueous dispersions of whey protein isolate (6 % and 10% w/w) was investigated. Based on findings, H2O2, by oxidizing the sulfhydryl (SH) groups, prevented the formation of S–S bonds, therefore prevented thermal aggregation. The presence of SHMP synergistically enhanced the effect of H2O2 by reducing its required concentration. The majority of H2O2 treated samples remained soluble over long cold storage period. This study proved the abilities of H2O2 and SHMP in preventing protein denaturation and improving the thermal stability of whey protein isolate based drinks.

The behavior of whey protein isolate-curcumin complex at the oil-water interface

It was very common to use nanoparticles and nanoemulsions with the combination of proteins and hydrophobic bioactives to effectively prevent and treat chronic diseases. This work was to evaluate the stability of whey protein isolate (WPI) and curcumin (CUR) complex made with the anti-solvent precipitation technique and the pH shifting methods in oil-water bulk and interface. The interaction between WPI and CUR were investigated using fluorescence spectroscopy, Fourier transform infrared spectroscopy and molecular docking. The changes of the WPI-CUR in the oil-water bulk and interface were characterized by the circular dichroism spectroscopy, UV spectroscopic, confocal laser scanning microscopy and molecular dynamics simulation. Results indicated that the interactions between WPI and CUR were hydrogen bonding and hydrophobic interaction. The WPI-CUR complex was unstable at the oil-water interface, CUR detached from the complex and migrated to the oil phase. These findings would be of importance in illustrating the behavior of whey protein isolate-curcumin complex at the oil-water interface.

Effect of transglutaminase cross-linking and emulsification on the stability and digestion of limonene emulsions

Transglutaminase (TG) cross-linked whey proteins are used to prepare a D-limonene emulsion, which can solve the problems of easy oxidation and poor water solubility of D-limonene. TG cross-linking can improve the emulsion stability of whey protein isolate (WPI). SDSPAGE results showed that TG cross-linked WPI and limonene were emulsified under high-pressure homogenization to form the emulsion (WPI-TG-Oil), which had more molecular polymers. The adsorption rate of interfacial protein of the WPI-TG-Oil emulsion was significantly increased by 5.15 % compared to the WPI limonene emulsion cross-linked with TG (WPI-Oil-TG). After a 10-day storage interval, the CDs and POV showed that the WPI-TG-Oil emulsion had the strongest oxidation stability and a thickened interfacial layer. It was also noted that WPI-TG-Oil was difficult to hydrolyze during the digestion process due to the large degree of cross-linking and many high molecular weight polymers. The WPI-TG-Oil emulsion was more stable with a high molecular weight and improved the overall properties. Moreover, these findings provide basic theoretical and technical support for improving the stability of D-limonene emulsions. The most suitable processing method was TG-crosslinked WPI to form a stable emulsion, which improved the physiochemical and emulsifying properties of its emulsion for potential uses in food, cosmetics, and other industries.

Epicatechin Inhibited Lipid Oxidation and Protein Lipoxidation in a Fish Oil-Fortified Dairy Mimicking System

In this study, a typical tea polyphenol epicatechin (EC) was investigated for its impact on the oxidative stability of whey protein isolate (WPI) in a fish oil-fortified emulsion. The oil-in-water emulsion system consisted of fish oil (1%, w/w), WPI (6 mg/mL), and EC (0.1, 1, and 2 mM), and the oxidation reaction was catalyzed by Fenton's reagent at 25 °C for 24 h. The results showed EC exhibited a dose-dependent activity in the reduction of lipid oxidation (TBARS) and protein carbonylation. A Western blot analysis demonstrated that protein lipoxidation was inhibited by EC via interrupting the covalent binding of lipid secondary oxidation products, MDA, onto proteins. In addition, protein lipoxidation induced a loss of tryptophan fluorescence, and protein hydrolysis was partially recovered by EC. The findings of this study provide an in-depth understanding of the performance of phenolic antioxidants in relieving lipid oxidation and subsequent protein lipoxidation in oil-containing dairy products.

Stability of whey protein bioactive peptide‐stabilised nanoemulsions: effect of pH, ions, heating and freeze–thawing

SummaryWhey protein hydrolysates are important food emulsifiers and bioactive ingredients. This study investigated the stability of whey protein isolate (WPI) bioactive peptide fraction nanoemulsions under representative food processing and storage conditions: pH (3–9), ion concentration (Na+, 0–200 mm and Ca2+, 0–15 mm), thermal treatment (30–90 °C) and freeze–thawing. Bioactive peptide fractions, UC–10 and UP–10, were obtained by ultrafiltration of chymotrypsin or pepsin WPI hydrolysates, respectively. The nanoemulsions produced with these fractions had droplet diameters of 177 ± 3.5 nm (UC–10) and 154 ± 1.6 nm (UP–10). Nanoemulsions destabilised at pH 3–5, around the isoelectric point of WPI proteins but were stable at higher pH values, 6–9. Nanoemulsion instability escalated above critical Na+ (25 mm) and Ca2+ (2.5 mm) concentrations, but Ca2+ accelerated droplet aggregation more strongly than Na+. Furthermore, nanoemulsions were moderately stable to heating and freeze–thawing. Overall, both WPI bioactive peptide‐stabilised nanoemulsions showed consistent stability to the processing conditions. This study expands on designing, producing and utilising nanoemulsions based on WPI bioactive peptides.

Effects of tocopherols on the stability of flaxseed oil-in-water emulsions stabilized by different emulsifiers: Interfacial partitioning and interaction

The potential effects of tocopherols (100 μM in emulsions) on the physicochemical stability of whey protein isolate (WPI), soy lecithin (SL), or Tween 20 (TW) stabilized flaxseed oil (FO)-in-water emulsions were investigated. During the storage (18 days at 55 ℃), the particle size, microstructure, and multiple light scattering results showed WPI-stabilized emulsions exhibited better physical stability when tocopherols were added hydroperoxides and TBARS concentration in TW-stabilized emulsions were higher than those of SL or WPI, which were suppressed differently by tocopherols. Among homologues, δ-tocopherol was more effective in inhibiting lipid oxidation than α-tocopherol, which was related to the higher interface partitioning. Moreover, the increased interfacial tension indicated tocopherols, especially δ-tocopherol, were adsorbed on the interface and interacted with WPI or SL via hydrophobic or electrostatic interactions determined by isothermal titration calorimetry. Our results suggest tocopherols are more applicable in WPI emulsion systems to achieve steady-state delivery of ALA.

Effects of salt ions and heating on the behaviour of whey protein particle dispersions

We investigated the aggregation stability of whey protein isolate (WPI) particles in the presence of different salts (NaCl, MgCl2, and AlCl3) and the heat stability of dispersions in the presence of protein (native WPI) and polysaccharides (dextran and gum Arabic, GA). WPI particles coagulated either at pH values close to the iso-electric point of proteins or at high salt concentrations. Critical coagulation concentration (CCC) for different salts decreased with increasing valence of ions. CCC values for colloidal WPI particle dispersions closely followed the Schulze-Hardy rule, which is derived from the DLVO theory; however, deviations from the theory, particularly in the case of multivalent ions, showed that the specific ion adsorption also played a role. To investigate the heat stability of WPI particles, particle size and viscosities of dispersions containing different biopolymers were measured. Using dynamic viscosity of dilute dispersions, with the assumption of no particle aggregation after heating, swelling ratio (SR) of particles was estimated. Increasing concentrations of biopolymers decreased the SR of particles, and the presence of GA totally inhibited the swelling. Shear viscosity of concentrated dispersions showed an increase and shear-thickening behaviour after heating, when native WPI or dextran was present, whereas viscosity did not change when GA was present in the continuous phase. At low volume fractions, swelling was more likely to occur; whereas at high volume fractions, possibly both swelling and aggregation occurred. In addition, concentration and type of biopolymer were found to be important for the heat stability of dispersions.

Adsorption kinetics and foaming properties of soluble microalgae fractions at the air/water interface

Microalgae as a novel food ingredient are of increasing interest as they can be grown on non-arable land and fixate CO2 when grown photoautotrophically. Here, we employ proteins extracted from Arthrospira platensis biomass to be used for the stabilization of fluid interfaces, which is one of the most important techno-functional applications of proteins. Model foams were prepared from crude A. platensis powder and A. platensis isolate and whey protein isolate as a reference. The derived A. platensis isolate exceeded the overrun and the foam stability of whey protein isolate. The comparable low surface activity of crude A. platensis powder emphasizes the need for the extraction process. The neutral color of the A. platensis isolate indicates that the valuable natural pigments present in A. platensis were retained while achieving relevant techno-functional properties with the residual biomass. Physical treatment with nanosecond pulsed electric fields further increased the biomass yield without impeding the techno-functional properties of the derived isolates. Thus, protein extraction from microalgae biomass is an interesting approach to obtain techno-functional proteins and increase microalgae production efficiency.

Effect of pH-shifting treatment on structural and functional properties of whey protein isolate and its interaction with (−)-epigallocatechin-3-gallate

Effect of pH-shifting on structural and functional properties of whey protein isolate and its interaction with (−)-epigallocatechin-3-gallate were investigated. Circular dichroism spectra showed that pH-shifting induced the decrease in α-helix content by 12.18% and β-sheet content by 3.24%, but β-turn and random coil content increased by 4.26% and 5.91%, respectively. Increase of fluorescence intensity and red-shift of maximum emission wavelength indicated the structural unfolding and exposure of tyrosine. The treatment also significantly increased the surface hydrophobicity, disulfide bonds content, solubility, emulsifying activity and emulsion stability of whey protein isolate at P < 0.05 level. Fluorescence quenching analysis revealed that treated whey protein isolate have a stronger binding affinity to (−)-epigallocatechin-3-gallate, resulting a better protection against the degradation of (−)-epigallocatechin-3-gallate and its antioxidant activity. This study confirmed that pH-shifting treatment can improve functional properties of whey protein isolate and its potential as a protective carrier for polyphones.

The influence of flaxseed gum on the microrheological properties and physicochemical stability of whey protein stabilized β-carotene emulsions.

The impact of flaxseed gum (FG) on the microrheological properties and physicochemical stability of whey protein isolate (WPI) stabilized β-carotene emulsions at pH 3.0 was studied. A layer-by-layer electrostatic deposition method was used to prepare multilayered β-carotene emulsions with interfacial membranes consisting of WPI and FG. The microrheological behavior of the multilayered β-carotene emulsions was measured through the diffusive wave spectroscopy technique. WPI alone and WPI-FG (concentration of FG = 0.1, 0.2, 0.3 wt%) stabilized β-carotene emulsions were purely viscous giving a mean square displacement that scaled linearly with decorrelation time (τ). The presence of 0.01, 0.02, and 0.05 wt% FG in the WPI-stabilized emulsions caused them to exhibit viscoelastic properties. Meanwhile, the increase in τ reflected the increase in the length scale of connectivity in the emulsions until a "cluster" was formed and the droplets were not free to move due to droplet-network interaction. The apparent increase in the macroscopic viscosity and elasticity index and decrease in the solid lipid balance and fluidity index of emulsions with lower concentrations (0.01, 0.02, 0.05 wt%) of FG indicated that the bridging flocculation of FG had a much more appreciable influence on the microrheological properties than depletion flocculation (higher concentrations, 0.1, 0.2, 0.3 wt%). Droplet size, zeta-potential, and transmission profiles using the centrifugal sedimentation technique and β-carotene degradation during storage were also characterized. With the addition of FG, the zeta-potential of WPI coated β-carotene droplets decreased from positive to negative, and an increase in the apparent droplet size was also noted. LUMISizer analysis exhibited an improvement in physical stability with the addition of 0.1 wt% FG. FG also helped to chemically stabilize the WPI emulsions against β-carotene degradation mainly by slowing down the mobility of the droplets.

Improved heat stability of whey protein isolate stabilized emulsions via dry heat treatment of WPI and low methoxyl pectin: Effect of pectin concentration, pH, and ionic strength

In this study, Whey Protein Isolate (WPI) was conjugated with Low Methoxyl Pectin (LMP) as a means to improve the heat stability of whey protein stabilized oil in water (o/w) emulsions. Hereby, the emulsifying activity and heat stability of the emulsions (10% w/w of oil) stabilized by 0.5% WPI-LMP conjugates were compared to the stability of emulsions stabilized by either 0.5% WPI, 0.5% of a mixture of WPI-LMP, or 0.5% dry heated WPI. The influence of LMP concentration, pH (i.e. 6.5 versus 5), and ionic strength (i.e. 0 and 30 mM of NaCl) on the stability of the emulsions was studied. It was found that unheated emulsions stabilized by WPI-LMP conjugates had a relatively small droplet size and were stable against creaming, irrespective of the pH and ionic strength of the emulsions. Results also showed that not only the pH sensitivity, but also the heat-sensitivity of WPI-stabilized emulsions could be significantly improved by application of pectin. Upon heating at 80 °C and 120 °C up to 20 min, there was almost no change in the particle size distribution of the conjugate-stabilized emulsions after heating. Viscosity measurements showed a similar trend; heat treated emulsions stabilized by conjugates did not show any change in consistency. This pronounced heat stabilizing effect of LMP, however, was not observed in emulsions stabilized by a mixture of WPI-LMP. With regard to the dry heat incubation time, a 2 days incubation period was sufficient to produce a WPI-derived emulsifier with superior stability towards both pH and heat treatment.

Effect of xanthan/enzyme-modified guar gum mixtures on the stability of whey protein isolate stabilized fish oil-in-water emulsions

The effect of xanthan gum (XG) and enzyme-modified guar (EMG) gum mixtures on the physicochemical properties and oxidative stability of 2wt% whey protein isolate (WPI) stabilized oil-in-water (O/W) emulsions containing 20%v/v fish oil was investigated. EMG was obtained by hydrolyzing native guar gum using α-galactosidase enzyme. At higher gum concentrations (0.2 and 0.3wt%), the viscosity of the emulsions containing XG/EMG gum mixtures was significantly higher (P<0.05) of all emulsions. Increasing concentrations (0–0.3wt%) of XG/EMG gum mixtures did not affect the droplet size of emulsions. Microstructure images revealed decreased flocculation at higher concentrations. Primary and secondary lipid oxidation measurements indicated a slower rate of oxidation in emulsions containing XG/EMG gum mixtures, compared to XG, guar (GG), and XG/GG gum mixtures. These results indicate that XG/EMG gum mixtures can be used in O/W emulsions to increase physical and oxidative stabilities of polyunsaturated fatty acids in foods.

Effect of sulphydryl reagents on the heat stability of whey protein isolate

The effects of sulphydryl (–SH) reagents on protein aggregation reactions in heated whey protein isolate (WPI) and pure α-lactalbumin (α-La) were investigated. In contrast to its previously reported effect with pure β-Lg, dihydrolipoic acid (DHLA) markedly reduced the heat stability of WPI, especially the α-La component, which aggregated much more readily in the presence of DHLA than in WPI alone. Whilst pure α-La is quite stable to heat, it is much less stable in the presence of DHLA. An effect similar to DHLA was observed with reduced glutathione (GSH). N-ethylmaleimide (NEM), and to a lesser extent, dithio(bis)-p-nitrobenzoate (DTNB), improved the heat stability of WPI; these reagents had little effect on α-La.

Sequential preheating and transglutaminase pretreatments improve stability of whey protein isolate at pH 7.0 during thermal sterilization

Whey protein isolate (WPI) is a potential ingredient to manufacture shelf-stable transparent beverages if proteins are heat stable, i.e., without causing turbidity, precipitation and gelation after the required thermal processing to obtain commercial sterility (138 °C for 8 s or longer). However, information is lacking about stability of WPI during heating at 138 °C. Furthermore, novel technology and mechanistic understanding on how to produce clear products after heating systems with >5% WPI, particularly with salt, is needed. In this work, 5% w/v WPI was pretreated by microbial transglutaminase (mTGase) at three levels for 1–15 h at 50 °C, with and without prior preheating at 80 °C for 15 min. Heat stability of the pretreated samples at pH 7.0 and 0, 50, and 100 mM NaCl was evaluated at 138 °C. Samples pretreated by mTGase for a greater extent demonstrated improved heat stability. Samples subjected to sequential preheating and mTGase pretreatments produced clear dispersions even after heating at 138 °C for 30 min in the presence of 0 and 50 mM NaCl at pH 7. All pretreatments increased the magnitude of zeta-potential and resistance against thermal denaturation. The sequentially-pretreated WPI was the most heat-resistant, having decreased hydrodynamic diameter (<36 nm) during extended heating at 138 °C and 50 mM NaCl. The present study demonstrates the feasibility of using sequential preheating and mTGase pretreatments to develop sterilized beverage products with a high content (5% w/v) of whey protein and yet of transparent appearance at ambient temperatures.

Microemulsions as Nanoreactors To Produce Whey Protein Nanoparticles with Enhanced Heat Stability by Sequential Enzymatic Cross-Linking and Thermal Pretreatments

Sequential enzymatic cross-linking and heat pretreatments were used in this work to enhance the heat stability of whey protein isolate (WPI). In the first route, WPI was cross-linked by transglutaminase before incorporation in microemulsions for heat pretreatment at 90 degrees C for 20 min. In the second route, WPI was cross-linked by transglutaminase within microemulsions before thermal pretreatment. Particles produced from the two routes were different in dimension and heat stability and were also affected by the ratio of WPI and enzyme and cross-linking duration. At appropriate conditions, for example, 10 h of cross-linking by transglutaminase equivalent to 5% mass of WPI using the first route, a 5% dispersion (pH 6.8 and 100 mM NaCl) of the produced nanoparticles remained clear after heating at 90 degrees C for 20 min. In comparison, nanoparticles produced by thermal pretreatment only in a microemulsion corresponded to a translucent, flowable dispersion, whereas native WPI formed a gel. This novel approach can be used to manufacture heat-stable whey protein ingredients for clear beverage applications.

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.

Influence of hydrocolloids on phase separation and emulsion properties of whey protein isolate

The influence of ionic and neutral hydrocolloid gums (pectin, guar gum, iota-carrageenan) on phase separation, emulsion activity and emulsion stability of whey protein isolate (WPI) was investigated. Mixtures of WPI/pectin and WPI/guar gum exhibited phase separation. Analysis of each phase after centrifugation revealed the formation of two polymer-rich phases, a protein-rich phase at the top and a polysaccharide-rich phase at the bottom, indicating the thermodynamic incompatibility. A visual phase separation was not observed in WPI/ iota-carrageenan mixtures in either concentration. This was attributed to the high gelling ability of iota-carrageenan, which prevented the phase separation. Whey protein isolate-stabilized emulsions in the presence of hydrocolloid gums (pectin or guar gum) were prepared below the phase separation threshold and the emulsifying activity and emulsion stability were determined spectrophotometrically by measuring time-dependent changes in turbidity. The stability was observed to be changing with the concentration of hydrocolloids. Thus, stable emulsions were obtained as the concentration of gums increased. Also, an increase in the gum concentration decreased the creaming and a slow creaming was detected in the emulsions of WPI/guar gum as compared with WPI/pectin.

Improvement of Functional Properties of Whey Protein Isolate Through Glycation and Phosphorylation by Dry Heating

Whey protein isolate (WPI) was glycated with maltopentaose (MP) through the Maillard reaction, and the MP-conjugated WPI (MP-WPI) was then phosphorylated by dry heating in the presence of pyrophosphate. Glycation occurred efficiently, and the sugar content of WPI increased approximately 19.9% through the Maillard reaction. The phosphorylation of MP-WPI was enhanced with an increase in the dry-heating time from 1 to 5 d, and the phosphorus content of WPI increased approximately 1.05% by dry heating at pH 4.0 and 85°C for 5 d in the presence of pyrophosphate. The electrophoretic mobility of WPI increased with an increase in the phosphorylation level. The stability of WPI against heat-induced insolubility at pH 7.0 was improved by conjugation with MP alone, and further improved by phosphorylation. Although the emulsifying activity of WPI was barely affected by glycation and phosphorylation, the emulsifying stability of phosphorylated MP-WPI (5 d), was 2.2 times higher than that of MP-WPI. Gelling properties such as hardness, resiliency, and water-holding capacity of heat-induced WPI gel were markedly improved, and the gel was rendered transparent by phosphorylation. The calcium phosphate-solubilizing ability of WPI was enhanced by phosphorylation. These results suggested that phosphorylation by dry heating in the presence of pyrophosphate after conjugation with MP is a useful method for improving the functional properties of WPI.