Whey Protein Isolate Dispersions 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.

Interaction of whey protein isolate and natural deep eutectic solvents: Effect on conductivity, surface tension, stability, and flow behaviour

The present study aimed to understand the structural–functional relationships between whey protein isolate (WPI) and natural deep eutectic solvents (NADES) dispersion. Lactic acid, malic acid, glucose, and fructose-based NADES were used with 2.5 and 5 % WPI. WPI dispersion with lactic acid and malic acid NADES showed low pH, surface tension, thermal stability with high conductivity, and foam stability. On the other hand, WPI with glucose and fructose NADES showed the opposite behaviour to acid NADES. In FTIR, WPI and NADES were shown to have a substantial interaction. The dispersion of sugar NADES showed higher peak force and energy than acid NADES. The dispersion showed Newtonian as well as non-Newtonian flow behaviour. The dispersion with sugar showed non-Newtonian behaviour as n < 1; however, acid based WPI dispersion showed Newtonian as well as non-Newtonian flow behaviour. Therefore, the present study demonstrated a tailoring approach for WPI dispersion according to the purpose of use.

Exploration of the co-structuring and stabilising role of flaxseed gum in whey protein isolate based cryo-hydrogels

In the present work, the structuring and stabilising potential of flaxseed gum (FG) in whey protein isolate (WPI) cryo-hydrogels was investigated. The FG presence (0.1–1% wt.) in the heat-treated WPI dispersions (10% wt.) induced strong segregative phase separation phenomena, which were associated with a depletion flocculation mechanism. The cryotropic processing of the WPI-FG solutions led to the formation of diverse macroporous protein gel networks depending on the colloidal state of their biopolymeric precursors. Cryogel formation was primarily mediated via covalent (thiol-disulphide bond) bridging, whilst to a lesser extent, non-covalent interactions contributed to the overall stabilisation of the protein gel network. Although FG had a rather minor contribution to the formation of elastically active crosslinks (FG was partitioning mainly into the serum phase located in the macropores), its presence (at concentrations ≥0.75% wt.) improved the homogeneity and interconnectivity of the stranded protein network, whilst it reduced its colloidal instability and macroporosity.

High-pressure microfluidization of whey proteins: Impact on protein structure and ability to bind and protect lutein

Dynamic high-pressure homogenization microfluidization (DHPM) is a versatile emerging technology that may be applied to food processing to achieve several goals. DHPM may, depending on nature of the molecules and the working parameters, induce changes in protein structure, which may improve or impair their techno-functional properties and ability to bind other molecules. In this context, DHPM (12 passes, 120 MPa), coupled or not to a cooling device, was applied to β-lactoglobulin (β-lg) and whey protein isolate (WPI) dispersions. Minor changes in the structure of whey proteins were induced by DHPM with sample cooling; although, when sample cooling was not applied, aggregation and increases of around 30% of protein surface hydrophobicity were noticeable for the WPI dispersion. The association constant between the proteins and lutein was in the magnitude of 104 M−1, and lutein photodegradation constant diminished about 3 times in the presence of proteins, compared to in their absence.

Bioactives and extracts affect the physico-chemical properties of concentrated whey protein isolate dispersions

Non-covalent complexation interactions are known to occur between bioactive compounds and proteins. While formulating with these components can have positive outcomes such as stabilization of colors and actives, it can also result in changes to the structures and physical properties of proteins, affecting product functionality and sensory attributes. Previous experiments reported measurable changes in the physico-chemical properties of whey protein isolate (WPI) dispersions upon formulation with Aronia berry extract, ascribing changes to protein-polyphenol (PP) interactions in the systems. Pure gallotannin, beet extract, and cranberry extract, providing a diverse variety structures and sizes, were selected for further experimentation and comparison with the effects of Aronia extract. Concentrated dispersions with varying WPI:sucrose ratios, formulated with several bioactives contents from multiple different sources were analyzed to identify the effects of different bioactives on physico-chemical properties of dispersions. Dispersions formulated with cranberry extract demonstrated the largest increases in surface tensions, viscosities, and particle sizes, while those formulated with beet extract were the least affected by the presence of bioactives, suggesting that different bioactives and extracts had varying propensities for complexation interactions with WPI, despite their relatively low levels of addition (0, 0.5, and 1%).Graphical

Acid-induced gels from soy and whey protein thermally-induced mixed aggregates: Rheology and microstructure

In this study, we explored how substituting whey protein isolate (WPI) with soy protein isolate (SPI) affects the linear and non-linear rheological behavior of acid-induced gels, and their microstructures. Commercial SPI and WPI dispersions (pH 7.0, 3.0 mS/cm) were preheated (95 °C, 30 min) at different protein concentrations (2%, 4%, 6%, and 8% w/w) and SPI: WPI ratios (0: 4, 1: 3, 2: 2, 3: 1 and 4: 0). The resultant thermally-induced aggregates were characterized before gelation was induced by glucono-δ-lactone (GDL). Small and large amplitude oscillatory shear (SAOS and LAOS) tests showed that replacing WPI with SPI decreased the strength (lower G′) and stretchability (lower γc) of acid-induced gels in the linear viscoelastic (LVE) regime. Gels containing SPI behaved more similar to pure SPI gels in the non-linear viscoelastic (NLVE) regime: displaying a relatively elastic response at large strain and a gradual transition to plastic behavior. The changes in rheological properties were explained by the differences in the gel microstructures, via fractal scaling theory, multiphoton laser scanning microscopy (MLSM) and scanning electron microscopy (SEM). WPI gels formed denser and homogenous gel networks with very strong inter-floc links, while hybrid gels and pure SPI gels formed coarser and more porous networks with intermediate inter-floc links. The constituent flocs in the latter were larger, with rougher, more elongated and branched structures. The present results provide useful information for future attempts to replace WPI with SPI in food products based on acid-induced gelation.

Changes of structural and techno-functional properties of high hydrostatic pressure (HHP) treated whey protein isolate over refrigerated storage

This work assessed the effect of storage time on the structure and functionality of HHP-treated whey protein isolate (WPI). Different pressures (100–600 MPa) and treatment times (15–30 min) were applied to aqueous WPI dispersions (5% w/v). The induced degree of unfolding was evaluated to select optimal HHP treatment conditions of WPI before storage at 4 °C. Conformational and techno-functional properties of untreated and optimally HHP-treated WPI samples were determined by UV–Vis and IR spectroscopy, foaming capacity, and interfacial tension measurements, respectively. Further tests of HHP-assisted hydrolysis of WPI were performed by α-chymotrypsin, bromelain, or their mixture (1:1 w/w), with the degree of hydrolysis (DH%) and electrophoretic patterns analyzed.The maximum unfolding degree was detected after a treatment of 400 MPa and 15 min and, at these processing conditions, no aggregation occurred. However, the structural changes achieved upon HHP were gradually lost during storage through a first-order refolding process (kREF. = 0.031 h−1), with restoring of native functionality.Hydrolysis performances of selected enzymes towards WPI were significantly promoted by high-pressure. Interestingly, a clear synergistic effect of α-chymotrypsin and bromelain combination on the WPI hydrolysis yield was detected, which resulted in the highest protein rupture (DH = 17%).

High-intensity ultrasound pretreatment influence on whey protein isolate and its use on complex coacervation with kappa carrageenan: Evaluation of selected functional properties

The aim of this work was to evaluate the influence of high-intensity ultrasound (HIUS) treatment on whey protein isolate (WPI) molecular structure as a previous step for complex coacervation (CC) with kappa-carrageenan (KC) and its influence on CC functional properties. Protein suspension of WPI (1% w/w) was treated with an ultrasound probe (24 kHz, 2 and 4 min, at 50 and 100% amplitude), non HIUS pretreated WPI was used as a control. Coacervation was achieved by mixing WPI and KC dispersions (10 min). Time and amplitude of the sonication treatment had a direct effect on the molecular structure of the protein, FTIR-ATR analysis detected changes on pretreated WPI secondary structure (1600–1700 cm−1) after sonication. CC electrostatic interactions were detected between WPI positive regions, KC sulfate group (1200–1260 cm−1), and the anhydrous oxygen of the 3,6 anhydro-D-galactose (940–1066 cm−1) with a partial negative charge. After ultrasound treatment, a progressive decrease in WPI particle size (nm) was detected. Rheology results showed pseudoplastic behavior for both, KC and CC, with a significant change on the viscosity level. Further, volume increment, stability, and expansion percentages of CC foams were improved using WPI sonicated. Besides, HIUS treatment had a positive effect on the emulsifying properties of the CC, increasing the time emulsion stability percentage. HIUS proved to be an efficient tool to improve functional properties in WPI-KC CC.

Influence of high-pressure homogenization on structural properties and enzymatic hydrolysis of milk proteins

This study investigated the effects of HPH processing parameters on the conformational structure of bovine serum albumin (BSA) and whey protein isolate (WPI).BSA and WPI dispersions (1% w/v in phosphate buffer, pH = 7.5) were treated in a bench-scale HPH unit at different pressures (100, 150, 200 MPa) and number of passes (1, 2, 3, 5). The modifications of proteins' primary structure (carbonyl groups), secondary structure (α-helix, β-sheet, turn), tertiary and quaternary structure (free -SH groups) were analyzed together with their particle size distribution (PSD). HPH-assisted hydrolysis with trypsin and α-chymotrypsin was performed (200 MPa, 1 pass). Hydrolysis degree and molecular weight distribution of peptides were determined and compared with those of untreated protein dispersions.HPH treatments did not affect proteins' primary structure while slight modifications of secondary structure were detected. Interestingly, free - SH groups in BSA increased with increasing the pressure due to partial unfolding, while decreased in WPI, possibly due to disaggregation and compaction of native WPI aggregates. HPH pre-treatment allowed enhancing BSA hydrolysis reaction rate, while the compaction of WPI aggregates caused a reduced hydrolysis extent. In conclusion, HPH caused an appreciable modification of protein conformation and affected the degree of enzymatic hydrolysis.

Influence of Ultrasonic Power and Ultrasonic Time on the Physicochemical and Functional Properties of Whey Protein Isolate

Abstract The effects of ultrasonic powers (0, 200, 400, 600 or 800 W) and ultrasonic times (20 or 40 min) on the physicochemical and functional properties of whey protein isolate (WPI) dispersions were investigated. Particle size of WPI dispersions was minimized after sonication. Compared with untreated WPI, free sulfhydryl groups of ultrasound-treated WPI significantly decreased, while surface hydrophobicity of WPI was remarkably enhanced. After WPI dispersion was treated by ultrasound, its gel strength enhanced. Ultrasound treatment remarkably decreased turbidity of WPI suspension and its turbidity significantly decreased by 78.8 % at the ultrasonic power of 600 W for 40 min. Emulsification activity of sonicated WPI dispersions and its emulsion stability greatly increased. Therefore, ultrasound treatment could improve functional properties and change physicochemical properties.

Influence of calcium-binding salts on heat stability and fouling of whey protein isolate dispersions

The effect of the calcium-binding salts (CBS), trisodium citrate (TSC), tripotassium citrate (TPC) and disodium hydrogen phosphate (DSHP) at concentrations of 1–45 mm on the heat stability and fouling of whey protein isolate (WPI) dispersions (3%, w/v, protein) was investigated. The WPI dispersions were assessed for heat stability in an oil bath at 95 °C for 30 min, viscosity changes during simulated high-temperature short-time (HTST) and fouling behaviour using a lab-scale fouling rig. Adding CBS at levels of 5–30 mm for TSC and TPC and 25–35 mm for DSHP improved thermal stability of WPI dispersions by decreasing the ionic calcium (Ca2+) concentration; however, lower or higher concentrations destabilised the systems on heating. Adding CBS improved heat transfer during thermal processing, and resulted in lower viscosity and fouling. This study demonstrates that adding CBS is an effective means of increasing WPI protein stability during HTST thermal processing.

Fabrication and characterization of food‐grade fibers from mixtures of maltodextrin and whey protein isolate using needleless electrospinning

ABSTRACTFood‐grade fibers were fabricated from dispersions of maltodextrin and whey protein isolate (WPI) using needleless electrospinning. Two maltodextrins (DE 2) from different starch sources were used and the maltodextrin/WPI ratio was varied. Molecular weight, intrinsic viscosity, entanglement concentration, shear stability, and electrical conductivity were studied as function of maltodextrin type and mixing ratio and correlated to fiber production rate and morphology. The results show that a high molecular weight of the maltodextrin was beneficial to its spinnability. Waxy potato starch maltodextrin (P‐MD) (Mw = 129.6 kDa) and WPI produced fibers with diameters between 1.40 and 1.67 µm at production rates up to 1.65 g/h; while the dispersions with waxy maize starch maltodextrin (M‐MD) (Mw = 85.9 kDa) showed poor spinnability and ruptured fibers. P‐MD/WPI dispersions had a higher viscosity and stronger shear thinning behavior attributed to a stronger entangled polymer network which is beneficial to electrospinning. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46328.

The degree of protein aggregation in whey protein isolate-based dispersions modifies their surface and rheological properties

ABSTRACTThis work aims to study the effect of degree of protein aggregation on the surface and rheological properties of whey protein isolate dispersions with different concentrations (80, 100 and 120 g/kg), pHs (5.5 or 6.5) or NaCl contents (1 or 2 g/kg). Dispersions were thermally treated at 70, 75 and 80°C for different times. By mixing aggregated with native protein dispersions, different degrees of aggregation (0%, 20%, 40%, 60% and 80%) were obtained. Surface tension of the dispersions was determined by the pendant drop method, whilst their rheological properties were obtained from flow curve tests. A slight effect of the degree of aggregation over diffusion was found, which indicates that native proteins dominated the decrease in surface tension. The rheological behavior of dispersions with NaCl addition changed from Newtonian to shear thinning for aggregation degrees above 20%, whilst all dispersions at pH 5.5 and 6.5 presented a shear thinning behavior.

Rheology and microstructure of kefiran and whey protein mixed gels.

The effect of kefiran on cold-set gelation of whey protein isolate (WPI) at 25°C was studied using rheological measurements and environmental scanning electron microscopy (ESEM). The gelation of samples was induced by the addition of glucono-δ-lactone to the dispersions. WPI concentration was maintained at 8% (w/v) and the concentration of kefiran varied from 0 to 0.08% (w/v). According to rheological measurements, the addition of kefiran into WPI dispersions resulted in a significant increase in the gel strength, the yield stress, and the shear stress values at the flowing point. The gelling point and gelation pH of samples decreased significantly with an increase in kefiran concentration. ESEM micrographs showed that the presence of kefiran played an important role in the microstructure formation of gels. The microstructure of kefiran-WPI mixed gels was more compact and dense, compared to the WPI gel. Depletion interactions between kefiran and whey protein aggregates can be regarded as the chief factor which was responsible for these effects. The present work demonstrated that rheological and microstructural properties of acid-induced whey protein gels were improved by the addition of kefiran.

Control of heat treatment and storage temperature prevents the formation of visible aggregates in acidic whey dispersions over a 6-month storage period

Acidic whey protein isolate (WPI) dispersions are widely applied for translucent whey-based beverages. However, developing beverages that maintain clarity during extended storage can be a challenge. The formation of visible aggregates occurs recurrently during storage, leading to reduced consumer satisfaction. Batch-to-batch variation with respect to the degree of aggregation also is observed, which impairs shelf-life determination. In this study, two WPI batches (A and B) with different levels of visible aggregate formation during the storage of acidic dispersions were analyzed. Visual evaluations, oscillatory rheology, and absorbance measurements (A500) were applied to assess the formation of visible aggregates in 70 g protein L−1 WPI dispersions during a 6-month period. It was shown, that by changing the heat treatment from the conventional conditions of 95 °C for 180 s to 120 °C for 20 s and/or lowering the storage temperature from the conventional 20 °C–4 °C, the formation of visible aggregates was prevented over the 6-month storage period. The protein composition of the aggregates and the surrounding clear liquid was analyzed by 2-dimensional gel-electrophoreses. The visible aggregate was highly enriched by a low pI spot, possibly containing caseinomacropeptide and/or proteolytically truncated fragments of β-lactoglobulin and α-lactalbumin.

Concentrated whey protein ingredients: A Fourier transformed infrared spectroscopy investigation of thermally induced denaturation

Thermal denaturation of whey protein solutions was investigated from a structural perspective utilising attenuated total reflectance – Fourier transformed infrared spectroscopy (ATR‐FTIR). Solutions (100 g protein/L, pH 7) of commercial whey protein isolate (WPI) powders and enriched protein fractions of β‐lactoglobulin (β‐lg) and α‐lactalbumin (α‐la) were heat‐treated at temperatures of 50–90 °C. Subsequent analysis by ATR‐FTIR highlighted the structural changes occurring as a direct result of heat treatments. Molecularly, WPI dispersions exhibited pronounced differences in denaturation behaviour depending on their method of manufacture. ATR‐FTIR is an informative tool to discern the structural molecular interactions not apparent through physical analysis of concentrated ingredients.

Self-assembly of caseinomacropeptide as a potential key mechanism in the formation of visible storage induced aggregates in acidic whey protein isolate dispersions

Visible aggregates formed during storage in acidic whey protein isolate (WPI) dispersions represent a challenge to the beverage industry. Batch-to-batch variations are observed that prevents consistent quality and shelf-life prediction. Heat-treatment of WPI dispersions at 120 °C for 20 s instead of conventional heating at 95 °C for 180 s often prevents the aggregate formation, and varying levels of divalent cations were proposed to contribute to the observed batch-to-batch variations. In this study, the composition of the visible aggregates was examined. Caseinomacropeptide (CMP) was enriched in the visible aggregates compared with the surrounding clear liquid. Disruption of electrostatic interactions between glycosylated and non-glycosylated CMPs were studied by addition of calcium, acidification, and enzymatic de-sialidation. The treatment strategies each significantly decreased time-dependent turbidity development in acidic WPI dispersions. This suggests that the storage-induced aggregates may be prevented by disruption of electrostatic interactions between negatively-charged sialic acid residues and positively-charged amino acids.

Aerated whey protein gels as new food matrices: Effect of thermal treatment over microstructure and textural properties

Aerated gels (AG) contain both bubbles and entrapped water in their structure, thus offering ample versatility in product development. The objective of this study was to evaluate the effect of thermal treatment of whey protein isolate (WPI) dispersions over the microstructure and textural properties of AG fabricated with these dispersions. WPI dispersions (9% w/w) with NaCl (0.4% w/w) at three pH’s (6.50, 6.75 and 7.00) were prepared. Dispersions were subjected to thermal treatment at three temperatures (70, 75 and 80°C) at different times depending on the pH. After thermal treatment, dispersions were aerated by mechanical agitation at 2000rpm for 3min. Finally, aerated dispersions were cooled at 10°C for 24h to set the AG structure. AG were characterized in terms of their gas hold-up capacity, microstructure (bubble sizes) and textural properties. Thermal treatment temperature influenced the gas hold-up and mean diameter (DM) of air bubbles in the AG, both decreasing with an increase in temperature. Maximum gas hold-up was about 70% and DM were in the range of 530–700μm. The increase in apparent viscosity of thermally treated dispersions produced lower air incorporation in AG structure and smaller bubble sizes. Compression stress at break decreased with an increase in the thermal treatment temperature. Control of thermal treatment conditions for WPI dispersions allows to fabricate AG with different microstructural and textural properties which can be used as innovative food matrices for obesity control or delivery of bioactives.

Whey protein aerated gels as a new product obtained using ambient temperature magnesium and iron(II) induced gelation

The objective of the research was to obtain aerated gels by magnesium and iron(II) ion induced gelation of preheated whey protein isolate dispersions. Preliminary research allowed finding conditions of the pH, protein, and ion concentrations to produce aerated gels capable of holding air bubbles. A novel method applying gelation and aeration process simultaneously was used. Aeration using a laboratory mixer at 2000 r.p.m. produced stronger aerated gels than using a homogenizer at 8000 r.p.m. The gelation process was monitored using an ultrasound viscometer and a constant increase of dynamic viscosity was noted. A different aerated gel microstructure was observed for magnesium and iron(II) induced gels, which probably resulted in differences in the texture and viscosity, as well. The aeration process decreased hardness. In some cases texture parameters correlated with the viscosity measured using an ultrasound viscometer. Aerated whey protein gels could be applied as matrices for food applications or to controlled release of active ingredients.

Changes of secondary structure and surface tension of whey protein isolate dispersions upon pH and temperature

The secondary structure of proteins in unheated and heated whey protein isolate dispersions and the surface tension of the solutions were investigated at different pH. Heating protein solutions at 80&amp;deg;C results in an increase of unordered structure. Nevertheless, the difference between the contents of unordered structure in the unheated and heated samples increases with increasing pH of the solution. At low protein concentrations the surface tension decreased with increasing protein concentration to about 5 mg/ml. For the heated solution, a similar trend was observed in the decrease in the surface tension with increasing concentrations of protein. In both cases, the curves depicting the surface tension as a function of protein concentration could be fitted to the exponential function with a negative exponent, but with the heated solutions lower values of surface tension were observed. Studies on the surface tension of whey protein isolate solutions prove that the unfolding of whey proteins, revealed by changes in the secondary structure, causes a decrease in the surface tension.