Whey Protein Isolate Solutions Research Articles

The effect of calcium on the composition and physical properties of whey protein particles prepared using emulsification

Protein microparticles were formed through emulsification of 25% (w/w) whey protein isolate (WPI) solutions containing various concentrations of calcium (0.0–400.0mM) in an oil phase stabilized by polyglycerol polyricinoleate (PGPR). The emulsions were heated (at 80°C) and the microparticles subsequently re-dispersed in an aqueous phase. Light microscopy and scanning electron microscopy (SEM) images revealed that control particles and those prepared with 7.4mM calcium were spherical and smooth. Particles prepared with 15.0mM calcium gained an irregular, cauliflower-like structure, and at concentrations larger than 30.0mM, shells formed and the particles were no longer spherical. These results describe, for the first time, the potential of modulating the properties of dense whey protein particles by using calcium, and may be used as structuring agents for the design of functional food matrices with increased protein and calcium content.

Quality characteristics of egg-reduced pound cakes following WPI and emulsifier incorporation

The effect of partial (50wt%) or total liquid egg replacement by whey proteins in combination with emulsifiers, i.e. hydroxypropylmethylcellulose (HPMC) and sodium stearoyl-2-lactylate (SSL), on the quality of pound cakes was investigated. Cakes containing whey protein isolate (WPI) solutions of varying concentrations (i.e. 20, 17 and 14% w/v) were first prepared. Complete egg replacement by WPI led to the preparation of cake batter of increased specific gravity as well as to final cake products of inferior quality with regard to volume, texture and hardness increase upon storage, compared to the control. In the case of partial liquid egg replacement by WPI solutions, cakes with acceptable sensory and quality characteristics were obtained, which were further improved following the addition of emulsifiers. During a storage period of four days the egg-reduced cakes exhibited a significantly lower staling rate depending mainly on the concentration of WPI and the presence of emulsifiers. Finally, the analysis of cake microstructure confirmed the positive effect of the co-addition of whey proteins and emulsifiers in egg-reduced cakes. This work made it possible to develop an alternative, egg-reduced cake of satisfactory quality, by using a combination of whey proteins with two common baking additives.

Isolation of micro- and nano-crystalline cellulose particles and fabrication of crystalline particles-loaded whey protein cold-set gel

Micro- and nano-crystalline cellulose (MCC and NCC, respectively) particles isolated from cellulose filter papers via acid digestion were characterised and loaded into a heat-denatured whey protein isolate (WPI) solution which was subsequently cold-set-gelled. Both the MCC and NCC particles were rod-shaped and had higher crystallinity degrees than had the cellulose source they were isolated from. The hydrodynamic diameter of NCC particles was ≈15nm. Fourier transform infrared (FTIR) spectroscopy suggested more surface hydroxyl groups on the NCC than the MCC particles and complete digestion of hemicellulose on the cellulosic substrate by acid. MCC- and NCC-loaded WPI gel matrices were topographically less uniform and contained many more undulations in comparison to the crystal-free counterpart. It was found, using dynamic rheometry and penetration tests, that the crystal loading into WPI gels weakened the texture. Non-covalent interactions between the cellulose crystals and whey protein strands were proposed in the gel structure according to FTIR results.

Properties of Poly (ethylene oxide)/ whey Protein Isolate Nanofibers Prepared by Electrospinning

A mixture of solutions of whey protein isolate (WPI) and poly (ethylene oxide) (PEO) were employed to fabricate nanofibers by the electrospinning technique. The PEO/WPI ratio was varied in order to obtain PEO:WPI nanofibers with different concentrations of homopolymers. The dependence of morphology, viscosity, conductivity, surface tension, thermal and vibrational properties was studied as function of the PEO/WPI ratio. The results show that at higher viscosity, we obtained soft and smooth fibers with diameters ranging between 227 ± 36 nm and 264 ± 66 nm; while the solutions with low viscosity ( 527 μScm−1) promote the formation of beads. The nanofibers were thermally stable for temperatures below 200 °C and the initial thermal degradation temperatures is slightly affected by the PEO:WPI ratio. The FTIR results revealed that the crosslinking favors the formation of fibers. Rosmarinus officialis extract was used for explore a possible application of the nanofibers as a delivery system. The dissolution rate of the rosemary extract from the nanofibers was measured in phosphate buffer solutions with pH of 1.2, 7.5 and 9.0. The total rosemary content was dissolved from the nanofibers, in the aqueous medium, on a time with depends on the pH of the buffer solution.

Effects of thermally induced denaturation on technological-functional properties of whey protein isolate-based films

This study examined how and to what extent the degree of denaturation affected the technological-functional properties of whey protein isolate (WPI)-based coatings. It was observed that denaturation affected the material properties of WPI-coated films significantly. Surface energy decreased by approximately 20% compared with native coatings. Because the surface energy of a coating should be lower than that of the substrate, this might result in enhanced wettability characteristics between WPI-based solution and substrate surface. Water vapor barrier properties increased by about 35% and oxygen barrier properties increased by approximately 33%. However, significant differences were mainly observed between coatings made of fully native WPI and ones with a degree of denaturation of 25%. Higher degrees of denaturation did not lead to further improvement of material properties. This observation offers cost-saving potential: a major share of denatured whey proteins may be replaced by fully native ones that are not exposed to energy-intensive heat treatment. Furthermore, native WPI solutions can be produced with higher dry matter content without gelatinizing. Hence, less moisture has to be removed through drying, resulting in reduced energy consumption.

Influence of moderate electric fields on gelation of whey protein isolate

Proteins are one of the food constituents most affected by heating, and some of the changes involve their unfolding, denaturation and gelation. Ohmic heating has often been claimed to improve the quality of foodstuffs due to its uniform heating and (putative) presence of a moderate electric field (MEF). However, this is still subject to discussion, so it is important to determine the effect of ohmic heating and of its MEF upon food constituents. Hence, the aim of this work was to evaluate the effects of MEF on denaturation, aggregation and viscoelastic properties of whey protein isolate (WPI), and compare them with those obtained via conventional heating under identical treatment conditions (up to 30 min at 85 °C). Results have shown that MEF interferes with whey protein unfolding and aggregation pathways at relatively high temperatures. MEF treatments have resulted in WPI solutions possessing more 8 and 10% of native β-Lactoglobulin and α-Lactalbumin, respectively, after 30 s of heating at 85 °C, when compared with a conventional heating method. Protein aggregates from MEF-treated WPI solutions presented a maximum increase in size of 78 nm, whereas conventional heating produced an increase of 86 nm. Unlike in conventional heating, aggregation of whey proteins during MEF was not sufficiently strong to form a true elastic gel network, since decreases in both storage and loss modulus were observed following MEF treatment. Our results suggest that MEF may provide a novel method for production of a whey protein matrix with distinctive gel-forming properties.

Properties of konjac glucomannan–whey protein isolate blend films

Edible composite packaging has been developed by blending biocomponents for specific applications, aiming to take advantage of complementary functional properties or to overcome their respective flaws. The aim of this work was to study the effect of incorporation of whey protein isolate (WPI) on the properties of konjac glucomannan (KGM) based films. Five aqueous solutions of KGM and/or WPI were prepared by casting and solvent evaporation of 1:0, 0.8:3.4, 0.6:3.6, 0.4:3.8 and 0:4.2 g KGM:g WPI/100 g solution. Glycerol (Gly) was used as a plasticizer at 1.5 and 1.8 g/100 g solution. The result showed that incorporated WPI proportionally increased transparency of KGM-based films. An increase in proportion of WPI resulted in decreased tensile strength and elastic modulus as well as improved flexibility. The incorporation of WPI into the KGM matrix led to an increase in water insolubility which enhanced product integrity and water resistance. Nevertheless, WPI did not improve water vapor barrier of KGM–WPI films. WPI and blend film with the highest concentration of WPI could be heat sealed at 175 °C. Overall, the range of Gly in this study did not apparently affect properties of the films.

The effect of ultrasound treatment on the structural, physical and emulsifying properties of dairy proteins

The effect of ultrasound treatment on the structural, physical and emulsifying properties of three dairy proteins: sodium caseinate (NaCas), whey protein isolate (WPI) and milk protein isolate (MPI) was investigated. The pH of untreated NaCas, WPI and MPI solutions was 7.1, 6.8 and 6.7, respectively. Protein solutions were sonicated for 2 min with a power intensity of ∼34 Wcm-2. The structural and physical properties of the dairy proteins were studied in terms of changes in protein size, molecular structure and hydrodynamic radius using DLS, SDS-PAGE and intrinsic viscosity, respectively. The emulsifying properties of the sonicated proteins were compared to the untreated proteins and Tween 80. Ultrasound treatment reduced the size and hydrodynamic volume of the proteins, while there was no measurable reduction in molecular weight. Emulsions prepared with untreated NaCas and WPI had submicron sized droplets (∼120 nm), while emulsions produced with untreated MPI and Tween 80 had micron sized droplets (> 1 µm) at lower concentrations. Unexpectedly, emulsions produced with ultrasound treated NaCas and WPI had the same droplet sizes as untreated proteins at all concentrations, despite the reduction in protein size of the sonicated proteins. Emulsions prepared with sonicated MPI at concentrations ≤ 1 wt. % had smaller droplet sizes than the emulsions produced with untreated MPI. This effect was consistent with the observed decrease in interfacial tension for ultrasound treated MPI, which will facilitate droplet break-up during emulsification.

Complex Coacervation as a Novel Microencapsulation Technique to Improve Viability of Probiotics Under Different Stresses

A physicochemical approach has been undertaken to develop polymeric microcapsules for delivering probiotic bacteria with improved viability in functional food products. Two probiotic strains of Lactobacillus paracasei subsp. paracasei (E6) and Lactobacillus paraplantarum (B1), isolated from traditional Greek dairy products, were microencapsulated by complex coacervation using whey protein isolate (WPI, 3 % w/v) and gum arabic (GA, 3 % w/v) solutions mixed at 2:1 weight ratio. The viability of the bacterial cells during processing (heat treatment and high salt concentrations), under simulated gut conditions (low pH and high bile concentrations) and upon storage, was evaluated. Entrapment of lactobacilli in the complex coacervate structure enhanced the viability of the microorganisms when exposed to a low pH environment (pH 2.0). Both encapsulated strains retained high viability in simulated gastric juice (>73 %; log scale), especially in comparison with non-encapsulated (free) cells (<19 %). Moreover, after 60 days of refrigerated storage at pH 4.0, the viability of microencapsulated cells was more than 86 %, implying improved protection in comparison with the free cells (<59 %). Complex coacervation with WPI/GA has the potential to deliver live probiotics in low pH foods or fermented products; it is also important to note that the complexes can dissolve at pH 7.0 (gut environment) releasing the microbial cells (desired feature of target delivery systems).

Fabrication of whey protein–pectin conjugate particles through laccase-induced gelation of microemulsified nanodroplets

A mixed solution of whey protein isolate, sugar beet pectin and laccase was microemulsified as nanodroplets in a mixture of sunflower oil and span 80. The droplets were transformed into nanoparticles through laccase-induced cross-linking and in situ gelation of biopolymers. Entrapment of caffeine within the conjugate bulk gel of biopolymers postponed the gelation time indexed by dynamic rheometry and decreased the strength of the final gel. The mean size of conjugate particles was 109 nm. Scanning electron microscopy images revealed an almost spherical morphology for uniformly shaped particles. Fourier transform infrared spectroscopy suggested the cross-linking of protein and pectin with participation of ferulic acid groups of pectin. Heat scanning experiments carried out by differential scanning calorimetry indicated the transition of conjugate particles from glassy to rubbery state at lower temperatures than their parent biopolymers.

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.

Intragastric gelation of whey protein–pectin alters the digestibility of whey protein during in vitro pepsin digestion

The aim of this work is to investigate the effect of pectin on in vitro digestion of whey protein. Digestion of heated whey protein isolate (WPI) and pectin solutions (WPI-pectin) as influenced by pectin concentration and pH was studied under simulated gastric conditions. Electrophoresis, dynamic light scattering, colorimetric measurements, and gel microstructures were used to study the digestion pattern. At low pectin concentration (0.25% w/w), pectin did not significantly influence the degradation of whey protein. Increasing the pectin concentration to 1% led to extensive intragastric gelation immediately after mixing with simulated gastric fluid. The microstructure of intragastric gel from WPI-pectin at pH 6.0 showed a more interconnected and denser gel network than that at pH 7.0. More protein and pectin were involved in the gelation at pH 6.0 than pH 7.0. The digesta of samples at pH 6.0 was mainly composed of peptides, while that at pH 7.0 mostly consisted of aggregates and crosslinked peptides. This study suggests that WPI-pectin at high biopolymer ratio formed intragastric gel in simulated gastric models, which could delay protein digestion and potentially slow gastric emptying and promote satiety.

Impact of Heat and Laccase on the pH and Freeze-Thaw Stability of Oil-in-Water Emulsions Stabilized by Adsorbed Biopolymer Nanoparticles

The enzymatic cross-linking of adsorbed biopolymer nanoparticles formed between whey protein isolate (WPI) and sugar beet pectin using the complex coacervation method was investigated. A sequential electrostatic depositioning process was used to prepare emulsions containing oil droplets stabilized by WPI – nanoparticle – membranes. Firstly, a finely dispersed primary emulsion (10 % w/w miglyol oil, 1 % w/w WPI, 10 mM acetate buffer at pH 4) was produced using a high-pressure homogenizer. Secondly, a series of biopolymer particles were formed by mixing WPI (0.5 % w/w) and pectin (0.25 % w/w) solutions with subsequent heating above the thermal denaturation temperature (85 °C, 20 min) to prepare dispersions containing particles in the submicron range. Thirdly, nanoparticle-covered emulsions were formed by diluting the primary emulsion into coacervate solutions (0–0.675 % w/w) to coat the droplets. Oil droplets of stable emulsions with different interfacial membrane compositions were subjected to enzymatic cross-linking. We used cross-linked multilayered emulsions as a comparison. The pH stability of primary emulsions, biopolymer complexes and nanoparticle-coated base emulsions, as well as multilayered emulsions, was determined before and after enzyme addition. Freeze-thaw stability (−9 °C for 22 h, 25 °C for 2 h) of nanoparticle-coated emulsions was not affected by laccase. Results indicated that cross-linking occurred exclusively in the multilamellar layers and not between adsorbed biopolymer nanoparticles. Results suggest that the accessibility of distinct structures may play a key role for biopolymer-cross-linking enzymes.

Rheological and Microstructural Characteristics of Thermally Produced Flaxseed Gum–Whey Protein Isolate Mixed Solutions and Gels

The rheological, thermal gelation, and microstructural properties of flaxseed gum–whey protein isolate (WPI) mixtures were studied using steady shear viscometry, small amplitude oscillatory rheometry, differential scanning calorimetry (DSC), and confocal laser scanning microscopy (CLSM). The concentration of flaxseed gum was varied from 0.1%–0.5% (w/w) while the concentration of WPI was maintained at 20% (w/w). The addition of flaxseed gum increased the viscosity of flaxseed gum–WPI solutions and the strength of the mixed gels. The degree of increase in gel strength was found to depend on the concentration of flaxseed gum. The gel strength of the flaxseed gum–WPI mixed gels increased with the increase of flaxseed gum at low gum concentrations (0.1%–0.3% w/w). The gel strength of these mixed gels decreased (but it was still higher than WPI only gel) at high flaxseed gum concentration (0.5% w/w) due to excessive phase separation caused by thermodynamic incompatibility. This phase separation was clearly visible in micrographs obtained from CLSM.

Pilot-scale production of hydrolysates with altered bio-functionalities based on thermally-denatured whey protein isolate

Whey protein isolate (WPI) solutions (100 g L−1 protein) were subjected to a heat-treatment of 80 °C for 10 min. Unheated and heat-treated WPI solutions were hydrolysed with Corolase® PP at pilot-scale to either 5 or 10% degree of hydrolysis (DH). Hydrolysates were subsequently processed via cascade membrane fractionation using 0.14 μm, and 30, 10, 5 and 1 kDa cut-off membranes. The compositional and molecular mass distribution profiles of the substrate hydrolysates and membrane processed fractions were determined. Whole and fractionated hydrolysates were assayed for both angiotensin-I-converting enzyme (ACE) inhibitory activity and ferrous chelating capabilities. A strong positive correlation (P < 0.01) was established between the average molecular mass of the test samples and the concentration needed to chelate 50% of the iron (CC50) in solution. The lowest ACE inhibition concentration (IC50 = 0.23 g L−1 protein) was determined for the 1 kDa permeate of the heat-treated 10% DH hydrolysate.

Creating novel food textures: Modifying rheology of starch granule suspensions by cold-set whey protein gelation

There is increasing interest in creating novel structures in food products so as to create desirable textural characteristics. Cold-set gelation of pre-heated (90 °C/10 min) whey protein isolate (WPI) solutions (2.5, 5.0 and 10.0 g/100 g) and WPI-starch mixtures (2.5 g/100 g and 3.75 g/100 g, respectively) were initiated with calcium chloride (10 and 20 mmol/L). Calcium addition promoted gelation of the pre-heated systems at ambient temperature and led to increased turbidity, complex shear modulus (G*), and optical lightness. These measured properties increased with increasing protein and/or calcium concentration, which was attributed to more extensive protein network formation. In the WPI-starch mixed systems, the presence of swollen starch granules caused discontinuous protein network formation and led to lower gelation kinetics in comparison to protein-only WPI gels. Our results have useful implications for the formulation of semi-solid food products with specific rheological properties, i.e., gel-like or paste-like characteristics.

Influence of buffer on the preparation of multilayered oil-in-water emulsions stabilized by proteins and polysaccharides

This study describes the influence of buffer type and ionic strength on the stability of multilayered emulsions produced by biopolymers, such as fish gelatin, whey protein isolate (WPI) and sugar beet pectin. Primary oil-in-water emulsions (5% (w/w) rapeseed oil, and 0.95% (w/w) fish gelatin or WPI) were prepared in different buffers (5, 10, 25, and 100mM acetate or citrate buffer, pH 3.5) using a microfluidizer. These emulsions were mixed with aqueous sugar beet pectin solution and an appropriate buffer to yield secondary emulsions (0.5% (w/w) rapeseed oil, 0.095% (w/w) fish gelatin or WPI, and 0.2% (w/w) pectin). Secondary emulsions were then added to fish gelatin and WPI solution, respectively, to produce tertiary emulsions (0.1% (w/w) rapeseed oil, 0.019% (w/w) WPI or fish gelatin, 0.04% (w/w) pectin, and 0.5%, 0.6%, and 1.0% (w/w) WPI or fish gelatin, respectively). The influence of buffer type and ionic strength on the stability of primary, secondary and tertiary emulsions was determined by measuring particle size and ζ-potential, as well as assessing the microstructure by optical microscopy. WPI-stabilized primary emulsions produced in citrate buffer were prone to aggregation, especially at high ionic strengths unlike fish gelatin. Production of stable tertiary WPI-stabilized emulsions was only possible in acetate buffer, regardless of ionic strength. By comparison, triple-layered emulsions prepared in citrate buffer showed extensive aggregation. These findings provide a better understanding of the use of biopolymers to prepare multilayered emulsions.

Preparation and characterization of whey protein isolate films reinforced with porous silica coated titania nanoparticles

Whey protein isolate (WPI) films embedded with TiO2@@SiO2 (porous silica (SiO2) coated titania (TiO2)) nanoparticles for improved mechanical properties were prepared by solution casting. A WPI solution of 1.5wt% TiO2@@SiO2 nanoparticles was subjected to sonication at amplitudes of 0, 16, 80 and 160μm prior to casting in order to improve the film forming properties of protein and to obtain a uniform distribution of nanoparticles in the WPI films. The physical and mechanical properties of the films were determined by dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and tensile testing. Water vapor permeability (WVP) measurements revealed that the water vapor transmission rates are slightly influenced by sonication conditions and nanoparticle loading. The DMA results showed that, at high sonication levels, addition of nanoparticles prevented protein agglomeration. The thermal stability of the materials revealed the presence of 3–4 degradation stages in oxidizing the protein films. The addition of nanoparticles strengthens the WPI film, as evidenced by tensile stress analysis. Sonication improved nanoparticle distribution in film matrix; such films can potentially become effective packaging materials to enhance food quality and safety.

Nanoencapsulation of date palm pit extract in whey protein particles generated via desolvation method

An alkaline solution of whey protein isolate was charged with absolute ethanol resulting in precipitation of whey protein particles. The vacuum-dried particles were then dispersed either in water or aqueous ethanol. Heat-treatment of whey proteins before desolvation process decreased the mean size of particles when dispersed in aqueous ethanol from 280nm to 183nm. The range and mean size of particles prepared from heat-treated protein solution when dispersed in water were 41–212nm and 103nm, respectively. Date palm pit aqueous extract was encapsulated inside the particulating heat-treated whey proteins during the desolvation stage with encapsulation efficiency of ~78%. Extract-loaded particles had mean size of 163nm in alcoholic dispersion and 92nm in water dispersion. Scanning electron microscopy imaging showed spherical nanoparticles aggregated in dry state. Fourier transform infrared spectroscopy suggested that extract and whey proteins did not covalently bind. Heat-treatment of whey proteins before desolvation resulted in the absence of denaturation endotherm in differential scanning calorimetry curve of extract-free particles. Extract loading in particles interrupted the continuity of protein matrix causing the occurrence of mild glass transition phenomenon in extract-loaded particles when heated.

Exceptional heat stability of high protein content dispersions containing whey protein particles

Due to aggregation and/or gelation during thermal treatment, the amount of whey proteins that can be used in the formulation of high protein foods e.g. protein drinks, is limited. The aim of this study was to replace whey proteins with whey protein particles to increase the total protein content and heat stability. For this purpose whey protein particles with a size of a few micrometers were formed through emulsification and heat gelation of a 25% (w/w) whey protein isolate (WPI) solution at either pH 5.5 or at pH 6.8. Dispersion of whey protein particles formed at pH 5.5 showed an exceptional heat stability (at pH ∼ 7); the viscosity of the dispersions containing a total protein concentration around 18% (w/w) did not change after heating at 90 °C for 30 min, while a WPI solution already gelled under same heating conditions at protein concentrations around 11% (w/w). Additionally, no gelation was observed in the dispersions prepared by pH 5.5 particles, when the total protein concentration was increased above 20% (w/w). However, due to the increased particle concentration shear-thickening was observed in these samples. Whey protein particles prepared at pH 6.8 showed rather weak stability against heat treatment, mainly as a result of swelling. Protein particles were not resistant to gastric digestion and complete degradation of the particles was observed after a short incubation time under pancreatic conditions. In conclusion, the use of dense whey protein particles has been shown to be a useful strategy to counter aggregation and/or gelation problems in high protein foods.