Rheology of galactomannan–whey protein mixed systems

The rheological behaviour of whey protein/galactomannan mixtures in aqueous solutions was studied under gelling conditions of the protein component, at neutral pH and at a pH close to the protein isoelectric point. The presence of the neutral polysaccharide had significant effects on the formation and viscoelastic behaviour of the cured gels. This effect was dependent on the structural organisation of the protein network. At pH 7 the galactomannan had a general positive effect on WPI gel formation. It is suggested that under these conditions, the protein network forms a continuous phase that accommodate the polysaccharide chains, acting as a filler of the protein network. The minimum protein concentration for gelation to occur, the gelation temperature and time all decrease in the presence of the galactomannan. Under pH conditions near the whey protein isoelectric point, different effects were observed as a result of the galactomannan addition. At low WPI concentration, the galactomannan had a detrimental influence on the protein network formation, but a negligible effect or even a positive influence on the gelation process at higher concentrations.     

Gelation of mixed systems whey protein concentrate–gluten in acidic conditions

Gels of whey protein concentrate (WPC)–gluten were prepared by heating WPC–gluten dispersions (10% whey protein/0–5–10% gluten protein, w/w; pH 3.75 or 4.2). Gels were characterized through solubility assays in different extraction solutions, measures of water-holding capacity (WHC), firmness, elasticity and relaxation time, and light microscopy. Differential scanning calorimetry (DSC) of WPC–gluten dispersions was also performed. Gluten increases the firmness and elasticity of gels, mainly at pH 4.2. The WHC also increases with gluten content, being higher at pH 3.75 than at pH 4.2. Solubility assays indicate that electrostatic forces, hydrophobic and H bindings would be involved in maintaining the gel structure of WPC gels at pH 3.75 and 4.2, whereas in mixed gels of WPC–gluten, the principal forces responsible for the maintenance of the gel structure at these pHs would be hydrophobic and H bindings, and in gels prepared at pH 4.2 also disulfide bonds, but in a minor extent. The presence of gluten shifts the apparent transition temperature for whey protein denaturation towards lower temperatures. Gels with gluten present a smooth network with gaps and a more elastic appearance, as observed by light microscopy.     

Protein–protein interactions of a whey–pea protein co-precipitate

The aim of this study was to investigate the mechanisms behind protein–protein interactions in a co-precipitate of whey protein isolate (WPI) and pea protein isolate (PPI). A co-precipitate and blend, consisting of 80% WPI and 20% PPI, were compared. Covalent disulphide interactions were studied by blocking of free thiols with N-Ethylmaleimide (NEM), while electrostatic interactions were studied in systems with 0.5 m NaCl and hydrophobic interactions with 0.2% SDS. Protein solubility, stability and secondary, tertiary and quaternary protein structures were analysed. Co-precipitation did not introduce different protein–protein interactions than the direct blending of proteins. SDS affected solubility (P < 0.05), secondary and tertiary structure. However, the effects of NEM and NaCl were significant greater (P < 0.05) on the same parameters and thermal stability, especially when combined (P < 0.01). Thus, the protein–protein interactions in a whey–pea co-precipitate and protein blend consisted of disulphide bonds and electrostatic interactions.     

Casein–whey protein interactions in heated milk: the influence of pH

Heat-treatment of milk causes denaturation of whey proteins, leading to a complex mixture of whey protein aggregates and whey protein coated casein micelles. In this paper we studied the effect of pH-adjustment of milk (6.9–6.35) prior to heat-treatment on the distribution of denatured whey proteins in aggregates and coating of casein micelles. Proteins were fractionated using an alternative fractionation technique based on renneting. Acid- and rennet-induced gelation of these milks were used to obtain more information on the characteristics of the milk. Acid-induced gelation appeared to be mainly influenced by the presence of whey protein aggregates. Rennet-induced gelation was determined by the whey protein coating of the casein micelles. Both the quantity of whey proteins present on the surface of the casein micelles and the homogeneity of the coating were determining the renneting properties. These results extend the current knowledge on pH dependent casein–whey protein interactions. In order to present a clear picture of the changes occuring during heat treatment of milk at various pH, the results are summarized in a model. In this model we propose that heating at a pH>6.6 lead to a partial coverage of the casein micelles and the formation of separate whey protein aggregates. Heating at a pH<6.6 lead to an attachment of all whey proteins to the casein micelles. At pH 6.55 the coverage is rather homogeneous but lowering the pH further lead to an inhomogeneus coverage of the casein micelles. Surprisingly small changes of the pH at which the milk was heated had considerable effects on the gelation behaviour both in renneting and in acid gelation.     

Progressive freeze concentration of whey protein–sucrose–salt mixtures

Progressive freeze concentration of whey protein solutions is evaluated. Since solutions in industry are more complex, the effect of the addition of sodium chloride and sucrose on the inclusion behaviour is studied as well. Using a progressive freeze concentrator solutions of whey protein and mixtures of whey protein and/or sucrose and/or sodium chloride were freeze concentrated. At an initial concentration of 4%(w/w), whey proteins were not included in the ice fraction. At higher concentrations the inclusions are caused by the increase in viscosity in the boundary layer, impeding mass transfer. The addition of sucrose caused a similar effect. Presence of sodium chloride causes inclusions through the occurrence of a zone where the solution is locally super-cooled and leads to the formation of dendritic ice which encapsulates pockets of solution in the ice layer. Mixtures of both sucrose and sodium chloride gave no additive effect on solute inclusion but just a concurrent effect.     

Surface dilatational properties of whey protein and hydroxypropyl-methyl-cellulose mixed systems at the air–water interface

In this work we have studied the impact of the competitive adsorption of a whey protein concentrate (WPC) and three well characterized hydroxypropyl-methyl-cellulose (HPMCs), commercially known as E4 M, E50LV and F4 M, on the surface dilatational properties (surface dilatational modulus, E, surface dilatational elasticity, E_d, and loss angle tangent, tan δ) of mixed films adsorbed at the air–water interface. The increase in E_d values with adsorption time could be associated with biopolymer adsorption at the interface. The surface dilatational properties depend on the WPC and HPMC concentrations in the aqueous phase and on the WPC/HPMC ratio. Although the values of E_d were mainly determined by HPMC at short adsorption times, for mixed systems with the lowest protein concentration (1 × 10⁻⁴ wt%) the E_d values were close to those of HPMCs, even at long term adsorption. The values of tan δ indicate the formation of adsorbed mixed films with high viscoelasticity, with a gel structure, which in turn should be attributed to the association of biopolymer molecules occurring at the interface. Only one biopolymer is the dominant one in the solid character of these mixed systems. HPMC at high concentrations slightly reduced the long-term solid character of the films confirming the existence of competition for the air–water interface as expected with two surface-active biopolymers with high molecular weight.     

Characterization of chitosan–whey protein films at acid pH

The capability to produce blend chitosan–whey protein films at acidic pH, carrying a high amount of protein, is demonstrated, even though under these conditions a pure whey protein film could not be obtained. The films are biphasic and characterized by a compositional gradient, with the downward film surface containing a lower amount of protein than the upward surface. The surface richer in protein was more hydrophobic than that richer in chitosan. The difference in composition and hydrophilicity between both surfaces increases with the amount of protein incorporated in the film. Increasing the protein amount decreased elongation at break and tensile strength but, in general, had little effect on water vapor permeability. Although some of the film functionality might be compromised due to the incompatibility between the polysaccharide and protein components within the film matrix, the blended films, especially those with intermediated protein amount, may have useful applications on those food systems where the edible films should break up during the cooking or mastication process.     

Rheological properties and structure of inulin–whey protein gels

The rheological properties, structure and synergistic interactions of whey proteins (1–7%) and inulin (20% and 35%) were studied. Gelation of whey proteins was induced with Na⁺. Inulin was dissolved in preheated whey protein solutions (80 °C, 30 min). Inulin gel formation was strongly affected by whey proteins. The presence of whey proteins at a level allowing for protein gel network formation (7%) significantly increased the G′ and G″ values of the gels. Scanning electron micrographs showed a thick structure for the mixed gel. Whey proteins at low concentrations (1–4%) were not able to form a gel; further, these low concentrations partly or wholly impaired formation of a firm inulin gel. Although interactions between inulin and whey proteins may be concluded from hydrophobicity measurements, the use of an electrophoretic technique did not show any inulin–whey protein complexes.     

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.     

Partitioning of α-lactalbumin and β-lactoglobulin in whey protein concentrate/hydroxypropylmethylcellulose aqueous two-phase systems

Whey protein concentrate (WPC) was fractionated by using hydroxypropylmethylcellulose (HPMC) at pH 6.5. Incompatible mixtures with different proportions of HPMC and WPC were prepared. After phase separation, the protein concentration in both phases was determined by the Kjeldahl method and the proportion of each protein by SDS-PAGE combined with image analysis. The results show that the low molecular weight proteins α-lactalbumin (α-lac) and β-lactoglobulin (β-lg) were retained in high proportion in the upper phase (about 90% compared to 64% of WPC). The most efficient condition to fractionate β-lg and α-lac was the phase separation of an incompatible mixed system with a high initial concentration of WPC and a low initial concentration of HPMC i.e., WPC 20%, wt/wt/HPMC 0.5%, w/w. It can be concluded that the thermodynamic incompatibility which arises from mixing WPC with HPMC could be used as a method for fractionation of whey proteins.     

Integrated production of whey protein concentrate and lactose derivatives: What is the best combination?

In order to model and analyze the techno-economic feasibility of a whey processing unit for the production of whey protein concentrate (WPC) integrated with processing of lactose, the present study utilized the software SuperPro Designer® for modeling of the processes, including risk analysis and study of reduced pollution impacts. Six models were constructed for the production of WPC and processing of lactose, which were (1) WPC 34, (2) WPC 34 and lactose powder, (3) WPC 34 and hydrous ethanol fuel, (4) WPC 80, (5) WPC 80 and lactose powder, and (6) WPC 80 and hydrous ethanol fuel. The economic evaluation was performed by analysis of the Payback Period (PP), Net Present Value (NPV), Breakeven Point (BP) and Internal Rate of Return (IRR). Probability distributions obtained by fitting of historical data for whey prices and the final products were used to perform the risk analysis, submitted to a Monte Carlo simulation using the @Risk software. The project showed to be feasible due to the elevated IRR and NPV values, coupled with low BP and PP. When evaluating the individual production of ethanol, it was verified that the production cost of this product was superior to the sale price, making independent production of ethanol from lactose present in the whey uneconomical. Plants with production of lactose powder were more economically attractive and also presented greater reduction of Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD). The financial indices suggested greater feasibility of WPC 80 compared to WPC 34.     

Isolation and characterisation of κ-casein/whey protein particles from heated milk protein concentrate and role of κ-casein in whey protein aggregation

Milk protein concentrate (79% protein) reconstituted at 13.5% (w/v) protein was heated (90 °C, 25 min, pH 7.2) with or without added calcium chloride. After fractionation of the casein and whey protein aggregates by fast protein liquid chromatography, the heat stability (90 °C, up to 1 h) of the fractions (0.25%, w/v, protein) was assessed. The heat-induced aggregates were composed of whey protein and casein, in whey protein:casein ratios ranging from 1:0.5 to 1:9. The heat stability was positively correlated with the casein concentration in the samples. The samples containing the highest proportion of caseins were the most heat-stable, and close to 100% (w/w) of the aggregates were recovered post-heat treatment in the supernatant of such samples (centrifugation for 30 min at 10,000 × g). κ-Casein appeared to act as a chaperone controlling the aggregation of whey proteins, and this effect was stronger in the presence of α_S- and β-casein.     

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

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

Performance of whey protein hydrolysate–maltodextrin conjugates as emulsifiers in model infant formula emulsions

Model infant formula emulsions containing 15.5, 35.0 and 70.0 g L⁻¹ protein, soybean oil and maltodextrin (MD), respectively, were prepared. Emulsions were stabilised by whey protein hydrolysate (WPH) + CITREM (9 g L⁻¹), WPH + lecithin (9 g L⁻¹) or WPH conjugated with MD (WPH–MD). All emulsions had mono-modal oil droplet size distributions post-homogenisation with mean oil droplet diameters (D_4,3) of <1.0 μm. No changes in the D_4,3 were observed after heat treatment (95 °C, 15 min) of the emulsions. Accelerated storage (40 °C, 10 d) of unheated emulsions resulted in an increase in D_4,3 for CITREM (2.86 μm) and lecithin (5.36 μm) containing emulsions. Heated emulsions displayed better stability to accelerated storage with no increase in D_4,3 for CITREM and an increase in D_4,3 for lecithin (2.71 μm) containing emulsions. No increase in D_4,3 over storage was observed for unheated or heated WPH–MD emulsion, indicating its superior stability.     

Emulsifying properties of soy whey protein isolate–fenugreek gum conjugates in oil-in-water emulsion model system

Soy whey protein isolate (SWPI)–fenugreek gum conjugates were prepared by Maillard type reactions in a controlled dry state condition (60 °C, 75% relative humidity for 3 days) to improve emulsification properties. SDS-PAGE electropherogram showed that conjugation formed high molecular weight products with the disappearance of 7S fraction, acidic subunits of the 11S fractions and protein band at molecular weight 21 and 24 kDa. However, the amount of protein at molecular weight 30 kDa remained unchanged. The protein solubility of SWPI–fenugreek gum conjugates improved as compared to SWPI and SWPI–fenugreek gum non-conjugated mixture especially at isoelectric point of protein when assessed in the pH range 3–8 at 22 °C. In comparison to SWPI, fenugreek gum and non-conjugated SWPI–fenugreek gum, SWPI–fenugreek gum conjugates had better emulsifying properties near the isoelectric pH of protein. Emulsification at near the isoelectric pH of protein was chosen as at this pH the proteins are prone to aggregate, which could destabilize the emulsion. Heating solutions of the conjugates prior to emulsification further improved their emulsification properties. The conjugates also showed a better emulsifying property at high salt concentration as compared to SWPI alone.     

Improved heat stability by whey protein–surfactant interaction

One of the main changes that occur during heat treatment of milk is whey protein denaturation, which in its turn may lead to protein aggregation and gelation. In this contribution, the effect of lysophospholipids, the main components of lysolecithins, as well as alternative surfactants, on heat-induced whey protein aggregation has been studied. Hereby, attention was paid to the relation between polar lipid molecular structure (e.g. effect of alkyl chain length, effect of polar head group) and heat-stabilising properties. Residual protein determination in the supernatant obtained after centrifugation of heated whey protein solutions learned that whey protein aggregation was at least partly prevented in the presence of surfactants. As the short alkyl chain lysophospholipids were particularly effective heat stabilisers, hydrophilic surfactants seemed to be most effective, which may be ascribed to their higher critical aggregation concentration. Upon more severe heat treatment, protein aggregation was probed either in-situ by oscillatory rheology, or ex-situ by yield rheometry. As some surfactants significantly reduced the gel strength, or even prevented heat-induced gel formation, these experiments corroborated the heat-stabilising effect of hydrophilic surfactants. Nuclear Magnetic Resonance (NMR) enabled a more direct evaluation of the protein–surfactant interaction. A strong hydrophobic interaction between small molecular weight surfactants and whey proteins became obvious from the chemical shift of the surfactant hydrophobic groups in the NMR spectrum and could be quantified by pulsed field gradient NMR (pfg-NMR) diffusiometry. The results indicated that protein–surfactant interaction did not occur upon thermal denaturation, but already took place at room temperature. However, the effect of this interaction became mainly obvious during thermal treatment.     

Barrier and tensile properties of whey protein–candelilla wax film/sheet

Barrier and tensile properties were compared for whey protein isolate- (WPI-) based solution-cast films, extruded sheets and extruded sheets subsequently thinned into films by compression. Solution-cast films were made from mixtures of WPI and glycerol (GLY) in water. Sheets were made by feeding WPI, GLY, and water to a twin-screw co-rotating extruder. In each case, candelilla wax (CAN) was added at 0, 5 or 7.5 g CAN/100 g dry mix to determine the effect on the barrier and tensile properties. Compressed extruded films were made by thinning extruded sheets using a Carver Press equipped with heated platens. Water vapor permeability (WVP), oxygen permeability (OP) and tensile properties were measured. Scanning electron microscopy (SEM) images were also taken.     

Assessment of the techno-functionality,starch digestion rates and protein quality of rice flour–whey protein instant powders produced in a twin extruder

Whey protein concentrate (WPC) is an important raw material for the production of instant beverages due to its protein properties. A central composite design was devised to analyse the effects of thermoplastic extrusion of 2:1 rice flour:WPC blends in physical, chemical–nutritional and functional properties. Three main factors were selected, screw speed (225–375 r.p.m.), conditioning moisture (17%–23%) and temperature (120–180 °C) to evaluate effects on water absorption (WAI) and solubility (WSI) indexes, viscoamylograph cold and final viscosities, in vitro protein and starch digestibilities and starch hydrolysis indexes (HI). A second-order model showed that linear parameters were significant for all variables studies. Conditioning moisture affected properties more significantly than temperature and screws speed. The best treatment (16% moisture conditioning, 180 °C last barrel zone and screws rotating at 350 r.p.m.) in terms of water solubility had high starch in vitro digestibility and excellent protein quality determined in vitro and in vivo with weanling rats.     

Co-precipitation of whey and pea protein – indication of interactions

The aim was to optimise the yield of co-precipitation of whey protein isolate (WPI) and pea protein isolate (PPI) and compare co-precipitates and protein blends with respect to solubility. The yield of co-precipitates was tested with different protein ratios of WPI and PPI in combination with different temperatures and acid precipitation (pH 4.6). The highest precipitation yield was obtained at protein ratios WPI < PPI, high temperature and alkaline protein solvation. The solubility was measured by an instability index and absorption spectroscopy of re-suspended precipitated proteins at pH 3, 7 and 11.5. Co-precipitates had significantly lower solubility than protein blends. Protein ratios WPI > PPI, low precipitation temperature and high pH showed the highest solubility. Differences in protein composition between co-precipitates and protein blends were observed with SDS-PAGE and matrix-assisted laser desorption ionisation time-of-flight, and indicated different protein–protein interaction in samples, which needs further investigations.