Enhancement of the functional properties of whey protein by conjugation with maltodextrin under dry‐heating conditions

Conjugation of whey protein isolate (WPI) and maltodextrin (MD, dextrose equivalent of 6) was achieved by dry‐heating at an initial pH of 7.0, at 60 °C and 79% relative humidity, with WPI: MD6 ratio of 1:1, for up to 24 h. Conjugation was achieved with limited development of colour and advanced Maillard products on 24 h of heating. Conjugation increased the protein solubility at pH 4.5, by 7.1–8.5%, compared to the unheated and heated WPI controls. Conjugation of WPI with MD6 enhanced the stability and retention of clarity in protein solutions heated at 85 °C for 10 min with 50 mM added NaCl.     

Effect of temperature,calcium and protein concentration on aggregation of whey protein isolate: Formation of gel-like micro-particles

Protein aggregation occurs in biological systems and industrial processes, affecting protein solubility and functional properties. In this study, whey protein isolate (WPI) obtained from bovine milk was used as a model to study the dependence of aggregation on pre-heating temperature and on protein and calcium concentrations. WPI solutions (0.1–5.0%, w/v) were heated at 25–85 °C for 30 min prior to cooling and calcium addition. Tryptophan shifted to a more hydrophilic environment as WPI concentrations and pre-heating temperatures increased. Pre-heated WPI solutions yielded soluble particles, which aggregated to form porous gel-like particles by addition of calcium chloride. WPI microgel particles could be prepared by using a cold gelation method and preheated the protein above 65 °C. The particle size was monodisperse with sizes of about 190 nm and 255 nm, respectively in solutions pre-heated to 75 or 85 °C and containing 5 mm calcium.     

Physicochemical properties of whey protein conjugated with starch hydrolysis products of different dextrose equivalent values

Conjugation of whey protein with maltodextrin (MD) or corn syrup solids (CSS) having dextrose equivalent (DE) values in the range 6–38 was achieved by heating solutions of 5% whey protein isolate and 5% MD or CSS, initial pH 8.2, at 90 °C for up to 24 h. Maximum conjugation, with production of limited colour and advanced Maillard products was achieved after 8 h of heating. The extent of conjugation increased with increasing DE value of the MD and CSS ingredients. Conjugation increased whey protein solubility at pH 4.5 from 9% for whey protein heated alone to 24% for whey protein heated in the presence of CSS38 at 90 °C for 8 h. Conjugation of whey proteins with MD6 or CSS38 enhanced the stability to heating of protein solutions at 85 °C for 3 min with 50 mm added NaCl.     

Improvement of the functional properties of whey protein hydrolysate by conjugation with maltodextrin

The impact of conjugation with maltodextrin on selected functional properties (i.e., solubility and thermal stability) of intact whey protein isolate (WPI) and whey protein hydrolysate (WPH) was determined. Conjugation of WPI and WPH (degree of hydrolysis 9.3%) with maltodextrin (MD) was achieved by heating solutions of 5% WPI or WPH with 5% MD, initial pH 8.2, at 90 °C for up to 24 h. The WPH had 55.4% higher levels of available amino groups compared with the WPI, which contributed to more rapid and extensive conjugation of WPH-MD, compared with WPI-MD. The WPI-MD and WPH-MD solutions heated for 8 h had significantly higher (P < 0.05) protein solubility than the respective WPI and WPH heated control solutions, in the pH range 4.0–5.0. Conjugation of WPI and WPH with MD enhanced the stability to heat-induced changes, such as turbidity development, gelation or precipitation, in the presence of 40 mm added NaCl.     

Zinc‐loaded whey protein nanoparticles prepared by enzymatic cross‐linking and desolvation

Zinc‐loaded whey protein nanoparticles were prepared by enzymatic cross‐linking whey protein followed by ethanol desolvation. Whey protein isolate (WPI) was denatured by heating (80 °C for 15 min) at pH 7.0 and then cross‐linked by transglutaminase at 50 °C for 4 h while stirring. Transglutaminase was inactivated by heating at 90 °C for 10 min, and then, ZnSO₄·7H₂O (1–10 mm ) was added. Zinc‐loaded whey protein nanoparticles were formed by adding ethanol at one to five times the volume of the protein solution at pH 9.0. The desolvated solutions were diluted by adding distilled water at ratio of 1:100 (w/v) immediately after desolvation. Dynamic light scattering (DLS) data showed that the particle size of zinc‐loaded whey protein nanoparticles increased with the amount of zinc and the volume of ethanol. Scanning electron microscopy micrographs revealed an almost spherical morphology for zinc‐loaded whey protein nanoparticles. The zinc loading efficiency was determined ranging from 76.7% to 99.2%. In vitro test data showed that the zinc release rate was low in simulated gastric fluid but high in simulated intestinal fluid. The results indicated that enzymatic cross‐linked whey protein nanoparticles may be used as a good vehicle to deliver zinc as a supplement.     

Rennet coagulation properties of UHT‐treated phosphocasein dispersions as a function of casein and NaCl concentrations

The renneting properties of whey protein‐free, UHT‐heated (140 °C/10 s) casein dispersions were investigated as a function of casein and NaCl concentration. It was found that the rennet coagulation time and gel firmness can be optimised when the whey protein‐free casein concentration is increased, while the added NaCl concentration is kept low. The strongest gel firmness occurs at 0.05 and 0.08 m NaCl addition and at a micellar casein concentration between 6.0 and 6.6 g/100 mL. Weak rennet gels were formed at 3.0–3.6 g/100 mL casein at all NaCl concentrations tested.     

Stability of oil‐in‐water emulsions as influenced by thermal treatment of whey protein dispersions or emulsions

Properties of whey protein concentrate stabilised emulsions were modified by protein and emulsion heat treatment (60–90 °C). All liquid emulsions were flocculated and the particle sizes showed bimodal size distributions. The state and surface properties of proteins and coexisting protein/aggregates in the system strongly determined the stability of heat‐modified whey protein concentrate stabilised emulsions. The whey protein particles of 122–342 nm that formed on protein heating enhanced the stability of highly concentrated emulsions. These particles stabilised protein‐heated emulsions in the way that is typical for Pickering emulsions. The emulsions heated at 80 and 90 °C gelled due to the aggregation of the protein‐coated oil droplets.     

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.     

Whey protein aggregate formation during heating in the presence of κ-carrageenan

The effect of a negatively charged polymer, κ-carrageenan, on the aggregation behaviour of whey proteins during heating was studied. Aqueous solutions of whey protein isolate (WPI) at 0.5% were heated in the presence of κ-carrageenan (0.1%) at pH 7.0. This concentration was chosen as optimal in the detection of the intermediate aggregates during chromatographic analysis. The residual unaggregated protein, the intermediate aggregates and the soluble aggregates were all examined as a function of heating time and temperature, using size-exclusion chromatography coupled with light scattering detection. The presence of κ-carrageenan did not affect the aggregation of whey proteins heated at 75 °C; however, a change in the mechanism of aggregation seemed to occur at higher temperatures, and intermediates with higher molecular mass formed at 85 °C. At 90 °C, in the presence of κ-carrageenan, the extent of WPI aggregation was much larger, as soluble aggregates were no longer present and less residual protein was recovered in the unaggregated peak.     

Effect of CMC Molecular Weight on Acid‐Induced Gelation of Heated WPI‐CMC Soluble Complex

Acid‐induced gelation properties of heated whey protein isolate (WPI) and carboxymethylcellulose (CMC) soluble complex were investigated as a function of CMC molecular weight (270, 680, and 750 kDa) and concentrations (0% to 0.125%). Heated WPI‐CMC soluble complex with 6% protein was made by heating biopolymers together at pH 7.0 and 85 °C for 30 min and diluted to 5% protein before acid‐induced gelation. Acid‐induced gel formed from heated WPI‐CMC complexes exhibited increased hardness and decreased water holding capacity with increasing CMC concentrations but gel strength decreased at higher CMC content. The highest gel strength was observed with CMC 750 k at 0.05%. Gels with low CMC concentration showed homogenous microstructure which was independent of CMC molecular weight, while increasing CMC concentration led to microphase separation with higher CMC molecular weight showing more extensive phase separation. When heated WPI‐CMC complexes were prepared at 9% protein the acid gels showed improved gel hardness and water holding capacity, which was supported by the more interconnected protein network with less porosity when compared to complexes heated at 6% protein. It is concluded that protein concentration and biopolymer ratio during complex formation are the major factors affecting gel properties while the effect of CMC molecular weight was less significant.     

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.     

Ionic strength and buffering capacity of emulsifying salts determine denaturation and gelation temperatures of whey proteins

Ionic conditions affect the denaturation and gelling of whey proteins, affecting the physical properties of foods in which proteins are used as ingredients. We comprehensively investigated the effect of the presence of commonly used emulsifying salts on the denaturation and gelling properties of concentrated solutions of β-lactoglobulin (β-LG) and whey protein isolate (WPI). The denaturation temperature in water was 73.5°C [coefficient of variation (CV) 0.49%], 71.8°C (CV 0.38%), and 69.9°C (CV 0.41%) for β-LG (14% wt/wt), β-LG (30% wt/wt), and WPI (30% wt/wt), respectively. Increasing the concentration of salts, except for sodium hexametaphosphate, resulted in a linear increase in the denaturation temperature of WPI (kosmotropic behavior) and an acceleration in its gelling rate. Sodium chloride and tartrate salts exhibited the strongest effect in protecting WPI against thermal denaturation. Despite the constant initial pH of all solutions, salts having buffering capacity (e.g., phosphate and citrate salts) prevented a decrease in pH as the temperature increased above 70°C, resulting in a decline in denaturation temperature at low salt concentrations (≤0.2 mol/g). When pH was kept constant at denaturation temperature, all salts except sodium hexametaphosphate, which exhibited chaotropic behavior, exhibited similar effects on denaturation temperature. At low salt concentration, gelation was the controlling step, occurring up to 10°C above denaturation temperature. At high salt concentration (>3% wt/wt), thermal denaturation was the controlling step, with gelation occurring immediately after. These results indicate that the ionic and buffering properties of salts added to milk will determine the native versus denatured state and gelation of whey proteins in systems subjected to high temperature, short time processing (72°C for 15 s).     

Gelation of single heated vs. double heated whey protein isolate

Gelation of single and double heated whey protein dispersions was investigated using Ca²⁺ as inducing agents. Whey protein isolate (WPI) dispersions (10% w/w) were single heated (30 min, 80 °C at pH 7.0) or double heated (30 min, 80 °C at pH 8.0 and 30 min, 80 °C at pH 7.0) and diluted to obtain the desired protein and/or calcium ions concentration (4–9% and 5–30 mm, respectively). Calcium ions were added directly or by using a dialysis method. Double-heated dispersions gelled faster at lower protein and calcium ion concentrations than single-heated dispersions. Gels obtained from double-heated dispersions had lower values of shear strain and shear stress at fracture than gels obtained from single-heated dispersions. Double heating caused a significant complex modulus (G*) increase at 4% WPI and 15 mm calcium ions in comparison with gels obtained from single-heated dispersion. Less significant differences between gels made from double and single-heated dispersions were observed at 6% WPI, however a higher value of complex modulus was obtained for 8% protein gels from the single-heated solution. Native and non-reduced SDS–PAGE did not show clearly the effect of different procedures of heating on the quantities of polymerised proteins. Proteins in double-heated dispersions had higher hydrophobicity. Increased calcium concentration caused decreased protein hydrophobicity for both single and double-heated solutions.     

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.     

Gelation of whey protein and xanthan mixture: Effect of heating rate on rheological properties

The effects of heating rate and xanthan addition on the gelation of a 15% w/w whey protein solution at pH 7 and in 0.1 M phosphate buffer were studied using small-amplitude oscillatory shear (SAOS) rheological measurements and uniaxial compression tests. WPI solutions were heated from 25 to 90 °C at five heating rates (0.1, 1, 5, 10 and 20 °C/min). Gelation temperature of WPI decreased with decreasing of heating rates and with xanthan addition. Under uniaxial compression, the WPI gels prepared with no more than 0.2% w/w xanthan exhibited distinct fracture point and were tougher (i.e. higher fracture stress and fracture strain) than the gels prepared with no less than 0.5% w/w xanthan. In general, the fracture strain of WPI gels increased with heating rate, though not significantly, at all xanthan contents investigated. However, the fracture stress of WPI gels, generally, decreased with heating rate when xanthan content was 0–0.2% and increased with heating rate when xanthan content was 0.5 and 1%.     

Inhibition of frozen storage‐induced oxidation and structural changes in myofibril of common carp (Cyprinus carpio) surimi by cryoprotectant and hydrolysed whey protein addition

The objective of the present study was to evaluate the efficacy of combined cryoprotectants (sucrose + sorbitol) and whey protein isolate (WPI) hydrolysates to inhibit protein oxidation and quality loss in common carp (Cyprinus carpio) surimi during frozen storage at ?25 °C. With increasing storage time, the carbonyl content of myofibrillar proteins increased from 4.02 nmolmg^‐1 protein (0 day) to 7.25, 6.31, 5.26 and 4.83 nmol mg^?1 protein (180 days; P < 0.05) for the control and samples with cryoprotectants, with cryoprotectants + WPI hydrolysates and with cryoprotectants + propyl gallate, respectively; protein surface hydrophobicity and turbidity increased in a similar trend, while sulfhydryl content, Ca‐ATPase activity, protein solubility and protein thermal stability decreased (P < 0.05). These results suggest that treatments with combined cryoprotectants and antioxidative WPI hydrolysates offer an effective approach to reducing the extent of protein oxidation in common carp surimi, thereby limiting protein structural changes known to impair texture of surimi products.     

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

BACKGROUND: Edible films and coatings based on protein/lipid combinations are among the new products being developed in order to reduce the use of plastic packaging polymers for food applications. This study was conducted to determine the effect of rapeseed oil on selected physicochemical properties of cast whey protein films. RESULTS: Films were cast from heated (80 °C for 30 min) aqueous solutions of whey protein isolate (WPI, 100 g kg^?1 of water) containing glycerol (50 g kg^?1 of WPI) as a plasticiser and different levels of added rapeseed oil (0, 1, 2, 3 and 4% w/w of WPI). Measurements of film microstructure, laser light‐scattering granulometry, differential scanning calorimetry, wetting properties and water vapour permeability (WVP) were made. The emulsion structure in the film suspension changed significantly during drying, with oil creaming and coalescence occurring. Increasing oil concentration led to a 2.5‐fold increase in surface hydrophobicity and decreases in WVP and denaturation temperature (T_max). CONCLUSION: Film structure and surface properties explain the moisture absorption and film swelling as a function of moisture level and time and consequently the WVP behaviour. Small amounts of rapeseed oil favourably affect the WVP of WPI films, particularly at higher humidities. Copyright © 2010 Society of Chemical Industry     

Properties of binary complexes of whey protein fibril and gum arabic and their functions of stabilizing emulsions and simulating mayonnaise

Food protein fibrillization is recently regarded as an attractive strategy to broaden and improve food protein functionality in food science. In the present work, whey protein isolate (WPI) solutions was heated at pH 2.0 and 80 °C for different time (1, 2, 4, 8, and 16 h) to prepare whey protein isolate fibrils (WPF), and the resulting WPF was mixed with gum arabic (GA) at pH 2.0–6.0 to explore the properties and functions of such mixtures. The fibril conversion rate of WPI continued to grow from 4% to 32% with the extension of heating time from 1 to 16 h. The phase behavior study showed that the insoluble WPF-GA binary complexes were formed at pH 4.6–6.0 due to the electrostatic interaction between amino groups of WPI and the carboxyl groups of GA. Compared to the WPI-GA complexes, the WPF-GA complexes had a higher GA content and coacervate yield, suggesting that the fibrillization contributes to the association of proteins with polysaccharides. WPF alone were linear, while fibril bundles appeared in the presence of GA. Such WPF-GA complexes exhibited an excellent capacity to prepare gel-like emulsions. The viscosity and strength of the prepared emulsions was gradually enhanced as the fibril conversion rate of WPI increased. Besides, the complexes of GA and WPF with a heat-treated time of 16 h showed the greatest potential to prepare mayonnaise analogues with a solid-like property, which possessed the similar storage modulus and smoothness to the commercial mayonnaise products.     

Heat stability of oil-in-water emulsions formed with intact or hydrolysed whey proteins: influence of polysaccharides

The heat stability of emulsions (4 wt% corn oil) formed with whey protein isolate (WPI) or extensively hydrolysed whey protein (WPH) products and containing xanthan gum or guar gum was examined after a retort treatment at 121 °C for 16 min. At neutral pH and low ionic strength, emulsions stabilized with both 0.5 and 4 wt% WPI (intact whey protein) were stable against retorting. The amount of β-lactoglobulin (β-lg) at the droplet surface increased during retorting, especially in the emulsion containing 4 wt% protein, whereas the amount of adsorbed α-lactalbumin (α-la) decreased markedly. Addition of xanthan gum or guar gum caused depletion flocculation of the emulsion droplets, but this flocculation did not lead to their aggregation during heating. In contrast, the droplet size of emulsions formed with WPH increased during heat treatment, indicating that coalescence had occurred. The coalescence during heating was enhanced considerably with increasing concentration of polysaccharide in the emulsions, up to 0.12% and 0.2% for xanthan gum and guar gum, respectively; whey peptides in the WPH emulsions formed weaker and looser, mobile interfacial structures than those formed with intact whey proteins. Consequently, the lack of electrostatic and steric repulsion resulted in the coalescence of flocculated droplets during retort treatment. At higher levels of xanthan gum or guar gum addition, the extent of coalescence decreased gradually, apparently because of the high viscosity of the aqueous phase.     

Influence of sucrose on cold gelation of heat‐denatured whey protein isolate

A solution of heat‐denatured whey proteins was prepared by heating 100 g kg⁻¹ whey protein isolate (WPI) at pH 7.0 to 75 °C for 15 min in the absence of salt. Heat treatment caused the globular protein molecules to unfold, but electrostatic repulsion opposed strong protein–protein aggregation and so prevented gel formation. When the heat‐denatured whey protein solution was cooled to room temperature and mixed with 15 mM CaCl₂, it formed a gel. We investigated the influence of the presence of sucrose in the protein solutions prior to CaCl₂ addition on the gelation rate. At relatively low concentrations (0–100 g kg⁻¹), sucrose decreased the gelation rate, presumably because sucrose increased the aqueous phase viscosity. At higher concentrations (100–300 g kg⁻¹), sucrose decreased the gelation rate, probably because sugar competes for the water of hydration and therefore increases the attraction between proteins. These data have important implications for the application of cold‐setting WPI ingredients in sweetened food products such as desserts. © 2000 Society of Chemical Industry