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.     

Controlling denaturation and aggregation of whey proteins during thermal processing by modifying temperature and calcium concentration

Whey protein isolate solutions (8.00 g protein/100 g; pH 6.8) were treated for 2 min at 72, 85 or 85 °C with 2.2 mM added calcium Ca to produce four whey protein systems: unheated control (WPI‐UH), heated at 72 °C (WPI‐H72), heated at 85 °C (WPI‐H85) or heated at 85 °C with added Ca (WPI‐H85Ca). Total levels of whey protein denaturation increased with increasing temperature, while the extent of aggregation increased with the addition of Ca, contributing to differences in viscosity. Significant changes in Ca ion concentration, turbidity and colour on heating of WPI‐H85Ca, compared to WPI‐UH, demonstrated the role of Ca in whey protein aggregation.     

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.     

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%.     

Encapsulation of eugenol using Maillard-type conjugates to form transparent and heat stable nanoscale dispersions

Maillard-type protein-carbohydrate conjugates are known for their excellent emulsifying properties and have been used to encapsulate volatile oils and flavor compounds. In the present study, eugenol was used as a model compound for encapsulation in conjugates of whey protein isolate (WPI) and maltodextrins (MD) made using different WPI:MD mass ratios and MD chain lengths. The encapsulation involved two steps, emulsifying an oil phase of eugenol dissolved in hexane into an aqueous phase with dissolved conjugates and spray drying the emulsion. Mass yield up to 82.7 g/100 g and encapsulation efficiency as high as 35.7 g/100 g eugenol were observed. After hydrating spray-dried powders, several samples with an eugenol content above its solubility limit demonstrated transparent dispersions at pH 3.0 and 7.0 after heating at 80 °C for 15 min, corresponding to mean diameters smaller than ca. 100 nm. One treatment also showed transparent dispersions after heating at pH 5.0, which is near the isoelectric point of whey proteins, in contrast to gel formation for a control prepared with a mixture of non-conjugated WPI and MD. The present study demonstrates potential to produce food grade nanoscale systems for delivering lipophilic bioactives in functional beverages, without adversely affecting their visual appearance.     

Improvement in emulsifying properties of soy protein isolate by conjugation with maltodextrin using high‐temperature,short‐time dry‐heating Maillard reaction

Soy protein isolate (SPI)–maltodextrin (MD) conjugates were synthesised using Maillard reaction under high‐temperature (90, 115 and 140 °C), short‐time (2 h) dry‐heating conditions. The loss of free amino groups in proteins and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS‐PAGE) profile confirmed that SPI‐MD conjugates were formed and higher dry‐heated temperatures could increase the glycosylation degree. The emulsifying properties of SPI and SPI‐MD conjugates were evaluated in oil‐in‐water emulsions. The emulsions stabilised with SPI‐MD conjugates synthesised at 140 °C exhibited higher emulsifying stability and excellent storage stability against pH, ionic strength and thermal treatment compared with those synthesised at 90 °C, 115 °C and SPI stabilised emulsions. This might be due to a greater proportion of conjugated MD in SPI‐MD conjugates synthesised at 140 °C because of the higher glycosylation degree, and more conjugated MD on the droplet surface could provide steric effect and enhance the stability of the droplets in the emulsions.     

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.     

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.     

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.     

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.     

Influence of Maillard reaction conditions on the antigenicity of bovine α‐lactalbumin using response surface methodology

BACKGROUND: Maillard reaction can modify functional properties of proteins. Bovine α‐lactalbumin (α‐LA) is often supplemented to the new generation of infant formulae, but it is considered to be a main allergen. However, there is little information on the effect of Maillard reaction on α‐LA antigenicity. The objective of this study was to investigate the influence of Maillard reaction on the antigenicity of α‐LA in conjugates of whey protein isolate (WPI) with glucose under different conditions of protein/sugar weight ratio (0.17–7.83), temperature (40–60 °C) and time (24–120 h) using response surface methodology. RESULTS: Conjugation of WPI with glucose markedly reduced the antigenicity of α‐LA. This reduction in antigenicity could be controlled by regulating the three independent variables weight ratio, temperature and time. A model of optimal reaction conditions for lower antigenicity of α‐LA was established. According to the model, the minimum antigenicity of α‐LA was achieved at 52.8 °C, 78 h and 5.96:1 WPI/glucose weight ratio. WPI/glucose weight ratio had the greatest effect on the antigenicity of α‐LA, while reaction temperature influenced α‐LA antigenicity to a lesser extent. CONCLUSION: Well‐controlled Maillard reaction between WPI and glucose is an efficient method to reduce α‐LA antigencity. Copyright © 2009 Society of Chemical Industry     

Physicochemical and antioxidant properties of Maillard reaction products formed by heating whey protein isolate and reducing sugars

This study was conducted to investigate the physicochemical and antioxidant properties of Maillard reaction products (MRP) prepared by heating whey protein isolate (WPI) and reducing sugars (glucose and galactose) to 95 °C for different lengths of time (0–6 h). The results revealed that the colour, intermediate products, browning intensity and the antioxidant activities of the MRP increased as the reaction time increased (P < 0.05), whereas the pH value and free amino group content decreased (P < 0.05). Sodium dodecyl sulphate–polyacrylamide gel electrophoresis indicated that the covalently linked conjugates of WPI and sugars were formed. The results indicate that the Maillard reaction could improve the antioxidant capacity of WPI.     

Foaming Properties of Whey Protein Isolate and λ‐Carrageenan Mixed Systems

Heating protein with polysaccharide under neutral or near neutral pH can induce the formation of soluble complex with improved functional properties. The objective of our research was to investigate the effects of λ‐carrageenan (λC) concentrations and pH on foaming properties of heated whey protein isolate (WPI) and λC soluble complex (h‐cpx) in comparison to heated WPI with added λC (pWPI‐λC), and unheated WPI with λC (WPI‐λC). In all 3 WPI‐λC systems at pH 7, increasing λC concentration led to improved foamability until a certain concentration before it decreased. Despite their higher viscosity, both heated systems (pWPI‐λC and h‐cpx) showed significantly better foamability and foam stability compared to WPI‐λC. Rheological results of foams with 0.25% λC suggested that higher elasticity and viscous films were produced in h‐cpx and pWPI‐λC systems corresponding to better foam stability. Foam microstructure images indicated that foams produced from h‐cpx had thicker film and consisted of smaller initial bubble area and more uniform bubble size. Results from the effect of pH (6.2, 6.5, and 7.0) further confirmed that stronger interactions between WPI and λC during heating contributed to the improved foaming properties. Foam stability was higher in h‐cpx system at all 3 pH levels, especially under pH 6.2 where there were strongest interactions between the biopolymers.     

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

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

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.     

pH and Heat Treatment Effects on Foaming of Whey Protein isolate

The overrun obtained by whipping whey protein isolate (WPI) was significantly (p<0.05) affected by changing pH. Heating WPI at pH 4.0 reduced rate and amount of overrun. The highest overrun values for unheated WPI were observed at pH 5.0 and 7.0 after heating at 55°C for 10 min. The maximum foam stability for unheated WPI was obtained at pH 5.0. Heat treatment had little effect on stability at pH 4.0 or 7.0 but at pH 5.0, 80°C for 10 min improved stability by 65%. Based on surface pressure data, the rate of adsorption of β-lactoglobulin interfacial films and the work of compression correlated with overrun, maximum overrun, overrun development and foam stability.     

Assessment of film-forming potential and properties of protein and polysaccharide-based biopolymer films

This study assessed the film‐forming abilities of six types of proteins, as well as six types of polysaccharides at various concentrations (proteins: 0–16%; polysaccharides: 0–4%) and heating temperatures (60–80 °C). Biopolymer films evaluated included: sodium caseinate (SC), whey protein isolate (WPI), gelatine (G); caboxymethyl cellulose (CMC), sodium alginate (SA) and potato starch (PS). Screening trials showed that optimal film‐forming conditions were achieved using SC and G (4% and 8%), WPI (8% and 12%), PS, CMC (2% and 3%) or SA (1% and 1.5%) solutions heated to 80 °C in combination with 50% (w/w) glycerol. Films manufactured from 1.5% SA, 8% G and 3% CMC had the highest tensile strength (24.88 MPa); flexibility (89.69%)/tear strength (0.30 N) and puncture resistance (22.66 N), respectively. SC, WPI and G‐based films were more resistant to solvent than SA, CMC and PS. Film permeability to water vapour and oxygen decreased in the order: 12% WPI to 1% SA and 12% WPI to 1% SA. All films tested were impermeable to oil.     

Heat stability of radio frequency dielectric heat treated low heat and high heat nonfat dry milk

The heat stability of low (LH) and high heat (HH) nonfat dry milk (NDM) that received a radio frequency dielectric heat (RFDH) treatment at 75, 80 or 85 °C for different periods of time (between 43 and 125 min) was assessed. NDM was reconstituted at 3.5% (w/w) protein. Heat stability was assessed at 140 °C by recording the heat coagulation time. Samples were evaluated at native pH, and adjusted pH from 6.4 to 7.2. LH samples heated to 75 °C or 80 °C showed greater heat stability than non-treated LH at pH 6.4 to 6.8. Data suggest that RFDH treatment of LH induced associations between whey proteins and casein micelles, which increased the heat stability in this pH region. The same effect was not observed in the HH samples, suggesting different reactions may be induced. Dry heating NDM may affect protein associations differently from liquid systems, depending upon the conditions.     

Effects of Polymerized Whey Proteins on Consistency and Water-holding Properties of Goat's Milk Yogurt

ABSTRACT The effects of polymerized whey proteins (PWP) on functional properties of goat's milk yogurt were investigated. PWP were prepared by heating whey protein isolate (WPI) dispersion (8.0% protein, pH 7.0) at 90 °C for 30 min. Three reconstituted goat milk (RGM) (12% total solids [TS] as control; RGM with 2.4% unheated WPI; and RGM with 2.4% PWP) and 1 RGM with 16.7% TS were prepared and inoculated with 0.04% yogurt starter culture. Inoculated milk was incubated at 43 °C for 5 h, cooled to 4 °C in an ice‐water bath, and then placed at refrigerator (4 °C) overnight before testing. Incorporation of PWP significantly (P < 0.001) increased the viscosity (by 80%) and decreased the syneresis (by 25%) of the yogurt samples, whereas addition of unheated WPI did not significantly affect the viscosity and syneresis compared with the control. There were no changes in pH, TS, ash, fat, protein, and lactose contents among yogurt samples except the solids fortified control. Yogurt with 16.7% TS had the lowest syneresis but did not improve in viscosity. Transmission electron microscopy micrographs demonstrated that the microstructure of the goat's milk yogurt gel with PWP was denser than the control. Results of this study indicate that polymerized whey proteins may be a novel protein‐based thickening agent for improving the functional properties of goat's milk yogurt and other similar products.