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.     

Effects of Succinylation on β-Lactoglobulin Foaming Properties

The extent of succinylation of β-lactoglobulin (β-Lg) increased logarithmically with increasing concentrations of succinic anhydride. The surface pressure of 27.5% succinylated β-Lg was higher than native (β-Lg but higher levels of succinylation (50% and 100%) reduced the surface pressure. Overrun and foam stability were reduced following succinylation. The electrostatic interaction caused by the addition of 100% succinylated β-lactoglobulin (0.5g/100 mL) to a solution (2.5%) of native β-lactoglobulin at pH 4.0 improved overrun (47%) and foam stability (61%).     

Characterization of the Composition, Physicochemical and Functional Properties of Acid Whey Protein Concentrates

Membrane-processed acid whey protein concentrates were studied for their foaming and emulsifying properties in dilute whey protein solutions and in a 30% fat emulsion. Among the compositional factors and physicochemical characters which significantly correlated with foaming and emulsifying properties were protein hydrophobicity, solubility, free-sulfhydryl content, phosphorus and β-lactoglobulin concentration. Heptane binding was negatively correlated with foam overrun and foam stability of whey protein solutions, whereas, exposed hydrophobicity was positively correlated with overrun in the whipped topping.     

Combined effect of dynamic heat treatment and ionic strength on the properties of whey protein foams – Part II

The aim was to investigate the effect of dynamic thermal treatment in a tubular heat exchanger on the denaturation and foaming properties of whey proteins, such as overrun, foam stability and texture. A 2% w/v WPI solution (pH 7.0), with and without NaCl addition (100 mM), was submitted to heat treatment at 100 °C. The results demonstrated that heat treatment slightly reduced overrun, whereas NaCl and heat treatment improved foam stability, enhanced texture and provided smaller bubble diameters with more homogeneous bubble size distributions in foams. The foaming properties of proteins, especially stability, were shown to depend not only on the amount of protein aggregates, but also on their size. While insoluble aggregates (larger than 1 μm diameter) accelerated drainage, soluble aggregates (about 200 nm diameter) played a key role on the stabilization of gas–liquid interfaces.     

Effects of sucrose on egg white protein and whey protein isolate foams: Factors determining properties of wet and dry foams (cakes)

The effects of sucrose on the physical properties of foams (foam overrun and drainage ½ life), air/water interfaces (interfacial dilational elastic modulus and interfacial pressure) and angel food cakes (cake volume and cake structure) of egg white protein (EWP) and whey protein isolate (WPI) was investigated for solutions containing 10% (w/v) protein. Increasing sucrose concentration (0–63.6 g/100 mL) gradually increased solution viscosity and decreased foam overrun. Two negative linear relationships were established between foam overrun and solution viscosity on a log–log scale for EWP and WPI respectively; while the foam overrun of EWP decreased in a faster rate than WPI with increasing solution viscosity (altered by sucrose). Addition of sucrose enhanced the interfacial dilational elastic modulus (E′) of EWP but reduced E′ of WPI, possibly due to different interfacial pressures. The foam drainage ½ life was proportionally correlated to the bulk phase viscosity and the interfacial elasticity regardless of protein type, suggesting that the foam destabilization changes can be slowed by a viscous continuous phase and elastic interfaces. Incorporation of sucrose altered the volume of angel food cakes prepared from WPI foams but showed no improvement on the coarse structure. In conclusion, sucrose can modify bulk phase viscosity and interfacial rheology and therefore improve the stability of wet foams. However, the poor stability of whey proteins in the conversion from a wet to a dry foam (angel food cake) cannot be changed with addition of sucrose.     

Protein–protein interactions: Their importance in the foaming of heterogeneous protein systems

Analysis of egg albumen foams by electrophoresis showed that the basic protein lysozyme (pI 10.7) was strongly retained. Addition of low concentrations (0.01–0.10% w/v) of the basic proteins clupeine (pI 12) and lysozyme to solutions (0.50% w/v) of several acidic proteins (pI 4.7–6.0) greatly improved their foaming properties at pH values between the isoelectric points. Sucrose strongly enhanced the action of the basic proteins, while not significantly affecting the foaming of the acidic proteins alone. Basic proteins did not enhance the foaming of ovalbumin and egg albumen in the absence of sucrose. Clupeine enhanced foaming more effectively than lysozyme under all conditions studied. Lysozyme was least effective near the isoelectric point of the acidic protein, where electrostatic interactions were weakest. Sodium chloride (0.1M ) had a detrimental effect on the action of lysozyme.     

Comparative effect of thermal treatment on the physicochemical properties of whey and egg white protein foams

The optimization of the functionalities of commercial protein ingredients still constitutes a key objective of the food industry. Our aim was therefore to compare the effect of thermal treatments applied in typical industrial conditions on the foaming properties of whey protein isolate (WPI) and egg white proteins (EWP): EWP was pasteurized in dry state from 1 to 5 days and from 60 °C to 80 °C, while WPI was heat-treated between 80 °C and 100 °C under dynamic conditions using a tubular heat exchanger. Typical protein concentrations of the food industry were also used, 2% (w/v) WPI and 10% (w/v) EWP at pH 7, which provided solutions of similar viscosity. Consequently, WPI exhibited a higher foamability than EWP. For WPI, heat treatment induced a slight decrease of overrun when temperature was above 90 °C, i.e. when aggregation reduced too considerably the amount of monomers that played the key role on foam formation; conversely, it increased foamability for EWP due to the lower aggregation degree resulting from dry heating compared to heat-treated WPI solutions. As expected, thermal treatments improved significantly the stability of WPI and EWP foams, but stability always passed through a maximum as a function of the intensity of heat treatment. In both cases, optimum conditions for foam stability that did not impair foamability corresponded to about 20% soluble protein aggregates. A key discrepancy was finally that the dry heat treatment of EWP provided softer foams, despite more rigid than the WPI-based foams, whereas dynamically heat-treated WPI gave firmer foams than native proteins.     

Proteose Peptones and Physical Factors Affect Foaming Properties of Whey Protein Isolate

Effects of peptides and nonprotein components of whey on whey protein isolate (WPI) were studied using a differential pressure method. Decay of WPI foam followed biphasic first-order kinetics, but was affected by solution conditions. WPI foam stability exhibited two pH optima (5.0 and 8.5). Addition of 0.02–0.15M NaCl progressively decreased foaming capacity and foam stability. Addition of 0.01–0.2% proteose-peptones caused a sharp decrease in foam stability, but did not affect WPI foaming capacity. Foam stability was increased by addition of up to 20% lactose. Removal of proteose-peptones should greatly improve foaming properties of whey proteins.     

Effect of protein–polysaccharide mixtures on the continuous manufacturing of foamed food products

The aim of this work is to understand the effects of protein and polysaccharide interactions on the physicochemical properties of highly viscous Newtonian model foods and their impact on continuous foaming operation in laminar flow conditions. Model foods consisted of modified glucose syrups. Foaming was carried out at constant gas-to-liquid flow rate ratio as a function of rotation speed. Overrun, mean bubble diameter d₃₂ and stability over time were used to characterize foams. Results showed that blow-by occurred during foaming of models including either 0.1% guar or xanthan without proteins, while 0.1% pectin allowed a total incorporation of the gas phase with large bubbles. For proteins, models with 2% whey protein isolate (WPI) were able to form foams with the desired overrun and small bubbles, while foaming was less effective with 2% Na-caseinates. With WPI, guar addition did not improve significantly foam properties. Overrun was reduced in WPI–xanthan mixtures, probably because the matrix exhibited viscoelastic trends even though xanthan decreased d₃₂. WPI–pectin mixtures provided abundant and stable foams with the smallest d₃₂ and the best stability because WPI reinforced the time-dependent behaviour of pectin recipes. However, blow-by was observed with 0.1% pectin when WPI was replaced by Na-caseinates, which demonstrates the key role of specific protein–polysaccharide interactions on overrun. Conversely, bubble diameters in foams were governed by process parameters and could be adequately described using a laminar Weber number based on foam viscosity measured during foaming for all model foods that provided stable foams.     

The stability and physical properties of egg white and whey protein foams explained based on microstructure and interfacial properties

The goal of this investigation was to determine if physical models, based on micro-scale (bubbles) and nano-scale (interface) properties, can be used to explain the macroscopic foaming properties of egg white protein (EWP) and whey protein isolate (WPI). Foam properties were altered by adding different amounts of sucrose (4.27–63.6 g/100 mL) and microstructures were observed using confocal laser scanning microscopy and bubbles were quantitatively measured using image analysis. Addition of sucrose decreased the initial bubble size, corresponding to higher foam stability and lower air phase fraction. EWP foams were composed of smaller bubbles and lower air phase fractions than WPI foams. Increased sucrose concentration caused a decreased liquid drainage rate due to a higher continuous phase viscosity and smaller bubble sizes. WPI foams had faster rates for liquid drainage and bubble coarsening than EWP foams. The differences were attributed to faster bubble disproportionation in WPI foams, caused by lower interfacial elasticity and lower liquid phase fractions. The experimentally fitted parameters for foam yield stress did not follow universal trends and were protein type dependent. EWP foams had higher yield stress than WPI foams due to smaller bubble sizes and higher interfacial elasticity. The yield stress of WPI foams increased slightly with addition of sucrose and cannot be accounted for based solely on model parameters. It appears that changes in stability of EWP and WPI foams can be explained based on physical models while unaccounted for protein-specific effects remain regarding foam yield stress.     

Foaming characteristics of β-lactoglobulin as affected by enzymatic hydrolysis and polysaccharide addition: Relationships with the bulk and interfacial properties

The objective of this work was to study the effect of enzymatic hydrolysis and polysaccharide addition on the foaming characteristics of β-lactoglobulin (β-LG). Enzymatic treatment was performed in the hydrolysis degree (HD) range of 0.0–5.0% using bovine α-chymotrypsin II immobilized on agarose microbeads. Anionic non-surface active polysaccharides (PS), sodium alginate (SA) and λ-carrageenan (λ-C) were studied in the concentration range of 0.0–0.5 wt.%. Foaming characteristics were determined by conductimetric and optical methods and were linked to protein diffusion kinetics, film mechanical properties and biopolymer molecular dynamics in solution. Experiments were performed at constant temperature (20 °C), pH 7 and ionic strength 0.05 M. Limited hydrolysis improved the formation and stability of β-LG foam possibly due to an increased protein diffusion rate and film dilatational elasticity. Furthermore, PS addition caused different effects on β-LG foaming characteristics depending on the PS type, their relative concentration and extent of enzymatic treatment (HD). Diffusion rate and interfacial rheological behavior of mixed systems could exert a decisive role in foaming characteristics of β-LG and its hydrolysates in close connection with biopolymer interactions in solution, e.g., macromolecule repulsion, protein segregation/aggregation and soluble complexes formation.     

Biopolymers Produced by Cross-linking Soybean 11S Globulin with Whey Proteins using Transglutaminase

Heterogeneity of biopolymers was determined by cross-linking acetylated-11S acidic subunits (Ac-11S) of soy protein with α-lactalbumin and β-lactoglobulin. The extent of polymerization was determined by electrophoresis and HPLC. Differential scanning calorimetry (DSC) was used to determine thermal properties of starting proteins and biopolymers. HPLC data demonstrated the absence of biopolymers from Ac-11S, acetylated α-lactalbumin and acetylated β-lactoglobulin when each was incubated separately with transglutaminase (TG). However, Ac-11S formed biopolymers with α-lactalbumin and β-lactoglobulin when TG was added. TG catalyzed the formation of heterologous and homologous biopolymers from whey protein isolate (WPI) and soybean 11S globulin (11S). Cross-linking WPI and 11S provided biopolymers with improved heat stability which may be useful to provide functionality to food products.     

Food Protein Functionality in a Liquid System: A Comparison of Deamidated Wheat Protein with Dairy and Soy Proteins

ABSTRACT: Solubility, surface properties, overrun, foam stability, apparent viscosity, and emulsification properties were evaluated for 3% protein dispersions of deamidated wheat protein (DWP), sodium caseinate (SC), soy protein isolate (SPI), and whey protein isolate (WPI). DWP dispersion had the highest apparent viscosity, 25% higher emulsion activity index (EAI), and 82% higher emulsion stability index (ESI) when compared to SPI dispersions. Dispersions of DWP had similar foaming properties and surface properties when compared to SC, but had 50% higher EAI and 1000% greater ESI when compared to the 2 dairy proteins. The utilization of DWP could be expanded into liquid food systems currently using dairy proteins.     

Whipping Studies with Partially Deloctosed Cheese Whey

Whipping properties of various whey preparations were studied by measuring overrun and stability of foams produced in a Hobart mixer. Presence of heat-labile whey proteins resulted in poor whippability, poor foam stability, and low overruns. Removal of the heat-acid coagulated proteins greatly improved wh’ppability, and foams resembled whipped egg whites with overruns of more than 2,500%. Increasing total solids by evaporation of the acid supernatant or by addition of sucrose or soluble starch decreased the overrun but increased foam stability. Air uptake and overrun were negatively affected by calcium hydroxide. Foams from dialyzed supernatants with addition of sucrose were successfully baked into meringues.     

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.     

Effect of ultrasound on the structure and functional properties of transglutaminase-crosslinked whey protein isolate exposed to prior heat treatment

Effects of ultrasound treatment (20 kHz, 41–45 W cm⁻², 0, 20, 40 or 60 min) on the physicochemical, functional properties and elements of the secondary structure of transglutaminase (TGase)-crosslinked whey protein isolate (WPI) exposed to prior thermal treatment (75 °C, 15 min) were investigated. The largest molecular size of proteins in the TGase-crosslinked WPI was observed after the ultrasound and thermal pre-treatment (HU-WPI-TGase). HU-WPI-TGase had the maximum intrinsic fluorescence intensity, with highest loss of free amino groups. Ultrasound-treated WPI (U-WPI) showed more (13%) emulsifying activity and more (63%) foaming ability than untreated WPI, but HU-WPI-TGase had higher foam stability and lower emulsifying activity than U-WPI. FTIR analysis indicated that ultrasound, heat treatment and TGase cross-linking had effects on the β-sheet, β-turn and random coil of WPI. The outcomes from this study show a potential application in providing novel functional ingredients for the dairy industry.     

Foams Prepared from Whey Protein Isolate and Egg White Protein: 1. Physical, Microstructural, and Interfacial Properties

ABSTRACT:  Foams were prepared from whey protein isolate (WPI), egg white protein (EWP), and combinations of the 2 (WPI/EWP), with physical properties of foams (overrun, drainage 1/2 life, and yield stress), air/water interfaces (interfacial tension and interfacial dilatational elasticity), and foam microstructure (bubble size and dynamic change of bubble count per area) investigated. Foams made from EWP had higher yield stress and stability (drainage 1/2 life) than those made from WPI. Foams made from mixtures of EWP and WPI had intermediate values. Foam stability could be explained based on solution viscosity, interfacial characteristics, and initial bubble size. Likewise, foam yield stress was associated with interfacial dilatational elastic moduli, mean bubble diameter, and air phase fraction. Foams made from WPI or WPI/EWP combinations formed master curves for stability and yield stress when normalized according to the above-mentioned properties. However, EWP foams were excluded from the common trends observed for WPI and WPI/EWP combination foams. Changes in interfacial tension showed that even the lowest level of WPI substitution (25% WPI) was enough to cause the temporal pattern of interfacial tension to mimic the pattern of WPI instead of EWP, suggesting that whey proteins dominated the interface. The higher foam yield stress and drainage stability of EWP foams appears to be due to forming smaller, more stable bubbles, that are packed together into structures that are more resistant to deformation than those of WPI foams.     

Foams Prepared from Whey Protein Isolate and Egg White Protein: 2. Changes Associated with Angel Food Cake Functionality

ABSTRACT:  The effects of sucrose on the physical properties and thermal stability of foams prepared from 10% (w/v) protein solutions of whey protein isolate (WPI), egg white protein (EWP), and their combinations (WPI/EWP) were investigated in wet foams and angel food cakes. Incorporation of 12.8 (w/v) sucrose increased EWP foam stability (drainage 1/2 life) but had little effect on the stability of WPI and WPI/EWP foams. Increased stability was not due to viscosity alone. Sucrose increased interfacial elasticity ( E  ') of EWP and decreased E' of WPI and WPI/EWP combinations, suggesting that altered interfacial properties increased stability in EWP foams. Although 25% WPI/75% EWP cakes had similar volumes as EWP cakes, cakes containing WPI had larger air cells. Changes during heating showed that EWP foams had network formation starting at 45 °C, which was not observed in WPI and WPI/EWP foams. Moreover, in batters, which are foams with additional sugar and flour, a stable foam network was observed from 25 to 85 °C for batters made from EWP foams. Batters containing WPI or WPI/EWP mixtures showed signs of destabilization starting at 25 °C. These results show that sucrose greatly improved the stability of wet EWP foams and that EWP foams form network structures that remain stable during heating. In contrast, sucrose had minimal effects on stability of WPI and WPI/EWP wet foams, and batters containing these foams showed destabilization prior to heating. Therefore, destabilization processes occurring in the wet foams and during baking account for differences in angel food cake quality.     

Effects of Heat Processing on the Functionality of Whey Protein Concentrates

The effects of heat processing on the composition and functionality of whey protein concentrations (WPC) were investigated. WPC was manufactured from milk, whey and retentate that had either been pasteurized at 72°C for 15 sec or had received no heat treatment. Eight combinations of heat treatment were utilized. Pasteurization of the milk had a positive effect on overrun and foam stability, but a negative effect on gel strength at pH 6.5, protein hydrophobicity, and neutral lipid content. Pasteurization of the whey resulted in decreased mineral content bud did not affect functionality. Pasteurization of the retentate caused a decrease in emulsion capacity, soluble β-lactoglobulin, solubility, whipped topping overrun and gel strength at pH 8.0.     

Charge and structural requirements of basic proteins for foam enhancement

Derivatives of β-lactoglobulin (β-LG) with isoelectric points (pIs) >7 enhanced the foaming of acidic proteins at pH 7. However, only basic proteins with pis >9.0 were capable of promoting foaming effectively in the presence of lipid. A derivative of mean pI 9.9 was particularly effective. Enzymic hydrolysis of clupeine (pI = 12; mol. wt = 4000) beyond a certain point caused a sudden reduction in foam-enhancing power, which coincided with a loss in the ability to form visible complexes (turbidity). Foam-enhancing properties of hydrolysed clupeine samples appeared to depend on their content of intact (enzyme-resistant) clupeine.