Whey Protein Isolate Foams Research Articles

Whey protein microgels for stabilisation of foams

Rheological, foaming and foam textural properties of whey protein isolate (WPI) microgels formed via cold-set gelation were investigated and compared with those of native WPI foams. The effect of CaCl2 concentration and cross-linking time on microgel formation was studied assessing particle size, rheology and foamability. Foams, produced by mechanical whipping, were assessed by overrun, stability and texture. WPI had lower viscosity than the microgels, producing foams with greater overrun. For microgels, higher concentrations of CaCl2 formed smaller particles and decreased microgel viscosity, causing higher overrun. Increasing cross-linking time from 0 to 24 h significantly (P < 0.05) increased G′ and G″ of the microgels, resulting in decreased overrun. Native WPI foams drained within 60 min. In contrast, negligible amounts of liquid drained from microgel foams, which remained stable for >2 years. This demonstrates that WPI microgels can be used as a novel functional application for creating ultra-stable foams for use in the food industry.

Foam-mat Drying of Carrot Juice and Thin Layer Modeling of Drying

Drying of fruit and vegetables are critical step of processing which can be very destructive for nutrients and especially for bioactive compounds. However, novel drying methods like foam-mat drying helps to decrease the drying period and exposure to drying air therefore protect the bioactives against thermal degradation as well as improving final powder quality. The foam-mat drying of carrot juice foams and modelling of experimental drying data with theoretical models has not yet been studied in the literature. In this study, the effects of foam-mat drying at 50, 60 and 70°C on the drying behavior of carrot juice with the addition of 15% egg albumen (EA) and 15% egg albumen+ 10% whey protein isolate (WPI) as foaming agents and thin-layer modeling of the foams at different thicknesses was evaluated. Compared to control sample (only carrot juice), the drying time of the foamed carrot juice was reduced by 25% to 60% depending on the foam thickness and drying temperature. This result was consistent with the effective diffusion coefficients, since the control sample had comparably low values than the 15% EA and 15% EA+10% WPI foams. Among the fitted mathematical models, Midilli et al. had better prediction capacity with the highest adjusted correlation coefficients, the lowest sum of squared error and root mean square error values for every formulation, foam thickness and drying temperatures compared to other theoretical models.

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.

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.

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.

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

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.

The Role of Copper in Protein Foams

Chefs have known that whipping egg white proteins (EWP) in a copper bowl will improve foam stability. The improved stability is attributed to a copper–conalbumin complex or alteration of sulfhydryl reactivity. Whey proteins bind copper and show copper-induced changes in disulfide bonds; therefore, they may also be responsive to whipping in a copper bowl. EWP and whey protein isolate (WPI) solutions were whipped in the presence of 1 mM CuSO4 or in a copper bowl with and without sugar followed by overrun and yield stress measurements and angel food cake formation. Dilational elasticity and surface tension were also measured for WPI solutions. Whipping in a copper bowl or adding 1 mM CuSO4 significantly improved stability of EWP foams while having no effect on WPI foams. Copper caused disulfide-linked dimer formation of β-lactoglobulin and decreased dilational elasticity and surface tension, but these modifications were insufficient to change the bulk properties of foams. The addition of 10 mM CuSO4 to WPI solutions was sufficient to increase foam stability to levels similar to EWP; however, the more stable foams formed less stable cakes. It was concluded that the effect of whipping in a copper bowl on foam properties is mainly dependent on the specific proteins forming the foam.

Comparisons of the foaming and interfacial properties of whey protein isolate and egg white proteins

Whipped foams (10%, w/v protein, pH 7.0) were prepared from commercially available samples of whey protein isolate (WPI) and egg white protein (EWP), and subsequently compared based on yield stress ( τ 0), overrun and drainage stability. Adsorption rates and interfacial rheological measurements at a model air/water interface were quantified via pendant drop tensiometry to better understand foaming differences among the ingredients. The highest τ 0 and resistance to drainage were observed for standard EWP, followed by EWP with added 0.1% (w/w) sodium lauryl sulfate, and then WPI. Addition of 25% (w/w) sucrose increased τ 0 and drainage resistance of the EWP-based ingredients, whereas it decreased τ 0 of WPI foams and minimally affected their drainage rates. These differing sugar effects were reflected in the interfacial rheological measurements, as sucrose addition increased the dilatational elasticity for both EWP-based ingredients, while decreasing this parameter for WPI. Previously observed relationships between τ 0 and interfacial rheology did not hold across the protein types; however, these measurements did effectively differentiate foaming behaviors within EWP-based ingredients and within WPI. Interfacial data was also collected for purified β-lactoglobulin (β-lg) and ovalbumin, the primary proteins of WPI and EWP, respectively. The addition of 25% (w/w) sucrose increased the dilatational elasticity for adsorbed layers of β-lg, while minimally affecting the interfacial rheology of adsorbed ovalbumin, in contrast to the response of WPI and EWP ingredients. These experiments underscore the importance of utilizing the same materials for interfacial measurements as used for foaming experiments, if one is to properly infer interfacial information/mechanisms and relate this information to bulk foaming measurements. The effects of protein concentration and measurement time on interfacial rheology were also considered as they relate to bulk foam properties. This data should be of practical assistance to those designing aerated food products, as it has not been previously reported that sucrose addition improves the foaming characteristics of EWP-based ingredients while negatively affecting the foaming behavior of WPI, as these types of protein isolates are common to the food industry.

Emulsifying and Foaming Properties of a Derivatized Whey Protein Ingredient

A derivatization procedure for the production of a cold gelling whey protein isolate (WPI) has been identified. The cold gelling derivatized whey protein isolate (dWPI) imparted greater viscosity and water holding ability when rehydrated at room temperature than unmodified whey powders. The objective of this study was to further characterize the foaming and emulsifying functionality of the derivatized ingredient. Samples were prepared by hydrating dWPI and WPI in deionized water and, when needed, adjusting the sample pH from 3.4 to 6.8, with 6M NaOH. Yield stress, drainage, and overrun were measured for 6.5% WPI and dWPI foams. Emulsifying capacity and creaming stability were determined for various WPI and dWPI emulsions. The overrun of dWPI foams was approximately 50% lower than WPI foams at pH 3.4 and 6.8. Foams of the derivatized ingredient were significantly more stable than WPI foams. The derivatized ingredient displayed a similar emulsifying capacity to WPI at pH 3.4 and pH 7.0, and differences were not observed in creaming of dWPI and WPI emulsions. Information on foaming and emulsifying ability of derivatized protein ingredients will expedite the development of applications with the novel dairy ingredient, particularly in those foods desiring an all-natural, or all dairy, food label.

Foaming and Interfacial Properties of Polymerized Whey Protein Isolate

ABSTRACT: Yield stresses (τ) of whipped foams prepared from various ratios of native whey protein isolate (WPI) and polymerized whey protein isolate (pWPI) were characterized by means of vane rheometry Yield stress displayed a parabolic response to increasing concentrations of pWPI, peaking at 50%. Foam air phase volume steadily decreased with increasing pWPI content, whereas equilibrium surface tension steadily increased. Dynamic surface tension measurements revealed that native WPI adsorbed much more rapidly than pWPI, presumably because of the latter's larger size. Interfacial dilatational elasticity (E') displayed a parabolic trend with increasing pWPI content, peaking at 50%. This suggested that pWPI coadsorbs with native WPI, bolstering E' of native WPI interfaces. However, too much pWPI caused a weakening of the network. A positive, curvilinear relationship between E' and τ was observed, consistent with a previous observation for WPI foams formed at various pH levels and salt concentrations, further suggesting a general link between these parameters.

Electrostatic effects on the yield stress of whey protein isolate foams

The mechanisms responsible for foam structure are of practical interest within the food industry. The yield stress ( τ) of whey protein isolate (WPI) foams as affected by electrostatic forces was investigated by whipping 10% (w/v) protein solutions prepared over a range of pH levels and salt concentrations. Measurements of foam overrun and model WPI interfaces, i.e. adsorption kinetics as determined via dynamic surface tension and dilatational rheological characterization, aided data interpretation. Interfacial measurements were also made with the primary whey proteins, β-lactoglobulin (β-lg) and α-lactalbumin (α-la). Yield stress of WPI foams was dependent on pH, salt type and salt concentration. In the absence of salt, τ was highest at pH 5.0 and lowest at pH 3.0. The addition of NaCl and CaCl 2 up to 400 mM significantly increased τ at pH 7.0 but not at pH 3.0. Furthermore, at pH 7.0, equivalent molar concentrations of CaCl 2 as compared to NaCl increased τ to greater extents. Salts had minimal effects on τ at pH 5.0. Comparisons with interfacial rheological data suggested the protein’s capacity to contribute towards τ was related to the protein’s potential at forming strong, elastic interfaces throughout the structure. The dynamic surface tension data for β-lg and α-la were similar to WPI, while the interfacial rheological data displayed several noticeable differences.

Properties of whey and egg white protein foams

Abstract Foams made of varying concentrations (2–20% w/v protein) of egg white and whey protein isolate were compared by measuring rheological and microstructural properties. Egg white proteins formed foams with higher yield stress (τ) at lower protein concentrations and less whipping time than whey protein isolate foams. The model of Princen and Kiss [J. Coll. Interf. Sci. 128 (1989) 176] predicts a relationship among τ, surface tension (σ), phase volume (φ), and bubble size (R32). This was supported by τ increasing with φ, and the relationship between τ and φ1/3 becoming more linear as protein concentration increased. However, egg white foams had yield stress values as much as 100 Pa greater than whey protein foams, despite having similar phase volumes, bubble size, and lower surface tensions. The experimentally determined factors, Y(φ), for egg white and whey protein isolate foams were within the range determined by Princen and Kiss [J. Coll. Interf. Sci. 128 (1989) 176] for concentrated emulsions. Egg white foams were different in that the values for Y(φ) increased at lower phase volumes than for whey protein isolate foams or concentrated emulsions. These results suggest that specific proteins contribute to foam τ by some means in addition to altering surface properties.

Effects of Calcium and Magnesium Ions on Aggregation of Whey Protein Isolate and Its Effect on Foaming Properties

The effects of calcium and magnesium ions on time-dependent aggregation of whey protein isolate (WPI) and the influence of the aggregates on the foaming properties of WPI have been studied. Both Mg 2+ and Ca 2+ induced formation of stable colloidal aggregates; the rate of aggregation was slow, and the rate and extent of aggregation were maximum at 0.02-0.04 M concentration. Both foamability and foam stability of WPI foams were affected by the concentration of the divalent ions, as well as incubation time in salt solutions before foaming: Maximum foamability and foam stability were observed when WPI was foamed immediately after the addition of the divalent salts, and they decreased progressively with incubation time, indicating that solution-phase aggregation of WPI adversely affected its foaming properties