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.     

Factors determining the physical properties of protein foams

Protein foams are an integral component of many foods such as meringue, nougat and angel food cake. With all these applications, the protein foam must first obtain the desired level of air phase volume (foamability), and then maintain stability when subjected to a variety of processes including mixing, cutting and heating. Therefore, factors determining foamability and stability to mechanical and thermal processing are important to proper food applications of protein foams. We have investigated the effects of protein type, protein modification and co-solutes on overrun, stability and yield stress. The level of overrun generated by different proteins was: whey protein isolate hydrolysates >whey protein isolate=β-lactoglobulin=egg white>α-lactalbumin. The level of yield stress generated by different proteins was: egg white>whey protein isolate hydrolysates≥β-lactoglobulin>whey protein isolate>α-lactalbumin. Factors that decreased surface charge (pH∼pI or high ionic strength) caused a more rapid adsorption of protein at the air–water interface, generally increased dilatational viscoelasticity and increased foam yield stress. The elastic component of the dilatational modulus of the air–water interface was correlated with foam yield stress. The properties of foams did not predict performance in making angel food cakes. A model for foam performance in angel food cakes is proposed.     

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.     

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.     

Partial Replacement of Egg White Proteins with Whey Proteins in Angel Food Cakes

This study was conducted to investigate the effects of partial replacement of egg white proteins (EWP) with whey protein isolate (WPI) on the appearance, structure, texture, and sensory properties of angel food cakes baked in conventional and microwave/conventional ovens. Factors studied were: 1) replacement of 25% or 50% of EWP with WPI; 2) added xanthan gum (XG), methyl cellulose (MC), cupric sulfate (Cu⁺²) or sodium phosphate (PHOS); and 3) conventional vs microwave/conventional oven baking. EWP replacement cakes without additives were generally inferior to 100% EWP control cakes, whereas EWP replacement cakes with added XG were most similar to 100% EWP control cakes with respect to appearance, texture, and sensory properties and those with added MC exhibited air cell size distributions that most closely resembled control cakes. The other additives and microwave/ conventional vs conventional baking had minor effects on the quality of EWP replacement cakes.     

Effects of Lysozyme, Clupeine, and Sucrose on the Foaming Properties of Whey Protein Isolate and β-Lactoglobulin

Lysozyme and clupeine interacted with β-lactoglobulin to form aggregates. Sucrose reduced the aggregation. The addition of lysozyme (0.5%) to β-lactoglobulin (2.5%) reduced the time required to reach an overrun maximum and increased foam stability and heat stability by 124% and 377%, respectively. Lysozyme (0.5%) also improved overrun (98%), foam stability (114%) and heat stability of the foams (12%) made with whey protein isolate (WPI, 5%). Lysozyme and sucrose further improved the foaming properties of β-lactoglobulin and WPI. The addition of clupeine and sucrose gave similar results. The foaming properties of β-lactoglobulin and WPI with the inclusion of sucrose and lysozyme were superior to those of egg white.     

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.     

Rheological properties of angel food cake made with pH unfolded and refolded egg albumen

Angel food cake was made using egg albumen subjected to the pH-induced unfolded and refolded treatment. The effect of treatment on the rheological properties of angel food cake was investigated. Egg albumen solutions were prepared and pH was adjusted to 1.5, 4.5, 8.5 or 12.5 and then held 60 min to unfold the proteins. After holding, the solutions were readjusted to pH 4.5 or 8.5, and held for 45 min to partially refold the proteins. Egg white foam with sucrose was whipped and flour and the rest of sucrose were folded into the foam. The foam batter was heated in a TA Instrument AR 2000 controlled stress rheometer equipped in a parallel geometry. Samples were heated from 21 °C to 150 °C at a rate of 8.5 °C per min and then cooled down to 21 °C to bake the angel food cake. At 21 °C, oscillatory stress sweep was performed. There was no relationship between the G′ value of angel cake batter and its G′ value at 150 °C. Changes in rheological properties of batters and angel food cakes using different combinations of ingredients were studied. The pH unfolding and refolding procedure led to more rigid final products compared to the controls with egg albumen samples not subjected to pH treatment. Adding sucrose to the flour increased the starch gelation temperature up to 82 °C. Higher protein concentrations resulted in better foams in the cake batter, but the batter made with an intermediate protein concentration produced the most rigid angel food cake. Adding egg albumin did not change gelation temperature of the starch. It appears that incorporation of flour with the egg white foam, leads to about a ten times decrease in the strength of the foam, and a decrease in the gelatinization process of starch after adding sugar, are crucial in forming of an angel food cake texture.     

Influence of protein heat treatment on the continuous production of food foams

The influence of WPI heat treatment on the continuous production of food foams was investigated using a model food including xanthan. The temperature of heat treatment was increased up to 90 °C using a plate heat exchanger; a rotor–stator unit was used for aeration purpose. The aim was to determine the interplay between heat-induced protein denaturation and aggregation, and the process parameters of aeration operation: namely, rotation speed, residence time and operating pressure. Microstructure, texture and stability of 200% overrun foams were analysed. Experimental results demonstrated that foam microstructure, namely overrun and bubble size distribution, was governed by the process parameters of aeration and depended only slightly on thermal treatment. Conversely, foam stability was strongly improved by heat treatment. These trends agreed roughly with results obtained in a batch kitchen mixer, but batch methods remained unable to predict quantitatively the behaviours observed in continuous aeration operation.     

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.     

Heat-induced Changes in Angel Food Cakes Containing Egg-white Protein or Whey Protein Isolate

ABSTRACT: Angel food cakes made from egg white or whey protein foams were compared. Cakes were evaluated based on final volume, dynamic volume change, and rheological transitions during baking. Cake expansion during baking was a function of protein concentration regardless of protein type. Cakes containing whey proteins had a lower ability to prevent collapse once starch gelatinization started during baking. Heat-treating whey proteins or adding xanthan gum increases cake volume, but not to the extent of egg-white proteins. Cakes containing egg-white proteins became more elastic at 60 to 85 °C than those containing whey proteins, indicating physical differences in the heat-set protein foam network associated with protein type.     

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.     

Use of applied air pressure to improve the baking properties of whey protein isolates in angel food cakes

Whey protein isolate (WPI) possesses limited application in angel food cake baking compared to liquid egg white (LEW). This study was conducted to determine whether applying air pressure in the oven during baking would improve the baking properties of WPI in angel food cakes. A special oven was designed for baking at oven air pressures up to 1.5 bar. Control angel food cakes were formulated with LEW (100/0) as its protein source and WPI-containing cakes were formulated with a mixture of 75 mL/100 mL LEW and 25 mL/100 mL WPI solution (75/25) or a mixture of 50 mL/100 mL LEW and 50 mL/100 mL WPI solution (50/50). Cakes were baked at atmospheric air pressure (AP) and at constant applied air pressure (CAP) or variable applied air pressure vs. baking time (VAP) to prevent overexpansion and collapse of WPI-containing cake batter. Cakes 75/25 and 50/50 baked at VAP exhibited improved physical, textural and sensory properties compared to those baked at AP or CAP conditions. Cakes 75/25 baked at VAP compared well with control angel food cakes baked at AP. Although 50/50 cakes baked at VAP were improved slightly over those baked at AP, none of them exhibited satisfactory properties. Therefore, additional research is needed to optimize baking conditions for cakes formulated with less than 75 mL/100 mL LEW.     

Quality characteristics of angel food cake and muffin using lentil protein as egg/milk replacer

Replacement of animal proteins could be interesting for the food industry because it allows long‐term cost savings, among other reasons. Replacing egg/milk protein (50–100 wt%) by lentil protein (LP) was evaluated on angel cake/muffin quality. The replacement did not significantly affect final product volume, neither the muffins nor the angel food cakes. LP did not affect dough formation and contributed to hold crumb structure building an entangled network in both cake products. In addition, angel cakes and muffins containing LP had significantly lower baking loss than the control. Inferior quality for angel cakes and muffins containing LP was observed regarding hardness and chewiness that increased upon storage, compared to the control. For sensory evaluation in angel cakes, appearance of LP formulations showed lower scores than the control, likely due to the change of crumb colour. Other attributes were not significantly impacted by LP presence. For muffins, M‐100‐LPC formulation showed significant differences with the control for most of the attributes, except appearance and flavour. Indeed, consumers preferred muffins with 100% egg/milk protein replacement, which received higher acceptability scores than control. They also appreciated the ‘nutty’ flavour and moisture of angel cake with 50% egg protein replacement. This research suggests that lentil protein can totally or partially substitute egg/milk protein as foam and emulsion stabiliser in cakes, producing products with satisfactory quality.     

Improvement of Foaming Property of Egg White Protein by Phosphorylation through Dry-Heating in the Presence of Pyrophosphate

ABSTRACT:  Egg white protein (EWP) was phosphorylated by dry-heating in the presence of pyrophosphate at pH 4 and 85 °C for 1 d, and the foaming properties of phosphorylated EWP (PP-EWP) were investigated. The phosphorus content of EWP increased to 0.71% as a result of phosphorylation. To estimate the foaming properties of EWP, the foams were prepared by 2 methods: bubbling of the 0.1% (w/v) protein solution and whipping of the 10% (w/w) protein solution with an electric mixer. The foaming power, which was defined as an initial conductivity of foam from 0.1% (w/v) protein solution, was a little higher in PP-EWP than in native EWP (N-EWP), and the foaming stability of PP-EWP was much higher than that of dry-heated EWP (DH-EWP) and N-EWP. The microscopic observation of foams from the 10% (w/w) solution showed that the foams of PP-EWP were finer and more uniform than those of N- and DH-EWP. Although there were no significant differences in the specific gravity and overrun of the foams between PP- and DH-EWP ( P  < 0.05), the specific gravity and overrun of the foams from PP-EWP were smaller and higher, respectively, than that of the foams from N-EWP. The drainage volume was smaller in the foams from PP-EWP than in those from N- and DH-EWP. These results demonstrated that phosphorylation of EWP by dry-heating in the presence of pyrophosphate improved the foaming properties, and that it was more effective for the foam stability than for the foam formation.     

Quality characteristics of egg-reduced pound cakes following WPI and emulsifier incorporation

The effect of partial (50 wt%) or total liquid egg replacement by whey proteins in combination with emulsifiers, i.e. hydroxypropylmethylcellulose (HPMC) and sodium stearoyl-2-lactylate (SSL), on the quality of pound cakes was investigated. Cakes containing whey protein isolate (WPI) solutions of varying concentrations (i.e. 20, 17 and 14% w/v) were first prepared. Complete egg replacement by WPI led to the preparation of cake batter of increased specific gravity as well as to final cake products of inferior quality with regard to volume, texture and hardness increase upon storage, compared to the control. In the case of partial liquid egg replacement by WPI solutions, cakes with acceptable sensory and quality characteristics were obtained, which were further improved following the addition of emulsifiers. During a storage period of four days the egg-reduced cakes exhibited a significantly lower staling rate depending mainly on the concentration of WPI and the presence of emulsifiers. Finally, the analysis of cake microstructure confirmed the positive effect of the co-addition of whey proteins and emulsifiers in egg-reduced cakes. This work made it possible to develop an alternative, egg-reduced cake of satisfactory quality, by using a combination of whey proteins with two common baking additives.     

Effect of dynamic heat treatment on the physical properties of whey protein foams

The influence of dynamically heat-induced aggregates on whey protein foams was investigated as a function of the thermal treatment applied with the aim of determining the optimal temperature for the production of heat-induced aggregates dedicated to foaming. The native protein solutions (2% w/v WPI; 50 mM NaCl) at neutral pH were heat-treated using a tubular heat exchanger between 70 °C and 100 °C. Protein denaturation and aggregation were followed by micro-differential scanning calorimetry, size exclusion chromatography, laser diffraction and dynamic light scattering. The protein solutions were whipped using a kitchen mixer to produce foams. Foam overrun, stability against drainage, texture and bubble size distribution were measured.     

Effect of whey protein concentrate addition on the physical properties of homogenized sweetened dairy creams

The influence on their whipping properties of homogenization at first and second stage pressures of 3.5/1.5 MPa and addition of whey protein concentrate (WPC) powder at three different (0.7, 1.4, and 2.1 wt percentage) concentrations to sweetened and homogenized creams was studied. Homogenization of cream significantly decreased maximum overrun and made the foam microstructure less open, while increasing whipping time, cream and foam lightness (Hunter L -value) and apparent viscosity. It also resulted in a less elastic foam structure with an increased drainage. Addition of WPC decreased the amount of maximum overrun, foam drainage and its lightness in parallel with developing a more compact microstructure. It increased the whipping time, apparent viscosity of unwhipped creams and foams, and resulted in a less elastic foam structure. The apparent viscosity of whipped cream with 2.1 wt percentage WPC, however, was lower than that of whipped cream with 1.4 wt percentage WPC, due most probably to the start up of gel formation at 2.1% WPC concentration in sweetened cream when it was sheared. Fresh foam whipped from sweetened cream with 2.1 wt percentage WPC also tended to have a slightly but not statistically significant lower elastic modulus (G') than fresh foam whipped from sweetened cream with 1.4 wt percentage WPC. This concentration can be considered as the critical value for gel formation in sweetened creams enriched by whey proteins when sheared. This study indicated the potential of WPC powder for reducing foam drainage from whipped homogenized sweetened cream.