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

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.     

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.     

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.     

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.     

High Fructose Corn Syrup: Replacement for Sucrose in Angel Cake

High fructose corn syrup (HFCS) (42% fructose) was used to replace 25, 50, 75 or 100% of the sucrose in angel cakes. Replacement with HFCS of 50, 75 or 100% of sucrose resulted in foams with lower specific gravities; decreased foam beating time; and cakes with lower volume, browner crusts, yellower crumb, firmer texture, and decreased sweetness. Replacement of 25% sucrose with HFCS did not affect greatly the physical measurements or sensory characteristics studied.     

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.     

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.     

Rheology and Oxidative Stability of Whey Protein Isolate-Stabilized Menhaden Oil-in-Water Emulsions as a Function of Heat Treatment

ABSTRACT:  Menhaden oil-in-water emulsions (20%, v/v) were stabilized by 2 wt% whey protein isolate (WPI) with 0.2 wt% xanthan gum (XG) in the presence of 10 mM CaCl₂ and 200 μM EDTA at pH 7. Droplet size, lipid oxidation, and rheological properties of the emulsions were investigated as a function of heating temperature and time. During heating, droplet size reached a maximum at 70 °C and then decreased at 90 °C, which can be attributed to both heating effect on increased hydrophobic attractions and the influence of CaCl₂ on decreased electrostatic repulsions. Combination of effects of EDTA and heat treatment contributed to oxidative stability of the heated emulsions. The rheological data indicate that the WPI/XG-stabilized emulsions undergo a state transition from being viscous like to an elastic like upon substantial thermal treatment. Heating below 70 °C or for less than 10 min at 70 °C favors droplet aggregation while heating at 90 °C or for 15 min or longer at 70 °C facilitates WPI adsorption and rearrangement. WPI adsorption leads to the formation of protein network around the droplet surface, which promotes oxidative stability of menhaden oil. Heating also aggravates thermodynamic incompatibility between XG and WPI, which contributes to droplet aggregation and the accumulation of more WPI around the droplet surfaces as well.     

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.     

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 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.     

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.     

Effects of heating rate and pH on fracture and water-holding properties of globular protein gels as explained by micro-phase separation

The effect of heating rate and pH on fracture properties and held water (HW) of globular protein gels was investigated. The study was divided into 2 experiments. In the 1st experiment, whey protein isolate (WPI) and egg white protein (EWP) gels were formed at pH 4.5 and 7.0 using heating rates ranging from 0.1 to 35 °C/min and holding times at 80 °C up to 240 min. The 2nd experiment used one heating condition (80 °C for 60 min) and probed in detail the pH range of 4.5 to 7.0 for EWP gels. Fracture properties of gels were measured by torsional deformation and HW was measured as the amount of fluid retained after a mild centrifugation. Single or micro-phase separated conditions were determined by confocal laser scanning microscopy. The effect of heating rate on fracture properties and HW of globular protein gels can be explained by phase stability of the protein dispersion and total thermal input. Minimal difference in fracture properties and HW of EWP gels at pH 4.5 compared with pH 7.0 were observed while WPI gels were stronger and had higher HW at pH 7.0 as compared to 4.5. This was due to a mild degree of micro-phase separation of EWP gels across the pH range whereas WPI gels only showed an extreme micro-phase separation in a narrow pH range. In summary, gel formation and physical properties of globular protein gels can be explained by micro-phase separation. PRACTICAL APPLICATION: The effect of heating conditions on hardness and water-holding properties of protein gels is explained by the relative percentage of micro-phase separated proteins. Heating rates that are too rapid require additional holding time at the end-point temperature to allow for full network development. Increase in degree of micro-phase separation decreases the ability for protein gels to hold water.     

Impact of protein self-assemblages on foam properties

The influence of dynamically heat-induced aggregates on whey protein foams was investigated as a function of the thermal treatment applied to WPI using a bubbling technique. The aim was to determine the interplay between the size/shape/proportion of the heat-induced aggregates and the properties of protein foams (formation and stability). Results showed that insoluble protein aggregates were highly branched and cohesive, whereas soluble aggregates were constituted by subunits, associated by hydrophobic bonds and formed by α-La and β-Lg monomers linked by disulfide bridges. Using the bubbling procedure, protein aggregates were shown to slow down significantly foam formation. However, the rate of foam formation remained nearly unchanged for wet foams when the amount of insoluble aggregates was inferior to 5% and when their size remained lower than 100 μm. Similarly, protein aggregates did not seem to affect the destabilisation kinetics of wet foams, regardless of amount, size, shape and proportion.     

Hot-stage Microscopy of Cake Batter Bubbles during Simulated Baking: Sucrose Replacement by Polydextrose

A hot-stage video microscopical technique was developed to study the effects of sucrose replacement by polydextrose (weight for weight basis) on the foam characteristics of cake batters, before and during heating. Polydextrose substitution increased the mean size of air-bubbles in the cake batter and introduced a larger variation in bubble size distribution than the sucrose batter. The differences between sucrose and polydextrose batters on initial bubble size distribution were reflected in expansion rates of bubble populations during heating. The lack of uniformity in the bubble distribution of batters containing polydextrose increased the rate of gas diffusion from small bubbles to larger ones. On heating, the bubble population of sucrose batters expanded more than that of polydextrose substituted batters.     

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.     

Foaming Properties of Lipid-Reduced and Calcium-Reduced Whey Protein Concentrates

The ability of whey protein concentrates (WPC) to form highly expanded and stable foams is critical for food applications such as whipped toppings and meringue-type products. The foaming properties were studied on six experimental and three commercial WPC, manufactured by membrane fractionation processes to contain reduced lipids and calcium. Lipid-reduced WPC had excellent foaming properties. Experimental delipidized WPC MF 0.45 and commercial delipidized WPC E had higher (P < 0.05) foam expansion than egg white protein (EWP). However. WPC B made bv low-pH UF and isoelectric orecinitation did not form a foam. Lipids and ash were the main factors affecting foaming properties.