Standardized Procedure for Measuring Foaming Properties of Three Proteins, A Collaborative Study

A collaborative study involving nine laboratories was conducted over four years to evaluate a rapid, simple and reliable whipping method for measuring overrun and foam stability. Effectiveness of the method was assessed by measuring the characteristics of foams formed by three protein solutions (5%): sodium caseinate, milk protein isolate, and egg white protein; identifying and systematically eliminating sources of variability. Major sources of variability were protein dispersing technique, the mixer, and the care exercised by the operator during sampling and weighing. The method detected differences in foam stability between egg white, casein and milk protein isolate (pooled SD = 4.5) using different mixers.     

A Method for the Measurement of Foam Formation and Stability

A whipping method for the measurement of overrun and foam stability was developed. Using this method the characteristic foams formed by the following proteins were studied: sodium caseinate, milk protein isolate and whey protein. The method was able to detect differences between foams produced by different proteins. The effects of copper sulfate and proteose-peptone on egg white foams were studied to show the reliability of the method. It was demonstrated that the addition of ImM copper sulfate stabilized (p < 0.05) foams made from both fresh and powdered egg white. Addition of proteose-peptone (0.05% and 0.1%) reduced the overrun and destabilized egg white foams.     

不同打发状态蛋清泡沫及其凝胶特性的比较

蛋清具有良好的起泡性和凝胶性,其在充气食品中具有难以取代的地位。为研究不同状态蛋清泡沫凝胶的理化性质,该文在室温条件下以恒定搅拌速率（980 r/min）制备了不同打发状态（打发时间为0、50、70和90 s）的蛋清泡沫,并测定了蛋清泡沫的理化特性。随后将不同打发时间的蛋清泡沫加热固化,制备了蛋清泡沫凝胶,通过显微观察、色度、质构和流变分析考察了蛋清泡沫凝胶的特性。实验结果表明,在恒定的搅拌速率下蛋清泡沫的气泡状态会随打发时间的变化而变化。适当延长打发时间,有利于形成比重较低的（0.16～0.17）、具有高起泡性和泡沫稳定性的固态泡沫。打发70 s的蛋清泡沫（蛋清泡沫呈小弯钩状,比重为0.165）稳定性最佳,且经加热固化后,该蛋清泡沫凝胶的亮度（L*=90.28）显著升高,硬度（27.69 g）和弹性（0.78 mm）显著降低（P<0.05）,凝胶性质优良。结果揭示了蛋清泡沫的流变学性质能显著影响蛋清泡沫及其凝胶的性能,为蛋清泡沫在充气食品中的应用提供了理论参考。     

Characterization of Apple Juice Foams for Foam-mat Drying Prepared with Egg White Protein and Methylcellulose

ABSTRACT: Intrinsic stability and rheological properties of apple juice foams for foam mat drying were studied. Foams were prepared from clarified apple juice by adding various concentrations of 2 foaming agents of different nature: a protein (egg white at 0.5%, 1%, 2%, and 3% w/w) and a polysaccharide (methylcellulose at 0.1%, 0.2%, 0.5%, 1%, and 2% w/w), and whipping at different times (3, 5, and 7 min). In general, egg white foams were less stable but showed a higher degree of solidity (stronger structures), higher foaming capacity, and smaller bubble average diameter than methylcellulose foams. Foam stability increased with increasing concentrations of either methylcellulose or egg white. Increasing whipping times increased the stability of egg white foams only. Stability parameters (maximum drainage and drainage half-time) were correlated in terms of rheological parameters of the continuous phase (consistency index and apparent viscosity at 30/s, respectively). The correlations ( R ²= 0.766 and 0.951, respectively) were considered acceptable because they were independent of whipping time and foaming agent nature and concentration. Results on foam rheology obtained by dynamic and vane tests were in agreement, but the latter method was more sensitive. Optimal concentrations to obtain the most solid foams (0.2% methylcellulose and 2% to 3% egg white, respectively) were the same concentrations required for maximum foaming capacity. Based on this observation and previous models, an empirical expression was proposed to predict the degree of solidity (in terms of inverse phase angle and yield stress) only as a function of foam structural properties (air volume fraction and average bubble size). The model proved to be satisfactory to fit experimental results ( R ²= 0.848 and 0.975, respectively), independently of whipping time, foaming agent nature and concentration.     

CERTAIN FUNCTIONAL PROPERTIES OF SUNFLOWER MEAL PRODUCTS

Certain functional properties including water absorption, fat absorption, emulsification, whippability and foam stability were determined on the sunflower flour, protein concentrates and isolate. The results were also compared to those obtained on soy products. Data on water and fat absorption studies suggest that soy products are more hydrophilic in nature while sunflower material exhibited greater lipophilic properties than the soy products. Emulsification tests showed that sunflower flour was superior to all other soy and sunflower products. In general, whipping properties of soy and sunflower isolates were similar, while less whippability was observed for the soy flour and protein concentrates. Whipped foams produced by soy and sunflower protein isolates and sunflower flour were more stable than soy flour, soy and sunflower protein concentrates.     

Effects of soy protein isolate and egg white solids on the physicochemical properties of gluten-free bread

Gluten-free formulations are often supplemented with proteins to improve their quality. To determine the effects of alternative proteins on a hydroxypropyl methylcellulose (HPMC)-treated gluten-free dough system, soy protein isolate was added at 1%, 2% and 3% while egg white solids were investigated at 5%, 10% and 15%. The formulated doughs were analysed using thermoanalytic and rheological techniques to determine the role of water and subsequent flow behaviour upon hydrocolloid addition. The baked loaves were measured for specific loaf volume and tensile strength to determine bread quality. The addition of soy protein isolate and egg white solids (5% and 10%) reduced dough stability by suppressing HPMC functionality, reducing available water, weakening HPMC interactions with the starch matrix and reducing foam stability. At 15% addition, egg white solids became the primary protein scaffolding in the dough and overcame negative interactions with HPMC, improving the loaf volume. However, this formulation may need further optimisation to meet full consumer acceptability.     

Improving Foaming Properties of Yolk-Contaminated Egg Albumen by Basic Soy Protein

ABSTRACT:  Yolk contamination of egg white is a common problem in the egg breaking industry. Foaming properties of egg white protein are affected by such contamination, but proteins of basic nature may restore the foaming properties of the yolk-contaminated egg white protein. The purpose of this study was to chemically modify a soy protein, that is, to esterify the acidic groups on the protein and to study the potential of such modified protein in improving foaming. We showed that the modification changed the isoelectric point of soy protein isolate (SPI) from 4.5 to about 10. Sonication was proven to be a very effective means to redisperse the methanol-denatured soy protein during reaction, as shown by the improved solubility profile. Such modified basic protein, that is, the sonicated-modified SPI (SMSPI), when added to the yolk-contaminated (at 0.4% level, as-is basis) egg white, gave significantly improved foaming properties. We have shown that the slight change in pH due to the addition of SMSPI was not the reason for improved foaming performance; instead, the modified protein itself was the main reason for such improvement. Addition of SMSPI increased the foaming performance of both pure egg white and yolk-contaminated egg white. SMSPI consistently performed better than the unmodified SPI for improving foaming. Addition of SMSPI (16%, based on dry egg white, and 1.6% based on liquid egg white) fully restored foam expansion and foam liquid stability of 0.4% yolk-contaminated egg white, and it even out-performed the foaming of pure white protein. Therefore, a feasible solution to restore the foaming properties of yolk-contaminated egg white has been identified. It is expected that such modified SPI can be used as an additive or ingredient in foaming formulation, especially when the egg white protein is suspected of lipid contamination.     

Foaming Properties of Proteins as Affected by Concentration

Commercial sodium caseinate and whey protein isolate were evaluated at protein concentrations 0.25 to 16% with ovalbumin solutions as reference. Logarithmic models were developed to express the effect of protein concentration on foam expansion and serum drainage. The kinetics of gas release from milk protein-stabilized foams followed a three-phase pattern. Low foam collapse rates were observed in initial and final phases while rapid collapse occurred during the transition phase. No transition was observed for ovalbumin-stabilized foams. Globally, foam collapse rate increased with increasing protein concentration. Apparent viscosity of protein-stabilized foams increased with concentration to a maximum; beyond which, a reverse trend was observed. Maximum viscosities of milk protein foams were at concentrations & lt;0.5%, while ovalbumin foams showed maximum viscosity around 2% protein.     

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.     

A comparison of the buttermilk solids functional properties to nonfat dried milk,soy protein isolate,dried egg white,and egg yolk powders

Physicochemical (i.e., sulfhydryl group, protein, and total solubility) as well as functional properties (i.e., water-holding and fat-absorption capacity, foaming and emulsification capacity, and stability) of commercial buttermilk solids (BMS) were compared to nonfat dried milk, soy protein isolate, and dried egg yolk and egg white powders on an equivalent protein basis. BMS showed limited functional properties in water-holding capacity (0.75 g water/g protein) and fat-absorption capacity (1.2 g of oil/g of protein), and foaming capacity (0.5 ml of foam/ml of solution) and stability. However, emulsifying capacity and stability of BMS was not significantly different from other dried protein powders. Results indicated that 0.9 g of protein (approximately 0.45%, wt/vol, concentration) from BMS was needed to emulsify a maximum oil concentration of 50% in water at temperatures up to 50 degrees C. Denaturation of protein, quantified by free sulfhydryl groups, was a critical factor affecting the functionality of BMS and all other protein powders tested. The milk fat globule membrane present in BMS did not enhance either emulsifying capacity or stability.     

大豆分离蛋白发泡剂的泡沫染色

采用搅打发泡的方法研究了大豆分离蛋白浓度、pH值、表面活性剂对大豆分离蛋白泡沫性能的影响;选取多个有利于泡沫性能的因素,以大豆蛋白泡沫作为染料载体,选用活性黄染料对纯棉织物进行了泡沫染色的探究,测试了染色织物的匀染性、拉伸性和色牢度。结果表明,在pH值为7,大豆分离蛋白质量分数2%,十二烷基硫酸钠(SDS)质量浓度1g/L,Tween-80质量浓度2g/L的条件下,泡沫性能最优。泡沫染色织物的匀染性、色牢度均优于常规水浴染色,织物强力提高。     

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.     

Heat Denaturation of the Ovomucin-Lysozynie Electrostatic Complex-A Source of Damage to the Whipping Properties of Pasteurized Egg White

SUMMARY– A longer whip time is usually required to obtain a meringue of the same specific gravity from pasteurized egg white as from unpasteurized egg white. We have determined the rate at which this change in whipping properties occurs as a function of heating time and pH. The rate of damage is minimal at neutral pH. The activation energy for whipping property damage at pH 7.5 is 140 kcal. Experiments in which either ovomucin or lysozyme concentration of egg white was increased and decreased showed that the reaction producing damage to the whipping properties is first order with respect to both ovomucin and lysozyme concentration. Since an increase of 0.33 in the ionic strength of egg white produces a ten-fold decrease in the rate of whipping property damage, the reactants are probably present as the ovomucin-lysozyme electrostatic complex. The product appears to be an irreversibly denatured ovomucin-lysozyme aggregate or network. Removal of the product restores the whipping properties of the egg white. The whipping property damage is a decrease in the mechanical stability of the foam. For this reason a longer time is needed to whip pasteurized egg white to a satisfactory meringue. Whipping aids such as triethyl citrate or triethyl phosphate compensate for the damage to the whipping properties, but do not appear to reverse the reaction producing damage to the whipping properties of the egg white.     

Interfacial and foaming properties of soy protein and their hydrolysates

The objective of the work was to study the impact of soy protein hydrolysis on foaming and interfacial properties and to analyze the relationship between them. As starting material a sample of commercial soy protein isolate was used (SP) and hydrolysates were produced by an enzymatic reaction, giving hydrolysates from 0.4% to 5.35% degree of hydrolysis (DH).In this contribution we have determined foam overrun (FO), stability against liquid drainage and foam collapse, and the apparent viscosity of foams produced by a whipping method. The surface properties determined were the adsorption isotherm and surface dilatational properties of two hydrolysates (2 and 5.35% DH, H1 and H2 respectively).The hydrolysis of soy proteins increased the surface activity at bulk concentrations where SP adopts a condensed conformation at the monolayer. At concentrations where it adopts a more expanded conformation a very low degree of hydrolysis (H1) also promoted the enhancement of surface activity. However, at 5.35% degree of hydrolysis (H2) the surface activity decreased. Moreover, H2 presented lower surface activity than H1 at every bulk concentration.The hydrolysis increased the elastic component of the dilatational modulus and decreased phase angle of films at bulk concentrations below that corresponding to the collapse of SP monolayer (2% bulk protein).SP hydrolysis increased foam overrun and the stability against drainage that could be related to increased surface activity of protein hydrolysates. However, the collapse of foams was promoted by hydrolysis and could be ascribed to a decrease of the relative viscoelasticity (higher phase angle) of surface films.The results point out that a low degree of hydrolysis (2–5%) would be enough to improve the surface activity of SP, decrease foam drainage and maintaining a considerable viscoelasticity of the surface films to retard foam collapse.     

Effects of foaming agents and foam density on drying characteristics and textural property of banana foams

The technique of foaming has proved effective in creating a porous structure, which is an important requirement for crisp food. Foam density and the type of foaming agent indeed play a key role in determining the drying kinetics and textural property of the foamed food. The influences of the foam density and the types of foaming agents on the moisture diffusivity as well as the quality in terms of microstructure, texture and volatile losses of banana foams were therefore investigated. Three foaming agents, i.e., fresh egg albumen (EA), soy protein isolate (SPI) and whey protein concentrate (WPC) were used. The experimental results showed that WPC banana foam could retain more open structure during drying. This morphology provided less shrinkage and led to higher values of the effective diffusivity as compared with that of SPI and EA banana foams. In terms of the textural properties, WPC and EA banana foams were spongy and less crisp than SPI banana foam. Samples with lower foam densities exhibited higher values of the effective diffusivity, smaller hardness and lower crispness than those with higher foam densities. The losses of volatile substances were substantial during all processing steps, but the major losses were during the foaming step.     

Influence of pasteurisation,freezing and storage on properties of egg products made from eggs stored for 7 and for 28 days

The influence of the age of eggs before breaking, pasteurisation, freezing and storage at —17°c and the method of whipping on the foaming power, foam stability and viscosity of liquid egg albumen and liquid whole egg were studied. The foaming power (relative volume of foam) and the foam stability were determined with the aid of a Hobart whipping machine N 50. The viscosity was measured with a Brookfield viscometer type LV. Liquid egg albumen from 28-day-old eggs had a better foaming power with better stability than that from 7-day-old eggs. The viscosity of the liquid egg albumen from 7-day-old eggs was higher than that from 28-day-old eggs. When pasteurised with aluminium sulphate, the foaming power and the foam stability of all liquid egg albumens increased. When pasteurised without aluminium sulphate, both properties increased for liquid egg albumen from 7-day-old eggs and decreased for that from 28-day-old eggs. During the first weeks of storage of the egg white at −17°C, the foaming power, foam stability and viscosity gradually increased. Whipping for 1 min at setting 2 and 2 mill at setting 3 yielded a higher foaming power and a higher stability of the foam than whipping for 1 min at setting 2 and then a few minutes at position 3 until visually the optimum had been reached. These differences were significant (P < 0·01) for the foaming power and foam stability. There was no significant difference between the foaming power and stability of the foam for liquid whole egg prepared from 7-day-old eggs and that from 28-day-old eggs. Pasteurisation (3 min at 65°c) gave a decrease in foaming power and foam stability and an increase in viscosity. These differences were significant (P < 0·07) for the foaming power and viscosity. Storage resulted in lower foaming power and higher foam stability. In this case, higher viscosity values were also obtained. The whipping method did not give any significant differences.     

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.     

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.     

Measurement of the Yield Stress of Protein Foams by Vane Rheometry

The yield stresses of protein foams made from varying protein types (spray dried egg white and whey protein isolate), protein concentrations, whip times, and mixer models were evaluated using vane rheometry. Two methods of analysis (point and slope methods) were investigated. Yield stress values determined by slope and point methods were similar for egg white protein foams but did not agree in the analysis of whey protein foams. Point method values were very reproducible in all foams tested. Egg white protein solutions formed stiffer foams more rapidly and at lower protein concentrations than foams made from whey protein isolate. Vane rheometry was shown to be a reliable method of determining yield stress in protein foams.     

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.