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.     

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.     

米糠蛋白的起泡特性及其泡沫微观形态

考察pH值和NaCl浓度对米糠蛋白起泡特性及泡沫微观形态的影响,并对二者之间的内在关系进行阐述。结果表明,当米糠蛋白溶液中不添加NaCl、pH?4时起泡能力较差,但泡沫稳定性可达最大值（88.3±7.3）%,而当溶液的pH值偏离4时起泡能力增加,在pH10和12条件下起泡能力分别可达（73.3±0）%和（168.9±10.2）%,泡沫稳定性分别为（74.7±2.5）%和（68.5±2.1）%;另外在米糠蛋白溶液pH值为4和7条件下分别添加1%的NaCl后,可显著提高起泡能力至（77.8±3.8）%和（90.0±5.8）%。米糠蛋白泡沫的微观形态随时间变化规律说明,不同pH值条件下起始阶段气泡的直径大小分布与泡沫稳定性相关,而当添加NaCl后米糠蛋白起泡能力和泡沫稳定性的改变则与气泡数量和平均面积二者的综合效应有关。     

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.     

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.     

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.     

High hydrostatic pressure modification of whey protein concentrate for improved body and texture of lowfat ice cream

Previous research demonstrated that application of high hydrostatic pressure (HHP), particularly at 300 MPa for 15 min, can enhance foaming properties of whey protein concentrate (WPC). The purpose of this research was to determine the practical impact of HHP-treated WPC on the body and texture of lowfat ice cream. Washington State University (WSU)-WPC was produced by ultrafiltration of fresh separated whey received from the WSU creamery. Commercial whey protein concentrate 35 (WPC 35) powder was reconstituted to equivalent total solids as WSU-WPC (8.23%). Three batches of lowfat ice cream mix were produced to contain WSU-WPC without HHP, WSU-WPC with HHP (300 MPa for 15 min), and WPC 35 without HHP. All lowfat ice cream mixes contained 10% WSU-WPC or WPC 35. Overrun and foam stability of ice cream mixes were determined after whipping for 15 min. Ice creams were produced using standard ice cream ingredients and processing. The hardness of ice creams was determined with a TA-XT2 texture analyzer. Sensory evaluation by balanced reference duo-trio test was carried out using 52 vol.nteers. The ice cream mix containing HHP-treated WSU-WPC exhibited the greatest overrun and foam stability, confirming the effect of HHP on foaming properties of whey proteins in a complex system. Ice cream containing HHP-treated WSU-WPC exhibited significantly greater hardness than ice cream produced with untreated WSU-WPC or WPC 35. Panelists were able to distinguish between ice cream containing HHP-treated WSU-WPC and ice cream containing untreated WPC 35. Improvements of overrun and foam stability were observed when HHP-treated whey protein was used at a concentration as low as 10% (wt/wt) in ice cream mix. The impact of HHP on the functional properties of whey proteins was more pronounced than the impact on sensory properties.     

Functional properties of whey proteins as affected by dynamic high-pressure treatment

An ultra high-pressure homogenizer was used to treat whey protein isolate solutions (3%, w/w). The treated solutions (up to 300 MPa) were characterised for both physico-chemical properties (particle size distribution, surface hydrophobicity and structural conformation) and functional properties (solubility, foaming stability and interfacial rheology). Dynamic high-pressure treatment did not affect the conformation of the proteins (determined by micro-calorimetry, size-exclusion chromatography and electrophoretic technique). This treatment dissociated large protein aggregates leading to unmasking of the buried hydrophobic groups without affecting protein solubility. Interactions may then occur between these groups that enhance the viscoelasticity of air-water interfaces (assessed by drop tensiometry) and improve foam stability (evaluated by sparging method). Dynamic high-pressure-treated whey proteins showed better foaming and stabilising properties.     

The significance of critical processing steps in the production of dried egg albumen powder on gel textural and foaming properties

The purpose of the present work was to study the variation in egg albumen functional properties as a function of seven selected processing steps from the initially raw liquid albumen to the final dried egg albumen powder. Albumen samples in six replicates were analysed for dry matter, pH, glucose, triglycerides, albumen gel properties (ie textural stress and Hencky strain, water‐ and protein‐binding capacity and gel colour L*, a*, b*), foaming properties (ie overrun, stability against drainage and bubble breakdown) and surface tension. The gel texture and water‐holding capacity significantly decreased during the processing steps from raw albumen through storage, centrifugation and ion exchange, whereas the final dry‐pasteurisation resulted in increased gel properties. Covalently linked protein polymers formed during the dry‐pasteurisation, as revealed by SDS‐PAGE, may explain this improvement. The foam overrun increased twofold during the three final steps of ultrafiltration, spray‐drying and dry‐pasteurisation compared with the raw albumen; however, the foam stability decreased, ie drainage and foam volume breakdown rates increased. The surface pressure increase was positively correlated with the foam overrun. This paper reveals at which processing steps the control of functional properties of egg albumen powder can take place. Copyright © 2004 Society of Chemical Industry     

Influence of pH on surface properties of aqueous egg albumen solutions in relation to foaming behaviour

The surface properties of aqueous egg albumen protein solutions (0.1 g litre⁻¹) were studied at pH values of 4.8, 7.0, 9.2 and 10.7 and related to foaming behaviour such as bubble size distribution, overrun and drainage. By measurements far from equilibrium of dynamic steady state surface dilation using the overflowing cylinder technique, egg albumen showed ability to slow down surface expansion and to lower the dynamic surface tension. The pH‐effect was small, but at pH 4.8 the film length, at which a motionless surface was created, was longer than at higher pH indicating a somewhat more rigid surface at low pH. Near equilibrium sinusoidal surface area deformation resulted in relatively high moduli of egg albumen, with a significant effect of pH. The surface modulus E showed at pH 4.8 an increase in the course of time, but at higher pH it was constant. Large deformation of egg albumen surface was not destructive, and for all pH values the surface behaved viscoelastic, with highest loss modulus E″ and tan θ values at pH 4.8. Surface deformation frequency sweeps revealed the relaxation processes to be relatively slow at pH 4.8 and faster at pH 7.0–10.7. Foamability measured as overrun of foam as a result of shaking and stirring was highest at pH 4.8 and lowest at pH 10.7. Foam stability against drainage was best at pH 7.0 after 30 min, but at a long‐term scale foam at pH 4.8 was most resistant to drainage. Foam samples were subjected to microscopy and image analysis. The smallest bubbles were found at pH 4.8 (mean diameter 142 µm) and the largest at pH 7.0 (mean diameter 328 µm). In conclusion, the foaming behaviour of an aqueous egg albumen solution at pH 4.8 can be related to dynamic surface properties as follows: the more rigid behaviour of the surface at this pH favours a small bubble size and slow drainage of liquid from the foam. The high overrun at this pH can be explained by a lower dynamic surface tension, but also here film stability during foam making can be promoted by a more rigid liquid surface. © 1999 Society of Chemical Industry     

High hydrostatic pressure modification of whey protein concentrate for improved functional properties

Whey protein concentrate (WPC) has many applications in the food industry. Previous research demonstrated that treatment of whey proteins with high hydrostatic pressure (HHP) can enhance solubility and foaming properties of whey proteins. The objective of this study was to use HHP to improve functional properties of fresh WPC, compared with functional properties of reconstituted commercial whey protein concentrate 35 (WPC 35) powder. Fluid whey was ultrafiltered to concentrate proteins and reconstituted to equivalent total solids (8.23%) as reconstituted commercial WPC 35 powder. Solutions of WPC were treated with 300 and 400 MPa (0- and 15-min holding time) and 600 MPa (0-min holding time) pressure. After HHP, the solubility of the WPC was determined at both pH 4.6 and 7.0 using UDY and BioRad protein assay methods. Overrun and foam stability were determined after protein dispersions were whipped for 15 min. The protein solubility was greater at pH 7.0 than at pH 4.6, but there were no significant differences at different HHP treatment conditions. The maintenance of protein solubility after HHP indicates that HHP-treated WPC might be appropriate for applications to food systems. Untreated WPC exhibited the smallest overrun percentage, whereas the largest percentage for overrun and foam stability was obtained for WPC treated at 300 MPa for 15 min. Additionally, HHP-WPC treated at 300 MPa for 15 min acquired larger overrun than commercial WPC 35. The HHP treatment of 300 MPa for 0 min did not improve foam stability of WPC. However, WPC treated at 300 or 400 MPa for 15 min and 600 MPa for 0 min exhibited significantly greater foam stability than commercial WPC 35. The HHP treatment was beneficial to enhance overrun and foam stability of WPC, showing promise for ice cream and whipping cream applications.     

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.     

复合米糠蛋白-卵白蛋白的起泡特性及相关机理分析

考察复合米糠蛋白（rice bran protein,RBP）-卵白蛋白（ovalbumin,OVA）的起泡特性,并分析在特定pH值与NaCl浓度下溶液与泡沫中不同蛋白质的物化性质,以阐述两种蛋白之间相互作用对起泡特性的影响。结果表明,在pH 4.0条件下,两种蛋白质在起泡能力上可以产生协同作用,且当RBP-OVA质量比为3:1时,添加1% NaCl后RBP-OVA复合蛋白的起泡能力和泡沫稳定性均显著增加;而在pH 7.0、无NaCl的情况下两种蛋白在起泡特性上没有表现出特别明显的协同作用,当添加1% NaCl后二者在起泡能力方面反而表现出一定的拮抗作用。通过对pH 4.0、1% NaCl条件下溶液与泡沫中蛋白质的物化性质进行分析可知,因两种蛋白质在物化性质方面具有一定的互补性,可通过蛋白质之间的相互作用从不同的物化性质角度改善RBP-OVA复合蛋白的起泡能力与泡沫稳定性。     

Micro-scale Method for Determining Foaming Properties of Protein

A 5% protein suspension (4 mL) was whipped in a modified 50-mL centrifuge tube using a tissumizer equipped with a flat-bottom generator. Drainage time at 50% liquid weight and the weight of the foam formed/unit volume were used for calculating foam stability and foam overrun, respectively. The foaming properties of a variety of milk proteins were determined using this method. This method distinguished differences in foaming properties among the proteins. Values for overrun confirmed published results. Compared with standard methods, this method required much less sample (about 1/20) and less measuring time (about 1/5 to 1/10).     

Surface Properties of Heat‐Induced Soluble Soy Protein Aggregates of Different Molecular Masses

Suspensions (2% and 5%, w/v) of soy protein isolate (SPI) were heated at 80, 90, or 100 °C for different time periods to produce soluble aggregates of different molecular sizes to investigate the relationship between particle size and surface properties (emulsions and foams). Soluble aggregates generated in these model systems were characterized by gel permeation chromatography and sodium dodecyl sulfate‐polyacrylamide gel electrophoresis. Heat treatment increased surface hydrophobicity, induced SPI aggregation via hydrophobic interaction and disulfide bonds, and formed soluble aggregates of different sizes. Heating of 5% SPI always promoted large‐size aggregate (LA; >1000 kDa) formation irrespective of temperature, whereas the aggregate size distribution in 2% SPI was temperature dependent: the LA fraction progressively rose with temperature (80→90→100 °C), corresponding to the attenuation of medium‐size aggregates (MA; 670 to 1000 kDa) initially abundant at 80 °C. Heated SPI with abundant LA (>50%) promoted foam stability. LA also exhibited excellent emulsifying activity and stabilized emulsions by promoting the formation of small oil droplets covered with a thick interfacial protein layer. However, despite a similar influence on emulsion stability, MA enhanced foaming capacity but were less capable of stabilizing emulsions than LA. The functionality variation between heated SPI samples is clearly related to the distribution of aggregates that differ in molecular size and surface activity. The findings may encourage further research to develop functional SPI aggregates for various commercial applications.     

苦杏仁蛋白的功能特性

采用稀盐溶液浸提及等电点盐析相结合的方法提取制备苦杏仁蛋白,研究pH值、NaCl浓度、蛋白质量浓度和温度等因素对苦杏仁蛋白功能特性(溶解性、持水性、吸油性、乳化性及乳化稳定性、起泡性及起泡稳定性)的影响。结果表明：在等电点pI附近时,苦杏仁蛋白的溶解性、持水性、乳化性及乳化稳定性、起泡性最差;在较低NaCl浓度范围内(0～0.8mol/L)提高NaCl浓度可促进蛋白溶解性、乳化性及乳化稳定性、起泡性及起泡稳定性的提高,而较高的NaCl浓度对蛋白功能特性提高具有抑制作用;当蛋白质量浓度达到一定水平时(3～4g/100mL),蛋白功能特性(乳化性及乳化稳定性、起泡性及起泡稳定性)提高趋于平缓;在适宜的温度范围内,提高温度可有效提高苦杏仁蛋白各项功能特性,但当温度继续上升,各项功能特性持续降低。     

Effects of sucrose and sodium chloride on foaming properties of egg white proteins

Egg white proteins are extensively utilised in the food industry as foaming agents. A number of factors, singly or in combination, can affect the foaming characteristics of egg albumen. In this study, egg white protein solutions heated at various temperatures in the presence of variable concentrations of sucrose and NaCl were whipped for different periods of time. All factors had a significant impact on the foaming properties of egg albumen. Increasing NaCl content and whipping time enhanced protein adsorption at the air–water interface. The presence of sucrose delayed foam formation but contributed to the stability of the aerated system. Controlled denaturation of the protein solutions induced by mild heat treatment enhanced the foaming properties of egg white proteins. This data indicates that the foaming properties of egg white proteins can be manipulated by altering the effect of extrinsic factors in order to achieve optimal formulations for food industrial applications.     

羊肝蛋白稳定性及NaCl质量分数对其功能特性的影响

采用差式扫描量热法、激光粒径分布仪等仪器分析法研究了羊肝蛋白的稳定性,同时研究了NaCl质量分数(0.0%,1.8%,3.6%)对羊肝蛋白的乳化性与起泡性等功能特性及分子量分布和表面疏水性的影响。结果表明:随着NaCl质量分数的增加,水溶性羊肝蛋白(Water soluble liver proteins,WSLP)和盐溶性羊肝蛋白(Salt soluble liver proteins,SSLP)的表面疏水性也增加;SSLP的变性温度为87.9℃,高于WSLP的变性温度(74.4℃),表现出较好的热稳定性;WSLP的粒径分布较为集中,且电位绝对值小于SSLP;WSLP和SSLP均显示出良好的乳化性能和泡沫稳定性,NaCl质量分数的增加降低了WSLP的乳化性能,而对SSLP的乳化性能则没有明显影响。NaCl质量分数为1.8%时可提高WSLP和SSLP的起泡能力,而且不会影响其泡沫稳定性;而NaCl质量分数(3.6%)的进一步增加会降低起泡能力和泡沫稳定性。     

High hydrostatic pressure modification of whey protein concentrate for use in low-fat whipping cream improves foaming properties

Whey is the inevitable by-product of cheese production. Whey can be incorporated into a variety of foods, but little has been done to investigate its suitability in whipping cream. The objective of this work was to evaluate the foaming properties of selected low-fat whipping cream formulations containing whey protein concentrate (WPC) that did or did not undergo high hydrostatic pressure (HHP) treatment. Fresh whey was concentrated by ultrafiltration, pasteurized, and standardized to 8.23% total solids and treated with HHP at 300 MPa for 15 min. Viscosity, overrun, and foam stability were determined to assess foaming properties. Sensory evaluation was conducted with 57 panelists using a duo-trio difference test. The optimal whipping time for the selected formulations was 3 min. Whipping cream containing untreated WPC and HHP-treated WPC resulted in greater overrun and foam stability than the control whipping cream without WPC. Panelists distinguished a difference between whipping cream containing untreated WPC and whipping cream containing HHP-treated WPC. High hydrostatic pressure-treated WPC can improve the foaming properties of low-fat whipping cream, which may justify expansion of the use of whey in whipping cream and application of HHP technology in the dairy industry.     

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

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