Modification of functional properties of egg‐white proteins

Egg‐white proteins are extensively utilised as food ingredients due to their unique functional properties. Several attempts have been made in order to improve the functional properties of egg‐white proteins and to identify the optimal formulations for unique food products. Experimental data proves that controlled denaturation of egg‐white proteins can have a beneficial impact on various functional applications in the food industry such as emulsifying ability, heat stability, gelation. This review describes the effect of heat‐induced denaturation on protein structure and functionality. Studies on the impact of Maillard reaction, which aim to elucidate the structure‐function relationship of egg‐white proteins, are presented. A novel approach which could be the basis for the development of new methods aiming to improve the functional properties of egg‐white proteins is also discussed.     

Effects of temperature on food proteins and its implications on functional properties

This article surveys the knowledge in the area of protein structure and chemistry of denaturation prior to an indepth review of the effects of heat on soy, milk, and egg proteins. It also reviews the methods available to assess denaturation of proteins. Protein denaturation is an ambiguous phenomenon and the consequences of denaturation on the functional properties of proteins is further confounded by this ambiguity. For each of the three food proteins, the known chemistry of individual proteins is reviewed followed by observations made on changes induced by heat in each protein group. Food proteins are not pure entities and purification and physicochemical characterization of various components of the food proteins have not been thoroughly investigated. Further, food is a complex milieu of water, fat, carbohydrate, vitamin, minerals, etc. along with proteins, and processing affects not only each individual component in the food but also the nature and intensity of intercomponent interactions in a food.     

White lupin protein isolate as a foaming agent

 In this work the foaming ability of white lupin protein isolates was investigated in order to evaluate the potential use of these isolates as functional additives in food products and to find a vegetable alternative to egg-white foams. Lupinus albus protein isolate, modified in order to improve its foaming ability, was tested. Thermal denaturation, chemical treatment (acylation) and enzymatic hydrolysis (with vegetal proteases) were used, and the best results were obtained by using an optimised thermal denaturation method. A series of additives was tried out in order to further improve foam stability; xanthan gum gave the best results. Prior heat treatment of the protein and the conditions under which foam was generated were optimised using response surface methodology. Texture and microstructure of the optimised lupin foam were objectively evaluated. The lupin foam, when boiled in water for 5 min became very similar in texture and microstructure to uncooked egg-white foams. This shows, therefore, some promise as a substitute of the latter for products like fruit and chocolate "mousses", with the advantage of being able to withstand heat treatments. Received: 30 October 1997 / Revised version: 21 January 1998     

Proteins of Amaranth (Amaranthus spp.), Buckwheat (Fagopyrum spp.), and Quinoa (Chenopodium spp.): A Food Science and Technology Perspective

There is currently much interest in the use of pseudocereals for developing nutritious food products. Amaranth, buckwheat, and quinoa are the 3 major pseudocereals in terms of world production. They contain high levels of starch, proteins, dietary fiber, minerals, vitamins, and other bioactives. Their proteins have well‐balanced amino acid compositions, are more sustainable than those from animal sources, and can be consumed by patients suffering from celiac disease. While pseudocereal proteins mainly consist of albumins and globulins, the predominant cereal proteins are prolamins and glutelins. We here discuss the structural properties, denaturation and aggregation behaviors, and solubility, as well as the foaming, emulsifying, and gelling properties of amaranth, buckwheat, and quinoa proteins. In addition, the technological impact of incorporating amaranth, buckwheat, and quinoa in bread, pasta, noodles, and cookies and strategies to affect the functionality of pseudocereal flour proteins are discussed. Literature concerning pseudocereal proteins is often inconsistent and contradictory, particularly in the methods used to obtain globulins and glutelins. Also, most studies on protein denaturation and techno‐functional properties have focused on isolates obtained by alkaline extraction and subsequent isoelectric precipitation at acidic pH, even if the outcome of such studies is not necessarily relevant for understanding the role of the native proteins in food processing. Finally, even though establishing in‐depth structure–function relationships seems challenging, it would undoubtedly be of major help in the design of tailor‐made pseudocereal foods.     

Modifying the Functional Properties of Egg Proteins Using Novel Processing Techniques: A Review

Egg proteins can be used in a wide range of food products, owing to their excellent foaming, emulsifying, and gelling properties. Another important functional property is the susceptibility of egg proteins to enzymatic hydrolysis, as protein digestion is closely related to its nutritional value. These functional properties of egg proteins are likely to be changed during food processing. Conventional thermal processing can easily induce protein denaturation and aggregation and consequently reduce the functionality of egg proteins due to the presence of heat‐labile proteins. Accordingly, there is interest from the food industry in seeking novel nonthermal or low‐thermal techniques that sustain protein functionality. To understand how novel processing techniques, including high hydrostatic pressure, pulsed electric fields, ionizing radiation, ultraviolet light, pulsed light, ultrasound, ozone, and high pressure homogenization, affect protein functionality, this review introduces the mechanisms involved in protein structure modification and describes the structure–functionality relationships. Novel techniques differ in their mechanisms of protein structure modification and some have been shown to improve protein functionality for particular treatment conditions and product forms. Although there is considerable industrial potential for the use of novel techniques, further studies are required to make them a practical reality, as the processing of egg proteins often involves other influencing factors, such as different pH and the presence of other food additives (for example, salts, sugar, and polysaccharides).     

A study of the baking process by differential scanning calorimetry

The denaturation of the components of a baked product such as cake or bread can be observed under simulated baking conditions by differential scanning calorimetry. When starch or protein denaturation occurs, an increased flow of heat shows the temperature range over which that process takes place. Experimental results are presented for angel cake. In the absence of sucrose, the egg-white proteins are denatured predominantly near 65 and 85°C. For wheat flour, starch denaturation is observed near 65°C, and protein denaturation over a broad range from 80 to 110°C. In the presence of the concentration of sucrose used in a standard batter, both the starch and the major portion of the egg-white proteins are denatured near 95°C, at approximately the maximum temperature attained by the cake when it reaches maximum volume in the oven. Apparently, the main function of sucrose in an angel cake is to raise the denaturation temperature ranges of the starch and protein. Decreasing the amount of sucrose in batters designed for high altitudes causes denaturation of starch and protein at the lower maximum temperatures attained at those altitudes. This assures formation of a structural framework of denatured starch and protein which will not allow the cake to “fall” after it attains its maximum volume.     

Modification methods and applications of egg protein gel properties: A review

Egg protein (EP) has a variety of functional properties, such as gelling, foaming, and emulsifying. The gel characteristics provide a foundation for applications in the food industry and research on EP. The proteins denature and aggregate to form a dense three-dimensional gel network structure, with a process influenced by protein concentration, pH, ion type, and strength. In addition, the gelation properties of EP can be altered to varying degrees by applying different treatment conditions to EP. Currently, modification methods for proteins include physical modification (heat-induced denaturation, freeze–thaw modification, high-pressure modification, and ultrasonic modification), chemical modification (glycosylation modification, phosphorylation modification, acylation modification, ethanol modification, polyphenol modification), and biological modification (enzyme modification). Pidan, salted eggs, egg tofu, and other egg products have unique sensory properties, due to the gel properties of EP. In accessions, EP has also been used as a new ingredient in food packaging and biopharmaceuticals due to its gel properties. This review will further promote EP gel research and provide guidance for its full application in many fields.     

Food protein-based materials as nutraceutical delivery systems

Incorporation of bioactive compounds–such as vitamins, probiotics, bioactive peptides, and antioxidants etc.–into food systems provide a simple way to develop novel functional foods that may have physiological benefits or reduce the risks of diseases. As a vital macronutrient in food, proteins possess unique functional properties including their ability to form gels and emulsions, which allow them to be an ideal material for the encapsulation of bioactive compounds. Based on the knowledge of protein physical–chemistry properties, this review describes the potential role of food proteins as substrate for the development of nutraceutical delivery systems in the form of hydrogel, micro-, or nano- particles. Applications of these food protein matrices to protect and delivery-sensitive nutraceutical compounds are illustrated, and the impacts of particle size on release properties are emphasized.     

Physical effects upon whey protein aggregation for nano-coating production

Production of edible nanostructures constitutes a major challenge in food nanotechnology, and has attracted a great deal of interest from several research fields — including (but not limited to) food packaging. Furthermore, whey proteins are increasingly used as nutritional and functional ingredients owing to their important biological, physical and chemical functionalities. Besides their technological and functional characteristics, whey proteins are generally recognized as safe (GRAS). Denaturation and aggregation kinetics behavior of such proteins are of particular relevance toward manufacture of novel nanostructures possessing a number of potential uses. When these processes are properly engineered and controlled, whey proteins may form nanostructures useful as carriers of bioactive compounds (e.g. antimicrobials, antioxidants and nutraceuticals). This review discusses the latest advances in nano-scale phenomena involved in protein thermal aggregation aiming at formation of bio-based nano-coating networks. The extent of aggregation is dependent upon a balance between molecular interactions and environmental factors; therefore, the impact of these conditions is addressed in a critical manner. A particular emphasis is given to the effect of temperature as long as being one of the most critical variables. The application of moderate electric fields (MEF), an emergent approach, as such or combined with conventional heating is considered as it may inhibit/prevent excessive denaturation and aggregation of whey proteins — thus opening new perspectives for development of innovative protein nanostructures (i.e. nano-coatings). A better understanding of the mechanism(s) involved in whey protein denaturation and aggregation is crucial as it conveys information relevant to select methods for manipulating interactions between molecules, and thus control their functional properties in tailor-made applications in the food industry.     

Effect of denaturation during extraction on the conformational and functional properties of peanut protein isolate

Peanut protein isolate (PPI) was extracted by alkali dissolution and acid precipitation from defatted peanut flour. The effects of extraction conditions on the denaturation and functional properties of PPI were investigated. In comparison with native peanut protein (NPP) which was extracted by ammonium sulfate, the PPI extracted by alkali dissolution and acid precipitation had a higher extent of denaturation. Arachin was affected more easily by the extraction process than conarachin and led to a noticeable decrease of thermal stability of PPI. PPI contained much lower sulfhydryl and disulfide bond contents than NPP. The analyses of intrinsic fluorescence spectra indicated a more compacted tertiary conformation of NPP than PPI. Extraction process influenced the functional properties of PPI, such as protein solubility, emulsifying activity index and foaming capacity. The relatively poor functional properties of PPI might be associated with protein denaturation/unfolding and subsequent protein aggregation.

Industrial relevance

Peanut is an important oilseed crop and a well-accepted food. After oil production through thermal treatment, the defatted peanut flour is the main byproduct, which possesses a large amount of proteins. However, due to the low extraction yield and poor functional properties of these proteins, they are not well utilised in industry till now. In this work, peanut proteins were extracted by two techniques. The results indicated that extraction technique could significantly modify the functional properties of peanut proteins. Therefore, this work is helpful for industrial utilisation of peanut proteins.     

Modulation of globular protein functionality by weakly interacting cosolvents

Globular proteins are utilized in food, pharmaceutical, and health-care products because of their unique functional attributes, for example, enzyme catalysis, ligand binding and transport, surface activity and self-association. The expression of these functional attributes in a particular product depends on the molecular structure, chemical environment and thermal-mechanical history of the proteins. The optimization of the design and operation of processing technologies used to manufacture protein-containing materials depends on a thorough understanding of the influence of processing conditions and material composition on protein properties. This paper focuses on the impact of weakly interacting neutral cosolvents (such as sugars and polyols) on the structural, thermodynamic and functional properties of globular proteins in foods. The physicochemical mechanisms by which these cosolvents can modulate protein functionality are highlighted, that is, differential interactions and steric exclusion. Previous studies of the impact of cosolvents on protein functionality that are relevant to foods are reviewed, for example, water solubility, stabilization, emulsification, foaming, gelation, enzyme catalysis, and flavor binding.     

PROTEIN-CARBOHYDRATE INTERACTIONS AT ELEVATED TEMPERATURES*

A series of protein types have been characterized with respect to their interaction with low dextrose equivalent corn starch hydrolysates. From an assessment of the chemical modification of selected functional groups, classical denaturation studies, gel filtration and precipitation with tri-chloro-acetic acid, the partial basis for molecular interaction has been elucidated. Although all proteins under investigation were prominent components of a variety of food systems, particular emphasis was placed on the behavior of β-lactoglobulin and selected soy fractions. Results from the modification and denaturation studies indicated that several factors are required to account for the extent of interaction, but that the predominant effect appears to be non-covalent in nature. In the case of commercial soy proteins, considerable polydispereity was detected prior to the interaction - much of which was doubtless induced during isolation. Many such fragments of this preparation showed self-interacting properties, which could provide a basis for texture in the reported system. The starch hydrolysates appear to exhibit a protective effect against excessive protein aggregation, which could have significance in retention of nutritional value during food processing.     

Functional properties and essential amino acid composition of proteins extracted from black soldier fly larvae reared on canteen leftovers

This study investigated the functional properties and essential amino acid composition of proteins extracted from black soldier fly larvae which represent a good source of proteins (30.12% dry matter). The proteins extracted in alkaline conditions (pH 11) were then isolated using two different recovery methods, (i) ultrafiltration, and (ii) isoelectric precipitation. Ultrafiltration provided higher purity of proteins (96.42%) but a lower extraction yield (24.30%) compared to isoelectric precipitation which provided a protein purity of 76.02% and higher extraction yield (37.22%). All essential amino acids were present in adequate quantities for human requirements. The fraction of proteins obtained by ultrafiltration had significantly higher oil holding capacity and foaming capacity than isoelectrically precipitated proteins. The protein fractions obtained by ultrafiltration and isoelectric precipitation had oil holding capacity of 125.8% and 81.6%, while the foaming capacity was 141.9% and 114.3%, respectively. These technological functionalities can be used to improve human food characteristics, thus resulting in enhanced consumer acceptance.Industrial relevanceThe food industry seeks alternative and sustainable sources of proteins, such as insect proteins, to reduce the environmental impact (i.e., greenhouse gas emissions). Consumers' acceptance is the main barrier to adopting edible insects in commercial applications. The acceptance increases when the insect proteins are incorporated in food products as ingredients rather than consuming the whole insect. Hence, this study focuses not only on extraction of proteins but also on functional properties of those proteins making it easier to target specific food formulations (i.e., whipped toppings), which require specific functionalities (i.e., foaming capacity and stability). The protein purity was increased by including an ultrafiltration step. The proteins obtained through the ultrafiltration method showed better oil holding capacity and foaming stability compared to proteins obtained by isoelectric precipitation. The strategies assessed in the present study help enhance the purity of larval proteins and improve their functional properties, thereby opening up new opportunities to incorporate this ingredient into targeted food formulations and improve consumer acceptance.     

蛋白质微胶的制备、形成机制及应用

蛋白质微胶具有优异的尺寸效应、生物兼容性和疏水分子荷载能力,可望成为新一代功能性食品配料。本文对蛋白微胶的制备技术,形成机制及调控进行了综述,重点讨论蛋白质聚集行为控制与蛋白质微胶形成的关系;提出营养微胶的概念;对蛋白质微胶形成时蛋白与植物多酚的相互作用进行了分析;阐述了蛋白质微胶的界面吸附行为和凝胶特性及其在真实食品体系的应用情况。     

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.     

Recent advances in enzymatic modifications of food proteins for improving their functional properties

The tailoring of food proteins by enzymes is a powerful tool to improve their functional properties. Mainly proteinases from various origins have been used for such purposes. Controlled proteolysis leads generally to more soluble products with improved emulsifying properties but relatively poor foaming properties. This latter was the case in our studies on proteolysis of wheat gluten. We also have demonstrated that polypeptides characterized by a high functionality could be produced by proteolysis of wheat gluten. Depending on the conditions of the proteolytic attack, the cleavage sites as well as the type of generated peptides could be modified. In the case of milk proteins, peptic action on the proteins in ethanolic medium or on moderately esterified proteins results in unique fragmentation. Besides fragmentation achieved by proteases, the cross-linking of proteins to yield higher molecular size forms with transglutaminases was shown to improve the functional properties of proteins. These enzymes catalyse the binding of amines to proteins, cross-link the polypeptide chains and deamidate the glutaminyl residues. In the case of soybean isolates, gelification was obtained with lower protein concentrations. In the case of wheat gliadins, enzymatic deamination increased drastically the solubility in a wide range of pH. Additionally, enzymatically deaminated gliadins were shown to be very efficient in stabilizing emulsions, due to the formation of soluble polymers.     

The effect of proteolytic enzymes on the thermostability of egg-white

The effect of proteolytic enzyme preparations such as Proteopol PB (bacterial origin), ficin, and pancreatin on the thermostability of egg-white proteins during pasteurization was investigated. Proteolytic activities of each enzyme were measured at three different doses which were calculated by the ANSON method. The degree of white protein degradation was evaluated by the determination of amino-nitrogen. Effectiveness in reducing the coagulation of egg-white proteins varied, depending on the type and dose of enzyme used. Proteopol PB showed only little effect, ficin demonstrated the best anticoagulation properties at the lowest dose, while for pancreatin the middle dose proved to be the most effective. It was concluded that moderate proteolysis is useful for improving the thermostability of egg-white proteins during pasteurization. Total bacterial counts increased considerably after incubation of egg-white with enzyme preparations, but after pasteurization the number of bacteria decreased to levels which were compatible with bacteriological standards for egg-white products.     

Effect of pH at pressure treatment on the acid gelation of skim milk

Skim milk at pH between 6.4 and 7.3 was pressure treated at 200–600 MPa for 30 min and then slowly acidified with glucono-δ-lactone to form acid gels. Milks at low pH produced acid gels with low elastic moduli (final G′) and yield stresses and those at higher pH produced acid gels with higher final G′ and yield stresses. Pressure treatment disrupted the casein micelles at all pH and transferred high levels of casein to the serum phase. Denaturation of α-lactalbumin occurred at a pressure of 600 MPa only, and the level of denaturation increased with increasing pH. Denaturation of β-lactoglobulin (β-LG) occurred at all pressures, with the level of denaturation increasing with the magnitude of the pressure treatment and with pH. The denaturation of the whey proteins and the disruption of the casein micelles could not entirely account for the changes in the rheological properties of the acid gels, as denaturation of up to 50% of the whey proteins produced acid gels with very low final G′ and yield stresses. It is proposed that the pH and the magnitude of the pressure treatment affect the interactions of the denatured β-LG with the casein proteins in the pressure-treated milks, and that this affects the ability of the denatured β-LG to participate in the acid gel structures.Industrial relevanceThe control and manipulation of the firmness of acid skim milk gels is important in many dairy food applications such as yogurts and some types of cheeses. This study has demonstrated that acid gel firmness can be substantially manipulated when the milk is pH adjusted and pressure treated before acidification, and that these effects are different to those obtained through heating. The commercial uptake of high pressure processing in the dairy industry is dependent on this technology producing unique functional properties in milk when compared with traditional processing. The results of this study indicates that high pressure processing of milk may offer unique functional properties in acid gel applications which could be used for the development of new or improved dairy products.     

A Kinetic Study on the Heat-Induced Changes of Whey Proteins Concentrate at Two pH Values

Whey protein concentrate (WPC) is used as food ingredients due to their commercially important functional properties. The effects of heat treatment on the components of milk are very important for the final product character, since they undergo modifications that affect sensorial and nutritional quality of milk. The heat-induced changes on dispersions of whey proteins concentrate were monitored by measurement of thiol availability, protein solubility, and turbidity at pH 6.6 and 7.5. The fractional conversion model was used to quantitatively describe the effect of different temperature–time combination on denaturation mechanism. The results demonstrate that heat-induced changes of WPC greatly influence their solubility, expressed as degree of denaturation at pH 4.6 and were related to the heating conditions. The denaturation mechanism involved a number of consecutive conformational changes in the molecules. A curvature in Arrhenius plots was observed around 75 °C, indicating changes in the reaction mechanism. The deflection of Arrhenius plot reflects the generally accepted two-step denaturation/aggregation process of whey proteins.     

Functional properties of isolated porcine blood proteins

The isolated proteins contained in the blood from slaughterhouses could be recovered and used to improve the functional and nutritional properties of food products. In this work some functional properties, namely solubility, emulsifying capacity, gelling and foaming capacity have been tested for different protein fractions of porcine blood. The blood proteins studied were globins (α, β and γ), albumin and fibrinogen and the whole plasma from the plasmatic fraction, and haemoglobin and globin obtained from the haemoglobin by a chemical method from the cellular fraction. The effect of pH and protein concentration on functional properties was determined. Results indicate that blood proteins present good functional properties specially solubility, gellation and emulsifying capacities that could make blood protein useful as food additives in the formulation of food products.