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The effects of electrostatic repulsion (pH6.5) and attraction (pH4.6) between biopolymers on the physicochemical and foam properties of ovalbumin (OVA)/carboxymethylcellulose (CMC) mixtures subjected to mild heat treatment (60–75 °C) were comparatively investigated. It was found that electrostatic binding between OVA and CMC at pH 4.6 resulted in an increase in the peak temperature of thermal denaturation (T d) of OVA from 71.3 °C to 74.4 °C, while no significant effect was observed at pH 6.5. Thus, 60 and 65 °C below T d were chosen to further investigate the effects of heating on the degree of thermal aggregation, protein conformation and foam properties of OVA/CMC mixtures. Confocal laser scanning microscopy observations and rheological results indicated that electrostatic binding between OVA and CMC at pH 4.6 significantly reduced the degree of protein thermal aggregation, while on the contrary, electrostatic repulsion between proteins and polysaccharides at pH 6.5 promoted OVA thermal aggregation. Raman spectroscopic characterisation indicated that mild heat treatment mainly led to a change in the microenvironment polarity of OVA tyrosine and tryptophan residues, as well as an increase in the content of random coil in the amide III band irrespective of pH. Moreover, after heating at 65 °C for 20 min, The foaming ability of the OVA/CMC mixtures at pH 6.5 and 4.6 increased by approximately 32% and 36% respectively compared to pure OVA. These findings have a positive value for enhancing the heat sterilisation strength of egg white proteins. [Display omitted] • Electrostatic binding enhanced the thermal denaturation temperature of ovalbumin. • Electrostatic binding inhibited thermal aggregation of ovalbumin. • Electrostatic repulsion promoted thermal aggregation of ovalbumin. • Both electrostatic attraction and repulsion enhance the foamability of heated ovalbumin. [ABSTRACT FROM AUTHOR]

Ormosia, as one of the consumer's favorite grains, is rich in protein, but its application is limited by the naturally low solubility of its protein. In order to improve its application capability, the Ormosia protein (OSP) is modified by high-intensity ultrasounds (HIUS), and the effect of ultrasound on the secondary and tertiary structure, as well as the improvement of its foaming property due to the alteration in protein structure, were systematically explored. It has been observed that HIUS greatly reduced the particle size of the OSP, and significantly affected the secondary and tertiary structure. These fundamental changes improved the ability of the OSP to stabilize foam at the water-air interface, and thus the HIUS-treated OSP possessed an excellent foaming property. The results of this study are expected to provide a theoretical basis for expanding the application of the OSP in the food industry. [Display omitted] • HIUS affected the secondary and tertiary structures of OSP. • HIUS enhanced the foam-capacity ability of OSP. • HIUS enhanced the foam-stability ability of OSP. [ABSTRACT FROM AUTHOR]

Abstract The effect of temperature (below denaturation temperature) on protein foam formation and stabilization is potentially large, but has received little attention. This study aims to identify the effect of temperature (15–60 °C) on ovalbumin-stabilized foams at different concentrations (0.05–50 g L−1), and place this in a theoretical perspective. With increasing temperature the initial adsorption rate (dΠ/dt) increased logarithmically from 0.006 mN m−1 s−1 at 5 °C to 0.084 mN m−1 s−1 at 60 °C. A concentration increase resulted in a linear increase of dΠ/dt. This concentration effect was also observed in the foam ability, although the foam ability increased logarithmically rather than linearly with concentration, as expected based on theory and dΠ/dt. The foam ability was hardly affected by temperature (in contrast to theory and dΠ/dt). This was attributed to the strong decrease of foam stability with increasing temperature, which was expected based on theory. At elevated temperatures, the poor foam stability interferes with the foam ability (i.e. foam stability ≈ timescale of foam formation), a situation also happening at low concentrations. When formation was faster than destabilization, the foam ability relates to the effective adsorption rate. The effective adsorption rate includes the decrease in adsorption probability with increasing surface coverage. The observed balance between the effect of adsorption rate and foam stability on foam ability is not quantitatively predictable based on current theoretical models. Graphical abstract Image 1 Highlights • An increase of temperature accelerates adsorption, but hardly affects foam ability. • An increase of temperature strongly decreases foam stability. • When stability ≤ time of formation, low foam ability due to poor foam stability. • When stability > time of formation, foam ability relates to effective adsorption rate. • Combination of foam stability and effective adsorption rate determines foam ability. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the possibility of stabilising foam bubbles in water by adsorption of calcium carbonate (CaCO 3 ) particles. Because CaCO 3 is hydrophilic and not surface-active, particles were hydrophobised in situ with several emulsifiers. The used emulsifiers were food-grade and negatively charged at the pH employed. The effect of particle addition on foamability and foam stability of solutions containing either β-lactoglobulin, sodium caseinate, Quillaja, sodium dodecanoate (SD) or sodium stearoyl-2-lactylate (SSL) was studied. It was found that the ability of the emulsifiers to induce surface activity such that the particles are able to adsorb to the air-water interface is related to their structure. The structure needs to consist of a well-defined hydrophobic part and a charged part. Large emulsifiers with a complex structure, such as β-lactoglobulin, sodium caseinate and Quillaja, were able to partially hydrophobise the particles but were not able to act synergistically with the particles to increase the foam stability. Low molecular weight emulsifiers, however, consisting of a single tail with one charged group, such as SD and SSL, adsorbed at the particle surface rendering the particles partially hydrophobic such that they adsorb to the air-water interface. In a subsequent investigation, the pH was changed to a value typical for food products (pH 6–7) and the addition of milk salts on the foamability and foam stability was assessed. Based on these results, the use of food-grade CaCO 3 particles hydrophobised in situ with food-grade surfactants (SD or SSL) to prepare ultra-stable aqueous foams is demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: Class II hydrophobin (HFBII) is a highly surface active molecule and in the context of aeration can be considered to be an air structuring protein conferring exceptional stability to foams for periods far in excess of that obtained with any other commonly used protein. This is of interest to the food industry, since producing shelf stable foams in food formulations is very difficult. Although HFBII has proven to be very promising in terms of foam stability when used alone, it is still unknown whether HFBII will be able to maintain its functionality when other surface active agents are present, such as in real food systems. The surface rheology: surface shear viscosity (η s) and surface dilatational elasticity (ε), for HFBII and β-casein mixes at various ratios is described in this paper and how this relates to bubble stability. The addition of β-casein up to a certain ratio seems to increase η s significantly, whilst ε is less affected. This is accompanied by improved stability of air bubbles to coalescence and allows the formation of very small air bubbles that remain extremely stable to disproportionation. Overall, there is the suggestion of some kind of synergy between the two proteins. The exact nature of this interaction is unknown. Measurements of the ζ-potential of the proteins suggest that electrostatic interactions are probably not important at the pH investigated (pH 7). Confocal microscopy of individual bubbles over prolonged periods of time, stabilized by HFBII and a fluorescently labeled β-casein, suggests that the enhanced stability is due to highly unusual and complicated interfacial packing phenomena plus local bubble curvature effects that require further investigation. [Copyright &y& Elsevier]

Abstract: Food protein functionality has classically been viewed from the perspective of how single molecules or protein ingredients function in solutions and form simple colloidal structures. Based on this approach, tests on protein solutions are used to produce values for solubility, thermal stability, gelation, emulsifying, foaming, fat binding and water binding to name a few. While this approach is beneficial in understanding the properties of specific proteins and ingredients, it is somewhat restricted in predicting performance in real foods where the complexities of ingredients and processing operations have a significant affect on the colloidal structures and therefore overall properties of the final food product. In addition, focusing on proteins as just biopolymers used to create food structures ignores the biological functions of proteins in the diet. These can be beneficial, as in providing amino acids for protein synthesis or bioactive peptides, or these can be detrimental, as in causing a food allergic response. This review will focus on integrating the colloidal/polymer and biological aspects of protein functionality. This will be done using foams and gels to illustrate colloidal/polymer aspects and bioactive peptides and allergenicity to demonstrate biological function. [Copyright &y& Elsevier]

Abstract: Protein–polysaccharide interactions find many applications in food engineering and new food formulations. This review article describes recent research on the effect of protein–polysaccharide interactions on the properties of air–water and oil–water interfaces, as affected by their behaviour in the bulk phase. The interfacial behaviour of protein–polysaccharide mixtures exhibiting associative (i.e., net attractive) interactions as well as their performance in food emulsions and foams has been the subject of several reviews in the last decade. Much less attention has been paid to the interfacial behaviour of protein–polysaccharide mixtures exhibiting unfavourable interactions. Thus we are concerned here with the interfacial behaviour of both kinds of mixtures. [Copyright &y& Elsevier]

Abstract: Food and pharmaceutical industries all over the world are witnessing an increasing demand for collagen and gelatin. Mammalian gelatins (porcine and bovine), being the most popular and widely used, are subject to major constraints and skepticism among consumers due to socio-cultural and health-related concerns. Fish gelatin (especially from warm-water fish) reportedly possesses similar characteristics to porcine gelatin and may thus be considered as an alternative to mammalian gelatin for use in food products. Production and utilization of fish gelatin not only satisfies the needs of consumers, but also serves as a means to utilize some of the byproducts of the fishing industry. This review focuses on the unique features, advantages, constraints, and challenges involved in the production and utilization of fish gelatin in order to provide a comprehensive look and deeper insight on this important food ingredient, as well as prospects for its future commercial exploitation and directions for future studies. [Copyright &y& Elsevier]

Abstract: This study was undertaken to characterize the interfacial and foaming properties of different mixtures at the air–water interface under the same concentration range, and to put into light putative particular behaviors of mixtures. Different complementary techniques have been coupled such as null ellipsometry, surface tension and shear elastic constant measurements as well as polarization-modulation infrared reflection–absorption spectroscopy (PM-IRRAS). Moreover, the foaming properties were also investigated by a bubbling method. Solutions of either ovalbumin or lysozyme exhibit different interfacial behaviors. Ovalbumin does not form multilayers, even at high concentration. Conversely, lysozyme forms films that are much thicker than a protein monolayer whereas the surface pressure is definitely smaller than that ovalbumin. It thus seems that ovalbumin is much more surface active than lysozyme. The ellipsometric angles for the binary mixtures are much higher than those of films formed by the pure proteins, independently of the molar ratio. These results suggest that there is a synergy in the interfacial adsorption between the two proteins, which is confirmed by PM-IRRAS measurements, most likely due to the electrostatic interactions between the oppositely charged lysozyme and ovalbumin. Moreover, shear elastic constant measurements suggest that lysozyme has a strong effect on the organization of the interfacial film. The foaming properties of the mixtures are, however, always close to those of the pure ovalbumin solution. Therefore, lysozyme does not foam alone, but is able to foam as well as pure ovalbumin after addition of a very small amount of ovalbumin, which suggests that the synergy between proteins has an impact on the foaming properties. [Copyright &y& Elsevier]

Abstract: In this work, we have studied dynamic surface pressure and surface dilatational characteristics of diglycerol esters (diglycerol monolaurate and diglycerol monostearate) and β-lactoglobulin mixed films adsorbed at the air–water interface. The concentrations of protein and lipid and the protein/lipid ratio in the aqueous bulk phase were studied as variables, while pH (7), ionic strength (0.05M) and temperature (20°C) were maintained constant. We have observed competitive adsorption from aqueous solutions of mixed emulsifiers (β-lactoglobulin and diglycerol esters) and/or the displacement between emulsifiers at the air–water interface depending on the chemistry of the lipid and on the protein/lipid ratio. For the mixed systems a lag period was not observed, even for low concentrations of emulsifiers in solution. During the initial period the kinetics of adsorption of mixed emulsifiers at the air–water interface are controlled by a diffusion mechanism. At long-term adsorption the rate of penetration controls the adsorption of mixed emulsifiers at the interface, which increases with the lipid concentration in solution and is faster for diglycerol monostearate than for diglycerol monolaurate. From a rheological point of view, mixed films behave as viscoelastic (practically elastic) with a loss angle tangent higher than zero. The evolution of surface dilatational modulus (E) with surface pressure (π) for β-lactoglobulin–diglycerol ester mixed films reflects the amount of emulsifier adsorbed at the interface (giving high values of E at the higher π) and confirms the idea that the protein–lipid interactions at the air–water interface are somewhat weak, there even being the possibility of phase separation. [Copyright &y& Elsevier]

Abstract: Plant proteins are increasingly being used as an alternative to proteins from animal sources in human nutrition. In this contribution we are concerned with the analysis of interfacial (adsorption isotherm, rate of adsorption, and surface dilatational properties) and foaming characteristics (foaming power and foam stability) of a sunflower protein isolate (SPI) and its hydrolysates with different degrees of hydrolysis (DH), as a function of the protein concentration in aqueous solution. Caseinate has been utilized as a protein of reference. We have observed that the adsorption and foaming power (foam capacity, gas and liquid retention in the foam, and foam density) increases with the protein concentration in the aqueous phase, depending on the DH. The adsorption kinetic at short adsorption time is diffusion controlled. However, the controlling mechanism at long-term adsorption is the penetration of the protein at the interface. A close relationship was observed between foaming and the rate of diffusion of the protein to the air–water interface. The foam stability—quantified by the relaxation time due to drainage (t d) and disproportionation/coalescence (t dc)—correlates with the equilibrium surface pressure (π e) of the film adsorbed from aqueous solutions of the protein. [Copyright &y& Elsevier]

Abstract: The foaming and emulsifying characteristics of proteins are important attributes during the production stage, storage, transport, and consumer perception of quality (appearance) of food dispersions (emulsions and foams). In this contribution, we are concerned with the analysis of interfacial, foaming, and emulsifying characteristics of a typical milk protein (sodium caseinate) as a function of protein concentration in aqueous solution (C, % w/w). We have observed that there exists close relationships between foaming (power of foaming, foam capacity, foam density, and foam conductivity) and the rate of diffusion (slope of π vs. t1/2) of caseinate to the air–water interface. The foam stability (quantified by the relaxation time (t) due to drainage and disproportionation/collapse) correlates linearly with the equilibrium surface pressure (πe) of aqueous solutions of caseinate. At surface pressures lower than that of monolayer saturation (at C<1×10-3%, w/w) the foaming is zero. The emulsifying capacity (quantified by the droplet size and the specific surface area) was correlated with the protein concentration in solution (surface pressure at equilibrium). Coalescence was observed only at the lower caseinate concentration in solution (C<0.1%, w/w). As a coherent protein layer (multilayer) saturates the interface, at higher protein concentrations, the emulsion instability is due to flocculation and/or creaming. The coalescence and creaming rates correlate well with the protein concentration in solution (thus with the surface pressure and/or surface dilatational modulus). [Copyright &y& Elsevier]

Abstract: The objective of the work was to study the effect of different non-surface active polysaccharides on the foaming properties of intact and hydrolysed sunflower protein isolate (SP) (degree of hydrolysis of 1.5 and 9.8%) at neutral pH where a limited incompatibility between macromolecules can occur. Foams were obtained by whipping and the overrun, liquid drainage and collapse of the height of foams were evaluated. A limited enzymatic treatment substantially enhanced foaming properties of sunflower protein. A small degree of hydrolysis (DH=1.5%) enhanced both foam overrun and foam stability against liquid drainage and collapse. However, an increase of DH to 9.8% did not further improve foaming properties. The overrun of foams was decreased in the presence of all the polysaccharides but the performance of polysaccharides as stabilizers of foams depended on the protein hydrolysis, the structure of the polysaccharide and its concentration in the liquid used to make the foam. Xanthan gum at 0.25 and 0.5%, due to its high viscosity performed as stabilizer of both intact and hydrolysed SP foams. The other polysaccharides at 0.25% performed as stabilizers when added to the intact SP foams but destabilized the foams containing the hydrolysed SP. By increasing PS concentration, the detrimental effect could be partially reverted. The results may be interpreted in terms of the bulk and surface rheological properties of the mixed protein/polysaccharide foams and suggest that protein–polysaccharide interactions are strongly affected by the hydrolysis of the protein. [Copyright &y& Elsevier]

The interfacial properties of homogenised mixtures of monoglycerides and milk proteins (casein) have been examined using dynamic surface rheology. Using applied oscillation it was shown that the adsorption and surface properties of these mixtures varied considerably in comparison with the individual components. Homogenised dispersions made with casein and saturated monoglycerides (C16) at 40 °C displayed controlled deposition of monoglyceride at the air–water interface. Cooling of the solution to 5 °C resulted in crystallisation of the monoglyceride at the air–water interface. This was characterised by increasing surface elasticity and viscosity. Both surface elasticity and viscosity reached steady state, implying that there was no adsorption from bulk phase to the interface. Similar adsorption behaviour was observed when an unsaturated monoglyceride (C18:1) was used, although the steady-state values for surface elasticity on cooling were consistently lower in comparison with the saturated monoglycerides. The shorter chain length monoglyceride, monolaurin, was found not to produce a metastable dispersion on homogenisation, and consequently controlled deposition at the air–water interface was not observed. The results have some important implications for foam stabilisation using monoglycerides and other food grade surfactants. [Copyright &y& Elsevier]