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International audience; The formation of dense protein interfacial layers at afree air−water interface is known to result from both diffusion andadvection. Furthermore, protein interactions in concentrated phasesare strongly dependent on their overall positive or negative net charge,which is controlled by the solution pH. As a consequence, aninteresting question is whether the presence of an advectionflow ofwater toward the interface during protein adsorption producesdifferent kinetics and interfacial structure of the adsorbed layer,depending on the net charge of the involved proteins and, possibly, onthe sign of this charge. Here we test a combination of the followingparameters using ovalbumin and lysozyme as model proteins: positiveor negative net charge and the presence or absence of advectionflow. The formation and the organization of the interfacial layers arestudied by neutron reflectivity and null-ellipsometry measurements. We show that the combined effect of a positive charge oflysozyme and ovalbumin and the presence of advectionflow does induce the formation of interfacial multilayers. Conversely,negatively charged ovalbumin forms monolayers, whether advectionflow is present or not. We show that an advection/diffusionmodel cannot correctly describe the adsorption kinetics of multilayers, even in the hypothesis of a concentration-dependent diffusioncoefficient as in colloidalfiltration, for instance. Still, it is clear that advection is a necessary condition for making multilayers througha mechanism that remains to be determined, which paves the way for future research.

International audience; Proteins digestion is a complex and dynamic process involving several proteases that particularly differ in their specificity. The specificity of pepsin, the major protease of gastric digestion, has been previously investigated, but only regarding the primary sequence of the protein substrates.The present study aimed to consider in addition physicochemical and structural characteristics, at the molecular and sub-molecular scales. For six different proteins submitted to in vitro gastric digestion, the peptide bonds cleaved were determined from the peptides released and identified by LC-MS/MS. An original statistical approach, based on propensity scores calculated for each amino acid residue on both sides of the peptide bonds, concluded that preferential cleavage occurred after Leu and Phe, and before Ile. Moreover, reliable statistical models developed for predicting peptide bond cleavage, highlighted the predominant role of the amino acid residues at the N-terminal side of the peptide bonds, up to the seventh position (P7 and P7’). The significant influence of hydrophobicity, charge and structural constraints around the peptide bonds was also evidenced

Eggs are a whole food which affordably support human nutritional requirements worldwide.\ud Eggs strongly resist bacterial infection due to an arsenal of defensive systems, many of which\ud reside in the egg white. However, despite improved control of egg production and distribution,\ud eggs remain a vehicle for foodborne transmission of Salmonella enterica serovar Enteritidis, which\ud continues to represent a major public health challenge. It is generally accepted that iron deficiency,\ud mediated by the iron-chelating properties of the egg-white protein ovotransferrin, has a key role\ud in inhibiting infection of eggs by Salmonella. Ovotransferrin has an additional antibacterial activity\ud beyond iron-chelation, which appears to depend on direct interaction with the bacterial cell surface,\ud resulting in membrane perturbation. Current understanding of the antibacterial role of ovotransferrin\ud is limited by a failure to fully consider its activity within the natural context of the egg white, where a\ud series relevant environmental factors (such as alkalinity, high viscosity, ionic composition, and egg\ud white protein interactions) may exert significant influence on ovotransferrin activity. This review\ud provides an overview of what is known and what remains to be determined regarding the antimicrobial\ud activity of ovotransferrin in egg white, and thus enhances understanding of egg safety through\ud improved insight of this key antimicrobial component of eggs.

International audience; Background: Since the early 1990s, major health and environmental concerns have developed and driven the emergence of diets involving a lower consumption of animal products. However, the transition towards greener diets is being hampered by the poor acceptance of vegan foodstuffs among western consumers. Mixed animal/ plant alternatives to familiar dairy or egg products offer a new field of innovation. Scope and approach: This review focuses on innovative mixes of egg or milk with plant ingredientsespecially legumesto develop products in which interactions between animal and plant are not usually expected, such as dairy or egg gels, emulsions or foams. The opportunities offered by such products in terms of consumer acceptance, nutrition, digestibility and techno-functional properties are reviewed and discussed with respect to their risk-benefit ratios. Key findings and conclusions: In many cases, animal/plant mixes offer enhanced protein stability and synergistic interfacial or textural properties that make them a flexible tool for food design. Fermentation offers important prospects for the nutritional and sensorial enhancement of animal/plant mixes, through the multi-criteria application of microbial consortia. Animal/plant mixes enable reduction in animal protein consumption while preserving amino acid and micronutrient intakes and sensory properties. However, their acceptability to consumers and society will also depend on controlled safety, especially regarding allergies or contaminants, on affordability, their degree of novelty or (ultra)processing, their actual environmental footprint and whether they meet consumer expectations for innovative foods in the transition towards greener diets.

International audience; Milk fat globule membrane conditions the reactivity and enzymatic susceptibility of milk lipids. The use of bovine membrane extracts to make infant formulas more biomimetic of human milk has been suggested recently. A comparison of the physico-chemical behavior of human and bovine milk membrane extracts and their interaction with gastric lipase is here undertaken using biophysical tools. Milk membrane extracts (70% of polar lipids) were obtained either pooling of mature human milk (n = 5) or bovine buttermilk. Human extract contained more anionic glycerophospholipids, less phosphatidylethanolamine and more unsaturated fatty acids (57% versus 46%) than bovine extract. Human extract presented a higher compressibility, with slower increase of surface pressure, than bovine extract. Micronic liquid condensed (LC) domains were evidenced in both extracts at 10 mN/m, but the evolution differs upon compression. Upon gastric lipase addition, an adsorption preference for liquid expanded phase (LE) was observed for both extracts. However, insertion was more homogeneous in terms of height level in human extract and impacted less its lipid lateral organization than in bovine extract. Both membrane extracts share close physico-chemical properties, however human membrane higher compressibility may favour gastric lipase insertion and higher interfacial reactivity in gastric conditions.

Hydrophobisation of whey proteins, followed by erythritol addition into the hydrophobised protein dispersion, enables formation of water-in-water (W/W) emulsions of the proteins and alginate. In this study, we investigated the interfacial and gel rheology of whey proteins as affected by hydrophobisation, heat denaturation and erythritol addition. Additionally, the gel rheology of the resultant W/W emulsion was assessed. Hydrophobisation shortened the linear viscoelastic region and decreased the surface storage modulus ( G s ' ), the flow stress and the flow strain of protein layer at the air-liquid interface. Erythritol addition into the hydrophobised protein caused a further reduction of G s ' . In accordance with interfacial rheology, protein hydrophobisation and erythritol addition decreased the dynamic moduli of acid-induced protein gels. Frequency sweep tests indicated that the gelled emulsion had higher dynamic moduli than all WPI gels. The higher firmness of the emulsion gel was ascribed, based on microstructural images, to micro-phase separation of alginate droplets.

Whey protein microparticles are of great potential in diverse applications such as fat replacement, emulsification, cargo delivery and formulation of high-protein beverages. We developed a method by which the major whey protein, β-lactoglobulin, (β-lg) is at first encapsulated through a facile procedure within CaCO3 micro-templates, followed by enzymatic crosslinking of the protein and succeeding removal of the template to form protein microparticles. Protein encapsulation increased the colloidal stability and influenced the micro-morphology of CaCO3 microparticles. Dynamic light scattering and ζ-potential measurements, supported by gel electrophoresis indicated that β-lg was entrapped in monomeric form. Heating of the protein-loaded CaCO3 microparticles to gel protein as an alternative to enzymatic crosslinking, was not feasible because pH reduction to 7.0 before heating caused considerable agglomeration and deformation of the carbonate particles. In subsequent to enzymatic crosslinking and template dissolution, confocal laser scanning microscopy illustrated that the resulting protein particles were spherical, micron sized (≈3μ) and structurally homogenous. It was found based on Fourier transform infra-red spectroscopy that enzymatic crosslinking twisted the β-sheet structures of β-lg. Gel electrophoresis and intrinsic fluorescence measurement showed that in addition to the enzymatic polymerization, thiol-disulfide exchange reactions contributed in protein particles formation. It was also concluded based on intrinsic fluorescence measurement that tryptophan microenvironment was not influenced by the enzymatic crosslinking. The fabricated β-lg particles did not undergo significant denaturation by subsequent heating. This may open a route to deliver near-native whey protein microparticles to final consumers.

International audience; The stability and flow properties of surfactant-stabilised aqueous foams are keys to their use invarious application contexts. The main destabilisation processes in aqueous foams are liquiddrainage, coalescence and disproportionation. They behave as yield-stress fluids, in which flowleads to film-scale topological rearrangements known as T1s.Still, the contribution to these features of the properties imparted by the surfactants to the air-liquid interface is far from fully understood.Proteins are amphiphilic macromolecules. They lower the air-water surface tension, as small-molecular-weight surfactants do, but in contrast with the latter, they adsorb irreversibly to theinterface and give specific interfacial visco-elasticity.In order to correlate the stability and rheology of protein foams to the properties of interfaces,we adopted a multi-scale approach combining the interfacial rheology, the dynamics of foamfilms after T1 topological rearrangements, and macroscopic foam characterisations: the foamstability against drainage was evaluated by following the evolution of the liquid fraction as afunction of both time and height in the foam column[1], and the foam complex modulus and yieldstress were measured under oscillatory shear. We investigated the behaviour of dairy proteins(whey protein isolate or purified β-lactoglobulin), either in the native state or after modificationby dry-heating and/or pH adjustment prior to dehydration, to vary interfacial properties.Our results show that small-extent structural modifications of proteins had a dramatic impact oninterfacial rheology, liquid film dynamics, foam stability and foam rheology.This approach, correlating multiple investigation scales, sheds light on the contribution of theinterfacial rheology to protein foam properties, in particular through the involvement of filmrelaxation dynamics.

International audience; The main destabilisation processes in aqueous foams are liquid drainage, coalescence and disproportionation. In food sciences, the measurement of protein foam stability generally integrates all of them in a “global stability”, and a challenge is to correlate the stability and rheology of foams to the properties of interfaces. We adopted a multi-scale approach by combining the interfacial rheology of proteins adsorbed at the air–water interface, the dynamics of protein films after T1 topological rearrangements (Fig. 1), and macroscopic foam characterisations: the foam stability against drainage was evaluated by following the evolution of the liquid fraction as a function of time and height (Fig. 2) [1], and the foam complex modulus and yield stress were measured under oscillatory shear. We investigated the behaviour of dairy proteins (whey protein isolate and purified β-lactoglobulin), either in the native state or after modification by dry-heating and/or pH adjustment prior to dehydration. Our results show that small-extent structural modifications of proteins have a dramatic impact on interfacial rheology, liquid film dynamics, foam stability and foam rheology. This approach, correlating multiple investigation scales, sheds light on the contribution of the interfacial rheology to protein foam properties, in particular through the involvement of film relaxation dynamics.

International audience; Soft matter approaches for food proteins: interfacial and foaming properties. STLOpendays

International audience; In the present work, we investigated the effects of powder dry-heating parameters on whey protein foams stability, especially against drainage.To this aim, whey protein isolate solutions were prepared at various pH (3.5, 5.0, 6.5), with or without a prior dialysis step to reduce the lactose content, freeze-dried, adjusted to various levels (0.12, 0.23, 0.52) of powder water activity aw and dry-heated at 70 °C for up to 125 h. Protein solutions were then reconstituted at pH 7.0 and foams prepared by air bubbling.An original approach was followed to study the foam stability against drainage, involving monitoring of the liquid fraction as a function of both height in the foam column and time, and analysing the whole set of time and height liquid fraction profiles using multivariate statistics.The effects of dry-heating parameters were markedly interdependent, resulting in complex effects on foam stability. However, the results suggest that dry-heating at pH 3.5 increased foam stability. Moreover, the aw adjustment step, though consisting in a two-week pre-conditioning at room temperature, also had a significant effect on the foam stability, of the same order of magnitude as dry-heating effects.

The surface of milk fat globules consists of a biological membrane rich in polar lipids and glycoproteins. However, high shear stress applied upon homogenization disrupts the membrane and leads to the adsorption of casein micelles, as the major protein fraction of milk. These changes in the interface properties could affect the interactions between native or homogenized milk fat globules and the surrounding protein matrix, at neutral pH and upon acidification. In this study, macroscale rheometry, microscopic observations, nanoscale AFM-based force spectroscopy and physico-chemical analysis were combined to examine the interfacial composition and structure of milk fat globules and to evaluate their interactions with casein micelles. We showed that the surface properties of milk fat globules (biological membrane vs. caseins) and pH govern their interactions with casein micelles. The adhesion between individual fat globules and casein micelles was higher upon homogenization, especially at acid pH where the work of adhesion increased from 3.3 x 10-18 to 14 x 10-18 J for native and homogenized fat globules, respectively. Consequently, casein-coated homogenized fat globules yield stiffer milk acid gels. These findings cast light on the importance of colloidal particle’s surface properties and pH on their connectivity with the surrounding matrix, which modulates the bulk microstructure and rheological properties with potential functional consequences, such as milk lipid digestion.

International audience; Animal-and plant-based proteins are present in a wide variety of raw and processed foods. They play an important role in determining the final structure of food matrices. Food proteins are diverse in terms of their biological origin, molecular structure, and supramolecular assembly. This diversity has led to segmented experimental studies that typically focus on one or two proteins but hinder a more general understanding of food protein structuring as a whole. In this review, we propose a unified view of how soft-matter physics can be used to control food protein assembly. We discuss physical models from polymer and colloidal science that best describe and predict the phase behavior of proteins. We explore the occurrence of phase transitions along two axes: increasing protein concentration and increasing molecular attraction. This review provides new perspectives on the link between the interactions, phase transitions, and assembly of proteins that can help in designing new food products and innovative food processing operations.

International audience; In their native state, milk lipids are present in the form of dispersed droplets called Milk Fat Globules (MFG, diameter 0.1-20 μm, average = 4 μm in bovine milk) [1,2]. The native MFG is constituted by a triglyceride core covered with an external trilayered membrane inherited from its secretory past. This membrane is mainly based on polar lipids (glycerophospholipids, sphingolipids and glycosphingolipids), proteins (25 % of total membrane with high proportion of glycoproteins and enzymes), neutral lipids and minor components. The major biological function of the MFG is to deliver energy to the mammal newborn, for that, the MFG has to be hydrolyzed in the gastro-intestinal tract by lipases, in successive steps. The lipases should interact with the MFG membrane and diffuse into the supramolecular object. The aim of this work was to determine the mechanisms involved in the enzymatic hydrolysis along the digestive process. We used millifluidic cells designed to trap MFG or model droplets and injected successively each lipase (gastric, pancreatic related 2, pancreatic triglyceride lipase) involved in the digestion process and thus mimicking different physiological stages (preterm infant, fullterm infant and adult). Thanks to the deep UV-microscope present at DISCO beamline, the autofluorescence of tryptophan (and tyrosine) of lipase aminoacids allowed protein observation without external labeling. The gastric and intestinal neonatal disintegration of milk fat globules (human or bovine) or other model systems (bovine anhydrous milk fat droplets stabilized by bovine milk membrane extracts or soy lecithin) was approached through transmission images recording. The analysis of the number of globules and their state of aggregation/coalescence during digestion (approached via diameter, size, mode and specific surface evolution against time) gave indication on the kinetics and mechanisms of lipolysis. Fluorescence (327-335 nm) image indicated lipase distribution. Gastric phase was mainly marked by the heterogeneous adsorption of the gastric lipase in the MFG membrane. Afterwards, heterogeneous adsorption of pancreatic triglyceride lipase could also be observed followed by the disappearance of the MFG core. The progression of lipases fronts was monitored and the kinetics of lipolysis characterized allowing the differentiation of substrate and of in vitro digestion models (full term infant, versus preterm infant versus adult). The microfluidics set up was a very interesting tool to follow sequentially the action of lipases, to save volume of purified lipase and to image simultaneously several positions. The high sensitivity of the DISCO beamline allowing the detection of digestive lipases auto-fluorescence, is a unique tool to unravel their mechanisms of adsorption onto complex substrate using free-label imaging and has generated useful data for infant formula optimization

International audience; Hypothesis: The effective contribution of interfacial properties to the rheology of foams is a source of many open questions. Film dynamics during topological T1 changes in foams, essentially studied for low molecular weight surfactants, and scarcely for proteins, could connect interfacial properties to protein foam rheology. Experiments: We modified whey protein isolate (WPI), and its purified major protein b-lactoglobulin (b-lg) by powder pre-conditioning and dry-heating in order to obtain a broad variety of interfacial properties. We measured interfacial properties, film relaxation duration after a T1 event and bulk foam rheology. Findings: We found that, for b-lg, considered as a model protein, the higher the interfacial elastic modulus, the longer the duration of topological T1 changes and the greater the foam storage and loss moduli and the yield stress. However, in the case of the more complex WPI, these correlations were less clear. We propose that the presence in WPI of other proteins, lactose and minerals modify the impact of pre-conditioning and dry-heating on proteins and thereby, their behaviour at the interface and inside the liquid film.

International audience; In their native state, milk lipids are present in the form of dispersed droplets called Milk Fat Globules (MFG, diameter 0.1-20 μm, average = 4 μm in bovine milk). The native MFG is constituted by a triglyceride core covered with an external trilayered membrane inherited from its secretory past. This membrane is mainly based on polar lipids (glycerophospholipids, sphingolipids and glycosphingolipids), proteins (25 % of total membrane with high proportion of glycoproteins and enzymes), neutral lipids and minor components. The major biological function of the MFG is to deliver energy to the mammal newborn, for that, the MFG has to be hydrolyzed in the gastro-intestinal tract by lipases, in successive steps. The lipases should interact with the MFG membrane and diffuse in the supramolecular object. The aim of this work is to determine the mechanism involved in the enzymatic hydrolysis along the digestive process. Indeed, we used millifluidic cells designed to bloc MFG and injected successively each lipase involved in the digestion process. Thank to the UV-microscope developed on the DISCO beamline, the autofluorescence of tryptophan (and tyrosine) present in the lipase amino-acid sequences had allowed the protein observation without external labeling. The gastric and intestinal neonatal disintegration of milk fat globules has been approached through transmission images recording and analysis of the number of globules and their state of aggregation/coalescence during digestion (approached via diameter, size, mode and specific surface evolution against time). In this presentation, the first results of these experiments will be showed. Mainly, in the stomach, the gastric lipases bind the MFG surface. Then, the MFG decreased in size in the intestinal phase releasing the intact lipid membrane suggesting that the core is hydrolyzed through the external membrane.

International audience; The main destabilisation processes in aqueous foams are liquid drainage, coalescence and disproportionation. Due to their amphiphilic nature, proteins can reduce surface tension ϒ, increase liquid phase viscosity and form a visco-elastic interfacial film surrounding the gas bubbles. A correlation is believed to exist between surface rheology of the protein interfacial film and foam stability. Indeed, surface rheology on protein films helps the understanding of foam stability. Two kinds of surface deformation may be applied on a single planar protein film, shearing and expansion/compression (or dilatation). The dilatational elasticity modulus must be larger than 2ϒ to prevent disproportionation. A higher surface shear viscosity is correlated with a better stability against drainage. More generally, higher surface shearing modulus improved stability. However, full understanding still is a challenge because of foam complexity. Foams have confined interstices and spontaneous dynamic rearrangements happen, which cannot be reproduced using only single planar interfaces. Thus, the goal of this work is to bring a multi-scale approach by combining dynamical T1 topological rearrangements of protein films to interfacial rheology measurements.T1 rearrangements occur spontaneously during a foam lifetime or as it flows inside a pipe for example. For small-molecular-weight surfactants, their kinetics have been shown to be an important parameter for the foam stability. In the present work, we aimed at studying the relationship between the rheology of protein interfacial films and the kinetics of T1 rearrangements in protein foams.Two dairy commercial products were studied, sodium caseinate and whey protein isolate (WPI). They differ by their molecular structure and surface rheological properties. Purified β-Lactoglobulin, the main protein in WPI, has also been evaluated. Links between T1, surface rheology and foaming properties will be discussed.

• Protein interactions play a key role in determining the final structure and properties of products.

International audience; In their native state, milk lipids are present in the form of dispersed droplets called Milk Fat Globules (MFG, average diameter of 4 µm in human and bovine milks) that have been recently pointed out as key elements of early nutritional programming. The native MFG is a unique biophysical element differing from other lipoproteic objects by its external trilayered membrane inherited from its secretory past. To play its major biological function, i.e. deliver energy to the mammal newborn, the MFG has to be hydrolyzed in the gastro-intestinal tract by lipases. This hydrolysis is typically a heterogeneous phase reaction, in which the lipase has to diffuse and get adsorbed onto the lipid phase before the formation of the enzyme-substrate complex, and the onset of the proper catalytic action. Very few techniques allow assessing the mechanism involved in the enzymatic hydrolysis of complex supramolecular substrates such as milk fat globules in emulsion. To get a better insight of this mechanism, 4-D imaging of gastric and pancreatic lipases enzymes using synchrotron SOLEIL UV fluorescence microscopy was applied. This methodology allowed mapping the adsorption and diffusion of lipases onto/within human or bovine MFG or biomimetic droplets devoid of membrane proteins. These data were completed with simultaneous transmission light imaging of MFG disintegration during hydrolysis. The high sensitivity of the DISCO beamline allowed detecting the auto-fluorescence of the digestive lipases, is a unique tool to unravel their mechanisms of adsorption onto complex substrate using free-label imaging and has generated useful data for infant formula optimization.

This study aimed to investigate the effect of lactose on the ageing-induced structural changes through a varying lactose content in whey protein powders. In this scope, four powders differing in their lactose content (0.1–16 w/w %) were stored at 40 °C and 60 °C for up to 3 months and sampled periodically. A small variation in lactose content of WPI powders was found to affect the level of structural and functional changes during powders ageing. At a higher lactose content (2.6 w/w %), proteins were more rapidly lactosylated and aggregated, with a higher rate than the control WPI powder; whereas at a lower content (0.1 w/w %) the rate of lactosylation and aggregation was considerably limited. These results highlighted the great contribution of the Maillard reaction during ageing of WPI powders. Reducing lactose content in the WPI powders is a promising way to extend their stability among storage.

International audience; Increasing bacterial resistance towards antibiotics has stimulated research for novel antimicrobials. Proteins acting on bacterial membranes could be a solution. Lysozyme has been proven active against E. coli by disruption of both outer and cytoplasmic membranes, with dry-heating increasing lysozyme activity. Dry-heated lysozyme (DH-L) is a mixture of isoforms (isoaspartyl, native-like and succinimide lysozymes), giving rise to two questions: what effects does each form have, and which physicochemical properties are critical as regards the antibacterial activity? These issues were investigated by fractionating DH-L, analyzing structural properties of each fraction, and testing each fraction in vivo on bacteria and in vitro on membrane models. Positive net charge, hydrophobicity and molecular flexibility of the isoforms seem key parameters for their interaction with E. coli membranes. The succinimide lysozyme fraction, the most positive, flexible and hydrophobic, shows the highest antimicrobial activity, induces the strongest bacterial membrane disruption and is the most surface active on model lipid monolayers. Moreover, each fraction appears less efficient than DH-L against E. coli, indicating a synergetic cooperation between lysozyme isoforms. The bacterial membrane modifications induced by one isoform could facilitate the subsequent action of the other isoforms.

The impact of egg white gel (EWG) structure on the process of digestion was investigated using an in vitro digestion model and a multi-scale characterization of the EWG structure. Four different structures of EWG were prepared combining various pH and ionic strength conditions before heating. The extent of digestion, estimated by the appearance of soluble peptides, was greater for the particulate gel comprising spherical aggregates as compared to the filamentous gel comprising linear aggregates. This result may be explained by an alteration of enzyme diffusion due to the microstructural characteristics of the gel, or an alteration of digestive enzyme adsorption or catalytic activity due to local differences in pH within the gel matrices. Peptide identification using LC-MS/MS highlighted that the aggregate morphology modulated ovotransferrin hydrolysis which resulted in the release of specific peptides depending on the EWG structure. This work illustrates the links existing between two multi-step processes, protein structuration into gel matrices and matrix destructuration by digestive enzymes. Such quantitative and qualitative differences reinforce the importance of the food matrix on the digestibility of food and its subsequent nutritional quality.

International audience; 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.

International audience; Dry-heating is considered to be one of the most promising approaches to improving the functionality of food proteins. It has been shown that even if only minor structural modifications occur during dry-heating, the foaming properties of proteins are highly improved. With the recent results obtained in the field of foam stabilization by nanoparticles or protein aggregates in mind, a study was undertaken on the impact of dry-heating of lysozyme, used as a model protein, on its foaming properties. This work highlighted the fact that dry-heated hen egg white lysozyme simultaneously exhibited enhanced foaming properties and aggregation capacity. Although the conditions that favored bulk aggregation (high ionic strength, pH, treatment duration, and protein concentration) also favored foaming properties, the large bulk aggregates were not essential to obtain the best functionality. It is envisaged that heat-treated lysozyme may self-associate at the air/water interface, stabilizing air bubbles.

International audience; The enzymatic lipolysis of complex natural lipoproteic assemblies such as milk fat globules is central in neonatal digestion. This process first requires the rapid adsorption of a lipolytic enzyme, gastric lipase, onto the membrane enveloping the triglyceride substrate before the onset of catalytic activity. The interactions governing lipase adsorption onto this complex lipid/water interface are not fully elucidated. This study was designed to unravel the interactions of recombinant dog gastric lipase (rDGL) with model monolayers presenting liquid-liquid phase coexistence and mimicking the outer leaflet of the milk fat globule membrane. Combining biophysical tools (ellipsometry, tensiometry and atomic force microscopy), it was evidenced that rDGL partitions toward liquid expanded phase and at phase boundaries. rDGL gets adsorbed at several levels of insertion suggesting molecular cooperation that may favor insertion and strongly impacts on the lipid phase lateral organization. The addition of phosphatidylserine, negatively charged, reinforced adsorption; hence besides hydrophobic interactions and as further investigated through surface potential modeling, rDGL adsorption is favored by electrostatic interactions

This work explores the influence of both the physicochemical characteristics of solutes and the solute-matrix interactions on diffusion in casein systems. Diffusion coefficients of three solute groups (dextrans, proteins, and peptides) presenting different physicochemical characteristics, such as molecular flexibility and charge, were measured using the technique of fluorescence recovery after photobleaching (FRAP). The casein systems had the same casein concentration, but different microstructures (suspension or gel), and/or a different pH (5.2 or 6.6). Flexible solutes diffused more rapidly through the casein systems than the rigid ones. Electrostatic interactions between charged solute molecules and the casein matrix were partly screened due to the high ionic strength of the systems. As a consequence, it was the flexibility of the solute molecule (rather than its charge) that most influenced its diffusion through casein systems.

Food products are complex matrices. They contain molecules from several families that interact with each other to generate specific structures and functionalities. These molecules may include proteins and peptides resulting from protein hydrolysis, e.g. in cheese. It is still difficult to establish a clear relationship between a pool of peptides and their techno-functionalities such as emulsifying, foaming, gelling or even texture properties within a complex matrix. Among the data usually known, there is the degree of hydrolysis that provides information about the average size of the peptides formed. A high degree of hydrolysis induces the production of a pool of small-size peptides (less than 20 amino acids). Advances in identification methods have made the identification of peptides present in food products possible. The size, charge, hydropathy index and isoelectric point of the peptide, as well as its secondary structure, can be calculated on the basis of the peptide sequence. The aim of this study was to determine which physicochemical and structural characteristics of peptides are involved in the cheese stretchability. This work is a re-evaluation, using multivariate exploratory analysis, of the experimental data obtained from a former study (Sadat-Mekmene et al., 2013) in which one typical functionality criterion of Swiss-type cheese (stretchability) was measured and peptides were identified. This methodology, based on Principal Component Analysis and Correspondence Analysis, is one way to establish a relationship between peptide characteristics and their techno-functional property within a complex dairy matrix. This statistical approach showed that the peptides predominantly involved in cheese stretchability were a mixture of both hydrophobic and hydrophilic peptides and that they are large enough to interact with each other and with native proteins. This approach could be applied to better understand the impact of peptides on various food matrices and food techno-functionalities.

We examine the internal structure of milk casein micelles using the contrast variation method in Small-Angle Neutron Scattering (SANS). Experiments were performed with casein dispersions of different origins (i.e., milk powder or fresh milk) and extended to very low q-values (∼9 × 10(-4) Å(-1)), thus making it possible to precisely determine the apparent gyration radius Rg at each contrast. From the variation of I(q → 0) with contrast, we determine the distribution of composition of all the particles in the dispersions. As expected, most of these particles are micelles, made of casein and calcium phosphate, with a narrow distribution in compositions. These micelles always coexist with a very small fraction of fat droplets, with sizes in the range of 20-400 nm. For the dispersions prepared from fresh milk, which were purified under particularly stringent conditions, the number ratio of fat droplets to casein micelles is as low as 1 to 10(6). In that case, we are able to subtract from the total intensity the contribution of the fat droplets and in this way obtain the contribution of the micelles only. We then analyze the variation of this contribution with contrast using the approach pioneered by H. B. Stuhrmann. We model the casein micelle as a core-shell spherical object, in which the local scattering length density is determined by the ratio of calcium phosphate nanoclusters to proteins. We find that models in which the shell has a lower concentration of calcium phosphate than the core give a better agreement than models in which the shell has a higher density than the core.

Milk lipids supply most of the calories necessary for newborn growth in maternal milk or infant formulas. The chemical composition of infant formulas has been optimized but not the structure of the emulsion. There is still a major difference between the native emulsions of milk fat globules and processed submicronic emulsions in infant formulas. This difference may modify the kinetics of digestion of emulsions in newborns and influence lipid metabolism. To check this, semi-dynamic gastric in vitro digestions were conducted on three matrices: a standardized milk emulsion containing native milk fat globules referred to as minimally-processed emulsion and two processed model infant formulas (homogenized or homogenized/pasteurized). Gastric conditions mimicked those reported in newborns. The minimally-processed emulsion was lipolyzed and proteolyzed slower than processed formulas. The difference in initial structure persisted during digestion. The surface of the droplets was the key parameter to control gastric lipolysis kinetics, the pattern of released fatty acids and proteolysis by faster hydrolysis of adsorbed proteins.

The effect of heat treatment of milk on the formation of acid gels was investigated using model protein systems. Protein systems contained micellar casein alone (35 g kg −1 ) (systR) or in the combination with either β -lactoglobulin ( β LG) (4 g kg −1 ; systB) or egg ovalbumin (4 g kg −1 ; systO). Proteins in a milk ultrafiltrate (UF) were heat-treated at 90°C for 24 min. The same heat-treated systems without casein were also prepared: the UF alone (systUFR), with β LG (4 g kg −1 ; systUFB) and with ovalbumin (4 g kg −1 ; systUFO). Proteins in pellet and supernatant fractions were analysed using reverse-phase high-pressure liquid chromatography and sodium dodecyl sulphate polyacrylamide gel electrophoresis. The solubility of globular proteins in heated systUFB and heated systUFO was determined at pH 1.6–6.5 by absorbance measurements. Rheological changes during gelation with a starter at 42°C were determined and microstructures of gels by scanning electron microscopy. High quantities of κ -casein and β LG in the form of complexes (disrupted by 2-mercaptoethanol) were found in supernatant of heated systB and not in that of systO. The gelation pH was related to the solubility of the globular proteins, and the gelation pattern for systB and systO resembled that of heated milk and the systR pattern resembled that of unheated milk. The gels of systR were coarse and consisted of large particles. Particles in gels from systB and systO were smaller and less clustered. Although the two globular proteins behave differently during heating, they both confer to the casein micelles their solubility properties as a function of pH. A model is presented where both soluble and colloidal complexes including the globular protein interact at pH 5.5 and initiate the acid gelation.

International audience; We have compared the behavior of ovotransferrin at the air-solution interface in the presence of a monovalention (acetate), or a divalent ion (citrate), the latter being known to induce conformational changesof this protein upon interaction with its iron-binding sites. We have characterised the adsorption layer atthe air–water interface in terms of homogeneity, surface concentration excess and rheological propertiesat pH 4.0. Besides we have investigated the bulk conformation in the presence of the two anions. In thepresence of citrate only, interfacial layers display well-defined domains of higher overall surface concentrationsuggesting multilayers adsorption. Citrate also induces higher helical content and stabilizes theprotein against thermal denaturation. Hence we propose that these changes are involved in the propensityof ovotransferrin to self-assemble at the air–water interface resulting in thick and heterogeneousinterfacial layer.

Adsorption of purified diphosphorylated Al-ovalbumin at the air–water interface was studied by ellipsometry, surface tension, and shear elastic constant measurements. The value of pH did not significantly affect the final value of surface concentration. It affected slightly the kinetics of surface pressure increase and the final value of surface pressure. The interfacial rheology was affected strongly by pH. The interface exhibited a maximum of the shear elastic constant at a pH close to the isoelectric pH of ovalbumin. The bulk protein concentration also had a more pronounced effect on the surface rheology when the protein net charge was low. At a pH where the protein net charge is negative, an increase of the ionic strength increased the final value of the shear elastic constant. The results suggest that interactions between adsorbed ovalbumin molecules, which form slowly in the adsorbed layer upon conformational rearrangements, impart rigidity to the interface, and that these intermolecular associations are hindered at high protein net charge.

Globular milk proteins have lots of potential applications in the form of highly purified fractions due to their numerous biological, nutritional and functional properties. Membrane filtration is now envisaged as a promising purification technology as it can be more environmental-friendly than chromatography and quite as efficient as this current technique. However, the impact of membrane filtration on the final properties of proteins still needs to be clarified and especially in case of metalloproteins as they have the specificity to bind one cofactor entity which is highly decisive for the preservation of their structure and functionality. In this study, the impact of dead-end ultrafiltration on the properties of the metalloprotein a-lactalbumin (a-LA) was described depending on the membrane cut-off. For membranes with a cut-off larger than a-LA molecular weight (30 or 100 kg mol 1), structural and functional modifications evidenced after permeation of a mixture between the apo- (without cofactor) and holo-form (native form) were consistent with an increase in the holo-a-LA content but did not point out any physical impact on a-LA structure. The modification of a-LA properties was rather attributed to the displacement of the equilibrium between the apo- and holo-forms during filtration. With a membrane cut-off close to a-LA molecular weight (10 kg mol 1), structural and functional properties of the protein observed after permeation could not be reasonably associated with the increase in the holo-a-LA content. Results suggested that shear stress inside membrane pores slightly impacted a-LA structure and thus dictated final properties of the permeated fraction especially in terms of solubility and thermal stability. The impact of dead-end UF through the 10 kg mol 1 membrane was supposed to be moderate and to affect less than 30–40% of permeated proteins.

ATPase activity of the F 1 -ATPase from the thermophilic Bacillus PS3 (TF 1 ) was measured as a function of ATP concentration at three different magnesium ion concentrations. A high-performance chromatographic method was used to determine directly ADP concentration in the reaction medium and to measure the steady-state rate of its appearance. Multiphasic curves of ATPase activity versus ATP concentration were obtained, with a first saturating rate mode at low ATP concentrations, a higher rate mode which became predominant at ATP concentrations depending on magnesium concentration, and a marked inhibition of ATP hydrolysis at high ATP concentrations. These curves could be simulated with equivalent residual error either by assuming that the ATP-magnesium chelate is the substrate of the enzyme, free magnesium being an inhibitor, or that free ATP is the substrate, free magnesium being an essential activator. In both cases, the observed hydrolysis rate was assumed to be the sum of two independent rates with different kinetic parameters, as would be the case for an enzyme with functionally heterogeneous and independent catalytic sites. Cross-checking of the different series of kinetic parameters with the binding affinity of TF 1 for ATP, measured by a high-performance chromatographic method, is in favour of a model in which the hydrolysis rate is determined by the concentration of free ATP, free magnesium being an essential activator.

Precipitation of calcium phosphates occurs in dairy products and depending on pH and ionic environment, several salts with different crystallinity can form. The present study aimed to investigate the effects of NaCl and citrate on the characteristics of precipitates obtained from model solutions of calcium phosphate at pH 6·70 maintained constant or left to drift. The ion speciation calculations showed that all the starting solutions were supersaturated with respect to dicalcium phosphate dihydrate (DCPD), octacalcium phosphate (OCP) and hydroxyapatite (HAP) in the order HAP>OCP>DCPD. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analyses of the precipitates showed that DCPD was formed at drifting pH (acidic final pH) whereas poor crystallised calcium deficient apatite was mainly formed at constant pH (6·70). Laser light scattering measurements and electron microscopy observations showed that citrate had a pronounced inhibitory effect on the crystallisation of calcium phosphates both at drifting and constant pH. This resulted in the decrease of the particle sizes and the modification of the morphology and the microstructure of the precipitates. The inhibitory effect of citrate mainly acted by the adsorption of the citrate molecules onto the surfaces of newly formed nuclei of calcium phosphate, thereby changing the morphology of the growing particles. These findings are relevant for the understanding of calcium phosphate precipitation from dairy byproducts that contain large amounts of NaCl and citrate.

International audience; Identification of the key physicochemical parameters of proteins that determine their interfacial properties is still incomplete and represents a real stake challenge, especially for food proteins. Many studies have thus consisted in comparing the interfacial behavior of different proteins, but it is difficult to draw clear conclusions when the molecules are completely different on several levels. Here the adsorption process of a model protein, the hen egg-white lysozyme, and the same protein that underwent a thermal treatment in the dry state, was characterized. The consequences of this treatment have been previously studied: net charge and hydrophobicity increase and lesser protein stability, but no secondary and tertiary structure modification (Desfougères, Y.; Jardin, J.; Lechevalier, V.; Pezennec, S.; Nau, F. Biomacromolecules 2011, 12, 156-166). The present study shows that these slight modifications dramatically increase the interfacial properties of the protein, since the adsorption to the air-water interface is much faster and more efficient (higher surface pressure). Moreover, a thick and strongly viscoelastic multilayer film is created, while native lysozyme adsorbs in a fragile monolayer film. Another striking result is that completely different behaviors were observed between two molecular species, i.e., native and native-like lysozyme, even though these species could not be distinguished by usual spectroscopic methods. This suggests that the air-water interface could be considered as a useful tool to reveal very subtle differences between protein molecules.

International audience; Adsorption of purified apo-ovotransferrin at the air-water interface was studied by ellipsometry, surface tension, polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS), and shear elastic constant measurements. No significant difference was observed between pH 6.5 and 8.0 as regards the final value of surface concentration and surface pressure. However at low concentration, a weak barrier to adsorption is evidenced at pH 6.5 and confirmed by PM-IRRAS measurements. At a pH where the protein net charge is negative (pH 8.0), the behavior of ovotransferrin at the air-water interface is more influenced by charge effects rather than bulk concentration effects. At this pH, the interface exhibits a low shear elastic constant and a spectral signature not usual for globular proteins.

Protein chemical degradations occur naturally into living cells as soon as proteins have been synthesized. Among these modifications, deamidation of asparagine or glutamine residues has been extensively studied, whereas the intermediate state, a succinimide derivative, was poorly investigated because of the difficulty of isolating those transient species. We used an indirect method, a limited thermal treatment in the dry state at acidic pH, to produce stable cyclic imide residues in hen lysozyme molecules, enabling us to examine the structural and functional properties of so modified proteins. Five cyclic imide rings have been located at sites directly accessible to solvent and did not lead to any changes in secondary or tertiary structures. However, they altered the catalytic properties of lysozyme and significantly decreased the intrinsic stability of the molecules. Moreover, dimerization occurred during the treatment, and this phenomenon was proportional to the extent of chemical degradation. We propose that succinimide formation could be responsible for covalent bond formation under specific physicochemical conditions that could be found in vivo.

International audience; We have studied single curved films stabilized by globular proteins, using small angle scattering. By combining both the use of in-house X-ray and synchrotron radiation, we have measured the structural properties of films (thickness, electronic density) by controlling the physicochemical properties of protein (ovalbumin, pH 7, bulk concentration 10 g L−1). For each experiment, solutions of highly purified protein were freshly prepared to eliminate any problem of aging. The observation of Kiessig fringes shows that the films are thin with an average thickness of 60 nm. Benefiting from the fine angular resolution and the short acquisition time of a synchrotron source, we have highlighted a stratification formation inside the films. This phenomenon suggests protein structural reorganization under confinement, possibly driven by high osmotic pressure.

Heat treatment of milk at 85–95 °C has long been reported to increase the pH of gelation and firmness of acid milk gels; hence its wide application in yoghurt manufacture. These changes have been attributed to the formation of heat-induced whey protein/κ-casein complexes in the milk, to which heat-denatured whey protein ingredients may be substituted. However, variations in resulting gels show that a possible role of κ-casein in determining the functional acid-gelation property of the complexes needs investigating. Model heat-induced whey protein/κ-casein complexes were produced of κ-casein content from 0 to 40% (w/w), but of similar size, secondary structure, surface hydrophobicity and thiol/disulphide distribution. These complexes were added to whey protein-free skim milk systems and the resulting acid-gelation behaviour of the milks was evaluated. The results showed a modification of the pH of gelation that was explained more by variation of the pI of complexes than by the κ-casein content.

International audience; Understanding filtration mechanisms at a molecular level is important for predicting structural and functional properties of globular milk proteins after membrane operations. This stage is thus highly decisive for the further development of membrane separations as an efficient alternative to chromatographic processes for the fractionation of milk proteins. In this study, we proposed an original and complete analytical package for the examination of the putative effect of filtration at both macroscopic and molecular levels. We then investigated the pertinence of this analytical package during ultrafiltration (UF) of globular milk proteins in both dead-end and crossflow modes. Reverse-phase HPLC combined with statistical computing was shown to be relevant for the assessment of even slight physically induced modifications. Adaptations of circular dichroism and solubility measurements, regarding their respective dependence on temperature and pH, were also useful for an accurate evaluation of functional modifications. At last, immunochemistry was proven to be a pertinent tool for the specific detection of modifications affecting a targeted protein, even in mixed solutions. Moreover, results obtained by such methods were shown to be coherent with data obtained from classical techniques such as fluorescence. For β-lactoglobulin, some physically induced modifications were noticed in the permeate because of shear stress inside membrane pores. In the case of α-lactalbumin dead-end UF, permeation was shown to affect protein characteristics because of an increase in the relative calcium content responsible for a conformational transition from the apo-form to the holo-form of the protein. Finally, during crossflow UF with limited transmission of BSA, observations were coherent with a partial aggregation because of the circulation of proteins in the filtration pilot. Such a hypothesis corroborates results previously mentioned in the literature.

International audience; The aim of this work was to get further insight into the formation of the interfacial film by ovalbumin and lysozyme in equimolar binary solutions, as well as the organization of these proteins inside the interfacial film. Our approach consisted in the sequential adsorption of the two proteins, with or without previous replacement of the sub-phase with protein-free buffer before injection of the second protein. The results suggest that ovalbumin controls surface pressure of the interfacial film and whatever the order of adsorption, there would be a specific and stratified organization of the two proteins inside the interfacial film: an ovalbumin monolayer in direct contact with the air-water interface and multilayers of lysozyme below this top layer. The experiments of replacement of the sub-phase suggest that, for both proteins, the adsorption film is almost resistant to this replacement with protein-free buffer, showing an apparently irreversible adsorption for the time-scale considered and at high concentrations. Moreover, the synergy between ovalbumin and lysozyme put into evidence during the concomitant adsorption of the two proteins in a previous work (Le Floch-Fouéré et al., 2009, Food Hydrocolloids 23, 352-365) is a phenomenon which occurs as the result of adsorption of the proteins at the air-water interface.

International audience; Dry heating is performed in egg product industries to pasteurise egg white powder. This treatment (55 to 80°C during a few days) is also used to improve egg white powder functional properties among other foaming properties. Several studies have shown this foaming properties' improvement with dry heating length (Kato et al, 1989; Baron et al, 2003; Van der Plancken et al, 2007; Talansier et al, 2009) that Kato et al (1989) attributed to protein surface hydrophobicity increase. However, during these treatments, soluble and insoluble covalent aggregates were also generated (Kato, 1989; Van der Plancken et al, 2007; Talansier et al, 2009) that may be involved in foaming properties improvement. Conclusions from such a complex protein solution as egg white are difficult to draw; this is the reason why we choose ovalbumin, the major egg white protein (54% of total protein amount) to identify the molecular species generated by dry heating that are responsible for foaming properties' improvement. Ovalbumin foaming properties are improved after dry heating (Kato, 1990a) and the protein undergoes some mild conformational changes close to the molten globule state as well as aggregation driven by hydrophobic interactions and disulfide bonding (Kato, 1990b; Matsudomi, 2001). The present study has been performed to identify the molecular species generated by dry heating responsible for foaming properties improvement. Most of the data of the literature were confirmed as we found that ovalbumin aggregated and that deamidation occurred. We also identified less negatively charged ovalbumin that we attributed to dephosphorylation. We performed surface pressure and ellipsometric angle measurement on dry heated ovalbumin but also on dephosphorylated, desamidated and aggregated forms. Dry heated ovalbumin shows faster adsorption kinetics to air water interface than non-treated one. However the equilibrium surface pressure and surface concentration are quite close. Shear elastic constant measurement showed far higher values for dry heated Ovalbumin. Foaming properties of the different molecular species were also measured when possible. This multidimensional approach helped in the understanding of the characteristic of the interfacial film that explain foaming properties.

International audience; The dragline fiber of spiders is composed of two proteins, the major ampullate spidroins I and II (MaSpI and MaSpII). To better understand the assembly mechanism and the properties of these proteins, the adsorption behavior of the recombinant proteins of the spider Nephila clavipes produced by Nexia Biotechnologies Inc. has been studied at the air-water interface using ellipsometry, surface pressure, rheological, and infrared measurements. The results show that the adsorption is more rapid and more molecules are present at the interface for MaSpII than for MaSpI. MaSpII has thus a higher affinity for the interface than MaSpI, which is consistent with its higher aggregation propensity in water. The films formed at the interface consist of networks containing a high content of intermolecular beta-sheets as revealed by the in situ polarization modulation infrared absorption reflection spectra. The infrared results further demonstrate that, for MaSpI, the beta-sheets are formed as soon as the proteins adsorb to the interface while for MaSpII the beta-sheet formation occurs more slowly. The amount of beta-sheets is lower for MaSpII than for MaSpI, most likely due to the presence of proline residues in its sequence. Both proteins form elastic films, but they are heterogeneous for MaSpI and homogeneous for MaSpII most probably as a result of a more ordered and slower aggregation process for MaSpII. This difference in their mechanism of assembly and interfacial behaviors does not seem to arise from their overall hydrophobicity or from a specific pattern of hydrophobicity, but rather from the longer polyalanine motifs, lower glycine content, and higher proline content of MaSpII. The propensity of both spidroins to form beta-sheets, especially the polyalanine blocks, suggests the participation of both proteins in the silk's beta-sheet crystallites.

International audience; The interfacial properties (kinetics of adsorption at the air/water interface, rheology of the interfacial layer) of ovalbumin molecules, unheated or previously heat-denatured in solution (10 g L(-1), pH 7, NaCl 50 mM) under controlled conditions (up to 40 min at 80 degrees C), were investigated. Heat treatments induced the formation of covalent aggregates which surface exhibits a higher hydrophobicity and an increased exposition of sulfhydryl groups when compared to native ovalbumin (unheated). Although they have a larger hydrodynamic size, aggregates adsorb as fast as native ovalbumin at the air/water interface. However, aggregates are able to established rapid contacts in the interfacial layer as shown by the fast increase of both surface pressure and shear elastic constant. In contrast, native ovalbumin needs longer time to developed intermolecular contacts and exhibits lower foam stability even if the shear elastic constant on aging reached higher value than for ovalbumin aggregates.

Correction for ‘Structural heterogeneity of milk casein micelles: a SANS contrast variation study’ by Antoine Bouchoux et al., Soft Matter, 2015, DOI: 10.1039/c4sm01705f.

The interfacial properties (kinetics of adsorption at the air/water interface, rheology of the interfacial layer) of ovalbumin molecules, unheated or previously heat-denatured in solution (10 g L(-1), pH 7, NaCl 50 mM) under controlled conditions (up to 40 min at 80 degrees C), were investigated. Heat treatments induced the formation of covalent aggregates which surface exhibits a higher hydrophobicity and an increased exposition of sulfhydryl groups when compared to native ovalbumin (unheated). Although they have a larger hydrodynamic size, aggregates adsorb as fast as native ovalbumin at the air/water interface. However, aggregates are able to established rapid contacts in the interfacial layer as shown by the fast increase of both surface pressure and shear elastic constant. In contrast, native ovalbumin needs longer time to developed intermolecular contacts and exhibits lower foam stability even if the shear elastic constant on aging reached higher value than for ovalbumin aggregates.

International audience