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Acid milk gels with fat (3.5 or 10%) or without fat containing 0.2–1% of whey proteins (WP) or 0.2–1.5% of protein aggregates (fractal aggregates, microgels and mixed casein/WP aggregates with an 80/20 ratio) were investigated. The fat-containing systems were homogenized and the systems were preheated (90 °C, 11 min) and acidified to a pH of 4.6 by adding glucono-delta-lactone. The protein composition of the fat droplet interface was characterized by SDS-PAGE and the textural and rheological properties, microstructure, and whey separation of acid networks were determined. WP and fractal aggregates showed the best ability to improve the textural properties and microstructure of all acid milk gels and reduce whey separation. Increasing the concentrations in microgels and mixed aggregates did not lead to an increase in gel firmness or generate a strong impact on the protein network, but a high concentration in mixed aggregates could reduce whey separation. The fat droplet interface was made almost exclusively of caseins, even if the fractal aggregates could also be adsorbed when the interfacial surface was increased either through fat content or through an increase in homogenization pressure. Adding proteins changes the textural properties of the acid gels in all the systems, mainly due to their role in the continuous phase.

Soybean protein isolates (SPI) represent an important source of proteins that are used to prepare oil-in-water (o/w) emulsions. The influence of an innovative treatment (high hydrostatic pressure, HHP) combined with calcium addition at different pH levels and protein concentrations on the formation and stability of o/w SPI emulsions was evaluated in this work. When applied separately, calcium addition or HHP treatment produced different effect at pHs 5.9 and 7.0. Calcium addition led to stable emulsions with decreased flocculation index (FI) at pH 5.9 and low protein concentration (5 g L−1), whereas at pH 7.0, this effect was observed at high protein concentration (10 g L−1). In these conditions, calcium would favor the arrival of big aggregates to interface, which would be modified and adsorbed during homogenization. Treatment with HHP decreased FI and stabilized emulsions during storage at pH 7.0 (but not at pH 5.9) when prepared from 10 g L−1 protein dispersions. In these conditions, protein unfolding due to HHP-induced denaturation, and high ζ-potential would be responsible for emulsion improvement. Combination of calcium addition and HHP treatment impaired both formation and stabilization abilities of SPI at both pHs. Bridging flocculation was enhanced in these samples while interfacial protein concentration and percentage of adsorbed protein were increased. Thus, soybean proteins that were subjected to combined calcium addition and HHP treatment exhibited a great ability to associate each other, what can be useful to improve other functional properties such as gelation., Centro de Investigación y Desarrollo en Criotecnología de Alimentos

Pasteurised liquid egg products represent around 70% of total egg products. Pasteurisation, necessary for microbiological safety, is a unit operation undergone by the totality of liquid whole egg commercialized. The present work aims to investigate the impact of a wide range of pasteurisation rates (among those classically used in industry) on the interfacial properties, in vitro digestibility and antigenicity of whole egg proteins, in order to optimize the unit operation parameters to ensure all whole egg qualities. Pasteurisation from 4 to 10 min at 60 °C improved protein interfacial properties, in vitro digestibility and decreased ovomucoid antigenicity but did not significantly change ovotransferrin and lysozyme antigenicity. On the opposite, pasteurisation from 4 to 10 min at 66 °C decreased protein in vitro digestibility and increased drastically ovotransferrin antigenicity. Pasteurisation from 4 to 10 min at 60 °C enabled to reach all whole egg properties, but for safety reasons, higher pasteurisation rates at 62 or 64 °C are good compromises to ensure microbiological safety without excessively damaging the functional properties.

Egg white is a key ingredient in many food products as it combines high nutritional quality with excellent functional properties. However, it is also one of the leading causes of food allergy in childhood. Dehydrated egg white is a common form of industrial egg white. To increase the functional properties, egg white powders are heated which may change protein antigenicity and susceptibility to digestion. The present work highlighted the effect of a wide range of dry heating rates (from 1 to 10 days between 60 and 90 °C) simultaneously on the interfacial properties, antigenicity and susceptibility to in vitro digestion of egg white proteins. Thanks to a powerful statistical methodology, i.e. multiple factor analysis (MFA), that enables to consider all the data in a common space, intermediate dry heating treatments (2–5 days at 70 °C or 1–2 days at 80 or 90 °C) were found to be good compromise to improve egg white functionality without enhancing too much protein resistance to digestion or protein antigenicity.

Most studies on functionality of soybean proteins have been made with total protein isolates, with the drawback to limit the knowledge of phenomena due to the important complexity of protein composition. In this study we have tried to better understand the behavior of soy emulsions by using their two partially purified fractions: β-conglycinin (7S) and glycinin (11S). Furthermore, we have assessed the combined effect of temperature (20-60 ºC) and high pressure (0.1-600 MPa) on physicochemical, microstructural and rheological properties of oil-in-water emulsions prepared with 7S or 11S proteins at 7% (w/v). Our results show that 7S and 11S emulsions behaved differently under the combined treatments and that 7S protein was responsible for the global properties of soybean emulsions, whereas 11S proteins exerted a negligible effect. From 400 MPa and at 60 ºC, we have noticed for 7S emulsions an increase of flocculation and gelation, largely confirmed by confocal microscopy due to aggregation between adsorbed and aqueous 7S proteins. Globally we have evidenced that temperature reinforces the effect of high pressure and that the threshold to obtain some changes is 400 MPa. The very different behavior of 7S and 11S proteins in emulsions under treatments could help to orientate their commercial use as function of planed treatments Fil: Puppo, Maria Cecilia. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; Argentina Fil: Beaumal, Valérie. Instituto National de Recherches Agronomiques. Biopolymères Interactions Assemblages; Francia Fil: Speroni Aguirre, Francisco José. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; Argentina Fil: De Lamballerie, M.. Genie Des Procedes - Environnement - Agro-alimentaire. Genie Des Procedes - Environnement - Agro-alimentaire Sede Oniris; Francia. Centre National de la Recherche Scientifique; Francia Fil: Añon, Maria Cristina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; Argentina Fil: Anton, Marc. Instituto National de Recherches Agronomiques. Biopolymères Interactions Assemblages; Francia

Low-density lipoproteins (LDL) are considered to be the main contributors to the exceptional emulsifying activity of hen egg yolk. However, the lack of understanding of the molecular basis for LDL functionality is a significant obstacle for good control of yolk emulsions. Consequently, we have attempted to link the structure and the characteristics of LDL with their emulsifying properties. After purification of LDL, we have determined their protein and lipid compositions, their ultrastructure, and then extracted their apoproteins for physicochemical characterisation. LDL are composed of about 12% of proteins and 87% of lipids and present a spherical shape with a mean diameter of about 35 nm. LDL solubility is high, whatever the medium conditions, because of their low density. LDL contain five major apoproteins out of which the apoprotein of 15 kDa is considered to be the most surface-active. After extraction, this apoprotein showed a high proportion of amphipathic α-helix chains, explaining the high capacity of this apoprotein to adsorb at the oil–water interface.

This study aimed to evaluate the effect of the processing and storage conditions on the physical and functional properties of egg yolk (EY) powders. The spray-drying temperature (160 °C vs . 180 °C), storage temperature (15 °C vs. 30 °C) and time (1, 2, 4 and 8 months) and n−3 enrichment through hen diet were investigated. The spray drying temperature and storage conditions modified the water content, water activity and the particle size distribution of EY powders. Flowability of the powders and the emulsifying properties were not significantly affected from an industrial point of view. On the opposite, the viscosity increased with the spray-drying temperature as well as the temperature and time of storage in rehydrated powders. Powders prepared with n−3 enriched egg yolks exhibited lower melting peaks temperatures, a marked yellow colour and higher fluidity of the solutions, but the overall properties remained unchanged. This study clearly attests the possibility of an industrial production of n−3 enriched EY powders.

International audience; Interfacial and emulsifying properties of rice protein concentrate (RPC) have been studied in order to evaluate its potential application to stabilize O-W emulsions. The interfacial behaviour of adsorbed proteins films constituted with RPC has been studied at the air-water and oil-water interfaces at two pH values (2 and 8). The type and the amount of soluble proteins have been determined in aqueous dispersions and results put forward the presence of most frequent rice protein profile and a significant degree of protein denaturation with a very low solubility. Air-water and oil-water interfacial properties have been determined as a function of time, concentration and pH: air-water by surface pressure under compression-expansion cycles and oil-water by interfacial tension. Interfacial rheology has been studied under dilatational deformations, either at the initial step of film formation or once the interfacial tension was at equilibrium (the film was completely formed). RPC stabilised O-W emulsions has been also analysed by Droplet Size Distribution (DSD) measurements and interfacial protein concentration. Both interfacial and bulk emulsion properties reveal that RPC showed an enhanced potential as emulsifier at low pH. Globally; results indicate clearly important differences in the structural characteristics of rice protein films between pH 2 and 8 that impact on emulsifying properties.

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; International audience; Interfacial and emulsifying properties of potato protein isolate (PPI) have been studied to evaluate its potential application to stabilize oil/water emulsions at two pH values (2 and 8). The amount, type, and solubility of proteins and the size of aggregates have been determined in aqueous dispersion. Air water and oil-water interfacial properties (adsorption, spreading, and viscoelastic properties) have been determined as a function of concentration and pH using soluble phases of PPI The behavior of PPI stabilized oil/water emulsions has been then analyzed by droplet size distribution measurements and interfacial Concentration. PPI exhibits low solubility over a wide range of pH values, with the presence of submicrometer aggregates. The pH value exerts a negligible effect on interfacial tension (oil water) or surface pressure (air water) but displays very important difference in viscoelastic properties of the interfacial films formed between oil and water. In this sense, pH 8 provides a major elastic response at Oil Water interfaces as compared to pH 2. In relation with this result, a much higher ability to produce fine and stable emulsions is noticed at pH 8 as compared to pH 2. Consequently, there is an evident relationship between the theological properties of the oil water interfacial films and the macroscopic emulsion behavior.

International audience; The interfacial behaviour of adsorbed protein films constituted with a crayfish protein derivate that is typically produced as by-product from the food industry, has been studied at the air water and oil water interfaces. An analysis of the surface pressure under compression-expansion cycles of this protein was carried out as a function of time, concentration and pH (2 and 8). Besides, interfacial tension and adsorption kinetics also were determined as a function of time at different concentrations and pH values. Interfacial theological properties were studied under dilatational deformations applied to a single droplet, either at the initial step of film formation or once the interfacial tension was at equilibrium and the film was completely formed. The contribution of the interfacial properties to the behaviour of oil-in-water emulsions stabilised with this protein derivative were also analysed. Finally, droplet size distributions obtained for concentrated emulsions stabilised by crayfish protein were analysed and related to the interfacial tension behaviour. We have demonstrated that crayfish proteins at pH 8 show higher solubility, smaller aggregates and better interfacial activity (higher surface pressure and lower interfacial tension) with higher interfacial viscoelasticity, than at pH 2. A two-dimensional model of the results showed that oil water and air water interfaces are clearly related to the improved stability of emulsion made with crayfish proteins at pH 8. (C) 2011 Elsevier Ltd. All rights reserved.

International audience; The effect of high-pressure treatment on structural and rheological properties of soybean protein dispersions was studied. A sequential high-pressure/thermal treatment was also analyzed. Dissimilar effects on soy protein isolate (SPI) and the enriched soybean protein fractions: β-conglycinin (βCEF) and glycinin (GEF) were observed. High pressure (600 MPa) promoted βCEF gelation, but did not modify the rheological properties of GEF in spite of its complete denaturation. Pressure treatment also induced the establishment of hydrophobic interactions and disulfide bonds that allowed the formation of soluble high molecular mass aggregates from the different polypeptides of both β-conglycinin and glycinin. Protein strands formation was detected in matrix microstructure of HP-treated SPI and βCEF dispersions in accordance with their rheological behavior of weak gels. In the case of GEF modifications induced by HP in the microstructure (apparition of large granules) were not accompanied by rheological changes. Heating process after HP treatment induced protein gelation. A decrease in the temperature of onset of matrix formation of SPI and βCEF samples was observed. The magnitude of this effect was proportional to the intensity of HP treatment. Contrarily, HP provoked a delay in gelation process of GEF dispersions. During the thermal cycle, previous HP treatment diminished the ability of both soybean globulins to establish hydrophobic interactions on heating and hydrogen bonds on cooling, thus obtaining gels with small elastic modulus.

International audience; Processing treatments such as temperature or high pressure (T/HP) can modify the structure and emulsifying properties of soybean protein isolates (SPIs). Few studies concern the processing of previously prepared oil-in-water emulsions stabilized with SPIs. Furthermore, the combined effects of T and HP were not assessed. Consequently, the aim of this study was to better understand the impact of the combined T/HP (T 20-60 degrees C/HP 0.1-600MPa) treatment on physicochemical and rheological properties of emulsions prepared with native SPIs at 7% (w/v). Our results show that the size and aggregation of oil droplets of emulsions prepared with SPI 7% (w/v) solutions are not altered by the combined T/HP treatment. Such emulsions did not flocculate or coalesce. Simultaneously, we observed a significant increase of the apparent viscosity with the intensification of pressure, which was reinforced by temperature. This phenomenon can be attributed to gelation of non-adsorbed soybean proteins facilitated by their high concentration. Furthermore, temperature seems to improve this gelation process but only until 400 MPa. For higher pressure, the combined effect of temperature and pressure conduced to dissociation of the protein aggregates, lowering gelation. This distinct behavior could be used to obtain SPI emulsions with modulated rheological properties.

International audience; In this study, the impact of mechanical treatments on the physicochemical and emulsifying properties of hen egg yolk and its fractions plasma and granules has been assessed. Yolk, plasma, and granule dispersions at pH 4.0 and 0.75 M NaCl were subjected to rotor-stator and high-pressure pretreatments at different dynamic pressure levels: 30, 100, and 200 bar at 20 degrees C. Physicochemical characteristics (protein solubility, rheological behavior, and micro- and ultra-structures) and emulsifying properties (oil/water 60:40 emulsions: droplet size and flocculation, protein adsorption) of control dispersions and dispersions subjected to mechanical pretreatments (rotor-stator or high pressure) were compared. Homogenization at high pressures (100 and 200 bar) led to a decreased protein solubility and to an increase in apparent viscosity of yolk and plasma dispersions. These pressures certainly disrupted low-density lipoproteins (LDL) particles and generated aggregates of protein! s liberated from LDL and livetins in the plasma fraction, and led to a moderated reorganization of the microstructure of granules. Despite the modifications observed in the pretreated plasma and granules dispersions, the oil droplet diameter and the bridging flocculation obtained in emulsions made with these dispersions were similar to that obtained with untreated dispersions. Results concerning interfacial protein adsorption suggested that preformed or natural aggregates at least partially persist at the oil-water interface.

International audience; Low density lipoproteins (LDL) from egg yolk have a classical structure of lipoprotein with a core of neutral lipids surrounded by a monolayer of apoproteins and phospholipids. This structure collapses during adsorption and all constituents spread at the interface. To understand better the nature of the interactions between apoproteins and lipids at the interface, we have deposited LDL at an air-water interface and analysed the isotherms during their compression on a Langmuir trough. Then, these LDL films were studied by atomic force microscopy (AFM) imaging. To identify the protein and lipid structures, we imaged films before and after lipid solubilisation by butanol. To study the interactions in the LDL films, we have varied the pH, ionic strength and used simplified model systems. We also studied the correlation between observed structures and interfacial rheology of the film. The isotherms of interfacial LDL films were similar for pH 3 and 7, but their structures observed in AFM were different. At surface pressures below the transition corresponding to the demixion of apoprotein-neutral lipid complexes, the LDL film structure was not governed by electrostatic interactions. However, above this surface pressure transition (45mN/m), there was an effect of charge on this structure. Around the transition zone, the rheological properties of LDL films at pH 3 were different as a function of pH (viscous at pH 3 and visco-elastic at pH 7). So, the rheological properties of LDL films could be linked to the structures formed by apoproteins and observed in AFM.

International audience; To identify apoproteins present in purified low-density lipoproteins from hen egg yolk in relation with their emulsifying properties, they have been separated by SDS-PAGE. We identified two different proteins by liquid chromatography-tandem mass spectrometry analysis of the peptides obtained by the trypsin digestion of protein gel bands. Apovitellenin I was identified as a monomer and a dimer. Its amino acid sequence was totally confirmed, and molecular mass determination by liquid chromatography-mass spectrometry showed that it did not present post-translational modifications but only a slight heterogeneity by the loss of one or two amino acids at the C-terminal part of the protein. Apolipoprotein B was identified into seven bands corresponding to fragments resulting of a processing of the hen blood apo-B protein. The identity of the fragments was determined by the observation of the sequence coverage by trypsin peptides and the sequence alignment with homologous human blood apolipoprotein B-100.

International audience; Hen egg yolk is largely used as an ingredient in food emulsions due to its exceptional emulsifying properties. Low- density lipoproteins ( LDL) are the main egg yolk constituents and the most important contributors to yolk emulsifying properties. To better understand the LDL adsorption mechanism and spreading at the interface, we extracted and studied LDL at different interfaces. At the air- water interface, the LDL film isotherm presents three transitions, and two were identified by each lipid class present in LDL. The last transition should be due to apoproteins- lipids complexes. During LDL adsorption, the presence of apoproteins at the LDL surface and the neutral lipid core is necessary. At pH 3 and pH 7, LDL are disrupted and spread quasi- similarly at the air- water interface, contrary to the oil- water interface where LDL spread more at pH 7 than at pH 3.

This study evaluated the potentiality of high-pressure treatment to stabilise microbiologically emulsions made with yolk without causing destabilisation and gelation. The effects of two levels of treatment (200 or 500 MPa) on the properties (oil droplet size, interfacial protein concentration and composition), the rheology, and the microbiology of yolk emulsions prepared at two pH values (3.0 and 7.0) were determined. Our results showed that, oil droplet size, interfacial protein concentration and composition were not altered by the high-pressure treatments. The rheological study demonstrated that high-pressure treatment induced a significant increase of viscosity in emulsions prepared at pH 7.0, whereas no obvious thickening was noticed in emulsions prepared at pH 3.0. Furthermore, as the protein concentration increased, the effect of high-pressure was more pronounced. Microbial analysis revealed that high-pressure treatment allowed an efficient reduction of the microbial charge of emulsions and that this effect was better at acidic pH than at neutral pH. Consequently, high-pressure treatment could be used to stabilise yolk emulsions in acidic conditions.

Hen egg yolk is a traditional ingredient used in a wide variety of food emulsions, especially fluid sauces. Industrial processing of these sauces generally involves heat treatments in order to pasteurise or sterilise them. These heat treatments may cause undesired gelation of the emulsion, because egg yolk proteins are particularly thermosensitive. Heat gelation of oil-in-water emulsions prepared with egg yolk may differ from that of egg yolk solutions, because of the influence of oil droplets on network formation. In this study, we investigated the influence of oil droplets on the gelation of oil-in-water emulsions made with yolk. We studied three pH values: 3.0, 5.0 and 7.0 with a constant NaCl concentration: 0.55 M. Oil droplet size was controlled after emulsification, gelation of solutions and emulsions was monitored in situ by coupling heating with recording viscoelastic properties, and transmission electron microscopy was conducted in heat-set emulsion gels. In an attempt to target the proteins that impose the kinetic of gelation of egg yolk, we repeated the experiment with plasma and granules, the main fractions of yolk. In situ rheology showed that, in our experimental conditions [especially oil volume fraction (0.3) and oil droplet size (d3.2=1mgr;m)], emulsions made with yolk and plasma have a similar gelation process with oil droplets acting as inactive fillers. Furthermore, transmission electron microscopy showed similar network characteristics between heated emulsions made with yolk and plasma. Moreover, we demonstrated that acidic conditions provided the fastest gelation of yolk solutions and emulsions. On the other hand, in emulsions prepared with granules, oil droplets behaved as active filler particles and reinforced the gel strength.

Comprehension of hen egg yolk emulsifying properties remains incomplete because competition between its various emulsifiers (proteins and lipoproteins containing phospholipids) has not been clearly elucidated and colloidal interactions between yolk-stabilised oil droplets have not been documented. Recent studies emphasised the interest of the fractionation of yolk into plasma and granules to improve this comprehension. In the present study, we characterised, concurrently, emulsion properties (oil droplet size and stability against creaming) and interface attributes (interfacial concentrations of proteins and phospholipids, SDS-PAGE profiles of adsorbed proteins and zeta potential) in oil-in-water (O/W) emulsions prepared with yolk, plasma and granules. We observed these features at four physicochemical conditions (pH 3.0 or 7.0 and at 0.15 or 0.55 M NaCl). Emulsion properties in emulsions made with yolk or plasma varied similarly as a function of pH and NaCl concentration whereas granules emulsions exhibited distinct properties. Therefore the main contributors to yolk emulsifying properties are to be sought for among plasma constituents (proteinaceous or phospholipids). Since, in plasma emulsions, variations of emulsion stability against creaming correlated exclusively to variations of protein interfacial concentration, a driving contribution of the proteinaceous part of plasma, namely apo-LDL, was hypothesised. In the pH and ionic strength ranges studied, zeta potentials of the interfaces were low, excluding extended electrostatic repulsion between oil droplets. We deduced that steric repulsion is the main interaction opposing to droplet aggregation in food emulsions made with yolk.