Interfacial properties, film dynamics and bulk rheology:A multi-scale approach to dairy protein foams

International audienceHypothesis: 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

Stability and rheology of liquid foams from dry-heated whey protein powders

L’objectif de ce travail est d’identifier les conditions et les mécanismes permettant la création d'aptitudes nouvelles ou améliorées des protéines du lactosérum à la stabilisation et texturation des mousses alimentaires.À cette fin, nous avons étudié la rhéologie interfaciale de protéines adsorbées à l’interface eau/air, les réarrangements topologiques à l’échelle de quelques films liquides, la stabilité et la rhéologie de mousses de protéines. L’étude a porté à la fois sur un mélange de protéines du lactosérum et sur sa protéine majoritaire purifiée, la ß-lactoglobuline. Pour identifier les liens avec leurs propriétés structurales et physico-chimiques, des modifications des protéines ont été générées par étuvage de poudres. Plusieurs paramètres d’étuvage ont été variés simultanément. Une large gamme de modifications structurales des protéines a été obtenue grâce au contrôle de ces paramètres. Nous avons mis en évidence que de petites modifications structurales des protéines ont des conséquences majeures sur la rhéologie interfaciale, la dynamique des réarrangements de films, la stabilité et la rhéologie des mousses.Les effets de l’étuvage des poudres sur les propriétés des mousses sont complexes, car ils dépendent étroitement de la combinaison des effets des paramètres d’étuvage, comme de la propriété de la mousse qui est mesurée. Parallèlement, l’examen de la variabilité des comportements à plusieurs échelles apporte un éclairage original sur la contribution de la rhéologie interfaciale aux propriétés de mousses de protéines. Il met notamment en évidence l’intérêThe objective of this work is to identify the conditions and mechanisms of the creation or improvement of the stability and rheology of whey proteins foams. To this aim, we studied the interfacial rheology of protein layers adsorbed at the air/water interface, the liquid films dynamics after a topological rearrangement, the stability and rheology of whey protein foams. Both a mixture of whey proteins and purified ß-lactoglobulin, used as a model protein, were studied. To study the relationships with protein structure, proteins were modified by dry-heating of whey protein powders. A wide variety of structural changes was obtained by varying simultaneously multiple dry-heating parameters.Interestingly, low-extent structural modifications have a dramatic impact on interfacial rheology, liquid film dynamics, foam stability and foam rheology. The effects of dry-heating parameters on the foam properties are complex and depend on their combination and the considered foam feature. Our original multiscale approach (interface, film dynamics and foam) sheds light on the contribution of the interfacial rheology to protein foam properties. In particular, foam dynamics have been shown to play a predominant role

Stabilisation et texturation de mousses liquides par des protéines de lactosérum chauffées à l'état de poudre

The objective of this work is to identify the conditions and mechanisms of the creation or improvement of the stability and rheology of whey proteins foams. To this aim, we studied the interfacial rheology of protein layers adsorbed at the air/water interface, the liquid films dynamics after a topological rearrangement, the stability and rheology of whey protein foams. Both a mixture of whey proteins and purified ß-lactoglobulin, used as a model protein, were studied. To study the relationships with protein structure, proteins were modified by dry-heating of whey protein powders. A wide variety of structural changes was obtained by varying simultaneously multiple dry-heating parameters.Interestingly, low-extent structural modifications have a dramatic impact on interfacial rheology, liquid film dynamics, foam stability and foam rheology. The effects of dry-heating parameters on the foam properties are complex and depend on their combination and the considered foam feature. Our original multiscale approach (interface, film dynamics and foam) sheds light on the contribution of the interfacial rheology to protein foam properties. In particular, foam dynamics have been shown to play a predominant role.L’objectif de ce travail est d’identifier les conditions et les mécanismes permettant la création d'aptitudes nouvelles ou améliorées des protéines du lactosérum à la stabilisation et texturation des mousses alimentaires.À cette fin, nous avons étudié la rhéologie interfaciale de protéines adsorbées à l’interface eau/air, les réarrangements topologiques à l’échelle de quelques films liquides, la stabilité et la rhéologie de mousses de protéines. L’étude a porté à la fois sur un mélange de protéines du lactosérum et sur sa protéine majoritaire purifiée, la ß-lactoglobuline. Pour identifier les liens avec leurs propriétés structurales et physico-chimiques, des modifications des protéines ont été générées par étuvage de poudres. Plusieurs paramètres d’étuvage ont été variés simultanément. Une large gamme de modifications structurales des protéines a été obtenue grâce au contrôle de ces paramètres. Nous avons mis en évidence que de petites modifications structurales des protéines ont des conséquences majeures sur la rhéologie interfaciale, la dynamique des réarrangements de films, la stabilité et la rhéologie des mousses.Les effets de l’étuvage des poudres sur les propriétés des mousses sont complexes, car ils dépendent étroitement de la combinaison des effets des paramètres d’étuvage, comme de la propriété de la mousse qui est mesurée. Parallèlement, l’examen de la variabilité des comportements à plusieurs échelles apporte un éclairage original sur la contribution de la rhéologie interfaciale aux propriétés de mousses de protéines. Il met notamment en évidence l’intér

[Invited Seminar] Comportement et Caractérisation de BioMolécules aux Interfaces Fluides

National audienc

Propriétés interfaciales et moussantes de protéines globulaires laitières étuvées

National audienceEn plus de leurs propriétés nutritionnelles, les protéines laitières ont des propriétés fonctionnelles jouant un rôle essentiel dans l'appétence et la qualité organoleptique des aliments. En particulier, les protéines laitières ont des propriétés moussantes résultant de leur aptitude à s’adsorber rapidement à l’interface eau/air, se déployer à l’interface et former un film interfacial résistant mécaniquement. (1) L’auto-assemblage des protéines globulaires à l’interface et les propriétés mécaniques du film sont sensibles à leur structure. Des modifications structurales de faible ampleur, affectant peu la structure tertiaire, peuvent avoir d’importantes conséquences sur leurs propriétés interfaciales et sur leurs propriétés moussantes. (2) Notre objectif est d’étudier le lien entre la structure des protéines du lactosérum, leurs propriétés interfaciales et leurs propriétés moussantes. Ainsi, après avoir procédé à des modifications structurales de faible ampleur de protéines de lactosérum, nous étudions leurs propriétés moussantes. Nous travaillons sur un produit industriel laitier, un isolat de protéines sériques (WPI) et sur de la β-lactoglobuline purifiée (β-Lg), qui en est le principal constituant. Pour modifier la structure des protéines, nous effectuons un étuvage ou traitement thermique à sec. Ce procédé est connu pour améliorer les propriétés moussantes de protéines globulaires d'autres origines. (2) L’effet de différents paramètres d’étuvage sont étudiés : l’activité de l'eau de la poudre, le pH avant déshydratation et la durée de l’étuvage. Les agrégats solubles et insolubles, éventuellement générés, sont éliminés avant d’effectuer des analyses structurales et d’évaluer les propriétés moussantes. En particulier, du fait de la présence résiduelle de lactose dans le WPI, l'impact sur les propriétés moussantes d'une éventuelle lactosylation non enzymatique des protéines dans les conditions de l'étuvage est évalué, grâce à la comparaison avec la β-Lg purifiée. Les liens entre les modifications des propriétés moussantes et celles du comportement des protéines à l'interface eau-air seront discutés

[Invited Seminar] BioMolécules aux interfaces fluides

International audienc

How foam stability against drainage is affected by conditions of prior whey protein powder storage and dry-heating: A multidimensional experimental approach

International audienceIn 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

Topological rearrangements and surface rheology: a multi-scale approach on dairy proteins foams

International audienceThe 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

New approach for the characterisation of dairy protein foams stability

The main destabilisation processes in aqueous foams are liquid drainage, coalescence and disproportionation. In food sciences, the measurement of protein foam stability integrates all of them in a “global stability” and a challenge is to correlate foam stability to film interfacial properties. However, foam stability is complex because each of these mechanisms contributes to the foam lifetime and may occur simultaneously. Thus, understanding the respective relation of these mechanisms to interfacial properties may help to understand foam stability. Several methods have been developed to study foam stability, essentially for low-molecular-weight (LMW) surfactants. First, electrical conductivity measurements of foams as a function of height and time (A) may be converted into liquid fraction 835 f11 using an empirical relationship. When drainage is the only instability phenomenon, the variation of the liquid fraction 835 f11 within a foam as a function of time follows a power-law: 835 f11∝ 835 c61− 835 efc where α, the drainage rate, is related to interfacial mobility (A. Saint-Jalmes and D. Langevin, Journal of Physics: Condensed Matter 14 (40): 9397-9412, 2002). Foam stability is also related to structural dynamics and to the aptitude of films to resist to topological rearrangements, which may lead to coalescence. T1 rearrangements happen spontaneously during the foam lifetime and their film relaxation time (B) is related to surface properties (A.L Biance, A. Delbos and O. Pitois, Physical Review Letters 106 (6), 2011). Thus, the goal of this work is to adapt methodologies essentially applied to LMW surfactants to macromolecules such as dairy proteins and to enlighten multiple dimensions of protein foam stability. Whey protein isolate (WPI) and purified β-Lactoglobulin, the main protein in WPI, have been evaluated. The impact of protein modifications has been also studied. Links between global stability, drainage rate, coalescence and film relaxation time will be discusse

Stability and rheology of protein foams: contribution of interfacial properties, involvement of film relaxation dynamics

International audienceThe 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