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Le besoin de développer la nano-instrumentation intégrée de détection, à bas coût à haute sensibilité sur des principes de résonances est un défi majeur et crucial pour les domaines industriels de la cosmétique, de l’agroalimentaire, de la pharmacologie galénique, de la biologie, et du biomédical ; la nécessité étant d’assurer les diagnostiques à réaliser en termes d’analyses, de contrôle qualité et de sécurité des substances, des aliments, des médicaments en solutions, des lotions actives, des crèmes, des mousses... L’ensemble de ces états de la matière en chimie et physique se nomme la matière molle et ses changements les transitions d’états, de phases ou de consistances… A titre d’exemple non exhaustif dans le domaine de la pharmacologie galénique, certaines solutions fluides avec principes actifs incorporés en suspension seront actives tant que les éléments ne sédimentent pas ; caractéristique qui induirait une qualité moindre de la solution médicamenteuse ou bien une forme de péremption. Sur ce principe d’interaction matière-lumière résonante sur puce intégrée, des mesures fines sur la nouvelle plateforme et le suivi dynamique des dits produits et substances ont permis de détecter des transitions de phases (gel/fluide/mixe émulsion/poudre solide), de mesurer des vitesses de sédimentation et même des phénomènes et mécanismes comme le séchage, la floculation, les effets Marangoni, ou encore les effets spontanées d’émulsion encore incompris [1-3]…

National audience

International audience; The production of milk powders is a strategic sector of the dairy industry. Due to its complex macromolecular composition, shedding light on the mechanisms governing milk drying constitutes a main industrial concern and a scientific challenge at the same time. In this study, we used the single droplet[1] and the directional drying[2] approaches to investigate the evaporation of colloidal mixes of the two major milk proteins (whey protein isolates and native phosphocaseinates). Notably, we observed the crack development in the samples to evaluate the competitive impact of the physico-chemical properties of whey proteins (rigid globular shape) and casein micelles (deformable sponge-like structure) on the drying process. Our outcomes are potentially useful to better control the functional properties of milk powders. Furthermore, they contribute to improve the understanding of the drying mechanisms in binary colloidal systems, which are still far from being fully elucidated.

International audience; Spray drying is a well-established process, but the phenomena ruling droplet-to-particle transition remain black box, resulting in variable powder properties and drying performances. Therefore, understanding precisely how the particle is formed and how to control its properties remain a major challenge. This work aims to breakdown the complexity of the drying phenomena using an exploratory multi-scale approach. Particle formation of different milk proteins (whey proteins and casein micelles) was investigated using different experimental systems (single pendant droplet, mono-dispersed droplets and spraying cone droplets) in controlled drying environments. The results showed that the drying of a single protein droplet included three distinct stages highlighting the occurrence of specific morphological events (constant rate shrinkage, buckling instability, vacuole nucleation). According to the type of proteins, these stages differed in drying kinetics and droplet dynamics, leading to characteristic and reproducible particle shapes irrespective of the droplet configuration and the drying conditions. These different drying behaviors were related to specific skin formation mechanisms at droplet air-liquid interface and consequent responses of the protein material to internal stresses. In this work, we aimed at understanding how the different physico-chemical properties of whey proteins (rigid globular shape) and casein micelles (deformable sponge-like structure) affect the mechanisms of formation of such a skin, and from this the particle final shape. However, the full understanding of the drying process of biocolloids is far to be achieved and, notably, the impact of solute properties on the morphological characteristics of the evaporating droplets, such as colloid segregation, skin formation and crack pattern development is not elucidated yet. To this aim, the use of model colloidal solutions, whose rheological behavior is more easily deducible, could represent a significant boost. Consequently, we compared the drying of droplets of whey proteins and casein micelles to that of dispersions of silica particles and polymer-coated silica particles, respectively. The mechanical behavior of such biological colloids and model silica dispersions was investigated through the analysis of crack formation, and the measurements of their mechanical properties using indentation testing. The study reveals numerous analogies between dairy and corresponding model systems, thus confirming these latter as powerful tools to highlight the signature of the matter on the drying process and at the molecular scale. The outcomes presented in this work represent a first step to shed light on the physics of drying dairy droplets; they open the road to further investigation about mixes of milk proteins. Moreover, the observation of mixtures of dairy colloids would contribute to improve the knowledge about the evaporation of colloidal polydisperse systems, which represents a current scientific challenge.

Mécanismes de formation de l’interface au cours du procédé de séchage : approche multiéchelles appliquée aux poudres laitières. journée scientifique "science des aliments et valorisation des bio-produits"

Spray-drying - concentrated matrices –functionalities team objectives. STLOpendays

Similarity in the drying behavior between biological colloids and model colloidal dispersions . Première réunion plénière du GDR SLAMM (Solliciter LA Matière Molle)

Drying is ubiquitous in industry and our everyday life. It is a priori a complex process involving coupled vapor diffusion and liquid transport through a complex, multi-scale, soft or solid, porous structure. Despite this complexity, many recent researches now provide insight in, and rationalization of, the physical processes at work in drying of soils, building materials, colloids, gels, model porous systems, etc. The aim of this meeting, within the frame of the Chair Innovating solutions for sustainable housing (Saint-Gobain –Ecole des Ponts ), is to gather experts and review significant improvements in our understanding in this scientific field.

The production of milk powders involves nowadays a significant portion of the dairy industry. Due to its rich composition in terms of proteins and macromolecules, shedding light on the mechanisms characterizing the evaporation of milk is a scientific challenge and an industrial need at the same time. In this study, we use a multi-scale approach to investigate the separate roles of the two major milk protein components (whey protein isolates and native micellar caseins) on the drying of droplets with different whey protein to casein ratio. The evolution of the desiccation phases and the morphology of the samples are observed coupling mass measurements, optical/confocal microscopy and ultrasounds. Our outcomes highlight how the physico-chemical properties at the molecular scale significantly affect dried particle formation and their final shape and mechanical behavior. We show that the sol-gel transition governs the development of the particle skin in case of single dairy protein solution, regardless of the type. The case of the whey protein / micellar caseins mixes is discussed in a second time.

Steam-jet granulation is a process used in dairy industry to produce instant agglomerated milk powder. Agglomerated instant powders exhibit improved wettability and rehydration behaviour, which are essential attributes for coffee whiteners applications. Although there is a growing interest for research in this area, the steam-jet granulation process has been little studied to date and the quality control at industrial scale remains experimental and empirical. Moreover, the multi-factorial causes at the root of the rehydration properties of the final agglomerates make it difficult to identify the key process parameters that should be controlled to meet the quality requirements. The present study investigated industrial data to study how different raw materials properties and process parameters interact and contribute to the production of skim milk agglomerates with improved functional properties. Dynamic vapour sorption and differential scanning calorimetry were used to characterize both the native raw materials and the agglomerated powders. A multivariate data analysis was used to identify correlations between the raw material properties, the process parameters and the physicochemical and functional properties of the products. The water content of the native raw material and the post-drying temperature were found to be critical in controlling the humidity and thermodynamical properties (glass transition temperature) of the agglomerates. These properties were correlated to the wetting time and showed their significant influence on the rehydration behaviour of the agglomerates. Recommendations concerning production parameters are given to avoid conform rehydration behaviour in industrial agglomerated skim milk powder.

Steam-jet granulation is a process used in the dairy industry to produce instant agglomerated milk powder. The agglomerate growth process includes wetting of the particle surface, collisions of sticking particles and consolidation of the agglomerates by drying. The aim of this study was to evaluate the influence of the raw material properties (initial particle size and humidity) and processing conditions (liquid/solid ratio and post-drying conditions) on the growth mechanisms and agglomerates properties. Skim milk powders were granulated using steam-jet granulation pilot and characterized via the in-size distribution, water content, structure, thermodynamical and functional properties. The water content and the post-drying time were identified as key process parameters to control in order to obtain instant agglomerated milk powders

Particle formation during dairy powders production is ruled by protein mechanical properties. Drying Days Conference

To produce instant agglomerated milk powder, industrial producers receives milk powders from several different suppliers. However, despite the implementation of a strict requirement specification to reach a constant quality of final product, differences can be observed depending on the origin of raw material and the processing parameters. In this work, the quality control result from 8 different skim milk powder sources used over one year of production (275 batches) were collected to observe data on composition (proteins and fat content), humidity (water content and activity), density criteria (aerial and bulk), pH and ageing. These data were statistically analyzed using a principal component analysis (PCA). Almost 65% of the total variability was represented by the projection of the experimental set up on the map defined by the first two principle components (PC) of the PCA. A hierarchical cluster analysis performed on the PCA data made it possible to distinguish 3 different classes of raw material depending on their physicochemical characteristics: – Class one corresponding to the major part of the raw materials. – Class two corresponding to one specific differentiated from the others by higher density characteristics and less proteins. – Class three corresponding to one other highly differentiated from the others on all criteria (humidity, composition, density, ageing). Thus, statistical analysis of the production data made it possible to obtain a global characterization of the different skim milk powders, and to distinguish two of them although close to the others when considering their characteristics one by one.

National audience; Les protéines amphiphiles se concentrent aux interfaces avec des fractions volumiques localement élevées. Ce mécanisme est le principal stabilisateur des interfaces des milieux divisés (mousses, émulsions). La nature attractive ou répulsive des interactions entre protéines est modulée par la charge de ces dernières et nous avons émis l’hypothèse que la couche interfaciale est affectée par la nature de l’interaction. Les protéines utilisées pour notre étude sont des protéines basiques (lysozyme, avidine) et acides (ovalbumine, serum-albumine bovine, alpha-lactalbumine) et nous avons modifié leur charge par le pH de la solution tampon.Nous avons mis en évidence, par suivi ellipsométrique de la quantité de protéine adsorbée à l’interface eau-air, que lorsque les interactions protéine-protéine sont répulsives, une monocouche se forme à l’interface alors que des interactions de nature attractives conduisent à la formation de multicouches. Il semble que dans ce dernier cas l’advection soit un ingrédient nécessaire.

Spray drying is a well-established technique to convert a liquid solution into individual and solid particles which is widely used in food industry especially in the dairy sector. This process allows formation of a large range of particle morphology all distinct from each other by their physical characteristics (distribution of the particle size, particle shape and particle density) providing to particles a typical aerodynamic behaviour and determining their final functionality (flowability, dispersibility, wettability, etc.). In dairy industries, controlling physical properties of powder represent a key issue to facilitate the industrial hand-use and optimize the rehydration. Therefore, understanding how the final shape of the particle is formed has recently become a huge scientific concern. So far, much attention has been paid to the so called process – product relationships, most often considering theoretical models based on drying kinetics to predict the shell formation and the morphology of dairy powders. However, the way the protein kind influence the particle morphology remains a hot topic. In this study we focused on the drying behaviour of two major milk protein concentrates: whey protein isolate and native micellar caseins. To acquire a better understanding on the role of each protein in the particle forming mechanisms, seven mixtures containing different ratios of caseins and whey proteins were investigated. A micro-fluidic-jet-spray-dryer (MFJSD) was used to produce uniform particles by drying monodisperse droplets in a hot and dry air flow. Powders were characterized with regard to their physical characteristics and their rehydration properties. Besides, characterisation of particle size and shape was ensured by means of a dynamic image analysis system. It is shown that particle morphology is mainly governed by the protein material type, almost regardless of the drying kinetics; controlling the product formulation thus represents a potential means to tune particle morphology, and therefore powder functional properties

National audience; Many food proteins as egg white or milk protein show tensioactive properties. This means that one region of the protein has affinity for polar environment and another region of the protein prefers an apolar environment. For that reason, these proteins tend to adsorb to amphiphilic-hydrophobic interfaces such as air-water interface of bubble surface in case of foams or oil-water interface of droplets surfaces in case of emulsions. In both cases, food proteins act as stabilizers of the dispersed medium. In addition, and in contrast with small-molecular weight surfactants, proteins can also self-associate and form an interfacial film with viscoelastic properties, which also contributes to stabilization.However, their tensioactive properties confer to food proteins striking associative properties that this presentation will illustrate following three ideas:The mixture of two proteins as components of a dispersed medium can lead to enhanced bulk properties compared to the case where each protein is alone, even if one protein is in very small amount in the mixture. This property offers the possibility to modulate bulk properties of a mixture using one protein as an additive. The case of foaming properties of ovalbumine-lysozyme will illustrate this idea. We have shown (1,2) that the interaction between proteins preferentially takes place at the air-water interface and that the interfacial adsorbed film is stratified, the most tensioactive protein being adsorbed first.The association of two proteins can lead to the formation of monodisperse microspheres, the ratio of each protein in the microsphere depending on the charge ratio. This property is illustrated by the case of the mixture alpha-lactalbumine/lysozyme (3). We have shown that the first steps of these bulk associative properties are revealed by the interfacial properties of these proteins.The last part of this presentation shows how very slight modifications of a protein, hardly detectable with standard bulk caracterisation tools, can lead to drastic changes in foaming and interfacial properties. The case of dry-heated lysozyme will be exposed, for which we haveshown (4) that a modification of one unique aminoacid greatly affects the interfacial properties of the protein and consequently greatly enhance the bulk properties of the foam. It evidences that small changes on a protein can act as a swich relative to the bulk properties of the dispersed media stabilized with this protein

Aujourd’hui, le séchage du lait ne vise plus uniquement à prolonger sa conservation mais à produire des poudres dont les propriétés fonctionnelles telles que la solubilité et l’aptitude à mousser sont parfaitement maîtrisées. Cela suppose une compréhension fine des mécanismes impliqués dans l’obtention de ces poudres. L’étude de l’évaporation d’une goutte a en effet permis de comprendre l’influence de la nature des protéines laitières lors de la transformation de la goutte de lait en grain de poudre. L’implication de ces protéines a des répercussions directes sur la morphologie des grains et par suite sur les propriétés des poudres obtenues. Ces résultats, validés à échelle semi-industrielle, contribuent conceptuellement à une meilleure compréhension du comportement des constituants du lait en milieu concentré. Ils ouvrent la voie à terme à la prédiction et au contrôle de la qualité des poudres laitières.