Emulsions stabilised by whey protein microgel particles: Towards food-grade Pickering emulsions

We have investigated a new class of food-grade particles, whey protein microgels, as stabilisers of triglyceride-water emulsions. The sub-micron particles stabilized oil-in-water emulsions at all pH with and without salt. All emulsions creamed but exhibited exceptional resistance to coalescence. Clear correlations exist between the properties of the microgels in aqueous dispersion and the resulting emulsion characteristics. For conditions in which the particles were uncharged, fluid emulsions with relatively large drops were stabilised, whereas emulsions stabilized by charged particles contained smaller flocculated drops. A combination of optical microscopy of the drops and spectrophotometry of the resolved aqueous phase allowed us to estimate the interfacial adsorption densities of the particles using the phenomenon of limited coalescence. We deduce two classes of particle arrangement. Complete adsorption of the particles was obtained when they were neutral or when their charges were screened by salt resulting in at least one particle monolayer at the interface. By contrast, only around 50% of the particles adsorbed when they were charged with emulsion drops being covered by less than half a monolayer. These findings were supported by direct visualization of drop interfaces using cryo-scanning electron microscopy. Uncharged particles were highly aggregated and formed a continuous 2-D network at the interface. Otherwise particles organized as individual aggregates separated by particle-free regions. In this case, we suggest that some particles spread at the interface leading to the formation of a continuous protein membrane. Charged particles displayed the ability to bridge opposing interfaces of neighbouring drops to form dense particle disks protecting drops against coalescence; this is the main reason for the flocculation and stability of emulsions containing sparsely covered drops. © 2014 the Partner Organisations

Synthèse et propriétés électrorhéologiques de matériaux composites silice/silicone

Une synthèse de particules de silice par hydrolyse d'alcoxysilane a été optimisée afin d'obtenir des nanosphères monodisperses. En dispersion dans de l'huile silicone, elles constituent la phase solide d'un fluide électrorhéologique, fluide à viscosité électriquement contrôlable. La description théorique des interactions entre particules hors et sous champ électrique donne les outils nécessaires à la compréhension des effets de champ sur les propriétés d'écoulement des fluides. L'expérience valide ce travail. En effet, la contrainte seuil des fluides à faibles cisaillements augmente avec le taux d'eau adsorbée sur les particules, mais la réversibilité des systèmes est alors médiocre. Elle sera nettement améliorée par adsorption, en surface de la silice, de cations alcalins hydratés. Les propriétés structurales des fluides, déduites des spectres de diffusion de neutrons aux petits angles, révéleront un confinement des particules en colonnes dans la direction du champ électrique.The composite material formed from monodispersed silica nanospheres dispersed in silicone oil form a so-called electrorheological fluid. The silica spheres were synthesized by alkoxysilane hydrolysis that was optimized in order to control the final size and monodispersity of the spheres. The description of the electrorheological phenomena is based on a theoretical approach of the interparticular interactions under the influence or not of an applied electric field. Experimentally, the flow properties of the fluids agreed well with the theory. The yield stress increased with the amount of water adsorbed on the particles at low shear rate, but the reversibility of the system was poor. It was greatly improved when the surface properties were modified by adsorption of hydrated alkaline cations on the silica particles. The fluid structure was deduced from small angle neutron scattering data. The particles were found to be organized in chain-like structures in the electric field direction.BESANCON-BU Sciences Staps (250562103) / SudocSudocFranceF

Protonation of carboxyl latex particles in the presence of a strong cationic polyelectrolyte

The charging behavior of carboxyl latex surface in the presence of poly(diallyl dimethyl ammonium chloride) (DADMAC) was investigated by means of potentiometric titrations and electrophoretic mobility. The titration curves at different ionic strengths show a common crossing point, which coincides with the point of zero mobility, and can be identified with the point of zero charge (PZC). This characteristic behavior is due to the adsorption of the strong cationic polyelectrolyte on the weak acid particle surface, leading to an additional positive charge, and a corresponding shift of the surface potential. These features can be quantified in terms of modified Stern model and the standard electrokinetic model. This model predicts the PZC very well, while the magnitude of the charge and its ionic strength dependence are reproduced only semi-quantitativel

Super-Stoichiometric Charge Neutralization in Particle−Polyelectrolyte Systems

The adsorption of poly(vinylamine) (PVA) on poly(styrene sulfate) latex particles is studied, and its consequences on the charging behavior and suspension stability are investigated. The adsorption process is assessed by batch depletion experiments and time-resolved electrophoretic mobility measurements. The adsorption of PVA appears to be basically irreversible. The rate of adsorption decreases with decreasing polymer dose. At low polymer dose, the polymer coverage corresponds to the amount of the polyelectrolyte added, while at high polymer dose, the polymer coverage saturates the surface. Stability ratios are determined by dynamic light scattering, and strongly depend on the polymer dose and salt level. The aggregation is rapid near the isoelectric point (IEP), and it slows down when moving away from it. The charge neutralization is highly nonstoichiometric with charging ratios (CR) larger than unity, meaning that several charges on an adsorbed polyelectrolyte chain are necessary to neutralize a single charge on the particle surface. By comparing the IEP for particles and polyelectrolytes of different charge densities, we find a strong dependence of the CR on the mismatch between the average distances between individual charges on the surface and on the polyelectrolyte. A simple model is proposed to explain this trend

AVIS relatif aux masques dans le cadre de la lutte contre la propagation du virus SARS-CoV-2 (HCSP, Avis et Rapports)

International audienceAvis relatif aux masques dans le cadre de la lutte contre la propagation du virus SARS-CoV-2 (HCSP, Avis et Rapports)Le HCSP présente les caractéristiques, les performances, les indications et les publics concernés par les différents types de masque disponibles : appareil de protection respiratoire de type « FFP2 », masque à usage médical type « masque chirurgical », et masque « grand public ».Quel que soit le type de masque, afin de protéger les autres et soi-même, celui-ci doit être correctement ajusté sur le nez (éviter l’émission de gouttelettes par l’éternuement et assurer une étanchéité du masque par le haut), la bouche (éviter l’expulsion de gouttelettes lors de l’élocution et la toux) et le menton (fixation du masque en bas du visage afin d’éviter les fuites).En population générale, le port du masque, y compris par les personnes asymptomatiques, réduit fortement la transmission du SARS-CoV-2, en association avec les autres mesures barrières. Le HCSP recommande le port d’un masque grand public en tissu réutilisable, répondant aux spécifications Afnor S76-001, de préférence de catégorie 1 (UNS1) dans tous les lieux clos publics et privés collectifs notamment pour les professionnels. Il est nécessaire, avant d’utiliser un masque réutilisable, de lire la fiche technique comportant sa composition et de suivre les recommandations du fabricant, notamment le lavage avant le premier emploi et après chaque utilisation, le port de 4 heures maximum et le remplacement des masques dès qu’ils sont humides.Un masque de fabrication artisanale est plus protecteur que l’absence de masque, sans atteindre le niveau de protection des masques normés. Ainsi, en l’absence de masques UNS1, ou normes étrangères équivalentes, les masques grand public de catégorie 2 (UNS2) peuvent être utilisés par la population générale dans les établissements recevant du public.En cette période et/ou zone de circulation très active du virus SARS-CoV-2 et par précaution, le port d’un masque grand public adapté par les enfants dès l’âge de 6 ans à l’école élémentaire (du CP au CM2) est recommandé, en respectant les difficultés spécifiques, notamment comportementalesLe HCSP précise qu’il n’existe pas de contre-indications dermatologiques, pneumologiques, ORL et phoniatriques ou psychiatriques actuellement documentées au port du masque, quel que soit son type. Concernant les effets indésirables, il est recommandé de consulter un médecin pour avis spécialisé en cas de d’irritation cutanée relative au port de masque pour une prise en charge dermatologique adaptée.Le HCSP émet d’autres recommandations concernant notamment l’entretien des masques grand public, l’information, la communication et la sensibilisation pédagogique au port du masque en population générale. Des conseils pour les enseignants confrontés au port prolongé du masque sont également présentés en annexe.Zeina MANSOUR, Daniel CAMUS, Christian CHIDIAC, Jean-François GEHANNO, Philippe MINODIER, Nicole VERNAZZA, Serge AHO-GLELE, Didier LEPELLETIER, Jean-Marc BRIGNON, Evelyne GEHIN, Philippe HARTEMANN, Yves LEVI, Francelyne MARANO, Jean-Louis ROUBATY, Fabien SQUINAZI, Agathe BILLETTE de VILLEMEUR, Isabelle MILLOT-VAN VLIERBERGHE, Anne BERGER-CARBONNE, Gilles SALVAT, Thierry SIRDEY, Marie BEYLOT-BARRY, Bruno GRANDBASTIEN, Marie-Cécile BAYEUX-DUNGLAS, Éric GAFFET, Joseph HAJJAR, Brigitte MOLTRECHT, Yannick MOREL, Camille BRUAT, Ann PARIENTE-KHAYAT, Soizic URBAN-BOUDJELABVersion du 29 Octobre 2020(52 pages)https://www.hcsp.fr/explore.cgi/avisrapportsdomaine?clefr=943Lire aussi :Coronavirus SARS-CoV-2 : risques liés à la réutilisation des masques à usage unique ou à la prolongation de leur port du 29 avril 2020Coronavirus SARS-CoV-2 : actualisation de la prise en charge du 23 juillet 2020Coronavirus SARS-CoV-2 : recommandations relatives aux textiles et aux commerces de chaussures et d’habillement du 6 mai 2020Coronavirus SARS-CoV-2 : nettoyage des locaux d’un patient confirmé et protection des personnels du 18 février 2020Ministère des solidarités et de la santé : information aux professionnels de sant

Retinoic acid receptors: From molecular mechanisms to cancer therapy

Retinoic acid (RA), the major bioactive metabolite of retinol or vitamin A, induces a spectrum of pleiotropic effects in cell growth and differentiation that are relevant for embryonic development and adult physiology. The RA activity is mediated primarily by members of the retinoic acid receptor (RAR) subfamily, namely RARα, RARβ and RARγ, which belong to the nuclear receptor (NR) superfamily of transcription factors. RARs form heterodimers with members of the retinoid X receptor (RXR) subfamily and act as ligand-regulated transcription factors through binding specific RA response elements (RAREs) located in target genes promoters. RARs also have non-genomic effects and activate kinase signaling pathways, which fine-tune the transcription of the RA target genes. The disruption of RA signaling pathways is thought to underlie the etiology of a number of hematological and non-hematological malignancies, including leukemias, skin cancer, head/neck cancer, lung cancer, breast cancer, ovarian cancer, prostate cancer, renal cell carcinoma, pancreatic cancer, liver cancer, glioblastoma and neuroblastoma. Of note, RA and its derivatives (retinoids) are employed as potential chemotherapeutic or chemopreventive agents because of their differentiation, anti-proliferative, pro-apoptotic, and anti-oxidant effects. In humans, retinoids reverse premalignant epithelial lesions, induce the differentiation of myeloid normal and leukemic cells, and prevent lung, liver, and breast cancer. Here, we provide an overview of the biochemical and molecular mechanisms that regulate the RA and retinoid signaling pathways. Moreover, mechanisms through which deregulation of RA signaling pathways ultimately impact on cancer are examined. Finally, the therapeutic effects of retinoids are reported