Publications by authors named "Marie-Hélène Ropers"

16 Publications

  • Page 1 of 1

digestion of food grade TiO (E171) and TiO nanoparticles: physicochemical characterization and impact on the activity of digestive enzymes.

Food Funct 2021 Jul;12(13):5975-5988

INRAE, UR1268 Biopolymères Interactions Assemblages, 44300 Nantes, France.

Titanium dioxide is a food additive that has raised some concerns for humans due to the presence of nanoparticles. We were interested in knowing the fate of TiO2 particles in the gastro-intestinal tract and their potential effect on digestive enzymes. For this purpose, we analysed the behaviour of two different food grade TiO2 samples (E171) and one nano-sized TiO2 sample (P25) through a standardized static in vitro digestion protocol simulating the oral, gastric and intestinal phases with appropriate juices including enzymes. Both E171 and P25 TiO2 particles remained intact in the digestive fluids but formed large agglomerates, and especially in the intestinal fluid where up to 500 μm sized particles have been identified. The formation of these agglomerates is mediated by the adsorption of mainly α-amylase and divalent cations. Pepsin was also identified to adsorb onto TiO2 particles but only in the case of silica-covered E171. In the salivary conditions, TiO2 exerted an inhibitory action on the enzymatic activity of α-amylase. The activity was reduced by a factor dependent on enzyme concentrations (up to 34% at 1 mg mL-1) but this inhibitory effect was reduced to hardly 10% in the intestinal fluid. In the gastric phase, pepsin was not affected by any form of TiO2. Our results hint that food grade TiO2 has a limited impact on the global digestion of carbohydrates and proteins. However, the reduced activity specifically observed in the oral phase deserves deeper investigation to prevent any adverse health effects related to the slowdown of carbohydrate metabolism.
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http://dx.doi.org/10.1039/d1fo00499aDOI Listing
July 2021

Repeated exposure of Caco-2 versus Caco-2/HT29-MTX intestinal cell models to (nano)silver in vitro: Comparison of two commercially available colloidal silver products.

Sci Total Environ 2021 Feb 17;754:142324. Epub 2020 Sep 17.

Toxalim, Université de Toulouse, INRAE, INP-ENVT, INP-EI-Purpan, Université de Toulouse 3 Paul Sabatier, Toulouse, France. Electronic address:

Colloidal silver products are sold for a wide range of disinfectant and health applications. This has increased the potential for human exposure to silver nanoparticles (AgNPs) and ions (Ag), for which oral ingestion is considered to be a major route of exposure. Our objective was to evaluate and compare the toxicity of two commercially available colloidal silver products on two human intestinal epithelial models under realistic exposure conditions. Mesosilver™ and AgC were characterized and a concentration range between 0.1 and 12 μg/mL chosen. Caco-2 cells vs. co-culture of Caco-2 and mucus-secreting HT29-MTX cells (90/10) were used. Repeated exposure was carried out to determine cell viability over 18 days of cell differentiation in 24-well plates. Selected concentrations (0.1, 1, and 3 μg/mL) were tested on cells cultured in E-plates and Transwells with the same repeated exposure regimen, to determine cell impedance, and cell viability and trans-epithelial electrical resistance (TEER), respectively. Silver uptake, intracellular localisation, and translocation were determined by CytoViva™, HIM-SIMS, and ICP-MS. Genotoxicity was determined on acutely-exposed proliferating Caco-2 cells by γH2AX immunofluorescence staining. Repeated exposure of a given concentration of AgC, which is composed solely of ionic silver, generally exerted more toxic effects on Caco-2 cells than Mesosilver™, which contains a mix of AgNPs and ionic silver. Due to its patchy structure, the presence of mucus in the Caco-2/HT29-MTX co-culture only slightly mitigated the deleterious effects on cell viability. Increased genotoxicity was observed for AgC on proliferating Caco-2 cells. Silver uptake, intracellular localisation, and translocation were similar. In conclusion, Mesosilver™ and AgC colloidal silver products show different levels of gut toxicity due to the forms of distinct silver (AgNPs and/or Ag) contained within. This study highlights the applicability of high-resolution (chemical) imaging to detect and localize silver and provides insights into its uptake mechanisms, intracellular fate and cellular effects.
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http://dx.doi.org/10.1016/j.scitotenv.2020.142324DOI Listing
February 2021

The complex puzzle of dietary silver nanoparticles, mucus and microbiota in the gut.

J Toxicol Environ Health B Crit Rev 2020 10;23(2):69-89. Epub 2020 Jan 10.

Toxalim (Research Centre in Food Toxicology), Université de Toulouse, INRA, ENVT, INP-Purpan, UPS, Toulouse, France.

Hundreds of consumer and commercial products containing silver nanoparticles (AgNPs) are currently used in food, personal-care products, pharmaceutical, and many other applications. Human exposure to AgNPs includes oral intake, inhalation, and dermal contact. The aim of this review was to focus on oral intake, intentional and incidental of AgNPs where well-known antimicrobial characteristics that might affect the microbiome and mucus in the gastrointestinal tract (GIT). This critical review summarizes what is known regarding the impacts of AgNPs on gut homeostasis. It is fundamental to understand the forms of AgNPs and their physicochemical characterization before and during digestion. For example, lab-synthesized AgNPs differ from "real" ingestable AgNPs used as food additives and dietary supplements. Similarly, the gut environment alters the chemical and physical state of Ag that is ingested as AgNPs. Emerging research on and rodent and human indicated complex multi-directional relationships among AgNPs, the intestinal microbiota, and the epithelial mucus. It may be necessary to go beyond today's descriptive approach to a modeling-based ecosystem approach that might quantitatively integrate spatio-temporal interactions among microbial groups, host factors (e.g., mucus), and environmental factors, including lifestyle-based stressors. It is suggested that future research (1) utilize more representative AgNPs, focus on microbe/mucus interactions, (2) assess the effects of environmental stressors for longer and longitudinal conditions, and (3) be integrated using quantitative modeling.
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http://dx.doi.org/10.1080/10937404.2019.1710914DOI Listing
August 2020

Evaluation of the content of TiO nanoparticles in the coatings of chewing gums.

Food Addit Contam Part A Chem Anal Control Expo Risk Assess 2018 Feb 20;35(2):211-221. Epub 2017 Oct 20.

a UR1268 BIA (Biopolymères Interactions Assemblages), INRA , Nantes , France.

Titanium dioxide is a metal oxide used as a white pigment in many food categories, including confectionery. Due to differences in the mass fraction of nanoparticles contained in TiO, the estimated intakes of TiO nanoparticles differ by a factor of 10 in the literature. To resolve this problem, a better estimation of the mass of nanoparticles present in food products is needed. In this study, we focused our efforts on chewing gum, which is one of the food products contributing most to the intake of TiO. The coatings of four kinds of chewing gum, where the presence of TiO was confirmed by Raman spectroscopy, were extracted in aqueous phases. The extracts were analysed by transmission electron microscopy (TEM), X-ray diffraction, Fourier Transform Raman spectroscopy, and inductively coupled plasma atomic emission spectroscopy (ICP-AES) to establish their chemical composition, crystallinity and size distribution. The coatings of the four chewing gums differ chemically from each other, and more specifically the amount of TiO varies from one coating to another. TiO particles constitute the entire coating of some chewing gums, whereas for others, TiO particles are embedded in an organic matrix and/or mixed with minerals like calcium carbonate, talc, or magnesium silicate. We found 1.1 ± 0.3 to 17.3 ± 0.9 mg TiO particles per piece of chewing gum, with a mean diameter of 135 ± 42 nm. TiO nanoparticles account for 19 ± 4% of all particles, which represents a mass fraction of 4.2 ± 0.1% on average. The intake of nanoparticles is thus highly dependent on the kind of chewing gum, with an estimated range extending from 0.04 ± 0.01 to 0.81 ± 0.04 mg of nano-TiO per piece of chewing gum. These data should serve to refine the exposure scenario.
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http://dx.doi.org/10.1080/19440049.2017.1384576DOI Listing
February 2018

Impact of food grade and nano-TiO particles on a human intestinal community.

Food Chem Toxicol 2017 Aug 28;106(Pt A):242-249. Epub 2017 May 28.

Department of Biology, Queen's University, Kingston ON K7L 3N6, Canada; Department of Biomedical and Molecular Sciences, School of Environmental Studies, Queen's University, Kingston, ON K7L 3N6, Canada. Electronic address:

Titanium dioxide (TiO) nanoparticles (NPs) are used as an additive (E171 or INS171) in foods such as gum, candy and puddings. To address concerns about the potential hazardous effects of ingested NPs, the toxicity of these food-grade NPs was investigated with a defined model intestinal bacterial community. Each titania preparation (food-grade TiO formulations, E171-1 and E171-6a) was tested at concentrations equivalent to those found in the human intestine after sampling 1-2 pieces of gum or candy (100-250 ppm). At the low concentrations used, neither the TiO food additives nor control TiO NPs had an impact on gas production and only a minor effect on fatty acids profiles (C16:00, C18:00, 15:1 w5c, 18:1 w9c and 18:1 w9c, p < 0.05). DNA profiles and phylogenetic distributions confirmed limited effects on the bacterial community, with a modest decrease in the relative abundance of the dominant Bacteroides ovatus in favor of Clostridium cocleatum (-13% and +14% respectively, p < 0.05). Such minor shifts in the treated consortia suggest that food grade and nano-TiO particles do not have a major effect on human gut microbiota when tested in vitro at relevant low concentrations. However, the cumulative effects of chronic TiO NP ingestion remain to be tested.
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http://dx.doi.org/10.1016/j.fct.2017.05.050DOI Listing
August 2017

The miscibility of milk sphingomyelin and cholesterol is affected by temperature and surface pressure in mixed Langmuir monolayers.

Food Chem 2017 Jun 18;224:114-123. Epub 2016 Dec 18.

STLO, UMR1253, INRA, Agrocampus Ouest, 35000 Rennes, France. Electronic address:

The miscibility of milk sphingomyelin (milk-SM) and cholesterol was investigated in this study. The effect of different physical states of milk-SM on its interactions with cholesterol was determined by the recording of isotherms of compression of Langmuir films for temperatures above and below the gel to Lα phase transition of milk-SM (T∼34°C). For T=15°CT, the milk-SM molecules were in a LE phase regardless of the surface pressure applied. A phase diagram pressure - milk-SM/cholesterol composition was established. This study demonstrated that both temperature and surface pressure affected the miscibility between the milk-SM and cholesterol. The strongest attractive forces (i.e. condensing effect) were identified for 30mol% cholesterol when the milk-SM was in the LE phase state.
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http://dx.doi.org/10.1016/j.foodchem.2016.12.035DOI Listing
June 2017

Criteria to define a more relevant reference sample of titanium dioxide in the context of food: a multiscale approach.

Food Addit Contam Part A Chem Anal Control Expo Risk Assess 2017 May 14;34(5):653-665. Epub 2017 Feb 14.

a UR1268 BIA (Biopolymères Interactions Assemblages) , INRA , Nantes , France.

Titanium dioxide (TiO) is a transition metal oxide widely used as a white pigment in various applications, including food. Due to the classification of TiO nanoparticles by the International Agency for Research on Cancer as potentially harmful for humans by inhalation, the presence of nanoparticles in food products needed to be confirmed by a set of independent studies. Seven samples of food-grade TiO (E171) were extensively characterised for their size distribution, crystallinity and surface properties by the currently recommended methods. All investigated E171 samples contained a fraction of nanoparticles, however, below the threshold defining the labelling of nanomaterial. On the basis of these results and a statistical analysis, E171 food-grade TiO totally differs from the reference material P25, confirming the few published data on this kind of particle. Therefore, the reference material P25 does not appear to be the most suitable model to study the fate of food-grade TiO in the gastrointestinal tract. The criteria currently to obtain a representative food-grade sample of TiO are the following: (1) crystalline-phase anatase, (2) a powder with an isoelectric point very close to 4.1, (3) a fraction of nanoparticles comprised between 15% and 45%, and (4) a low specific surface area around 10 m g.
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http://dx.doi.org/10.1080/19440049.2017.1284346DOI Listing
May 2017

The benefits of liposomes for chilling canine sperm for 4 days at 4°C.

Anim Reprod Sci 2016 May 2;168:100-109. Epub 2016 Mar 2.

Laboratory of Biotechnology and Pathology of Reproduction, ONIRIS: The National Veterinary, Food Agriculture, and Food Hygiene School of Loire Atlantique, BP 40706, 44307 Nantes, France. Electronic address:

This study comprises 3 experiments exploring the possible benefits and mechanism of action of liposomes for chilling (4°C) canine sperm over a period of 4 days. In the first experiment, 20 ejaculates collected from 5 Beagle dogs were chilled in an extender containing 6% low density lipoproteins (LDL) (Control), or one of 7 extenders containing different concentrations (2, 4, 6, 8, 10, 15, 20%) of liposomes (LIPO). These ejaculates were chilled over 4 days and motility was assessed daily using a Hamilton Thorne analyzer (HTM-IVOS, 14.0). The 2% LIPO obtained the best results (p=0.038) after four days (72.55% motile spermatozoa and 31.4% progressive spermatozoa). In experiment 2, 10 ejaculates were collected from same 5 dogs and chilled in 6% LDL or 2% LIPO-based extenders. Sperm integrity characteristics were assessed prior to refrigeration and every 48h for four days (D0, D2, and D4). Acrosome integrity was assessed using the FITC-PSA test (Fluorescein IsoThiocyanate-Pisum Sativum Agglutinin), plasma membrane (PM) integrity using both the hypo-osmotic swelling test (HOSt) and SYBR14/Propidium Iodide test (SYBR14/PI), and DNA integrity using the Acridine-Orange test (AO). The 2% LIPO extender provided equivalent preservation of sperm integrity parameters to the reference extender (6% LDL). In experiment 3, a Langmuir-Blodgett trough was used to evaluate the mechanistic interactions between LDL, LIPO, prostatic fluid, and the canine spermatozoal membrane during chilling. Results indicate that LDL and LIPO interact differently with the biomimetic membrane. The most likely conclusion of these findings is that LDL and liposomes employ different protective mechanisms during the chilling (4°C) of canine spermatozoa.
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http://dx.doi.org/10.1016/j.anireprosci.2016.02.032DOI Listing
May 2016

Interactions between phospholipids and titanium dioxide particles.

Colloids Surf B Biointerfaces 2014 Nov 16;123:150-7. Epub 2014 Sep 16.

Institut Matériaux Jean Rouxel IMN, UMR 6502, Univ Nantes, CNRS, F-44322 Nantes 3, France.

A systematic study was carried out on monolayer films and lipid vesicles to elucidate the interactions between membrane lipids and commercial particles of titanium dioxide TiO2 (TiO2-P25). Pressure-area isotherms of lipids at various pH values were recorded on a Langmuir trough with or without TiO2-P25 and NaCl in the subphase. Electrophoretic mobilities of lipid vesicles and TiO2-P25 particles were measured to identify the pH range where attractive electrostatic interactions between lipids and TiO2-P25 could take place. The results show that (i) the surface of TiO2-P25 particles interacts only with some phospholipids, (ii) the driving forces are electrostatic and (iii) non-electrostatic interactions were also observed, depending on the molecular structure. More precisely, the phospholipids 1,2-dimyristoyl-sn-glycero-3-phosphate monosodium salt (DMPA), 1,2-dimyristoyl-sn-glycero-3-phospho-rac-1-glycerol (DMPG) and 1',3'-bis[1,2-dimyristoyl-sn-glycero-3-phospho]-sn-glycerol (TMCL) interacted strongly with the TiO2-P25 surface through electrostatic interactions, providing they were oppositely charged, i.e. for pH between 2 and 6.6. For TMCL and DMPG, interactions with the surface of TiO2-P25 in non-favourable electrostatic conditions, suggested another kind of binding, probably through the hydroxyl groups of the terminal glycerol. Weaker attractive interactions were demonstrated for 1,2-dimyristoyl-sn-glycero-3-phospho-l-serine (DMPS) and the synthetic lipid dihexadecyl phosphate (DHP). For DMPS, the carboxylate group is involved in the adsorption onto TiO2. The other membrane lipids such as 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (DMPE) and sphingomyelin (SM) did not interact with TiO2-P25 regardless of pH.
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http://dx.doi.org/10.1016/j.colsurfb.2014.09.010DOI Listing
November 2014

Modifications of interfacial proteins in oil-in-water emulsions prior to and during lipid oxidation.

J Agric Food Chem 2012 Sep 22;60(35):8659-71. Epub 2012 Aug 22.

INRA, UR1268 Biopolymères Interactions Assemblages, F-44316 Nantes, France.

Lipid oxidation is a major cause for the degradation of biological systems and foods, but the intricate relationship between lipid oxidation and protein modifications in these complex multiphase systems remains unclear. The objective of this work was to have a spatial and temporal insight of the modifications undergone by the interfacial or the unadsorbed proteins in oil-in-water emulsions during lipid oxidation. Tryptophan fluorescence and oxygen uptake were monitored simultaneously during incubation in different conditions of protein-stabilized oil-in-water emulsions. Kinetic parameters demonstrated that protein modifications, highlighted by decrease of protein fluorescence, occurred as an early event in the sequence of the reactions. They concerned more specifically the proteins adsorbed at the oil/water interface. The reactions led in a latter stage to protein aggregation, carbonylation, and loss of protein solubility.
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http://dx.doi.org/10.1021/jf300490wDOI Listing
September 2012

Effect of lateral heterogeneity in mixed surfactant-stabilized interfaces on the oxidation of unsaturated lipids in oil-in-water emulsions.

J Colloid Interface Sci 2012 Jul 7;377(1):244-50. Epub 2012 Apr 7.

INRA, UR1268 Biopolymères Interactions et Assemblages, F-44316 Nantes, France.

The development of lipid oxidation in oil-in-water (O/W) emulsions is widely influenced by the properties of the interfacial layer, which separates the oil and water phases. In this work, the effect of the structure of the interface on the oxidative stability of surfactant stabilized O/W emulsions was investigated. Emulsions were prepared with either single Tween 20 or Tween 20/co-surfactant mixtures in limiting amounts. The co-surfactants, Span 20 and monolauroyl glycerol have the same hydrophobic tail as Tween 20 but differ by the size and composition of their polar headgroup. Metal-initiated lipid oxidation, monitored through the measurement of oxygen uptake, formation of conjugated dienes and volatile compounds, developed more rapidly in the emulsions stabilized by the surfactant mixture than in the single Tween 20-stabilized emulsion. The reconstitution of Tween 20/co-surfactant films at the air-water interface and their surface-pressure isotherms highlighted that, contrary to single Tween 20 molecules, Tween 20/co-surfactant mixtures exhibited an heterogeneous distribution within the interfacial layer, offering probably easier access of water-soluble pro-oxidants to the oil phase. These observations provide direct information about the link between the homogeneity of the interface layer and the oxidative stability of emulsions.
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http://dx.doi.org/10.1016/j.jcis.2012.03.084DOI Listing
July 2012

Contribution of the interfacial layer to the protection of emulsified lipids against oxidation.

J Agric Food Chem 2011 May 11;59(9):5052-61. Epub 2011 Apr 11.

INRA, UR1268 Biopolymères Interactions Assemblages, Nantes, France.

The oxidative stability of oil-in-water (O/W) emulsions is highly dependent on the type of emulsifier. The purpose of this work was to investigate the specific role of the adsorbed emulsifiers on lipid oxidation of O/W emulsions. Emulsions of similar droplet size distribution stabilized by minimum amounts of proteins or surfactants were oxidized at 25 °C in the presence of equimolar iron-EDTA complex. The pH and the amount of emulsifier in the aqueous phase were also varied to investigate the role of the droplet charge and the emulsifier in the aqueous phase. Oxygen uptake, conjugated dienes (CD), and volatile compound formation demonstrated that the protein-stabilized interfaces are less efficient at protecting emulsified lipids against oxidation than surfactant-stabilized interfaces. The antioxidant effect of unadsorbed proteins was also confirmed.
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http://dx.doi.org/10.1021/jf200086nDOI Listing
May 2011

Quantification of unadsorbed protein and surfactant emulsifiers in oil-in-water emulsions.

J Colloid Interface Sci 2011 Feb 27;354(2):739-48. Epub 2010 Nov 27.

UR1268 Biopolymères Interactions Assemblages, INRA, F-44316 Nantes, France.

Unadsorbed emulsifiers affect the physical and chemical behaviour of oil-in-water (O/W) emulsions. A simple methodology to quantify unadsorbed emulsifiers in the aqueous phase of O/W emulsions has been developed. Emulsions were centrifuged and filtered to separate the aqueous phase from the oil droplets and the concentration of unadsorbed emulsifiers in the aqueous phase determined. The quantification of unadsorbed surfactants based on the direct transesterification of their fatty acids was validated for Tween 20, Tween 80, citric acid ester (Citrem), Span 20 and monolauroyl glycerol. To determine unadsorbed proteins, results obtained with Folin-Ciocalteu reagent or UV-spectrophotometry were compared on emulsions stabilized by β-lactoglobulin (BLG), β-casein (BCN) or bovine serum albumin (BSA). The first method gave more accurate results especially during aging of emulsions in oxidative conditions. The whole methodology was applied to emulsions stabilized with single or mixed emulsifiers. This approach enables optimization of emulsion formulations and could be useful to follow changes in the levels of unadsorbed emulsifiers during physical or chemical aging processes.
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http://dx.doi.org/10.1016/j.jcis.2010.11.055DOI Listing
February 2011

Engineering of caseins and modulation of their structures and interactions.

Biotechnol Adv 2009 Nov-Dec;27(6):1124-1131. Epub 2009 May 20.

UR 1268 Biopolymères Interactions Assemblages, INRA, 44300 Nantes, France. Electronic address:

Beta-casein (beta-CN) is a milk protein widely used in food industries because of its mild emulsifying properties due to its amphiphilicity. However, the elements determining its micellization behavior in solution and interfacial behavior at the air-water interface are not well known. In order to study how the forced dimerisation influences functional properties of beta-CN, recombinant wild-type beta-CN was produced and distal cysteinylated forms of recombinant beta-CN were engineered. We show that 1) cysteinylated beta-CN formed mainly dimers bridged by disulfide bonds; 2) the process of dimerization adds to the micellization process with temperature and is poorly reversible; 3) covalent disulfide linkage forms at the air-water interface at a lower temperature than in bulk. In conclusion, the location of the cysteinylation in the C-terminus or N-terminus or both is of importance for the properties of beta-CN.
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http://dx.doi.org/10.1016/j.biotechadv.2009.05.011DOI Listing
January 2010

Caleosin of Arabidopsis thaliana : Effect of Calcium on Functional and Structural Properties.

J Agric Food Chem 2008 Dec;56(23):11217-24

JRU Chimie Biologique, Agro Paris Tech, Thiverval Grignon, France.

A non-radioactive blot binding assay has proved the capacity of a purified recombinant form of Arabidopsis thaliana caleosin (AtClo1), a key protein of this plant oil body, to bind calcium. Calcium affected recombinant caleosin aggregation state, solubility, and electrophoretic mobility on SDS-PAGE. The effect of calcium on interfacial behavior of recombinant caleosin was studied at three interfaces: air/water (A/W), purified oil/water (O/W), and air/phosholipid/water (A/PLs/W). Recombinant caleosin was able to decrease interfacial tension (IFT) at A/W and O/W interfaces as a function of concentration and calcium, whereas no interaction was detected at the A/PLs/W interface. Effect of calcium was time dependent, and its amplitude strongly varied with the interface considered. Reconstituted oil bodies were used to prove the involvement of recombinant caleosin in their calcium-driven aggregation and coalescence. Calcium ions at concentration as low as 100 nM were able to strongly modify the shape and aggregation state of purified oil bodies, as well as their behavior within a monolayer, reflecting potentially profound changes in their structure and dynamic.
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http://dx.doi.org/10.1021/jf802305bDOI Listing
December 2008

Pectin-lipid assembly at the air-water interface: effect of the pectin charge distribution.

Biomacromolecules 2008 Apr 11;9(4):1306-12. Epub 2008 Mar 11.

UR1268 Biopolymères Interactions Assemblages, INRA, F-44300 Nantes, France.

Pectins are anionic polysaccharides that are sensitive to cations, a property that is widely used in food science. The interactions of a cationic lipid film (dimethyldioctadecylammonium bromide, DODAB) with a set of pectins bearing the same charge, which was either distributed randomly or pseudorandomly or blockwise, are investigated. The combination of Brewster angle microscopy BAM and infrared reflection-absorption spectroscopy IRRAS at the air-water interface reveals that pectin strongly binds to the cationic lipid film in forming a stacked layer underneath the lipid film. The detailed vibrational study of this stable mixed film indicates furthermore that pectin induces a disorder in the internal structure of the cationic film. The strong binding induces a splitting of the carboxylate stretching mode of pectin that is pressure and charge distribution dependent. The occurrence of an intermediate plateau below the collapse of the mixed film originates probably from a change in conformation of the pectin structure underneath the film.
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http://dx.doi.org/10.1021/bm7013685DOI Listing
April 2008
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