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International audience; Lipid droplets are the major stock of lipids in oleaginous plant seeds. Despite their economic importance for oil production and biotechnological issues (biofuels, lubricants and plasticizers), numerous questions about their formation, structure and regulation are still unresolved. To determine water accessible domains of protein coating at lipid droplets surface, a structural proteomic approach has been performed. This technique relies on the millisecond timescale production of hydroxyl radicals by the radiolysis of water using Synchrotron X-ray white beam. Thanks to the evolution of mass spectrometry analysis techniques this approach allows the creation of a map of the solvent accessibility for proteins difficult to study by other means. Using these results, a S3 oleosin water accessibility map is proposed. This is the first time that such a map on an oleosin co-purified with plant lipid droplets and other associated protein is presented. Biological significance: Lipid droplet associated proteins function is linked to stability, structure and probably formation and lipid mobilization of droplets. Structure of these proteins in their native environment, at the interface between bulk water and the lipidic core of these organelles is only based on hydrophobicity plot. Using hydroxyl radical footprinting and proteomics approaches we studied water accessibility of one major protein in these droplets: S3 oleosin of Arabidopsis thaliana seeds.

Background The cellular morphology of plant organs is strongly related to other physical properties such as shape, size, growth, mechanical properties or chemical composition. Cell morphology often vary depending on the type of tissue, or on the distance to a specific tissue. A common challenge in quantitative plant histology is to quantify not only the cellular morphology, but also its variations within the image or the organ. Image texture analysis is a fundamental tool in many areas of image analysis, that was proven efficient for plant histology, but at the scale of the whole image. Results This work presents a method that generates a parametric mapping of cellular morphology within images of plant tissues. It is based on gray level granulometry from mathematical morphology for extracting image texture features, and on Centroidal Voronoi Diagram for generating a partition of the image. Resulting granulometric curves can be interpreted either through multivariate data analysis or by using summary features corresponding to the local average cell size. The resulting parametric maps describe the variations of cellular morphology within the organ. Conclusions We propose a methodology for the quantification of cellular morphology and of its variations within images of tissue sections. The results should help understanding how the cellular morphology is related to genotypic and / or environmental variations, and clarify the relationships between cellular morphology and chemical composition of cell walls.

International audience; Fenton reaction kinetics, which involved an Fe(II)/Fe(III) oxidative redox cycle, were studied in a liquid medium that mimics meat composition. Muscle antioxidants (enzymes, peptides, and vitamins) were added one by one in the medium to determine their respective effects on the formation of superoxide and hydroxyl radicals. A stoichio-kinetic mathematical model was used to predict the formation of these radicals under different iron and H2O2 concentrations and temperature conditions. The difference between experimental and predicted results was mainly due to iron reactivity, which had to be taken into account in the model, and to uncertainties on some of the rate constant values introduced in the model. This stoichio-kinetic model will be useful to predict oxidation during meat processes, providing it can be completed to take into account the presence of myoglobin in the muscle.

International audience; The first step of odour perception is an interaction between odorants and olfactory receptors [1]. Moreover, odours perceived in our environment are mainly the result of mixtures of odorants; however, the specific mechanisms involved in their processing remain poorly understood [2]. In previous studies performed at INRA-CSGA [3], the perception of a mixture of ethyl isobutyrate (Et-iB, strawberry-like odour, STR) and ethyl maltol (Et-M, caramel-like odour, CAR) was investigated in comparison with a reference (allyl hexanoate, Al-H, pineapple-like odour, PNA) chosen to evoke an odour close to the one expected in the mixture. The binary specific mixture of Et-iB and Et-M was judged as more typical of a pineapple odour than the individual components. Some studies highlight the significance of the biological function of odorant, that is to say their odour, to understand odorant discrimination [4, 5]. From this perspective, we focused on all the odours shared by the molecules having at least one of the odours STR, CAR or PNA in their odorant description (respectively 22, 154 and 129 molecules). We based this approach on our recent work related to the analysis of a large odorants database [6]. We applied the notion of "social network", used in the social sciences to study relationships between individuals. We followed here a similar approach to describe the network of odours linked to STR, CAR and/or PNA. Thus, if two odours co‐exist in the odorant description of one or several odorants, they are “linked at level L1”. The number of links between two odours is the number of molecules described with these two odours. We identified 348 pairs of odours involving a total of 113 odours. The analysis of the links between the odours revealed strong L1 association between STR and CAR, as well as smaller L1 association between STR and PNA (respectively 40% and 14% of the molecules described with STR odour). Conversely, only one molecule is described with CAR and PNA odours (Furfuryl pentanoate “Fruity-pineapple-apple, caramellic odour”) [7]. Interestingly, the network of the odours highlights numerous links at level L2 between CAR and PNA: 15 odours connect the three odours STR, CAR and PNA, and 24 odours connect CAR and PNA; only 4 and 2 odours connect STR respectively to CAR and PNA. Our hypothesis is that the analysis of L1 and L2 links between odours from large database of odorants would constitute an essential key to identify potential odours/odorants triplets able to form a blending mixture. 1. Buck L, Axel R. Cell, 1991, 65, 175-187. 2. Thomas-Danguin T, Sinding C, et al. Front. Psychol., 2014, 5, 504. 3. Le Berre E, Thomas-Danguin T, et al. Chem. Senses, 2008, 33, 193-199. 4. Ma LM, Qiu Q, et al. Proc. Natl. Acad. Sci. U. S. A., 2012, 109, 5481-5486. 5. Poivet E, Tahirova N, et al. Sci. Adv., 2018, 4, eaao6086. 6. Tromelin A, Chabanet C, et al. Flavour Frag. J., 2018, 33, 106-126. 7. Flavor-Base 9th Ed. (2013). Leffingwell & Associates, http://www.leffingwell.com/flavbase.htm.

A reaction–diffusion mathematical model has been developed to predict the gastric digestion of meat proteins. The model takes into account pepsin diffusion and proton diffusion in bolus particles and the pH buffering capacity of meat. The computations show that the size of bolus particles and the change in gastric pH have a substantial effect on the percentage of protein digested in the stomach and that the pH buffering capacity of meat has to be accounted for to properly calculate the gastric digestibility of meat. The intensity of surface transfers between stomach fluid and bolus particles has a significant impact on protein digestibility, whereas the variation in pepsin content in the stomach between individuals appears to have little effect on protein digestibility. From a nutritional standpoint, the simulations show that meat protein digestibility is high under normal physiological stomach conditions. However, in a situation where masticatory capacity, hydrochloric acid secretion and gastric motor function performances are reduced, such as with advancing age, protein digestibility rapidly decreases, ultimately leading to near-zero digestibility value in the stomach in extreme cases.

International audience; The enzymatic lipolysis of complex natural lipoproteic assemblies such as milk fat globules is central in neonatal digestion. This process first requires the rapid adsorption of a lipolytic enzyme, gastric lipase, onto the membrane enveloping the triglyceride substrate before the onset of catalytic activity. The interactions governing lipase adsorption onto this complex lipid/water interface are not fully elucidated. This study was designed to unravel the interactions of recombinant dog gastric lipase (rDGL) with model monolayers presenting liquid-liquid phase coexistence and mimicking the outer leaflet of the milk fat globule membrane. Combining biophysical tools (ellipsometry, tensiometry and atomic force microscopy), it was evidenced that rDGL partitions toward liquid expanded phase and at phase boundaries. rDGL gets adsorbed at several levels of insertion suggesting molecular cooperation that may favor insertion and strongly impacts on the lipid phase lateral organization. The addition of phosphatidylserine, negatively charged, reinforced adsorption; hence besides hydrophobic interactions and as further investigated through surface potential modeling, rDGL adsorption is favored by electrostatic interactions

International audience; Cell walls are complex structures surrounding plant cells with a composition that varies among species and even within a species between organs, cell types and development stages. For years, cell walls in wheat grains were described as simple walls consisting mostly of arabinoxylans and mixed-linked beta glucans. Proteomic and transcriptomic studies identified enzyme families involved in the synthesis of many more cell wall polysaccharides in the wheat grains. Here we describe the discovery of pectic domains in wheat grain using monoclonal antibodies and enzymatic treatment to degrade the major cell wall polymers. Distinct spatial distributions were observed for rhamnogalacturonan I present in the endosperm and mostly in the aleurone layer and homogalacturonan especially found in the outer layers, and tight developmental regulations were unveiled. We also uncovered a massive deposition of homogalacturonan via large vesicular bodies in the seed coat (testa) beneath a thick cuticle during development. Our findings raise questions about the function of pectin in wheat grain.

Adhesion of bacteria to mucus may favor their persistence within the gut and their beneficial effects to the host. Interactions between pig gastric mucin (PGM) and a natural isolate of Lactococcus lactis (TIL448) were measured at the single-cell scale and under static conditions, using atomic force microscopy (AFM). In parallel, these interactions were monitored at the bacterial population level and under shear flow. AFM experiments with a L. lactis cell-probe and a PGM-coated surface revealed a high proportion of specific adhesive events (60%) and a low level of non-adhesive ones (2%). The strain muco-adhesive properties were confirmed by the weak detachment of bacteria from the PGM-coated surface under shear flow. In AFM, rupture events were detected at short (100-200 nm) and long distances (up to 600-800 nm). AFM measurements on pili and mucus-binding protein defective mutants demonstrated the comparable role played by these two surface proteinaceous components in adhesion to PGM under static conditions. Under shear flow, a more important contribution of the mucus-binding protein than the pili one was observed. Both methods differ by the way of probing the adhesion force, i.e. negative force contact vs. sedimentation and normal-to-substratum retraction vs. tangential detachment conditions, using AFM and flow chamber, respectively. AFM blocking assays with free PGM or O-glycan fractions purified from PGM demonstrated that neutral oligosaccharides played a major role in adhesion of L. lactis TIL448 to PGM. This study dissects L. lactis muco-adhesive phenotype, in relation with the nature of the bacterial surface determinants. 8;11

International audience; This work was devoted to probe, at the entire population level, interactions between mucins and Lactococcus lactis, using QCM-D. Real-time monitoring of adsorption on polystyrene of PGM (Pig Gastric Mucin) and subsequent adhesion of L. lactis was performed for IBB477 and MG1820 strains. Measuring simultaneously shifts in resonance frequency and dissipation on the polystyrene-coated crystal demonstrated a two-phase process for PGM adsorption. XPS analysis confirmed the presence of adsorbed mucin. The Voigt-based model was used to describe the QCM-D outputs. The predicted thickness of the PGM layer was consistent with the AFM experimental value. Adhesion of L. lactis to bare or PGM-coated polystyrene was then monitored, in combination with DAPI cell counting. Positive frequency shifts were caused by adhering bacteria. The presence of adsorbed PGM strongly reduced bacterial adhesion. However, adhesion of IBB477 to the PGM coating was greatly increased in comparison with that of MG1820. Muco-adhesion may be a highly variable and valuable phenotypic trait among L. lactis strains.

International audience; The spreading capacity and surface layer characteristics (morphology and mechanical properties) of different hydrocolloids emulsifiers were compared at air-water interfaces. Acacia senegal, Acacia seyal (AcSey), sugar beet pectin (SBP) in conventional and matured states and two conventional samples of gum Ghatti (GG) were studied in aqueous solutions at pH 4.5 and 3.1. Samples were analysed by their Langmuir compression isotherms. At pH 4.5, the conventional A. senegal (GAc) and A. seyal (AcSeyc) samples exhibited low spreading capacity compared with the other hydrocolloids. The capacity to spread on the surface was improved by the maturation process applied to A. senegal gums and to SBP, but had little effect on the A. seyal samples. The elasticity at zero deformation rate was homogenous for the hydrocolloids. Only A. seyal samples showed high resistance to layer compression, probably due to their low specific volume because of their more compact structure. The matured A. senegal gum was hydrophobically fractionated to separate the main components which were studied individually. The arabinogalactan protein (AGP) component dominates the surface behaviour of this hydrocolloid, and it was confirmed that the arabinogalactan (AG) component did not exhibit surface activity. Acidification of the sub-phase to pH 3.1 improved the spreading and mechanical properties of the layers for all conventional and matured samples, which is in agreement with previous results at n-hexadecane-water interface. However, the GG samples were not affected by pH changes and exhibited similar Langmuir isotherms at both pH values. A. senegal gums were further studied by atomic force microscopy (AFM) and ellipsometry. In aqueous solutions circular particles of about 11 nm in diameter were detected at pH 4.5 for GAc, whereas matured A. senegal gum (designated as EM2) showed circular objects of about 25 nm diameter. Aggregated particles were observed in both samples, but their proportion in EM2 was higher than for GAc. By AFM analysis, the film layer formed by EM2 samples at the air-water interface (pH 4.5) at a surface pressure of 28 mN/m was thick (about 3 times the height of the particles). The roughness and larger particle sizes were more evident for EM2 samples. AFM and ellipsometry at pH 3.1 showed that the surface layer of both samples were thicker and made up of a higher proportion of aggregates.

International audience; A cinnamoyl-CoA reductase 1 knockout mutant in Arabidopsis thaliana was investigated for the consequences of lignin synthesis perturbation on the assembly of the cell walls. The mutant displayed a dwarf phenotype and a strong collapse of its xylem vessels corresponding to lower lignin content and a loss of lignin units of the noncondensed type. Transmission electron microscopy revealed that the transformation considerably impaired the capacity of interfascicular fibers and vascular bundles to complete the assembly of cellulose microfibrils in the S(2) layer, the S(1) layer remaining unaltered. Such disorder in cellulose was correlated with X-ray diffraction showing altered organization. Semi-quantitative immunolabeling of lignins showed that the patterns of distribution were differentially affected in interfascicular fibers and vascular bundles, pointing to the importance of noncondensed lignin structures for the assembly of a coherent secondary wall. The use of laser capture microdissection combined with the microanalysis of lignins and polysaccharides allowed these polymers to be characterized into specific cell types. Wild-type A. thaliana displayed a two-fold higher syringyl to guaiacyl ratio in interfascicular fibers compared with vascular bundles, whereas this difference was less marked in the cinnamoyl-CoA reductase 1 knockout mutant.