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International audience; Over the last 15 years, research efforts have been dedicated to identifying the factors that influence lignocellulosic biomass (LB) enzymatic deconstruction to develop alternatives to fossil carbon resources [1]. Accessibility of LB is an important parameter influencing the biomass deconstruction and is guided by many factors contributing to recalcitrance which can be separated between factors related to the composition of the LB (hemicelluloses, lignin or hydroxycinnamic acids content) and structural factors (the chemical structure and interaction of cell wall polymers, cell wall porosity …) [2].. This study focused on the hot water pretreatment (HWP) of maize internodes during 20 or 40 minutes, which induces disruptions within the tight inter-polymers association mainly through the breakdown of inter- and intra-polymer bonds and a reorganization of the network.The chemical characterization showed that HWP modified the cell wall composition with a loss of hemicelluloses (up to 45% for HWP 40 min) and of ferulic acid cross-linking, associated with a lignin enrichment.Impact of HWP on cellulose supramolecular organization was highlighted with the 13C CPMAS sequence [3], showing an increase of cellulose crystallinity concomitant with an increase of.agregate dimension. This acquisition also shown that the lignin structure is altered, related through a decrease of β-O-4 bonds.The study of the kinetics of polarization transfer made it possible, by using a model using two proton reservoirs [4], to characterize, on the one hand, the increase in the molecular order (T1ρH), and on the other hand, the presence of a greater density of water molecules in the macromolecular assembly (THH).Low-field T2 measurement at two different hydration levels spotlights a modulation of the domains and promotes the creation of new domains where the water is more constrained and which can be associated with pore sizes between 5 and 15 nm. This increase of the porosity, seen by NMR and Simons’ staining, should favour the mobility of enzymes and thus facilitate their catalytic activity.The results obtained by the combined use of these different NMR modalities, associated with the results obtained using chemical analyzes, were synthesized in a diagram illustrating the evolution of interactions within the macromolecular assembly.This study highlights that the loss of hemicelluloses and changes in polymers structural features induced by HWP leads to a reorganization of the cell walls. These modifications induce an increase in the specific surface area and a water redistribution allowing an increase in the accessibility of cellulases and an enhancement of the hydrolysis yield [5].

International audience

International audience; Cereal grain cell walls are studied for their nutritional benefits (dietary fibre), their adverse effects on the digestive health of livestock such as poultry and pigs, and their effects on grain usage (bread making, pasta, brewing...). In wheat grain, the two major cell wall polysaccharides, arabinoxylans and β-glucans, have been extensively studied. By contrast, mannan was poorly documented. Nevertheless, this hemicellulosic polysaccharide might have a determinant role in wheat grain development since, in Arabidopsis thaliana, mutants with a reduced amount of mannan show an altered seed development. Our project aimed at deciphering the biochemical structure and the biological function of mannan. To study the biological function of mannan, we have studied its occurrence during wheat grain development. The detection of mannan using monoclonal antibodies showed that mannan is mainly located in the grain endosperm and that its deposition starts at an intermediate step of endosperm cellularization. We have purified mannan from wheat endosperm to determine its fine structure. Former studies have speculated that the class of mannan present in wheat was glucomannan. Our data suggest that this class of hemicelluloses is only represented by short unsubstituted chains of 1,4 linked D-mannose residues that are weakly acetylated [1]. We identified candidate mannan biosynthetic genes expressed in the endosperm. After unsuccessful attempts to generate wheat lines depleted in mannan, the heterologous expression of our best candidate genes was carried out in Pichia pastoris and Arabidopsis triple mutant depleted in glucomannan. Introducing TaCslA12 gene in yeast and Arabidopsis led to the production of wheat-like linear mannan lacking glucose residues and with moderate acetylation [2]. Therefore, this gene encodes a mannan synthase and is responsible for the synthesis or wheat endosperm mannan.

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International audience; Apple processing for juice production suffers from yield variability due to varietal, physiological and postharvest handling factors. In order to identify markers to be used by the profession to class fruit lots and adapt process, a study was engaged on the contribution of apple cell wall on the viscoelastic mechanical properties of desert and cider varieties.

By mimicking the cutin natural polyester networks of plant cuticles, we produced hydrophobic elastomers by a sustainable process, i.e., using a catalyst- and solvent-free polycondensation of glycerol and hydroxy fatty acids, two by-products of the agro-food industry. The hydroxy-fatty acid fraction was obtained by alkaline hydrolysis in ethanol of peels from industrial tomato pomaces. This industrial-like fatty acid fraction contained more than 90% wt. of 9(10)-16 dihydroxyhexadecanoic acid (diOHC16). The co46 polyesters were designed by increasing the ratio of esterified glycerol/diOHC16 in a range observed in plant cutins (up to 6% wt.). Their structure and functional properties (thermal, mechanical, gas permeability, interaction with bacterial cells) were characterized. Increasing the glycerol contents induced a significant decrease in the reticulation degree of the polyesters and the formation of crystalline domains with an hexagonal organization. These structural modifications were related to a marked increase of elastomeric extensibility (up to 217%). While water vapor permeability was not impacted, the increase of glycerol content induced a significant decrease of oxygen permeability. None of the polyesters displayed biocide activity, but an increase of glycerol content significantly reduced the adhesion of bacterial cells, potentially giving rise to antifouling applications. Finally, the increasing content of free hydroxyl groups of the co-polyesters offer opportunities of grafting and covalent substitution for tailored functionalization; Bioinspired co-polyesters of hydroxy-fatty acids extracted from tomato peel agro-wastes and glycerol with tunable mechanical, thermal and barrier properties

International audience; The aim of the present study is to improve the understanding of the evolution of flax fibre(Linum usitatissimum L.) ultrastructure and properties caused by the retting process at the cellwall scale. The dew retting is a natural bioprocess, where the various microorganisms presentin the soil colonize the flax stems. The enzymes they secrete make it easier to extract the bastfibre bundles during the scutching stage.In this study, six different stages of retting were investigated. Differences between rettingstage 1 (R1, earlier) and the retting stage 6 (R6, over retted) are +17% and +23% with AFMPF-QNM and nanoindentation measurements, respectively.An over retting results in the loss of the cellulose that makes up the fibres (Placet et al. 2017),arguably due to secretion of cellulase. To obtain information on the supramolecular structureof cellulose fibrils in the plant cell walls, the model of Larsson and Wickholm (Larsson et al.,1997) could be used for deconvoluate the C4 region between 77 and 92 ppm. In addition, themechanical properties of flax cell walls during could be investigated by AFM Peak ForceQuantitative Nano-Mechanical property mapping (AFM PF-QNM) (Goudenhooft et al. 2018).Two complementary structural investigating technic will be presented, namely using X-RayDiffraction (XRD) and solid state Nuclear Magnetic Resonance (NMR). An estimation of thecellulose crystallinity index by XRD measurements, confirmed by NMR, shows an increaseof 8% in crystallinity with retting, mainly due to the disappearance of amorphous polymer. Inaddition, NMR investigations show a compaction of inaccessible cell wall polymers,combined with an increase in the relaxation times of the C4 carbon.One highlight of the work is that NMR results show a significant evolution in the cell wallultrastructure of flax during the retting stages. The improvement observed in the mechanicalperformance of flax cell walls can be explained by the compaction of inaccessible zones.Based on the NMR results, a schematic representation of the flax cellulose elementarymicrofibrils structure of R1 and R6 was hypothesised. In this flax cellulose evolution modelduring retting, we have considered in particular the lateral fibril dimension (LFD) and the thelateral fibril aggregate dimension (LFAD). As illustration, the LFD of samples R1 and R6 are4.1 and 4.5 nm, respectively, while the LFAD slightly decreases during retting from 17.1 nmfor R1 to 16.3 nm for R6.