Luc Saulnier

Agricultural Plant Science, Food Science

PhD
39.00

Publications

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    ABSTRACT: Composite films made with Arabinoxylans (AXs) (with high, middle and low level of substitution by arabinose) and (1→3)(1→4)-β-d-glucans (BGs) extracted from cereal cell walls have been prepared and analyzed using microscopy (SEM and LSCFM), DSC, mechanical tests and TD-NMR spectroscopy. The objectives were to correlate molecular and physico-chemical properties of films with mechanical and hydration properties of wheat cell walls. A phase separation phenomenon was observed for films made with highly substituted AXs and BGs at a ratio AX/BG of 60/40. This phase separation was correlated with lower dipolar interactions between polysaccharide chains and a decrease of ultimate strain and stress of films. Highly substituted AX and BG composite films exhibited very weak mechanical properties in agreement with weaker interactions between the polymer chains. This effect was supported by NMR results showing that interactions between AXs and BGs decreased with increased substitution of AXs in composite films. Lower dipolar interactions between polysaccharides favored the water mobility in relation with a higher specific surface area of polysaccharides in films but also higher distances between polysaccharide chains so larger nanopores in composite films made within highly substituted AXs. These multiscale characterizations agreed with the structural changes observed in wheat grain during its development. Copyright © 2015 Elsevier Ltd. All rights reserved.
    Carbohydrate Polymers 05/2015; 122. DOI:10.1016/j.carbpol.2015.01.014 · 3.92 Impact Factor
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    ABSTRACT: Arabinoxylan (AX) is the dominant component within wheat (Triticum aestivum L.) endosperm cell walls, accounting for 70% of the polysaccharide. The viscosity of aqueous extracts from wheat grain is a key trait influencing the processing for various end uses, and this is largely determined by the properties of endosperm AX. We have previously shown dramatic effects on endosperm AX in transgenic wheat by down-regulating either TaGT43_2 or TaGT47_2 genes (orthologues to IRX9 and IRX10 in Arabidopsis, respectively) implicated in AX chain extension and the TaXAT1 gene responsible for monosubstitution by 3-linked arabinose. Here, we use these transgenic lines to investigate the relationship between amounts of AX in soluble and insoluble fractions, the chain-length distribution of these measured by intrinsic viscosity and the overall effect on extract viscosity. In transgenic lines expressing either the TaGT43_2 or TaGT47_2 RNAi transgenes, the intrinsic viscosities of water-extractable (WE-AX) and of a water-insoluble alkaline-extracted fraction (AE-AX) were decreased by between 10% and 50% compared to control lines. In TaXAT1 RNAi lines, there was a 15% decrease in intrinsic viscosity of WE-AX but no consistent effect on that of AE-AX. All transgenic lines showed decreases in extract viscosity with larger effects in TaGT43_2 and TaGT47_2 RNAi lines (by up to sixfold) than in TaXAT1 RNAi lines (by twofold). These effects were explained by the decreases in amount and chain length of WE-AX, with decreases in amount having the greater influence. Extract viscosity from wheat grain can therefore be greatly decreased by suppression of single gene targets. © 2015 Society for Experimental Biology, Association of Applied Biologists and John Wiley & Sons Ltd.
    Plant Biotechnology Journal 03/2015; DOI:10.1111/pbi.12361 · 5.68 Impact Factor
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    ABSTRACT: The filamentous fungus Talaromyces versatilis is known to improve the metabolizable energy of wheat-based poultry diets thanks to its ability to produce a pool of CAZymes and particularly endo-β(1,4)-xylanases. In order to appreciate their in vivo mode of action, the supplementation effect of two of its xylanases, XynD and XynB from families GH10 and GH11 respectively, have been evaluated on two different wheat cultivars Caphorn and Isengrain, which were chosen amongst 6 varieties for their difference in non starch polysaccharides content and arabinoxylan composition. Polysaccharides digestion was followed during 6 h along the digestive tract using the TNO gastrointestinal model-1, to mimic monogastric metabolism. Polysaccharide degradation appeared to occur mainly at the jejunal level and was higher with Isengrain than with Caphorn. For both cultivars, XynD and XynB supplementation increased notably the amount of reducing end sugars into the jejuno-ileal dialysates, which has been confirmed by a valuable increase of the soluble glucose into the jejunal dialysates. The amounts of arabinose and xylose into the dialysates and ileal deliveries increased consequently mainly for Caphorn, suggesting that XynD and XynB supplementation in wheat-based diet could alleviate the anti-nutritional effects of arabinoxylans by limiting the physical entrapment of starch and could increase the available metabolizable energy.
    02/2015; 6(1). DOI:10.1186/s40104-015-0002-7
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    ABSTRACT: The aim of this article is to compare two different sets of optimal conditions for twin-screw extraction of xylans and define their influence on the purification steps, combining ultrafiltration and industrial chromatography. Two xylan extracts were obtained by twin-screw extrusion of straw and bran. Condition 1 used a high straw/bran ratio (equal to 6) and high sodium hydroxide content, and condition 2 used a lower straw/bran ratio (equal to 2) and low sodium hydroxide content. Arabinoxylan extraction yields are slightly higher for conditions with low straw content (5.1% versus 4.4%). Nevertheless, these recovery yields remain between 9% and 10%. Ultrafiltration is as efficient as evaporation for polysaccharide concentration, with lower energy consumption, but also demineralizes the solution. The combination of ultrafiltration and chromatography gives partial purification of the extract with a final arabinoxylan purity ranging from 16% to 26%. This is slightly higher than by direct precipitation, but limited because all the large molecules such as proteins and lignins were retained by ultrafiltration. Copyright © 2014 Elsevier Ltd. All rights reserved.
    Carbohydrate Polymers 02/2015; 116:86-94. DOI:10.1016/j.carbpol.2014.06.071 · 3.92 Impact Factor
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    ABSTRACT: A process for hemicellulose fractionation and purification from wheat straw and bran has been investigated. The aim was to define the efficiency of a pilot scale process combining twin-screw extrusion and refining steps such as ultrafiltration and chromatography, to replace alcoholic precipitation.
    PROCESS BIOCHEMISTRY 02/2015; 50(4). DOI:10.1016/j.procbio.2015.01.015 · 2.52 Impact Factor
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    ABSTRACT: Dough liquor (DL) is considered as a good model of bread dough liquid phase which plays an important role in alveolar structure creation. In this work, DL was extracted from dough pieces of various contents (g for 100 g flour) of water (55–70), sugar (0–15), rapeseed oil (0–10) and bran (0–20). The extraction yield of DL was 5.0 ± 2.4% and its dry matter content varied between 10.8 and 27.2% of total DL mass. Its composition has been determined in terms of lipids content (≤0.08 mg/mL), polysaccharides, mostly arabinoxylans (0.9–4.7 mg/mL), arabinogalactan-proteins (AGP) and soluble proteins (20.7–38.0 mg/mL). The rheological properties (bulk and surface) of fresh DL, and foaming properties of diluted DL (1/10), were determined using cone-plate rheometry, pendant drop method and Foamscan device, respectively. DL behaved like a macromolecular solution, displaying a slight shear-thinning behavior with an apparent viscosity varying between 0.03 and 0.6 Pa sn, at shear rate 10 s−1. Its surface tension varied between 35 and 45 mN/m. Its adsorption kinetics, governed by protein diffusion to the interface, followed two regimes, the first one depending on sugar content, and the second one on AGP content. Drainage and foam stability kinetics were influenced by neutral sugars, probably through the impact of glucose and mannose on DL viscosity. The understanding of the mechanisms of fermented dough stability could be improved by taking the results of DL surface tension into account.
    Food Hydrocolloids 01/2015; 43:114-124. DOI:10.1016/j.foodhyd.2014.05.003 · 4.28 Impact Factor
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    ABSTRACT: Lignins and their cross-linking to hemicelluloses detrimentally affect the cellulose-to-ethanol conversion of grass lignocelluloses. Screening appropriate grass cell walls and their compositional changes during the various steps of the process calls for a high throughput analytical technique. Such a performance can be fulfilled by Fourier transform mid-infrared (FT-MIR) spectroscopy. In the present paper, a set of maize cell walls from mature stems were selected, including brown midrib samples. Lignin fractions were isolated by mild acidolysis to obtain a set of purified maize lignin standards. The lignin content and the percentage of lignin derived p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) thioacidolysis monomers were determined. In addition, the composition of cell wall polysaccharides, as well as the amount of ester-linked p-coumaric (CA) and ferulic (FA) acids, was measured by wet chemistry. Partial least square (PLS) analyses were applied to infrared and chemical data of cell walls. The resulting models showed a good predictive ability with regard to the lignin content, to the frequency of S (or G) thioacidolysis monomers, and to the level of ester-linked CA of maize cell walls. The loading plots and regression coefficients revealed relevant infrared absorption bands.
    Applied Spectroscopy 11/2014; 68(12). DOI:10.1366/14-07472 · 2.01 Impact Factor
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    ABSTRACT: Bread is one of the main sources of starch of the French diet. Starch is the principal source of energy for humans; the glycemic index (GI) allows to classify the glycemic response to different types of food. Consumption of low GI food is generally recognized as beneficial for human health. Bread GI varies quite largely (40–85) according to the processes that determine the structure of baked products, especially density and crumb texture. For very different baked products such as sandwich bread and French bread, the production of denser bread leads to a lower GI. The densification of bread improves its nutritional profile but largely impacts its sensorial features. Consumer's acceptability of denser products depends on the bread texture; products with an irregular crumb structure, like traditional French bread, tend to be better appreciated.
    Cahiers de Nutrition et de Diététique 04/2014; DOI:10.1016/j.cnd.2014.01.004
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    ABSTRACT: Arabinoxylans (AX) and (1→3),(1→4)-β-glucans (BG) are the major components of wheat grain cell walls. Although incompletely described at the molecular level, it is known that the chemical and distributional heterogeneity of these compounds impacts the quality and use of wheat. In this work, an emerging technique based on MALDI mass spectrometry imaging (MSI) was employed to map variations in the quantity, localization, and structure of these polysaccharides in the endosperm during wheat maturation. MALDI MSI couples detailed structural information with the spatial localization observed at the micrometer scale. The enzymic hydrolysis of AX and BG was performed directly on the grain sections, resulting in the efficient formation of smaller oligosaccharides that are easily measurable through MS, with no relocation across the grain. The relative quantification of the generated oligosaccharides was achieved. The method was validated by confirming data previously obtained using other analytical techniques. Furthermore, in situ analysis of grain cell walls through MSI revealed previously undetectable intense acetylation of AX in young compared to mature grains, together with findings concerning the feruloylation of AX and different structural features of BG. These results provide new insights into the physiological roles of these polysaccharides in cell walls and the specificity of the hydrolytic enzymes involved.
    Journal of Experimental Botany 03/2014; 65(8). DOI:10.1093/jxb/eru065 · 5.79 Impact Factor
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    ABSTRACT: The development of enzyme-mediated glycosynthesis using glycoside hydrolases is still an inexact science, because the underlying molecular determinants of transglycosylation are not well understood. In the framework of this challenge, this study focused on the family GH51 α-l-arabinofuranosidase from Thermobacillus xylanilyticus, with the aim to understand why the mutation of position 344 provokes a significant modification of the transglycosylation/hydrolysis partition. Detailed kinetic analysis (kcat, KM, pKa determination and time-course NMR kinetics) and saturation transfer difference nuclear magnetic resonance spectroscopy was employed to determine the synthetic and hydrolytic ability modification induced by the redundant N344 mutation disclosed in libraries from directed evolution. The mutants N344P and N344Y displayed crippled hydrolytic abilities, and thus procured improved transglycosylation yields. This behavior was correlated with an increased pKa of the catalytic nucleophile (E298), the pKa of the acid/base catalyst remaining unaffected. Finally, mutations at position 344 provoked a pH-dependent product inhibition phenomenon, which is likely to be the result of a significant modification of the proton sharing network in the mutants. Using a combination of biochemical and biophysical methods, we have studied TxAbf-N344 mutants, thus revealing some fundamental details concerning pH modulation. Although these results concern a GH51 α-l-arabinofuranosidase, it is likely that the general lessons that can be drawn from them will be applicable to other glycoside hydrolases. Moreover, the effects of mutations at position 344 on the transglycosylation/hydrolysis partition provide clues as to how TxAbf can be further engineered to obtain an efficient transfuranosidase.
    Biochimica et Biophysica Acta 10/2013; 1840(1). DOI:10.1016/j.bbagen.2013.10.013 · 4.66 Impact Factor
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    ABSTRACT: The cell walls of wheat starchy endosperm are dominated by arabinoxylan (AX), accounting for 65-70% of the polysaccharide content. Genes within two glycosyl transferase (GT) families, GT43 (IRX9, IRX14) and GT47 (IRX10), have previously been shown to be involved in the synthesis of the xylan backbone in Arabidopsis, and close homologues of these have been implicated in the synthesis of xylan in other species. Here homologues of IRX10 TaGT47_2 and of IRX9 TaGT43_2, which are highly expressed in wheat starchy endosperm cells, were suppressed by RNAi constructs driven by a starchy endosperm-specific promoter. The total amount of AX was decreased by 40-50% and the degree of arabinosylation was increased by 25-30% in transgenic lines carrying either of the transgenes. The cell walls of starchy endosperm in sections of grain from TaGT43_2 and TaGT47_2 RNAi transgenics showed decreased immunolabelling for xylan and arabinoxylan epitopes and ~50% decreased cell wall thickness compared to controls. The proportion of AX that was water-soluble was not significantly affected, but average AX polymer chain length was decreased in both TaGT43_2 and TaGT47_2 RNAi transgenics. However, long AX chains seen in controls were absent in TaGT43_2 RNAi transgenics but still present in TaGT47_2 RNAi transgenics. The results support an emerging picture of IRX9-like and IRX10-like proteins acting as key components in the xylan synthesis machinery in both dicots and grasses. Since AX is the main component of dietary fibre in wheat foods, the TaGT43_2 and TaGT47_2 genes are of major importance to human nutrition.
    Plant physiology 07/2013; DOI:10.1104/pp.113.222653 · 7.39 Impact Factor
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    ABSTRACT: Arabinoxylans (AX) and (1→3)(1→4)-β-d-glucans (BG) are the main components of the cell walls in the endosperm of wheat grain. The relative occurrence of these two polysaccharides and the fine structure of the AX are highly variable within the endosperm. Films of AX and BG were used as models of the cell wall to study the impact of polymer structure on the hydration and mechanical properties of the cell walls. Effective moisture diffusivities (Deff) of AX and BG films were determined from 0 to 95% relative humidity (RH) at 20°C. Deff was influenced by the water content, and the structure of polysaccharides. Higher Deff was obtained for films made with highly substituted AX compared to values obtained for films made with BG or lowly substituted AX. Proton dipolar second moments M2 and water T2 relaxation times measured by TD-NMR, indicated that the highly branched AX films exhibited a higher nano-porosity, favoring water motions within films. Results from traction tests showed significant different mechanical properties between the AX and BG films. BG films exhibited much higher extensibility than AX films. Strength and extensibility of AX films decreased with increasing arabinose to xylose ratio. Our results show that the water motions and the mechanical properties of AX and BG films can be linked to the polysaccharide chains interactions that modulate the nanostructure of films.
    07/2013; 96(1):31-38. DOI:10.1016/j.carbpol.2013.03.090
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    ABSTRACT: This work aimed to elucidate the effect of wheat aleurone integrity on its fermentability, i.e. the formation of short-chain fatty acids (SCFA) and microbial phenolic metabolites, in an in vitro model using human faecal microbiota as an inoculum. The structure of aleurone was modified by mechanical (dry grinding) or enzymatic (xylanase with or without feruloyl esterase) treatments in order to increase its physical accessibility and degrade its complex cell-wall network. The ground aleurone (smaller particle size) produced slightly more SCFA than the native aleurone (102.5 and 101 mmol/L, respectively), but showed a similar colonic metabolism of ferulic acid (FA). The enzymatic treatments of aleurone allowed a higher solubilization of arabinoxylan (up to 82%) and a higher release of FA in its conjugated and free forms (up to 87%). The enzymatic disintegration of aleurone's structure led to a higher concentration and formation rate of the colonic metabolites of FA (especially phenylpropionic acids), but did not change significantly the formation of SCFA (81 mmol/L for enzyme treated vs. 101 mmol/L for the native aleurone).
    Journal of Agricultural and Food Chemistry 05/2013; 61(24). DOI:10.1021/jf4001814 · 3.11 Impact Factor
  • A Rakha, L Saulnier, P Aman, R Andersson
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    ABSTRACT: Enzymatic fingerprinting of arabinoxylan (AX) and β-glucan using endo-xylanase and lichenase, respectively, helps determine the structural heterogeneity between different cereals and within genotypes of the same cereal. This study characterised the structural features of AX and β-glucan in whole grains of eight triticale cultivars grown at two locations, 20 barley cultivars/lines with wide variation in composition and morphology and five tritordeum breeding lines. Principal component analysis (PCA) resulted in clear clustering of these cereals. In general, barley and tritordeum had a higher relative proportion of highly branched arabinoxylan oligosaccharides (AXOS) than triticale. Subsequent analysis of triticale revealed two clusters based on growing region along principal component (PC) 1, while PC2 explained the genetic variability and was based on mono-substitution and di-substitution in AX fragments. PCA of β-glucan features separated the three cereals based on β-glucan content. The molar ratio of trisaccharide to tetrasaccharide was 2.5-3.4 in triticale, 2.3-3.3 in barley and 2.8-3.4 in tritordeum. Barley showed a strong positive correlation (r=0.86) between β-glucan content and relative proportion of trisaccharide. The results show that structural features of AX and β-glucan vary between and within triticale, barley and tritordeum grains which might be important determinants of end-use quality of grains.
    10/2012; 90(3):1226-34. DOI:10.1016/j.carbpol.2012.06.054
  • Luc Saulnier
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    ABSTRACT: After a fast reminder on the use of cereals, the biochemical, technological and nutritional characteristics of the various classes of nutrients (starch, proteins, dietary fibres, lipids, vitamins, minerals and phenolic compounds) are presented, in connection with the diversity of composition of the different tissues of the grain and the specificities of main cereals: wheat, corn (maize), rice, rye, barley and oat. Thanks to their richness in starch, cereal grains are an essential part of the diet. They are also a source of dietary fibres and macronutrients (vitamins, minerals, etc.), interesting constituents for health, essentially concentred in the external parts of the kernel. Despite these common characteristics, cereals show various nutritional assets, partly depending on vegetal species, but mostly on technological processes used in flours and foods productions.
    Cahiers de Nutrition et de Diététique 09/2012; 47(1):S4-S15. DOI:10.1016/S0007-9960(12)70292-4
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    ABSTRACT: There is an amazing diversity of cell wall composition and cell wall polysaccharide structure in wheat grain that is only partly explained by the complexity of plant tissues and cell type functions present in this organ. This review presents the state of the art on the structure and diversity of cell wall polymers in mature wheat grain and recent knowledge on cell wall metabolism with a focus on development-associated changes in wheat grain cell wall polysaccharides and genes controlling their biosynthesis. The diversity of polysaccharide structure observed in endosperm cell walls is tentatively explained on the basis of polysaccharide properties and cell type function.
    Journal of Cereal Science 07/2012; 56(1-1):91-108. DOI:10.1016/j.jcs.2012.02.010 · 1.94 Impact Factor
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    ABSTRACT: The consumption of wholegrain wheat is associated with a number of health benefits which may relate to the presence of a range of dietary fibre, phytochemical, vitamin and mineral components. Analysis of 150 bread wheat lines within the HEALTHGRAIN programme showed wide variation in content and composition of bioactive components within 150 bread wheat lines. Furthermore, in some cases (notably arabinoxylan in flour and tocols, sterols and alkylresorcinols in wholemeal) this variation was highly heritable and hence accessible to plant breeders. A number of tools are therefore being developed to facilitate the selection of these components in plant breeding programmes including molecular markers, biochemical kits and NIR calibrations.
    Trends in Food Science & Technology 06/2012; 25(2):70-77. DOI:10.1016/j.tifs.2012.01.003 · 4.65 Impact Factor
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    ABSTRACT: Immunolabeling can be used to locate plant cell wall carbohydrates or other components to specific cell types or to specific regions of the wall. Some antibodies against xylans exist; however, many partly react with the xylan backbone and thus provide limited information on the type of substituents present in various xylans. We have produced a monoclonal antibody which specifically recognizes glucopyranosyl uronic acid (GlcA), or its 4-O-methyl ether (meGlcA), substituents in xylan and has no cross-reactivity with linear or arabinofuranosyl-substituted xylans. The UX1 antibody binds most strongly to (me)GlcA substitutions at the non-reducing ends of xylan chains, but has a low cross-reactivity with internal substitutions as well, at least on oligosaccharides. The antibody labeled plant cell walls from both mono- and dicotyledons, but in most tissues an alkaline pretreatment was needed for antibody binding. The treatment removed acetyl groups from xylan, indicating that the vicinity of glucuronic acid substituents is also acetylated. The novel labeling patterns observed in the xylem of tree species suggested that differences within the cell wall exist both in acetylation degree and in glucuronic acid content.
    Planta 04/2012; 236(2):739-51. DOI:10.1007/s00425-012-1653-7 · 3.38 Impact Factor
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    M.R. Cyran, Luc Saulnier
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    ABSTRACT: Viscosity is one of the most important attributes of rye-based products related to some health benefits. To identify the factors affecting arabinoxylan-dependent extract viscosity (AX-EV) of rye bread, the structural features of water-extractable arabinoxylans (WE-AXs) and their ammonium sulphate precipitated subfractions were investigated in breads with varied viscosities. Also, an endoxylanase activity in the starting flours was examined. The HPSEC-RI profiles revealed the higher extent of AX depolymerisation in whole-meal bread (WMB) when compared to that in endosperm bread (EB), resulting in its lower AX-EV. This was mostly related to lower molecular weight of the parent WE-AX fraction with distinctly lower proportion of 2-Xylp in the chain. The AX-EV of rye bread decreased with decreasing proportion of AX-I, the major subfraction with 3-Xylp as only branching site. The endoxylanase activity was at least two times lower in endosperm flour than that in WM and negatively correlated with the AX-EV of WMB. The importance of densely substituted AX subfractions with exclusively 2-Xylp and 2,3-Xylp branches, protecting the AX-I from enzymic degradation during bread-making, has been evidenced.
    Food Chemistry 03/2012; 131(2):667-676. DOI:10.1016/j.foodchem.2011.09.054 · 3.26 Impact Factor

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