Possible adsorption sites of cellulases on crystalline cellulose

AbstractThe possible adsorption sites of cellulases on crystalline cellulose were investigated by molecular graphic representation of a crystal of cellulose and estimation of the accessibility of the various glycosidic bonds to enzymatic attack. The results show that only certain glycosidic bonds of certain surface cellulose chains are susceptible to enzymatic hydrolysis. These preferential sites correlate well with previous electron microscopy observations of the adsorption sites of 1,4-β-D-glucan cellobiohydrolase I (CBHI) from Trichoderma reesei on Valonia cellulose

Structural modifications and thermal transitions of standard maize starch after DIC hydrothermal treatment

International audienceStandard maize starch was hydrothermally treated by Instantaneous Controlled Pressure Drop (DIC) process at three pressure levels (1, 2 and 3 bar) corresponding to the temperatures of 100, 122 and 135 C (at 13–27% moisture), respectively. The structural effects of various hydrothermal conditions were examined with differential scanning calorimetry (DSC) and wide-angle X-ray diffraction. In order to understand the changes that occur during DIC treatment, melting endotherms of native maize starch at various moisture contents were determined. The gelatinization temperatures of DIC treated standard maize starch increased with DIC treatment. The transition temperatures (To, Tp) are closely related to the combined effect of pressure and processing time. At approximately 10 min of processing time, To and Tp were 65.7 and 72.3, 68.8 and 73.6 C, 74.8 and 79.8 C for pressure levels of 1, 2 and 3 bar, respectively (against 63.1 and 69.6 C for native starch). DIC treatment narrowed the gelatinization temperature range and decreased gelatinization enthalpy (DH), as the severity of processing conditions increased. DH decreased from 11.4 J g1 (native) to 11.0 (1 bar), 9.0 (2 bar) and 1.7 J g1 (3 bar) for treated maize starch during approximately 10 min. Relative crystallinity of hydrothermally treated starch decreased with increasing DIC conditions. The A-type crystalline pattern was progressively lost (at pressure level P2 bar) and substituted by the Vh-type X-ray diffraction pattern, corresponding to the formation of amylose–lipid complexes. For severe DIC conditions (pressure level of 3 bar), the substitution was completed. Microscopic observations revealed progressive loss of the birefringence of DIC treated starch granules except at low pressure (1 bar), while the integrity of starch granules was preserved for all the conditions. These modifications that reveal important changes in the crystalline organization of the starch granules are related to their functional properties

Physico-chemical characterisation of sago starch

The physico-chemical characteristics of various sago starch samples from South East Asia were determined and compared to starches from other sources. X-ray diffraction studies showed that all the sago starches exhibited a C-type diffraction pattern. Scanning electron microscopy showed that they consist of oval granules with an average diameter around 30 μm. Proximate composition studies showed that the moisture content in the sago samples varied between 10.6% and 20.0%, ash between 0.06% and 0.43%, crude fat between 0.10% and 0.13%, fiber between 0.26% and 0.32% and crude protein between 0.19% and 0.25%. The amylose content varied between 24% and 31%. The percentage of amylose obtained by colourimetric determination agreed well with the values obtained by fractionation procedures and potentiometric titration. Intrinsic viscosities and weight average molecular weight were determined in 1M KOH. Intrinsic viscosity for amylose from sago starches varied between 310 and 460 ml/g while for amylopectin the values varied between 210 and 250 ml/g. The molecular weight for amylose was found to be in the range of 1.41×106 to 2.23×106 while for amylopectin it was in the range of 6.70×106 to 9.23×106. The gelatinisation temperature for the sago starches studied varied between 69.4°C and 70.1°C. The exponent ‘a’ in the Mark–Houwink equation and the exponent ‘α’ in the equation Rg=kMα was found to be 0.80 and 0.58, respectively for amylose separated from sago starch and these are indicative of a random coil conformation. Two types of pasting properties were observed. The first was characterised by a maximum consistency immediately followed by sharp decrease in consistency while the second type was characterised by a plateau when the maximum consistency was reached

Étude des interactions entre la cellulose et les xyloglucanes via des systèmes modèles de parois végétales primaire

Le travail a consisté à examiner les interactions des xyloglucanes, composé hémicellulosique majoritaire des parois primaires végétales de dicotylédones, avec la cellulose. L'influence des paramètres structuraux de la cellulose a été étudiée à partir de complexes cellulose/xyloglucanes formés in vitro. Les isothermes d'adsorption correspondants montrent de faibles interactions compte tenu des surfaces accessibles...NANTES-BU Sciences (441092104) / SudocSudocFranceF

Les amidons et leurs derives dans les industries des cereales

58 ref.National audienc

Mémoire de forme et matériaux à base d'amidon (propriétés et mécanismes impliqués )

Cette étude porte sur la caractérisation et la compréhension de l effet mémoire de forme dans les matériaux en amidon extrudé. Les performances de mémoire de forme, définie par (i) la fixité de forme, (ii) la recouvrance de forme, (iii) la recouvrance de contrainte, d un amidon thermoplastique sont comparables à celles observées pour les polymères de synthèse. Dans des conditions optimales, la fixité est proche de 98%, la recouvrance de forme de 95% et la recouvrance de contrainte environ 3MPa. Pour l amidon, l effet mémoire de forme peut être déclenché par la température et l humidité. La spectroscopie infrarouge polarisée et la diffusion des rayons X ont été adaptées afin d élucider l organisation amorphe, siège de la mémoire de forme pour l amidon extrudé. Grâce à ces techniques d analyses, il à pu être mis en évidence la présence d une orientation de la phase amorphe induite lors de la déformation ainsi que la présence d un ordre local qui serait constitué de fragments d hélices. Cet ordre local permet aux chaînes de s orienter sans qu il y ait de glissement. La recouvrance de forme à lieu au passage de la transition vitreuse est conduit à un état isotrope. Il a été mis en évidence que la déformation conduit à la formation de contraintes résiduelles, dont l intensité est linéairement dépendante de niveau d orientation. Dans la forme temporaire une diminution de la mobilité moléculaire est observée, elle pourrait être liée à la présence d un réseau secondaire, formé durant la déformation. Les résultats sont discutés sur la base des hypothèses émises pour les mécanismes de mémoire de forme dans les polymères synthétiques.The main objective of this study was to characterize the shape memory effect in extruded starch-based materials and to understand the related structure implicated in this particular effect. The shape memory performances of thermoplastic starch are very similar to those of most synthetic polymers, with for optimized conditions, a fixity about 98%, a shape recovery of 95% and a recovery stress close to 3MPa. Moreover, the shape change of starch-based materials can be triggered by both humidity and temperature. Synchrotron radiation polarized infrared microspectroscopy and wide angle x-ray scattering experiments evidence a orientation of amorphous segments and the presence of a local order constituted of helical fragments. This local order allow chains orientation without slippage. Shape recovery stimulated at the glass transition lead to a isotropic state. It has been shown that the deformation induce the formation of residual stresses, linearly dependent on the orientation of the amorphous chains. In the temporary shape a lower molecular mobility is observed. This lower mobility can results from the formation of a secondary network, created during the deformation and seems to be due to hydrogen bonds. The results are discussed in terms of usual mechanisms proposed for shape memory synthetic polymersNANTES-BU Sciences (441092104) / SudocSudocFranceF

Chemical characteristics of insoluble glucans from the cell wall of the marine green alga Ulva lactuca (L.) Thuret

International audienc

Caractérisation par RMN des biopolymères d'origine végétale, de la molécule à l'organisation supramoléculaire

National audienceNMR investigations of plant biopolymers, from the molecule to the supramolecular organisation. Various NMR techniques have been used to characterize plant biopolymers, isolated or in interaction with other macromolecules in complex composites. In our investigations, 1H and 13C NMR spectroscopy is used to study, at the molecular scale, complex biochemical processes as those involved during fruit ripening. NMR informs also about the fine structure of biopolymers, about their polymorphism and their crystallinity. At supramolecular scales, measurements of self-diffusion coefficients complement the low-field relaxometry approaches in order to estimate pore sizes in composite systems of biopolymers

Système modèle de cristallisation de l'amylose A

L'AMIDON, PRINCIPAL GLUCIDE DE RESERVE DES VEGETAUX SUPERIEURS ET L'UNE DES SOURCES CALORIQUES MAJEURES DE L'ESPECE HUMAINE, SE PRESENTE SOUS LA FORME DE GRAINS MICROSCOPIQUES (1-100 MICRONS) CONSTITUES D'UN MELANGE DE DEUX HOMOPOL YMERES DE GLUCOSE, L'UN LINEAIRE (L'AMYLOSE) ET L'AUTRE RAMIFIE (L'AMYLOPECTINE). LA CRISTALLINITE DE L'AMIDON NATIF (DE L'ORDRE DE 35%) TROUVE SON ORIGINE DANS L'ORGANISATION EN GRAPPE DE L'AMYLOPECTINE. LES COURTES BRANCHES DE LA MACROMOLECULE FORMENT DES DOUBLES HELICES QUI S'ASSOCIENT LATERALEMENT POUR FORMER DES LAMELLES CRISTALLINES. LA CARACTERISATION DE CES CRISTALLITES DANS LE GRAIN A UNE ECHELLE LOCALE RESTE PROBLEMATIQUE. POUR ETUDIER LA CRISTALLISATION DE L'AMIDON, ON PEUT AUSSI CONCEVOIR DES SYSTEMES lN VITRO SIMPLIFIES OU MODELES ET S'INTERESSER AU COMPORTEMENT DE COURTES CHAINES DONT LE DEGRE DE POLYMERISATION EST D L'ORDRE DE CELUI DES COURTES BRANCHES DE L'AMYLOPECTINE. AU COURS DE CE TRAVAIL, NOUS AVONS PREPARE DES FRACTIONS DE COURTES CHAINES D'AMYLOSE PAR HYDROLYSE D'AMIDON NATIF ET PAR SYNTHESE ENZYMATIQUE lN VITRO. CES FRACTIONS EN SOLUTIONS AQUEUSES DILUEES ONT ETE CRISTALLISEES PAR DIFFUSION LENTE D'UN PRECIPITANT. NOUS AVONS ETUDIE L'INFLUENCE DE PARAMETRES MOLECULAIRES (DEGRE DE POLYMERISATION, POLYDISPERSITE, TAUX DE BRANCHEMENT) OU OPERATOIRES (CONCENTRATION, TEMPERATURE, PRESENCE DE SUBSTRATS INDUCTIFS) SUR LE MODE DE CRISTALLISATION ET LA MORPHOLOGIE DES PRODUITS. UNE ANALYSE CRISTALLOGRAPHIQUE DETAILLEE DES MONOCRISTAUX PAR DIFFRACTION AINSI QU'UNE DESCRIPTION DE LEUR STRUCTURE LAMELLAIRE SONT AUSSI PRESENTEES.STARCH, THE MAIN CARBOHYDRATE RESERVE OF HIGHER PLANTS AND ONE OF THE MAJOR SOURCES OF CALORIES lN THE HUMAN DIET, OCCURS lN THE FORM OF MICROSCOPIC GRANULES (1-100 MICRONS) CONSISTING OF A MIXTURE OF TWO HOMOPOL YMERS OF GLUCOSE, NAMEL Y LlNEAR AMYLOSE AND BRANCHED AMYLOPECTIN. THE CRYSTALLINITY OF NATIVE STARCH (ABOUT 35%) RESULTS FROM THE CLUSTER ORGANIZATION OF AMYLOPECTIN. THE SHORT BRANCHES 0, THE MACROMOLECULE FORM DOUBLE HELICES THA T ASSOCIA TE LA TERALL Y TO FORM CRYST ALLINE LAMELLAE. THE CHARACTERIZATION OF THESE CRYSTALLITES lN THE GRANULE AT A LOCAL SCALE REMAINS PROBLEMATIC. TO STUDY . THE CRYSTALLIZATION OF STARCH, ONE CAN ALSO DEVELOP SIMPLIFIED OR "MODEL" lN VITRO SYSTEMS AND FOCUS ON THE BEHAVIOUR OF SHORT CHAINS WITH A DEGREE OF POLYMERIZATION THAT IS SIMILAR TO THAT OF THE SHORT BRANCHES OF AMYLOPECTIN. DURING THIS WORK, WE HAVE PREPARED FRACTIONS OF SHORT AMYLOSE CHAINS BY HYDROLYZING NATIVE STARCH GRANULES AND BY lN VITRO ENZYMATIC SYNTHESIS. THESE FRACTIONS HAVE BEEN CRYSTALLIZED lN DILUTE AQUEOUS SOLUTIONS BY SLOW DIFFUSION OF A PRECIPTANT. WE HAVE STUDIED THE INFLUENCE OF VARIOUS PARAMETERS (DEGREE OF POLYMERIZATION, POLYDISPERSITY, CONCENTRATION, TEMPERATURE) ON THE MODE OF CRYSTALLIZATION AND MORPHOLOGY OF THE PRODUCTS. A DETAILED CRYSTALLOGRAPHIC ANAL YSIS OF SINGLE CRYSTALS BY DIFFRACTION AND A DESCRIPTION OF THEIR LAMELLAR STRUCTURE ARE PRESENTED AS WELL.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Étude structurale et mécanismes de formation de complexes amylose-ligand (Influence sur la rétention de composés d'arôme dans une matrice amylacée)

L'objet de ce travail est d'étudier les mécanismes de complexation de l'amylose par des composés d'arômes et la nature des structures formées, afin d'appréhender l'influence de l'amidon sur la rétention d'arômes dans une matrice alimentaire (génoise). La structure semi-cristalline et la morphologie des 3 types de complexe obtenus ont été approchées par diffraction des rayons X, MET et modélisation moléculaire. La localisation des composés d'arômes et leur teneur dans les zones amorphes et cristallines ont été déterminées par utilisation couplée de spectroscopie FT-IR et d'hydrolyses acides. L'étude des cinétiques de cristallisation/fusion par AED et FT-IR a permis de proposer 2 mécanismes de complexation et de déterminer la stabilité thermique des différents complexes étudiés. L'ensemble des résultats suggèrent une réelle implication des complexes d'amylose sur la rétention des arômes dans une matrice alimentaire. Ceci a pu être vérifié au cours de la préparation d'une génoise.This work aims at studying the complexing of amylose by a series of aroma compounds in order to grasp the influence of starch on the trapping of flavours in food matrices as sponge-cakes. The semi-crystalline structure (crystallinity, polymorphic type, inclusion of the aroma compound in and between amylose helices) of the resulting 3 types of complex and the related morphology were assessed by X-Ray scattering, TEM. and molecular modelling. The location and the respective amount of aroma compounds in amorphous and crystalline regions stoichiometry were determined by using both FT-IR spectroscopy and acid hydrolysis. The kinetics of crystallisation and the thermal stability were investigated by DSC and FT-IR . It allowed to propose 2 different complexing mechanisms. The results suggest a real involvement of amylose complexes on the retention of flavours in real food matrices. This point was verified during sponge-cake baking.NANTES-BU Sciences (441092104) / SudocSudocFranceF