Search

The many studies about amylolysis have collected considerable information regarding the contribution of the starch physico-chemical properties. But the inherent elaborate and variable structure of granular starch and, consequently, the multifactorial condition of the system hinders the interpretation of the experimental results. The immediate benefit of multivariate statistical analysis approaches with that regard is twofold: considering the factors, possibly interrelated, all together and not independently, providing a first estimation of the magnitude and confidence level of the relations between factors and amylolysis kinetic parameters. Based on data of amylolysis of 13 starch samples from wild type, single and double mutants of maize by porcine pancreatic α-amylase (PPA), a multivariate analysis is proposed. Amylolysis progress-curves were fitted by a Weibull function, as proposed in a previous work, to extract three kinetic parameters: the reaction rate coefficient during the first time-unit, k , the reaction rate retardation over time, h , and the final hydrolysis extent, X ∞ . Multivariate models relate the macromolecular composition and the fractions of crystalline polymorphic types to the kinetic parameters. h and X ∞ are found to be highly related to the measured properties. Thus the amylose content appears to be significantly correlated to the hydrolysis rate retardation, which sheds some light on the probable contribution of the amylose molecules contained in the granules. The multivariate models give correct prediction performances except for k whose a part of variability remains unexplained. A further analysis points out the extent of the characterisation effort of the granule structure needed to extend the fraction of explained variability. [ABSTRACT FROM AUTHOR]

Abstract: Background: Native starch accumulates as granules containing two glucose polymers: amylose and amylopectin. Phosphate (0.2–0.5%) and proteins (0.1–0.7%) are also present in some starches. Phosphate groups play a major role in starch metabolism while granule-bound starch synthase 1 (GBSS1) which represents up to 95% of the proteins bound to the granule is responsible for amylose biosynthesis. Methods: Synchrotron micro-X-ray fluorescence (μXRF) was used for the first time for high-resolution mapping of GBSS1 and phosphate groups based on the XRF signal of sulfur (S) and phosphorus (P), respectively. Wild-type starches were studied as well as their related mutants lacking GBSS1 or starch-phosphorylating enzyme. Results: Wild-type potato and maize starch exhibited high level of phosphorylation and high content of sulfur respectively when compared to mutant potato starch lacking glucan water dikinase (GWD) and mutant maize starch lacking GBSS1. Phosphate groups are mostly present at the periphery of wild-type potato starch granules, and spread all over the granule in the amylose-free mutant. P and S XRF were also measured within single small starch granules from Arabidopsis or Chlamydomonas not exceeding 3–5μm in diameter. Conclusions: Imaging GBSS1 (by S mapping) in potato starch sections showed that the antisense technique suppresses the expression of GBSS1 during biosynthesis. P mapping confirmed that amylose is mostly present in the center of the granule, which had been suggested before. General significance: μXRF is a potentially powerful technique to analyze the minor constituents of starch and understand starch structure/properties or biosynthesis by the use of selected genetic backgrounds. [Copyright &y& Elsevier]

A new and efficient method for the preparation in one step of water-soluble cellulose acetate sulfate derivatives (CAS) is reported. Acetylation and sulfation were carried out simultaneously, using a mixture of acetic anhydride and sulfuric acid in glacial acetic acid. The reaction time and the amount of acetic anhydride were optimized and the method provided water-soluble esters, with a degree of acetylation in the range 1.6 and 2.4 and a degree of sulfation of 0.3. This method has been successfully applied to pure cellulose and to cellulose-enriched materials obtained from agricultural by-products. The product exhibited a high viscosity in aqueous solution suggesting interesting rheological properties. [Copyright &y& Elsevier]

Abstract: The aim of this work was to characterize the amylopectin of low amylose content cassava starches obtained from transgenesis comparatively with a natural waxy cassava starch (WXN) discovered recently in CIAT (International Center for Tropical Agriculture). Macromolecular features, starch granule morphology, crystallinity and thermal properties of these starches were determined. of amylopectin from the transgenic varieties are lower than WXN. Branched and debranched chain distributions analyses revealed slight differences in the branching degree and structure of these amylopectins, principally on DP 6–9 and DP>37. For the first time, a deep structural characterization of a series of transgenic lines of waxy cassava was carried out and the link between structural features and the mutated gene expression approached. The transgenesis allows to silenced partially or totally the GBSSI, without changing deeply the starch granule ultrastructure and allows to produce clones with similar amylopectin as parental cassava clone. [Copyright &y& Elsevier]

Abstract: Two new mutant cassava starches with extreme amylose contents (0 and 30–31%) have been recently reported. These mutants are drastically different from normal cassava starch whose amylose content typically ranges between 15 and 25%. The new mutants were compared with five normal cassava starches (ranging from 16.8 to 21.5% amylose) and commercial versions of amylose-free or normal potato and maize starch. Macromolecular features, crystallinity, granule sizes, and thermal properties of these starches were compared. The structure of cassava amylopectin was not modified by the waxy mutation and waxy cassava starch exhibited properties similar to the ones of waxy maize starch. Waxy cassava and maize show similar and of amylopectin (between 408×106 gmol−1 and 520×106 gmol−1; 277–285nm, respectively), whereas waxy potato amylopectin has lower and . On the contrary, the higher-amylose mutations induced by gamma rays radiation in cassava, modified deeply the branching pattern of amylopectin as well as the starch characteristics and properties: and decreased, while branching degree increased. These modifications resulted in changes in starch granule ultrastructure (e.g. decreased starch crystallinity), a weak organized structure, and increased susceptibility to mild acid hydrolysis. The distinctive properties of the new cassava starches demonstrated in this article suggest new opportunities and commercial applications for tropical sources of starch. [Copyright &y& Elsevier]

Water-soluble cellulose acetate sulfate derivatives (CAS) have been prepared through chemical reaction involving sulfuric acid as a catalyst. These CAS have been obtained from cellulosic materials of different origins (pure cellulose, wheat bran, maize bran) and their rheological behavior in salt-free aqueous solution has been estimated in dilute and semi-dilute regime using dynamic viscoelastic and viscosity measurements. Influence of concentration, temperature of solubilization and temperature of measurement has been investigated. Weak gel-like properties were exhibited at elevated concentration (typically above 7–8 g/L). These systems also exhibited thixotropic properties: the structure was partly broken down upon shearing and recovered at rest. They also displayed thermoreversibility with large hysteresis, the melting temperature being ∼15 °C higher than the temperature at which gelation took place. These overall observations clearly indicate that these distinctive properties arise from intermolecular association of the macromolecular chains of the cellulose derivative. [Copyright &y& Elsevier]

In this paper, a detailed characterization of the mechanisms at the origin of the shape-memory effect in amorphous potato starch is presented. Using different treatments (annealing) and preparation methods (hot casting and extrusion), the local structures responsible for the shape-memory were disrupted, as evidenced in the first part of the article detailing the macroscopic properties: mechanical, calorimetric and shape-memory. In the second part the macromolecular scale is investigated using X-rays diffraction and CP-MAS NMR, and thus allows making the link between the structural differences and the macroscopic properties. Finally we discuss the origin of shape-memory in amorphous starch. [ABSTRACT FROM AUTHOR]

Debranched waxy rice starch (DWRS) and debranched normal rice starch (DNRS) were crystallized into spherulites from aqueous solutions. DNRS, which contained extra-long chains, yielded small sintered-like spherulites with rough surface, which exhibit positive birefringence and, therefore, had radial orientations. Large spherulites with smooth surfaces, negative birefringence and tangential orientation were formed with DWRS which essentially contained short linear chains. Both spherulites showed a B-type crystalline structure with an exceptionally high crystallinity and a similar melting behavior. However, DWRS spherulites had higher resistance to enzymatic hydrolysis than DNRS spherulites. The higher enzyme resistance of DWRS spherulites was attributed to their tangential organization and their smoother and denser surface as observed by light microscopy and scanning electron microscopy. The impact of the different structural features of the two types of spherulites is discussed in relation to their resistance to enzymatic hydrolysis. [ABSTRACT FROM AUTHOR]

The effects of chain distribution, concentration, temperature and hydrothermal treatments on the recrystallization behavior and formation of resistant starch (RS) were investigated. Waxy and normal rice starches were debranched at 10 and 21% w/w solid concentrations, incubated at 25 or 50 °C, and further subjected to annealing or heat moisture treatment (HMT) to enhance RS formation. The crystallization at 25 °C favored the formation of the B-type structure, whereas crystallization at 50 °C led to the A-type structure with a higher melting temperature (100-120 °C) and a higher RS content (52%). All incubated samples showed an increase in RS content after subsequent hydrothermal treatments. The sample incubated at a high temperature contained the highest RS content (74.5%) after HMT with larger/perfect crystallites. These results suggested that the RS formation could be manipulated by crystallization conditions and improved by hydrothermal treatments which are dependent on the initial crystalline perfection. [ABSTRACT FROM AUTHOR]

1–10% starch/clay bionanocomposites with shape memory properties were obtained by melt processing. X-ray diffraction (XRD) and TEM evidenced the presence of a major fraction of clay tactoids, consisting of 4–5 stacked crystalline layers, with a thickness of 6.8 nm. A significant orientation of the nanoparticles induced by extrusion was also observed. Tensile tests performed above the glass transition of the materials showed that the presence of clay nanoparticles leads to higher elastic modulus and maximum stress, without significant loss in elongation at break which typically reached 100%. Samples submitted to a 50% elongation and cooled below the glass transition showed shape memory behavior. Like unreinforced starch, the bionanocomposites showed complete shape recovery in unconstrained conditions. In mechanically constrained conditions, the maximum recovered stress was significantly improved for the bionanocomposites compared to unreinforced starch, opening promising perspectives for the design of sensors and actuators. [ABSTRACT FROM AUTHOR]

Abstract: Background: Glycogen and starch branching enzymes catalyze the formation of α(1→6) linkages in storage polysaccharides by rearrangement of preexisting α-glucans. This reaction occurs through the cleavage of α(1→4) linkage and transfer in α(1→6) of the fragment in non-reducing position. These enzymes define major elements that control the structure of both glycogen and starch. Methods: The kinetic parameters of the branching enzyme of Rhodothermus obamensis (RoBE) were established after in vitro incubation with different branched or unbranched α-glucans of controlled structure. Results: A minimal chain length of ten glucosyl units was required for the donor substrate to be recognized by RoBE that essentially produces branches of DP 3–8. We show that RoBE preferentially creates new branches by intermolecular mechanism. Branched glucans define better substrates for the enzyme leading to the formation of hyper-branched particles of 30–70nm in diameter (dextrins). Interestingly, RoBE catalyzes an additional α-4-glucanotransferase activity not described so far for a member of the GH13 family. Conclusions: RoBE is able to transfer α(1→4)-linked-glucan in C4 position (instead of C6 position for the branching activity) of a glucan to create new α(1→4) linkages yielding to the elongation of linear chains subsequently used for further branching. This result is a novel case for the thin border that exists between enzymes of the GH13 family. General significance: This work reveals the original catalytic properties of the thermostable branching enzyme of R. obamensis. It defines new approach to produce highly branched α-glucan particles in vitro. [Copyright &y& Elsevier]

Abstract: A novel class of complex oligosaccharides with a backbone made of twelve β-(1→4)-d-glucosyl units that may be regularly substituted on their primary position with α-d-xylosyl or β-d-(1→2)-galactosyl-α-d-xylosyl residues were readily synthesized using enzymatic hydrolysis of the plant polysaccharide xyloglucan (XG), followed by chemical modifications of the well-defined oligosaccharides and their enzymatic coupling catalyzed by the Cel7B E197A glycosynthase from Humicola insolens. These complex oligosaccharides proved useful for a better understanding of the effects of structural variation of xyloglucan on interactions with bacterial microcrystalline cellulose (BMCC). [Copyright &y& Elsevier]

Abstract: A new α-amylase from Anoxybacillus flavothermus (AFA) was found to be effective in hydrolyzing raw starch in production of glucose syrup at temperatures below the starch gelatinization temperature. AFA is very efficient, leading to 77% hydrolysis of a 31% raw starch suspension. The final hydrolysis degree is reached in 2–3h at starch concentrations lower than 15% and 8–24h at higher concentrations. AFA is also very efficient in hydrolyzing the crystalline domains in the starch granule. The major A-type crystalline structure is more rapidly degraded than amorphous domains in agreement with the observed preferential hydrolysis of amylopectin. Amylose–lipid complexes are degraded in a second step, yielding amylose fragments which then re-associate into B-type crystalline structures forming the final α-amylase resistant fraction. The mode of action of AFA and the factors limiting complete hydrolysis are discussed in details. [Copyright &y& Elsevier]

Abstract: The effectiveness of wheat straw fine to ultra-fine grindings at pilot scale was studied. The produced powders were characterised by their particle-size distribution (laser diffraction), crystallinity (WAXS) and enzymatic degradability (Trichoderma reesei enzymatic cocktail). A large range of wheat-straw powders was produced: from coarse (median particle size ∼800μm) to fine particles (∼50μm) using sieve-based grindings, then ultra-fine particles ∼20μm by jet milling and ∼10μm by ball milling. The wheat straw degradability was enhanced by the decrease of particle size until a limit: ∼100μm, up to 36% total carbohydrate and 40% glucose hydrolysis yields. Ball milling samples overcame this limit up to 46% total carbohydrate and 72% glucose yields as a consequence of cellulose crystallinity reduction (from 22% to 13%). Ball milling appeared to be an effective pretreatment with similar glucose yield and superior carbohydrate yield compared to steam explosion pretreatment. [Copyright &y& Elsevier]

Abstract: A-type single crystals were prepared in dilute water/acetone solutions by crystallizing narrow fractions of short amylose chains biosynthesized in vitro. The 5 μm-long spindle-shaped crystals were observed by scanning and transmission electron microscopy. Electron diffraction patterns were recorded from frozen-hydrated crystals at different tilt angles around selected crystallographic axes. In particular, a series of patterns corresponding to [hk0] zone axes was collected by rotation around the long dimension of the crystal. A description of the crystal habit was proposed by correlating the electron diffraction data with the microscopy images. The double helices are oriented along the long dimension of the crystal (c-axis) and packed in a parallel fashion into lamellae with a parallelogram cross-section defined by the a and b axes of the monoclinic unit cell. A-amylose single crystals are polar objects that grow in the direction of the reducing end of the amylose chains, and the c-axis is oriented opposite to the growth direction. [Copyright &y& Elsevier]

Abstract: Lowering of the CO2 concentration in the environment induces development of a pyrenoidal starch sheath, as well as that of pyrenoid and CO2-concentrating mechanisms, in many microalgae. In the green algae Chlamydomonas and Chlorella, activity of granule-bound starch synthase (GBSS) concomitantly increases under these conditions. In this study, effects of the GBSS-defective mutation (sta2) on the development of pyrenoidal starch were investigated in Chlamydomonas. Stroma starch- and pyrenoid starch-enriched samples were obtained from log-phase cells grown with air containing 5% CO2 (high-CO2 conditions favouring stromal starch synthesis) and from those transferred to low-CO2 conditions (air level, 0.04% CO2, favouring pyrenoidal starch synthesis) for 6h, respectively. In the wild type, total starch content per culture volume did not increase during the low-CO2 conditions, in spite of the development of pyrenoidal starch, suggesting that degradation of some part of stroma starch and synthesis of pyrenoid starch simultaneously occur under these conditions. Even in the GBSS-deficient mutants, pyrenoid and pyrenoid starch enlarged after lowering of the CO2 concentration. However, the morphology of the pyrenoid starch was thinner and more fragile than the wild type, suggesting that GBSS does affect the morphology of pyrenoidal starch. Surprisingly normal GBSS activity is shown to be required to obtain the high A-type crystallinity levels that we now report for pyrenoidal starch. A model is presented explaining how GBSS-induced starch granule fusion may facilitate the formation of the pyrenoidal starch sheath. [Copyright &y& Elsevier]

Self-diffusion coefficient of an aroma molecule (4-ethyl guaicol) was measured using the pulsed field gradient spin echo NMR (PGSE-NMR) method in order to investigate the influence of a macromolecular matrix on its diffusion and release processes. Iota (ι)-carrageenan was used for its ability to form thermoreversible gels in aqueous salt solutions. Variations of the ι-carrageenan and the salt concentrations permitted various gels with different thermal and rheological properties to be obtained. These latter were modified by an isotope effect obtained by preparing gels in D2O. The NMR self-diffusion measurements realised for water and the aroma molecules indicated neither chemical interactions with ι-carrageenan, nor obstruction effects from the polysaccharide chains. In ι-carrageenan gels, the diffusional phenomenon was highly dependent on the heterogeneous gel structure and controlled by hydrodynamic interactions due to frictional drag between each molecule of the system and water microviscosity changes. [Copyright &y& Elsevier]

Amylose complexes were prepared, as lamellar single crystals and polycrystalline powders, from aqueous solutions by adding small flavor molecules. The morphology, crystal structure, and thermal properties of complexes with fenchone, menthone, and geraniol were determined using transmission electron microscopy, wide-angle X-ray diffraction, and differential scanning calorimetry. The crystal structure was found to be similar to that of V amylose complexes with isopropanol. This implies that the crystallosolvates contain sixfold helices packed in orthorhombic unit cells, with the ligands possibly lying in the interhelical space. Different drying procedures were also studied leading to less resolved X-ray diagrams. The thermoanalysis confirmed that complexes with a relatively high crystallinity were formed. [Copyright &y& Elsevier]

The chemical structure and interactions of the cell wall polysaccharides from the red edible seaweed Palmaria palmata were studied by liquid-like magic-angle-spinning (MAS) and cross-polarization MAS (CPMAS) solid-state 13C NMR spectroscopy. The liquid-like MAS and CPMAS 13C NMR spectra of the rehydrated algal powder revealed the presence of β-(1→4)/β-(1→3)-linked d-xylan with chemical shifts close to those observed in the solution 13C NMR spectrum of the polysaccharide. Observation of mix-linked xylan in the liquid-like MAS 13C NMR spectrum indicated that part of this cell wall polysaccharide is loosely held in the alga. The CPMAS NMR spectrum of the dry algal powder alcohol insoluble residue (AIR) showed broad peaks most of which corresponded to the mix-linked xylan. Hydration of AIR induced a marked increase in the signal resolution also in the CPMAS NMR spectra together with a shift of the C-3 and C-4 signals of the (1→3)- and (1→4)-linked xylose, respectively. Such modifications were present in the spectrum of hydrated (1→3)-linked xylan from the green seaweed Caulerpa taxifolia and absent in that of (1→4)-linked xylan from P. palmata. This result emphasizes the important role of (1→3) linkages on the mix-linked xylan hydration-induced conformational rearrangement. The mix-linked xylan signals were observed in the CPMAS NMR spectrum of hydrated residues obtained after extensive extractions by NaOH or strong chaotropic solutions indicating strong hydrogen bonds or covalent linkages. T1ρ relaxations were measured close or above 10 ms for the mix-linked xylan in the dry and hydrated state in AIR and indicated that the overall xylan chains likely remain rigid. Rehydration of the mix-linked xylan lead to a decrease in the motion of protons bounded to the C-1 and C-4 carbons of the (1→4)-linked xylose supporting the re-organization of the xylan chains under hydration involving junction-zones held by hydrogen bonds between adjacent (1→4)-linked xylose blocks. The CPMAS NMR spectrum of both dry and rehydrated residues obtained after NaOH and HCl extractions demonstrated the presence of cellulose and (1→4)-linked xylans. The structures of the different polysaccharides are discussed in relation to their interactions and putative functions on the cell wall mechanical properties in P. palmata. [Copyright &y& Elsevier]