Molecular and supra-molecular structure of waxy starches developed from cassava (Manihot esculenta Crantz).

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. M¯(w) of amylopectin from the transgenic varieties are lower than WXN.

Hydrolysis of concentrated raw starch: A new very efficient α-amylase from Anoxybacillus flavothermus.

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.

In situ tracking of enzymatic breakdown of starch granules by synchrotron UV fluorescence microscopy.

Synchrotron UV fluorescence microscopy was used for the first time to visualize the adsorption and diffusion of an enzyme while degrading a solid substrate. The degradation pathway of single starch granules by two amylases, optimized for biofuel production and industrial starch hydrolysis, was followed by tryptophan fluorescence (excitation at 280 nm, emission filter at 300-400 nm) and visible light imaging. Thus, both the adsorption of enzyme onto starch granules at 283 nm resolution and the resulting morphological changes were recorded at different stages of hydrolysis.

In depth study of a new highly efficient raw starch hydrolyzing α-amylase from Rhizomucor sp.

A new α-amylase from Rhizomucor sp. (RA) was studied in detail due to its very efficient hydrolysis of raw starch granules at low temperature (32 °C). RA contains a starch binding domain (SBD) connected to the core amylase catalytic domain by a O-glycosylated linker.

Molecular size and mass distributions of native starches using complementary separation methods: asymmetrical flow field flow fractionation (A4F) and hydrodynamic and size exclusion chromatography (HDC-SEC).

Starch consists of a mixture of two α-glucans built mainly upon α-(1,4) linkages: amylose, an essentially linear polymer, and amylopectin, a branched polymer containing 5-6% of α-(1,6) linkages. The aim of the present work was to analyze the structural properties of native starches displaying different amylose-to-amylopectin ratios and arising from different botanical sources, using asymmetrical flow field flow fractionation (A4F) and a combination of hydrodynamic and size-exclusion chromatography (HDC-SEC) coupled with multiangle laser light scattering, online quasi-elastic light scattering, and differential refractive index techniques. The procedure, based upon dimethyl sulfoxide pretreatment and then solubilization in water, generates a representative injected sample without altering the initial degree of polymerization.

Online determination of structural properties and observation of deviations from power law behavior.

Synthetic amyloses, pullulans, phytoglycogen, rabbit liver glycogen, oyster glycogen, and dextrans were studied using high-performance size-exclusion chromatography combined with multiangle laser light scattering (MALLS) and online quasi-elastic light scattering (QELS), which provided the RH distributions up to 65 nm. Different structural parameters were extracted from entire molar mass distributions, including the slope of the log-log plot of R H(i) versus M(i)and the rho(i )= R(Gi)/R(Hi)ratio. This approach enabled to observe deviations from the De Gennes scaling law concept.

Branching features of amylopectins and glycogen determined by asymmetrical flow field flow fractionation coupled with multiangle laser light scattering.

The aim of this work was to characterize starch polysaccharides using asymmetrical flow field flow fractionation coupled with multiangle laser light scattering. Amylopectins from eight different botanical sources and rabbit liver glycogen were studied. Amylopectins and glycogen were completely solubilized and analyzed, and high mass recoveries were achieved (81.

Soluble starch synthase I: a major determinant for the synthesis of amylopectin in Arabidopsis thaliana leaves.

A minimum of four soluble starch synthase families have been documented in all starch-storing green plants. These activities are involved in amylopectin synthesis and are extremely well conserved throughout the plant kingdom. Mutants or transgenic plants defective for SSII and SSIII isoforms have been previously shown to have a large and specific impact on the synthesis of amylopectin while the function of the SSI type of enzymes has remained elusive.

Mutants of Arabidopsis lacking a chloroplastic isoamylase accumulate phytoglycogen and an abnormal form of amylopectin.

Mutant lines defective for each of the four starch debranching enzyme (DBE) genes (AtISA1, AtISA2, AtISA3, and AtPU1) detected in the nuclear genome of Arabidopsis (Arabidopsis thaliana) were produced and analyzed. Our results indicate that both AtISA1 and AtISA2 are required for the production of a functional isoamylase-type of DBE named Iso1, the major isoamylase activity found in leaves. The absence of Iso1 leads to an 80% decrease in the starch content in both lines and to the accumulation of water-soluble polysaccharides whose structure is similar to glycogen.

Origin of the limited alpha-amylolysis of debranched maltodextrins crystallized in the A form: a TEM study on model substrates.

The detailed ultrastructure of a new type of resistant starch and the way that it is modified during hydrolysis by alpha-amylases were studied by transmission electron microscopy (TEM) on model starch crystals. The selected substrates were waxy maize starch lintners and A-type crystals prepared from low degree of polymerization (DP) amylose. A model describing the stacking of double helices is proposed for A-type low DP amylose crystals.

Volumetric behaviour of maltose-water, maltose-glycerol and starch-sorbitol-water systems mixtures in relation to structural relaxation.

The densities of amorphous maltose-water, maltose-glycerol and starch-sorbitol-water mixtures were measured using a vibrating-tube density meter and pycnometry. The volumetric change on mixing was investigated through the calculation of the quantity DeltaV/V, the difference between (experimental) volume of the mixture and the linear composition weighted pure constituent volumes (ideal mixing). For all of the systems studied the quantity DeltaV/V was negative and approached a minimum of -0.

Structural relaxation and physical ageing of starchy materials.

The structural relaxation during the ageing of an amorphous maltose and a starch-sorbitol mixture was examined using a range of physical techniques. Heat capacity, measured by differential scanning calorimetry, showed an overshoot in the glass-transition region, the size of which was temperature and time dependent. Volume relaxation measurements were made at different ageing temperatures in the range T(g) -15 to -30 K.