"Mapuey" tubers in Venezuela are staple food for indigenous peoples from the Caribbean coast and Amazon regions. Noticeable differences between genotypes of yam starches were observed. Granules were large, triangular, or shell-shaped with monomodal particle size distribution between 24.5 and 35.5 μm. Differential scanning calorimetry (DSC) analyses revealed onset gelatinization temperatures from 69.1 to 73.4 °C with high gelatinization enthalpy changes from 22.4 to 25.3 J g(-1). All X-ray diffractograms of starches exhibit B-type crystallinity. Crystallinity degrees varied from 24% to 40%. The highest crystallinity was found for the genotype having the highest amylose content. Iodo-colorimetric, amperometric, and DSC amylose determinations varied from 1.4 to 8.7%, 2.2 to 5.9%, and 1.4 to 3.5% for Amazonian genotypes, in comparison with commercial Mapuey starches: 12.0, 9.5, and 8.7%, respectively. Solubility and swelling power at 90 °C varied from 2.1 to 4.4% and 20.5 to 37.0%, respectively. Gel clarity fluctuated from 22.4 to 79.2%, and high rapid visco analyzer (RVA) viscosity was developed at 5% starch suspension (between 1430 and 2250 cP). Amylopectin weight average molar mass M(w), radius of gyration R(G), hydrodynamic coefficient ν(G), and apparent molecular density d(Gapp) were determined using high-performance size exclusion chromatography (HPSEC) and asymmetrical flow field flow fractionation (A4F) techniques coupled with multiangle laser light scattering (MALLS) on the Dioscorea trifida genotypes exhibiting the lowest and highest amylose contents. Amylopectins showed very similar molecular conformations. M(w) values were 1.15 × 10(8) and 9.06 × 10(7) g mol(-1) using HPSEC and A4F, respectively, thus, 3-5 times lower than those reported with the same techniques for other yam species, and very close to those of potato and cassava amylopectins. This discovery of a new natural amylose-free starch in the neglected yam "Mapuey" could present some potential for the food industry.

Starches from ten yam (Dioscorea) species were compared with those of maize, wheat, potato and cassava, and characterized by high-performance size-exclusion chromatography coupled with multiangle laser light scattering. Treatment with 95% (v/v) dimethylsulphoxide and microwave heating in a high-pressure vessel led to complete dissolution of the starch samples. For yam starches, M w were between 1.88 × 10 8 and 3.27 × 10 8 g mol −1 and R G were between 258 and 396 nm. The hydrodynamic coefficients of amylopectins were between 0.36 and 0.44, indicating that those of maizes and esculenta 5 and dumetorum yam species had particularly highly branched structures. Multidimensional analysis of the macromolecular characteristics of yam starches indicated three classes: dumetorum cultivar (Dioscorea dumetorum), esculenta 5 cultivar (Dioscorea esculenta) and the other eight yam starches, including cultivars of Dioscorea alata and Dioscorea cayenensis-rotundata species. Some yam starches were also leached at 90 • C. The macromolecular characteristics of the leached fractions confirmed the previous typology.

The destructuration of native maize starch in mixtures of water and ionic liquids (ILs) containing acetate anions was studied in dynamic heating conditions, combining calorimetry, rheology, microscopy and chromatographic techniques.

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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. The amylopectin weight-average molar masses and radii of gyration were around 1.0 × 10(8)-4.8 × 10(8) g mol(-1) and 110-267 nm, respectively. For each starch sample, the hydrodynamic radius (R(H)) distributions and the molar mass distributions obtained from the two fractionation systems coupled with light scattering techniques were analyzed. The size determination scales were extended by means of R(H) calibration curves. HDC-SEC and A4F data could be matched. However, A4F enabled a better separation of amylopectins and therefore an enhanced structural characterization of the starches. The two advantages of this experimental approach are (1) it can directly obtain distributions as a function of both molar mass and size, while taking account of sample heterogeneity, and (2) it is possible to compare the results obtained using the different techniques through the direct application of R(H) distributions.

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Native starch containing 12% water was melt processed in presence of 23% of various plasticizers at 120°C, either by simple compression molding or by extrusion using a laboratory scale microcompounder. Glycerol, a typical starch plasticizer, was used as a reference and compared to three choline salts: raw choline chloride (which is a solid in dry state with a melting point above 300°C), and two ionic liquids synthesized from this precursor (choline acetate and choline lactate, liquids below 100°C). These ionic plasticizers were shown to allow a more efficient melting of native starch in both processes. The investigation of macromolecular structure changes during processing shows that this efficiency can be ascribed to a starch chain scission mechanism, resulting in lower specific mechanical energy input need for starch thermoplasticization compared to glycerol plasticized starch. Compared to the synthesized ionic liquids, raw commercial choline chloride leads to a good compromise between limited chain scission, and final water uptake and thermomechanical properties.

Glycogen biosynthesis requires the coordinated action of elongating and branching enzymes, of which the synergetic action is still not clearly understood. We have designed an experimental plan to develop and fully exploit a biomimetic system reproducing in vitro the activities involved in the formation of α(1,4) and α(1,6) glycosidic linkages during glycogen biosynthesis. This method is based on the use of two bacterial transglucosidases, the amylosucrase from Neisseria polysaccharea and the branching enzyme from Rhodothermus obamensis . The α-glucans synthesized from sucrose, a low cost agroresource, by the tandem action of the two enzymes, have been characterized by using complementary enzymatic, chromatographic, and imaging techniques. In a single step, linear and branched α-glucans were obtained, whose proportions, morphology, molar mass, and branching degree depended on both the initial sucrose concentration and the ratio between elongating and branching enzymes. In particular, spherical hyperbranched α-glucans with a controlled mean diameter (ranging from 10 to 150 nm), branching degree (from 10 to 13%), and weight-average molar mass (3.7 × 10(6) to 4.4 × 10(7) g.mol(-1)) were synthesized. Despite their structure, which is similar to that of natural glycogens, the mechanisms involved in their in vitro synthesis appeared to be different from those involved in the biosynthesis of native hyperbranched α-glucans.