Julien Ricci

Isolated starches from yams (Dioscorea sp) grown at the Venezuelan Amazons: structure and functional properties.

This work aimed to characterize the molecular structure and functional properties of starches isolated from wild Dioscorea yams grown at the Amazons, using conventional and up-to-date methodologies. Among the high purity starches isolated (≥99%), the chain lengths were similar, whereas variations in gelatinization profile were observed. Starches have shown varied-shaped granules with monomodal distribution, and B-type crystallinity. Variations in amylose contents found by three analyses were hypothesized being related to intermediate material. Linear chain lengths were similar, and their amylopectins showed a dense, spherical conformation and similar molecular characteristics. The average molar mass and the radius of gyration of the chromatograms of the yam amylopectin, M¯W and R¯G were ranging between 174×10(6) g mol(-1) and 237×10(6) g mol(-1), and 201 nm and 233 nm, respectively. The white yams starches were more sensible to enzymes than the other two. All starches have shown a wide range of functional and nutritional properties.

Digestibility prediction of cooked plantain flour as a function of water content and temperature

The effect of temperature (T=55-120°C) and water content (X1=1.4-2.0 kg kg(-1) dry basis) on the gelatinization and digestibility of plantain flour (Dominico Harton genotype) were investigated. The degree of plantain starch gelatinization (α) was measured by DSC and modelled as a function of T and X1, using the Weibull model. Rapidly digestible starch (RDS) and resistant starch (RS) fractions were evaluated for different α values. An appropriate dimensionless variable was introduced to the analyzed and modelled RDS and RS as a function of α. Starch gelatinization begins at a temperature above 59.6 ± 0.5°C and α is strongly dependent on T in non-limiting water conditions. The combined effects of T and X1 on the RDS and RS can be explained by α. We demonstrate that various heat treatments and water contents lead to the same α, with the same RDS and RS values.

Lineage-Specific Evolutionary Histories and Regulation of Major Starch Metabolism Genes during Banana Ripening

Starch is the most widespread and abundant storage carbohydrate in plants. It is also a major feature of cultivated bananas as it accumulates to large amounts during banana fruit development before almost complete conversion to soluble sugars during ripening. Little is known about the structure of major gene families involved in banana starch metabolism and their evolution compared to other species. To identify genes involved in banana starch metabolism and investigate their evolutionary history, we analyzed six gene families playing a crucial role in plant starch biosynthesis and degradation: the ADP-glucose pyrophosphorylases (AGPases), starch synthases (SS), starch branching enzymes (SBE), debranching enzymes (DBE), α-amylases (AMY) and β-amylases (BAM). Using comparative genomics and phylogenetic approaches, these genes were classified into families and sub-families and orthology relationships with functional genes in Eudicots and in grasses were identified. In addition to known ancestral duplications shaping starch metabolism gene families, independent evolution in banana and grasses also occurred through lineage-specific whole genome duplications for specific sub-families of AGPase, SS, SBE, and BAM genes; and through gene-scale duplications for AMY genes. In particular, banana lineage duplications yielded a set of AGPase, SBE and BAM genes that were highly or specifically expressed in banana fruits. Gene expression analysis highlighted a complex transcriptional reprogramming of starch metabolism genes during ripening of banana fruits. A differential regulation of expression between banana gene duplicates was identified for SBE and BAM genes, suggesting that part of starch metabolism regulation in the fruit evolved in the banana lineage.

Starch gelatinization and in vitro digestibility behaviour after heat treatment: Comparison between plantain paste and piece of pulp.

Over the 65-100°C range and at a water content of 1.6kgkg(-1)db, a comparison was conducted between plantain paste (dispersion made of flour and water) and pulp pieces after cooking to evaluate their respective degree of starch gelatinization (α) and in vitro digestibility. Below 76°C and at 100°C, the gelatinization behaviour of starch into pulp pieces and paste was similar, whereas at 85°C a significant mean relative difference was observed in between. For α in the 0-1 range, pieces of plantain pulp exhibited a lower rapidly digestible starch fraction (30%) and a higher resistant starch fraction (33%) than the flour paste, suggesting some structural effects. Both Weibull and exponential models showed a good fit for α over temperature range and starch digestibility fractions over α. Although no explicit relationship was established between the intact pulp structure and grinded flour state of plantain, the evaluation of the degree of starch gelatinization and digestibility of a plantain flour paste, could be used to predict the gelatinization and digestibility behaviour of plantain starch in entire pieces of pulp.