Abdellah Arhaliass

Melt growth and shrinkage at the exit of the die in the extrusion-cooking process

Melt expansion by extrusion-cooking was investigated when processing corn grits in a twin-screw extruder. A growth phase followed by a shrinkage phase were experimentally observed through an image processing method, and analysed by use of classical expansion indices: sectional, longitudinal and volumetric expansion indices, for both growth and shrinkage phases. It was shown that the expansion phenomenon was strongly dependent on the geometrical characteristics of the die insert, and particularly on die insert diameter. Melt growth developed more in the radial direction which revealed an important structural anisotropy of the expanding melt, due probably to the elastic properties of the biopolymer-based melt. Melt shrinkage which occurred further, contributed to a significant decrease in the bulk density of the expanding melt, and could arise from either surface tension forces, or from the recovery of melt elasticity.

Kinetics modeling of alginate alkaline extraction from Laminaria digitata

Alginates being depolymerized during their alkaline extraction, reducing extraction time could help producing higher rheological quality alginates. The purpose of the present work is to study fresh Laminaria digitata destructuration during alkaline extraction and its link to extraction kinetics. Both alginate extraction yield and mean diameter of algae particles were followed for different values of agitation level and initial size of algae pieces. Results highlighted the existence of a link between extraction yield and algal destructuration. Those elements and the specificity of L.digitata structure have been taken into account to propose a kinetics model based on a fluid-particle reaction with decreasing size particles. The model parameters have been adjusted thanks to acquisition data and its predictive capacity was assessed by validation data. Provided predictions appeared to be relevant and the model structure suitability was confirmed, as extraction yield kinetics specific shape was quite reliably described.

Characterization of an easy-to-use method for the routine analysis of the central metabolism using an affordable low-resolution GC–MS system: application to Arthrospira platensis

We developed an easy-to-use method for the routine analysis of the central metabolism using an affordable low-resolution GC–MS system run in SIM mode. The profiling approach was optimized for the derivatization protocol of some 60 targeted metabolites. The performance of two silylation reagents (MSTFA and BSTFA) that allowed the comprehensive derivatization of 42 key intermediary metabolites of the 60 initially targeted (organic acids, phosphate derivatives, monosaccharides and amino acids) was measured. The experimental results unequivocally showed that the MSTFA reagent met mandatory criteria including ease of handling (a very simple one-step protocol was developed), comprehensiveness of derivatization (the 42 compounds covered the extended metabolic pathways of the central carbon metabolism, with a coverage percentage ranging from 17% for the worst to 90% for the best result), optimized response coefficient of the whole derivatives (median value greater than the others by one order of magnitude) and repeatability of the protocol (RSD value below 25% for the whole procedure). When tested in real conditions (cyanobacteria polar extract), the experimental results showed that the profiling methodology was adequately repeatable (RSD = 35%) to ensure quantification results comparable with much more sensitive analytical techniques (capillary electrophoresis/mass spectrometry and liquid chromatography/triple quadrupole mass spectrometry system), while needing only about twice the quantity of biomass.Graphical abstractSchematic overview of an easy-to-use profiling method for the routine analysis of the central metabolism using a low-resolution GC-MS system