Xavier Rouau

Dry fractionation process as an important step in current and future lignocellulose biorefineries: a review.

The use of lignocellulosic biomass is promising for biofuels and materials and new technologies for the conversion need to be developed. However, the inherent properties of native lignocellulosic materials make them resistant to enzymatic and chemical degradation. Lignocellulosic biomass requires being pretreated to change the physical and chemical properties of lignocellulosic matrix in order to increase cell wall polymers accessibility and bioavailability. Mechanical size reduction may be chemical free intensive operation thanks to decreasing particles size and cellulose crystallinity, and increasing accessible surface area. Changes in these parameters improve the digestibility and the bioconversion of lignocellulosic biomass. However, mechanical size reduction requires cost-effective approaches from an energy input point of view. Therefore, the energy consumption in relation to physicochemical properties of lignocellulosic biomass was discussed. Even more, chemical treatments combined with physicochemical size reduction approaches are proposed to reduce energy consumption in this review.

Influence of Natural Fermentation and Drying Conditions on the Physicochemical Characteristics of Cassava Starch

The physicochemical characteristics of cassava starches sampled at a pilot plant in Colombia during fermentation and drying processes were determined in relation to their ability for making specific bread-like products that inflate during baking. Nitrogen compounds and non-starch polysaccharides are minor components which were unlikely to be involved in the baking expansion property of fermented cassava starch. Thirty percent of the lactic acid synthesised during the fermentation step was not recovered after sun-drying whereas it remained constant when oven-dried. The crystalline structure of starch was not changed by the fermentation and drying processes whereas the behaviour of starch polysaccharides in water was dramatically modified. This behaviour seemed to be related to the baking expansion potential of cassava starches; the lower the intrinsic viscosity, the hot paste viscosities and the hydrodynamic volumes of the starchy components, the higher the baking expansion ability. These results suggest the occurrence of an oxidative modification of starch molecules, such as depolymerisation, due to the joint action of fermentation and sun-drying.

A rapid semi-automated method for the determination of total and water-extractable pentosans in wheat flours

A rapid, semi-automated method for the determination of total and water-extractable pentosans in wheat flours is described. Total pentosans are solubilized by hot dilute acid within 10 min, and water-extractable pentosans by aqueous treatment within 15 min. The solubilization/extraction steps have been optimized with respect to accuracy (weighing of large amounts of sample), rapidity and yield of pentosans. The extracts are analyzed for pentose content by an automated adaptation of the phloroglucinol method of Douglas, on a continuous flow analyzer. The circuit allows the continuous generation of unstable phloroglucinol/acid reagent. The rate of analysis has been fixed at 40 samples h−1. The pentosan content of 15 flour samples (total and water-extractable pentosans, in duplicate extractions), that is, 60 colorimetric determinations, may be carried out in one day by a single trained operator. The method is rapid, sensitive and reproducible (CV% < 3) and correlates well with other methods of pentosan determination. No interference has been found from the major components of wheat flours (starch, gluten). On the other hand, the presence of high levels of some sugars, possibly encountered in cereal-based products, can result in an underestimation (fructose, sucrose) or an overestimation (uronic acids) of the pentosan concentration.

Large scale isolation of water-soluble and water-insoluble pentosans from wheat flour

Abstract A procedure has been developed which allows the isolation of enriched pentosan fractions from wheat flour. The procedure is based on mixing flour and water (50 kg/150L). After centrifugation the supernatant is heat-treated and then concentrated by cross-flow ultrafiltration to give water-soluble pentosans, whereas the insoluble residue is treated with Alcalase and then Termamyl to give water-insoluble pentosans. Starting from 50 kg of flour from three different varieties (Soissons, Thesee, Apollo), water-soluble and water-insoluble pentosans containing respectively 100–200 g of water-soluble and 250–350 g of water-insoluble arabinoxylans, were prepared within 2 d. Water-soluble pentosans are constituted of approx. 40% arabinoxylans and are contaminated by proteins, whereas water-insoluble pentosans are composed of arabinoxylans (ca. 30%) and are contaminated by residual starch (ca 40%). Enrichment factors in arabinoxylans ranged from 98 to 66 for water-soluble and 27 to 19 for water-insoluble pentosans as compared with initial flour.

Characterisation of the extractable pectins and hemicelluloses of the cell wall of carrot

Abstract Pectic and hemicellulosic polysaccharides were successively extracted from an alcohol-insoluble residue (AIR) from carrot root by the actions of Pronase, hot dilute acid, cold dilute alkali, and concentrated alkali in yields corresponding to 12.6, 13.5, 21.7, and 6.7% of AIR, respectively. The first two products were fractionated further by ion-exchange chromatography. Carrot pectins contained 61.3–66.0% of galacturonic acid and 16.0–19.9% of neutral sugars, mainly galactose, arabinose, and rhamnose. Except for the alkali-soluble pectins, the degrees of methylation were high (62.9–67.1) and there was a significant degree of acetylation (7.2–13.5). Pectin fractions were homogeneous in gel-filtration chromatography with viscosity-average molecular weights varying between 36,200 and 56,500. Methylation analysis indicated the presence of arabinogalactans in the pectins extracted during the proteolysis, and fairly long chains of (1→4)-linked galactan with a branched arabinan in the two other pectic fractions. The hemicellulose fraction was mainly composed of (1→4)-linked glucan, (1→4)-linked mannan, (1→4)-linked xylan, and small but significant amounts of pectic polysaccharides. The possible association of cell-wall polymers is discussed.

Isolation and characterisation of the cell-wall fibres of carrot

Abstract Cell-wall fractions have been prepared from an alcohol-insoluble-residue of carrot root by treatment with (a) Pronase to remove the cytoplasmic proteins, (b) hot dilute acid and cold dilute alkali to give pectin-free residues, and (c) concentrated alkali to leave the α-cellulose and lignin. The purified cell-wall material still contained ∼ 1% protein and was composed mainly of cellulose, lignin, methyl-esterified galacturonic acid, and smaller amounts of galactose and arabinose. Methylation analysis of the insoluble residues indicated the presence, in order of decreasing concentration, of rhamnogalacturonan with the rhamnosyl residues carrying side chains at position 4, cellulose, (1→4)-linked galactan, (1→5)-linked arabinan, (1→4)-linked xylan, (1→4)-linked mannan, and xyloglucan.

Studies on enzymic hydrolysis of polysaccharides in sugar beet pulp

Beet fibres have been prepared from sugar beet pulp and degraded with three enzymic preparations (SP 249 from Aspergillus aculeatus, Driselase from Irpex lacteus and Onozuka from Trichoderma viride) which have been characterised for their activities towards polysaccharides. The overall extent of hydrolysis was ∼ 48% with Onozuka and up to ∼ 80% with the other preparations. These values may be increased to ∼ 90% by some chemical pretreatments including persulphate, chlorite or hydrogen peroxide.

Influence of Arabinoxylans and Endoxylanases on Pasta Processing and Quality. Production of High-Quality Pasta with Increased Levels of Soluble Fiber

ABSTRACT As part of a general study aiming to clarify the role of arabinoxylans (AX) in pasta processing and quality, AX were modified by the addition of endoxylanases during pasta processing. The influence on processing parameters and quality were determined. Pasta (800 g) was produced from two commercial semolinas (semA and semB) using dosages of Bacillus subtilis (XBS) and Aspergillus niger (XAN) endoxylanases of 0–0.225 Somogyi units/g of semolina. Increased dosages resulted in a drop of extrusion pressure. The endoxylanase treatments had no great effect on the resulting pasta quality (color of dry products and surface condition, viscoelastic index, and resistance to longitudinal deformations of cooked products). High dosages of XAN and XBS resulted in high levels of solubilized AX (as an extra source of soluble dietary fiber) of low molecular weight which were expected to easily leach out during the cooking process of pasta. Surprisingly, only low levels of AX were found in the cooking water, even wi...

Innovative combined dry fractionation technologies for rice straw valorization to biofuels

The separation of lignocellulose into its major components (cellulose, hemicelluloses and lignin) is a key step in lignocellulosic biorefineries. Most pretreatments of lignocellulosic biomass into chemicals or biofuels are currently based on expensive chemical and energy consuming processes, which entail significant resource consumption (e.g. water) and generate a number of residual streams. In this work, two innovative dry fractionation technologies (physical fractionation: turbo- and electrostatic separation of lignocellulose particles) have been developed for rice straw “RS” fractionation and bioconversion to sugars and biofuels. Turbo-fractionation technology (TF-T) comprises particle separation according to their size and density, whereas electrostatic fractionation technology (EF-T) is based on the separation of particles according to their surface properties (chemical composition and charges). TF-T and EF-T are suitable for producing lignocellulose fractions displaying very different structures, biochemical compositions and reactive surfaces without extensively damaging the raw fibers as well as minimizing waste generation (E-factor: 0.7–0.75). The produced fractions could be hydrolyzed, being able to produce large quantities of glucose (250–280 g kg−1 RS) after 72 h of hydrolysis and subsequently ethanol (130–150 g kg−1 RS) after fermentation. TF-T and EF-T can therefore improve the economic feasibility by low energy consumption and produce reactive lignocellulose particles with different physicochemical structures in a short time, which can be easily converted to biofuels, minimizing waste (no effluent generation).

A Dry Platform for Separation of Proteins from Biomass‐Containing Polysaccharides, Lignin, and Polyphenols

License to mill: Proteins were continuously extracted from polysaccharides, lignin, and polyphenol by combining ultrafine milling with electrostatic separation. Such a fractionation process does not involve any solvent, catalyst, or external source of heating. In addition, this dry process is compatible with downstream enzymatic reactions, thus opening an attractive route for producing valuable chemicals from biomass.