Flax (Linum usitatissimum) seed cake: a potential source of high molecular weight arabinoxylans?

Water-soluble polysaccharides were extracted from flaxseed cake and analyzed. Two groups were separated by anion-exchange chromatography. The first one (nonretained) was the major fraction (83%) and possessed a high molecular weight (HMW) arabinoxylan (56%) with an Ara/Xyl ratio of 0.32 and an M(w) of 846 000. This polymer was accompanied by a smaller galactoglucan (44%), with an M(w) of 6.5 x 10(4). The latter group (17%), retained by the gel, was further described as a HMW pectin heterogeneous group, with, respectively, 3.1 x 10(5) and 1.3 x 10(5). Despite the presence of HMW arabinoxylans, the investigation of rheological flow sweep at the concentration of 2% (w/v) has shown a slight shear thinning behavior with a small zero-rate viscosity at 9.6 Pa.s.

Structural investigations of the neutral polysaccharide of Linum usitatissimum L. seeds mucilage.

The heterogeneity of the purified water-soluble neutral fraction coming from the mucilage extract of the yellow flaxseed was investigated. After fractionation by size-exclusion chromatography, the analyse of the neutral monosaccharides composition showed a mixture of three major families of polymers. They were all identified as arabinoxylans with a constant A/X ratio of 0.24, but varying in their galactose and fucose residues in the side chains. Furthermore, the molecular weight (M(w)) analysis acquired by multi-angle laser light scattered, revealed the association of two high M(w) polymers [5.7x10(6) (11.1%) and 9.3x10(5) (42.4%) g mol(-1)] with a smaller one [3.2x10(5) g mol(-1) (45.3%)].

Contributions of intermolecular interactions between constitutive arabinoxylans to the flaxseeds mucilage properties.

The main fraction (about 75%) of the mucilage extracted from seeds of Linum usitatissimum which consists of arabino-xylans (AX) has been studied in dilute and semidilute regimes by SEC/MALLS analysis and rheology, respectively. It has been found that AX contains 3 populations of about 5 000 000 g mol(-1) (less than 10%), 1 000 000 g mol(-1) (about 40%), and 200 000 g mol(-1) (about 50%). We have also observed a great retention of polymer during the filtration procedure, which is much pronounced as the AX concentration increases. This evidences the presence of large aggregates in the solution. The retention can be greatly diminished if the filtration is conducted under higher temperature. Aggregation could result from the establishment of intermolecular associations via hydrogen bonds. This hypothesis seems to be confirmed by the two higher populations in molar masses which present a random coil conformation consistent with a low degree of branching. Rheological measurements, conducted at 20 g L(-1), have confirmed the association tendency leading to pseudo gels behavior. Viscoelastic properties have been evidenced by time-temperature master curves of dynamic spectra. Such master curves have also been established with addition of chaotropic (i.e., KSCN) and lyotropic (i.e., NaCl) salts. It has been shown that intermolecular associations are greatly diminished under chaotropic salts influence. This has been also confirmed by SEC/MALLS analysis. These results point out the role of hydrogen bonds in the organization of the AX system.