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Successive extraction of mechanically-isolated flax fibres with ethylene-diaminetetraacetic acid partially neutralized with NAOH EDTA-Na 2 and NaOH solubilized about 25% of the mass of fibres. The cation exchange capacity (CEC) of the fibres decreased from 0.100 ± 0.025 meq g −1 to 0.035 ± 0.015 meq g −1 after EDTA-Na2 extraction and then was reduced to virtually nil by extraction with NaOH. This final reduction in CEC by alkali was accompanied by the extraction of small charge molecules, notably phenolic acids. These may influence the binding selectivity of the fibre towards monovalent cations. Polymers solubilized by this extraction procedure included two main types of galactans; the first type consisted of β-1→4 galactans attached to a rhamnogalacturonan I-like polymer and the second type was β-1→3, β-1→6 linked galactans attached to proteins in some unknown manner. In addition, some β-1→3 glucan, β-1→4 glucan and glucomannan-like polymers were detected.

Molecular size distribution of Acacia senegal gum on Sephacryl gel S-400 is compared before and after incubation with the proteolytic enzyme Pronase. The profile and elution volumes of chromatograms are greatly modified: a rather broad system of high molecular weight peaks near the exclusion volume is resolved into a single peak at lower molecular weight. Physicochemical data from isolated Pronase-treated samples tend to favour, for crude Acacia senegal gum, a structure where varying numbers of polysaccharide units of MW ca 2×105 are linked to a protein core. The effect of Pronase on Acacia mearnsii and Combretum nigricans gums was also investigated. Our results are discussed in relation to structural models proposed for these arabinogalactan-protein complexes.

Fractionation of Acacia senegal gum has been carried out on Sephacryl gels S-400 and S-500. The shape and relative height of the chromatograms are sample dependent. Physicochemical data including circular dichroism and the weight-average molecular weights distribution show that about 70% of the material is composed of homogeneous polysaccharide chains with a very low nitrogen content. The remaining material is a combination of polysaccharide and nitrogen moieties (probably an arabinogalactan-protein complex). Our data are consistent with the new and simplified structural models proposed recently for this polysaccharide.