Key Findings:
With the growing interest and dietary need for fiber, this paper provides an assessment of the types and amounts of fiber in flaxseed. Water soluble mucilage is found in the epidermal cells of the seed coats of flaxseed. Once released, mucilage will form a gel-like capsule. Flaxseed multiage is characterized by t-Araf residues attached to both the O-2 and O-3 of the (1/4)-b-D-xylan chain to form doubly branched residues on the arabinoxylan backbone of the mucilage. The arabinoxylan is weakly acidic, owing to thet-GlcA residues also attached to the xylan chain. The side group structure of the flax RG I is also atypical, with single nonreducing terminal L-Gal and L-Fuc residues attached to the O-3 position instead of the O-4 position. The paper provides information on the functional attributes of the flaxseed fiber residues.
ABSTRACT:
The viscous seed mucilage of flax (Linum usitatissimum) is a mixture of rhamnogalacturonan I and arabinoxylan with novel side group substitutions. Therhamnogalacturonan I has numerous single non reducing terminal residues of the rare sugar L-galactose attached at theO-3 position of the rhamnosyl residues instead of the typicalO-4 position. The arabinoxylan is highly branched, primarily with double branches of non reducing termina lL-arabinosylunits at the O-2 and O-3 positions along the xylan backbone. While a portion of each polysaccharide can be purified by anion-exchange chromatography, the side group structures of both polysaccharides are modified further in about one-third of the mucilage to form composites with enhanced viscosity. Our finding of the unusual side group structures for two well-known cell wall polysaccharides supports a hypothesis that plants make a selected few ubiquitous backbone polymers onto which a broad spectrum of sidegroup substitutions are added to engender many possible functions. To this end, modification of one polymer may be accompanied by complementary modifications of others to impart functions to heterocomposites not present in either polymer alone. (Author’s abstract)