Soluble polysaccharides from flaxseed kernel as a new source of dietary fibres: Extraction and physicochemical characterization

- It is the first time to study of dietary fibres from flaxseed kernel (FKDF).
- Five FKDF fractions were obtained as a new source of dietary fibres.
- Potential applications of FKDF in related food products were evaluated.

Flaxseed (Linum usitatissimum L.) is rich in soluble and insoluble dietary fibres. Recent study in our research group discovered that the kernel of flaxseed contained about 20% (w/w) of dietary fibres, which has not been reported before. Scanning electron microscope (SEM) images revealed that flaxseed kernel dietary fibres (FKDF) are mostly in the supporting structure of the cell walls. To study the structure and physicochemical properties of FKDF, a modified sequential extraction and fractionation procedure was utilised, and five separate FKDF fractions were obtained as flaxseed kernel (FK) water-extracted polysaccharides (FK-WP), FK EDTA-extracted polysaccharides (FK-EP), FK Na2CO3-extracted polysaccharides (FK-NP), FK 1 M KOH-extracted polysaccharides (FK-KPI), and FK 4 M KOH-extracted polysaccharides (FK-KPII). FKDF fractions were all water-soluble. The average molecular weight of FK-WP was 486 kDa, FK-EP 593 kDa, FK-NP 704 kDa, FK-KPI 770 kDa, and FK-KPII 1660 kDa. Monosaccharide compositions were different among FKDF fractions; alkaline solution extracted FKDF fractions had relatively higher percentage of arabinose, but relatively lower content of glucose compared with FK-WP and FK-EP. All FKDF fractions had the ability to lower the surface tension of water, among which FK-KPI exhibited the best surface activity. Rheological properties showed that FKDF fractions had low viscosity and 2% (w/v) FKDF water solution exhibited viscoelastic behaviour at 25 °C. Those findings could benefit the related food industries for providing healthier and more value-added flaxseed products.