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Dietary Fibres from Flaxseed Kernel: Structural and Conformational Characterization, and Structure-Function Relationship

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Title: Dietary Fibres from Flaxseed Kernel: Structural and Conformational Characterization, and Structure-Function Relationship
Author: Ding, Huihuang
Department: Department of Food Science
Program: Food Science
Advisor: Goff, H. Douglas
Abstract: Flaxseed (Linum usitatissimum L.), one of the most economically important oilseed crops, is also rich in soluble and insoluble dietary fibres. Scanning electron microscope (SEM) images revealed that flaxseed kernel dietary fibres (FKDF) are mostly in the supporting structure of the cell walls. Five separate FKDF fractions were obtained by a sequential extraction and fractionation procedure, which were flaxseed kernel (FK) water-extracted polysaccharides (FK-WP), FK EDTA-extracted polysaccharides (FK-EP), FK Na2CO3-extracted polysaccharides (FK-NP), FK 1M KOH-extracted polysaccharides (FK-KPI), and FK 4M KOH-extracted polysaccharides (FK-KPII). 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, respectively. 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. FK-KPI, which had the highest yield and best surface activity, was chosen as a representative to elucidate the detailed structures of FKDF. The structures of two major fractions of FK-KPI (KPI-ASF and KPI-EPF) were proposed as RG-I bridge-linked arabinans and xyloglucans. The absolute Mw of KPI-ASF ranged from 550 to 596 kDa with a highly branched and more sphere-like molecular structure. The absolute Mw of KPI-EPF was calculated to be 1506 kDa by SLS, and the ρ value of KPI-EPF (1.44) also confirmed the highly branched structure of extracted xyloglucans from flaxseed kernel cell wall. These two fractions were subjected to in vitro fermentation by pig colonic digesta with psyllium fibre as the reference. All fibre grown cultures showed a significant increase in total short chain fatty acids (SCFAs) after 72 h fermentation. Acetic acid was the major SCFAs produced, followed by propionic acid and butyric acid. Flaxseed dietary fibres were relatively slower fermentable dietary fibres as compared with psyllium fibre, and they sustained the production of SCFAs with prolonged fermentation. Enhanced understanding of the structure-function relationship is hoped to promote the potential application of flaxseed dietary fibres in related industries.
Date: 2015-04
Rights: Attribution 2.5 Canada
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Attribution 2.5 Canada Except where otherwise noted, this item's license is described as Attribution 2.5 Canada