Flaxseed (Linum usitatissimum L.), one of the most important oilseed crops, is also rich in soluble and insoluble dietary fibres. Our research discovered that the kernel of flaxseed contained about 20% of dietary fibre. The structure of two major fractions of flaxseed kernel dietary fibre (FKDF) were proposed as RG-I bridge-linked arabinans and xyloglucans, respectively. These two fractions were subjected to in vitro fermentation by pig colonic digesta with psyllium fibre as the reference. FKDF grown cultures showed increased levels of short chain fatty acid (SCFA) content. Acetic acid was the major SCFA produced, followed by propionic acid and butyric acid during 72 h fermentation. Psyllium gums, which are mainly composed of arabinoxylan, had the highest level of total SCFA after 24 h and 48 h incubation. Both flaxseed kernel xyloglucans and RG-I bridge-linked arabinans had higher total SCFA production than psyllium fibre after 72 h incubation. Flaxseed proved to contribute promising dietary fibre sources, which contained relatively slowly fermentable dietary fibres as compared with psyllium fibre. Future studies are hoped to optimize colonic health based on more balanced diets with both grain and oilseed.
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