Short-chain fatty acid profiles from flaxseed dietary fibres after in vitro fermentation of pig colonic digesta: Structure–function relationship

Flaxseed (Linum usitatissimum L.) is rich in dietary fibres. There are four major soluble dietary fibre fractions, and their molecular structures have been characterised; however, the structure–function relationship on the short-chain fatty acid (SCFA) profiles is still unknown. SCFA profiles produced by in vitro fermentation of pig colonic digesta with soluble flaxseed dietary fibre fractions were determined by gas chromatography with psyllium arabinoxylans as the reference fibres. The results revealed that total SCFA production from all tested dietary fibres were significantly higher than negative control (NC) after 72 h fermentation. Acetic acid was the major SCFA produced, followed by propionic acid and butyric acid during 72 h fermentation. The acetic acid production from flaxseed kernel xyloglucans, and butyric acid production from flaxseed mucilage arabinoxylans were significantly higher than negative control (NC) after 48 h fermentation. Both psyllium and flaxseed mucilage arabinoxylans promoted butyric acid production more effectively than other tested dietary fibres during 48 h fermentation, while flaxseed kernel xyloglucans and flaxseed RG-I were more effective on promoting acetic acid production. The dietary fibre strucutre played major roles on promoting specific SCFAs, and the conformational characteristics might contribute to the difference of fermentability rates. Flaxseed dietary fibres were relatively slower fermentable dietary fibres as compared with psyllium fibres, and all flaxseed dietary fibres had higher level of total SCFA production than psyllium fibres after 72 h incubation. This research should further promotes the utilisation of flaxseed dietary fibres, and contributes to the optimisation of colonic health based on more balanced diets with both grain and oilseed.