The effect of in vitro gastrointestinal conditions on the structure and conformation of oat β-glucan

A plethora of studies have shown that the physicochemical properties of oat β-glucan determine its health benefits. However, the impact of the passage through the gastrointestinal tract on the conformational and structural characteristics is not fully understood. The present study aims to elucidate the structure and conformation of gently extracted oat β-glucan before and after in vitro gastric and gastrointestinal digestion utilizing asymmetric flow field-flow fractionation (AF4) and NMR spectroscopy. The structural features and the bile acid-binding capacity of oat β-glucan were probed with NMR. Oat β-glucan without digestion presented primary aggregates with fringed micelle structure, and other high molar mass supramolecular secondary aggregates were detected. Under gastric conditions, the molar mass was reduced and an increase in apparent density, suggesting more compact and disrupted aggregates, was observed. In the intestinal phase, the conformation was restored as prior digestion. No effect of the digestive enzymes on the conformation of oat β-glucan was shown, except from a modest effect of pepsin under gastric conditions. In contrast, the bile acids induced alterations to the apparent density of the oat β-glucan aggregates indicating a molecular interaction which was further confirmed with NMR by observing numerous changes in the resonance of bile acids' carbons in presence of oat β-glucan. In conclusion, the examination of oat β-glucan under in vitro gastrointestinal conditions with AF4 and NMR sheds light on the aggregation behavior and interaction mechanisms and enables a rich gain of knowledge for its physiological effects.