Application of a dynamic gastrointestinal in vitro model combined with a rat model to predict the digestive fate of barley dietary fibre and evaluate potential impact on hindgut fermentation

Processing affects the composition, structure and physico-chemical characteristics of dietary fibres, and further changes can occur along the gastro-intestinal tract before entering the colon where undigested carbohydrates may serve as a substrate for the microbiota. To elucidate the effects of dietary fibre characteristic and the impact of processing on the digestive fate of dietary fibre components, in the stomach and the small intestine, a dynamic gastrointestinal in vitro model (TIM-1) was used. Three barley malt and one brewers’ spent grain, with different contents of soluble fibre, arabinoxylan (total and soluble), and β-glucan with varying Calcofluor average molecular weight (Mcf) and molecular weight distribution were evaluated in the in vitro model. Additionally, a rat model was used to study the colonic fermentation of the dietary fibre components in the barley products. The transit time through the stomach and small intestine of the in vitro model was slowest for barley malts with the highest content of soluble fibre and β-glucan. The β-glucan Mcf decreased with digestion time for all test meals, and the molecular weight distributions in the various barley products differed markedly. The highest β-glucan Mcf was found for Cinnamon malt, which also contained the highest proportion of soluble fibre. The hindgut fermentation of fibre and the proportions of caecal propionic acid were highest in rats fed barley products high in soluble fibre, β-glucan (content and Mcf), soluble arabinoxylan, and with slowest transit during digestion in the in vitro model.