In vitro study for investigating the impact of decreasing the molecular weight of oat bran dietary fibre components on the behaviour in small and large intestine

Abstract

The objective of this work was to evaluate the role of β-glucan molecular weight (M_w) and the presence of other carbohydrates on the physiological functionality of oat bran via an in vitro digestion study. A complete approach using three different in vitro digestion models (viscosity of the small intestine digest, reduction of bile acids and on-line measurement of gas evolution) was used to predict the physiological functionality of enzymatically modified oat bran concentrate (OBC). OBC was enzymatically treated with two β-glucanase preparations at three different levels in order to specifically decrease β-glucan M_w (Pure: purified β-glucanase) or β-glucan and other cell wall polysaccharides (Mix: commercial food-grade cell wall degrading enzyme preparation). The M_w of β-glucan in OBC was tailored to high (1000 kDa), medium (200-500 kDa) and low (<100 kDa) values. The amount of arabinoxylan-oligosaccharides varied from 0.3 to 4.7 g per 100 g of OBC when OBC was treated with the Mix enzyme at the highest dosage. When the enzymatically treated OBCs were studied in an upper gut model, a decrease in the viscosity of the digest simultaneously with the reduction of β-glucan M_w was observed. At a similar β-glucan M_w range, OBC samples treated with the Pure enzyme had lower viscosity than the samples treated with the Mix one, which also contained arabinoxylan-oligosaccharides. After enzymatic hydrolysis, the capacity of OBC to reduce bile acid was decreased regardless of the enzyme treatment used, and a positive correlation was found between β-glucan M_w and bile acid reduction (r = 0.99**). The production of colonic gases by the enzymatically treated OBC samples in an in vitro colon model showed an inverse correlation between β-glucan M_w and initial rate of gas formation (r = -0.9**), but no impact of arabinoxylan-oligosaccharides was observed. This study emphasised the complexity of factors affecting the functionality of oat components under physiological conditions and demonstrated the possibility to produce M_w-tailored oat fibre ingredients that could contribute to gut mediated health benefits.