Abstract
Different extraction, purification and digestion methods were used to investigate the molecular properties of carbohydrates in arabinoxylan and β-glucan concentrates, dietary fiber (DF) rich breads and ileum content of bread fed pigs. The breads studied were: a low DF wheat bread (WF), whole meal rye bread (GR), rye bread with kernels (RK), wheat bread supplemented with wheat arabinoxylan concentrate (AX) and wheat bread supplemented with oat β-glucan concentrate (BG). The weight average molecular weight (Mw) of extractable carbohydrates in β-glucan concentrate decreased eight-fold after inclusion in the BG bread when exposed to in vitro digestion, while the Mw of purified extractable carbohydrates in AX bread was reduced two-fold, and remained almost unaffected until reaching the terminal ileum of pigs. Similarly, the Mw of purified extractable carbohydrates in GR and RK bread was not significantly changed in the ileum. The AX bread resulted in the highest concentration of dissolved arabinoxylan in the ileum among all the breads that caused a substantial increased in ileal AX viscosity. Nevertheless, for none of the breads, the Mw of extractable carbohydrates was related neither to the bread extract nor ileal viscosity.
Highlights
Arabinoxylan and β-glucan naturally occur in the endosperm and aleurone cell walls of cereal grains with varying degrees of solubility
Breads, 87% of the arabinoxylan in the arabinoxylan concentrate (AX) bread was soluble compared to only 47%–48% in the grain rye breads without (GR)
In vitro and in vivo digested breads had a markedly reduced molecular weight (Mw) compared to water extracted breads and the fiber sources extracted under mild alkali conditions
Summary
Arabinoxylan and β-glucan naturally occur in the endosperm and aleurone cell walls of cereal grains with varying degrees of solubility. The content of rye and wheat arabinoxylan varies in the range of 6%–12% in the whole grain, and 21%–25% in the bran [1,2,3]. Due to the capability of soluble arabinoxylan and β-glucan to increase viscosity, they have physiologically gained a lot of interest as polysaccharides that can attenuate blood glucose and insulin responses and lower blood cholesterol [2,8,9]. The viscosity-elevating properties of arabinoxylan and β-glucan have been shown to slow the rate of gastric emptying and reduce the motility of human small intestine, which may reflect a prolongation of satiety [10]. Raised gastrointestinal viscosity can reduce the rate of digestion and absorption of macronutrients, including fat, protein and carbohydrates [8,10] which may have a different effect on weight management [11,12]
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