Abstract
Beta (β)-glucan (BG) from cereal grains is associated with lowering post-prandial blood glucose but the precise mechanism is not well-elucidated. The main aim of this study was to understand the mechanism through which BG from barley affects post-prandial glycemic response. Waffles containing 0, 1, 2, and 3 g barley BG and the same amount of available carbohydrate (15 g) were fed to the TIM-1 dynamic gastrointestinal digestion system to study the effect of BG on starch hydrolysis. Intestinal acetone powder and Xenopus laevis oocytes were used to study BG's effect on mammalian intestinal α-glucosidase and glucose transporters. The presence of BG did not significantly affect the in vitro starch digestion profiles of waffles suggesting that BG does not affect α-amylase activity. Intestinal α-glucosidase and glucose transport activities were significantly (p < 0.0001) inhibited in the presence of barley BG. Interestingly, BG viscosity did not influence α-amylase, α-glucosidase, GLUT2, and SGLT1 activities. This study provides the first evidence for the mechanism by which BG from barley attenuates post-prandial glycemic response is via alteration of α-glucosidase, GLUT2, and SGLT1 activity, but not amylolysis of starch. The decrease in post-prandial blood glucose in the presence of BG is likely a consequence of the interaction between BG and membrane active proteins (brush border enzymes and glucose transporters) as opposed to the commonly held hypothesis that increased viscosity caused by BG inhibits starch digestion.
Highlights
Several human feeding studies have shown that beta (β)-glucan (BG) from barley can mitigate the rise in post-prandial glycemic response after consuming a high available carbohydrate meal, but the results are not consistent [1,2,3]
Comparing the digestion profiles of the matched wheat-based waffle and a barley waffle delivering 1.2 g Beta (β)-glucan (BG), the results indicate that addition of BG did not affect the digestion profile except at 60 min
This suggests that barley flour may have a higher amount of rapidly available carbohydrate compared to wheat
Summary
Several human feeding studies have shown that beta (β)-glucan (BG) from barley can mitigate the rise in post-prandial glycemic response after consuming a high available carbohydrate meal, but the results are not consistent [1,2,3]. These inconsistencies have been attributed to the changes in concentration, type of BG, or the BG to available carbohydrate ratio present. The drawback of the hypothesis related to viscosity is that the viscosity of soluble fiber is highly susceptible to shear thinning [12] and BG viscosity may be drastically reduced or nullified in the presence of the intestinal peristaltic force during digestion [13]
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