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Enzymic hydrolysis of barley and other beta-glucans by a beta-(1--4)-glucan hydrolase.

ABSTRACT: 1. A barley glucan with 68% of beta-(1-->4)-linkages and 32% of beta-(1-->3)-linkages was exhaustively hydrolysed with an Aspergillus niger beta-(1-->4)-glucan 4-glucanohydrolase (EC 3.2.1.4) (Clarke & Stone, 1965b). The hydrolysis products were separated and estimated. 2. The lower-molecular-weight products were identified as: glucose, 1.4%; cellobiose, 11.9%; 3(2)-O-beta-glucosylcellobiose, 45.0%; a tetrasaccharide(s), which was a substituted cellobiose, 16.4%. A series of unidentified higher-molecular-weight products (26.5%) were also found. 3. The identity of the products suggests that the A. niger beta-(1-->4)-glucan hydrolase hydrolyses beta-glucosidic linkages joining 4-O-substituted glucose residues. 4. When an enzyme fraction containing the beta-(1-->4)-glucan hydrolase and an exo-beta-(1-->3)-glucan hydrolase was used, the same products were found, but the higher-molecular-weight products were observed to have only a transient existence in the hydrolysate and were virtually absent after prolonged incubation. It is suggested that these oligosaccharides are resistant to attack by beta-(1-->4)-glucan hydrolase but are partially hydrolysed by the exo-beta-(1-->3)-glucan hydrolase and therefore possess one or more (1-->3)-linked glucose residues at their non-reducing end.

SUBMITTER: Clarke AE

PROVIDER: S-EPMC1265044 | biostudies-other | 1966 Jun

REPOSITORIES: biostudies-other

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Project description:The physiological cholesterol-lowering benefits of β-glucan have been well documented, however, whether modulation of gut microbiota by β-glucan is associated with these physiological effects remains unknown. The objectives of this study were therefore to determine the impact of β-glucan on the composition of gut microbiota in mildly hypercholesterolemic individuals and to identify if the altered microbiota are associated with bioactivity of β-glucan in improving risk factors of cardiovascular disease (CVD). Using a randomized, controlled crossover study design, individuals received for 5-week either a treatment breakfast containing 3 g high molecular weight (HMW), 3 g low molecular weight (LMW), 5 g LMW barley β-glucan, or wheat and rice. The American Heart Association (AHA) diet served as the background diet for all treatment groups. Phases were separated by 4-week washout periods. Fecal samples were collected at the end of each intervention phase and subjected to Illumina sequencing of 16S rRNA genes. Results revealed that at the phylum level, supplementation of 3 g/d HMW β-glucan increased Bacteroidetes and decreased Firmicutes abundances compared to control (P < 0.001). At the genus level, consumption of 3 g/d HMW β-glucan increased Bacteroides (P < 0.003), tended to increase Prevotella (P < 0.1) but decreased Dorea (P < 0.1), whereas diets containing 5 g LMW β-glucan and 3 g LMW β-glucan failed to alter the gut microbiota composition. Bacteroides, Prevotella, and Dorea composition correlated (P < 0.05) with shifts of CVD risk factors, including body mass index, waist circumference, blood pressure, as well as triglyceride levels. Our data suggest that consumption of HMW β-glucan favorably alters the composition of gut microbiota and this altered microbiota profile associates with a reduction of CVD risk markers. Together, our study suggests that β-glucan induced shifts in gut microbiota in a MW-dependent manner and that might be one of the underlying mechanisms responsible for the physiological benefits of β-glucan.

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Enzymic hydrolysis of barley and other beta-glucans by a beta-(1--4)-glucan hydrolase.

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