Barley β-glucan improves glucose and lipid metabolism even when moderately reduced in molecular weight


【Background】
One of the mechanisms by which barley β-glucan intake improves sugar and lipid metabolism is due to the viscous effect of barley β-glucan. When barley is processed into cookies and bread, the molecular weight of barley β-glucan may decrease due to hydrolysis and pyrolysis, resulting in a decrease in viscosity.

Few reports have examined the effects of differences in the molecular weight of barley β-glucan on digestion and absorption of nutrients and intestinal fermentation. In this study, we used barley flour in which β-glucanase partially hydrolyzed barley β-glucan, an intrinsic degrading enzyme in barley, to investigate the effects of barley β-glucan with different molecular weights on sugar and lipid metabolism, intestinal microflora, and production of short-chain fatty acids.

【Methods】
High β-glucan barley, “Beaufiber” flour (BF) were kept in distilled water at 37°C for 2 hours (PHEB-2h) or 8 hours (PHEB-8h), then freeze-dried and ground and β-glucanase was inactivated with ethanol. The molecular weight of β-glucan in each sample was measured by HPLC.

Four-week-old male C57BL/6J mice were acclimated for 1 week and then divided into 4 groups (8 mice per group) fed with high-fat diet (Control), high-fat diet + untreated BF (BF), high-fat diet + PHEB-2h (PHEB-2h), and high-fat diet + PHEB-8h (PHEB-8h) for 89 days. All diets were adjusted to contain 5% dietary fiber.

Feed intake and body weight were measured three times a week, and an oral glucose tolerance test was performed at week 11. At the end of the rearing period, the animals were dissected and various biochemical tests were performed, including measurements of adipose tissue, cecum, and liver weight, measurement of short-chain fatty acids in cecal contents, and analysis of intestinal microflora by real-time PCR.

【Results】
The average molecular weights of β-glucan in the three samples added to the diet were 360,000 for BF, 110,000 for PHEB-2h, and 50,000 for PHEB-8h. The total dietary fiber and β-glucan contents were similar in the three samples.

There was no difference in feed intake between the groups, but PHEB-8h had less weight gain and lower feed efficiency than Control. Liver weight was lighter in the other three groups than in Control, and mesenteric fat weight was lighter in PHEB-8h than in Control. The weight of the cecum was heavier in BF and PHEB-2h than in Control.

Non-HDL-cholesterol was lower in BF than in Control. Leptin concentration did not differ between groups. Insulin concentration was lower in PHEB-8h than in Control, and liver cholesterol and triglyceride accumulation were lower in the other three groups than in Control. Oral glucose tolerance test tended to be lower at 30 min in PHEB-8h compared to Control.

The amount of acetic acid and total short-chain fatty acids in the cecal contents were higher in the other three groups than in Control. The amount of propionic acid was higher in PHEB-8h than in Control. The amount of succinate was higher in BF and PHEB-2h than in Control.

At the phylum level, Bacteroidetes and Firmicutes were more abundant in BF and PHEB-8h than in Control. At the genus level, Bacteroides were higher in BF and PHEB-8h, Bifidobacterium was higher in PHEB-2h, and Lactobacillus was higher in BF than in Control.

The amount of acetic acid in the cecum was positively correlated with the number of bacteria in the genus Bifidobacterium. The amount of leptin was negatively correlated with the number of bacteria of the genus Bacteroides. At the portal level, it tended to be negatively correlated with Bacteroidetes.

【Discussion and conclusion】
It was suggested that even if the molecular weight of β-glucan is reduced by β-glucanase intrinsic to barley, the functionality of barley β-glucan, which improves the metabolism of sugar and lipid, suppresses the accumulation of visceral fat, is maintained.

Acetic acid and total short-chain fatty acid levels were significantly higher in all three groups added barley. The production of short-chain fatty acids by cecal fermentation seems to be unaffected by differences in the molecular weight of barley β-glucan. A previous in vitro study showed that low molecular weight barley β-glucan increased propionic acid production by fermentation *1, which is consistent with the results of this study. Low-molecular-weight barley β-glucan may promote an increase in propionic acid-producing intestinal bacteria.

Bacteria in the phylum Bacteroidetes and Firmicutes ferment indigestible polysaccharides and produce short-chain fatty acids *2. Barley β-glucan, regardless of its molecular weight, increased the number of these intestinal bacteria. There was a negative correlation trend between the number of bacteria in the phylum Bacteroidetes and serum leptin concentration and a clear negative correlation with the number of bacteria in the genus Bacteroides, which belongs to the phylum Bacteroidetes. This increase in the number of bacteria in the phylum Bacteroidetes may improve obesity and obesity-related metabolic syndrome.

【Research institution】
Otsuma Women's University,
National Agriculture and Food Research Organization (NARO)

*1 Molecules 24, 5, 828, 2019
*2 World J Gastrointest Pathophysiol 6, 4, 110-9, 2015


Effects of barley β-glucan with various molecular weights partially hydrolyzed by endogenous β-glucanase on glucose tolerance and lipid metabolism in mice
Cereal Chemistry Aug 4, 2020