【Background】
A variety of barley, BARLEYmax (BM), contains fermentable dietary fibers such as fructan, beta-glucan, and resistant starch. The fermentation rate of fructan is the fastest, and that of resistant starch is the slowest, suggesting that the gradual fermentation of these dietary fibers in BM in the intestine may produce short-chain fatty acids in a wide area from the cecum to the distal colon. In this study, the fermentation characteristics of BM were examined in comparison with those of BG012 (BG), a β-glucan-rich barley variety.
【Methods】
Four-week-old Sprague-Dawley rats were acclimatized for 7 days and divided into two groups (8 rats each): one group was fed a diet with 5% cellulose based on the AIN-93G composition (control group, CO group), and the other group was fed a diet with BM or BG added to make the dietary fiber content 5% (BM group and BG group, respectively). The amount of protein and fat in the diet of the BM and BG groups was adjusted to be the same as that of the CO group using casein and soybean oil. Food intake and body weight were measured three times a week, and dietary efficiency was calculated as the ratio of body weight gain per food intake.
Fresh feces were collected on days 26-27 of the study. Digests of the cecal, proximal colon, and distal colon were collected at dissection. The short-chain fatty acids contained were quantified by gas chromatography-mass spectrometry. The gut microbiota in the digestive products of the cecum and distal colon were analyzed by 16S rRNA analysis.
【Results】
The final body weight, weight gain, and dietary efficiency were not significantly different among the three groups. Still, the food intake of the BM group was significantly lower than that of the CO group. Cecal digesta weight was significantly higher in the BM group than in the CO and BG groups. There was no significant difference in liver weight among the three groups.
Acetic acid and n-butyric acid in cecal digesta were significantly higher in the BM and BG groups than in the CO group. Total short-chain fatty acid content was significantly higher in the BM group than in the CO group. The amount of short-chain fatty acid in the proximal colon digest were lower than those in the ceca and distal colon digest in all groups, and there was no significant difference among the three groups. In distal colon digestive products, acetic acid and total short-chain fatty acids were significantly higher only in the BM group than in the CO group. There was no significant difference between the BG group and the other two groups.
The presence ratios of bacterial phylum in cecal and distal colon digests were compared. In both groups, Bacteroidetes were significantly higher in the BM group than in the CO group and tended to be higher in the BG group. Proteobacteria were significantly higher in the BM group than in the BG group in the cecal digestive products and significantly higher in the BM and BG groups than in the CO group in the distal colon digestive products.
The genus levels of Bifidobacterium and Sutterella were significantly higher in BM and BG groups than in CO group in cecal and distal colon digests, Ruminococcus was significantly lower in BG group than in CO group in cecal digests and was significantly lower in BM and BG groups than in CO group in distal colon digests. Parabacteroides was significantly higher in the BM group than in the CO group in cecal digesta, Oscillospira was significantly higher in the BM group than in the CO group in distal colon digesta, and Clostridium was significantly lower in the BM group than in the CO group in cecal and distal colon digesta, but significantly lower in the CO and BG groups in distal colon digesta. \
The diversity indices were significantly lower in the BM group than in the BG group for OTUs and Shannon indices in cecal digesta, and significantly lower for Chao1 in distal colon digesta in addition to these indices.
【Discussion and conclusion】
BM increased the amount of short-chain fatty acids in the distal colon more than BG, which is rich in β-glucan, suggests that several fermentable dietary fibers in BM reach and ferment in the distal colon. The total short-chain fatty acids in the proximal colon digest were the lowest among the sites examined. There was no difference in the amount of various short-chain fatty acids contained among the three groups. This suggests that the short-chain fatty acids were rapidly absorbed in the proximal colon. Since fructans are rapidly fermented, and resistant starch is slowly fermented, fructans and β-glucans are thought to be fermented mainly in the cecum and resistant starch primarily in the distal colon.
In the comparison of the intestinal microflora, Bacteroidetes was more abundant, and Firmicutes was lower abundant in the BM and BG groups than in the CO group at the portal level, which may be due to the effect of β-glucan. It has been reported that secretory IgA, which binds to pathogens and toxins on the intestinal mucosal surface and disables their functions, increases in the presence of Bacteroidetes. Therefore, the increase of Bacteroidetes by BM and BG is expected to contribute to preventing colorectal diseases. Therefore, the increase of Bacteroidetes by BM and BG is expected to contribute to preventing colorectal diseases *1.
The diversity of intestinal bacteria in the cecum and distal colon was higher in the BG group than in the BM group. A human study reported that administration of 5 g/day of low-molecular-weight β-glucan altered β-diversity, while 3 g/day did not. This may be due to the difference in the amount of β-glucan contained in BM and BG, but further investigation is needed *2.
The ratio of Parabacteroides, which has been reported to inhibit inflammation of intestinal epithelial cells *3, was significantly higher in the BM group than in the CO group in the cecum. The increase of Parabacteroides by BM is expected to enhance the immune function of the intestine. Sutterella *4, which has been shown to promote immune defense function in vitro studies, was significantly higher in the BM and BG groups than in the CO group in the cecum and distal colon and was higher in the BM group than in the BG group in the cecum.
Both BM and BG increased acetate and n-butyrate in the cecum and Bifidobacterium in the cecum and distal colon. BM also increased total short-chain fatty acids in the cecum and acetate and total short-chain fatty acids in the distal colon, which may be due to the presence of fructans and resistant starch in addition to β-glucans.
BM dietary fibers reach the distal colon and increase short-chain fatty acids, improving the intestinal microflora from the cecum to the distal colon. This effect was more effective than that of BG, which is rich in beta-glucan.
【Research institution】
Otsuma Women's University,
Teijin Ltd.
*1 Mucosal Immunol, 4, 6, 603-11, 2011
*2 Front Microbiol, 7, 129, 2016
*3 Am J Physiol Gastrointest Liver Physiol, 298, 6, G807-19, 2010
*4 Proc Natl Acad Sci U S A, 114, 40, 10719-24, 2017
Effects of BARLEYmax and high-β-glucan barley line on short-chain fatty acids production and microbiota from the cecum to the distal colon in rats
PLoS One 14, 6, e0218118, 2019
