Microbial Degradation of Whole-Grain Complex Carbohydrates and Impact on Short-Chain Fatty Acids and Health

Abstract

Whole-grain cereals have a complex dietary fiber (DF) composition consisting of oligosaccharides (mostly fructans), resistant starch, and nonstarch polysaccharides (NSPs); the most important are arabinoxylans, mixed-linkage β(1,3; 1,4)-d-glucan (β-glucan), and cellulose and the noncarbohydrate polyphenolic ether lignin. The highest concentration of NSPs and lignin is found in the outer cell layers of the grain, and refined flour will consequently be depleted of a large proportion of insoluble DF components. The flow and composition of carbohydrates to the large intestine are directly related to the intake of DF. The type and composition of cereal DF can consequently be used to modulate the microbial composition and activity as well as the production and molar ratios of short-chain fatty acids (SCFAs). Arabinoxylans and β-glucan in whole-grain cereals and cereal ingredients have been shown to augment SCFA production, with the strongest relative effect on butyrate. When arabinoxylans were provided as a concentrate, the effect was only on total SCFA production. Increased SCFA production in the large intestine was shown by the concentration in the portal vein, whereas the impact on the concentration in peripheral blood was less because the majority of propionate and butyrate is cleared in the liver. Active microbial fermentation with increased SCFA production reduced the exposure of potentially toxic compounds to the epithelium, potentially stimulating anorectic hormones and acting as signaling molecules between the gut and the peripheral tissues. The latter can have implications for insulin sensitivity and glucose homeostasis.

Comparisons of Effects on Intestinal Short-Chain Fatty Acid Concentration after Exposure of Two Glycosidase Inhibitors in Mice

“…It is clear that acetate can affect the fermentation of Escherichia coli, 48) propionate is associated with liver clearance, 49) and butyrate may be associated with inflammatory reaction. 21) We can not decide which inhibitor is better because there is no suitable criterion, but in our opinion, compared with acarbose-treatd group, voglibosetreated group would maintain a lower level of inflammation with the same anti-digestion effect of starch.…”

Impacts of resistant starch and wheat bran consumption on enteric inflammation in relation to colonic bacterial community structures and short-chain fatty acid concentrations in mice

“…Dietary fibers are defined as carbohydrates with three or more polymerized saccharide units that resist digestion in the small intestine by host-derived intestinal enzymes, and are only susceptible to fermentation by bacteria in the intestine [3]. They differ from one another in their water solubility, viscosity, and effects on the intestinal microbiota [4, 5]. Fermentation rates can vary depending on the chemical structure of DFs, and characteristics such as chain length, quantity of saccharide units, and the number of sugar linkages regulate the efficiency of carbohydrate fermentation [6].…”

“…Fermentation rates can vary depending on the chemical structure of DFs, and characteristics such as chain length, quantity of saccharide units, and the number of sugar linkages regulate the efficiency of carbohydrate fermentation [6]. Certain enteric bacterial species possess specialized metabolic enzymes that ferment specific forms of DFs, and products of fermentation contribute to the bacterial diversity within the intestinal microbiota [4, 7, 8]. By-products of bacterial fermentation are mainly composed of short-chain fatty acids (SCFAs) such as acetate, propionate, and butyrate [9, 10] as well as gases.…”

“…The complex structure and low percentage of soluble fiber present in WB contributes to slower fermentation rates by intestinal bacteria, and as such, is important for the increase in fecal bulking and stool frequency [20]. The fermentation of WB also improves intestinal lipid profiles that may lower the risk of intestinal cancer development [4, 7, 21]. Similarly to RS digestion, bacterial fermentation of WB can affect bacterial communities within the intestine.…”

Emerging Technologies for Gut Microbiome Research

“…Most microbial metabolic processes like carbohydrate fermentation generate byproducts that impact the community as well as the host. One example is the fermentation of carbohydrates into short-chain fatty acids [49], which act as signaling molecules to both host and other microbes [50, 51]. Traditionally, mass spectrometry (MS) and nuclear magnetic resonance (NMR) have been the primary tools used in metabolomics analyses.…”