Regulation of short-chain fatty acid production

Abstract

Short-chain fatty acid (SCFA) formation by intestinal bacteria is regulated by many different host, environmental, dietary and microbiological factors. In broad terms, however, substrate availability, bacterial species composition of the microbiota and intestinal transit time largely determine the amounts and types of SCFA that are produced in healthy individuals. The majority of SCFA in the gut are derived from bacterial breakdown of complex carbohydrates, especially in the proximal bowel, but digestion of proteins and peptides makes an increasing contribution to SCFA production as food residues pass through the bowel. Bacterial hydrogen metabolism also affects the way in which SCFA are made. This outcome can be seen through the effects of inorganic electron acceptors (nitrate, sulfate) on fermentation processes, where they facilitate the formation of more oxidised SCFA such as acetate, at the expense of more reduced fatty acids, such as butyrate. Chemostat studies using pure cultures of saccharolytic gut micro-organisms demonstrate that C availability and growth rate strongly affect the outcome of fermentation. For example, acetate and formate are the major bifidobacterial fermentation products formed during growth under C limitation, whereas acetate and lactate are produced when carbohydrate is in excess. Lactate is also used as an electron sink inClostridium perfringensand, to a lesser extent, inBacteroides fragilis. In the latter organism acetate and succinate are the major fermentation products when substrate is abundant, whereas succinate is decarboxylated to produce propionate when C and energy sources are limiting.

In vitro production of short-chain fatty acids from resistant starch by pig faecal inoculum

“…Notwithstanding, results from our study showed that molar ratios of butyrate released during in vitro fermentation were affected by the RS sources. This might be ascribed to the extent at which substrate is available to microbiota (Jha et al, 2011a), which, in turn, could enhance the proliferation of butyrate-producing bacteria (MacFarlane and MacFarlane, 2003;Pieper et al, 2008). Our results are also supported by findings of Martin et al (2000), where heterogeneous RS sources induced different appearance of butyrate in the portal blood of pigs during a 14 h test period.…”

“…As the post-hydrolysis RS fractions were characterized by heterogeneous chemistry and structure, different fermentation kinetics may occur. Generally, formation of SCFA depends on several factors such as chemical composition, physical form and availability of specific substrate fermented In vitro fermentation of resistant starch (Brouns et al, 2002;MacFarlane and MacFarlane, 2003), as well as on the microbial population during the fermentation process . Wang et al (2002) reported different SCFA productions in mice from day 3 to day 8 of the experimental period after feeding diets formulated with different types of dietary starches, probably related to a variation in composition and population of indigenous colonic bacteria.…”

“…As substrates must be depolymerized by bacterial hydrolytic enzymes before the fermentation process, the rate of substrate depolymerization strongly influenced the rate at which carbohydrates become available for bacteria (MacFarlane and MacFarlane, 2003). In general, highly branched polymers (i.e., amylopectin) can provide a lot of cleaving sites for exo-enzymes, producing larger amounts of monomers and dimers that can be readily fermented by microbiota, whereas degradation of more linear polymers (i.e., amylose) yields large oligomers, which cannot be used directly by bacteria (Jonathan et al, 2012).…”

Pigs that are divergent in feed efficiency, differ in intestinal enzyme and nutrient transporter gene expression, nutrient digestibility and microbial activity

“…The phyla Bacteroidetes, Firmicutes and Actinobacteria are the most abundant in the pig intestine. The result of fermentation by Bacteroidetes is predominately acetate and propionate, where as butyrate is the primary end product of fermentation by Firmicutes (Macfarlane and Macfarlane, 2003). In this study, LRFI pigs had increased lactobacilli numbers in the caecum compared to HRFI pigs with no differences between the other measured bacteria in either the caecum or colon (P < 0.05; Table 4).…”

Effects of Proteoglycan on Dextran Sulfate Sodium-Induced Experimental Colitis in Rats

“…The principal SCFAs that result from fermentation of both carbohydrates and amino acids are acetate, propionate, and butyrate, although formate, valerate, caproate, and the branched-chain fatty acids formed during the catabolism of branched-chain amino acids (valine, leucine, and isoleucine) are also produced in lesser amounts [34]. It has been reported that germinated barley foodstuff containing protein and hemicellulose significantly increases the concentrations of n-butyrate in normal rats and rats with DSS-induced colitis [35,36].…”