Factors Involved in theIn VitroFermentability of Short Carbohydrates in Static Faecal Batch Cultures

Abstract

In recent years, research has focused on the positive effects of prebiotics on intestinal health and gut microbiota. The relationship between their chemical structure and their fermentation pattern by human intestinal microbiota is still not well understood. The aim of this study was to improve understanding of this relationship and identify factors that may be used to design galactooligosaccharides that reach more distal regions than commercial prebiotics which mainly target the proximal colon. The following factors were investigated: monomer type, linkage, substitution, and degree of polymerisation. Total organic acid production from sugars by faecal bacteria was fitted to a model which allowed an estimate of the time when half of the maximal organic acid concentration was reached (T50) in static faecal batch cultures. The different factors can be grouped by their effectiveness at prolonging fermentation time as follows: substitution is most effective, with methylgalactose,β-galactose-pentaacetate, D-fucose, and galactitol fermented more slowly than D-galactose. Monomers and linkage also influence fermentation time, with L rhamnose, arabinose, melezitose, and xylose being fermented significantly slower than D-glucose (P<0.05), maltose, isomaltose, cellobiose, and gentiobiose showing that Glcα1-6Glc and Glcβ1-4Glc were utilised slowest. Chain length had the smallest effect on fermentation time.

Impact of Glycosidic Bond Configuration on Short Chain Fatty Acid Production from Model Fermentable Carbohydrates by the Human Gut Microbiota

“…The reasons for this selective increase in butyrate production with α(1-1) glycosidic bond configuration are not clear and warrant further investigation. In another study, diglucose α(1-4) and diglucose α(1-6) linkages led to non-significant increases in propionate and butyrate production [ 21 ]. However, comparisons between these studies and the present study are difficult to interpret because of their short fermentation duration and the low number of subjects.…”

“…With 10 incubations the study was powered (0.8) to observe a 9.5 mM (0.47 mmol/g carbohydrate/day) difference in propionate production, an additional 5 incubations provided the power (0.8) to observe a 7.5 mM (0.37 mmol/g carbohydrate/day) difference in propionate production. Previous in vitro fermentation studies have shown similar differences in propionate production between different fibers [ 35 ] and between simple sugars [ 21 ].…”

“…The profile of SCFA production is thought to be related to the physicochemical properties of NDCs reaching the colon, which in turn may determine which members of the gut microbiota consortium are able to derive energy from NDC fermentation, yielding SCFA as the reduced end-products [ 20 ]. Factors which have been shown to influence SCFA production profile include monosaccharide composition and distribution, glycosidic bond linkage and NDC chain length and branching [ 21 , 22 , 23 ]. Soluble NDC appear more readily fermented than insoluble NDC, and previous studies have suggested that solubility (or chain length) may influence the profile of SCFA produced [ 24 ].…”

“…Fermentation of some mono- and di-saccharides appears to favor selective SCFA production. In vitro, sorbitol fermentation selectively increased butyrate production whereas glucose, xylose, and fructose fermentation selectively increased acetate production [ 21 , 23 ]. Rhamnose has been shown, in both in vitro fermentations and in vivo feeding studies, to selectively increase propionate production [ 27 , 28 ].…”

Prebiotic galactooligosaccharides activate mucin and pectic galactan utilization pathways in the human gut symbiont Bacteroides thetaiotaomicron

“…When consumed, GOS reach the distal colon similar to HMOs where they are degraded by resident bacteria28, promoting the growth of bacterial families, including Bifidobacteriaceae and Bacteroidaceae , in the intestine of infants in a similar ratio to that found in the gut microbiota of breast-fed infants. GOS are very complex mixtures25, and very little is known about what components within GOS offer the same HMOs-like effects.…”