Fecal microbiota composition affects in vitro fermentation of rye, oat, and wheat bread

Abstract

Fermentation of dietary fiber by gut microbes produces short-chain fatty acids (SCFA), but fermentation outcomes are affected by dietary fiber source and microbiota composition. The aim of this study was to investigate the effect of two different fecal microbial compositions on in vitro fermentation of a standardized amount of oat, rye, and wheat breads. Two human fecal donors with different microbial community composition were recruited. Bread samples were digested enzymatically. An in vitro fermentation model was used to study SCFA production, dietary fiber degradation, pH, and changes in microbiota. Feces from donor I had high relative abundance of Bacteroides and Escherichia/Shigella, whereas feces from donor II were high in Prevotella and Subdoligranulum. Shifts in microbiota composition were observed during fermentation. SCFA levels were low in the samples with fecal microbiota from donor I after 8 h of fermentation, but after 24 h acetate and propionate levels were similar in the samples from the different donors. Butyrate levels were higher in the fermentation samples from donor II, especially with rye substrate, where high abundance of Subdoligranulum was observed. Dietary fiber degradation was also higher in the fermentation samples from donor II. In conclusion, fermentation capacity and substrate utilization differed between the two different microbiota compositions.

Whole-grain cereals in dog food : Effects on metabolism and gut microbiota

“…However, after 62 24 h the initially Prevotella-dominated inocula was still dominated by Prevotella in oat and wheat substrates, whereas in rye substrate the genus Subdoligranulum dominated. Similarly to the study by , they also found that the Bacteroides-dominated inocula had a more diverse composition after 24 h compared with the Prevotella-dominated inocula (Pirkola et al 2023). Thus it is not clear why consumption of rye would promote Prevotella and in fact it does not consistently do so.…”

“…In the same study, diversity in the Bacteroides cultures was higher after 24 h than in the Prevotella cultures, where one Prevotella OTU outcompeted other major taxa when fermenting the substrates. Another similar in vitro study examining fermentation and microbial shifts in inocula of human fecal origin dominated by either Prevotella or Bacteroides using rye, oat or wheat breads as substrates did likewise observe faster fermentation rate in the Prevotelladominated inoculum for all substrates (Pirkola et al 2023). However, after 62 24 h the initially Prevotella-dominated inocula was still dominated by Prevotella in oat and wheat substrates, whereas in rye substrate the genus Subdoligranulum dominated.…”

“…Two of these clusterings (Prevotella-and Bacteroides-dominated) have been further corroborated . Studies on these two enterotypes have shown that they differ in their fiberutilizing capacity and SCFA production Pirkola et al 2023). They have also been observed to result in different metabolic outcomes Eriksen et al 2020).…”

“…However, this also means that digestion of fiber in the OAT diet could have occurred more proximally in the intestine, and thus SCFA could also have been absorbed more proximally. However, the results from an in vitro study comparing fermentation on breads made from rye or oats indicated that rye resulted in more SCFA, especially when the inoculum was Prevotella-dominated (Pirkola et al 2023).…”