Pathogens 2021 , 10 , 235
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flour (POF) at a concentration of 1.4 g β -glucan/day, where a marked, but not statistically significant ( p = 0.211), increase in butyrate levels was still observed (+13.2 mM). The latter could be due to the fact that lactate most strongly accumulated (Figure 1) for this condition (i.e., an average increase in lactate levels of 11.3 mM). While acetate and propionate levels were not significantly different as a consequence of the supplementation of old-fashioned oats (OFO) relative to POF at a concentration of 1.4 g β -glucan/day in the PC, butyrate levels were significantly higher upon treatment with OFO in the PC ( p < 0.0001), with an additional average increase of 8.3 mM upon OFO fermentation as compared to POF. In the DC, no significant differences in acetate and butyrate production were observed between supplementation of OFO and POF at a concentration of 1.4g β -glucan/day, whereas POF more strongly enhanced propionate production as compared to OFO (i.e., on average an additional increase of 10.2 mM) in this colonic region ( p = 0.007). With respect to the different doses of POF, acetate, propionate, and butyrate levels increased in a dose- dependent manner in the distal colon (DC), with the highest final SCFA levels observed upon supplementation of the highest concentration of POF. In terms of lactate production (Figure 1), a significant increase in lactate levels was observed in the PC in response to the different treatments, whereas lactate levels remained around the detection limit in the DC. In both colon regions, lactate levels were not signif- icantly different between OFO and POF dosed at a concentration of 1.4 g β -glucan/day. Furthermore, lactate levels increased in a dose-dependent manner in the PC for the differ- ent doses of POF, with the highest lactate levels being observed upon supplementing the highest dose of POF. With respect to markers of proteolytic fermentation (Figure 1), all treatments signifi- cantly increased ammonium and bCFA levels in response to the treatment in both colon regions, except for bCFA levels in the PC upon supplementation of POF at a concentration of 1.4g β -glucan/day ( p = 0.279). Overall, significantly lower ammonium and bCFA levels were observed in the PC for POF versus OFO at a concentration of 1.4 g β -glucan/day ( p < 0.0001). Furthermore, in the PC, supplementation of POF at the highest concentration tested resulted in the lowest production of bCFA and ammonium, indicating the presence of a dose-response effect. In the DC, an opposite trend was observed. 2.2. Altered Microbial Composition in Response to Oat Treatment in vitro To compare the prebiotic properties of the different test products and conditions, qPCR analysis of specific health-related groups ( Bifidobacterium spp. and Lactobacillus spp.) was performed (Table 1). First, luminal Lactobacillus levels increased significantly in both colon regions upon treatment with the different test products. Overall, the strongest increase was observed upon supplementation of POF at a concentration of 1.4 g β -glucan/day, resulting in significantly higher Lactobacillus levels as compared to the other test conditions (only POF at a concentration of 1.0 g β -glucan/day resulted in similar increases in the luminal DC). Similar effects were observed for Bifidobacterium levels, which significantly increased in the luminal environment of both colon regions upon treatment with all the different test products. It was noted that OFO more strongly stimulated Bifidobacterium levels than POF at a concentration of 1.4 g β -glucan/day in the PC. Overall, effects on mucosal microbes (Table 1) were similar to the changes reported for the luminal microbiota, even though less pronounced, showing that the test products were able to stimulate the luminal and the mucosal levels of bifidobacteria and lactobacilli.
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