Prebiotic dietary fiber supplements are commonly consumed to help meet fiber recommendations and improve gastrointestinal health by stimulating beneficial bacteria and the production of short-chain fatty acids (SCFAs), molecules beneficial to host health. The objective of this research project was to compare potential prebiotic effects and fermentability of five commonly consumed fibers using an in vitro fermentation system measuring changes in fecal microbiota, total gas production and formation of common SCFAs. Fecal donations were collected from three healthy volunteers. Materials analyzed included: pure beta-glucan, Oatwell (commercially available oat-bran containing 22% oat β-glucan), xylooligosaccharides (XOS), WholeFiber (dried chicory root containing inulin, pectin, and hemi/celluloses), and pure inulin. Oatwell had the highest production of propionate at 12 h (4.76 μmol/mL) compared to inulin, WholeFiber and XOS samples (p < 0.03). Oatwell’s effect was similar to those of the pure beta-glucan samples, both samples promoted the highest mean propionate production at 24 h. XOS resulted in a significant increase in the genus Bifidobacterium after 24 h of fermentation (0 h:0.67 OTUs (operational taxonomic unit); 24 h:5.22 OTUs; p = 0.038). Inulin and WholeFiber increased the beneficial genus Collinsella, consistent with findings in clinical studies. All analyzed compounds were fermentable and promoted the formation of beneficial SCFAs.

Resistant starches are non-digestible starches that are fermented in the colon by microbiota. These carbohydrates are prebiotic and can be beneficial to consumer health. Many types of resistant starch exist with varying physical properties that may result in differences in fermentability. The objective of this research project was to compare potential prebiotic effects and fermentability of four novel resistant starches using an in vitro fermentation system and measuring changes in total gas production, pH, and formation of SCFAs (short chain fatty acids). Fecal donations were collected from seven healthy volunteers. Four novel resistant starches, modified potato starch (MPS), modified tapioca starch (MTS), and modified maize starches (MMS-1 and MMS-2), were analyzed and compared to polydextrose and short chain fructooligosaccharides (FOS) as controls. After twenty-four hours of fermentation, MPS and MTS responded similarly in gas production (74 mL; 70.6 mL respectively), pH (5.93; 5.93 respectively), and SCFA production (Acetate: 115; 124, Propionate: 21; 26, Butyrate: 29; 31 μmol/mL respectively). While MMS-1 had similar gas production and individual SCFA production, the pH was significantly higher (6.06). The fermentation of MMS-2 produced the least amount of gas (22 mL), with a higher pH (6.34), and lower acetate production (78.4 μmol/mL). All analyzed compounds were fermentable and promoted the formation of beneficial SCFAs.

Scientific research demonstrates that two indigenous gut bacteria, Lactobacillus and Bifidobacterium can contribute to human health. Although these bacteria can be consumed as probiotics, they can also be produced in the gut by bacteria, and are then called prebiotics. The primary objective of this in vitro study was to quantitatively analyze at the genus level how two dietary fibers, wheat dextrin (WD) and partially hydrolyzed guar gum (PHGG) changed the levels of these two gut bacteria at 12 and 24 h, via real time qualitative polymerase chain reaction (qPCR). Secondary objectives were changes in fecal pH, short chain fatty acids (SCFAs) and total gas volume produced. At 12 h WD was more bifidogenic (9.50 CFU log₁₀/mL) than PHGG (9.30 CFU log₁₀/mL) (p = 0.052), and also at 24 h WD (9.41 CFU log₁₀/mL) compared with PHGG (9.27 CFU log₁₀/mL) (p = 0.043). WD produced less total SCFAs at both 12 and 24 h than PHGG, and produced significantly lower amounts of gas at 12 and 24 h (p < 0.001). Both PHGG and WD also promoted growth of Lactobacilli when measured at 12 and 24 h compared with the 0 h analysis, indicating that both fibers are lactogenic. These results demonstrate the prebiotic effect of WD and PHGG. Based on fermentation kinetics, PHGG is more rapidly fermented than WD, and both fibers show prebiotic effects as early as 12 h.