In vitro FERMENTATION OF Bifidobacterium lactis-BASED SYNBIOTICS BY HUMAN FAECAL BACTERIA

Synbiotics are recognized means of modulating gut microbiota composition and activities; however, the development of effective synbiotic combinations remains a challenging issue. This study aimed to investigate the in vitro potential fermentation properties of two synbiotic mixtures on human faecal bacteria of healthy humans. The selected synbiotics [fructooligosaccharides (FOS) (1% w/v) combined with Bifidobacterium lactis BB12 or Bifidobacterium lactis HN019 (106 colony-forming units (CFU)/mL)] were added to 48-hours pH-controlled anaerobic batch cultures reflective of the distal region of the human large intestine. Maltodextrin, FOS with a degree of polymerization < 10 and the probiotic strains were also tested alone. Effects upon major groups of the microbiota and levels of short-chain fatty acids (SCFA) were assessed over 48 hours. Quantitative analysis of bacterial populations revealed that there was a significant increase in bifidobacteria numbers in vessels with maltodextrin, FOS and the synbiotic mixtures compared to the negative control and probiotics. An increase in Atopobium cluster and Clostridium coccoides-Eubacterium rectale group was also observed with FOS and maltodextrin fermentation, respectively. Trends to increases in maltodextrin, FOS and both synbiotic vessels were observed for total bacterial levels; however, no significant changes were found. Additionally, vessels containing carbohydrates promoted shifts in the production of SCFA. Fermentation of maltodextrin, FOS and synbiotic mixtures at all time points resulted in a greater production of acetate and butyrate compared to a negative control, whereas the concentrations of iso-valerate were lower in these three treatments. Propionate was increased in all vessels compared with 0 h; however, because of high variations between the volunteers, the increase of this SCFA with maltodextrin, FOS and synbiotic fermentation was not significant compared to the negative control. Lactate concentrations were higher only after 8h of fermentation in the vessels containing carbohydrates. In conclusion, the synbiotic mixtures was not more effective than FOS or probiotic alone to modulate the human faecal bacteria. B. lactis strains fermentation had no significant effect upon relevant microbial populations and SCFA, whereas maltodextrin may exert a prebiotic effect because of the increase in bifidobacteria and Eubacterium rectale numbers with the subsequent increase in butyrate concentrations, giving an added possible health.