Diets supplemented with chickpea or its main oligosaccharide component raffinose modify faecal microbial composition in healthy adults

The effects of diets supplemented with either chickpea or its main oligosaccharide raffinose on the composition of the faecal microbial community were examined in 12 healthy adults (18-65 years) in a randomised crossover intervention study. Subjects consumed their usual diet supplemented with soups and desserts that were unfortified, or fortified with either 200 g/d of canned chickpeas or 5 g/d of raffinose for 3 week periods. Changes in faecal bacterial populations of subjects were examined using 16S rRNA-based terminal restriction fragment length polymorphisms (T-RFLP) and clone libraries generated from the diet pools. Classification of the clone libraries and T-RFLP analysis revealed that Faecalibacterium prausnitzii, reported to be an efficient butyrate producer and a highly metabolically active bacterium in the human intestinal microbiota, was more abundant in the raffinose diet and the chickpea diet compared to the control diet. However, no significant difference was observed in the faecal total short chain fatty acid concentration or in the levels of the components (butyrate, acetate and propionate) with the chickpea diet or the raffinose diet compared to the control diet. Bifidobacterium species were detected by T-RFLP in all three diet groups and quantitative real-time PCR (qPCR) analysis showed a marginal increase in 16S rRNA gene copies of Bifidobacterium with the raffinose diet compared to control (P>0.05). The number of individuals showing TRFs for the Clostridium histolyticum - Clostridum lituseburense groups, which include pathogenic bacteria species and putrefactive bacteria, were lower in the chickpea diet compared to the other two treatments. Diet appeared to affect colonisation by a high ammonia-producing bacterial isolate which was detected in 83%, 92% and 42% of individuals in the control, raffinose and chickpea groups, respectively. Our results indicate that chickpea and raffinose have the potential to modulate the intestinal microbial composition to promote intestinal health in humans.