Abstract/Summary

Health benefits from consuming herbs/spices are associated with their polyphenol-rich content, however the exact method that confers these advantages is not fully known. Prebiotics are substrates selectively utilised by host microorganisms conferring a benefit to the host. They positively modulate gut microbiota, promote health and can include polyphenols. Hence, polyphenol-rich herbs/spices may contain prebiotic-capacity. As few human studies feature impact of herbs/spices on human-gut microbiota and limited confirmed prebiotics exist, discovery of natural substrates with prebiotic-capacity warrants further investigation. This work investigated the impact of select herbs/spices on human-gut microbiota through in vitro and in vivo methods. Nine whole herbs/spices were screened for prebiotic potential with pH-controlled, stirred anaerobic batch culture systems simulating the distal colon. Ginger and triphala showed continuous, but non-significant growth of Bifidobacterium spp. Significant changes in total bacteria were seen with ginger, peppermint and Bacteroidaceae-Prevotellaceae (BAC) groups for chamomile which prompted significant increases in acetate, propionate and butyrate short-chain fatty-acids (SCFA). Three-stage continuous-flow systems which simulated proximal (V1), transverse (V2) and distal (V3) regions of the human colon, indicated areas partial to SCFA production with ginger, liquorice, triphala and ginger-liquorice treatment. Ginger significantly reduced Clostridial cluster IX, while triphala decreased BAC. Ginger increased butyrate and propionate in most areas. Liquorice and ginger-liquorice decreased butyrate. Triphala increased propionate in V2. Triphala was then trialled in a human intervention-study to further assess prebiotic-potential. Gut composition was characterised with fluorescent in-situ hybridisation and amplicon sequencing. Biomarkers of health and inflammation were monitored 28 days. Triphala consumption significantly reduced Desulfobacterota, improved stool consistency and decreased diastolic blood pressure. In conclusion, herbs/spices investigated here impacted human gut microbiota. Ginger and triphala showed promising prebiotic-capacity in modulating gut microbiota and should receive further investigation. Triphala may repress pathogenic bacteria and support metabolic health, however larger human studies are needed to clarify full prebiotic-capacity and health implications.