Abstract:
Tannins represent a heterogeneous group of high-molecular-weight polyphenols that are
ubiquitous among plant families, especially in cereals, as well as in many fruits and vegetables.
Hydrolysable and condensed tannins, in addition to phlorotannins from marine algae, are the
main classes of these bioactive compounds. Despite their low bioavailability, tannins have many
beneficial pharmacological effects, such as anti-inflammatory, antioxidant, antidiabetic, anticancer,
and cardioprotective effects. Microbiota-mediated hydrolysis of tannins produces highly bioaccessible
metabolites, which have been extensively studied and account for most of the health effects attributed
to tannins. This review article summarises the effect of the human microbiota on the metabolism
of different tannin groups and the expected health benefits that may be induced by such mutual
interactions. Microbial metabolism of tannins yields highly bioaccessible microbial metabolites
that account for most of the systemic effects of tannins. This article also uses explainable artificial
intelligence to define the molecular signatures of gut-biotransformed tannin metabolites that are
correlated with chemical and biological activity. An understanding of microbiota–tannin interactions,
tannin metabolism-related phenotypes (metabotypes) and chemical tannin-metabolites motifs is
of great importance for harnessing the biological effects of tannins for drug discovery and other
health benefits.
