Tea Microbiomes and Metabolic Transformations From Fresh Leaf to Fermentation and Gut: Implications for Quality and...

Microbiomes influence tea quality, safety, and health from production to consumption, yet most studies and reviews examine individual stages. This review uses the Tea Plant-Fermentation-Gut Continuum to assess cross-stage microbial and metabolic connectivity, not as an established transmission chain. It separates microbial origin and persistence from processing-associated chemical transformation and host responses. At the leaf-to-processing interface, phyllosphere and endophytic communities may contribute to the processing microbial pool, but taxonomic overlap does not demonstrate directional transmission, and strain-level persistence remains unproven. During processing, plant enzymes and microbial activities shape tea chemistry differently across tea types, affecting pigment and aroma development. At the processing-to-gut interface, current evidence mainly supports chemical and metabolic continuity: tea- and fermentation-derived compounds reach the gut and are metabolized by resident microbiota, whereas evidence that fermentation-associated microorganisms survive, persist, or colonize the gut remains insufficient. These metabolites are linked to FXR-FGF15, AMPK, and AhR signaling and to metabolic, anti-inflammatory, and neuroprotective effects, mostly in preclinical models; human evidence remains limited. Together, the evidence does not support an uninterrupted microbial transmission pathway across these stages. Key gaps remain in microbial origin, persistence, activity, causality, and host relevance. Shared taxa may reflect persistence, environmental acquisition, or compositional overlap rather than direct transmission; tea type, cultivar, processing, dose, and host microbiota limit generalization. Strain-resolved tracking, controlled experiments, functional omics, and metabolic tracing are needed to distinguish association from persistence, activity, and causal function. Addressing these gaps will support evidence-based tea processing, precision fermentation, and microbiome-informed nutrition.