Black tea-processed Toona sinensis leaves alleviate DSS-induced ulcerative colitis in mice by enriching flavonoids and modulating gut microbiota.

Ulcerative colitis (UC) is a chronic inflammatory bowel disease for which safe dietary interventions remain limited. Toona sinensis leaves, a traditional medicinal food rich in polyphenols and flavonoids, exhibit anti-inflammatory potential; however, how processing techniques modulate their functional nutrition and anti-colitis activity is poorly understood. In the present study, we compared hot air-dried T. sinensis leaves (TL) and black tea-processed leaf tea (TLT) in a mouse model of DSS-induced colitis (n = 8 per group) at a dose of 20 mg/ml (approximately 3.33 g/kg body weight per day) via drinking water, with Keemun black tea (BT) as a positive plant-based dietary control. Both TL and TLT significantly mitigated DSS-induced colitis; notably, TLT showed significantly stronger efficacy than TL (p < 0.05) and exhibited efficacy comparable to BT. TLT restored colonic histopathology, upregulated tight junction proteins (ZO-1 and Occludin), and suppressed pro-inflammatory cytokines (IL-1β and TNF-α). Black tea processing of T. sinensis leaves increased bioactive components including total flavonoids and polyphenols, which strongly correlated with protective indicators (|r| > 0.6, p < 0.01). TLT also restored gut microbial diversity and enriched SCFA-producing genera such as Akkermansia, Odoribacter. Untargeted metabolomics identified 23 key anti-inflammatory metabolites including kaempferol and quercetin glycosides. Multi-omics integration revealed significant correlations among metabolites, gut microbiota, and protective endpoints. Collectively, these results demonstrate that dietary intervention with black tea-processed T. sinensis leaves alleviates UC primarily by increasing flavonoid content, protecting intestinal barrier integrity, and remodeling gut microbiota homeostasis. This study provides a theoretical basis for the value-added utilization of T. sinensis leaves as a functional food for dietary intervention against inflammatory bowel disease.