Heat-inactivated probiotic-fermented tamarind pulp alleviates constipation by modulating gut tryptophan catabolism and the AhR NLRP3 axis

INTRODUCTION: Constipation is a common gastrointestinal disorder with gut dysbiosis, and existing laxatives often have limitations, necessitating the development of safer and more effective nutritional interventions. OBJECTIVE: This study aimed to investigate the alleviating effects and potential mechanisms of probiotic-fermented tamarind pulp (FTP) on loperamide-induced constipation in mice. METHODS: A constipated mouse model was established and treated with low and high-dose FTP (LD‑FTP and HD‑FTP). Assessments included gastrointestinal transit, histopathology, serum neurotransmitters/inflammatory factors, gut microbiota (16S rRNA amplicon sequencing), functional predictions generated using PICRUSt2, and fecal metabolomics (LC-MS). RESULTS: FTP dose-dependently alleviated loperamide‑induced constipation. Compared with the model group, HD‑FTP increased small intestinal transit rate by 57.2% (to 92.95%, p < 0.001) and fecal water content by 65.9% (to 70.52%, p < 0.001), both effects superior to the positive control bisacodyl. HD‑FTP also reduced serum IL‑6, IL‑1β, and TNF‑α by 60.0%, 43.5%, and 45.4%, respectively (all p < 0.001), and elevated total short-chain fatty acids (SCFAs) by 107.4% (p < 0.001). FTP exhibited significantly superior constipation‑alleviating efficacy compared to unfermented tamarind pulp (UFTP). FTP also increased microbial richness, enriched potentially beneficial SCFA-producing taxa, and restored microbial metabolic pathways associated with SCFA biosynthesis. Notably, fermentation enhanced tryptophan metabolism toward indole and serotonin pathways, which correlated with increased aryl hydrocarbon receptor (AhR) activation and reduced NLRP3 inflammasome signaling in the colon. CONCLUSION: FTP effectively alleviated constipation by improving intestinal function, reducing inflammation, and remodeling the gut microbiota-metabolite axis. Mechanistically, fermentation-driven tryptophan catabolism and quercetin biotransformation converge on the AhR-NLRP3 axis. These findings highlight FTP as a superior nutritional strategy over UFTP.