Degradation of ethyl carbamate by Lichtheimia ramosa EC-2 from Baijiu Daqu: Optimization, metabolites, and key enzymes.

چکیده اصلی

Ethyl carbamate (EC), a carcinogenic contaminant widely found in fermented foods, poses significant public health risks. Here, EC formation and degradation during fermentation using two types of Daqu, screened for high-efficiency EC-degrading strains, characterized their degradation mechanisms, and evaluated their enzymatic and fermentation applications were investigated. Sichuan Baijiu Daqu produced substantially less EC than Putong Daqu under both urea-present and urea-absent conditions, supported by more favorable pH, organic acid profiles, and microbial functional diversity, and it generated richer flavor compounds such as higher alcohols and esters. A fungal isolate, designated EC-2 and identified as Lichtheimia ramosa through morphology and ITS sequencing, degraded 42.29% of EC (5 g·L-1, pH 7) within 7 days and up to 59.98% under optimized conditions. Integrated transcriptomic and metabolomic analyses demonstrated that EC-2 enhanced stress tolerance via antioxidant enzyme induction and redirected carbon metabolism toward acetyl-CoA synthesis by upregulating pathways including β-alanine metabolism, fatty acid degradation, and tryptophan metabolism. These shifts coordinated a dynamic, acetyl-CoA-centered carbon flux and regulated the function of microbial community by strengthening carbon and nitrogen cycling while suppressing arginine-derived EC precursor formation, establishing a positive feedback loop of "EC degradation-functional enhancement." EC-2 also secreted a novel amidase, TR3551 (Kcat/Km = 79.6 mM-1 min-1), which degraded 18.95% of EC within 6 h and remained stable at 50 °C with tolerance to 20% ethanol. These findings provided promising fermentation additives and enzymatic tools for mitigating EC in Baijiu production.

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