Precision Fermentation of Polygonatum cyrtonema Hua Using Lactobacillus plantarum P9: Deciphering the Critical Quality Control Window via Time-Resolved Metabolomics and Intelligent Sensory Analysis

Polygonatum cyrtonema Hua ( P. cyrtonema ) serves as a promising functional food ingredient; however, its broader application is limited by suboptimal raw sensory quality and the inefficiency of traditional repeated steaming methods. This study employed a controlled fermentation strategy using Lactobacillus plantarum P9 (hereafter, P9) to assess the time-dependent evolution of the sensory quality and chemical composition of P. cyrtonema . Over a 60-h fermentation period, dynamic changes in microstructure, non-volatile metabolites, volatile compounds and sensory characteristics were monitored using UPLC-Q-TOF-MS/MS, HS-GC-MS, e-nose, e-tongue and human sensory analyses. Fermentation progressively restructured the plant matrix and modified both volatile and non-volatile profiles, with multivariate analysis identifying 30 h as the critical quality inflection point. At this point, favourable aroma-active compounds, particularly 2,6-dimethylpyrazine and 3-methylbutanal, were significantly enriched, correlating with enhancements in aroma, taste, texture and overall acceptability. Concurrently, the levels of several fermentation-responsive non-volatile markers, including salicylic acid and flavonoid-related compounds, were elevated. In contrast, prolonged fermentation beyond 30 h led to the accumulation of sulphur-related off-notes, exemplified by the accumulation of carbonyl sulphide, along with a decline in sensory acceptance. Seven candidate process-monitoring markers were identified for endpoint determination. These findings suggest that P9 fermentation serves as a controllable alternative to conventional processing and provides an integrated chemical-sensory framework for the quality control of fermented P. cyrtonema -based functional food materials.