Remodeling of phenolic compounds from celery pulp driven by Lactobacillus plantarum NCU116 fermentation: insights from omics, targeted quantification, and microstructural imaging

Celery ( Apium graveolens L . ) is rich in phenolic compounds, yet their transformation mechanisms during fermentation remain unclear. This study investigated the metabolic remodeling of phenolics in celery pulp fermented by Lactiplantibacillus plantarum NCU116 ( L. plantarum NCU116) using an integrated omics approach. Untargeted metabolomics, transcriptomics, targeted quantification, enzymatic assays, and structural imaging were employed. A total of 63 free and 29 bound phenolic compounds were identified. Notably, the levels of representative flavonoid glycosides, including apiin and graveobioside A, significantly decreased to 0.76 and 0.73 times their original levels, respectively, while 3′-methoxy apiin showed a slight decrease to 0.90 times. Transcriptomic analysis revealed upregulation of β-glucosidase genes ( bglB , bglH ), consistent with elevated enzyme activity. Confocal laser scanning microscope (CLSM) confirmed progressive cell wall depolymerization and reduced lignin autofluorescence, coinciding with the release of bound phenolics. These findings demonstrate that phenolic conversion in fermented celery is co-regulated by microbial enzymatic hydrolysis and structural remodeling of the plant matrix.