Microbial Bioprocessing of Plant-Based Food Matrices: From Conventional Analysis to In Situ Characterization of Cell Wall-Bound Phenolic Release

The release mechanisms of bound phenolics (BPs) from plant cell walls during bioprocessing, such as microbial fermentation, are highly dynamic and exhibit microscopic spatial selectivity. While conventional chemical analysis can provide macroscopic data on BPs release, it fails to reveal the microscopic spatial heterogeneity and causal relationships underlying the cell wall degradation process. This review examines both conventional extraction-based analytical methods and emerging in situ imaging technologies, such as Raman/FTIR spectroscopy, confocal laser scanning microscopy, immunofluorescence, and mass spectrometry imaging, highlighting their complementary roles and current technical bottlenecks in characterizing BPs release and cell wall degradation. Furthermore, a unified multiscale, multimodal framework is proposed, integrating high-resolution imaging, dynamic fluorescence probes, multidimensional spectroscopy, and machine-learning-assisted data fusion. This holistic characterization strategy elucidates the precise mechanisms governing phenolic release, providing a theoretical basis to guide the targeted enrichment of BPs and advance the efficient utilization of plant biomass and agricultural residues.