Chemical Fate of Polyphenols in Food Systems: Processing-Induced Modifications, Matrix Effects, and Implications for Bioaccessibility

Polyphenols are bioactive compounds abundant in plant-based foods, contributing to antioxidant, anti-inflammatory, and antimicrobial effects. Their stability, bioaccessibility, and functional potential are influenced by chemical structure, food matrix composition, and processing. Thermal, non-thermal, and fermentation-based treatments can either degrade sensitive polyphenols or enhance extractability and biological activity, depending on the matrix. Interactions with proteins, polysaccharides, and lipids modulate release during digestion, with bound or complexed forms often exhibiting delayed bioaccessibility and colonic microbial transformation. Accurate characterization relies on analytical methods ranging from spectrophotometry to HPLC–MS/MS, NMR, and metabolomics, yet methodological limitations can obscure functional content. This review integrates current knowledge on polyphenol chemistry, processing effects, matrix interactions, bioaccessibility, and analytical approaches, highlighting practical implications for functional food development and research gaps for future studies.