Antioxidants in Plant-Based Food Matrices: From Structure-Activity and Degradation Kinetics to Formulation Design

Plant-based antioxidants are widely incorporated into foods to retard oxidative deterioration and to deliver health-related benefits. Yet, their in-product and in vivo performance frequently diverges from predictions based on solution-phase chemical assays, because matrix interactions, processing history, and host metabolism reshape both stability and bioactivity. This review integrates molecular mechanisms, structure-activity relationships (SARs), and degradation kinetics with food-matrix and human-relevance considerations to explain when, where, and how plant-based antioxidants act. Evidence is collated across polyphenols, carotenoids, tocopherols and tocotrienols, and selected alkaloids, linking hydrogen-atom, single-electron, and proton-coupled transfer pathways. Together, with those evidences, transition-metal chelation, interactions with proteins and polysaccharides, interfacial partitioning in emulsions, and metal-catalyzed oxidation are discussed. The influence of conventional and emerging processing, storage, and delivery systems (Pickering and double emulsions, spray drying/chilling, complex coacervation, ionic gelation) on antioxidant stability, localization, and bioaccessibility is also examined. Across systems, efficacy is governed less by intrinsic reactivity or nominal polarity than by effective interfacial concentration, partitioning behavior, and metal management. Encapsulation, when matched to matrix and process, improves antioxidant retention. Combinations of antioxidants may act cooperatively under one set of conditions and become antagonistic, or even pro-oxidant, under high oxygen availability or at suboptimal molar ratios. In this review, solution-phase rankings (DPPH, ABTS, FRAP, ORAC) are interpreted as descriptors of intrinsic reactivity. They cannot, on their own, predict performance in real food matrices or the post-digestion metabolite pool reaching systemic circulation. Effective use of plant antioxidants in foods therefore requires that formulation choices be informed by interfacial kinetics, food-component interactions during digestion, gut-microbiota metabotypes, and biomarker-validated estimates of dietary intake.