Bioavailability of dietary polyphenols and plant bioactives in functional foods: insights and limitations from in vitro digestion models.

This review provides a comprehensive evaluation of how bioactive compounds within plant- and animal-derived food matrices interact with human physiology and metabolic pathways, with a particular focus on secondary metabolites synthesized or transformed via microbial pathways. The manuscript covers a diverse range of lipophilic and hydrophilic bioactive molecules, critically analysing these components from biological and technological perspectives. From a processing perspective, the mechanisms by which fermentation enhances antioxidant capacity by converting complex molecular structures into highly active aglycone forms are detailed. Concurrently, from an engineering perspective, the efficiency of nanoliposomes, solid lipid nanoparticles (SLNP), and biopolymeric carrier systems is assessed. Rather than claiming that encapsulation technologies can entirely overcome bioavailability limitations, this review critically assesses their potential to improve the stability, bioaccessibility and targeted release of sensitive components during gastrointestinal transit. Ultimately, by bridging microbial biotransformation with advanced delivery systems, this study offers a unified framework for optimizing the bioaccessibility of complex dietary compounds under simulated gastrointestinal conditions.