Plant In Vitro Production of Phenolic Bioactives: Molecular Regulation, Functional Equivalence and Translational Challenges

Phenolic compounds are important plant secondary metabolites with broad biological activity and potential applications in pharmaceutical, food, cosmetic, nutraceutical, and veterinary sectors. Conventional production from field-grown plants is limited by environmental variability, seasonality, and difficulties in standardizing metabolite composition. Plant in vitro cultures provide controlled systems for modulating secondary metabolism and producing phenolic compounds under defined conditions. This review summarizes current advances in plant in vitro platforms for phenolic production and discusses regulation through elicitation, metabolic modulation, molecular approaches, and bioreactor cultivation. The distinctive focus of this review is the critical evaluation of how culture type, production stability, metabolite composition, and structural variation affect biological performance and functional equivalence. Current evidence indicates that increased metabolite accumulation alone does not ensure preserved biological properties or translational applicability. Functional equivalence is therefore considered as a framework integrating chemical profiling, batch-to-batch reproducibility, biological validation, bioavailability, and application-oriented evaluation of in vitro-derived phenolics. Future progress will depend not only on increasing yield but also on achieving stable production, predictable composition, reproducible biological performance, and translational reliability.