Microgreen Roots as a Promising Plant-Derived Side Stream: Bioactive Compounds, Analytical Approaches, and Valorization Pathways

This narrative review critically examines microgreen roots as an understudied side-stream fraction generated during the production of fresh functional foods. It focuses on the potential use of roots from different microgreen species as sources of phenolic compounds, vitamins, pigments, glucosinolates, isothiocyanates, organic acids, and other low-molecular-weight metabolites. A supplementary targeted literature search identified only six studies directly investigating the chemical or biochemical characteristics of microgreen roots, of which only one examined extractable organic bioactive compounds. Accordingly, findings from harvested microgreens, sprouts, mature roots, and root exudates are treated as indirect comparative evidence rather than proof of root-specific chemical composition. The effects of growing media, light, mineral nutrition, and stress on biomass production and the accumulation of bioactive compounds are discussed separately, together with methods for obtaining aqueous and hydroalcoholic extracts.