From Glucosinolate Content to Isothiocyanate Yield: Rethinking Brassica Functionality

Background/Objectives: Brassica vegetables are widely promoted as health-promoting foods, but their functional value is still commonly inferred from glucosinolate content alone. However, glucosinolates are biologically inactive precursors whose nutritional relevance depends on their conversion into bioactive hydrolysis products, particularly isothiocyanates (ITCs). This review aims to reconsider Brassica functionality through an ITC-yield-centered perspective rather than a precursor-content-based approach. Methods: This narrative review synthesizes current evidence on the biochemical, technological, gastrointestinal, and analytical determinants of glucosinolate hydrolysis and ITC formation. Particular attention is given to myrosinase activity, specifier proteins, pH, temperature, tissue disruption, food matrix effects, processing conditions, gastrointestinal transformation, inter-individual microbial variability, and the limitations of precursor-based interpretation. Results: The reviewed evidence indicates that similar glucosinolate profiles can result in markedly different levels of bioactive exposure depending on enzymatic activity, processing history, matrix context, and host-related factors. Therefore, precursor abundance alone is an unreliable surrogate for functional efficacy. Functional optimization should not aim at indiscriminate maximization of glucosinolate breakdown, but rather at selective promotion of beneficial ITC-forming pathways while limiting nitriles, epithionitriles, and goitrogenic products such as goitrin. Conversion efficiency emerges as a critical analytical bridge between glucosinolate abundance and food-level ITC formation, while subsequent bioaccessibility and host-related factors determine realized exposure. Conclusions: Brassica functionality could be more meaningfully evaluated through an ITC-yield-centered framework in which precursor abundance and conversion efficiency determine food-level ITC formation, while subsequent bioaccessibility and host-related factors shape realized exposure. This approach provides an integrative basis for breeding, food processing, product development, dietary guidance, and future evaluation of Brassica foods.