QSAR-based physicochemical properties of isothiocyanate antimicrobials against gram-negative and gram-positive bacteria

Isothiocyanates (ITCs) derived from Brassicaceae are potential food preservatives. Their antimicrobial ac-tivity is strongly influenced by their subclass and side chain. This is the first quantitative structure-activity relationships (QSAR) study of ITCs as antibacterials. Twenty-six ITCs covering 9 subclasses were tested against Escherichia coli and Bacillus cereus. Minimum inhibitory concentration (MIC) and growth inhibitory response (GIR) were determined and used to develop QSAR models. MIC of the most active ITCs was 6.3–9.4 μg/mL. The QSAR models were validated with leave-one-out cross validation. The proposed models had a good fit (R²_adj 0.86–0.93) and high internal predictive power (Q²_adj 0.80–0.89). Partial charge, polarity, reactivity, and shape of ITCs were key physicochemical properties underlying antibacterial activity of ITCs. Furthermore, ITC compositions and antibacterial activity of Sinapis alba, Brassica napus, B. juncea, B. oleracea, and Camelina sativa extracts were determined, after myrosinase treatment. B. oleracea ITC-rich extract showed promising activity (MIC 750–1000 μg/mL) against both bacteria. C. sativa ITC-rich extract showed promising activity (MIC 188 μg/mL) against B. cereus. The QSAR models successfully predicted activity of the extracts based on ITC compositions. The models are useful to predict antibacterial activity of new ITCs and ITC-rich mixtures. Brassicaceae ITC-rich extracts are promising natural food preservatives.