The interplay between antimicrobial activity and reactivity of isothiocyanates
2020
Andini, Silvia | Araya-Cloutier, Carla | Waardenburg, Leonie | Besten, den, Heidy M.W. | Vincken, Jean Paul
This study aimed to determine antimicrobial activity (minimum inhibitory concentration, MIC; minimum bactericidal/fungicidal concentration, MBC/MFC) of novel ITCs against food spoilage and pathogenic Gram<sup>–</sup> bacteria, Gram<sup>+</sup> bacteria, and fungi. The activity of the long-chain (C9) 9-(methylthio)nonyl ITC (9-MTITC), 9-(methylsulfinyl)nonyl ITC (9-MSITC), and 9-(methylsulfonyl)nonyl ITC (9-MSoITC) was determined for the first time. Due to the electrophilicity of ITCs, the activity of ITCs was evaluated in nucleophile-rich and nucleophile-poor growth media. ITCs reacted via conjugation with components in a nucleophile-rich growth medium at a rate of 39–141 μmol L<sup>−1</sup> h<sup>−1</sup>, depending on their side chain configuration and temperature. The reaction rates were lowered by a factor of 2–21 when using nucleophile-poor growth media. Consequently, the activity of ITCs was generally improved, with MSITC and MSoITC being the most positively affected (activity increased by a factor of > 4). 9-MSITC and 9-MSoITC had good activity (MIC ≤ 25 μg/mL) against Gram<sup>+</sup> bacteria and fungi. The short-chained (C3) analogues had good activity against Gram<sup>+</sup> bacteria and Gram<sup>–</sup> bacteria. The highest bactericidal/fungicidal activity was obtained for 9-MSITC and 9-MSoITC (MBC/MFC 17.5–25 μg/mL). Overall, MSITC and MSoITC might be potential new natural food preservatives, but their reactivity with food matrix components should be considered.
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