Antilisterial activity of broccoli stems (Brassica oleracea) by flow cytometry

Studies have demonstrated the presence of antimicrobial compounds in vegetal species. However, natural components can be found not only in raw materials, but also in agro-industrial wastes. Their reuse as source of natural preservatives in food and beverage industry can promote sustainable practices since environmental risks caused by its discard are reduced. The antimicrobial activity of broccoli stems (Brassica oleracea) aqueous extracts (1:20 w/v) against Listeria monocytogenes was evaluated by detection of Minimal Inhibition Concentration (MIC) and flow cytometry analysis. The chemical composition of major compounds was detected by Gas Chromatography with Mass Spectrometry (CG-MS). Broccoli stems extract showed antimicrobial activity against L. monocytogenes, which MIC was 102.4 mg/mL. Analysis by CG-MS allowed the identification of organic acids, as ascorbic and malic acids, and phenolic compounds, as sinapinic, ferulic and caffeic acids. The use of flow cytometry to evaluate the antimicrobial activity of the extracts was very suitable, enabling to infer their action mechanisms. In face of the difficulty to avoid the food contamination by this pathogen, the study of vegetal residues as source of natural preservatives in food and beverage industry is very promising.