Antibacterial potential of black seed oil and its nanoemulsion against Listeria monocytogenes and Salmonella Typhimurium in yoghurt

Abstract

The current study aimed to evaluate the antibacterial efficacy of black seed oil (BSO) and its nanoemulsion (BSO-NE) against two foodborne pathogens, Listeria monocytogenes and Salmonella Typhimurium, during the processing and storage of yoghurt. Additionally, the sensory properties of the resulting yoghurt were assessed. Firstly, BSO-NE was prepared and characterized using zeta-sizer and Transmission electron microscopy (TEM). Then, the antibacterial activity and minimum inhibitory concentration (MIC) were determined via a resazurin-based microtiter dilution assay. Fresh buffalo’s milk was inoculated with L. monocytogenes and Salmonella Typhimurium (1×10⁵ CFU/ml) with the addition of either BSO or BSO-NE. The inoculated milk was then used for yoghurt making. The organoleptic properties and bacterial load of the obtained yoghurt were evaluated during storage in comparison to a control group. This study elucidated that BSO can be successfully produced in a nanoemulsion form, exhibiting acceptable particle size, stability, and morphology. The results demonstrated a strong antibacterial activity of BSO-NE (3.125 mg/mL) against both L. monocytogenes and Salmonella Typhimurium compared to the control and pure oil groups. Notably, complete eradication of L. monocytogenes and Salmonella Typhimurium was observed in yoghurt formulated with BSO-NE on the 8th day of storage. Interestingly, the antibacterial effect of BSO and BSO-NE on Salmonella Typhimurium was approximately similar throughout the experiment. Moreover, the results indicated that the addition of BSO-NE to yoghurt enhanced its organoleptic properties. Overall, these findings suggest that yoghurt can be fortified with BSO-NE to prevent bacterial contamination by L. monocytogenes and Salmonella Typhimurium in the dairy industry.