Antimicrobial activity of PIT-fabricated cinnamon oil nanoemulsions: Effect of surfactant concentration on morphology of foodborne pathogens

The impact of surfactant concentration (10 to 20 wt%) on the antimicrobial activity of cinnamon oil nanoemulsions formed by the phase inversion temperature (PIT) method was studied against a number of foodbome pathogens: Escherichia coli, Salmonella Typhimurium, Staphylococcus aureus and Vibrio parahaemolyticus. Minimum inhibitory concentration (MIC), dynamic time kill, and changes in bacteria morphology were determined. Increasing non-ionic surfactant (Tween.80) concentration from 10 to 20 wt% increased the MIC values of the nanoemulsions. However, dynamic time kill plots revealed that nanoemulsions with higher surfactant concentrations (15 and 20 wt%) led to faster or more prolonged inhibition of bacteria compared to those with lower concentration (10 wt%) or with bulk cinnamon oil. Morphological changes of the bacteria were more promoted for nanoemulsions containing higher surfactant concentrations as shown by field emission scanning electron microscopy (FE-SEM). The antimicrobial activity of the cinnamon oil nanoemulsions was attributed to their ability to disrupt bacterial cell wall structures and promote expulsion of internal cellular material.