Citral and linalool nanoemulsions: impact of synergism and ripening inhibitors on the stability and antibacterial activity against Listeria monocytogenes

The present work explored the influence of individual and combinations of citral and linalool along with different Ostwald ripening inhibitors on the nanoemulsion stability and their antibacterial activity against Listeria monocytogenes. Nine different nanoemulsions (N1-N9) containing individual or combinations of citral, linalool with or without ripening inhibitors (medium chain triglycerides, coconut oil, sesame oil and castor oil) were formulated with 5% Tween-80 using ultrasonic emulsification. N1 formulation containing 5% citral without ripening inhibitors showed the least mean droplet diameter of 20.44 nm. Addition of linalool with the citral nanoemulsions was found to have deleterious effect on the thermodynamic and kinetic stabilities. Incorporation of ripening inhibitors controlled the increase of droplet size and polydispersity index in N6-N9 during the 90 days storage period, but decreased their antibacterial activity. N8 formulation containing sesame oil as ripening inhibitor was found to be the best in controlling Ostwald ripening. N1 formulation which showed the best antibacterial activity (MIC 0.312%) was found to disrupt the bacterial membrane integrity. N1 formulation also showed a promising biofilm inhibition of 83.51%. Therefore, N1 formulation containing 5% citral could be recommended as an efficient disinfectant against food-borne pathogen Listeria monoctyogenes in food industry. Moreover, addition of sesame oil in the nanoemulsion formulation of citral or linalool could increase their stability.