Antimicrobial and antibiofilm effects of trans-cinnamic acid nanoemulsion and its potential application on lettuce

A stable low-energy spontaneous trans-cinnamic acid (trans-CA) nanoemulsion with a particle size of 46.7 ± 1 nm, polydispersity indice of 0.27 ± 0.01 was formulated. Antimicrobial effects of trans-CA nanoemulsion displayed minimum inhibitory concentration (MIC) of 0.78 mg/mL and minimum bactericidal concentration (MBC) of 3.13 mg/mL for Staphylococcus aureus while Salmonella typhimurium had MIC and MBC of 1.56 and 3.13 mg/mL, respectively. However, Pseudomonas aeruginosa showed an MIC and MBC of 3.13 and 6.25 mg/mL respectively. Biofilm formation inhibition showed that the concentrations of trans-CA nanoemulsion required to inhibit ≥50% biofilm formation by S. aureus, S. typhimurium and P. aeruginosa were 0.1, 0.2 and 0.39 mg/mL respectively. As for biofilm eradication, the concentrations required to eradicate ≥80% biofilm formed by S. aureus, S. typhimurium and P. aeruginosa were 0.78, 6.25 and 6.25 mg/mL, respectively. When applied to fresh-cut lettuce, nanoemulion displayed 65% reduction of aerobic mesophilic bacteria and 61% reduction of aerobic psychrophilic bacteria. These results demonstrated that trans-CA nanoemulsion has potential to be used in preservation and extension of fresh-cut lettuce shelf-life.