Insight into the antibacterial property of chitosan nanoparticles against Escherichia coli and Salmonella Typhimurium and their application as vegetable wash disinfectant

Abstract

This study investigated the influence of molecular weight (Mw) and particle size characteristics on the antibacterial property of chitosan nanoparticles (CNs) for application as a vegetable wash disinfectant. Formulations prepared from two different Mw of chitosan resulted in three different size ranges of CNs; 300–400 nm (i.e. LS and HS), 500–600 nm (i.e. LL) and 700–800 nm (i.e. HL). A time-dependent antibacterial assay against Escherichia coli was used as a model and showed that CNs with smaller size (i.e. LS and HS) produced from either low or high Mw of chitosan were effective antibacterial agents, leading to an approximate 2 log reduction in the number of bacteria within 12 h. Once demonstrated to have good antibacterial activity, all CNs were formulated as vegetable wash disinfectants in citric acid and evaluated using an in vitro inactivation assay with E. coli and a pathogenic bacterium (Salmonella Typhimurium), known to be possible contaminates on fresh vegetables. The results showed that the smallest CNs could significantly reduce the number of E. coli at 3.38 log CFU/mL within 15 min. On the other hand, the number of S. Typhimurium was significantly reduced 2.83 log CFU/mL within 15 min using the largest CNs. Finally, the formulations with the highest antibacterial activity were selected to evaluate their ability to reduce the number of inoculated bacteria under simulated vegetable washing condition on fresh lettuce. The wash solution containing CNs was found to be the most effective in killing more than a 1 log reduction of both inoculated E. coli and S. Typhimurium populations, suggesting their potential use as effective disinfectant in washing fresh vegetables.