Effect of chitosan and nanochitosan on reducing acid tolerance of Listeria monocytogenes

Chitosan, a natural nontoxic biopolymer is derived by deacetylation of chitin, has received considerable attention for its commercial applications in the food industry. In the present study, the ability of chitosan and chitosan nanoparticles to sensitize Listeria monocytogenes to low pH was assessed. To achieve this purpose, cells of L. monocytogenes were exposed to pH 4 and 5 adjusted by adding hydrochloric and acetic, acids into TSB, in the presence of 0.0, 0.05, 0.1 and 0.2 % chitosan, for one hour. Chitosan did not show antibacterial activity at pH 5, while 0.2 % nanochitosan made L. monocytogenes cells more sensitive to this pH. However, antibacterial activity of both chitosan and nanochitosan were higher at pH 4, where 0.2 % chitosan and 0.1 and 0.2 % nanochitosan made significant reductions in viable population of this bacterium in comparison with the control and the lower concentrations (p<0.05). Furthermore, results showed that, in the presence of both the acids, the effect of nanochitosan on reduction of the acid tolerance of the bacterium was significantly more than chitosan (p<0.05). Results of the fluorescent staining demonstrated that chitosan and nanochitosan exerted their effect by disrupting the cellular membrane of the cells and in the same concentrations, nanochitosan had higher effect than chitosan (p<0.05).