DDA (degree of deacetylation) and pH-dependent antibacterial properties of chitin nanofibers against Escherichia coli

Abstract

Partially deacetylated chitin nanofibers (PD-ChNFs) with different degrees of deacetylation (DDA: 16%, 29%, 38%, 47%) that represented different amino group contents were prepared by partial deacetylation treatment under the desired conditions and the subsequent mechanical treatment. Higher concentration of NaOH or treating for longer time will result a higher DDA. An equation for the calculation of the cationic amino group contents of PD-ChNFs was derived for the evaluation of the antibacterial effect of chitin nanofibers as a function of the DDA and pH. The amount of cationic amino groups was correlated with a higher DDA of PD-ChNFs and a lower pH. Furthermore, the antibacterial property of chitin nanofibers depended strongly on the pH and secondary on DDA that indicated better antibacterial properties were obtained with a higher amount of cationic amino groups. When the pH was higher than 7, there are almost no cationic amino groups and no obvious antibacterial effect was observed. For a pH lower than 5, almost all the amino groups were cationized and the growth of E. coli was effectively inhibited. And if pH was between 5 and 7, PD-ChNFs possessed higher DDA at lower pH carry more cationic amino group and show better antibacterial activity. Besides, the chitin nanofibers with higher amino group contents with a higher DDA prepared by more caustic deacetylation treatment tended to have smaller size, which might be another reason for the better antibacterial effect.