Biocatalyzed route for the preparation of surface-deacetylated chitin nanofibers

Abstract

The crude chitin deacetylase (a novel bacterial CDA) with a molecular mass of approximately 31 kDa was produced by culturing the bacteria of Acinetobacter schindleri MCDA01. The produced CDA was directly applied to surface deacetylation of crab shell α-chitin. For enzyme production, a maximum total enzyme activity of 150.09 ± 1.66 U mL⁻¹ was achieved through submerged fermentation following 72 hours of incubation. Increased enzyme activity was observed with EDTA and metal ions of Fe³⁺, Ba²⁺, Sr²⁺, K⁺, Na⁺ and Li⁺, while enzyme activity was inhibited by Co²⁺ or Cd²⁺. The degree of deacetylation (DDA) was increased from 6.46% to 30.58% when the chitin was treated by 12 000 U of CDA at 30 °C and pH 7.0 for 96 h. The high crystallinity of original chitin was maintained, with yield greater than 90% after enzymatic deacetylation, indicating that the CDA deacetylation occurred on the surface of crystalline chitin fibrils without destroying the crystal structure. The chitin nanofibers (CDA-ChNs) were obtained with widths mostly between 25 and 45 nm and lengths of more than several micrometers by sonication of the CDA-treated surface-deacetylated chitin (CDA-Ch) aqueous suspensions at pH 3–4. The application of bacterial CDA on chitin provides a new path to the biorefinery of chitin nanofibers, and the resulting CDA-ChNs might exhibit advanced performance in forming multifunctional materials because of their unique fiber size and high aspect ratio.