Green and Efficient Preparation of Nano-chitin for Enzymatic Preparation of <i>N</i>-Acetylchitooligosaccharides
Aijia Xing, Francesco Secundo, Changhu Xue, Yang Hu, Xiangzhao Mao
Abstract
High Resolution Image Download MS PowerPoint Slide An eco-friendly pretreatment method, ball milling, was reported to efficiently prepare nano-chitin for the enzymatic production of N -acetylchitooligosaccharides (NCOS). In this process, α-chitin and β-chitin were milled into nano-chitin with an average degree of polymerization of 20–25 without any chemical additives. The milling process damaged the intersheet and intrasheet hydrogen bonding of chitin, resulting in a decrease in chitin crystallinity and average molecular weight and making the obtained nano-chitin dispersible in aqueous solution, confirmed by transmission electron microscopy (TEM), X-ray diffraction (XRD), gel permeation chromatography (GPC), and transmittance spectra. The ball milling pretreatment enhances the affinity between chitinase and milled chitin confirmed by the decrease of K m value from 12.66 to 3.75 mg mL –1 . Moreover, using milled nano-chitin as the substrate, the catalytic efficiency of chitinase could achieve 4.49 mg mL –1 s –1, which was comparable to that employed colloidal chitin (4.84 mg mL –1 s –1 ), and the conversion rate of milled α-chitin was 80.5% of that of colloidal chitin. The reported ball milling pretreatment could produce nano-chitin substrate without the requirement of chemical reagents, showing the potential to replace acid treatment for the preparation of chitin substrate in NCOS enzymatic production.