Abstract: Natural chitin has a highly ordered crystal structure and strong intermolecular and intramolecular hydrogen bonds, and is insoluble in water, so it is difficult to enzymatically degrade. In order to improve the enzymatic degradation efficiency of chitin, combined treatment of ultra-micro grinding and high-pressure homogenization was used to modify chitin in this study. The physicochemical properties of modified chitin were determined, and its microstructure was characterized by Fourier transform infrared (FTIR) spectroscopy, elemental analysis, X-ray diffraction, thermogravimetric-differential scanning calorimetric (TG-DSC) analysis and scanning electron microscopy (SEM). Besides, non-specific enzymatic hydrolysis experiments were carried out to validate the effect of the combined treatment on the hydrolysis efficiency of chitin. The results showed that after the modification treatment, the average particle size of chitin decreased by 99.71%, the specific surface area increased by 85.11%, the pore volume increased by 29.03%, the viscosity-average molecular mass decreased by 85.80%, and the expansion ratio increased by 2.02 times as compared from tap density. Moreover, the intensity of the absorption peaks near 3 448 and 3 263 cm?1 increased, whereas the absorption intensity of the absorption peak at 896 cm?1 decreased. However, there was no obvious change in the degree of deacetylation. The crystallinity index on the (110) and (020) plane decreased by 17.49% and 1.31%, respectively. The thermal stability was destroyed. The structure became loose and porous. The modified chitin was more easily degraded by cellulase and papain. In addition, the combined treatment was more effective than either treatment alone. In summary, the combined treatment of ultra-micro grinding and high-pressure homogenization can effectively modify the physicochemical properties and microstructure of natural chitin, thus improving the enzymatic hydrolysis efficiency of chitin.

Key words: chitin; ultra-micro grinding; high-pressure homogenization; physicochemical properties; microstructure; enzymatic hydrolysis