Abstract:

The chitin obtained as light yellow powder from the residue of silkworm chrysalis left after oil and protein extraction was utilized as the start material to prepare highly deacetylated chitosan in the present study. On the basis of single-factor investigations, quadratic orthogonal rotation combination design was employed to investigate the effects of soaking time in absolute ethanol, NaOH concentration, thermal treatment temperature and duration and material/liquid ratio on deacetylation degree of chitosan. An orthogonal regression model for deacetylation degree of chitosan against the above five factors was constructed. Using frequency analysis method, the optimal conditions for the preparation of highly deacetylated chitosan were determined as follows: soaking time in absolute ethanol, 1.7 h; NaOH concentration, 44%; thermal treatment temperature, 94 ℃; treatment time, 9 h; material/liquid ratio (g/mL), 1:28; and replacement frequency of NaOH, once every two hours. Under these conditions, a product with 95.96% deacetylation degree, 7.45×105 relative molecular mass, 56.98% yield, 3.20% moisture content, 0.35% ash content was obtained as natural white chitosan and each of its major quality indexes met the relevant industrial standards.

Key words: silkworm chrysalis residue, chitosan, high deacetylation degree, preparation process