| The silkworm chrysalis residue, in which the oil and protein has been extracted in former processing, was used as raw material to abstract the chitin. The optimum conditions for chitin were researched by quadratic orthogonal rotation combination design and the qualities of products were analyzed. Chitosan prepared from silkworm chrysalis chitin by a method combining absolute alcohol soaktime with intermittent type treatment to deacetylate. Quadratic orthogonal rotation combination design was used to investigate the best preparation techniques for high deacetylated degree chitosan. By controlling treatment time, three different deacetylated degree chitosans were prepared from silkworm chrysalis chitin. Fourier-transform infrared(FTIR), scanning electron microscopy(SEM) and X-ray diffraction(XRD) patterns were used to characterize chemical constitution, surface structure and microcrystalline structure of chitin and three chitosans. Three classical antioxidant assessment methods were chosen to evaluate scavenging abilities of three different deacetylated degree chitosans to free radical including hydroxyl radical(·OH), superoxide anion radical(O2-·), and DPPH radical(DPPH·). Three chitosans were assessed against nine bacteria at different pH and temperature with oxford plate method. Effects of deacetylated degree, solid/solvent ratio, time, pH value and temperature on adsorption abilities of chitosans to Pb2+ were also examined.The main research findings are as follows:1. The better extraction range and the optimum preparation conditions for chitin from silkworm chrysalis residue were obtained by frequency analysis. The results were as follows:the adequate concentration of NaOH solution was mass 7.85%, treatment temperature was 87℃, processing time was 260 min, and ratio of solid to solvent was 1:10 (g/mL), others are:the adequate concentration of HCl solution was mass 5%, treatment temperature was 30℃, processing time was 4 h, and ratio of solid to solvent was 1:4 (g/mL); the adequate concentration of H2O2 solution was mass 8%, treatment temperature was 70℃, processing time was 4 h, and ratio of solid to solvent was 1:4 (g/mL). The proof test was made and the result was that nitrogen content of chitin was 6.32% which was in contiguity with predicted value 6.30%. Under above conditions, the chitin product was straw yellow powder with 6.32% nitrogen content,91.27% extraction yield,8.60% moisture content and 0.67% ashy substance. All the main indexes of chitin were in conformity with the relevant corporate standards.2. The better preparation technique range and the optimum preparation conditions were obtained by frequency analysis. The results were as follows:the soak time of absolute alcohol was 1.7 h, the adequate concentration of NaOH solution was mass 44 %, treatment temperature was 94℃, processing time was 9 h, and ratio of solid to solvent was 1:28 (g/mL). The confirmatory experiment was made and the result was that deacetylated degree of chitosan was 95.96% which was higher than predicted value 95.39%. The model was proved to be reasonable. Under above conditions, the deacetylated degree of chitosan was 95.96%, molecular weight was 7.45×105, rate of production was 56.98%, moisture content was 3.20%, ashy substance was 0.35%, and the tincture was white nature color. The quality indexes of chitosan were better than the relevant corporate standards.3. When treatment time were 5,7 and 9 h, deacetylated degree of chitosans were 78.12%,86.45% and 95.96%, respectively. The critical value of acetic acid solution which could dissolve three chitosans completely were 0.18 g/100 mL,0.21 g/100 mL and 0.25 g/100 mL, respectively. The variation of apparent viscosity was not so much when dissolving different deacetylated degree of chitosans in acetic acid solution with different concentration.4. The differences of FIIR spectrum of chitin and three chitosans from silkworm chrysalis were mainly manifested in the amino band(1590 cm-1) and acidamide bands(1655 cm-1). Chitin had a very small absorption peak at 1590 cm-1. As deacetylated degree increased, the adsorption strength of three chitosans at 1590 cm-1 intensified, and at 1655 cm-1,the adsorption strength weakend with deacetylated degree increased. SEM images of chitin and chitosan were present the cellular structure. The honeycomb shape units of chitin were relatively flat, almost all for the oval. As deacetylated degree increased, its honeycomb structure units became thinner and more flat, when deacetylated degree was 95.96%, its every structure unit was relatively rules of the pentagon. X-ray diffraction mapping showed that the crystallinity of chitosans were better than that of chitin. The microcrystalline structure of chitin and chitosans were all a type, which indicated that acetyl reaction could not change the natural configuration of samples.5. The antioxidative activity test in vitro showed:When chitosan solution concentration was 8 mg/mL, the scavenging rates of chitosans whose deacetylated degree were 78.12%,86.45% and 95.96% to·OH were 22.58%,32.18% and 35.13%, to O2-·were 16.76%,25.89% and 29.87%, to DPPH·were 74.51%,82.05% and 91.92%, respectively, which were higher than that of chitosans from shrimps and crabs. The scavenging rates raised with deacetylated degree increased.6.Three chitosans had obvious antimicrobial activities on Bacillus cereus, Bacillus typhi murium, Bacillus subtilis, candida albillus, Bacillus pyocyaneus, Escherichia coli and Staphylococcus aureus. The MIC of chitosan whose deacetylated degree was 95.96% were 0.625 g/L,0.625 g/L,0.313 g/L,0.625 g/L,0.625 g/L,1.250 g/L and 2.500 g/L. Chitosans can suppress the bacteria completely when pH was 4.0～5.0, but did not have antimicrobial activities when pH was 6.0. High deacetylated degree chitosan from silkworm chrysalis could keep its antimicrobial activity steadily as preservative in hot-working foods.7. The optimum adsorption technology to Pb2+ of chitosan from silkworm chrysalis. were obtained by single-factors experiments. The results were as follows:chitosan whose deacetylated degree was 86.45% was chosen as sample to chelate Pb2+ in the aqueous solution. The concentration of Pb standard solution was 0.5μg/mL, ratio of solid to solvent was 0.30:25 (g/mL), time was 3 h, pH value was 5, and temperature was 50℃. Under above conditions, average adsorption rate to Pb2+ was 90.28%, and average adsorbance was 45.19μg/g, which could be used as a kind of better chelant for Pb2+.
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