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由蟹壳制备壳聚糖的过程分两步：首先蟹壳分别在稀酸和稀碱中脱除钙和蛋白质得到甲壳素；然后甲壳素在浓碱中脱乙酰基制成壳聚糖．在此过程中由于反应条件非常苛刻，极易造成天然高分子的降解，使壳聚糖产品的粘度大大降低．本文采用正交实验法设计实验方案，优化实验条件，分别得到了两种制备高粘度天然高分子壳聚糖的最佳条件：方法一是蟹壳在室温下用5％的稀盐酸处理一天，脱色时间为60min，脱乙酞温度为550℃，脱乙酰化时间是16h；方法二是蟹壳在室温下用稀盐酸处理一天，脱色时间为60min，脱乙酰温度为110℃，脱乙酰时间是1h．实验条件的优化不但增加了产品的粘度，而且提高了脱乙酰度．
Chitosan prepared from the crab shell in two steps: First, the crab shell in dilute acid and dilute alkali were removed calcium and protein chitin; then chitin in concentrated alkali deacetylation of chitosan. In this process, due to the very harsh reaction conditions, it is easy to cause the degradation of natural polymers, so that the viscosity of chitosan products is greatly reduced. In this paper, the orthogonal experimental design of experimental programs to optimize the experimental conditions were obtained two best conditions for the preparation of high viscosity natural polymer chitosan: First, the crab shell at room temperature with 5% diluted hydrochloric acid for one day, The decolorization time is 60min, the temperature of deacetylphthalein is 550 ℃ and the deacetylation time is 16h. The second method is that the crab shell is treated with diluted hydrochloric acid at room temperature for one day, the decolorization time is 60min, the deacetylation temperature is 110 ℃, the deacetylation time is 1h. Optimization of experimental conditions not only increases the viscosity of the product, but also increases the degree of deacetylation.