Purification of chitosan by using sol–gel immobilized pepsin deproteinization

The residual proteins in commercially available chitosan products potentially induce immunological responses, thus compromising their clinical usage. Conventional deproteinization processes use diluted base and heat. However this heterogeneous hydrolysis is inefficient. In the present study, pepsin was selected and immobilized with tetramethoxysilane (TMOS) and 3-aminopropyltriethoxysilane (APTES). The immobilized pepsin was utilized in an alternative approach for the purification of chitosan. Optimum deproteinization was carried out at pH 4.5 and 45 °C. Amino acid analysis proved a removal of 53.8–80.4% protein in chitosan after 160 min incubation, which was more efficient than conventional sodium hydroxide deproteinization. When chitosan was deproteinizated by immobilized pepsin, its molecular weight decreased, but in a much milder manner than the free pepsin. The study revealed that immobilized pepsin was an efficient method for deproteinizing chitosan.