Enzymatic preparation of chitosan from the waste Aspergillus niger mycelium of citric acid production plant

A new route had been devised for obtain chitosan with stable properties and good quality suitable for medical, cosmetic and other purposes. Waste Aspergillus niger mycelia from a citric acid production plant were used as a source of chitosan. The extraction of chitosan was operated with lysozyme, snailase, neutral protease and novel chitin deacetylase from Scopulariopsis brevicaulis at the optimum condition of every enzyme. The optimum dosage of neutral protease and chitin deacetylase were 0.17 g (5100 units) per 100 g fresh mycelia and 1200 units per 100 g fresh mycelia, respectively. The deproteinization rate was 59.9%. The recovery rate of glucosamine was 50%. Weight-averaged molecular weight, degree of deacetylation of chitosan and the content of glucosamine were 267.97 kDa, 73.6 and 84.4%, respectively. Compared with chemical extraction methods, the weight-average molecular weight was three times higher whilst other parameters were very similar. The results of FT-IR, X-ray and elemental analysis proved that the structure of chitosan of enzymatic extraction was very similar to those of shrimp chitosan.