: Chitosan, a useful cationic polymer of glucosamine monomers, is industrially produced via chemical deacetylation of extracted chitin from shellfish. Recently, cell wall of zygomycetes fungi has been introduced as an alternative source for chitosan production, in which chitosan is produced via enzymatic deacetylation of chitin. In this study, a new method for optimum extraction of chitosan from fungal cell wall was suggested, and the effects of sulfuric, hydrochloric, nitric, acetic, and lactic acids on the phosphate removal from the cell wall and also preservation of chitin and chitosan were investigated. The efficient extraction method was involved employing sulfuric acid, as the best acid for phosphate removal, and treating with lactic acid, for dissolution and extraction of chitosan. Results showed that solutions of sulfuric acid caused chitosan to be insoluble in the acidic solutions at ambient temperature; however, alkali treatment recovered its solubility. The yield of cell wall was measured to be 0.16 grams per gram of dried biomass. Finally, chitosan was extracted from the cell wall remaining materials by lactic acid treatment at ambient temperature. Using the proposed method, the yield of chitosan for the cell wall of Rhizopus oryzae was measured to be 12.3 % at ambient temperature. It is noteworthy that the new method was performed for commercial chitosan, and the yield 86.9% was obtained. The viscosity of commercial chitosan was measured before and after the process, and the results showed that the viscosity remains unchanged during acid and alkaline treatments. Beside chitosan, the phosphate, protein, glucosamine, and n-acetyl glucosamine content of the fungal cell wall and commercial chitosan were also investigated, and the results showed that the impurities of Rhizopus oryzae and commercial chitosan after sulfuric acid treatment were reduced to 1 % and 0.7 %, respectively. Furthermore, the protein content of cell wall after alkali treatment was measured to be less than 5% of the dried biomass. The morphology of cell walls subjected to treatment with 5 different acids was monitored by scannin g electron microscopy (SEM). Keywords : Fungal chitosan, Released phosphate, Rhizopus oryzae, Cell wall, Sulfuric acid, Lactic acid.
