Chitosan is a novel biopolymer with numerous applications in food and biomedical industries. We studied the production of chitosan from mycelia of Absidia coerulea to improve the cell growth and chitosan productivity.
Chitosan productivity was highest when the initial concentrations of glucose, yeast extract, and ammonium sulfate were 20, 15, and 5 g/L, respectively. The cell growth, at initial concentrations of ammonium sulfate higher than 5 g/L, declined rapidly as the concentration of ammonium sulfate increases. But substrate inhibitions by glucose and yeast extract were insignificant.
In a 2 L batch fermentation, the pH of fermentation medium decreased from 6.3 to 4.8. Cell growth and chitosan productivity were improved by controlling pH at 4.5.
The morphology of Absidia coerulea mycelia must be controlled for higher growth rate. Agitation speeds were very important for the control of mycelia morphology. Pellets were not formed at a speed higher than 350 rpm, whereas the growth rate decreased due to the autolysis of cells at low speeds. The growth rate was highest when the agitation speed was 250 rpm. An increase in aeration rate from 1 to 2 vvm reduced the autolysis, and, in consequence, increased the cell mass. The highest productivity of chitosan in batch culture was 2.3 g/L, at the harvest time of 36 h.
Continuous fermentation was performed for higher productivity of chitosan. Too high concentration of ammonium sulfate in the medium distributed the formation of new growth spots during fermentation. A 0.52 g/L/h of chitosan productivity was obtained at a continuous fermentation with a dilution rate of $0.05 h^{-1}$.
