Enhancement of growth and chitosan production by Rhizopus oryzae in whey medium by plant growth hormones

The effect of some plant growth hormones, viz., gibberellic acid, indole-3-acetic acid, indole-3-butyric acid, and kinetin on chitosan production by Rhizopus oryzae in deproteinized whey was studied. Hormones, at different concentrations, increase the mycelial growth by 19–32%. However, increase in chitosan content of the mycelia was relatively small (1.7–14.3%) over the control. Maximum enhancement was observed with gibberellic acid. Fifty percent more chitosan could be obtained from 1 L of whey containing 0.1 mg/L gibberellic acid. Hormones, at higher dose, instead of stimulation inhibited both growth and mycelial chitosan content. This study showed that hormones have no influence on degree of deacetylation of chitosan but increase the quality of the chitosan by increasing weight average molecular weight and decreasing polydispersity. All the hormones had been found to enhance chitin deacetylase activity of R. oryzae by 1.067–1.267-fold and may be one of the reasons for increased chitosan production.