Lipolytic activity from Rhizopus arrhizus using solid state fermentation in biphasic system

ABSTRACT

The hydrolytic activity of extracellular lipases (Triacylglycerol hydrolase EC 3.1.1.3) from Rhizopus arrhizus; in a water-organic solvent biphasic system was investigated. The purpose of the work was to examine the conditions for best lipolysis reactions by microbial lipase in microaqueous biphasic system with special emphasis on the involvement of surfactants; metal ions and a chelating agent in the system for biocatalysis and enzyme stability. The lipases were produced from a Rhizopus arrhizus strain; using rice bran as solid substrate; by solid state fermentation. The activity of lipases was found to be optimum at 30 oC and pH 6.5. The effect of different solvents on hydrolytic activity was carried out and isooctane was selected as the solvent of choice. The hydrolytic power exhibited by lipases in a biphasic system was compared with that displayed in aqueous system (phosphate buffer pH 6.5). The effects of various metal ions and a chelating agent on hydrolytic activity in biphasic system were also studied. Among the metal ions tested; Ca2+ had an activating effect; Zn2+; Cu2+; Co2+ and the chelating agent (EDTA) had little inhibitory effect; and Fe3+ showed the highest inhibitory effect. The activating effect of Ca2+ on hydrolytic activity was highest at pH 6.5. Mg2+; Na+ and K+ had no significant effect on lipolysis. The Km value for the enzyme in the solvent isooctane (Km = 91.6 mg/ml) was less as compared to the Km value in the buffer (Km =110 mg/ml). Among the surfactants tested; non-ionic surfactants had the highest effect with Triton X-100