Increase in extracellular inulinase production for a new Rhizoctonia ssp. strain by using buckwheat (Fagopyrum esculentum) flour as a single carbon source.

A newly isolated strain of Rhizoctonia ssp. was used for the production of extracellular inulinase. Previously, the qualitative effects of some carbon and nitrogen sources from fermentative media and the physicochemical parameters for growth were established by Plackett-Burman analysis, and the main parameters that affect extracellular inulinase yield were identified. In this study, the quantitative effect of the carbon to nitrogen ratio in the fermentative medium and the growth temperature were studied and optimized using central composite design and response surface methodology. On the basis of optimization, the maximum extracellular inulinase activity was achieved when 2·5-6·5% buckwheat flour was used as a single carbon source and 4·6-5·0% yeast extract was used as nitrogen source, by submerged cultivation, after 48 h at an incubation temperature between 15 and 27·5°C. Under the fermentative conditions established in this study, a maximum extracellular inulinase yield of 1·8 UI ml⁻¹ was achieved. Rhizoctonia ssp. strain can be used for extracellular inulinase production. Also, buckwheat flour proved to be an inexpensive and abundant substrate suitable for obtaining inulinase. Inulinases are versatile tools for biotechnology as they can be used for a wide range of applications, including production of bioethanol, fructose syrup and inulo-oligosaccharides, lactic acid, citric acid and butanediol.