OPTIMIZATION OF NUTRIENT MEDIUM COMPOSITION BY MATHEMATICAL MODELING FOR PRODUCTION OF RHIZOPUS ARRHIZUS KB-2 LIPASE

R. Denkova, K. Milanova, B. Goranov, M. Yordanova, D. Nikolova, K. Bozhanchev, Y. Evstatieva, S. Ilieva

Abstract: Lipases are enzymes that hydrolyze mono-, di- and tri-acylglycerols present in the oil-water interface. Lipases have potential application in different industrial sectors such as waste water treatment, cosmetics, detergents and in the fuel sector. Among all lipase producing organisms, fungi are considered to be an effi cient source of lipase for industrial applications due to the production of extracellular enzymes and easy separation of fermentation medium. Fungi from Rhizopus sp. are important producers of lipases especially suited for interesterifi cation of fats and oils in both the food and pharmaceutical manufactures. In the last decades, various methods were employed to optimize fermentation conditions to enhance the lipase production, especially in designing media composition by mathematical modeling. Predictive models have been accepted as informative tools for rapid and cost effective study of microbial products development and scientifi c purposes. Response surface methodology (RSM) especially is a mathematical modelling system, which assesses the relationships between the response(s) and the independent variables. Central composite design (CCD) is an experimental design, useful in response surface methodology in order to defi ne the importance of the independent variables, alone or in combination, in the model. The current work proposes a simple mathematical model which relates the production of lipase with the concentration of different nutritive compounds used in fermentation medium. In this context, the influence of some carbon, nitrogen and phosphorus sources on lipase biosynthesis by the fungal strain Rhizopus arrhizus KB-2 during batch cultivation process was investigated in the present study. According to our previous experiments with a different nutritive compounds in the fermentation medium glucose, soy flour and yeast extract have a significant effect on the yield of lipase. Variation ranges of these components were also determined during individual cultivation processes. For optimization of the medium composition for extracellular lipase production by Rhizopus arrhizus KB-2 in submerged fermentation central composite design of type 23 was used in order to determine combined influence of the nutrients. It was found that glucose has to be in small amounts (4.3 g.dm–3) until soy flour and yeast extract have optimal values of 28.5 g.dm–3 and 9.3 g.dm–3 in the investigated factor space. Lipase activity of 60.72 FIP U.cm–3 was detected experimentally after optimization of the nutrient medium composition by the investigated mathematical model. Based on
the results obtained central composite design is suitable for optimization of medium composition for lipase production by the fungal strain Rhizopus arrhizus KB-2 during batch cultivation and significant enzyme activity was reached by using of minimum types of nutritive sources.

Keywords: lipase; mathematical modeling; Rhizopus

Date published: 2017-10-20