Abstract

The development and management of an inoculum through various stages has a definite effect on subsequent performance and economics of a microbial process. To achieve this, application of response surface modeling in the optimization of the primary and secondary inoculum build-up of Pseudomonas nitroreducens for enhanced rhamnolipid production was presented in this study. This involved systematic studies to understand the individual, cumulative and mutual interactive effects of the two parameters, inoculum age and size on rhamnolipid production. The optimal combination of factors was as follows: primary inoculum age = 61 h, primary inoculum size = 1% (v/v), secondary inoculum age = 28 h and secondary inoculum size = 20% (v/v). The model predicted a maximum rhamnolipid yield of 7.944 g/L. This was as a result of strong interaction between secondary inoculum age and size. The subsequent experiments with the optimized conditions yielded 6.97 g/L of rhamnolipid, which is very consistent with the prediction made by the model used.

Key words: Biosurfactants, inoculum age, inoculum size, Pseudomonas nitroreducens, response surface design, rhamnolipid.