Use of response surface design in the optimization of starter cultures for enhanced rhamnolipid production by Pseudomonas nitroreducens

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.Keywords: Biosurfactants, inoculum age, inoculum size, Pseudomonas nitroreducens, response surface design, rhamnolipidAfrican Journal of Biotechnology Vol. 12(19), pp. 2611-261

Changes in the enzymes, amino acids, metal ions and flavor profile during fermentation of African locust bean seeds ‘Parkia biglobosa’ to Daddawa

Daddawa/iru, a product of African locust bean (Parkia biglobosa) seeds, is widely used as food condiment by many tribes in West Africa. This study aimed to determine some of the changes which occur during the microbial fermentation of African locust bean seed. The daily changes in pH, amylase, lipase and protease secretion were monitored. Changes in amino acid concentration, mineral ion composition were also monitored; the presence of hydrocarbons and volatile flavor compounds were also determined. The pH increased throughout fermentation and was above 8.5 by 96 h fermentation. Enzyme production was highest after 48 h fermentation. The highest increase in amino acid concentration was observed after 72 h fermentation. The essential amino acids which increased after 72 h fermentation include arginine (48.8%), threonine (25.2%), valine (24.8%), and methionine (20.0%), histidine (10.3%), isoleucine (19.2%), leucine (15.9%), lysine (15.24%), phenylalanine (14.9%), and tryptophan (12.5%). A higher metal ion concentration was observed before fermentation (0 h) than during or after fermentation of the locust bean seeds. Various hydrocarbons, fatty acids, esters and alcohols were observed at different stages of the fermentation. &nbsp