Comparative study of various carbon sources on rhamnolipid production

This study aimed at comparing the effect of various carbon sources with a fixed nitrogen source for the syntheses of rhamnolipid biosurfactant using a strain of Pseudomonas aeruginosa. The carbon sources used were glycerol, glucose and waste cooking oil (WCO), for the benefit of utilising wastes. The characterized microbial strain was obtained from the Microbiology Department of Obafemi Awolowo University, Ile-Ife. It was grown on a surface culture before inoculation into a production culture. Each culture media were sterilized at 121 °C, 15 psi for 15 min and cooled before inoculation. Each procedure was carried out in duplicates and culture flasks incubated in a shaker for 7 days with 24-h monitoring. The growth of P. aeruginosa on the three carbon sources passed through the phases of formation of primary metabolites. The surface tensions of medium relative to water was reduced from 86.69 mNm−1 to 33.63 mNm−1, 36.44 mNm−1 and 18.02 mNm−1 for biosurfactant from use of glycerol, glucose and WCO as carbon sources respectively. Excellent emulsification index, E24, was obtained in the continuous media Heavy black oil and lubricating oil unlike in the other media: vegetable oil and kerosene. The FTIR spectra revealed that the glycerol- and glucose-based biosurfactants were di-substituted rhamnolipids with difference in the hydrophobic moieties. However, the biosurfactant formed with WCO was not a rhamnolipid but a lipopeptide.