Optimization of production parameters for enhanced production of sophorolipid by Rhodotorula babjevae YS3 using response surface methodology

Abstract

Sophorolipids (SLs), a sub-class of glycolipid biosurfactant, have garnered attention for their biodegradability, low toxicity, and broad industrial applicability. This study focuses on optimizing the production of sophorolipids by Rhodotorula babjevae YS3 (SL-YS3) using response surface methodology (RSM). Initial unoptimized production yielded 5 g/l SL-YS3 in Bushnell-Haas medium with glucose as the sole carbon source. A fractional factorial design (FFD) was employed to identify significant factors influencing SL production, including carbon source concentration, inoculum size, pH, and incubation temperature, while agitation was excluded due to its negligible effect. Subsequently, a central composite design (CCD) was utilized to model and optimize the process. Analysis of variance (ANOVA) confirmed the significance of the quadratic model (Pmodel < 0.0001), with high coefficients of determination (R2_adjusted = 0.9999, R2_predicted = 0.9991) and an insignificant lack-of-fit (P = 0.2393), ensuring model reliability. Glucose concentration exhibited the most substantial linear effect on SL-YS3 production, while quadratic terms indicated nonlinear interactions. The strongest positive interaction was observed between inoculum size and temperature, with optimal production occurring at mid to high temperatures. Optimization predicted a maximum yield of 21.789 g/l under the following conditions: 11.51% (w/v) glucose, 20.77% (v/v) inoculum size, pH 7.04, and temperature 19.39 °C. Experimental validation of optimised parameters yielded 21.727 ± 0.061 g/l SL-YS3, with a 4.3-fold improvement over initial yields, demonstrating the efficacy of RSM in enhancing SL production. The study provides a framework for the industrial-scale production of SLs, paving the way for their adoption as sustainable alternatives to synthetic surfactants.