Influence of bioprocess parameters on sophorolipid production from bakery waste oil

Secondary/waste streams have previously been used as feedstocks to produce sophorolipids (SLs), a biosurfactant with low eco-toxicity and high biodegradability, in order to reduce production costs and protect the environment. However, limited productivities and titres from these feedstocks remain as important challenges. Thus, the optimisation of fermentation medium using bakery waste oil (BWO) as a hydrophobic carbon source by Starmerella bombicola was investigated. The optimal conditions were determined by multiple linear regression. Inoculum concentration of 2% v v-1 and BWO and glucose concentrations of 60 g L-1 and 100 g L-1, respectively, resulted in an increase of 19.6% in the lactonic SL (67.8 +/- 11.5 g L-1). Further optimisation revealed the profound influence of KOH in pH regulation, i.e., compared with NaOH, KOH led to higher concentrations of biomass (p < 0.05), more BWO consumption, and thus, an increase of 42.2% in SL titre (96.4 +/- 9.1 g L-1) and corresponding volumetric and specific productivities of 0.446 g L- 1h- 1 and 0.027 g g CDW- 1h- 1, respectively. Multiple regression analysis demonstrated that pH and the concentration of BWO as the feeding medium were the most influential parameters in fermentative SL production. This study demonstrated that KOH offered additional benefit to improve SLs titre by maintaining high biomass during the bioprocess, displayed the importance of intracellular potassium in cell viability and improved the valorisation of BWO process.