Assessment of distillers corn oil as substrate for rhamnolipid biosurfactant production

Abstract

This study is the first to explore the potential of distiller's corn oil (DCO) for rhamnolipid biosurfactant production. Two strains of Pseudomonas aeruginosa (ATCC9027 [higher relative mono-rhamnolipid content] and LFM1201 [higher relative di-rhamnolipid content]) were used to evaluate the best biosurfactant producer. The biosurfactants were characterized in terms of kinetic, structural parameters, tensoactive parameters, and stability at high temperatures and varied pHs. Obtained results in flasks using DCO as substrate were: ATCC9027 (P = 4.6 g L⁻¹, Y_P/S = 0.16 g g⁻¹, Q_p = 14.9 mg L⁻¹ h); LFM1201 (P = 5.9 g L⁻¹, Y_P/S = 0.20 g g⁻¹, Q_p = 13.7 mg L⁻¹ h). Surface tension, interfacial tension and critical micellar concentration were respectively: 25.9, 4.7 mN m⁻¹, 81.0 mg L⁻¹ for ATCC9027, and 28.5, 7.8 mN m⁻¹ and 121.1 mg L⁻¹ for LFM1201. The main congeners were: Rha-C₁₀C₁₀ (m/z 503.3) for ATCC9027 and RhaRha-C₁₀C₁₀ (m/z 649.4) for LFM1201. Biosurfactants showed stability at high temperature and diverse pHs. Posteriorly, the carbon: nitrogen ratio of the cultivation medium was optimized, with an optimal value of 28:1. Finally, the optimized medium was used in a bioreactor in different operating modes: simple batch, pulse-fed batch and continuous process. The best strategy for producing rhamnolipids using DCO as a carbon source was through a continuous process in a bioreactor. This method boosted rhamnolipid production, reaching 6.82 g L⁻¹ (Y_p/s = 0.35 g g⁻¹). The results showed that DCO was a new and interesting substrate for rhamnolipid biosurfactant production, with characteristics suitable for future application in the biorefinery context, forming part of the circular economy concept.