Evaluation of surface activity of rhamnolipid biosurfactants produced from rice bran oil through dynamic surface tension

Abstract

Abstract The use of low-cost carbon substrates such as agricultural residues can drastically lower the cost of biosurfactant production. In this study, rice bran oil extracted from agricultural waste was used as a renewable carbon source for biosurfactant production using Pseudomonas aeruginosa PTCC 1340. The biosurfactant was characterized as a glycolipid derivative by thin-layer chromatography and Fourier transform infrared spectroscopy. The yields of biosurfactant from rice bran oil (YRL/S) and biosurfactant to biomass (YRL/X) were 0.246 and 2.81 (g/g), respectively. In addition, the surface activity of the produced biosurfactant was studied using dynamic surface tension measurements and a mono-exponential decay model by estimating the relaxation time of the biosurfactants at the interface. The biosurfactant exhibited acceptable performance in reducing surface tension, as confirmed by examining the dynamic surface tension state and the lowest adsorption time without being affected by the type of salt or concentration. It was found that the adsorption/relaxation of biosurfactants at the interface was considerably affected by the biosurfactant concentration. The produced biosurfactant by the strain considerably reduced the surface tension of water from 70.46 to 25.86 mN/m with a critical micelle concentration (CMC) of 0.09 g/L with rice bran oil as a carbon source. The biosurfactant was also found to be highly effective in suppressing one of the most destructive pathogenic fungi, Macrophomina phaseolina, in terms of its environmental impact. The enhanced physicochemical properties of biosurfactants, such as potential antifungal properties, oil displacement properties, and surface tension-reducing ability, demonstrate the potential of this biosurfactant as a bio-adjuvant and perfect replacement for chemical surfactants in addressing oil spills and environmental decontamination processes.

Keywords

• Antifungal
• Biosurfactant
• Pseudomonas aeruginosa
• Rhamnolipid
• Surface tension
• Rice bran oil