Low-cost substrates for rhamnolipid biosynthesis: optimization and application of waste-derived biosurfactants in fabric softening

Rhamnolipids produced by Pseudomonas aeruginosa are highly valued for their surface activity and biodegradability; however, their industrial application is limited by high production costs. This study investigates the valorization of waste cooking oil (WCO) and hydrolyzed grapevine pruning (VP) residues as sustainable carbon sources for rhamnolipid biosynthesis by P. aeruginosa #112. Optimization experiments indicated that 1 % (w/v) WCO served as the optimal hydrophobic inducer. Subsequently, alkali-pretreated VP extracts were employed as hydrophilic co-substrates, producing a maximum rhamnolipid titer of 2.63 g/L. High-performance liquid chromatography–mass spectrometry (HPLC-MS) characterization revealed a mixture predominantly composed of mono-rhamnolipid Rha-C10-C10 (43.0 %) and di-rhamnolipid Rha-Rha-C10-C10 (43.8 %). The application of these biosurfactants as eco-friendly fabric softeners was evaluated through sensory profiling with a panel of 20 participants. The biosurfactant-rich culture medium significantly enhanced fabric softness, achieving a sensory score of 7 out of 9, which was statistically superior ( p < 0.01) to the water control (score 4) and comparable to a commercial bio-based softener. These findings demonstrate the potential of integrating agro-industrial and food waste streams to develop cost-effective, high-performance biosurfactants for the textile industry.