Fatty Waste from Industrial Vegetable Oil Esterification as an Alternative Substrate for Rhamnolipid Production

Biosurfactants are amphiphilic molecules produced by microorganisms that have attracted increasing interest as alternatives to conventional surfactants. However, the use of low-cost substrates is essential for improving the economic and environmental feasibility of their production. This study evaluated fatty waste from industrial vegetable oil esterification reactions as an alternative substrate for rhamnolipid (RL) production by Pseudomonas aeruginosa LBI. The residue, consisting of a mixture of carboxylic acids and esters, was used as a carbon source in the culture medium. After 144 h of cultivation, 97% of the residue was consumed, resulting in 9.32 g/L of RL. Analysis of the residual substrate indicated preferential utilization of free fatty acids followed by ester compounds. The RL product exhibited a critical micelle concentration (CMC) of 44.3 mg/L, while chemical characterization confirmed the presence of RhaC₁₀C₁₀ and Rha₂C₁₀C₁₀ congeners. In detergency assays, the RL preparation promoted the removal of grease and tomato sauce soils from stainless steel and glass surfaces, providing preliminary evidence of the detergency potential of RL produced from the fatty residue. These findings demonstrate the potential of using the fatty residue from the chemical esterification process as a feedstock for RL production and highlight its value for waste valorization and the development of sustainable cleaning formulations.