Abstract
Deep eutectic solvents (DES), recognized as tunable green solvents, show significant potential for enhancing enzyme activity in biocatalytic applications. This study investigated the effect of choline chloride-ethylene glycol DES on the lipase activity of Aspergillus niger C2J6 whole cells, employing a self-isolated endophytic strain. By varying the molar ratio (1:2-1:4) and water content (0-80%), the highest lipase activity (142.31%) was observed at a 1:1.55 molar ratio with 46% water content. The effects of changes in the composition of DES on its main physicochemical properties (including surface tension, conductivity, density, viscosity, refractive index, polarity, and water activity) were investigated to reveal the intrinsic reasons for the influence of solvents on the relative enzyme activity of lipase. Mathematical models were developed to connect DES composition with key properties. Statistical analysis revealed that among the physicochemical properties of DES, polarity exhibited the most significant impact on enzymatic activity, followed by viscosity, surface tension, and conductivity. This study provides valuable insights for designing optimized DES systems to improve biocatalytic efficiency and precision.