This study investigates the activity and stability of lipase Km12 in various deep eutectic solvents (DESs) and its biodiesel synthesis potential. Lipase activity increased by 30–40% in Glycerol: Choline chloride (Gly: Cho) DESs with 1:2 and 2:1 molar ratios compared to aqueous media; the highest enhancement was due to stronger hydrogen bonding, which stabilizes the enzyme structure. Glycerol: Betaine (Gly: Bet) (2:1) improved lipase activity by approximately 20%, while other DESs showed lower enhancement. The optimal enzymatic activity was at 20% (v/v) DES concentration, decreasing to half at 60% concentration. The optimum pH in aqueous buffer, Gly: Cho (1:2), and Gly: Cho (2:1) solvents was at pH 8.0, while it was obtained at pH 9.0 in Gly: Bet (2:1) solvent. In pH 6.0, lipase activity increased about 12% and 18% in Gly: Bet and Gly: Cho (1:2) solvents, respectively, compared to aqueous buffer. Results of temperature activities showed the optimal temperature activity of lipase was 30 °C in Gly: Bet (2:1) and Gly: Cho (1:2), 40 °C in aqueous solvent, and 50 °C in Gly: Cho (2:1) solvents. Thermal stability at 60 °C was fully maintained (100% activity after 120 min) with Gly: Cho (1:2) DES, while 62% activity remained at 80 °C. Kinetic analysis showed a significant reduction in K m in DESs, especially Gly: Cho (1:2), and a two-fold increase in catalytic efficiency ( k cat/ K m). In biodiesel synthesis, lipase Km12 converted 37% without DESs; addition of Gly: Bet (2:1) and Gly: Cho (2:1) increased conversion by 1.9 and 2.1 times, respectively. These results indicate the importance of DES components and concentration in improving the lipase activity and stability by enhancing hydrogen binding interactions between solvents and lipase, disruption of enzyme aggregates, and protection of the enzyme structure against thermal denaturation.
Karami et al. (Mon,) studied this question.