Ultrasonication-assisted lipase-catalyzed esterification of chlorogenic acid: A comparative study using fatty alcohol and acids in solvent and solvent-free conditions.

Chlorogenic acid, a well-known antioxidant, has potential applications in health care, food, and cosmetic sectors. However, its low solubility hinders its application at the industrial scale. The primary goal of the present study was to increase the lipophilic property of chlorogenic acid through esterification using an ultrasonication approach and Novozym® 435 as the catalyst. The esterification was executed in two ways. In the first method, chlorogenic acid was converted to chlorogenic acid ester using octanol in a solvent-free reaction. Catalytic factors such as reaction time (12 h ∼ 36 h), enzyme dosage (10 ∼ 50 mg), and ultrasonication power (90 ∼ 150 W) were optimized using Box-Behnken design (BBD) while temperature (60 ℃) and molar ration (chlorogenic acid/octanol, 1:500) were kept constant. A maximum conversion rate of 95.3 % was achieved when the esterification was performed for 12 h at 120 W ultrasonication power and 50 mg enzyme dosage. Contrary to the first method, when esterification was done using caprylic acid in the presence of 2-methyl-2-butanol as a solvent, the conversion rate was relatively low. Despite optimization of factors including molar ratio, enzyme dosage, and reaction time, the highest conversion rate achieved was of only 36.8 %. Moreover, molecular docking results revealed that the lowest binding energy was between lipase and octanol. The finding of the study clearly stated that the esterification of chlorogenic acid was more effective in a solvent-free condition as compared to in the presence of solvent.