Enzymatic Synthesis of Aliphatic Esters of Phenolic Acids and Evaluation of Their Antioxidant Properties

The esterification activity of the commercial immobilized lipase CALB towards cinnamic acids and its derivative has been studied. Using cinnamic acid as substrate, the reaction rate constants (1.95 h-1 mM-1 for ethanol and 3.07 h-1 mM-1 for butanol) were more than four and nine times higher compared to those obtained with p-coumaric (0.47 h-1 mM-1) and p-methoxycinnamic acids (0.32 h-1 mM-1), respectively. Thus, esterification of cinnamic acid with ethanol by using C. antarctica lipase has selected as a model reaction for further study. Isooctane is shown to be the best solvent for this reaction even though solubility of cinnamic acid in this a polar solvent is very low. Highest esterification yield of ethyl cinnamate is obtained when initial molar ratio of substrates 1:3 (cinnamic acid is limiting substrate) is used. Esterification of cinnamic acid appeared to result in increasing radical-scavenging ability. The effect of esterification of cinnamic acid was also confirmed by electrochemical method using ethyl cinnamate which appeared to enhance the antioxidant activity. These findings should stimulate the application of such lipase-catalyzed reactions for the preparation of food acceptable esters of cinnamic acid as potential lipophilic antioxidants.