Effect of different reaction parameters on lipase-catalyzed esterification of naringin and esculin

Abstract

Fatty acid flavonoid esters are antioxidants with high potential for food, cosmetic and pharmaceutic industry. However, their application is still not wide-spread due to low efficiency of traditional chemical esterifications, as well as the necessity for comprehensive optimization of parameters for enzymatic synthesis to increase the economic viability of process. Hereby, esterification of two important flavonoid glycosides, naringin and esculin, with oleic acid as acyl donor using Novozym® 435 was optimized in order to broaden their commercial application. The effect of solvents, flavonoid concentrations, as well as substrate molar ratio on molar conversion and product yield, were investigated. The highest molar conversions of both flavonoids were reached in acetonitrile. Also, optimal flavonoid concentrations for synthesis of naringin and esculin esters were 30 mM and 70 mM, respectively achieving concentrations of 21.2 mg/ml naringin oleate and 27.5 mg/ml esculin oleate after 72h. Further investigation has shown that substrate molar ratio significantly influences esterification of both flavonoids and it was concluded that fivefold excess of oleic acid was optimal for both reactions. Maximum conversions of 70 and 86% were achieved with esculin and naringin, respectively, under optimized reaction conditions, making obtained results promising for further investigations, including product purification and process scale-up.