SOLVENT EFFECT OF ACETIC ESTERS ON SYNTHESIS OF ASPARTAME PRECURSOR BY FREE ENZYME, ACCOMPANIED BY EXTRACTION

Three kinds of acetic esters-ethyl acetate, butyl acetate and amyl acetate-were used as the organic component in an aqueous-organic biphasic mixture for aspartame precursor synthesis, accompanied by solvent extraction. Firstly, the distribution ratios of the substrates and product between organic and aqueous media were measured at various pH, and it was confirmed that these three acetic esters are suitable as the solvent in this reaction system. Secondly, the effect of acetic esters on the native enzyme activity was examined by using three solvent systems: water free from any ester, water saturated with the respective ester and aqueous-ester biphasic mixture. Comparison of the latter two with the former showed that the reaction rate was lowered in the acidic range in the case of ethyl acetate, but no remarkable effect was observed in the cases of butyl acetate and amyl acetate. Thirdly, using butyl acetate as the solvent for substrate feeding and product extraction the batchwise synthesis was performed repeatedly. It was found that free enzyme can be used repeatedly without its deactivation, merely by renewing the organic phase.