LIPASE SYNTHESIS OF SHORT-CHAIN FLAVOR THIOESTERS IN SOLVENT-FREE MEDIUM

This study demonstrates from a kinetic (initial rate) and thermodynami c (equilibrium yield) point of view the ability of an immobilised lipa se, Lipozyme(TM), to catalyse the synthesis of short-chain flavour thi oesters such as thioethyl thiobutyl and thiohexyl propionate, butyrate and valerate. The influence of different parameters such as temperatu re, acid/thiol molar ratio or water content was studied for the synthe sis of thiobutyl valerate. Optimisation of the esterification of valer ic acid and butanethiol was achieved and some optimal reaction conditi ons were defined. At 60 degrees C, with an acid/thiol molar ratio of a bout 1/5, in a free-solvent medium, the conversion yield of valeric ac id in thioester was higher than 40% in the presence of 100 gl(-1) mole cular sieves and a ratio of immobilised enzyme/molecular sieves of abo ut 1. Comparison between thioesterification and transthioesterificatio n shows that higher initial rates were obtained in the latter case whe n the acid/thiol molar ratio was 1/1. However, at equilibrium esterifi cation remained more efficient. Finally another immobilised Lipase, No vozym(TM) was assayed. The esterification and transesterification reac tions were accelerated but the thioester concentrations at equilibrium were the same as those obtained with Lipozyme(TM).