Enzymic synthesis of isoamyl isovalerate using immobilized lipase from Rhizomucor miehei:: a multivariate analysis

Isoamyl isovalerate, an ester with apple flavour was synthesized using Rhizomucor miehei lipase immobilized on a weak anion-exchange resin (Lipozyme IM-20) by the direct esterification of isoamyl alcohol and isovaleric acid. Various reaction parameters including substrate concentration, enzyme concentration, substrate molar ratio, temperature and incubation time affecting the synthesis of isoamyl isovalerate were investigated. A maximum yield of > 85% was obtained at 0.5 M (acid) substrate concentration (1.5:1 alcohol/acid ratio) using 10 g/l enzyme concentration and a reaction temperature of 50 degreesC for 144 h incubation time in n-hexane. A solvent screening study indicated that hydrophobic solvents including cyclohexane, hexane, heptane/isooctane are the most suitable ones for esterification. The feasibility of synthesizing the ester under solvent-free conditions has also been studied. However, the conversions were very low. The parameters influencing the yield were modeled using multivariate analysis. These equations can be applied to predict the yield at any other known values of the input parameter. (C) 2000 Elsevier Science Ltd. All rights reserved.