A kinetic study of the synthesis of ascorbate fatty acid esters catalysed by immobilized lipase in organic media

Abstract

The kinetics of the synthesis of L-ascorbyl laurate and L-ascorbyl palmitate catalysed by immobilized lipase from L-ascorbic acid and an acyl donor (lauric acid, palmic acid and their methyl and ethyl esters) in 2-methylbutan-2-ol have been investigated. The factors affecting the reaction rate (shaking speed, temperature, water activity, enzyme concentration as well as substrate concentration) are discussed. The reaction conditions have been optimized as follows: shaking speed 200 rev./min, temperature 55 degrees C, enzyme 17-20% (w/w of substrate) for these substrates. The most suitable substrate concentration for all of these substrates was 300 mmol/l. The reactions were modelled. For lauric acid, methyl laurate and ethyl laurate: K(m)=74.3, 48.97 and 55.8 mmol/l, respectively; and V(max)=0.010764, 0.0114, 0.01116 mmol.min(-1).g(-1), respectively. The most suitable substrate was methyl laurate. For palmic acid, methyl palmitate and ethyl palmitate: K(m)=102, 94.9 and 104 mmol/l, respectively; and V(max)=0.0417, 0.0424 and 0.0435 mmol.min(-1).g(-1), respectively. The most suitable substrate was methyl palmitate.