RESUMEN
The present study reports the improved enzymatic synthesis of ethyl valerate (green apple flavor) by esterification reaction of ethanol and valeric acid in heptane medium. Lipase from Thermomyces lanuginosus (TLL) was immobilized by physical adsorption on polyhydroxybutyrate (PHB) particles and used as a potential biocatalyst. The effect of certain parameters that influence the ester synthesis was evaluated by factorial design. The experimental conditions that maximized the synthesis of ethyl valerate were 30.5°C, 18% m/v of biocatalyst (TLL-PHB), absence of molecular sieves, agitation of 234 rpm, and 1,000 mM of each reactant (ethanol and valeric acid). Under these conditions, conversion percentage ≈92% after 105 min of reaction was observed. Soluble TLL was also used as biocatalyst and the highest conversion was of 82% after 120 min of reaction. Esterification reaction performed in a solvent-free system exhibited conversion of 13% after 45 min of reaction catalyzed by immobilized lipase, while the soluble lipase did not exhibit catalytic activity. The synthesis of the ester was confirmed by Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry analyses. After six consecutive cycles of ethyl valerate synthesis, the prepared biocatalyst retained ≈86% of its original activity.
Asunto(s)
Enzimas Inmovilizadas/metabolismo , Lipasa/metabolismo , Solventes/química , Valeratos/metabolismo , Ascomicetos/enzimología , EsterificaciónRESUMEN
Isoamyl butyrate (banana flavor) was synthesized by esterification reaction of isoamyl alcohol and butyric acid in heptane medium. Immobilized Thermomyces lanuginosus lipase (TLL) prepared via physical adsorption on mesoporous poly-methacrylate particles (PMA) was used as biocatalyst. The factors that affect the esterification reaction were optimized by response surface methodology (RSM). Under optimal experimental conditions, maximum ester conversion percentage of 96.1 and 73.6% was reached after 50 and 90 min, respectively, for esterification reaction performed at equimolar ratio alcohol:acid at 500 and 2000 mM of each substrate. Under these experimental conditions, the esterification reaction was not controlled by external and intra-particle mass transfer effects. The product (isoamyl butyrate) was confirmed by proton nuclear magnetic resonance ((1)H NMR) spectroscopy. Reusability tests showed that the biocatalyst retained around 96 and 31% of its initial activity after eight successive esterification cycles performed at 500 and 2000 mM, respectively. The application of the biocatalyst prepared showed to be a promising strategy to catalyze flavor ester synthesis in a non-aqueous medium.