Two-Step Method of Enzymatic Synthesis of Starch Laurate in Ionic Liquids

Abstract

Enzymatic esterification of starch with long-chain fatty acid was investigated by using ionic liquids 1-butyl-3-methylimidazolium choride ([BMIm]Cl) and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]) as reaction media. An industrial lipase produced by Candida rugosa was used to modify starch with lauric acid. The effect of reaction parameters such as the lipase dosage, the molar ratio of lauric acid/anhydroglucose unit (AGU) in starch, and the reaction temperature as well as the reaction time on the degree of substitution (DS) of long-chain fatty acid starch esters was studied. The maximum DS value was 0.171 under the given conditions. The maximum solubility of high-amylose starch measured by turbidity was 11.0/100 g of [BMIm]Cl. The esterification products were confirmed according to Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) analysis. The morphological and crystallographic properties of native starch were largely disrupted during modification process as indicated by scanning electron microscopy (SEM) and X-ray diffraction (XRD) data. The thermal stability of the starch laurates was found to decrease compared to native starch. After reaction, the ionic liquid was effectively recycled and reused. This paper explores the potential of ionic liquids as solvent for the enzymatic synthesis of long-chain fatty acid starch esters.