Lipase-catalyzed Synthesis of Starch Palmitate in Mixed Ionic Liquids

Lipase-catalyzed synthesis of starch palmitate was investigated in ionic liquid mixtures consisting of 1-butyl-3-methyl-imidazolium acetic ([BMIm]Ac) and 1-butyl-3-methyl-imidazolium tetraflouroborate ([BMIm][BF(4)]). The effect of reaction parameters such as the amount of enzyme used, the reaction temperature, the mass ratio of [BMIm][BF(4)]/[BMIm]Ac, the molar ratio of methyl palmitate/anhydroglucose unit in starch, and the reaction time on the degree of substitution was studied. The formation of starch esters was confirmed by the presence of the carbonyl signal in the FT-IR and NMR spectra. Scanning electron microscopy and X-ray diffraction data showed that the morphology and crystallinity of starch esters were largely disrupted. Thermogravimetric analysis suggested thermal stability of starch palmitate decreased compared to native starch. Water contact angle measurements revealed that the hydrophobicity of starch esters was improved after modification. The successful lipase-catalyzed synthesis of starch palmitate in ionic liquids suggested that ionic liquids could be used as a potentially attractive green alternative to harmful organic solvents for synthesis of high fatty acid starch ester.