Lipase‐catalyzed esterification of konjac glucomannan in isooctane

Konjac glucomannan (KGM) is an abundant natural polysaccharide that is renewable and fully biodegradable. Modification of KGM OH groups by esterification to form an appropriate degree of substitution (DS) imparts rheological property and water resistance to the KGM ester over the unmodified KGM. Chemical reaction catalyzed by enzyme is an environmentally friendly method which occurs under milder reaction condition. Lipase (Novozym 435) was used to catalyze the esterification reaction between oleic acid and KGM in isooctane. The DS of the esterified KGM was used to evaluate the extent of esterification. Five variables (water activity, reaction temperature, the ratio of oleic acid and KGM, phosphate buffer content, and reaction time) were investigated to optimize the experimental conditions of the KGM oleate synthesis. The optimal conditions for a DS of 0.370 are phosphate buffer solution 2.0% (v/v), a KGM/oleic acid weight ratio of 3 during 36 h of shaking at 55°C in isooctane. Phosphate buffer solution content of the reaction system played a key role in the esterification of KGM in isooctane. The structure of the modified KGM was checked by IR, fluorescence spectra, XRD, thermogravimetric analysis, and rheology. Results showed that hydrophobicity and hydrophilicity of KGM was significantly affected after esterification. The KGM fatty acid esters produced may have potential applications such as humidity‐sensitive coating and hydrophobic drug delivery. © 2016 American Institute of Chemical Engineers Environ Prog, 35: 1149–1155, 2016