Enzymatic modification of cassava starch by fungal lipase

Abstract

Esterification of starch was carried out to expand the usefulness of starch for a myriad of industrial applications. Lipase obtained from Candida rugosa (lipase AYS) was used for starch esterification by two methods: liquid state and microwave oven. The esterification of cassava starch with recovered coconut oil (lauric acid) using microwave heating gave a degree of substitution of 55.28% with degree of substitution (DS) 1.1 and liquid state esterification with palmitic acid gave a degree of substitution of 65.86% with DS 1.04. Esterification was confirmed by IR spectroscopy studies. Thermal gravimetric analysis (TGA) showed that the higher DS attributed to the thermostability, since onset of decomposition is at a higher temperature (390 °C) than the unmodified (280 °C) and was stable above 600 °C. α-Amylase digestibility was found to be reduced for modified starch compared to the control (76.5–4.6%). Viscosity differed with the acyl donor used, palmitic acid increased viscosity while hydrolysed coconut oil reduced viscosity of modified starch ester. Esterification of starch with long chain fatty acids like palmitic acid gives thermoplastic starch which has got wide use in plastic industry, pharmaceutical industries, and in biomedical applications such as materials for bone fixation and replacements, carriers for controlled release of drugs and other bioactive agents. Unlike chemical esterification, enzymatic esterification is ecofriendly and avoids the use of nasty solvents.