A green approach for starch modification: Esterification by lipase and novel imidazolium surfactant

• Development of a green technique for starch esterification using lipase.
• Synergistic effect of microwaves and novel surfactants on lipase was observed.
• Novel gemini surfactant increased the degree of substitution in less reaction time.
• Starch ester showed higher hydrophobicity and thermoplasticity.

Starch being one of the most abundant polysaccharides in nature has been subjected to modification to enhance its applicability. Modification by esterification involves acylation of hydroxyl groups of glucose units to form starch esters. Lipases, as catalysts have emerged as a promising alternative to chemical processes. Although ionic liquids and microwave assisted heating are emerging as green technology yet their use along with lipases for starch modification has not been probed. In the present study esterification of corn starch employing Rhizopus oryzae lipase, microwave irradiation and novel imidazolium surfactants has been attempted. At 80% irradiation, 1:3 starch/oleic acid molar ratio, 150 IU enzyme, and 50 μmol of [C16-3-C16im]Br2 maximum degree of substitution (DS = 2.75) was attained. The modified starch showed better hydrophobicity and thermoplasticity with corresponding structural changes depicted by FTIR, XRD and SEM. These properties advocate the usefulness of the modified starch in food and biopolymer sectors.