An efficient enzymatic modification of lily polysaccharide in ionic liquid under ultrasonic irradiation

• Enzymatic acylation of LP in ILs under ultrasonic irradiation was investigated.
• Appropriate ultrasonic power can accelerate enzymatic reaction.
• Much better enzyme performance under ultrasonic irradiation than magnetic stirring.

A comparative study was made on immobilized Burkholderia cepacia lipase (PSL-C)-catalyzed acylation of lily polysaccharide (LP) with vinyl acetate in the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluorobrate ([C4MIm][BF4]) under ultrasonic irradiation and magnetic stirring. The degree of substitution (DS) of the modified LP was used to evaluate the extent of acylation and thus enzymatic activity. The application of ultrasonic irradiation instead of magnetic stirring during acylation gave enhanced DS of the product in a shorter reaction time. The optimization studies also included variation in ultrasonic power, water activity and reaction time. PSL-C displayed higher operational stability and 56.0% of its original activity was maintained after being reused in 8 batches under ultrasonic irradiation. The acylation of LP in [C4MIm][BF4] was shown to be a regioselective one under both conditions, with C6OH being acylated. The results demonstrated that the combined application of ultrasonic irradiation and ILs as a medium may be an efficient approach for enzymatic modification of LP.