Fig. 5.

Operational stability of Novozym 435- catalysed synthesis of xylitol lauric acid esters by direct esterification of xylitol with lauric acid (1:2, mol/mol ratio) in solvent-free conditions and under ultrasound assistance (40% amplitude). Each cycle involved a 1 h (45 s/min pulses, 40% amplitude, 130 ± 5 W) ultrasonic pretreatment of the immobilized enzyme/lauric acid mixture at 40 °C. The synthetic process was started by adding the xylitol substrate, then allowed to proceed for 60 min under the same ultrasonic and temperature conditions.