Ultrasound assisted acid catalyzed lactose hydrolysis: Understanding into effect of operating parameters and scale up studies

Abstract

The current work deals with the value addition of lactose by transforming into hydrolyzed lactose syrup containing glucose and galactose in major proportion using the novel approach of ultrasound assisted acid catalyzed lactose hydrolysis. The hydrolysis of lactose was performed in ultrasonic bath (33kHz) at 50% duty cycle at different temperatures as 65°C and 70°C and two different hydrochloric acid (HCl) concentrations as 2.5N and 3N. It was observed that acid concentration, temperature and ultrasonic treatment were the major factors in deciding the time required to achieve ∼90% hydrolysis. The ultrasonic assisted approach resulted in reduction in the reaction time and the extent of intensification was established to be dependent on the temperature, acid concentration and time of ultrasonic exposure. It was observed that the maximum process intensification obtained by introduction of ultrasound in the lactose hydrolysis process performed at 70°C and 3N HCl was reduction in the required time for ∼90% hydrolysis from 4h (without the presence of ultrasound) to 3h. The scale-up study was also performed using an ultrasonic bath with longitudinal horn (36kHz as operating frequency) at 50% duty cycle, optimized temperature of 70°C and acid concentration of 3N. It was observed that the reaction was faster in the presence of ultrasound and stirring by axial impeller at rpm of 225±25. The time required to complete ∼90% of hydrolysis remained almost the same as observed for small scale study on ultrasonic bath (33kHz) at 50% duty cycle. The use of recovered lactose from whey samples instead of pure lactose did not result in any significant changes in the progress of hydrolysis, confirming the efficacy of the selected approach. Overall, the work has presented a novel ultrasound assisted approach for intensified lactose hydrolysis.