Effects of Microwave Pretreatment on Licorice Cell Structure, Components Content, and Physical Properties

Abstract

Microwave pretreatment, utilizing microwave thermal radiation to disrupt plant cell walls before the traditional extraction process, shows great promise in overcoming key challenges such as low extraction efficiency, high energy consumption, and excessive solvent usage in industrial licorice extraction. This study explored the effects of microwave pretreatment on cell structure, components content, and physical properties of licorice. Results revealed that microwave pretreatment disrupted the structural integrity of licorice cells, leading to a notable increase in the content of active ingredients. Specifically, the total of the five components peaked when treated at 500 W for 4 min. A comparison with the untreated group showed that glycyrrhizin, isoglycyrrhizin, liquiritigenin, isoliquiritigenin and glycyrrhizic acid increased by 29.09%, 25.09%, 21.82%, 16.04%, and 22.62%, respectively. Furthermore, differences in physical parameters such as electrical conductivity, solid content, pH, and relative density were observed between the microwave pretreated and untreated extracts, indicating variations in conductive substances, acidic components, substance quality, or types between the two extract groups. Infrared spectrum analysis demonstrated that microwave pretreatment did not alter the overall chemical composition of licorice extract, but increased the content of active substances such as flavonoids, saponins, amides, lipids, sugars, and proteins. In addition, the ratio of material to liquid postmicrowave pretreatment was 1 : 4, with each component’s content being equivalent to 1 : 12 in the untreated group. These findings provide strong evidence for the effectiveness of microwave pretreatment in enhancing the content of active ingredients in licorice, while simultaneously reducing solvent usage and energy consumption.