Particle size and root diameter effects on the extraction of glycyrrhizic acid from licorice using ultrasonic: Full factorial experimental design and response surface methodology

Licorice is one of the most important medicinal plants in the world. This plant has been used in the world for more than 2000 years and is applied in various industries including pharmaceutical, food and tobacco industries. Iran is one of the best regions in the world in terms of medicinal plants. The roots of the licorice plant are widely used in the food and pharmaceutical industries. These roots are strong natural sweeteners, about 50-170 times sweeter than sucrose. The value of this plant is related to its chemical components. Glycyrrhizin is the most abundant component of this plant and is present in licorice in the form of potassium or calcium salt of glycyrrhizic acid and is considered as an indicator of licorice quality. In recent years, novel extraction methods with different energy sources have been proposed for improving extraction efficiency. Higher extraction efficiencies can be achieved by using microwave, ultrasonic and high pressure methods. In the ultrasonic extraction method, the extraction rate increases due to the presence of cavitation. The cavities formed in the solvent grow and then collapse rapidly, releasing a large amount of energy that increases the local temperature and pressure. Therefore, the solvent penetrates more into the plant cell material and the contents of the plant cells are released into the solvent medium. Also, physical effects such as liquid circulation and turbulence produced by cavitation help to increase the contact surface between the solvent and the plant particles and lead to more solvent penetration into the plant matrix.

The aim of this study is to statistically investigate the effect of particle size and licorice root diameter on the rate of glycyrrhizic acid extraction using ultrasonic. The full factorial experimental design method and response surface methodology have been used to determine the levels of the parameters and to model the responses, respectively. Independent variables included particle size of licorice root at three levels (35-60, 60-120, ≥ 120 mesh) and licorice root diameter is at three levels (1-2, 2-3, ≥3 cm). Total extract and glycyrrhizinic acid yield are considered as response variables. The solvent used was ammonia and the analysis of glycyrrhizic acid in the extract was performed by HPLC method. The licorice root used in this research was from Bojnourd region. Monoammonium glycyrrhizic acid (99.5%) was purchased as an HPLC standard from Sigma and ammonia from Merck. The method of glycyrrhizic acid extraction from licorice root was based on the British Pharmacopoeia method in this research.

The results showed that regarding the response glycyrrhizic acid yield, the parameter licorice root diameter had a significant effect on the response, but the particle size parameter had no significant effect. Also, two parameters had interaction. Based on the modeling results of the extraction process, the optimal conditions for obtaining the maximum total extract of licorice root included particle size, 125 μm (120 mesh) and licorice root diameter, 3.28 cm, which leaded to 68.16 wt% total extract. The optimal response conditions for glycyrrhizic acid yield from licorice root included particle size, (120 mesh) and licorice root diameter, 2.72 cm, which leaded to the extraction of 6.02 wt%glycyrrhizic acid from the root. Also, a comparison was performed between glycyrrhizic acid extraction from licorice in ultrasonic bath and ultrasonic probe. The results showed that the amount of glycyrrhizic acid extraction was similar and was equal to 5.5 wt%. The effect of particle size distribution has also been investigated. According to the results in ultrasonic extraction, particle size distribution had a positive effect on extraction.According to the results of this research, the parameter of licorice root diameter had a significant effect on the response of glycyrrhizic acid yield and with decreasing licorice root diameter, the amount of glycyrrhizic acid extraction increased. Also, the efficiency obtained by extraction method in ultrasonic bath is compared with ultrasonic probe. It can be concluded that glycyrrhizic acid extraction from licorice with using ultrasonic is an effective method for extraction