Optimization of glycyrrhizic acid-assisted green extraction of curcumin from Curcuma longa: water solubility, bioactivity, and stability

Curcumin (CUR), as the main active substance of Curcuma longa. The process of glycyrrhizic acid-assisted extraction of CUR was optimized by a single-factor experiment combined with response surface methodology. The optimal extraction rate of 20.00 ± 0.03 mg/g, which was 40 times higher than water extraction under the same conditions, confirms the effectiveness of this assisted extraction method. The optimal extraction conditions were 1.29 h of extraction time, extraction temperature was 62.78 °C, liquid-to-solid ratio (R_L/S) was 19.06 mL/g, The mass ratio of glycyrrhizic acid (GA) to turmeric powder (R_G/T) was 0.7. Multiple characterization analyses showed that GA formed micellar encapsulation structure with curcumin through hydrogen bonding, which resulted in an amorphous morphology and a more homogeneous distribution of the particle size of the extracts, and the aqueous solubility, antioxidant activity, bacteriostatic activity and stability of CLE-GA (glycyrrhizic acid-assisted extract) were better than that of CLE (turmeric water extract). The CLE-GA system exhibits superior performance, which may stem from the stronger intermolecular binding ability between GA and CUR，improving the water solubility of CUR and synergizing the effect. In conclusion, this study confirms that glycyrrhizic acid-assisted extraction of curcumin is highly efficient, and the resulting extract combines high bioactivity, excellent aqueous solubility and stability, which provides a green and industrializable solution for the fields of functional foods and drug delivery systems.