Optimization of Ultra-High-Pressure Extraction and Comparative Evaluation of Antioxidant Activity and Flavonoid Composition in Guanxiang Leaves

This paper aimed to optimize the ultra-high-pressure extraction process of flavonoids from guanxiang leaves, evaluate their antioxidant capacity, and identify the flavonoids. Methods: Guanxiang leaves were used as the raw material. The extraction process was optimized through single-factor experiments and a response surface methodology. Ascorbic acid (Vc) was employed as a positive control, and the in vitro antioxidant activity of flavonoids was assessed by determining the DPPH radical-scavenging rate, ABTS radical-scavenging rate, and FRAP ferric-reducing ability. Results: The optimal extraction conditions were determined as follows: ethanol concentration of 50%, solid-to-liquid ratio of 1:60 (g/mL), extraction pressure of 300 MPa, and pressure-holding time of 3 min. Under these conditions, the yield of guanxiang leaf flavonoids was found to be 2.21%, better than the solvent extraction method (1.94%). The antioxidant test results indicated that the IC50 values of the extract from the ultra-high-pressure treatment of guanxiang leaves were 11.8 and 50.72 μg·mL−1 on DPPH and ABTS scavenging, which were lower than those of the solvent’s extract (13.40 and 54.29 μg·mL−1). Moreover, the antioxidant ability could also be confirmed by Fe3+ ion reduction. Mass spectrometry results indicate that ultra-high-pressure extraction can yield components such as spiraeoside, scutellarin, luteolin, and nepetin, which are not present in solvent extraction methods. Conclusions: Therefore, the ultra-high-pressure extraction method can help to improve the flavonoid yield and antioxidant activity as well as to obtain special product types, including spiraeoside, scutellarin, luteolin, and nepetin, than the solvent extraction method.