Ultrasonic‐assisted extraction of flavonoids from Nitraria sibirica leaf using response surface methodology and their anti‐proliferative activity on 3T3‐L1 preadipocytes and antioxidant activities

As both an edible and medicinal plant, Nitraria sibirica has been used as a natural remedy for indigestion and hypertension since ancient times in Central Asia. The ethanolic extract of N. sibirica leaves lowers blood pressure and blood lipids. We assume that these bioactivities are most likely related to the composition of flavonoids due to their dominant content. Therefore, we investigated bioactivity-oriented extraction parameters of flavonoids from N. sibirica. In this study, the ultrasonic-assisted extraction variables were optimized using a response surface methodology for optimal recoveries of total flavonoid content (TFC), anti-proliferative activity on 3T3-L1 preadipocytes and antioxidant capacities (DPPH) of N. sibirica leaf extract (NLE). The optimal extraction conditions of NLEs were as follows: ethanol concentration of 71.33%, feed-to-solvent ratio of 30.36 mL/g, extraction temperature of 69.48°C, extraction time of 25.27 min, extraction number of two times, the TFCs were 1.73 ± 0.01 mg RE/g d.w. (n = 4), IC50 value of preadipocytes was 259.42 ± 3.62 µg/mL (n = 4), and antioxidant capacity of 86.55 ± 3.71% (n = 4). After the purification of NLEs, the TFCs were 7.52 mg RE/g d.w., the inhibition capacity of IC50 was 143.50 µg/mL, and DPPH scavenging rate was 86.99%, which were approximately 4.34, 1.81, and 1.01 folds higher than before the purification of NLEs, respectively. Bioactive-oriented extraction of NLEs possessed the potential lipid lowering and antioxidant activities, which hold high research value for the development of natural medicines or new functional foods to treat or prevent metabolic diseases such as obesity.