Optimization of Ultrasonic-Enzymatic-Assisted Extraction of Flavonoids from Sea Buckthorn (Hippophae rhamnoides L.) Pomace: Chemical Composition and Biological Activities

Sea buckthorn pomace (SBP) is a rich source of flavonoid compounds with potential healthy properties. This study optimized ultrasonic-enzymatic-assisted extraction (UEAE) of flavonoids from SBP and investigated its chemical composition and biological activities. Under the optimal conditions (pectinase addition of 1500 U/g, ultrasonic power of 300 W, ethanol concentration of 48%, liquid-solid ratio of 34:1, extract temperature of 50 °C, and extraction time of 28 min), the yield of SBP flavonoid extracts (SBFEs) was 21.57 ± 0.45 mg/g, well-matched with the predicted value (21.72 mg/g). The chemical composition was detected by ultrahigh-performance liquid chromatography with quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS^E) and mainly including isorhamnetin, kaempferol, and quercetin's derivatives. After purification with AB-8 macroporous resin, the purified product (PSBFE) exhibited a significantly enhanced scavenging capability for 1,1-diphenyl-2-picryl-hydrazyl radical (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) (947.17 ± 3.85 and 427.33 ± 0.67 μmol Trolox/g, respectively) and ferric reducing antioxidant power (2.68 ± 0.01 mmol FeSO₄·7H₂O/g). Moreover, PSBFE possessed a pronounced inhibitory rate on α-glucosidase and α-amylase, with the IC₅₀ at 52.89 ± 0.09 and 97.81 ± 0.42 μg/mL, respectively. These findings indicate that it is a reliable, optimal extraction method to obtain potential antioxidant and hypoglycemic flavonoids from SBP for comprehensive development in functional food.