Optimized Conditions for the Extraction of Phenolic Compounds from Aeginetia indica L. and Its Potential Biological Applications

Aeginetia indica L., a parasitic root in the Orobanchaceae family, is used as a food colorant in traditional Thai desserts. However, scant information is available on its food applications as well as medicinal properties, while overharvesting by the local people has severely depleted wild plant populations. This research, thus, aimed to extract optimized total phenolic content (TPC) in varying extraction conditions using response surface methodology (RSM) and the Box–Behnken design (BBD). Results indicated that an extraction temperature of 90 °C, 80% (v/v) aqueous ethanol, and 0.5% (w/v) solid-to-liquid ratio yielded the highest TPC at 129.39 mg gallic acid equivalent (GAE)/g dry weight (DW). Liquid chromatography–electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) identified the predominant phenolics as apigenin (109.06 mg/100 g extract) and luteolin (35.32 mg/100 g extract) with trace amounts of naringenin and rutin. Under the optimal extraction condition, the plant extract exhibited antioxidant activities of 5620.58 and 641.52 µmol Trolox equivalent (TE)/g DW determined by oxygen radical absorbance capacity (ORAC) and ferric ion reducing antioxidant power (FRAP) assay, while the scavenging capacity of total radicals at 50% (SC₅₀) was determined to be 135.50 µg/mL using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay. The plant extract also exhibited inhibitory activities against the key enzymes relevant to type II diabetes, obesity, and Alzheimer’s disease, suggesting the potential for medicinal applications.