###### Abstract  
Extraction from edible plants is a highly important process that has various biological functions. To maximize biological activity, extraction methods should facilitate optimal extraction of functional phytochemicals. In this study, the optimal hydrothermal extraction conditions of _Acer tegmentosum_ were determined using response surface methodology (RSM), and HepG2 cells were treated with optimized extract and hydrogen peroxide. In a central composition design, the independent variables were extraction temperature (X\({}_{1}\): 70-90 \({}^{\circ}\)C), extraction time (X\({}_{2}\): 2-6 h), and solvent-to-solid ratio (X\({}_{3}\): 50-150). The maximum total phenolic contents (276.70 \(\pm\) 10.11 mg CAE/g) and DPPH (2,2-diphenyl-1-pictlyhydrazyl) activity (33.45 \(\pm\) 2.20%) of _A. tegmentosum_ were estimated at optimized extraction conditions, as follows: X\({}_{1}\): 89.34 \({}^{\circ}\)C, X\({}_{2}\): 7.36 h, X\({}_{3}\): 184.09. Using the calculated extraction conditions, functional phytochemicals were extracted by hydrothermal extraction and freeze-dried. _A. tegmentosum_ treatment (>10 ug/mL) of HepG2 cells remarkably attenuated hydrogen peroxide-inducible hepatic cellular death and reactive oxygen species production in vitro. Acer tegmentosum; antioxidant activities; response surface methodology +
Footnote †: journal: Applied Sciences  
including hot water extraction, Soxhlet extraction, microwave extraction, ultrasound-assisted extraction (UAE), and supercritical fluid extraction (SFE) [6]. These extraction methods directly affect the extraction rate and the application cost, and each method has different advantages. Hot water extraction is an easily accessible, widely acceptable, and economical extraction method. Soxhlet extraction involves continuously extracting phytochemicals from raw materials and uses relatively less solvent than a general extraction method by circulating the solvent [7]. Microwave-assisted extraction generates heat via conduction by applying a microwave to both solvent and sample. UAE involves eluting the desired functional material by destroying the cell wall of the sample tissue with ultrasonic vibration. In addition, SFE, a method for extracting a substance, has also been developed; supercritical fluid passes the critical point at which liquid and gas share characteristics, which accelerates solvent extraction at high temperature and pressure. Solvent is another factor that influences the extraction yield from raw materials. In simple extraction methods (macetation, infusion, decoction, and percolation), the elution yield is determined according to the polarity (polar solvent: methanol, ethanol, and water; nonpolar solvent: ethyl ester or chloroform) of the solvent and the substance [7]. When the solvent is determined by the extraction temperature and time, the solvent solubility, the ratio of the raw material, and the extraction solvent before extraction are important follow-up factors that should be harmonized. If the temperature during extraction is high, the elution rate of the functional material is accelerated; however, a high temperature may decrease the stability of the functional material. Similarly, a longer extraction time may increase the number of functional phytochemicals from the raw material, but it decreases the elution rate of functional substances after a certain time point, which may affect economic efficiency [8]. _Acer legentosum_ is a map tree distributed between Russia and Korea [9; 10]. Over the past few decades, several studies have been conducted to determine the medicinal functions (i.e., antioxidative, anti-inflammatory, antigastric, antiadipogenic, antiosteoclastic, and anticancerous properties) of _A. tegentosum_. In Korea, the leaf, branch, and bark of _A. tegentosum_ have been traditionally used for medical purposes, including treating hepatic and renal diseases [11; 12; 13]. The efficacy of _A. tegentosum_ has been reported in the aforementioned studies.