Phytochemical Characterization and Bioactivity Evaluation of Extracts Obtained via Ultrasound-Assisted Extraction of Medicinal Plant Phedimus aizoon

Phedimus aizoon has been utilized as a medicinal plant in Asia. However, the production of phytochemical-rich extracts from P. aizoon and the evaluation of their bioactivity are limited. Herein, phytochemical-rich extracts were prepared by ultrasound-assisted extraction of P. aizoon, with a high extraction yield of 16.56%. The extracts contained about 126 mg of phenolics and 31 mg of flavonoids per g of the extracts. The chromatographic analysis (GC-MS and HPLC analyses) identified 19 notable phytochemicals of the extracts from P. aizoon, including pentacosane, hexadecanoic acid, gallic acid, vanillic acid, and quercetin. The gallic acid content of the extracts was relatively high at 2.75 mg/g. The identified compounds are known to have various bioactivities, such as antioxidant, antibacterial, and antifungal activities. In fact, the prepared extracts exhibited antioxidant activity at 24–28% of that of ascorbic acid. In addition, it showed antibacterial activity against both Escherichia coli (Gram-negative bacteria) and Staphylococcus aureus (Gram-positive bacteria). This study highlights that P. aizoon deserves attention as a natural bioactive substance and emphasizes the need for applications of the extracts from P. aizoon.


Introduction
Phedimus aizoon (formerly known as Sedum aizoon) is a perennial herbaceous species of the Crassulaceae family and is widely distributed in China, Korea, Japan, and Mongolia [1].P. aizoon has been recognized as a medicinal and edible plant with various pharmacological effects, such as protecting the cardiovascular system, enhancing immunity, stopping bleeding, and tranquilizing the mind [2,3].The pharmacological effects of P. aizoon (or S. aizoon) were introduced in ancient medical classics in China [3].P. aizoon has been reported to contain a variety of bioactive constituents, such as flavonoids, phenolic acids, and triterpenes, which have been considered to contribute to its bioactivities [4,5].Nevertheless, compared to other medicinal plants, there are few reports on the phytochemical characteristics and bioactivities of P. aizoon.For the sustainable utilization of P. aizoon, efficient extraction, isolation, identification, and activity evaluation of bioactive compounds are needed.
As one of the strategies for recovering bioactive compounds from plant material, the extraction process (techniques and conditions) can be optimized to maximize the extraction yield of the target bioactive compound [6,7].Prior to this, the extracts must be systematically characterized in terms of the aspects of their phytochemical compositions and bioactivities [8].In previous studies, non-conventional techniques, such as ultrasoundassisted extraction (UAE) [9] and microwave-assisted extraction (MAE) [10], have been recommended as efficient methods to extract bioactive compounds including flavonoids from P. aizoon.However, the information on the phytochemical profiles and bioactivity of P. aizoon extracts obtained by using non-conventional techniques is limited.Previous studies detected bioactive compounds of P. aizoon extracts obtained by using a conventional extraction technique known as maceration, using various analyses such as chromatography, infrared spectroscopy, mass spectrometry, and nuclear magnetic resonance, and the following compounds were identified: caffeic acid, gallic acid, vanillic acid, luteolin, quercetin, kaempferol, myricetin, and rutin [3].In addition, Odeh et al. [11] reported the presence of caffeic acid, catechin, gallic acid, hesperidin, and rutin in S. rubens, another species of Sedum.These phenolics and flavonoids contribute to the bioactivities and medicinal functions of P. aizoon; thus, their contents should be studied after the extraction process.
Herein, we aimed to perform the phytochemical characterization and bioactivity evaluation of P. aizoon extracts obtained by UAE.Total phenol and flavonoid contents were quantified, and the phytochemicals were analyzed by gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC) analyses.In addition, the bioactivities (antioxidant and antibacterial) of P. aizoon extracts were evaluated.The present study aims to contribute to advancing our biochemical knowledge of the medicinal plant P. aizoon and, in particular, to explore the potential of its extracts, which are rich in bioactive compounds, from the UAE process.

Plant Material
Phedimus aizoon (L.) 't Hart was collected in Tsagaannuur district, Huvsugul province, Mongolia, and identified by Dr. Badamtsetseg Bazarragchaa at the National History Museum of Mongolia in August 2015 (Figure 1).A voucher specimen (accession number KRIB 0070462) of the retained material is preserved at the herbarium of KRIBB.

Ultrasound-Assisted Extraction (UAE) of Bioactive Compounds from Phedimus aizoon
A mixture of leaves, shoots, and flowers of P. aizoon was used for the extraction.The plant materials were dried in the shade and powdered (water content: 19.1%).In general, methanol is commonly used in the extraction process of bioactive compounds, including flavonoids; thus, methanol was used as an extraction solvent [10,12].A total of 55 g of plant material was immersed in 1 L of methanol (99.9%) and extracted using an ultrasonic extractor (SDN-900H, SD-ULTRASONIC, Co., Ltd., Seoul, Republic of Korea) for 30 cycles (40 KHz; 1500 W; 15 min sonication and 120 min standing) at room temperature.After extraction, the extracts were filtered and then concentrated at 45 • C using a rotary evaporator (N-1000SWD, EYELA, Tokyo, Japan) and freeze-dried.

Ultrasound-Assisted Extraction (UAE) of Bioactive Compounds from Phedimus aizoon
A mixture of leaves, shoots, and flowers of P. aizoon was used for the extraction.The plant materials were dried in the shade and powdered (water content: 19.1%).In general, methanol is commonly used in the extraction process of bioactive compounds, including flavonoids; thus, methanol was used as an extraction solvent [10,12].A total of 55 g of plant material was immersed in 1 L of methanol (99.9%) and extracted using an ultrasonic extractor (SDN-900H, SD-ULTRASONIC, Co., Ltd., Seoul, Republic of Korea) for 30 cycles (40 KHz; 1500 W; 15 min sonication and 120 min standing) at room temperature.After extraction, the extracts were filtered and then concentrated at 45 °C using a rotary evaporator (N-1000SWD, EYELA, Tokyo, Japan) and freeze-dried.

Estimation of Phenolic Content and Flavonoid Content
The total phenolic and flavonoid contents of the extracts from P. aizoon were measured according to our previous study [12].For the estimation of total phenolic content, 10 µL of the sample (i.e., the extracts dissolved in methanol), 790 µL of water, and 50 µL of Folin-Ciocalteu reagent were mixed and incubated at 30 °C.After 8 min, 150 µL of Na2CO3 (20% solution) was added and incubated at 25 °C.After 60 min, the absorbance (A) of the final mixture was recorded at 700 nm.The data are shown as mg caffeic acid equivalent (CAE) per g extracts.For the estimation of total flavonoid content, 50 µL of the sample and 30 µL of NaNO2 (5% solution) were mixed and incubated at 25 °C.After 6 min, 50 µL of AlCl3 (10% solution) was added and incubated at 25 °C.After 5 min, 300 µL of NaOH (1 M solution) and 1000 µL of water were added and incubated at 25 °C.After 15 min, the absorbance (A) of the final mixture was recorded at 510 nm.The data are shown as mg catechin equivalent (CE) per g extracts.The total phenolic and flavonoid contents of the extracts from P. aizoon were measured according to our previous study [12].For the estimation of total phenolic content, 10 µL of the sample (i.e., the extracts dissolved in methanol), 790 µL of water, and 50 µL of Folin-Ciocalteu reagent were mixed and incubated at 30

GC-MS Analysis
GC-MS analysis was performed according to previous studies [13,14] with minor modifications.The extracts from P. aizoon were dissolved in methanol, with a final concentration of about 5 µg/mL.The analysis was performed using GC 7890A, 5975C (Agilent, Santa Clara, CA, USA), equipped with a DB 5MS column (0.25 mm × 0.25 µm, 30 m length) with a single quadrupole detection system and an injection volume of 1 µL.The detailed conditions were set as follows: run time, 34 min; oven temperature, initially 60 • C and increased to 280 • C at a rate of 10 • C/min.The National Institute of Standards and Technology (NIST) Library database was used to identify compounds in P. aizoon extracts.

HPLC Analysis
For the quantification of several phytochemicals in the sample (i.e., the extracts dissolved in methanol), the HPLC-diode array detector (DAD) (G7117C, Agilent, Santa Clara, CA, USA) analysis was conducted according to our previous study [12].An INNO column C18 (5 µm, 4.6 mm × 250 mm) was used for analysis and the column temperature was set to 25 • C. A volume of 5 µL of the sample was injected, and the gradient mode was set as follows (solvent A, 0.03% phosphoric acid in deionized water; solvent B, acetonitrile): 0 min, 90% A; 15 min, 80% A; 28 min, 60% A; 36 min, 25% A; 38 min, 90% A; and 50 min, 90% A. The monitoring wavelengths were 250 nm (for vanillic acid), 280 nm (for caffeic acid and gallic acid), and 360 nm (for luteolin, quercetin, and kaempferol).The standard materials of the phytochemicals were selected based on a previous study, which reported the major phytochemicals of P. aizoon [3].

Assessment of Antioxidant and Antibacterial Activity 2.5.1. Antioxidant Activity
Various concentrations of the extracts (20-60 and 240-280 µg/mL) or ascorbic acid (7-11 and 50-90 µg/mL) were prepared and then used to evaluate their antioxidant activity.The ABTS method can be used to evaluate the antioxidant activity of hydrophilic and lipophilic compounds, whereas the DPPH method can only evaluate hydrophobic compounds.Therefore, the antioxidant activity of the extracts was assessed based on two methods [12,15].After the ABTS cation radical scavenging reaction of P. aizoon extracts, the absorbance (A) was recorded at 734 nm.The radical scavenging activity was calculated using Formula (1).After the DPPH free radical scavenging reaction of P. aizoon extracts, the absorbance (A) was recorded at 517 nm.The radical scavenging activity was calculated using Formula (1).

Radical scavenging activity
where A is the absorbance at 734 nm or 517 nm (blank solution: methanol).The data are expressed as the concentration of P. aizoon extracts required to scavenge 50% of the initial radicals (i.e., IC 50 ).

Antibacterial Activity
The antibacterial activity of P. aizoon extracts was evaluated according to Dutta et al. [16] with minor modifications.Escherichia coli and Staphylococcus aureus were cultured in a nutrient broth medium for 24 h.The cultured broth with an optical density at 600 nm (OD 600 nm ) = 0.1 was inoculated into 5 mL of the nutrient broth medium.P. aizoon extracts were not included in the control group, and the extracts were added to the experimental group (final concentration of extracts in medium = 1 g/L).The broth was incubated at 37 • C and 180 rpm for 1 day, and the OD 600 nm of the broth cultured for 4, 8, and 24 h was measured.In addition, to confirm viable cells, the broth cultured for 24 h was spread on a nutrient agar plate and incubated at 37 • C for 1 day.

Statistical Analysis
The extraction process was performed in triplicate to determine the extraction yield from P. aizoon.Phenol and flavonoid content determination and bioactivity (antioxidant and antibacterial activity) evaluation were performed in triplicate.All data are expressed as the mean ± standard deviation.Chromatographic analysis was performed once.Significant differences in antioxidant and antibacterial activities between the control (or reference group) and the experimental group were identified by a t-test with Sigmaplot (version 12.5; Systat Software Inc., San Jose, CA, USA).

Analysis of Phytochemicals in Extracts from Phedimus aizoon
Ultrasound-assisted extraction was performed to produce extracts from P. aizoon.As a result, the extraction yield was determined to be 16.56 ± 0.39% (dry weight basis) (Table 1).The content of phenolics and flavonoids in the extracts plays an important role in their bioactivity, and thus, the analysis was carried out on P. aizoon extracts.The total phenolic content and the total flavonoid content of the extracts from P. aizoon were determined to be 126.3 ± 2.2 mg caffeic acid equivalent (CAE)/g extracts and 31.0 ± 0.5 mg catechin equivalent (CE)/g extracts, respectively, which means that about 12.6% and 3.1% of the extracts were phenolics and flavonoids (Table 1).Considering the extraction yield (16.56%) and the phenol and flavonoid content in the extracts, the yield of phytochemicals recovered from 100 g of P. aizoon was estimated to be about 2.09 g phenol and 0.51 g flavonoid/100 g biomass (dry weight basis).

HPLC-DAD Analysis
Major bioactive compounds of P. aizoon, including phenolics and flavonoids, were analyzed by HPLC-DAD analysis (Figure A1).As known compounds of Phedimus, caffeic acid, gallic acid, vanillic acid, luteolin, quercetin, kaempferol, catechin, myricetin, rutin, and hesperidin were analyzed.Table 3 lists the detected compounds and their content in the extracts from P. aizoon.The contents (mg/g extracts) were high in the order of gallic acid (2.75), vanillic acid (0.50), quercetin (0.19), caffeic acid (0.13), luteolin (0.12), and kaempferol Plants 2024, 13, 1915 6 of 11 (0.06).Other bioactive compounds such as catechin, myricetin, rutin, and hesperidin were not detected.The antioxidant activity of P. aizoon extracts was evaluated based on radical scavenging activity.Two radicals (ABTS cation and DPPH free) were used for the evaluation, and the results are shown in Table 4.In an ABTS cation radical-based evaluation, 260.0 ± 2.6 µg/mL of the extracts was required for scavenging 50% of the radical.As a reference antioxidant, 72.9 ± 1.0 µg/mL of ascorbic acid was required for scavenging 50% of the ABTS cation radical.In a DPPH free radical-based evaluation, 41.0 ± 2.3 µg/mL of the extracts or 9.8 ± 0.2 µg/mL of ascorbic acid was required for scavenging 50% of the DPPH free radical.The results imply that the activity of the extracts to scavenge ABTS cation and DPPH free radicals is 28% and 24% of that of ascorbic acid, respectively.

Antibacterial Activity
The antibacterial activity of the extracts from P. aizoon was evaluated based on cell growth profiling.The medium with 1 g/L of the extracts from P. aizoon was used for the qualitative evaluation, and the results are shown in Figure 2. In the medium without the extracts from P. aizoon, the growth of E. coli (Gram-negative bacteria) and S. aureus (Gram-positive bacteria) was increased by 24 h.The cell growth (OD 600 nm ) of E. coli and S. aureus measured at 4, 8, and 24 h was approximately 0.12, 0.29, and 0.71 and 0.12, 0.19, and 0.90, respectively.In contrast, no growth of E. coli and S. aureus cells was observed in the medium with the extracts from P. aizoon at 24 h.Preliminary investigations on the antibacterial activity of the positive control (ampicillin) showed that the minimum inhibitory concentration against E. coli and S. aureus was about 1.6 and 0.8 mg/L, respectively.Agar plates spread with 24 h-cultured broth of two strains proved that there were no viable cells of the two strains (Figure 2).

Discussion
The extraction yield in the ultrasound-assisted extraction (UAE) process for P. aizoon was about 16.56%, and the total phenol and flavonoid contents of the extracts were 126.3 ± 2.2 and 31.0 ± 0.5 mg/g, respectively (Table 1).This means that the phenol yield and flavonoid yield were 1.69% (i.e., 1692.4 mg/g) and 0.42% (i.e., 415.4 mg/g), respectively.Few previous studies have quantified the total phenol and flavonoid contents (or yields) of P. aizoon extracts.Among the conventional extraction techniques, in the maceration process for P. aizoon, phenol or flavonoid yield was not available.In the Soxhlet extraction process for P. aizoon, the flavonoid yield was determined to be approximately 18.67 mg/g [10].In the case of non-conventional extraction processes, the flavonoid yield was achieved at approximately 24.87 mg/g under optimal MAE conditions (20 min, 57 °C, 20 mL solvent/g solid, and 80.6% ethanol) [10].Yin and Batbatan [9] reported the optimal conditions of the UAE process for P. aizoon, and the flavonoid yield was 10.77 mg/g under the optimal conditions (1 g solid/55 mL solvent, 60% ethanol, 45 °C, 25 min, and 150 W ultrasound power).The relatively high flavonoid yield in the present study can be attributed to the sufficient time (3 days in total) of the UAE process (see Section 2.3).Further studies should propose optimized UAE conditions to obtain high yields in a shorter time.
The results of the GC-MS analysis identified various phytochemical and bioactive compounds in the extracts from P. aizoon (Table 2).Cyclohexasiloxane, dodecamethyl-has been reported to have hair-conditioning, antimicrobial, antiseptic, and skin-conditioning activities [17].Cycloheptasiloxane, tetradecamethyl-also has various bioactivities such as antibacterial, immunomodulatory, antitumor, antifungal, and antifouling activities [17].In addition, the biological activities of various phytochemicals detected by GC-MS

Discussion
The extraction yield in the ultrasound-assisted extraction (UAE) process for P. aizoon was about 16.56%, and the total phenol and flavonoid contents of the extracts were 126.3 ± 2.2 and 31.0 ± 0.5 mg/g, respectively (Table 1).This means that the phenol yield and flavonoid yield were 1.69% (i.e., 1692.4 mg/g) and 0.42% (i.e., 415.4 mg/g), respectively.Few previous studies have quantified the total phenol and flavonoid contents (or yields) of P. aizoon extracts.Among the conventional extraction techniques, in the maceration process for P. aizoon, phenol or flavonoid yield was not available.In the Soxhlet extraction process for P. aizoon, the flavonoid yield was determined to be approximately 18.67 mg/g [10].In the case of non-conventional extraction processes, the flavonoid yield was achieved at approximately 24.87 mg/g under optimal MAE conditions (20 min, 57 • C, 20 mL solvent/g solid, and 80.6% ethanol) [10].Yin and Batbatan [9] reported the optimal conditions of the UAE process for P. aizoon, and the flavonoid yield was 10.77 mg/g under the optimal conditions (1 g solid/55 mL solvent, 60% ethanol, 45 • C, 25 min, and 150 W ultrasound power).The relatively high flavonoid yield in the present study can be attributed to the sufficient time (3 days in total) of the UAE process (see Section 2.3).Further studies should propose optimized UAE conditions to obtain high yields in a shorter time.
In fact, P. aizoon extracts showed antioxidant and antibacterial activities (Table 4 and Figure 2).Qi et al. [25] optimized process conditions to maximize the flavonoid extraction yield from P. aizoon and evaluated the ABTS cation and DPPH free radical scavenging activities of the extracts based on their flavonoid concentration: (1) P. aizoon extracts and vitamin C (i.e., ascorbic acid) at 0.3 mg/mL scavenged about 96.2% and 99.0% of ABTS cation radicals, respectively; (2) P. aizoon extracts and vitamin C at 2.0 mg/mL scavenged about 85.9% and 98.8% of DPPH free radicals, respectively [25].In this study, the IC 50 of the prepared P. aizoon extracts was 260 µg/mL and 41 µg/mL for ABTS cation and DPPH free radicals, respectively (Table 4).Nevertheless, due to the limited number of previous studies evaluating the antioxidant activity of P. aizoon in vitro and the different criteria for the concentration (extract or flavonoid), the antioxidant properties of P. aizoon extracts as natural antioxidants should be further evaluated.
P. aizoon extracts showed antibacterial activity against both E. coli and S. aureus (Figure 2).Several previous studies have reported the antibacterial activity of P. aizoon extracts against the Gram-negative bacteria Aeromonas [26], Shewanella putrefaciens [27], and Pseudomonas fragi [5].In contrast, Oyungerel and Kim [28] reported that P. aizoon extracts showed antibacterial activity against S. aureus, but not against E. coli.Based on these two previous studies and the current study, it is assumed that P. aizoon extracts have antibacterial activity against both Gram-negative and Gram-positive bacteria.The antimicrobial activity of P. aizoon extracts was summarized as the disruption of cellular metabolic processes, redox homeostasis, and the cause of damage to the bacterial surface and the membrane [3].The treatment of Gram-negative bacteria Pseudomonas fragi with flavonoids from P. aizoon resulted in the disruption of the intracellular sulfate assimilation pathway and disturbances in glutathione redox homeostasis [5].Therefore, the antibacterial activity of the extract prepared in this study against E. coli could be attributed to these mechanisms.Until now, regarding the antibacterial activity of P. aizoon extracts, advanced research (antibacterial mechanism, application as natural replacement for preservatives) has been focused on Gram-negative bacteria [5,26,27]; thus, further studies should be conducted in depth on Gram-positive bacteria.In addition, for industrial production of P. aizoon extracts, an evaluation of the usability of solvents that are generally recognized as safe (GRAS) and optimization of the extraction process can be performed [29].The produced P. aizoon extracts are expected to be utilized as bioactive compounds for the fabrication of antioxidant and antibacterial polymers and nanocomposites [30,31].

Conclusions
In conclusion, this study established the composition and bioactivity of phytochemicalrich P. aizoon extracts with high potential as natural bioactive substances.By applying the ultrasound-assisted extraction (UAE) process, the extracts were produced from P. aizoon with a yield of about 16.56%, of which more than 12.6% were phenolic compounds.Well-known bioactive compounds such as cyclohexasiloxane, dodecamethyl-, tetradecane, pentacosane, and hexadecanoic acid were identified, and six compounds were quantified, including gallic acid, vanillic acid, and quercetin.Of these, gallic acid was present in the

2. 4 .
Phytochemical Analysis 2.4.1.Estimation of Phenolic Content and Flavonoid Content • C.After 8 min, 150 µL of Na 2 CO 3 (20% solution) was added and incubated at 25 • C.After 60 min, the absorbance (A) of the final mixture was recorded at 700 nm.The data are shown as mg caffeic acid equivalent (CAE) per g extracts.For the estimation of total flavonoid content, 50 µL of the sample and 30 µL of NaNO 2 (5% solution) were mixed and incubated at 25 • C.After 6 min, 50 µL of AlCl 3 (10% solution) was added and incubated at 25 • C.After 5 min, 300 µL of NaOH (1 M solution) and 1000 µL of water were added and incubated at 25 • C.After 15 min, the absorbance (A) of the final mixture was recorded at 510 nm.The data are shown as mg catechin equivalent (CE) per g extracts.

Figure 2 .
Figure 2. The profiles of the cell growth (OD600 nm) of Escherichia coli (Gram-negative bacteria) and Staphylococcus aureus (Gram-positive bacteria) in nutrient broth media with (experimental group) or without (control group) extracts from Phedimus aizoon.Viable cells of both bacteria were not observed in the nutrient agar medium after being spread with the 24 h-cultured broth and incubated, as shown in the right side.The asterisk indicates a significant difference compared to the control group (p < 0.05).

Figure 2 .
Figure 2. The profiles of the cell growth (OD 600 nm ) of Escherichia coli (Gram-negative bacteria) and Staphylococcus aureus (Gram-positive bacteria) in nutrient broth media with (experimental group) or without (control group) extracts from Phedimus aizoon.Viable cells of both bacteria were not observed in the nutrient agar medium after being spread with the 24 h-cultured broth and incubated, as shown in the right side.The asterisk indicates a significant difference compared to the control group (p < 0.05).

Table 1 .
The extraction yield for Phedimus aizoon in the ultrasound-assisted extraction process and the contents of bioactive compounds in the extracts.

Table 2 .
Profiles of phytochemicals of extracts from Phedimus aizoon in GC-MS analysis.

Table 3 .
Major phenolic acids and flavonoids in extracts from Phedimus aizoon in HPLC analysis.

Table 4 .
ABTS cation and DPPH free radical scavenging activity of Phedimus aizoon extracts.The asterisk indicates a significant difference compared to the reference antioxidant (p < 0.05).