Polyphenol and Flavonoid Content and Antioxidant Activity of Hypericum perforatum L. (St. John’s Wort) Extracts for Potential Pharmaceutical and Cosmetic Applications

Abstract

St. John’s wort (Hypericum perforatum) has been used for centuries in traditional medicine owing to its high content of various bioactive metabolites and wide geographic occurrence. Nowadays, it plays an important role in the pharmaceutical industry and is increasingly significant in modern cosmetology. The objective of this study was to assess the antioxidant activity and compare the content of polyphenolic compounds in two commercial extracts of H. perforatum, glycerol–water and propylene glycol–water, which are used as cosmetic raw materials. The HPLC method was used to determine phenolic compounds. The total polyphenol content and total flavonoid content of H. perforatum extracts were determined using spectrophotometric methods. Free radical-scavenging properties were analyzed using a 2,2-diphenyl-1-picrylhydrazyl radical assay with electron paramagnetic resonance spectroscopy (DPPH-EPR assay), as well as the ferric reducing antioxidant power (FRAP) method. St. John’s wort extracts were able to scavenge free radicals, indicating beneficial cellular protection against oxidative stress. The use of non-toxic extractants makes it possible to obtain extracts with high antioxidant potential, which can be safely used in the pharmaceutical and cosmetics industries. The results of this study, i.e., the values for TPC, TFC, and antioxidant activity (DPPH and FRAP), suggest that Hypericum perforatum, especially the glycerol–water extract, has antioxidant potential.

1. Introduction

St. John’s wort is one of the most commonly used medicinal plants in the world due to its well-documented pharmacological activity, including antidepressant, antiviral, and antibacterial effects [1]. There are numerous products containing Hypericum perforatum in the form of dried aerial parts or various types of extracts that are used as phytopharmaceuticals and nutraceuticals, some of which are protected by patents. Most commercially available St. John’s wort preparations in Poland and Europe are ethanol–water extracts or dry extracts contained in solid forms such as tablets, capsules, or granules. Water infusions are currently used in the treatment of gastrointestinal diseases, while ethanol extracts containing hypericin and hyperforin affect the central nervous system [2]. The external use of H. perforatum preparations, mainly in oil or tinctures, has a long tradition. St. John’s wort preparations, such as Oleum Hyperici (oil macerates) and organic extracts, are often used externally in traditional medicine. The red, oily extract has traditionally been used to treat wounds, burns, and bruises. Products for external use also promote the healing of chronic and acute lesions and are indicated for the treatment of skin defects associated with skin disorders. The antibacterial, antiviral, anti-inflammatory, and anticancer properties, as well as the stimulation of tissue growth and differentiation, make St. John’s wort useful in dermatology, including in the treatment of atopic dermatitis, psoriasis, herpes infections, and skin cancer [3]. This plant is also a component of some cosmetic formulations, where it plays a role as an antiaging and exfoliating agent. It strengthens the barrier function of the skin, inhibits inflammatory mediators, protects against UV radiation, promotes epidermal regeneration, and inhibits tyrosinase, collagenase, and elastase [4].

Table 1. Topical uses for St. John’s wort products in dermatology and cosmetology.

Type of Preparation	External Use	Ref.
oil extract	diabetic surgical wounds, rats wound healing of diabetic oral mucosa, rats palatal mucosa wounds, rabbits incisional wounds on the interscapular region, rats burn wounds, rats pressure sores in intensive care unit patient	[5,6,7,8,9]
oil extract-incorporated chitosan film for wound dressing applications	antimicrobial test (Escherichia coli and Staphylococcus aureus), potential and novel biomaterial for wound healing applications	[10]
ointment	episiotomy wound, primiparous women patients with mild to moderate plaque-type psoriasis on both sides of the body, without medical treatment for the past 2 months	[11,12]
ethanolic extract	wound healing activity, chicken embryonic fibroblasts psoriasis-like keratinocytes in vitro and ex vivo anti-elastase and anti-collagenase	[13,14,15]
Gels
bigels containing either “free” extract or extract encapsulated in nanostructured lipid carriers	skin excision wound model, rats	[16]
gel containing niosomes with 80% ethanolic extracts	wound healing activity, mongrel dogs	[17]
gel contained methanolic extract	burn wounds, rats	[18]
Creams
cream containing 5% apolar extract, overcritical carbon dioxide as eluting agent	twenty-one patients suffering from mild to moderate atopic dermatitis	[19]
creams containing ethanolic extracts at 5% and 15% concentrations	antibacterial activities were tested using E. coli and S. aureus bacteria, potential use in the cosmetic sector	[20]
cream (O/W emulsion type) containing 15% oil extract	anti-inflammatory effect on sodium lauryl sulfate (SLS)-irritated human skin, antimicrobial activity	[21]
petroleum ether extract from root cultures	proliferative effect, human keratinocytes (HaCaT), and human dermal fibroblast monolayers	[22]
ethyl acetate, methanol, and water extracts	anti-tyrosinase, antioxidative properties	[23,24]

presents the use of various St. John’s wort preparations in the treatment of dermatological diseases and cosmetology.

Growing consumer awareness and demand for cosmetic products containing raw materials of plant origin stimulate scientists to search for new active substances and to improve existing raw materials used in the production of cosmetics. The chemical composition of H. perforatum, its biological properties, and its use in medicine and pharmacy are widely known. Despite well-documented effects on the skin, which include anti-inflammatory, anti-tyrosinase, anti-collagenase, anti-elastase, UV photoprotective, and wound healing properties, the potential of St. John’s wort is not fully used in cosmetology [4]. Several commercial extracts or isolated compounds obtained from H. perforatum are currently available in the Polish market and are utilized in facial/body care and cleansing cosmetic products.

Currently, the cosmetics industry must meet consumer safety requirements and comply with the principles of green chemistry. Using safe, ecological solvents and extractants is one of these principles. Available data on the biological activity of H. perforatum and other Hypericum spp. are mainly based on oil, alcoholic, or hydroalcoholic extracts, which have limited application to actual skin care products. From a practical point of view, plant extracts containing propylene glycol (PEG) as a solvent are more useful in the cosmetics industry. Glycol or water-glycol extracts are characterized by good solubility in water and stability. Using PEG reduces water activity and, thus, the risk of contamination of the cosmetic product. The application of PEG also reduces the amount of preservative(s) used in the finished product. PEG increases the solubility of other poorly soluble raw materials, increases the viscosity of the cosmetic, and acts as a humectant [25].

Glycerol (GL) is one of the most frequently used ecological extraction solvents and is also an important cosmetic raw material, acting as a humectant and an agent that prevents the cosmetic mass from drying out. It is a raw material of natural origin, odorless, non-toxic, and biocompatible [26,27]. GL can also be a component of natural deep eutectic solvents (NADES), defined as a combination of two or more natural compounds with the properties of accepting and delivering hydrogen bonds. In NADES, GL acts as a hydrogen bond donor, alongside other substances such as sugars, amino acids, succinic acid, citric acid, lactic acid, oxalic acid, and sodium acetate. Among others, these mixtures are characterized by low toxicity and high biodegradability, so they are environmentally friendly. NADES are regularly used in the extraction of plant material due to their ability to dissolve various types of natural bioactive compounds, including flavonoids and other phenolic compounds [27,28,29].

The aim of this study was to determine the content of polyphenolic compounds, including flavonoids, and to confirm the antioxidant properties of two commercial extracts from H. perforatum: glycerol–water (GL-WE) and propylene glycol–water (PEG-WE), which are used as cosmetic raw materials.

2. Materials and Methods

2.1. Plant Material and Reagents

A commercial glycerol–water extract (GL-WE) and a propylene glycol–water extract (PEG-WE) of H. perforatum (Greenvit, Radzymin, Poland) were used in this study. For both extracts, the drug/extract ratio (DER) was 1:5. GL-WE contained sodium benzoate and potassium sorbate as preservatives, as well as citric acid as a pH regulator, while PEG-WE did not contain any additional excipients.

Demineralized water, ethanol 96% p.a. (Avantor Performance Materials, Gliwice, Poland), gallic acid, Folin–Ciocalteau reagent, catechin, sodium carbonate, sodium nitrite, sodium hydroxide, aluminum chloride, DPPH, phosphate buffer, FeCl₃, TPTZ, HCl, and Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid) (Sigma Aldrich, Poznań, Poland), as well as formic acid 98–100% (Merck, Darmstadt, Germany) were used. All solvent chemicals were of analytical grade. Gradient-grade acetonitrile (Merck, Germany) was used for the HPLC analysis.

2.2. Determination of the Total Polyphenol Content (TPC)

The spectrophotometric method using Folin’s reagent was used to determine the total polyphenol content of H. perforatum [30]. Absorbance was measured using an Evolution 60S UV-Visible spectrophotometer (Thermo Scientific, Waltham, MA, USA) at a wavelength of λ = 765 nm. TPC was expressed as gallic acid equivalents (GAE) in milligrams per 100 mL [mg GAE/100 mL]. Three replicates were performed for each sample.

2.3. Determination of Total Flavonoid Content (TFC)

The spectrophotometric method described by Kim et al. [31] was used to determine the total flavonoid content of H. perforatum. Absorbance was measured using an Evolution 60S UV-Visible spectrophotometer (Thermo Scientific, Waltham, MA, USA) at a wavelength of λ = 510 nm. TFC was expressed as catechin equivalents (CA) in milligrams per 100 mL [mg CA/100 mL]. Three replicates were performed for each sample.

2.4. HPLC Analysis

Quantitative analysis was performed using a Hitachi Chromaster HPLC system with a DAD diode detector (model 5430), a gradient pump (model 5160), and a column thermostat (model 5310). The GLW-E and PEG-E were filtered through a 0.45 µm filter, and 20 μL was injected without dissolution into a Merck Purospher STAR RP-18e column (250 mm × 4.6 mm, 5 μm). Chromatographic separations were carried out at 30◦C, with a flow rate of 1 mL/min. The mobile phase gradient system consisted of 0.1% (v/v) formic acid (A) and acetonitrile (B), with the following gradient conditions: 0–35 min (10–20% B), 35–60 min (20–35% B), and 60–70 min (10% B). The chromatograms were monitored at 330 nm. For hypericin, the gradient elution was extended to 90%, but it was not observed. The content was calculated using calibration curves for 330 nm (for p-coumaric acid, 310 nm). All measurements were performed in triplicate.

Table 2. Concentration range, LOD detection limit, and LOQ qualification limit.

No.	Compound	RT (min)	Calibration Curve	R2	Linear Range (mg/mL)	LOD (mg/mL)	LOQ (mg/mL)
1	nCGA	8.5	A =19,417,474 * C − 34,606	0.999	0.01–1.00	0.003	0.010
2	p-Coumaric acid	12.5	A = 67,676,230 * C − 37,723	0.999	0.01–1.00	0.004	0.009
3	CGA	14.5	A = 22,172,995 * C − 59,822	0.999	0.01–1.00	0.003	0.009
4	Rutin	33.5	A = 10,349,788 * C − 10,128	0.999	0.01–1.00	0.009	0.027
5	Hyperoside	34.9	A = 15,145,554 * C − 139,314	0.999	0.01–1.00	0.006	0.017
6	Isoquercitrin	36.1	A = 22,172,995 * C − 59,822	0.999	0.01–1.00	0.006	0.0019

nCGA, neochlorogenic acid; CGA, chlorogenic acid; A, peak area; C, concentration (mg/mL) of the compound.

contains the limit of detection (LOD) and limit of quantification (LOQ). LOD and LOQ were determined according to the following formulas: LOD = 3.3 × σ/S and LOQ = 10 × σ/S (σ—the standard deviation of the y-intercept, and S represents the slope of the calibration curve). The % relative standard deviation (RSD) for intraday variation remained below 1%.

2.5. Evaluation of Antioxidant Activity

2.5.1. DPPH Assay

The antioxidant activity was measured by electron paramagnetic resonance (EPR) spectroscopy using microwaves with a frequency of 9.3 GHz from an X-band (Mini Scope MS 200 EPR spectrometer, Magnettech GmbH, Berlin, Germany) and 2,2-diphenyl-1-picrylhydrazyl radical (DPPH). EPR measurements were performed with the following parameters: microwave power: 12 mW, central field: 330.48 mT, sweep range: 9.92 mT, sweep time: 20 s, modulation amplitude: 0.10 mT, and room temperature: 25 °C. Briefly, 0.5 mL of DPPH solution was added to 50 μL of H. perforatum extract. A blank test was performed by replacing the extract with the solvent (ethanol). The samples were mixed and left in the dark at room temperature for 20 min. EPR spectra of the extract and blank were recorded as derivatives of absorption curves, and the absorption signal area was obtained by double integration. Three replicates were performed for each sample. Free radical-scavenging activity was expressed as the percentage of DPPH decrease based on the following formula:

DPPH scavenging activity (%) = [(I₀ − I₁)/I₀] × 100,

where

• I₀—the signal intensity of the DPPH radical from the control;
• I₁—the signal intensity of the DPPH radical from the sample.

2.5.2. FRAP Assay

The ferric reducing antioxidant power (FRAP) assay was conducted using the established methodology pioneered by Benzie and Strain [32]. The experimental apparatus employed for the measurements was a UV-Vis Evolution 60S spectrophotometer (Thermo Scientific, Waltham, MA, USA). The FRAP reagent was prepared by mixing three components in a ratio of 10:1:1 (v/v/v), i.e., acetate buffer (300 mM, pH 3.6), a 10 mM TPTZ solution in 40 mM HCl, and a 20 mM FeCl₃ solution. The FRAP mixture (1 mL) was added to the extract to be analyzed (50 µL), then thermostated at 37 °C for 4 min, and the absorbance was measured at λ = 593 nm. Trolox was used as a standard. The results were expressed as mmol Trolox equivalent (TE)/100 mL of extract.

2.6. Statistical Analysis

The Statistica program, version 12.0 (StatSoft, Krakow, Poland), was utilized for statistical evaluation. A one-way ANOVA was conducted, with a significance level of p ≤ 0.05. The Tukey test (n = 3) was used to assess differences between groups.

3. Results and Discussion

The genus Hypericum includes more than 500 species; however, Hypericum perforatum L. (St. John’s wort) has been studied intensively [33]. H. perforatum has been used to treat a wide spectrum of ailments owing to its high content of various bioactive metabolites, including flavonoids and biflavonoids, flavonoid glycosides (hyperoside), phloroglucinols (hyperforin), naphthodianthrones (hypericin), caffeic acid derivatives, and anthocyanidins [34]. Flavonoids are the major group of biologically active compounds in H. perforatum (ranging from 2% to 5%) and mainly include flavonols (kaempferol and quercetin) and quercetin glycosides (hyperoside, rutin, quercitrin, and isoquercitrin) [35]. They have been used in cosmetics, skin care products, and anti-wrinkle skin agents [36,37] but have had the most applications in the field of medicine. These biological activities depend on the type of flavonoid and its bioavailability.

Different solvents were observed to have varying efficiencies in recovering polyphenols, including flavonoids, from H. perforatum. In the present study, two commercial extracts of H. perforatum were investigated: glycerol–water (GL-WE) and propylene glycol–water (PEG-WE). The extracts were prepared according to a standardized protocol used by the manufacturer, with a DER of 1:5. Arsić tested St. John’s wort extract with the same DER value [38]. However, the German Pharmacopoeia recommends preparing oil extracts of the raw material using a DER value of 1:4 [39], which was used in the research conducted by Heinrich et al. [40].

3.1. TPC and TFC

A review of the literature shows that in most studies on H. perforatum, extraction was carried out using toxic solvents such as methanol and acetone, which are not compatible with food, cosmetic, or pharmaceutical applications. Moreover, industrial-scale production is costly and harmful to the environment. The most commonly used solvents are pure ethanol and methanol, but they may be even more efficient when mixed with water [41]. Other authors report the polyphenol content of the methanolic extracts as follows: 505.7 [35], 461.19 [42], 355.01 [23], and 64.08 [43] mg GAE/g dw. The values reported using ethanol or ethanol–water solvents vary within a vast range, from 15.54 [33] and 64.4 [44] to 104.18 mg GAE/g dw [45]. However, due to the different solvents used in the cited articles and the different units in which the results are presented, it is difficult to compare them with the results obtained in the present paper. This study was carried out using non-toxic extraction media (GL and PEG). The results of TPC and TFC determination in GL-WE and PEG-WE of H. perforatum are compared in

Table 3. Total polyphenol and flavonoid content of H. perforatum extracts.

H. perforatum Extract	TPC [mg GAE/100 mL ± SD]	TFC [mg CA/100 mL ± SD]
GL-WE	599.74 ± 1.60 a	16.90 ± 0.14 a
PEG-WE	265.64 ± 1.30 b	9.76 ± 0.02 b

GL-WE, glycerol–water extract; PEG-WE, propylene glycol–water extract; TPC, total polyphenol content; TFC, total flavonoid content; GAE, gallic acid equivalent; CA, catechin equivalent; SD, standard deviation. Mean values marked with different letters in columns differ statistically significantly (p ≤ 0.05), n = 3.

. A higher concentration of polyphenols was observed in GL-WE. Glycerol–water solvents have been successfully used to extract polyphenols from various plants [46,47,48,49]. Karakashov et al. [34] demonstrated that an extraction yield of total polyphenols (89.9 mg GAE/g dw) was achieved using 10% (w/v) aqueous glycerol, which was significantly higher than that attained with water. However, the use of GL for the preparation of plant extracts is not as common as the use of water or ethanol. GL is a suitable extraction solvent due to its low cost, lack of toxicity, incombustibility, low volatility, and easy blending with water (which allows for the extraction of polyphenolic compounds) [50]. According to bibliographic data for Hypericum spp. GL-WE, the following TFC values were obtained: 86.6 mg GAE/g dw [34] and 54.83 mg GAE/g dw [51].

It should be noted that polyphenols can be easily solubilized in polar protic media, such as ethanol–water and glycerol–water mixtures [34]. Higher yields have been obtained by increasing the polarity of the solvent, indicating that mainly hydrophilic compounds were extracted. Therefore, extraction using the tea method or a mixture of water and organic solvents resulted in higher yields compared with pure organic solvents or continuous boiling with water for extended periods [44].

3.2. HPLC Analysis

Extracts of St. John’s wort were analyzed qualitatively and quantitatively using HPLC chromatography. The GL-WE and PEG-WE contain chlorogenic acids, p-coumaric acid, rutin, hyperoside, and isoquercitrin (

Table 4. Content of phenolic acids and flavonoids in H. perforatum extracts.

	H. perforatum Extract	GL-WE [mg/100 mL ± SD]	PEG-WE [mg/100 mL ± SD]
1	nCGA	10.37 ± 0.04 a	16.36 ± 0.05 b
2	p-Coumaric acid	3.71 ± 0.01 a	2.09 ± 0.04 a
3	CGA	7.28 ± 0.04 a	10.94 ± 0.07 b
4	Rutin	40.65 ± 0.19 a	7.12 ± 0.09 b
5	Hyperoside	23.26 ± 0.12 a	9.01 ± 0.12 b
6	Isoquercitrin	10.47 ± 0.09 a	1.65 ± 0.05 b

GL-WE, glycerol–water extract; PEG-WE, propylene glycol–water; SD, standard deviation; nCGA, neochlorogenic acid; CGA, chlorogenic acid. Mean values marked with different letters in rows differ statistically significantly (p ≤ 0.05), n = 3.

); their chromatograms are shown in Figure 1. The differences in the composition of both extracts are noticeable. GL-WE contains more rutin, hyperoside, and isoquercitrin than PEG-WE, while the latter contains more chlorogenic acids. All mean values differ statistically significantly (p ≤ 0.05), except for the p-coumaric acid concentration.

There are no data in the literature regarding differences in the extraction efficiency of polyphenols for glycol and glycerol. Koigerova et al. [52] investigated the dependence of the total content of polyphenols, flavonoids, and antioxidants, as well as the scavenging of free radicals by DPPH and the concentration of flavonoid aglycones in the extract of Chamaenerion angustifolium L., on the type used for the extraction of NADES containing glycerol and propylene glycol. The highest yield of polyphenols was obtained using NADES containing glycerol; however, an important factor in this case was the type of hydrogen bond acceptor and temperature.

Classical liquid extraction using a water/glycerol mixture showed a high yield of polyphenols (chlorogenic acids and quercetin glycosides). In the GL-WE model examined, these substances were also predominant. Owing to the use of fatty oils containing medium-chain triglycerides as extractants, quercetin, kaempferol, biapigenin, hyperforin, and adhyperforin were extracted from the raw material [53].

Chromatographic analysis in our study did not show the presence of naphthodianthrones in the tested extracts, probably due to limited solubility in almost all solvents. Currently, according to the Polish Pharmacopoeia X, the raw material is standardized on the total content of hypericin, which must be no less than 0.08% [54]. The total content of hypericin depends on the latitude, time of harvest, plant’s habitat, drying and storage methods, and other factors [55,56]. Hypericin is a hydrophobic substance that is poorly soluble In water and oil; however, it is highly soluble in some solvents, such as ethanol, methanol, and ethyl acetate [57]. Nevertheless, some studies have identified hypericin in aqueous extracts [58,59]. Pseudohypericin is more soluble in polar solvents, which is mainly attributed to the presence of an additional hydroxymethyl moiety [60]. The use of hypericin in cosmetics is made difficult by its phototoxicity, poor water solubility, and high light sensitivity. In the GL- and PEG-based extracts examined in this study, the presence of naphthodianthrones, including hypericin, was not detected, which is advantageous for cosmetic applications. Moreover, hyperoside, a compound characteristic of H. perforatum, was present in predominant amounts alongside rutin in the GL-WE extract studied. In the study by Moukova et al. [61] it was shown that hyperoside acts as an effective protective compound against UV radiation. This was confirmed by atomic force microscopy, which examined morphological changes in HaCaT cells, and by a study conducted on a three-dimensional skin model. In the study by Mapoung et al. [62] it was demonstrated that the hyperoside-enriched fraction prepared from H. cordata leaf extract exhibited protective effects against UVB-induced skin photoaging in human skin fibroblasts through its antioxidant and anti-inflammatory properties. Moreover, hyperoside can induce collagen synthesis and inhibit MMP-1 expression by modulating the MAPK pathway and the nuclear transcription factor AP-1. A high content of rutin was observed in GL-WE, which exhibited antiaging activities through the inhibition of collagenase, tyrosinase, elastase, and hyaluronidase, and is therefore a valuable ingredient in plant raw materials used in cosmetic products [63].

3.3. Antioxidant Activity

Literature data and the results of the studies reported in this publication indicate that the chemical composition of extracts varies considerably depending on the extractant used, suggesting potential differences in the efficacy and use of each extract. The forms and stability of the compounds in the extracts from H. perforatum determine their biological activity. It appears challenging to obtain the complete chemical composition of this plant using a single extraction method and a single solvent. The choice of extraction method, in addition to extraction conditions such as temperature, solvent concentration, and duration, depends significantly on the compounds present in the plant and their properties (polarity and solubility). All of these factors may impact the bioactive properties of the obtained extract [64]. The available research results refer to extracts prepared using, among others, methanol or water, while no data are available on glycerol extracts, glycol extracts, or their mixtures with water. A study by Muzykiewicz et al. [65] showed that scavenging activity depended on the type of extractant, as well as the extraction time, ranging from 53.89% to 91.98%. The highest results were obtained for samples prepared in undiluted methanol and extracted for 60 min, whereas the antioxidant capacity of the aqueous extracts was low. The results presented in

Table 5. Antioxidant activity of H. perforatum extracts.

H. perforatum Extract	DPPH [% ± SD]	FRAP [mmol TE/mL ± SD]
GL-WE	79.44 ± 0.31 a	8.87 ± 0.38 a
PEG-WE	60.88 ± 0.30 b	6.75 ± 0.16 b

GL-WE, glycerol–water extract; PEG-WE, propylene glycol–water; DPPH, 2,2-diphenyl-1-picrylhydrazyl; FRAP, ferric reducing antioxidant potential; SD, standard deviation. Mean values marked with different letters in columns differ statistically significantly (p ≤ 0.05), n = 3.

indicate that the GL-WE of H. perforatum demonstrated stronger antioxidant properties than the PEG-WE due to higher DPPH scavenging activity and FRAP value.

The well-known antioxidant activity of H. perforatum extracts is related to the high content of phenolic compounds. However, there is still insufficient evidence to determine which class of phenols is most responsible for these antioxidant properties. In addition, the structures of antioxidants and the interactions between them play an important role in determining antioxidant activity [64]. It has been demonstrated that the free radical-scavenging activity is predominantly attributed to flavonoid glycosides and phenolic acids (such as chlorogenic acid), while phloroglucinols (which lack the polyphenolic structure), biflavonoids (which lack the catechol moiety), and naphthodianthrones exhibit no significant activity [66]. Flavonoid glycosides (mainly quercetin-3-O-rutinoside) and phenolic acids, in combination with a sugar unit (mainly galactoside and rhamnoside), appear to contribute significantly to the neutralization of free radicals, i.e., showing high antioxidant activity [67]. As demonstrated by Silva et al. [68], the antioxidant potential of H. perforatum ethanolic extracts is directly correlated with the presence of phenolic compounds, with quercetin and its glycosidic derivatives being primarily responsible for this property. These compounds play an important role in both radical scavenging and inhibiting lipid peroxidation activity. A study by Orčić et al. [69] showed that the antioxidant activity of extracts is strongly correlated with their composition; the most active fractions are those rich in flavonoid glycosides (followed by very small amounts of phenolic acids) and poor in biflavonoids (amentoflavone and biapigenin). In our study, the higher antioxidant activity of GL-WE compared to PEG-WE was also associated with a higher concentration of quercetin glycosides: isoquercitrin, rutin, and hyperoside. The rutin contained in GL-WE, as indicated by the literature data, has antioxidant and antiaging potential by inhibiting the mitochondrial aging process and increasing GSH content and SOD activity [70].

4. Conclusions

The findings of the studies presented herein, namely, total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity (DPPH and FRAP) values, indicate that H. perforatum, particularly GL-WE, possesses antioxidant potential. In the GL-WE extract, compounds such as rutin, hyperoside, and isoquercitrin, which show free radical-scavenging capacity, were identified, among others, and their content was significantly higher compared to the PEG-WE extract. The results of this study indicate the potential use of non-toxic polar extractants (glycerol–water and propylene glycol–water mixtures) and extracts based on these solvents in the cosmetics industry as valuable skin care raw materials, particularly for protecting the skin against free radicals that contribute to skin damage.