Fruits of Polish Medicinal Plants as Potential Sources of Natural Antioxidants: Ellagic Acid and Quercetin

Abstract

Due to their antioxidant and other beneficial properties, polyphenol-rich plants are important functional foods. The purpose of the study was to evaluate the content of two polyphenols—ellagic acid and quercetin—in fruits of wild medicinal plants of Polish origin, as potential sources of these compounds. The research material was chosen considering both the popularity of the fruits and their recognized medicinal and pharmaceutical properties. All selected fruits—barberry (Berberis vulgaris), blackthorn (Prunus spinosa), chokeberry (Aronia melanocarpa), elderberry (Sambucus nigra), hawthorn (Crataegus monogyna), lingonberry (Vaccinium vitis-idaea), rowanberry (Sorbus aucuparia), and sea-buckthorn (Hippophae rhamnoides syn. Elaeagnus rhamnoides)—are known for therapeutic use in Polish folk medicine. Extracts were analyzed for ellagic acid and quercetin content using UHPLC-ESI-MS/MS. Quantitative results revealed that barberries, blackthorn, and sea-buckthorn contained the highest amounts of ellagic acid, up to 3.29 ± 0.24, 3.50 ± 0.16, and 4.80 ± 0.18 μg/g dw, respectively, while lingonberry provided up to 196.20 ± 3.10 μg/g dw of quercetin, making it a valuable dietary source of this flavonoid. The study confirms that Polish wild medicinal plants are valuable reservoirs of key polyphenols relevant to human health and support their potential inclusion in dietary strategies for disease prevention.

1. Introduction

Ethnomedicinal plants are considered as the most natural, safe, and effective medicine [1]. The World Health Organization (WHO) promotes the use of Traditional Medicines in Primary Health Care (PHC) and recommends the appropriate use of ethnomedical plants as first-line treatment and prevention for various conditions such as cold, diarrhea, stomach pains, fevers, wounds, and metabolic diseases. The properties of medicinal fruits, included in ethnobotanical knowledge, represent a small area of “the precious traditional cultural treasure”. These plants were once an important component of life, later partially forgotten and undervalued, and now returning, in a slightly revised form. Modern research methods now allow for more precise knowledge about the same medicinal plants and rediscovery of their value. Plants can be used directly as therapeutic agents or serve as sources for novel drug structures. According to Newman and Cragg [2], the utility of natural products is still alive and well. Between 1981 and 2019, even up to 40% of approved drugs were derived—either directly or indirectly—from biological and natural products. Approximately 25% and 54.9% of molecules in the anticancer and antibacterial area, respectively, are obtained from natural products [2].

In Europe, hawthorn (Crataegusmonogyna) fruits have traditionally been used in the treatment of heart conditions due to their antispasmodic, cardiotonic, hypotensive, and antiatherosclerotic effects [3]. Extract from barberry (Berberis vulgaris) fruit lowers blood pressure [4]. Black chokeberry (Aroniamelanocarpa) can reveal wide antiviral efficacy against the multiplicity of the influenza virus strains and inhibits viral replication [5]. Elderberries (Sambucus nigra) are used in herbal remedies primarily for treating colds and flu [6]. Sloes, the fruit of blackthorn (Prunus spinosa), have been traditionally used as an astringent, diuretic, and purgative [7].

Fruits of wild plants are important not only for medicinal and pharmaceutical applications but also as ingredients in cosmetic products. Sea-buckthorn (Hippophae rhamnoides syn. Elaeagnus rhamnoides) extract or juice is used as a skin-conditioning and -protecting agent, while oil from the whole fruit or seeds serves as an emollient, and powder from the seed or husk shows abrasive properties. Fruit extracts from hawthorn, blackthorn, and barberry are also utilized in skincare formulations [8]. Moreover, fruits such as hawthorn, elderberry, and rowanberry (Sorbus aucuparia) are used as the components of food products, including liqueurs, vodkas, tea, jams, marmalades, and juices. The pharmacological activity of hawthorn fruits is attributed to bioactive compounds such as condensed proanthocyanidins and other glycosylated derivatives of flavonoids [3,9]. Additionally, the Polish Pharmacopoeia mentions hawthorn fruits as a medicinal plant.

Poland can be characterized as a country where the tradition of culinary use of wild plants became impoverished very early compared to some parts of Southern Europe. Although the contemporary use of wild plants is now almost entirely limited to fruits, these are becoming increasingly popular in cuisine due to growing media attention. Nowadays, barberry, blackthorn, elderberry, hawthorn, lingonberry (Vaccinium vitis-idaea), rowanberry, and sea-buckthorn are among the most popular wild fruits in Poland [10]. Moreover, some wild and native plants, including edible fruits, are sold at open-air markets in Poland, as they were in the past. The plants sold in such places are usually those that are culturally the most salient, especially wild fruits such as barberry, blackthorn, elderberry, hawthorn, lingonberry, rowanberry, and sea-buckthorn, but not chokeberry [10]. The same set of fruits was in a list of wild food plants used during the 20th and 21st centuries in Belarus, where the Polish–Lithuanian Commonwealth lived. Earlier, in the 19th century, barberry, blackthorn, lingonberry, and rowanberry fruits were already used in this area [11]. According to archival data from 1948 on wild food plants used in Poland, fruits were the most frequently gathered part of plants. The fruits were commonly consumed raw—especially by children as snacks—or processed into preserves. Among the most frequently collected fruits, lingonberry ranked 7th, while blackthorn, elderberry, and hawthorn are listed among the top 20 species [12]. The medicinal use of elderberry, lingonberry, and rowanberry is also mentioned in the paper concerning the folk culture of the Polish–Lithuanian–Belarusian borderland from the early 20th century [13]. Despite the health-related properties of chokeberry, its crop and usage spread in Poland relatively late, in the 20th century [5].

Fruits contain huge amounts of polyphenols, which are considered potent scavengers of free radicals and reactive oxygen species. Several studies have indicated that a high content of polyphenols corresponds to a high antioxidant capacity [14]. Among polyphenols, flavonoids are known to confer numerous health benefits in mammalian systems; thus, they act as antimicrobials, stimulate the production of antibodies, and exhibit hypotensive and anticancer effects due to their antioxidant properties [9]. Phenolic acids are involved in mechanisms of defense against biotic and abiotic stresses and may exhibit anticancer, anti-inflammatory, and antimicrobial potential [15]. The antioxidant properties of flavonoids and phenolic acids are associated with the presence of aromatic rings and free hydroxyl (–OH) groups in the structure [16].

Ellagic acid (EA, dilactone of hexahydroxydiphenic acid) and quercetin (Q, 3,3,4,5,7-pentahydroxylflavone) belong to the most well-known polyphenols—phenolic acids and flavonoids/flavonols, respectively. In plants, ellagic acid can occur in the free form (EA) or as conjugates with various sugars (EACs, glycosylated form), as well as polymeric ellagitannins (ETs) (hydrolysable tannins) from which it can be released upon hydrolysis [17]. Raspberries, strawberries, and pomegranates are well-recognized sources of EA and are available as dietary supplements. Quercetin is predominantly found in plants as glycosides (e.g., quercetinarabinosides in berries), while its aglycone form occurs less frequently [18].

EA and Q exhibit antiglycative functions, thereby reducing harmful effects associated with the formation of advanced glycation end products (AGEs) [16]. The ability to metabolize xenobiotics [19], hepatoprotective effects [20], and promising evidence about anticancer activity [21] of these polyphenols have also been reported. However, it should be highlighted that Q, at high concentrations, may exhibit mutagenic effects [22].

The purpose of this study was to verify whether fruits of Polish wild medicinal plants with known therapeutic uses can serve as good dietary sources of EA and Q. Taking into account both their popularity and medicinal/pharmaceutical properties, the following fruits were selected for this study: barberry, blackthorn/sloe, chokeberry, elderberry, hawthorn, lingonberry, rowanberry, and sea-buckthorn. In selecting these fruits, particular attention was given to species with a broad geographical distribution, ensuring their relevance not only within Poland but also across a significant part of Europe. Currently, little information is available on EA and Q content in these fruits. The determination of EA and Q in plant extracts was carried out using ultra-high-performance liquid chromatography–electrospray ionization tandem mass spectrometry (UHPLC-ESI-MS/MS).

2. Materials and Methods

2.1. Reagents

Ellagic acid (EA, 98%) and quercetin (Q, ≥95%) were purchased from LKT Laboratories, Inc. (St. Paul, MN, USA) and Sigma-Aldrich (St. Loius, MO, USA), respectively. Standard solutions of EA (0.1 mmol/L) and Q (1.0 mmol/L) were prepared in methanol and stored at 4 °C. Gradient-grade methanol (Merck, Darmstadt, Germany) was used for preparing plant extracts. For UHPLC-ESI-MS/MS analysis, hypergrade acetonitrile (Merck, Darmstadt, Germany) and formic acid (LC-MS grade, Sigma-Aldrich, St. Louis, MO, USA) were used. Ultrapure water was produced by a Direct Q 3 UV water purification system (Millipore, Molsheim, France).

2.2. Sample Collection

All fruit products, each containing only one plant ingredient, were randomly selected and purchased from Polish supermarkets, herbalist shops, and manufacturer websites (

Table 1. The studied materials.

Sample	Fruit	Latin Name	Type of Drying	Fineness	Producer
S1	barberry	Berberis vulgaris	dried	whole fruit	EkoHerba
S2	blackthorn	Prunus spinosa	dried	whole fruit	Rafex
S3	blackthorn	Prunus spinosa	dried	whole fruit	EkoHerba
S4	chokeberry	Aronia melanocarpa	lyophilized	powder	Premium Rosa
S5	chokeberry	Aronia melanocarpa	dried	powder	Rafex
S6	chokeberry	Aronia melanocarpa	lyophilized	whole fruit	Rafex
S7	chokeberry	Aronia melanocarpa	dried	whole fruit	Kawon
S8	elderberry	Sambucus nigra	lyophilized	powder	Premium Rosa
S9	elderberry	Sambucus nigra	lyophilized	whole fruit	Rafex
S10	elderberry	Sambucus nigra	dried	whole fruit	Rafex
S11	elderberry	Sambucus nigra	dried	whole fruit	Kawon
S12	hawthorn	Crataegus monogyna	dried	whole fruit	Rafex
S13	hawthorn	Crataegus monogyna	dried	whole fruit	Kawon
S14	hawthorn	Crataegus monogyna	dried	whole fruit	Dary Natury
S15	hawthorn	Crataegus monogyna	dried	whole fruit	EkoHerba
S16	lingonberry	Vaccinium vitis-idaea	lyophilized	powder	Premium Rosa
S17	lingonberry	Vaccinium vitis-idaea	dried	whole fruit	Rafex
S18	rowanberry	Sorbus aucuparia	dried	whole fruit	Rafex
S19	rowanberry	Sorbus aucuparia	dried	whole fruit	Dary Natury
S20	rowanberry	Sorbus aucuparia	dried	whole fruit	Flos
S21	rowanberry	Sorbus aucuparia	dried	whole fruit	EkoHerba
S22	sea-buckthorn	Hippophae rhamnoides	lyophilized	powder	Premium Rosa
S23	sea-buckthorn	Hippophae rhamnoides	dried	whole fruit	Rafex
S24	sea-buckthorn	Hippophae rhamnoides	dried	whole fruit	Farmvit

). All samples were purchased in dried or freeze-dried (lyophilized) form (Table 1), because fruits in dried form are readily available year-round to buyers and are easy to store and use, with a preference for powdered products.

A total of 24 fruit products of Polish origin were purchased from seven commercial brands in commonly sold amounts (50–100 g). The purchased materials were packaged in tightly sealed foil pouches, placed inside cardboard commercial packaging that included the botanical name of the product, country of origin (Poland), country of packaging (Poland), minimal shelf life date, manufacturer’s name, marketing information, storage recommendations (e.g., store in a dry and airy place), and occasionally a serving suggestion.

The samples were coded and assembled into eight groups based on plant origin: barberry, blackthorn/sloe, chokeberry, elderberry, hawthorn, lingonberry, rowanberry, and sea-buckthorn. The selection of the material included the available brands and did not consider different price categories.

2.3. Sample Preparation

Because some products (Table 1) were available only as uncrushed or whole fruits, it was necessary to use a laboratory vibratory micro-mill (FRITSCH analysette 3 SPARTAN pulverisette, Fritsch, Idar-Oberstein, Germany), with an amplitude of 1.5, to obtain the appropriate fineness of the ground material.

Samples were stored in an airtight plastic bag under dry conditions at room temperature. On the day of analysis, powdered plant material (0.5 g) was mixed with 25 mL of methanol, hand-shaken for 1 min, followed by vortex-shaking (30 s), and extracted further on an SSL4 see-saw rocker (Stuart, London, UK) for 15 min at 70 rpm speed range, under room conditions. After that, the samples were centrifuged for 5 min at 8000 rpm (5804 Centrifuge, Eppendorf, Hamburg, Germany). The supernatants were collected, filtered using syringe filters (Econofilter PTFE 13 mm, 0.5 μm and Agilent Technologies, PTFE, 13 mm, 0.22 μm), and subjected to UHPLC-ESI-MS/MS analysis.

2.4. Determination of Total Phenolic Content (TPC)

Total phenolic content (TPC) was measured using the Folin–Ciocalteu method as described by Beretta et al. [23] with slight modifications. Samples of dried materials (air- or freeze-dried) were extracted with distilled water (sample to water ratio: 1:20), sonicated for 10 min, mixed by vortex for 2 min, and centrifuged for 5 min at 8000 rpm (5804 Centrifuge, Eppendorf, Hamburg, Germany). Then, diluted fruit extract (250 μL) was mixed with 2.5 mL of Folin–Ciocalteu’s reagent (diluted 10-times in water). The mixture was vortexed, and absorbance was measured after 20 min in a quartz cuvette at 750 nm using a UV-visible spectrophotometer (Dynamica Halo DB-20S, Berkshire, UK). The gallic acid (GAE) standard curve (5–250 mg/L) was used, and TPC was expressed as milligram gallic acid equivalent per gram of sample (mg GAE/g dw). Determinations were carried out in two replicates for each fruit sample and every spectrophotometric measurement was triplicated.

2.5. Determination of Total Flavonoid Content (TFC)

The total flavonoid content (TFC) was determined using a spectrophotometric method as described by Mphahlele et al. [24] with slight modifications. Fruit samples (0.5 g) were treated with 5 mL of distilled water, sonicated for 10 min, vortexed for 2 min, and centrifuged for 5 min at 8000 rpm. The supernatant (0.5 mL) was mixed with distilled water (2 mL) and then with 0.15 mL of freshly prepared NaNO₂ solution (15%). After 6 min, 0.15 mL of an AlCl₃ solution (10%) was added and allowed to stand for 6 min, and then 2 mL of NaOH solution (4%) was added to the mixture. The volume was adjusted to 5 mL, and then the mixture was thoroughly mixed and allowed to stand for another 15 min. Absorbance was determined at 510 nm versus a water blank using a spectrophotometer (Dynamica Halo DB-20S). Catechin (CE, 5–200 mg/L) was used for the standard curve. The results were expressed as milligram catechin equivalent per gram of sample (mg CE/g dw). Determinations were carried out in duplicate for each sample and every spectrophotometric measurement was triplicated.

2.6. UHPLC-ESI-MS/MS Analysis

UHPLC-ESI-MS/MS determinations were performed on a 1290 infinity ultra-high-performance liquid chromatograph connected to a 6460 triple quadrupole mass spectrometer (Agilent Technologies, Santa Clara, CA, USA) equipped with an electrospray ion source (Agilent Jet Stream, Santa Clara, CA, USA). Separation of the target compounds was achieved on a Zorbax Eclipse Plus-C18 RRHT column (2.1 mm × 50 mm × 1.8 µm) integrated with a Zorbax Eclipse Plus-C18 Guard Column (2.1 mm × 12.5 mm × 1.8 µm), both purchased from Agilent Technologies. The mobile phase consisted of 1% (v/v) formic acid in water (solvent A) and 1% (v/v) formic acid in acetonitrile (solvent B). The gradient program was as follows: 0–5 min—5% to 70% B; 5–7 min—5% B (column re-equilibration). The post run was 1 min. The column temperature and mobile phase rate were 25 °C and 0.3 mL/min, respectively. The injection volume was 5 µL.

The ion source was operated in the negative ion mode. The ionization parameters were as follows: nebulizer: 35 psi; gas temperature: 300 °C; gas flow: 10 L/min; sheath gas temperature: 325 °C; sheath gas flow: 10 L/min; capillary voltage: 4000 V. The ions were monitored in dynamic Multiple Reaction Monitoring (dMRM) mode. MRM transitions set for EA were 301 > 284 (quantifier, fragmentor: 100 V; collision energy: 28 eV) and 301 > 229 (qualifier, fragmentor: 100 V; collision energy: 28 eV), and for Q, they were 301 > 151 (quantifier, fragmentor: 140 V; collision energy: 20 eV) and 301 > 179 (qualifier, fragmentor: 100 V; collision energy: 16 eV). EA and Q signals appeared at a retention time (RT) of 2.6 and 3.5 min, respectively (Figure 1).

For dMRM settings, the time window for each analyte transition was set to a ΔRT of 1 min. The instrument control and data analysis were carried out using the MassHunter Acquisition software v.B.08 and the MassHunter Quantitative Analysis software v.B.07 (Agilent Technologies), respectively.

Quantification was performed based on matrix-matched calibration curves, which were constructed for each type of plant material. Calibration solutions were prepared by fortifying plant extracts with EA and Q at different concentration levels (0.76–151.10 μg/g). The calibration curves exhibited linearity with a coefficient of determination (R²) greater than 0.99. The limit of detection (LOD) and limit of quantification (LOQ) were estimated using the formula LOD or LOQ [μg/g] = F × SD/b, where F is a factor of 3.3 or 10 for LOD and LOQ, respectively; SD is a standard deviation of the intercept of the regression line; b is a slope of the regression line.

2.7. Statistical Analysis

The results were processed using the statistical program StatgraphicsPlus 3.0 for Windows^® software. A comparison of the results was performed using the Tukey test. The difference between mean values with p < 0.05 was considered statistically significant.

3. Results

Selected medicinal plant fruits, air- and freeze-dried (Table 1), were analyzed using UHPLC-ESI-MS/MS to determine the presence of individual polyphenols: EA and Q. Additionally, the total phenolic content (TPC) and total flavonoid content (TFC) were measured using spectrophotometric methods.

Although rosehips also belong to one of the most frequently used wild fruits, they were excluded from this study, as they have already been extensively investigated for EA content [25].

LC-MS/MS using electrospray ionization (ESI) is susceptible to sample matrix components, which may lead to either suppression or enhancement of the signal of the analyte (so-called matrix effect). Through the determination of TPC and TFC, we can obtain general information about the compositional characteristics and diversity of the studied material, as well as predict potential matrix effects. Matrix-matched calibration can be used for compensation of the matrix effect and helps to obtain quantitatively accurate results [26]. Thus, we decided to apply this strategy in our study.

Regarding the unique composition of the studied fruits, for quantitative analysis, matrix-matched calibration curves were built for each plant material. The parameters of the calibration curves, LODs, and LOQs are summarized in

Table 2. Parameters of calibration curves, LODs, and LOQs for EA and Q determined for the studied fruit matrices.

Type of Fruit Matrix	Analyte	LR [μg/g]	EC	R2	LOD [μg/g]	LOQ [μg/g]
Barberry	EA Q	1.51–151.10 1.51–151.10	y = 24.9x − 57.3 y = 579.9x − 1274.3	0.997 0.992	0.45 0.45	1.36 1.51
Blackthorn	EA Q	1.51–151.10 7.55–151.10	y = 35.4x − 83.6 y = 880.6x − 8440.7	0.989 0.986	0.45 2.42	1.51 7.10
Chokeberry	EA Q	1.51–151.10 1.51–151.10	y = 46.7x + 42.2 y = 690.5x − 892.9	0.997 0.992	0.45 0.45	1.51 1.36
Elderberry	EA Q	0.76–151.10 1.51–151.10	y = 34.3x − 16.4 y = 655.3x + 6699.2	0.999 0.998	0.30 0.45	0.76 1.36
Hawthorn	EA Q	0.76–151.10 0.76–151.10	y = 59.5x + 25.0 y = 723.2x − 701.9	0.998 0.994	0.24 0.21	0.76 0.66
Lingonberry	EA Q	1.51–151.10 1.51–151.10	y = 39.1x + 29.5 y = 398.0x + 768.7	0.998 0.996	0.45 0.45	1.36 1.51
Rowanberry	EA Q	1.51–151.10 1.51–151.10	y = 32.3x − 0.5 y = 451.1x + 9411.4	0.990 0.993	0.45 0.45	1.36 1.21
Sea-buckthorn	EA Q	0.76–151.10 0.76–151.10	y = 52.6x + 104.1 y = 520.3x + 3036.8	0.998 0.994	0.15 0.30	0.60 0.76

LR—linear range of the calibration curve; EC—equation of the calibration curve; y—concentration of the analyte [μg/g]; x—peak area of the analyte; R²—the coefficient of determination.

.

Examples of chromatographic results for EA and Q determined in wild fruit extracts are presented in Figure 1.

The calculated contents of free EA and Q were expressed in μg per gram of dry material, and the obtained results are presented in

Table 3. Total phenolic content (TPC), total flavonoid content (TFC), ellagic acid (EA), and quercetin (Q) contents in studied materials (mean, ±SD).

Sample	Fruit	TPC ± SD [mg GAE/g dw] n = 6	TFC ± SD [mg CE/g dw] n = 6	EA ± SD [μg/gdw] n = 3	Q ± SD [μg/gdw] n = 3
S1	barberry (D)	17.78 ± 0.13 s	8.85 ± 0.22 m	3.29 ± 0.24 j	24.01 ± 0.25 i
S2	blackthorn (D)	1.28 ± 0.04 a	0.81 ± 0.01 a	2.79 ± 0.10 i	26.29 ± 0.68 j
S3	blackthorn (D)	1.81 ± 0.05 b	1.40 ± 0.01 c	3.50 ± 0.16 j	39.36 ± 0.45 l
S4	chokeberry (L)	8.56 ± 0.03 q	7.82 ± 0.10 l	1.40 ± 0.38 g	27.19 ± 1.18 j
S5	chokeberry (D)	3.06 ± 0.06 i	2.46 ± 0.05 e	0.71 ± 0.07 bcd	105.69 ± 2.45 m
S6	chokeberry (L)	8.89 ± 0.21 r	9.03 ± 0.15 n	nd a	24.51 ± 1.41 i
S7	chokeberry (D)	4.31 ± 0.18 l	2.94 ± 0.00 h	nd a	36.20 ± 0.20 k
S8	elderberry (L)	11.36 ± 0.15 t	10.34 ± 0.03 o	1.38 ± 0.26 g	13.84 ± 0.16 f
S9	elderberry (L)	11.59 ± 0.20 u	10.83 ± 0.25 p	0.92 ± 0.02 de	17.81 ± 0.17 g
S10	elderberry (D)	8.64 ± 0.03 q	7.75 ± 0.18 l	0.92 ± 0.09 de	25.65 ± 0.17 ij
S11	elderberry (D)	8.10 ± 0.16 p	5.58 ± 0.16 j	0.69 ± 0.04 bc	13.88 ± 0.30 f
S12	hawthorn (D)	4.82 ± 0.09 n	3.29 ± 0.13 h	1.28 ± 0.05 fg	9.17 ± 0.11 e
S13	hawthorn (D)	3.86 ± 0.02 j	1.78 ± 0.10 d	nd a	6.09 ± 0.07 d
S14	hawthorn (D)	2.93 ± 0.09 h	2.83 ± 0.12 g	nd a	8.90 ± 0.02 e
S15	hawthorn (D)	4.05 ± 0.04 k	2.61 ± 0.05 f	nd a	2.63 ± 0.04 ab
S16	lingonberry (L)	6.85 ± 0.03 o	6.75 ± 0.08 k	0.18 ± 0.05 a	123.42 ± 1.70 n
S17	lingonberry (D)	4.23 ± 0.08 l	3.44 ± 0.01 i	0.50 ± 0.05 b	196.20 ± 3.10 o
S18	rowanberry (D)	1.95 ± 0.02 c	0.92 ± 0.02 a	0.92 ± 0.06 cde	3.71 ± 0.51 bc
S19	rowanberry (D)	2.47 ± 0.02 f	1.39 ± 0.01 c	1.15 ± 0.26 ef	22.246 ± 1.06 h
S20	rowanberry (D)	2.13 ± 0.02 d	1.18 ± 0.01 b	0.57 ± 0.05 b	13.52 ± 0.64 f
S21	rowanberry (D)	1.71 ± 0.02 b	0.81 ± 0.02 a	1.13 ± 0.11 ef	1.44 ± 0.43 a
S22	sea-buckthorn (L)	4.66 ± 0.15 m	3.48 ± 0.02 i	4.80 ± 0.18 l	4.06 ± 0.30 bc
S23	sea-buckthorn (D)	2.71 ± 0.03 g	1.40 ± 0.03 c	2.53 ± 0.11 h	8.32 ± 0.38 e
S24	sea-buckthorn (D)	2.25 ± 0.07 e	1.33 ± 0.04 c	4.18 ± 0.15 k	5.36 ± 0.21 cd

(D)—dried; (L)—lyophilized; mg GAE/g dw—gallic acid equivalents, mg/g of dry weight; mg CE/g dw—catechin equivalents, mg/g of dry weight; nd—not detected (below LOD); SD—standard deviation (N = 3). Means followed by the same letter within a column indicate no significant difference (p < 0.05).

.

The determined EA contents varied among samples, ranging from below the LOD (in some chokeberry and hawthorn fruit samples) to over 3 μg/g dw. Blackthorn, barberry, and sea-buckthorn exhibited significantly (p < 0.05) higher EA content compared to other studied fruits (Figure 2A). The highest EA contents were found in sea-buckthorn (from 2.53 to 4.80 μg/g of dry material, mean 3.84 μg/g, n = 3).

Quercetin was present in all fruit samples at quantifiable concentration levels. Lingonberry contained the highest Q amount (from 123.42 to 196.20 μg/g dw, mean 159.81 μg/g dw). Furthermore, the measured Q content in lingonberry was significantly higher than in the other samples (p < 0.05) (Figure 2B). A relatively high Q content was also found in chokeberry. However, the determined Q contents in chokeberry are characterized by a large variation, ranging from 24.51 to 105.69 μg/g dw, mean 48.40 μg/g dw. The above data indicate that Polish medicinal fruits are worth taking into consideration as a source of these bioactive compounds.

The TPC and TFC values determined in the studied fruit are summarized in Table 2 and presented in Figure 3. Phenolic content varied across the samples, ranging from 1.28 to 11.59 mg GAE/g dw. The lowest value was observed in blackthorn (mean 1.54 mg GAE/g dw) (Figure 3A), while the highest values were found in rowanberry and barberry, with means of 9.92 and 10.78 mg GAE/g dw, respectively (p < 0.05). Flavonoid content in the eight groups of tested fruit was in the range from 0.81 to 10.83 mg CE/g dw, with the highest values (p < 0.05) determined in rowanberry (8.62 mg CE/g dw) and barberry (8.85 mg CE/g dw) (Figure 3B).

4. Discussion

For a very long time, wild fruits found in forests and orchards have been used in Polish folk medicine. Now, their popularity has been growing, and they have become increasingly available in shops and herbalists. Due to media coverage, an increase in the culinary use of some wild plants for food, drinks, and medicine can be observed.

Studies on polyphenols in the herein-selected fruits are often carried out using chromatographic or spectrophotometric methods. However, most of these studies focus on pooled and general characteristics, such as total phenolic content [14,27], total phenolic acids [27,28], total flavonoid content [7,29], total monomeric anthocyanin content [27], total antioxidant activity [14], or single polyphenolic compounds. Although EA and Q are very common among over 8000 of “phenolics”, there are surprisingly few papers specifically measuring the contents of these two compounds in Polish medicinal fruits. Discussing EA and Q together is valuable because, despite their structural differences, both have anticancer properties, and their activity is synergistic. It has been confirmed that EA and Q together have a greater effect on human leukemia cells than can be explained by a simple additive effect. Fruits like blueberries, raspberries, and strawberries, which contain both EA and Q, are used in studies examining biochemical interactions [30]. Their synergistic action has been demonstrated in studies of cytotoxicity in models using different human cancer cells (lung–line A549, colorectal–line HCT-116, and breast–line MDA-MB-231) [31]. Moreover, EA and Q have been identified together as distinctive tyrosinase (TYR) inhibitors in the study of Geranium sp. activity, used in folk medicine. TYR is a multifunctional enzyme associated with the pathogenesis of melanoma and other pigmentation disorders [32]. Furthermore, studies about EA and ellagitannins mainly focus on pomegranate extract and its vasculoprotective effects [33] and anticancer activity [34]. Our findings show that wild fruits of barberry, blackthorn, elderberry, lingonberry, rowanberry, and sea-buckthorn contain both EA and Q. In contrast, EA was not detected in some chokeberry and hawthorn samples. Thus, these wild plants can serve as promising materials for biochemical research.

We decided to determine the content of EA and Q in the unconjugated forms, as the final effects of dietary polyphenols—particularly those that are glycolysated or oligomeric/polymeric—depend on the composition and function of the gut microbiota [35]. Unbound forms are more readily bioavailable because they do not require multi-step catabolism, primarily hydrolysis mediated by the gut microbiota, which is highly variable and influenced by various factors [36].

Selected medicinal fruits, predominantly red or orange-red in color, represent complex matrices due to high anthocyanin content. Consequently, chromatographic analysis of such material employing an ultraviolet detector, such as HPLC-UV-Vis or HPLC-PDA, can be challenging. The usage of mass spectrometric detection allows for more accurate identification of compounds and shorter analysis time. Considering the above advantages, LC-MS or LC-MS/MS systems have increasingly been used for simultaneous or individual quantitative analysis of EA and Q in a variety of plant materials and food products [25,37,38].

Among the studied wild fruits, the highest contents of free EA were noted for sea-buckthorn. Interestingly, some other researchers did not find EA in this fruit [39].

In the available literature, these compounds are not extensively studied and described, but data on the free EA content in blackthorn, barberry, and elderberry fruits are very limited or researchers did not confirm the presence of this phenolic acid in medicinal fruit such as rowanberry (Table 4).

Table 4. Literature data on EA and Q content in studied medical fruits.

Fruit Matrix	Analyte	Content [μg/g]	Country of Origin	Source
Barberry	EA	n.d.	Poland	[29]
	Q	21.0–22.0 μg/g	China	[40]
Blackthorn	EA	94 μg/g	Romania	[41]
	Q	53 μg/g	Romania	[41]
		207.0 μg/g fw	Sweden	[42]
Chokeberry	EA	n.d.	Bulgaria	[43]
		15.7 μg/g fw	Canada	[44]
		4.0 ± 0.1 μg/g	Croatia	[45]
		n.d.	Croatia	[46]
		129 μg/g dw *	Romania	[47]
		n.d.	Spain	[48]
	Q	148 μg/g dw	Bulgaria	[43]
		2.1 μg/g fw	Canada	[44]
		92.2 μg/g *	Croatia	[45]
		437.8 μg/g fw	Croatia	[46]
		17.4 μg/g fw	Croatia	[49]
		89.0 μg/g *	Finland	[50]
		348.0 μg/g fw	Finland	[42]
		7 μg/g dw *	Romania	[47]
Elderberry	EA	6.0 μg/g	Argentina	[51]
		n.d.	Canada	[44]
		n.d.	Croatia	[46]
		n.d.	Germany	[48]
	Q	14.0	Argentina	[51]
		n.d.—256.0 μg/g fw *	Canada	[6]
		3.3 μg/g fw	Canada	[44]
		144.0 μg/g	Croatia	[45]
		138.0 μg/g fw	Croatia	[46]
		5.5 μg/g *	Romania	[52]
		28.9–45.0 μg/g fw *	Slovenia	[53]
		331.0 μg/g fw	Sweden	[42]
Hawthorn	EA	169 μg/g dw	Bulgaria	[43]
		303 μg/g	Romania	[41]
	Q	n.d.	Bulgaria	[43]
		0.015 μg/g	Romania	[41]
		n.d.—0.1 μg/g dw	Spain	[28]
Lingonberry	EA	13.6 μg/g fw	Canada	[[44]
	Q	2.3 μg/g fw	Canada	[44]
		74.0–146.0 μg/g *	Finland	[50]
		131.0 μg/g fw	Finland	[42]
		2.0–14.1 μg/g *	USA	[54]
Rowanberry	EA	n.d.	Bulgaria	[43]
	Q	n.d.	Bulgaria	[43]
		12.0 μg/g dw	Estonia	[55]
		63.0 μg/g *	Finland	[50]
		510.0 μg/g dw	Poland	[56]
Sea-buckthorn	EA	n.d.	Canada	[57]
		<LOD	Finland	[39]
		0.4–12.1 μg/g fw	Slovakia	[58]
	Q	67.0–175.0 μg/g fw *	Canada	[57]
		62.0 μg/g *	Finland	[50]
		172.0 μg/g fw	Finland	[42]
		106.4–122.6 μg/g	Romania	[59]
		n.d.	Slovakia	[58]

The asterisk (*) indicates the content in acidified methanolic extract (acetic, hydrochloric, or formic acid); <LOD—the content was below the limit of detection; n.d.—not detected; fw—fresh weight; dw—dry weight.

Table 4. Literature data on EA and Q content in studied medical fruits.

Fruit Matrix	Analyte	Content [μg/g]	Country of Origin	Source
Barberry	EA	n.d.	Poland	[29]
	Q	21.0–22.0 μg/g	China	[40]
Blackthorn	EA	94 μg/g	Romania	[41]
	Q	53 μg/g	Romania	[41]
		207.0 μg/g fw	Sweden	[42]
Chokeberry	EA	n.d.	Bulgaria	[43]
		15.7 μg/g fw	Canada	[44]
		4.0 ± 0.1 μg/g	Croatia	[45]
		n.d.	Croatia	[46]
		129 μg/g dw *	Romania	[47]
		n.d.	Spain	[48]
	Q	148 μg/g dw	Bulgaria	[43]
		2.1 μg/g fw	Canada	[44]
		92.2 μg/g *	Croatia	[45]
		437.8 μg/g fw	Croatia	[46]
		17.4 μg/g fw	Croatia	[49]
		89.0 μg/g *	Finland	[50]
		348.0 μg/g fw	Finland	[42]
		7 μg/g dw *	Romania	[47]
Elderberry	EA	6.0 μg/g	Argentina	[51]
		n.d.	Canada	[44]
		n.d.	Croatia	[46]
		n.d.	Germany	[48]
	Q	14.0	Argentina	[51]
		n.d.—256.0 μg/g fw *	Canada	[6]
		3.3 μg/g fw	Canada	[44]
		144.0 μg/g	Croatia	[45]
		138.0 μg/g fw	Croatia	[46]
		5.5 μg/g *	Romania	[52]
		28.9–45.0 μg/g fw *	Slovenia	[53]
		331.0 μg/g fw	Sweden	[42]
Hawthorn	EA	169 μg/g dw	Bulgaria	[43]
		303 μg/g	Romania	[41]
	Q	n.d.	Bulgaria	[43]
		0.015 μg/g	Romania	[41]
		n.d.—0.1 μg/g dw	Spain	[28]
Lingonberry	EA	13.6 μg/g fw	Canada	[[44]
	Q	2.3 μg/g fw	Canada	[44]
		74.0–146.0 μg/g *	Finland	[50]
		131.0 μg/g fw	Finland	[42]
		2.0–14.1 μg/g *	USA	[54]
Rowanberry	EA	n.d.	Bulgaria	[43]
	Q	n.d.	Bulgaria	[43]
		12.0 μg/g dw	Estonia	[55]
		63.0 μg/g *	Finland	[50]
		510.0 μg/g dw	Poland	[56]
Sea-buckthorn	EA	n.d.	Canada	[57]
		<LOD	Finland	[39]
		0.4–12.1 μg/g fw	Slovakia	[58]
	Q	67.0–175.0 μg/g fw *	Canada	[57]
		62.0 μg/g *	Finland	[50]
		172.0 μg/g fw	Finland	[42]
		106.4–122.6 μg/g	Romania	[59]
		n.d.	Slovakia	[58]

The asterisk (*) indicates the content in acidified methanolic extract (acetic, hydrochloric, or formic acid); <LOD—the content was below the limit of detection; n.d.—not detected; fw—fresh weight; dw—dry weight.

Data on EA content in other tested fruits remain limited. It shows that the fruits of these medicinal plants are still an undervalued and untested source of EA. Jakobek and Seruga [46] also measured the EA and Q content in various fruit samples and reported that EA contents in chokeberry and elderberry (expressed in fresh weight) were below the method’s LOD. In another study, the same researcher also quantified EA in chokeberry at 3.97 ± 0.1 µg/g fresh weight [45].

Quercetin has been more extensively studied in various berries compared to EA (Table 4). Among the tested medicinal fruits in our study, lingonberry exhibited the highest Q amounts, with a mean concentration of 159.81 μg/g dw. Our findings correspond with results obtained for Finnish lingonberries (74–146 μg/g) [42,50]. In contrast, lower Q concentrations have been observed in American and Canadian lingonberries [44,54].

According to Jakobek and co-workers [45], elderberry is a rich source of flavonols, with Q being the most dominant, reaching 144 µg/g fw. It is a higher value than that observed in our elderberry samples, which had a mean Q content of 17.81 µg/g dw (Figure 2B). Similarly, the high Q contents in elderberries have been determined in studies from Canada [6] and Sweden [42], where levels ranged from below LOD to as high as 256 and 331 μg/g fw, respectively.

The mean value of Q in chokeberry (calculated from four samples)was 48.40 μg/g dw, which is lower than the value obtained by Jakobek and co-workers [45], who found it to be 92.15 ± 0.5 µg/g fw. In another study by the same research group, wild chokeberry was investigated over 2 years, with determined Q levels at a much lower level, in the range from 5 to 17.4 µg/g fw [49]. In contrast, a higher value of Q content of 148 µg/g dw was reported by Denev et al. [43]. According to Häkkinen and co-workers, Q content amounted to 89, 63, and 62 mg/kg of fresh weight in chokeberry, rowanberry, and sea-buckthorn berry, respectively [50].

The Q content in fruit reported in review articles is often misleading, because some authors did not distinguish between content in extract and in acidified extract, which corresponds to Q released after acid hydrolysis from the flavonol glycosides. According to Määttä-Riihinen et al. [42], approximately 97% of the total Q in lingonberry is delivered from glycosides. Moreover, it also happens that in the same papers, amounts of quercetin as aglycons and glycosides are given, which would mean that despite the addition of acid and being left for 24 h, hydrolysis did not occur entirely [49].

Phenolic compounds and flavonoids represent major classes of natural antioxidants. Estimation of TPC and TFC provides valuable information regarding the phenolic composition of plant material and facilitates the prediction of its bioactive properties. The obtained results of TPC and TFC are summarized in Table 3. TPC values concur with those obtained in barberry—10.24 mg GAE/g fw [29]; blackthorn—1.51 mg GAE/g dw [60]; chokeberry—8.56–9.09 mg GAE/g fw [49]; lingonberry—6.52 mg GAE/g fw [61]; rowanberry 2.27 mg GAE/ g fw [62]; and sea-buckthorn—0.7–3.62 mg GAE/g fw [58] (Table 5). However, a comparison of our results with data from the literature is difficult due to the application of different extraction solvents and conditions or standards (catechin, quercetin, rutin) to express TPC and TFC presented for dried fruits by various researchers. Some authors compared the obtained results with two standards (Table 5).

The polyphenol content is affected by both the genetic background of the plant and growing and climatic conditions. These differences are particularly evident in the TPC of different cultivars of barberry, blackthorn, and sea-buckthorn (Table 5).

Fresh fruit consumption is limited, so air- and freeze-dried fruit are frequently consumed as snacks or added to products like oatmeal. However, active phenolic compounds, described by TPC and TFC, are often lost during the drying process [63]. In our observation, we found that lyophilization tends to preserve more of these active phenolic substances in the material compared to the traditional dried method, particularly in elderberry and sea-buckthorn samples (Table 2).

Table 5. Literature data on TPC and TFC in studied medical fruits.

Sample	TPC	TFC	Country of Origin	Sources
barberry	100.86 ± 1.97 mg GAE/g dw	8.31 ± 0.51 mg QE/g dw	Italy/ Romania	[64]
barberry	60.32 ± 0.21 mg GAE/g dw	38.97 ± 1.60 mg CE/g dw	Iran	[65]
barberry	184.10 ± 5.30 mg GAE/g dw	-	Iran	[66]
barberry	100 mg GAE/g	-	Iran	[67]
barberry	3.73–9.40 mg GAE/mL	2.22–7.67 mg QE/mL	Iran	[68]
barberry	10.24 ± 0.15 mg GAE/g fw	0.86 ± 0.02 mg RE/g fw	Poland	[29]
barberry	7.89 mg GAE/g fw	-	Türkiye	[69]
blackthorn	14.02 mg GAE/g dw	0.79 mg RE/g dw 0.45 mg QE/g dw	Bosnia and Herzegovina	[70]
				[70]
blackthorn	23.19 ± 2.52 mg GAE/g dw	2.96 ± 0.22 mg QE/g dw	Croatia	[71]
blackthorn, wild	40.27 mg GAE/g fw	-	Poland	[62]
blackthorn	83.40 mg GAE/g dw	8.68 mg CE/g dw	Portugal	[7]
blackthorn	1.51 ± 0.19 mg GAE/g dw	3.29 ± 0.08 mg RE/g dw	Serbia	[60]
blackthorn	327.02 ± 4.66 mg GAE/g dw	127.16 ± 0.82 mg RE/g dw	Spain	[72]
chokeberry	62.748 mg GAE/g dw	-	Bulgaria	[43]
chokeberry, wild	9.09–10.39 mg GAE/g fw	-	Croatia	[49]
chokeberry, harvested	8.56–12.06 mg GAE/g fw	-	Croatia	[49]
chokeberry, dried	24.66 mg GAE/g dw	13.94 mg GAE /g dw	Croatia	[73]
chokeberry, harvested	7.78–12.85 mg GAE/g fw	-	Czechia	[74]
chokeberry	10.49 mg GAE/g dw	-	Finland	[75]
chokeberry, dried	19.54 mg GAE/g dw	8.67 mg GAE/g dw	Germany	[73]
chokeberry, commercial	11.39 ± 0.17 mg GAE/g dw	7.75 ± 0.40 mg CE/g dw	Poland	[65]
chokeberry	78.49 mg GAE/g dw	-	Poland	[76]
chokeberry	27.99 mg GAE/g dw	5.23 mg CE/g dw	Romania	[47]
chokeberry, fresh	52.22 mg GAE/g dw	23.46 mg CE/g dw	Serbia	[63]
chokeberry, dried	11.69–19.19 mg GAE/g dw	8.00–10.37 mg CE/g dw	Serbia	[63]
chokeberry, wild	25.56 mg GAE/g fw	-	United States	[61]
elderberry	73.40 mg GAE/g dw	8.60 mg QE/g dw	Iran	[77]
elderberry	72.00–158.60 mg GAE/g of extract	19.60–45.60 QE mg/g of extract	Iran	[78]
elderberry, wild	5.36 mg GAE/g fw	-	Poland	[62]
elderberry	89.74 ± 0.37 mg GAE/g dw of extract	-	Türkiye	[79]
hawthorn	40.258 mg GAE/g dw	-	Bulgaria	[43]
hawthorn	52.62–61.91 mg GAE/g dw	44.25–55.96 mgCE/g dw	China	[80]
hawthorn	12.26–12.82 mg GAE/g dw	n.d. mg RE/g dw	France	[81]
hawthorn	23.37 ± 1.18 mg GAE/g dw	2.58 ± 0.24 mg QE/g dw	Italy/ Romania	[64]
hawthorn	132.14–204.29 mg GAE/g	-	Spain	[28]
lingonberry	6.52 mg GAE/g fw	-	Canada	[61]
lingonberry	6.21 mg GAE/g dw	-	Finland	[75]
lingonberry	7.17 mg GAE/g fw 13.30–13.50 mg GAE/g dw	-	Finland Romania	[82] [83]
lingonberry		-
rowanberry	21.482 mg GAE/g dw	-	Bulgaria	[43]
rowanberry, wild	4.27 ± 0.59 mg GAE/g fw	3.11 ± 0.27 mg RE/g fw	Czechia	[84]
rowanberry	4.56 mg GAE/g dw	-	Finland	[75]
rowanberry	5.50–10.14 mg GAE/g fw	-	Finland	[82]
rowanberry	26.8 mg GAE/g dw	-	Poland	[56]
rowanberry, wild	2.27 mg GAE/g fw	-	Poland	[62]
rowanberry, wild	20.00 mg GAE/g dw	3.50 mg RE/g dw	Serbia	[85]
sea-buckthorn, commercial	5.14 ± 0.21 mg GAE/g dw	2.70 ± 0.11 mg CE/g dw	Belarus	[65]
sea-buckthorn, harvested	12.51–14.42 mg CE/g dw	-	Belarus	[86]
sea-buckthorn, wild	32.20–33.51 mg GAE/g dw	3.52–8.96 mg RE/g dw	China	[87]
sea-buckthorn, harvested	11.80–15.95 mg GAE/g dw	1.81–2.86 mg RE/g dw	China	[87]
sea-buckthorn, commercial	8.48 ± 0.22 mg GAE/g dw	1.81 ± 0.03 mg RE/g dw	China	[87]
sea-buckthorn, harvested	8.62–14.17 mg GAE/g fw	4.18–7.97 mg RE/g fw	Czechia	[88]
sea-buckthorn	2.05–2.45 mg GAE/g dw	-	Finland	[75]
sea-buckthorn	1.86–3.81 mg GAE/g dw	-	Hungary	[89]
sea-buckthorn	8.82 ± 0.93 mg CE/g dw	-	Poland	[86]
sea-buckthorn	140.14 mg GAE/g dw	5.04 mg CE/g dw	Romania	[90]
sea-buckthorn, harvested	10.12–18.66 mg GAE/g fw	6.57–9.01 QE/g fw	Romania	[59]
sea-buckthorn	0.70–3.62 mg GAE/g fw	0.55–4.11 mg RE/g fw	Slovakia	[58]
sea-buckthorn, harvested	21.31–55.38 mg GAE/g dw	-	Türkiye	[91]

GAE—gallic acid equivalents, mg/g; QE—quercetin equivalents, mg/g; RE—rutin equivalents, mg/g; CE—catechin equivalents, mg/g.

Table 5. Literature data on TPC and TFC in studied medical fruits.

Sample	TPC	TFC	Country of Origin	Sources
barberry	100.86 ± 1.97 mg GAE/g dw	8.31 ± 0.51 mg QE/g dw	Italy/ Romania	[64]
barberry	60.32 ± 0.21 mg GAE/g dw	38.97 ± 1.60 mg CE/g dw	Iran	[65]
barberry	184.10 ± 5.30 mg GAE/g dw	-	Iran	[66]
barberry	100 mg GAE/g	-	Iran	[67]
barberry	3.73–9.40 mg GAE/mL	2.22–7.67 mg QE/mL	Iran	[68]
barberry	10.24 ± 0.15 mg GAE/g fw	0.86 ± 0.02 mg RE/g fw	Poland	[29]
barberry	7.89 mg GAE/g fw	-	Türkiye	[69]
blackthorn	14.02 mg GAE/g dw	0.79 mg RE/g dw 0.45 mg QE/g dw	Bosnia and Herzegovina	[70]
				[70]
blackthorn	23.19 ± 2.52 mg GAE/g dw	2.96 ± 0.22 mg QE/g dw	Croatia	[71]
blackthorn, wild	40.27 mg GAE/g fw	-	Poland	[62]
blackthorn	83.40 mg GAE/g dw	8.68 mg CE/g dw	Portugal	[7]
blackthorn	1.51 ± 0.19 mg GAE/g dw	3.29 ± 0.08 mg RE/g dw	Serbia	[60]
blackthorn	327.02 ± 4.66 mg GAE/g dw	127.16 ± 0.82 mg RE/g dw	Spain	[72]
chokeberry	62.748 mg GAE/g dw	-	Bulgaria	[43]
chokeberry, wild	9.09–10.39 mg GAE/g fw	-	Croatia	[49]
chokeberry, harvested	8.56–12.06 mg GAE/g fw	-	Croatia	[49]
chokeberry, dried	24.66 mg GAE/g dw	13.94 mg GAE /g dw	Croatia	[73]
chokeberry, harvested	7.78–12.85 mg GAE/g fw	-	Czechia	[74]
chokeberry	10.49 mg GAE/g dw	-	Finland	[75]
chokeberry, dried	19.54 mg GAE/g dw	8.67 mg GAE/g dw	Germany	[73]
chokeberry, commercial	11.39 ± 0.17 mg GAE/g dw	7.75 ± 0.40 mg CE/g dw	Poland	[65]
chokeberry	78.49 mg GAE/g dw	-	Poland	[76]
chokeberry	27.99 mg GAE/g dw	5.23 mg CE/g dw	Romania	[47]
chokeberry, fresh	52.22 mg GAE/g dw	23.46 mg CE/g dw	Serbia	[63]
chokeberry, dried	11.69–19.19 mg GAE/g dw	8.00–10.37 mg CE/g dw	Serbia	[63]
chokeberry, wild	25.56 mg GAE/g fw	-	United States	[61]
elderberry	73.40 mg GAE/g dw	8.60 mg QE/g dw	Iran	[77]
elderberry	72.00–158.60 mg GAE/g of extract	19.60–45.60 QE mg/g of extract	Iran	[78]
elderberry, wild	5.36 mg GAE/g fw	-	Poland	[62]
elderberry	89.74 ± 0.37 mg GAE/g dw of extract	-	Türkiye	[79]
hawthorn	40.258 mg GAE/g dw	-	Bulgaria	[43]
hawthorn	52.62–61.91 mg GAE/g dw	44.25–55.96 mgCE/g dw	China	[80]
hawthorn	12.26–12.82 mg GAE/g dw	n.d. mg RE/g dw	France	[81]
hawthorn	23.37 ± 1.18 mg GAE/g dw	2.58 ± 0.24 mg QE/g dw	Italy/ Romania	[64]
hawthorn	132.14–204.29 mg GAE/g	-	Spain	[28]
lingonberry	6.52 mg GAE/g fw	-	Canada	[61]
lingonberry	6.21 mg GAE/g dw	-	Finland	[75]
lingonberry	7.17 mg GAE/g fw 13.30–13.50 mg GAE/g dw	-	Finland Romania	[82] [83]
lingonberry		-
rowanberry	21.482 mg GAE/g dw	-	Bulgaria	[43]
rowanberry, wild	4.27 ± 0.59 mg GAE/g fw	3.11 ± 0.27 mg RE/g fw	Czechia	[84]
rowanberry	4.56 mg GAE/g dw	-	Finland	[75]
rowanberry	5.50–10.14 mg GAE/g fw	-	Finland	[82]
rowanberry	26.8 mg GAE/g dw	-	Poland	[56]
rowanberry, wild	2.27 mg GAE/g fw	-	Poland	[62]
rowanberry, wild	20.00 mg GAE/g dw	3.50 mg RE/g dw	Serbia	[85]
sea-buckthorn, commercial	5.14 ± 0.21 mg GAE/g dw	2.70 ± 0.11 mg CE/g dw	Belarus	[65]
sea-buckthorn, harvested	12.51–14.42 mg CE/g dw	-	Belarus	[86]
sea-buckthorn, wild	32.20–33.51 mg GAE/g dw	3.52–8.96 mg RE/g dw	China	[87]
sea-buckthorn, harvested	11.80–15.95 mg GAE/g dw	1.81–2.86 mg RE/g dw	China	[87]
sea-buckthorn, commercial	8.48 ± 0.22 mg GAE/g dw	1.81 ± 0.03 mg RE/g dw	China	[87]
sea-buckthorn, harvested	8.62–14.17 mg GAE/g fw	4.18–7.97 mg RE/g fw	Czechia	[88]
sea-buckthorn	2.05–2.45 mg GAE/g dw	-	Finland	[75]
sea-buckthorn	1.86–3.81 mg GAE/g dw	-	Hungary	[89]
sea-buckthorn	8.82 ± 0.93 mg CE/g dw	-	Poland	[86]
sea-buckthorn	140.14 mg GAE/g dw	5.04 mg CE/g dw	Romania	[90]
sea-buckthorn, harvested	10.12–18.66 mg GAE/g fw	6.57–9.01 QE/g fw	Romania	[59]
sea-buckthorn	0.70–3.62 mg GAE/g fw	0.55–4.11 mg RE/g fw	Slovakia	[58]
sea-buckthorn, harvested	21.31–55.38 mg GAE/g dw	-	Türkiye	[91]

GAE—gallic acid equivalents, mg/g; QE—quercetin equivalents, mg/g; RE—rutin equivalents, mg/g; CE—catechin equivalents, mg/g.

However, this finding should be verified with a larger set of samples. This has also been confirmed in studies on sea-buckthorn [87], where the TPC of freeze-dried berries was found to be 1.56–2.97 times higher than that of other dried berries, with similar trends observed for TFC values. However, the difference was not as significant as that for TPC.

Very weak correlations between EA-TPC (R² = 0.0162), EA-TFC (R² = 0.0230), Q-TPC (R² = 0.0000), and Q-TFC (R² = 0.0001) were observed, which implies that these compounds are not dominant in the studied samples. Moreover, it is suggested that the Folin–Ciocalteu method overestimates the real phenolic content in comparison to the chromatographic method, as it also quantifies polymeric phenolics and other nonphenolic metabolites [48].

5. Conclusions

This study looked into the evaluation of ellagic acid and quercetin contents in wild fruits as potential sources of these polyphenols. To ensure the integrity of the test material, our research focused on fruits of typical Polish medicinal plants. Methanolic extracts of eight different kinds of fruits were analyzed, revealing varying amounts of polyphenolic compounds. Among the studied fruits, barberries, blackthorn, and sea-buckthorn exhibited the highest amounts of ellagic acid, while lingonberry has been found as a good dietary source of quercetin. It seems advisable that further studies should include fruits confirmed to contain these two polyphenols with synergistic effects, and these are the wild fruits of barberry, blackthorn, elderberry, lingonberry, rowanberry, and sea-buckthorn, whereas in some samples of chokeberry and hawthorn EA was not detected. Overall, the presented data confirmed that the fruits of wild-growing Polish medicinal plants represent promising natural sources of ellagic acid and quercetin and may provide nutraceutical, pharmaceutical, and cosmetic benefits.

The presented ultra-high-performance liquid chromatography–electrospray ionization tandem mass spectrometry (UHPLC-ESI-MS/MS) method can be tentatively recommended for the analysis of ellagic acid and quercetin in other fruit matrices.

Future research should focus on elucidating the synergistic effects of these polyphenols and evaluating their actual health benefits in vivo, in order to substantiate their potential application in disease prevention and therapeutic strategies.