1. Introduction
Plant-based foods play an increasingly important role in modern consumer live styles due to changing behaviour and eating habits. The reasons for these changes vary; for example, changes in worldview that preclude the consumption of any or some animal products or beliefs related to the perception that raising animals for food causes more significant environmental damage than growing plants. Many consumers are also open to current nutritional recommendations that call for increasing the proportion of plant products in everyday food, mainly fruits and vegetables. It may be easier to change eating habits by expanding the range of available plant products with unknown or forgotten plant species. These sometimes include species that are difficult to cultivate or are unprofitable in large-scale farming.
The food group in question may include plants growing in the natural environment, i.e. in forest areas, wastelands, or abandoned/neglected human settlements. According to FAO [
1], this group of plants is referred to as wild edible plants. Such plants are usually very well known to local communities, especially in low-income areas, as they often supplement people's daily food. Such a situation was common in the past and now can be observed in poorly developed agricultural mountainous regions [
2,
3]. In Europe, an example is the Carpathian Mountains and their foothills. Therefore, the experiences of the people living in these areas can be used to promote plant foods by popularising forgotten edible plant species.
One of the most characteristic plants for the areas mentioned above is wild (bear) garlic (
Allium ursinum L.). Wild garlic belongs to the economically important genus and subgenus
Allium. Almost all of whose species are present in temperate Europe, the Mediterranean region, the Near and Middle East, the Caucasus, and northern Asia, with only a few species being found outside this area [
4,
5]. In the wild, it grows on the floor of wet, usually mountainous forests [
6,
7].
The characteristic and dominant flavour of Allium and its possible nutritional effects and medical applications have attracted food and medical researchers [
8]. Wild garlic's properties are similar to those of common cultivated garlic. Primarily, the plant's large, green leaves are gathered. There has been a growing interest in using wild garlic as a functional food and dietary supplement. Plants of the genus Allium, including wild garlic, contain active biological substances, phenolic and sulphur compounds, that are potentially useful for humans and animals [
9,
10].
Wild garlic is an interesting food product due to its early vegetation (March/April). It is one of the earliest spring plants in forests and wild areas near forests. It is also increasingly grown in home gardens and is used in the local cuisine. European people consume wild garlic as a fresh or processed vegetable or condiment. The leaves are added mainly for salads, soups, and as a component of pie fillings [
11]. In addition to its culinary uses, wild garlic is also increasingly used as an additive to processed food products. In Poland, Turkey, and Czechia, the leaves are added to local rennet and camembert cheeses [
12,
13].
This study aimed to compare the genome, and chemical composition of the wild garlic (Allium ursinum L.) leaves collected in four locations in southern Poland.
3. Results and Discussion
The frozen leaves of wild garlic after the harvest had a dry matter (DM) content ranging from 9.8–12.6 g/100 g of fresh matter (FM) (
Table 1). The leaves obtained in Krakow and Sucha Beskidzka had significantly higher DM content than those from Limanowa and Ropa. The last two had amounts similar to the value reported by Jędrszczyk et al. [
25] and Leahu [
26], 9.79–10.77 g/100 g and 9.75 g/100 g, respectively; these levels were higher than that found by Gîtin et al. (2012). However, according to Błażewicz-Woźniak [
27], the DM content in wild garlic leaves (6.69–15.7 g/100 g FM) largely depended on the ecotype and the year of cultivation. After drying to a constant weight, the air-dried leaves contained 85.5–92.7 g of DM, and the freeze-dried leaves had 94.3–96.9 g of DM per 100 g of FM. Tomšik et al. [
28] were able to dry wild garlic leaves up to 91.19 g and 92.03 g of DM per 100 g of FM using air at 40 °C and 60 °C, respectively.
Plant pigments, based on their chemical structure, can be classed into five families: tetrapyrroles (e.g. chlorophyll), carotenoids (e.g. β-carotene), phenolic compounds (e.g. theaflavins), and N-heterocyclic compounds (e.g. betalains) [
29]. Chlorophyll a and chlorophyll b are essential pigments of plant photosystems. Its concentration in leaves is a crucial parameter of the plants' photosynthetic mechanism and metabolism. Chlorophyll production mainly depends on the intensity of sunlight and the nitrogen content [
30]. Chlorophylls and carotenoids are responsible for the colour of plants and are even used as parameters of maturity, quality, and freshness of food crops. The amount of chlorophyll in the leaves is influenced by many environmental factors [
31]. The degradation of chlorophyll pigments during processing causes colour changes in the product; a change from green to yellow or red indicates that the carotenoids were uncovered by the destruction of chlorophyll [
32]. Chlorophyll is used as a photosensitiser for cancer therapy. The pigment and its derivatives have potent antioxidant and radioprotective effects. They inhibit lipid peroxidation, protein oxidation, DNA damage, and membrane damage [
33].
In the frozen and dried leaves of wild garlic, the sum of chlorophyll a and b was 638–1532 mg/100 g DM, depending on the location and processing methods. The fraction of chlorophyll a ranged from 68% to 74% (
Table 1), and the chlorophyll a:b ratio was 2–3:1, which is consistent with a study by Srichaikul et al. [
34]. For comparison, Luta et al. [
35] reported 174 mg of chlorophyll/100 g FM in fresh wild garlic leaves. Regardless of the processing method, the highest level of total chlorophyll was in the frozen material collected in the Limanowa region (a mountainous area), an average of 19%–89% more; the lowest content was in the leaves collected near Sucha Beskidzka (also mountainous). Among the preservation methods, freezing turned out to be the best and air-drying the worst way to protect the chlorophylls in garlic leaves. On average, the frozen product contained 15% more chlorophylls than the air-dried product. The decomposition of these pigments likely occurred due to the thin wild garlic leaves' tissue aeration and exposure to high temperatures (40 °C) for tens of hours. According to Rocha et al. [
36], a short steam blanching (15 s) can reduce the degradation of chlorophyll in basil leaves dried at high temperatures (60 °C). Still, if the samples were not blanched before drying, drying at low temperatures was the best method to prevent the degradation of chlorophylls.
In wild garlic leaves, 155–221 mg of β-carotene per 100 g of DM was measured (
Table 1). The most considerable amount of this discriminant was found in the leaves collected near Limanowa (a mountainous area). At the same time, in the case of other frozen products, the location did not affect the amount of β-carotene. The preservation method usually had little effect on the level, with the best process being freeze-drying. For comparison, Luta et al. [
35] found only 5.3 mg of total carotenoids in 100 g of fresh wild garlic leaves, using 80% acetone for the extraction. In turn, Stajner et al. [
37] showed that cultivated leaves of Allium vienale contain over two times more chlorophyll a and chlorophyll b in 100 g of FM than wild growing. Carotenoids are essential not only for the colouration of food but also for their acknowledged roles in health. They are vitamin A sources and a critical factor for human vision. In addition, they have an essential role in preventing various diseases associated with oxidative stress, such as cancer, cardiovascular diseases, and other chronic diseases [
38,
39].
Vitamin C is one of the most critical water-soluble vitamins with different essential biological functions. It is one of the most active antioxidants, which helps the body neutralise free radicals. It takes part in the biosynthesis of collagen, carnitine, hormones, immune response, and iron absorption. It is vulnerable to light, air, and high temperature and decomposes completely at approximately 190 °C [
40]. The content of vitamin C in fruits, vegetables, and herbs is highly variable and dependent on many factors: species, variety, climate, a season of the year, method of storage after harvest, and country of origin [
41]. Stajner et al. [
37] noted that cultivated leaves of Allium vienale contain over three times as much vitamin C (18 mg/100 g FM) as wild-growing varieties. In turn, Jędrszczyk et al. [
25] showed that the amount of vitamin C in wild garlic depends on the part of the plant because the leaves and stems contain 7–15 and 4–6 mg of vitamin C/100 g FM, respectively. In the wild garlic leaves analysed in this study, 20–1673 mg of vitamin C/100 g DM were measured, depending on the harvest site and the method of preservation (
Table 2). For comparison, in fresh wild garlic leaves, Luta et al. [
35] found only 80 mg of vitamin C per 100 g of FM. They determined the amount of vitamin C using titration, not chromatography.
The most vitamin C was found in the frozen material collected in the vicinity of Sucha Beskidzka (a mountainous area), whilst the lowest was in the material from Krakow (an urban area). Among the drying methods used, air-drying was the least favourable, usually resulting in almost complete decomposition of vitamin C. Vitamin C's low resistance to high temperatures might be related to its chemical structure [
41]. Wolska et al. [
42] noted that the brewing temperature significantly impacted the vitamin C content in infusions of nettle leaves. Brewing temperatures of 25–50 ℃ were more favourable than 70–80 ℃, and the optimal dewatering time was 10 min. According to Lee and Kader [
43], depending on the species, L-ascorbic acid (AA) accounted for 52%–93% and 73%–100% of the vitamin C in fruits and vegetables, respectively. In the product prepared from wild garlic leaves, the vitamin C contained up to 45%–50%, 25%–75%, and 41%–54% L-ascorbic acid in frozen, air-dried, and freeze-dried leaves, respectively; the rest was L-dehydroascorbic acid (DHAA). As a rule, a minor proportion of AA was recorded in leaves collected in Krakow (an urban area).
The total polyphenol (TP) content in frozen wild garlic leaves obtained from the four sites was in the range of 1.64–1.95 g gallic acid equivalent (GAE)/100 g DM (
Table 3). However, no difference was found between the frozen product gathered in Krakow and Sucha Beskidzka, whilst the product from Limanowa and Ropa contained significantly more of these compounds. The observed TP content was higher than that previously found in fresh leaves harvested in Poland – 1.48 g/100 g DM [
44] – but they were in the range of 1.31–2.11 g/100 g reported in garlic leaves from Montenegro and Bosnia and Herzegovina [
45]. These values, on the other hand, were lower than those of the leaves of wild garlic harvested in Serbia [
46,
47,
48] – 0.92–6.05 g/100 g DM, depending on the solvent used for extraction – and of garlic cultivated in Poland [
25] – 2.78–3.83 g/100 g DM. According to Gîtin et al. [
49] and Pop et al. [
50], there was even 24.6–27.0 g TP/100 g DM in garlic leaves.
The TP content in dried wild garlic leaves was 1.41–2.14 g/100 g DM. Compared to frozen leaves, air drying resulted in a slight increase in TP content in the leaves from Ropa and a decrease in leaves from Sucha Beskidzka. In contrast, the freeze-dried leaves of plants showed a reduction in TP content regardless of the place of harvest. The decline was not statistically significant in the case of dried products from raw materials obtained in Krakow. According to Tomšik et al. [
28], the TP content in frozen and dried leaves was much higher (9.18–10.10 /100 g DM) than in this study.
The antioxidant activity of wild garlic depends on the harvest date. Jędrszczyk et al. [
25] found that the antioxidant activity against DPPH differed almost twice between the harvest years. Similarly, Lachowicz et al. [
51] found higher antioxidant activity against ABTS and DPPH but lower using the FRAP method in leaves obtained in June than in March. Kovarovič et al. [
52] found that the antioxidant activity of wild garlic leaves against the DPPH radical is higher than that of white and yellow onion, leeks, and common garlic but half that of red onion. Krivokapič et al. [
48] demonstrated that the antioxidant activity (IC50) of wild garlic leaves against DPPH was in the range of 111–391 μg/mL of the extract, depending on the solvent used for extraction. Similar conclusions were reached by Pop et al. [
50]. According to Tomšik et al. [
28], wild garlic leaves dried at 40 °C, and 60 °C did not differ in their antioxidant activity against DPPH.
The antioxidant activity measured against the cation radical ABTS in the frozen leaves was at 347–511 µmol Trolox/g DM; the lowest level was observed in the leaves harvested in Krakow, whilst the highest was in those from Limanowa. The drying contributed to a significant increase in the antioxidant activity – 2.8 to 5.4 times more – compared to frozen leaves. These results were significantly higher in air-dried leaves than in freeze-dried leaves.
The antioxidant activity measured against the free radical DPPH in frozen leaves was 11–27 µmol Trolox/g DM. The dried leaves had a higher level of this index (36–131 µmol Trolox/g DM), and, as in the case of the measurements against ABTS, the freeze-dried leaves had higher antioxidant activity than air-dried ones.
The ferric-reducing antioxidant power (FRAP) of frozen wild garlic leaves was 707–798 µmol Fe2+/g DM. After drying, a significant increase in this indicator was found, in comparison to frozen: 47%–102% more in air-dried and 46%–81% more in freeze-dried. The advantage of air-drying was confirmed only for leaves from Limanowa and Ropa, while in the case of freeze-drying in leaves from Sucha Beskidzka. The drying method did not affect the antioxidant activity only in the leaves harvested in Krakow.
CDDP and PBA marker profiling
Different marker systems were developed within the trend toward gene-targeted functional markers rather than markers of non-coding regions. The conserved DNA-derived polymorphism technique (CDDP) and P450-based analogue markers (PBA) target candidate plant genes [
21,
53]. Similar to RAPD and ISSR techniques, the method is based on the single primer amplified region principle, as a single primer is used as a forward and reverse primer.
Different CDDP and PBA fingerprint profiles were obtained in accessions from the Krakow control sample and samples from the mountainous areas (
Table 4). Monomorphic profiles with no fingerprint changes were only for two primer combinations of CDDP analyse.
Barcoding analysis of ITS region
Primers for barcoding analyse were selected for their putative amplification of the DNA sequences that codify for small- (18S, SSU) and large-subunit (28S, LSU) ribosomal RNA (rRNA). The primers were selected for their previous use; they are considered standard primers for amplifying these regions in various species of fungi and higher plants [
24,
54]. According to many authors, thanks to their variability, ITS regions yielded sufficient molecular information, which can be directly used as identifiers or molecular markers in the phylogenetic analysis [
54,
55,
56]. In our case, the ITS product was variable in some nucleotide positions when compared to the ITS sequence of Allium ursinum stored in the NCBI database (
Figure 1). For comparison purposes, registered NCBI database sequences were used, and their sequences were compared with the BLAST algorithm.
Microsatellite markers assay
Based on Kumar et al. [
57], it was expected that clonal propagation would have little effect on the level of variation in the population structure. In our study, there were differences in the DNA fingerprinting of the garlic samples originating from different environmental conditions (
Figure 2). Our results are consistent with the variability in Indian garlic germplasm consisting of accessions obtained from public research organisations and farmers' markets (natural landraces). Similarly, cluster analysis based on microsatellite markers grouped garlic accessions according to their flowering behaviour, botanical variety, and ecophysiological characteristics [
58]. The potential of SSR markers in plant germplasm evaluation is also supported by the study of da Cunha et al. [
59], where hierarchical clustering (UPGMA dendrogram) analysis reflected the classification of garlic accessions according to maturity time (growth cycle).