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Article

Antioxidant Potentials of Different Genotypes of Cowpea (Vigna unguiculata L. Walp.) Cultivated in Bulgaria, Southern Europe

by
Milena Tankova Tzanova
1,*,
Tsvetelina Dimitrova Stoilova
2,
Mima Hristova Todorova
1,
Neli Yovcheva Memdueva
1,
Maria Asenova Gerdzhikova
1 and
Neli Hristova Grozeva
1
1
Faculty of Agriculture, Trakia University, Studentski Grad Str., 6000 Stara Zagora, Bulgaria
2
Institute of Plant Genetic Resources, Agriculture Academy, 2 Drugba Street, 4122 Sadovo, Bulgaria
*
Author to whom correspondence should be addressed.
Agronomy 2023, 13(7), 1684; https://doi.org/10.3390/agronomy13071684
Submission received: 19 May 2023 / Revised: 15 June 2023 / Accepted: 20 June 2023 / Published: 22 June 2023
(This article belongs to the Section Plant-Crop Biology and Biochemistry)
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Abstract

:
Recently, there has been a growing interest in protein-rich foods and functional foods, as well as plants characterized by high levels of drought resistance. Vigna unguiculata L. Walp. from the Fabaceae family, also known as cowpea, was chosen as the subject of the present study. The antioxidant potentials of 15 genotypes cultivated in Bulgaria, Southern Europe, were determined. The research focused on the green mass used as feed and on the seeds used as an “ancient” traditional crop. The total phenolic content (TPC), total flavonoid content (TFC), radical scavenging capacity, determined via the DPPH method, and crude protein content were measured. The seed coat extracts showed higher contents of phenolics (291.0 ± 4.6 mgGAE/g) and flavonoids (83.5 ± 1.1 mgCE/g) and a stronger radical scavenging capacity (50.4 ± 0.7 µmolTE/g) than those obtained from the leaves (22.0 ± 0.5 mgGAE/g, 13.7 ± 0.5 mgCE/g, and 19.7 ± 0.6 µmolTE/g, respectively). The protein content in the seeds ranged from 20.5% to 27.0%. According to the obtained results, the cowpea genotypes with dark-colored seed coats showed greater antioxidant potentials but lower protein contents. Due to its high antioxidant content, strong radical scavenging capacity, and high protein content, V. unguiculata L. shows great potential as a functional food for humans and animals.

1. Introduction

Cowpea (Vigna unguiculata L. Walp.) is a legume crop with high contents of protein, fiber, antioxidants, etc. [1]. It is a major source of protein for human populations in developing countries, as well as fodder for animals. V. unguiculata L. belongs to the Fabaceae family and is widespread. In many tropical and subtropical countries, cowpea provides the high-quality protein, vitamins, essential minerals, and high calories needed for human and animal quality nutrition [2,3,4].
The protein in cowpea seeds ranges from 17.4 to 31.7% [4]. It mainly consists of globulins (vicilins or 7S globulins), and albumins and prolamins are significantly less present [5]. Gonçalves et al. successfully obtained bioactive peptides with antioxidant activity extracted from cowpea seeds [5]. The ratio of essential to non-essential amino acids is very high and is over 50% of the human daily nutritional requirement [6]. Compared to other legumes, cowpea has a low fat content with a high level of unsaturated fatty acids [7]. A high proportion of carbohydrates, which are mainly dietary fiber, and resistant starch are also typical of cowpea [5].
In addition to high-quality nutrients, cowpea seeds contain bioactive byproducts that benefit human health [1]. Polyphenols are the most important group of these phytoconstituents and are concentrated mostly in the seed coat [8]. The legume seed coat is rich in phenols, although it constitutes 10% of the total seed weight [9,10].
Cowpea seeds are a good source of antioxidants [11,12]. As reviewed by Awika and Duodu, V. unguiculata L. species are rich in nutrients and byproducts with strong antioxidant potentials, and there is evidence of their beneficial health properties [13]. Cowpea extracts have shown antidiabetic, anticancer, antihyperlipidemic, anti-inflammatory, and anti-hypertensive effects in different in vitro and in vivo experiments [13].
Another great advantage this crop has is that it thrives in dry areas [14]. The subject of several studies was the phenotyping of genotypes for their drought resistance [15,16]. Ravelombola et al. [16] studied 331 cowpea genotypes for drought tolerance and concluded that there is a large variation in the traits evaluated.
Due to the increased interest in protein-rich crops, functional foods, and plants characterized by high drought tolerances, cowpea could become a valuable grain crop. The aim of our research was to determine the antioxidant potentials of different cowpea genotypes (Vigna unguiculata L. Walp.) cultivated in Bulgaria, Southern Europe. The research focuses on the green mass of this legume plant, which is used as feed, and the seeds used as a traditional crop in the southern and south-west regions of the country.

2. Materials and Methods

2.1. Plant Material

The objects of the present study were 15 genotypes of V. unguiculata L. The studied plant organs were leaves and seeds (Table 1). Detailed characteristics of the studied cowpea genotypes are presented in Table 1.
The plant material used was obtained from plants grown in the experimental field of the Institute of Plant Genetic Resources, Sadovo, Bulgaria, in 2022. The Institute is situated in the Thracian valley (the central part of Southern Bulgaria), where the soil is a fluvisol with a neutral pH. The cowpeas studied were sown manually in plots containing 4 rows, each 2 m long with an inter-row distance of 0.7 m, at 50 seeds per row in order to obtain 40 plants. The samples of different vegetative organs were collected manually during the different phenological stages of the plants: the leaves were collected before maturity (June), and the seeds were collected when the plants reached maturity (end of July and the middle of August) (Figure 1).

2.2. Sampling and Extract Preparation

The collected plant material was air-dried in shade at room temperature. The leaf samples were ground in a mechanical grinder to final particle size of less than 400 μm. The seeds were soaked in distilled water at room temperature for 24 h and pilled. The collected seed coats were air-dried in shade at room temperature and then pounded in a porcelain mortar. The samples were stored in dark and cool rooms at 16–18 °C prior to the analysis.
An amount of each ground sample was weighed on an analytical balance and suspended in 70% ethanol at a ratio of 1:10. The extraction was carried out via ultrasonication for 30 min at 40 °C. After its filtration through a 0.45 μm membrane, the solid residue was rinsed with 70% ethanol in triplicate. The alcoholic fractions from each sample were collected and adjusted to a final concentration of 1 mg/mL of extract.
The ultrasonication extraction technique and 70% ethanol as an extracting agent were used. Under these conditions, the extraction of polyphenolics and flavonoids is quantitative [17].

2.3. Determination of Total Phenolic Content (TPC)

The experimental protocol described by Tzanova et al. [18] was followed for the quantification of the TPC. In brief, 1 mL of the alcoholic plant extract was mixed with 5.0 mL of Folin–Ciocalteu’s reagent (10-fold diluted). Then, 4 mL of 7.5% Na2CO3 was added, and the tubes were left at room temperature for 60 min. The absorbance at 765 nm was measured against a blank on a Thermo Scientific Evolution 300 spectrophotometer. Gallic acid (Sigma-Aldrich, St. Louis, MO, USA) solutions in 70% ethanol ranging from 10 to 150 μg/mL were used for the calibration curve (R2 = 0.9996). The TPC of each sample was expressed as milligrams gallic acid equivalents (GAE) in 1 g of plant extract dry matter (dm).

2.4. Determination of Total Flavonoid Content (TFC)

For quantification of the TFC, the experimental procedure described by Dinev et al. [19] was followed. In brief, 1 mL of extract, 0.3 mL of 5% NaNO3, and 4 mL of deionized water were mixed in a 10 mL volumetric flask. After 5 min, 0.3 mL of 10% AlCl3 was added. After 6 min, 2 mL of 1 M NaOH was added, and the total volume was adjusted up to 10 mL by adding deionized water. The solution was homogenized, and the absorbance was measured against a blank at 510 nm on a Thermo Scientific Evolution 300 spectrophotometer. Standard solutions of catechin hydrate (Sigma Aldrich, St. Louis, MO, USA) in the range of concentration from 10 to 150 mg/L were used to plot the calibration curve (R2 = 0.9989). The TFC was expressed as mg catechin equivalent (CE) in 1 g of extract dm.

2.5. Determination of Radical Scavenging Capacity via the DPPH Method

The 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) used was purchased from Sigma-Aldrich (St. Louis, MO, USA). The method described by Tzanova et al. [18] was applied to measure the radical scavenging potentials of the alcoholic extracts obtained from different plant parts of the selected cowpea genotypes. In brief, 20 μL of extract was added to 2 mL of a 100 M solution of DPPH in methanol. The absorption at 517 nm was measured on a Thermo Scientific Evolution 300 spectrophotometer 30 min later. Since the composition of the extracts was complex, the results for their radical scavenging capacity were compared with Trolox and calculated via a regression analysis from the linear dependence between the concentration of Trolox and the absorption at 517 nm (R2 = 0.9995 for the linearity of the concentration range from 5 to 50 μmol/L). The results were expressed as µmol Trolox equivalent (TE) in 1 g of dm of plant extract.

2.6. Determination of Crude Protein Content via the Kjeldahl Method

The total protein was determined according to ISO 5983-1 [20]. Approximately 1 g of raw material was hydrolyzed with 15 mL of concentrated sulfuric acid (H2SO4) containing two copper catalyst tablets in a heat block at 420 °C for 1 h. After cooling, the hydrolysates were distillated. The determination was carried out on a KjeltecTM 8400 (Foss, Hilleroed, Denmark).

2.7. Statistical Analysis

The data were expressed as means  ±  standard deviations (SDs) from three replicates for each sample. An ANOVA (one way) and the Kruskal –Wallis statistical analysis were conducted to establish the relationship between the quality characteristics of the seeds and the studied biochemical parameters of V. unguiculata L. The significant differences were tested, and p values < 0.05 were considered statistically significant. The Pearson correlation test and linear regression analysis were also used to determine the relationships between the phenol content, total flavonoid content, and antioxidant activity. The statistical tests were established in XLSTAT 2023.1. 2 (1406), Lumivero (2023).

3. Results and Discussion

3.1. Antioxidant Potentials of Extracts Prepared from the Leaves of the Studied Genotypes of Vigna unguiculata L.

The obtained results are presented in Table 2. The total phenolic contents in the alcoholic extracts from the leaves ranged from 13.4 ± 0.5 mgGAE/g in the extract from genotype 6846 to 31.0 ± 0.5 mgGAE/g in the extract from genotype 6311. The next-best extracts had very close values: 29.3 ± 0.4 mgGAE/g (6319), 27.6 ± 0.9 mgGAE/g (5666), and 26.7 ± 0.6 mgGAE/g (576). The difference between the lowest and the highest values is almost double.
The lowest flavonoid content was in the leaf extract from the genotype 95210045, 9.3 ± 0.4 mg CE/g extract, and the highest flavonoid content was from genotype 6319, which was 18.4 ± 0.5 mg CE/g extract. From the leaves of genotype 6311, extracts with the strongest radical scavenging capacity, 23.6 ± 1.3 µmol TE/g dm, were obtained, and the extracts from genotype 85E164 showed the weakest radical scavenging capacity, 16.9 ± 0.3 µmol TE/g dm.
A significant relationship between the TPC and TFC in the leaves was observed (Table 3). The correlation coefficient was positive with a value of 0.873 because the flavonoid content increased with an increase in the phenol content. This was understandable since flavonoids belong to the polyphenol family. As humans use mainly cowpea seeds as food, the health potential of the other aerial parts has been poorly explored. Moloto et al. [14] established the phenolic profile of seven different cowpea cultivars. The authors found glycosides of gentisic acid, p-coumaric acid, ferulic acid, and quercetin in the leaf extracts. The phenolic content was more than 1000 mg/kg of fresh weight. In the same study, the relationship between cowpea leaf phytochemicals and its anti-diabetic activities was confirmed.
According to the results obtained in the present study, the extracts from cowpea leaves also showed high health potentials, and these cultivars can be defined as sources of “functional” feed.

3.2. Antioxidant Potentials of Extracts Prepared from Seeds of the Studied Genotypes of V. Unguiculata L.

In the case of the seeds, there was a greater accumulation of antioxidants and higher levels of free radical scavenging capacity (Table 4).
The total phenolic contents in the alcoholic extracts obtained from the cowpea seeds ranged from 78.2 ± 0.4 mg GAE/g dm in genotype 95210045, whose seeds were white, to 457.5 ± 5.2 mg GAE/g in genotype 576, which had brown seeds. Compared to the leaves (a 2-fold difference), in the seed coats, the ratio of the highest to the lowest TPC values was 6:1. For comparison, Gutiérrez-Uribe et al. determined a mean TPC value of 107.3 mg GAE/100 g DW in black-colored cowpea seeds [21]. Liyanage et al. [11] studied a few cowpea genotypes cultivated in Sri Lanka and found total phenolic contents in seeds that ranged from 2.4 ± 0.4 to 6.0 ± 0.2 mg equivalents/g DW. The researchers used tannin acid as a standard. Therefore, it is not easy to compare the results because there are differences in the sample preparation and in the expression of the results [13]. Sombié et al. [22] determined the total polyphenol contents of 31 different cowpea varieties from Burkina Faso, and the results were expressed as mg GAE/100 g of seeds DW. They varied widely from 692.0 ± 9.6 to 63.1 ± 4.5. The results obtained in the present study also varied over a large interval from 78.2 ± 0.4 to 457.5 ± 5.2 mg GAE/g dm. Here, the results are comparable. However, dark-coated beans definitely contain more phenolics [13,23,24].
Awika and Duodu concluded that cowpea beans contain high levels of polyphenols with unique profiles, which is not typical for other pulses [13]. Aldaric and methylaldaric acid esters of transferulic, trans-p-coumaric, and protochatechuic acids were identified. The authors reported a content range from 148 to 1176 mg/kg which depended on the genotype. Other common phenolic compounds were gentisic acid, ferulic acid, and quercetin [14]. Based on this unique phenolic profile, a number of working groups have examined the bioactivities of phenolic extracts from cowpea. An extract with a concentration of 100 mg GAE/L inhibited 65% of the proliferation of hormone-dependent mammary (MCF-7) cancer cells [21]. After analyzing a large volume of experimental data, Sreerama et al. demonstrated the antidiabetic and cardiovascular protective effects of phenolic extracts from cowpea [24]. Other researchers evaluated four cowpea types varying in phenol contents and flavonoid profiles for their anti-inflammatory effects [25], and the conclusion drawn was that the major determinant of the interaction between the cowpea extracts and the various cellular markers was the flavonoid profile. The most common flavonoids in the cowpea extracts were the flavonols, which are good radical scavengers [13].
In the present study, a similar trend was observed in the total flavonoid contents (Table 4). The light-colored seeds showed the lowest TFC values, with 22.8 ± 0.7 mg CE/g for genotype BOE0008 and the highest value of 131.4 ± 1.9 mg CE/g for the brown-colored seeds of genotype 576. The ratio is also 1:6. Here, the data from global scientific literature are also scarce. Gan et al. [10] measured a mean TFC of 1383 mg CE/100 g in extracts from the seed coats of cowpeas, and Sreerama et al. [24] found only 7.2 mg CE/g extracted from cowpea flour. Okafor et al. [26] analyzed the flavonoid and phenol acid profiles of cowpea from South Africa. Twenty-six phenol compounds were detected and determined quantitatively in a whole cowpea grain. Only 24 of them were qualified in vegetative organs. The researchers found that the catechin derivatives were the most present in the V. unguiculata seed extracts, and the highest content of 78.6 mg/g was found in the brown seeds. Gutiérrez-Uribe et al. reported interesting results [21]. In black seed coats, the authors found 1730 mg QE/100 g, 10 times more flavonoids compared to whole seeds (173.2 mg QE/100 g), and only traces of these compounds were determined in the cotyledons. Salawu et al. [27] conducted a research study seeking functional foods. The authors established that the phenolics in grains and legumes were bound to the cell walls, and they determined the phenol compositions and biologically active properties of whole grains of sorghum, tef, and cowpea. Whole grain extracts showed greater total contents of phenols (from 630 to 3 mg CE/g) and flavonoids (from 0.03 to 0.17 mg CE/g) compared to the total contents of the same compounds in cell walls (from 261 to 1 and from 0.01 to 0.05 mg CE/g, respectively). The cell walls of cereals and legumes can be considered important potential participants in human health protection due to their high phenol contents [28].
The most frequently represented flavonoids extracted from cowpea were flavonols, flavan-3-ols, and anthocyanins [23,29]. The most common are quercetin glycosides, catechin, and catechin glycosides [13]. Anthocyanines were found in black, green, grey, and blue-mottled cowpeas [30]. Only red-colored seeds have myricetin glycosides [31].
Flavonoids are widely investigated for their important health benefits. The unique flavonoid profiles of the cowpea extracts generate bioactive properties. Nderitu et al. reported that the dark red cowpea inhibited oxidative DNA damage [31]. A number of researchers investigated extracts from this legume and found evidence of their effects on cardiovascular disease [24,27], as well as anti-inflammatory effects [25].
Phenolics and flavonoids have proven antioxidant properties caused by different chemical reaction mechanisms. One mechanism is the donation of hydrogen atoms to reduce reactive oxygen and nitrogen species [32]: the relocation of the unpaired electron in the oxygen atom of the phenol group makes this reaction thermodynamically profitable, and the free radical can continue to react with a second one. This reaction turns the phenol group into a stable quinone structure. This makes them radical scavengers.
A number of authors indicate the high positive correlation between antioxidant activities (expressed as the radical scavenging capacities) and the contents of polyphenols extracted from the seeds of legumes [9,23,33]. Therefore, we measured the radical scavenging capacities of the extracts obtained from the cowpea genotypes, which were the object of our study.
The extracts with the strongest radical scavenging capacities were obtained from the seed coats of the mostly beige seed samples 72,103 and 6324 at 56.6 ± 0.4 and 56.3 ± 0.4 µmol TE/g dm, respectively. The genotypes 95210045, cultivar Hrisi, and VOE0008 with white-colored seeds had the lowest radical scavenging capacities, ranging from 32.6 ± 1.3 to 34.2 ± 1.0 µmol TE/g dm. Gan et al. [10] determined 112 μmol TE/g in red cowpea coats and 211 μmol TE/g in the mostly colored ones. The authors concluded that the pigmented seed coats of this legume have very high antioxidant potentials which are much higher than those of most common fruits and vegetables. However, according to the investigations by Gutiérrez-Uribe et al. [21], the radical scavenging capacity in the peel of black-colored seeds is only 15.5 μmol TE/g.
The correlation between the total phenolic contents and total flavonoid contents in the extracts from seed coats was even stronger. The correlation coefficient had a positive value of 0.921 (Table 3). A positive correlation was also found between leaves and seeds, where the R values were equal to 0.535 for the TFC in leaves to the TPC and equal to 0.562 for the TFC value vs. radical scavenging capacity in seeds. Linear regression was also used to evaluate to what extent variability could be explained by each independent variable (TPC or TFC) for the dependent variable (radical scavenging capacity) in seeds and seeds and leaves. Figure 2, Figure 3, Figure 4 and Figure 5 present the results graphically.
The presented figures and the obtained values of R2 clearly illustrate the correlation between the TPC, mg GAE/g dm, and the radical scavenging capacity and between the TFC and the radical scavenging capacity in seeds, where the values of R2 were 0.8096 and 0.7173, respectively. Most samples of the light seeds had lower contents of phenols and flavonoids than the samples of dark-colored seeds. The highest contents were found in the extracts from the genotypes with brown-, beige-, and black-colored coats, regardless of the fact that a relationship of the seed color to both TPC and TFC was not confirmed statistically.
In this study, the regression analysis performed between the TPCs and the radical scavenging capacities of the extracts obtained from the leaves and the seed coats was positive and characterized by a high coefficient of determination, R2 = 0.9314 (Figure 4). The same figure shows that the leaves had much lower values of the indicators measured than the seed coats. A similar trend was established between the TFC values and the radical scavenging capacities of the extracts obtained (Figure 5). The coefficient of determination R2 was also high, 0.8896, and again, the leaves had much lower values of the two parameters than the seeds. The phenolics contributed to the radical scavenging capacity slightly more than the flavonoids extracted from the investigated V. unguiculata samples. This corresponds to the unique polyphenol profile, which has a major impact on the bioactive properties [13]. Due to their polyphenolics, the cowpea extracts have significant antioxidant and anti-lipid peroxidation activities [21].

3.3. Crude Protein Content of Seeds of the Studied Cowpea Genotypes

V. unguiculata is rich in proteins, which are accumulated in the seeds and mobilized in the germination period. This nutrient fraction also contains lectins (agglutinins) and protease inhibitors, which are nutrient-inhibiting factors that serve to protect the seeds from negative biotic factors [13]. In addition, these compounds have anti-inflammatory [34], anticancer [35], and anti-obesity activities [36]. Bioactive peptides with antioxidant activities were successfully obtained from cowpea proteins via enzymatic proteolysis [5].
In the present study, the protein content in the seeds ranged from 20.5 ± 1.4% (genotype 5666 with brown-colored seeds) to 27.0 ± 2.2% (genotype 95210045 with white-colored seeds). The mean protein content was 23.5 ± 1.9%, which is in the ranges of 17.4–31.7% [4] and 22–30% [13], data which were reported and summarized in the global research literature. There was a relatively high negative correlation coefficient between the protein content and the variables TPC, TFC, and radical scavenging capacity (Table 3). The values of the Pearson correlation coefficient were between −0.675 and −0.601. The correlation between the protein content and the radical scavenging capacity is weaker than the correlations between the other parameters. Thumbrain et al. demonstrated the contribution of cowpea proteins to the antioxidant potential [5]. The authors found differences in the DPPH radical scavenging activity and the reducing power ability of protein isolates from cowpea seeds because of the different mechanisms of radical scavenging. The bioactivities of the cowpea proteins appear in the suppression of cancer cells and in the protection of stressed non-cancer cells [5].
However, the genotypes tested in the present study showed high protein contents in their seeds. What is interesting here is that the genotypes with dark-colored seed coats showed lower protein contents and the light-colored ones showed higher protein contents (Figure 6). A linear relationship between the protein content and TPC, mg GAE/g, was found, whose coefficient R2 is 0.46. The total variation in the values of the protein content can be regarded as composed of a variation explained by the linear regression model and an unexplained variation. The coefficient of determination is the proportion of the explained variation relative to the total variation, which in this case, was 46%.

4. Conclusions

The alcoholic extracts from the leaves and seed coats of the investigated V. unguiculata genotypes had high total phenolic and flavonoid contents and strong radical scavenging capacities. The seed coat extracts showed higher contents of the antioxidants determined and stronger radical scavenging capacities than those obtained from the leaves. Cowpea genotypes with dark-colored seed coats showed greater antioxidant potentials. In contrast to the leaves, in the case of the seeds, the correlation between the color of the seed and the content of antioxidants (phenols and flavonoids) and the radical scavenging capacity is more pronounced. The phenolics contributed to the radical scavenging capacity slightly more than the flavonoids extracted from the investigated genotypes. The amounts of protein in the dark-colored cowpea seeds were lower than in the light-colored ones. However, unpeeled beans benefit human health.
Due to its high antioxidant content, strong radical scavenging capacity, and high protein content, V. unguiculata L. shows great potential as a functional food for humans and animals.

Author Contributions

Conceptualization, T.D.S., N.H.G. and M.T.T.; methodology, M.T.T. and N.Y.M.; software, M.H.T. and M.A.G.; validation, M.T.T. and M.H.T.; formal analysis, M.T.T., M.H.T. and N.Y.M.; investigation, M.T.T. and T.D.S.; resources, T.D.S. and N.H.G.; data curation, M.T.T. and M.H.T.; writing—original draft preparation, M.T.T. and T.D.S.; writing—review and editing, M.H.T. and M.A.G.; visualization, M.H.T.; supervision, T.D.S. and N.H.G.; project administration, M.A.G.; funding acquisition, T.D.S. and N.H.G. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Bulgarian Scientific Research Fund under Contract No. KP-06-H56/13 from 19 November 2021. The topic of the scientific research national project is: “Bioactive substances from legumes and medicinal species–features and potential for use in changing climatic conditions”.

Data Availability Statement

All data are contained within the article.

Conflicts of Interest

The authors declare no conflict of interest.

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Agronomy 13 01684 g001 550
Figure 1. Seed samples of the 15 studied V. unguiculata L. genotypes.
Figure 1. Seed samples of the 15 studied V. unguiculata L. genotypes.
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Figure 2. Linear regression between total phenolic contents and radical scavenging capacities in seeds of different genotypes V. unguiculata L.
Figure 2. Linear regression between total phenolic contents and radical scavenging capacities in seeds of different genotypes V. unguiculata L.
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Figure 3. Linear regression between total flavonoid contents and radical scavenging capacities in seeds of different genotypes V. unguiculata L.
Figure 3. Linear regression between total flavonoid contents and radical scavenging capacities in seeds of different genotypes V. unguiculata L.
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Figure 4. Linear regression between total phenolic contents and radical scavenging capacities in both leaves and seeds of different genotypes V. unguiculata L.
Figure 4. Linear regression between total phenolic contents and radical scavenging capacities in both leaves and seeds of different genotypes V. unguiculata L.
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Figure 5. Linear regression between total flavonoid contents and radical scavenging capacities in both leaves and seeds of different genotypes V. unguiculata L.
Figure 5. Linear regression between total flavonoid contents and radical scavenging capacities in both leaves and seeds of different genotypes V. unguiculata L.
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Figure 6. Linear regression between protein and total phenolic contents in seeds of different genotypes V. unguiculata L.
Figure 6. Linear regression between protein and total phenolic contents in seeds of different genotypes V. unguiculata L.
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Table
Table 1. Description of the studied genotypes of V. unguiculata L.
Table 1. Description of the studied genotypes of V. unguiculata L.
NoCatalogue No.OriginColor of FlowerPlant Habit/TypeColor of SeedsShape of Seed
16311Bulgariapurpleerectblackrhomboid
26319Bulgariapurpleerectbeigekidney-shaped
36955Bulgariapurplesemi erectbeige with brown hilumrhomboid
45666Bulgariapurpleerectbrownegg-shaped
57291Bulgariapurpleerectgray with brown trimegg-shaped
672108Bulgariapurpleprostrategray with brown trimegg-shaped
785E164Bulgariapurpleerectbrownkidney-shaped
8576Bulgariawhitesemi erectbrownrhomboid
972103Bulgariapurplesemi erectbeigeegg-shaped
106846Bulgariapurpleprostratebeigekidney-shaped
1178197Bulgariapurpleprostrategrayegg-shaped
126324Bulgariapurpleerectbeige with black hilumkidney-shaped
1395210045Turkeywhitesemi erectwhite with brown hilumkidney-shaped
14HrisiSadovo, Bulgariawhiteerectwhite with black hilumkidney-shaped
15BOE0008Petrich, Bulgariawhiteerectwhite with black hilumegg-shaped
Table
Table 2. Concentration levels of the parameters measured in the leaves of V. unguiculata L.
Table 2. Concentration levels of the parameters measured in the leaves of V. unguiculata L.
Genotype,
Catalogue No.		Color of SeedsTotal Phenolic
Content,
Mg GAE/g dm		Total Flavonoid Content,
Mg CE/g dm		Radical Scavenging Capacity,
µmol TE/g dm
6311black31.0 ± 0.5 * a **17.4 ± 0.9 a23.6 ±1.3 a
6319beige29.3 ± 0.4 a18.4 ± 0.5 a22.9 ± 0.5 a
6955beige with brown hilum24.3 ± 0.4 a14.7 ± 0.7 a17.3 ± 0.5 a
5666brown27.6 ± 0.9 a,c17.9 ± 0.3 b,c18.7 ± 1.7 a
7291gray with brown trim21.8 ± 0.4 b,c14.8 ± 0.3 a,c22.7 ± 0.5 a
72108gray with brown trim25.5 ± 0.6 a16.6 ± 0.4 a20.2 ± 0.6 a
85E164brown22.3 ± 0.5 a12.2 ± 0.7 a16.9 ± 0.25 a
576brown26.7 ± 0.6 a,c16.7 ± 0.6 b,c17.3 ± 0.4 a
72103beige21.9 ± 0.3 a12.5 ± 0.6 a20.3 ± 0.5 a
6846beige13.4 ± 0.5 a,b13.4 ± 0.6 a,b19.6 ± 0.4 a
78197gray18.0 ± 0.3 a11.3 ± 0.4 a19.9 ± 0.3 a
6324beige with black hilum15.2 ± 0.7 a9.4 ± 0.5 a19.0 ± 0.4 a
95210045white with brown hilum17.2 ± 0.5 b,c9.3 ± 0.4 a,c18.6 ± 0.9 a
Hrisiwhite with black hilum17.1 ± 0.4 b,c9.8 ± 0.7 a,c18.4 ± 0.7 a
BOE0008white with black hilum18.0 ± 0.4 a11.3 ± 0.6 a20.5 ± 0.4 a
min 13.4 ± 0.59.3 ± 0.416.9 ± 0.3
max 31.0 ± 0.518.4 ± 0.523.6 ± 1.2
mean *color of seed22.0 ± 0.5 a13.7 ± 0.5 a19.7 ± 0.6 a
* The data are presented as means ± SDs; ** the same superscript letters within the same row represent significant differences at the level of significance p < 0.05.
Table
Table 3. Pearson correlation matrix of the studied biochemical parameters in leaves and seeds.
Table 3. Pearson correlation matrix of the studied biochemical parameters in leaves and seeds.
VariablesRadical
Scavenging Capacity, µmol TE/g dm *		TPC, mgGAE/g dm *TFC, mgCE/g dm *Radical
Scavenging Capacity, µmol TE/g dm **		TPC, mgGAE/g dm **TFC, mgCE/g dm **Protein, % **
Radical scavenging capacity, µmol TE/g dm *10.3220.3770.209−0.084−0.0210.429
TPC, mgGAE/g dm *0.32210.8730.4180.4320.328−0.085
TFC, mgCE/g dm *0.3770.87310.5350.5620.480−0.176
Radical scavenging capacity, µmol TE/g dm **0.2090.4180.53510.9000.847−0.601
TPC, mgGAE/g dm **−0.0840.4320.5620.90010.921−0.675
TFC, mgCE/g dm **−0.0210.3280.4800.8470.9211−0.606
Protein, % **0.429−0.085−0.176−0.601−0.675−0.6061
* Leaves; ** seeds. Values in bold are different from 0 with a significance level α = 0.05.
Table
Table 4. Concentration levels of the parameters measured in the seeds of V. unguiculata L.
Table 4. Concentration levels of the parameters measured in the seeds of V. unguiculata L.
Genotype, Catalogue No.Color of SeedsTotal Phenolic Content,
Mg GAE/g dm *		Total Flavonoid Content,
Mg CE/g dm *		Radical
Scavenging
Capacity,
µmol TE/g dm *		Protein, % *
6311black349.0 ± 5.2 * a **92.3 ± 0.4 a55.7 ± 0.4 a26.2 ± 2.1 a
6319beige277.0 ± 3.0 a84.7 ± 0.5 a55.6 ± 0.6 a23.7 ± 1.8 a
6955beige with brown hilum421.7 ± 3.5 a113.0 ± 1.9 a54.4 ± 0.3 a20.8 ± 1.6 a
5666brown363.8 ± 7.2 a80.7 ± 0.9 a55.2 ± 0.4 a20.5 ± 1.4 a
7291gray with brown trim317.3 ± 4.8 a87.0 ± 0.8 a57.4 ± 0.8 a23.1 ± 1.8 a
72108gray with brown trim277.2 ± 7.8 a81.8 ± 0.4 a49.4 ± 0.9 a25.7 ± 2.0 a
85E164brown334.8 ± 6.5 a86.6 ± 0.4 a55.0 ± 0.6 a22.7 ± 1.4 a
576brown457.5 ± 5.2 a131.4 ± 1.9 a53.3 ± 0.7 a21.7 ± 1.5 a
72103beige325.8 ± 4.3 a126.9 ± 2.7 a56.6 ± 0.4 a22.0 ± 1.6 a
6846beige352.0 ± 6.5 a115.7 ± 2.3 a53.5 ± 0.7 a23.2 ± 1.7 a
78197gray313.4 ± 5.4 a97.3 ± 0.9 a53.7 ± 0.4 a23.3 ± 1.7 a
6324beige with black hilum331.0 ± 6.0 a,b77.5 ± 0.7 b56.3 ± 0.4 a22.0 ± 1.5 b,c
95210045white with brown hilum78.2 ± 0.4 a,b25.5 ± 0.9 b32.6 ± 1.3 a27.0 ± 2.2 c
Hrisiwhite with black hilum78.8 ± 0.6 a,d28.8 ± 1.0 b,a33.5 ± 1.2 a23.5 ± 1.7 c
BOE0008white with black hilum87.8 ± 1.9 c,a,b22.8 ± 0.7 b,d34.2 ± 1.0 a26.5 ± 2.1 c
min 78.2 ± 0.422.8 ± 0.732.6 ± 1.320.5 ± 1.4
max 457.5 ± 5.2131.4 ± 1.957.4 ± 0.827.0 ± 2.2
mean *Color of seed291.0 ± 4.6 a83.5 ± 1.1 a50.4 ± 0.7 a23.5 ± 1.9 a
* The data are presented as means ± SDs; ** the same superscript letters within the same row represent significant differences at the level of significance p < 0.05.
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Tzanova, M.T.; Stoilova, T.D.; Todorova, M.H.; Memdueva, N.Y.; Gerdzhikova, M.A.; Grozeva, N.H. Antioxidant Potentials of Different Genotypes of Cowpea (Vigna unguiculata L. Walp.) Cultivated in Bulgaria, Southern Europe. Agronomy 2023, 13, 1684. https://doi.org/10.3390/agronomy13071684

AMA Style

Tzanova MT, Stoilova TD, Todorova MH, Memdueva NY, Gerdzhikova MA, Grozeva NH. Antioxidant Potentials of Different Genotypes of Cowpea (Vigna unguiculata L. Walp.) Cultivated in Bulgaria, Southern Europe. Agronomy. 2023; 13(7):1684. https://doi.org/10.3390/agronomy13071684

Chicago/Turabian Style

Tzanova, Milena Tankova, Tsvetelina Dimitrova Stoilova, Mima Hristova Todorova, Neli Yovcheva Memdueva, Maria Asenova Gerdzhikova, and Neli Hristova Grozeva. 2023. "Antioxidant Potentials of Different Genotypes of Cowpea (Vigna unguiculata L. Walp.) Cultivated in Bulgaria, Southern Europe" Agronomy 13, no. 7: 1684. https://doi.org/10.3390/agronomy13071684

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