Potential of cowpea genotypes for nutrient biofortification and cooking quality¹

Potencial de genótipos de feijão-caupi para biofortificação de nutrientes e qualidade de cozimento

ABSTRACT

- Cowpea is a very important food for the populations of the North and Northeast regions of Brazil, representing an excellent source of proteins and minerals. The purpose of this study was to evaluate the potential of 100 cowpea genotypes for biofortification of iron, zinc, and proteins, and cooking quality of the grain. The iron and zinc contents were analyzed by x-ray fluorescence spectrometry; protein content was based on nitrogen determination, using the Kjeldahl method; and cooking quality was assessed using an electric pressure cooker and Mattson cooker. The superiority of genotypes for iron, zinc, proteins, and cooking quality was carried out using the nutritional quality and cooking index. The iron content ranged from 3.58 to 6.06 mg 100g^-1, with an overall average of 4.66 mg 100g^-1, while the zinc content between 2.35 and 4.57 mg 100g^-1 and average of 3.31 mg 100g^-1. Protein range ranged from 20.82 to 26.92 g 100g^-1 and an average of 24.30 g 100g^-1. The percentage of cooked grains ranged from 20 to 98%, with an average of 68.7%. The line MNC11-1023E-28 has the best profile of nutritional and cooking quality, showing potential as a food to meet consumer demands and reverse iron and zinc deficiency in the Brazilian population.

Keywords:
Vigna unguiculata ; Protein.; Iron; Zinc.; Percentage of cooked grains

RESUMO

- O feijão-caupi é um alimento muito importante para as populações das regiões Norte e Nordeste do Brasil, representando uma excelente fonte de proteínas e minerais. O objetivo deste estudo foi avaliar o potencial de 100 genótipos de feijão-caupi para biofortificação de ferro, zinco e proteína, e qualidade de cozimento. Os teores de ferro e zinco foram analisados por espectrometria de fluorescência de raios X; o conteúdo de proteínas foi baseado na determinação de nitrogênio, pelo método de Kjeldahl; e a qualidade de cozimento foi avaliada com uso de panela de pressão elétrica e cozedor de Mattson. A superioridade dos genótipos para ferro, zinco, proteínas e qualidade de cozimento foi realizada utilizando-se o índice de qualidade nutricional e de cozimento. O teor de ferro variou de 3,58 a 6,06 mg 100g^-1, com uma média geral de 4,66 mg 100g^-1, enquanto o teor de zinco entre 2,35 e 4,57 mg 100g^-1 e média de 3,31 mg 100g^-1. O ter de proteínas apresentou amplitude de 20,82 a 26,92 g 100g^-1 e média de 24,30 g 100g^-1. A porcentagem de grãos cozidos variou de 20 a 98%, com média de 68,7%. Os grãos da linhagem MNC11-1023E-28 apresentam melhor perfil de qualidade nutricional e de cocção, apresentando potencial como um alimento para atender às demandas dos consumidores e reverter a deficiência de ferro, zinco e proteínas na população brasileira.

Palavras-chave:
Vigna unguiculata ; Proteína.; Ferro.; Zinco.; Porcentagem de grãos cozidos

INTRODUCTION

Cowpea [Vigna unguiculata (L.) Walp.] is a legume widely grown in Asia, the Americas and Africa due to the high genetic variability for agronomic, nutritional, and culinary characteristics (MAZIERO; RIBEIRO; STORCK, 2015; MOHAMMED; JAISWAL; DAKORA, 2018). It is a rustic crop due to its resistance to heat and drought, as well as its ability to grow in soils with low organic matter and fertility (IQBAL et al., 2018; SILVA et al., 2018).

Brazil is the third largest producer of cowpea in the world. In the 2019/2020 agricultural year, the crop occupied an area of 1,307,800 ha, with a production of 712,600 tons and a yield of 545 kg ha^-1 (COMPANHIA NACIONAL DE ABASTECIMENTO, 2020). It presents grains rich in nutrients that can be used in the population's diet, avoiding deficiencies caused by the lack of minerals, such as iron and zinc (DIAS-BARBOSA et al., 2021). In the Northeast region, about 25 million people, consume this culture, mainly to obtain proteins and minerals, such as iron and zinc, in substitution to the high-cost sources of animal protein.

Iron and zinc are essential micronutrients in the functioning of human metabolism and their deficiency can cause malnutrition or hidden hunger, which has a negative impact on health, affecting more than 2 billion people worldwide (FOOD AND AGRICULTURE ORGANIZATION OF UNITED NATIONS, 2019; LÓPEZ-MORALES et al., 2020; SILVA et al., 2021). Iron is a component of blood hemoglobin with a role in the transport of oxygen and its deficiency can lead to diseases such as anemia, while zinc is an essential mineral for increasing immunity against diseases and its deficiency has been related to many health problems (AYENI; IKWEBE; ONYEZILI, 2018; VAN DER STRAETEN et al., 2020).

Recent studies have revealed that the zinc concentration in cowpea grains is higher than that found in common bean grains (COELHO et al., 2021; GERRANO et al., 2019) and that there is a great genetic variability for the protein, iron, and zinc content in the cowpea germplasm grain (CARVALHO et al., 2012; DIAS-BARBOSA et al., 2021; SANTOS; BOITEUX, 2015; WENG et al., 2019). The determination of the iron and zinc contents in the grains of cowpea genotypes provide information that supports the selection and development of biofortified cultivars for these micro minerals (DIAS-BARBOSA et al., 2020).

In this sense, EMBRAPA, through the BioFort and HarvestPlus programs, has developed biofortified cowpea cultivars (BRS Aracê, BRS Tumucumaque, and BRS Xiquexique), which have high levels of iron and zinc in the grains (ROCHA; DAMASCENO-SILVA; MENEZES-JÚNIOR, 2017). The grains of biofortified cowpea cultivars have iron and zinc contents higher than 6.00 and 4.00 mg 100g^-1, respectively, while conventional cultivars presented lower contents for both micronutrients (FREIRE-FILHO, 2011). The new cowpea cultivars biofortified are a potential vehicle for improving the iron and zinc status in groups in which the micronutrient deficiency is prevalent (COELHO et al., 2021).

The incorporation of cooking quality in the evaluation of cultivars has contributed to improve culinary quality and consumer acceptance (CARVALHO et al., 2017). A long cooking time of cowpea leads to loss of nutrients, loss of useful time and greater energy expenditure (gas or firewood), whereas fast cooking has the potential to provide a highly nutritious food in less preparation time and less energy expenditure (ADDY et al., 2020; ROCHA; DAMACENO-SILVA; MENEZES-JÚNIOR, 2017).

In order to identify a food cowpea with best nutritional and cooking attributes to serve the consumer, the purpose of this study was to evaluate the potential of cowpea genotypes for iron, zinc, and protein biofortification and cooking quality.

MATERIAL AND METHODS

Raw material origin

Grain samples from 100 cowpea genotypes were provided by Embrapa Meio-Norte, in Teresina, PI, Brazil, from a cultivation carried out under irrigated conditions from April to June 2019.

Sample preparation

After the cultivation and harvesting of the assay, samples of grains from each genotype were taken at random, packed in plastic bags and then kept in a refrigerator until the time of analysis. Grain samples of 15 grams were ground in a zirconium ball mill and the resulting flour was used in the analysis of protein, iron, and zinc contents, carried out in triplicate. For the evaluation of cooking quality, samples of 50 grains per genotype were used, conducted in duplicate.

Laboratory analysis

Protein and cooking quality analyzes were carried out at the Bromatology Laboratory of Embrapa Meio-Norte, in Teresina, PI, Brazil, while analyzes of iron and zinc contents were conducted at the Physical-Chemical Analysis and Minerals Laboratory of Embrapa Agroindústria de Alimentos, in Rio de Janeiro, RJ, Brazil.

Experimental design

A completely randomized block design was adopted, with three replications for protein, iron, and zinc contents. For the analysis of the percentage of cooked grains, only two replications were used, due to the limited space of the electric pressure cooker used in the first step of evaluation of the cooking quality.

Analysis of protein content

The protein content was based on nitrogen determination, by Kjeldahl method, using the conversion factor 6.25 (ASSOCIATION OF OFFICIAL ANALYTICAL CHEMISTS, 2008). About 0.2 g of the sample was weighed on parchment paper and then the sample was transferred to digestion tubes. 5 ml of concentrated sulfuric acid and 2 g of catalytic mixture (96% of potassium sulphate and 4% of copper sulphate) were added, followed by heating in a digesting block at a temperature of 400°C, until the solution become blue-green, free of undigested material (black dots). After cooling the tubes, 10mL of distilled water was added and the tube was coupled to the distiller. In the Erlenmeyer 10mL of boric acid solution and indicators were added and coupled to collect the distillate.

From a 50% sodium hydroxide solution, 15 mL was removed and added to the flask with the digested sample, using a funnel with a tap until a slight excess of base was guaranteed. After boiling, distillation took place until 100mL of the distillate was obtained. Then, the distilled solution was titrated with 0.02N hydrochloric acid of known factor.

Analysis of iron and zinc contents

The iron and zinc contents were determined using the technique of x-ray fluorescence spectrometry (XRF). The analyzes were performed on the XRF equipment (S2 Ranger Bruker). A sample of flour from each genotype was used for the analyzes. Before starting the analyzes, the XRF equipment was checked for calibration, where the FLX-K04 (BAX) and FLX-C3 standards were placed in the sampler positions E5 and F5, respectively, in the sample chamber.

The samples were placed in a sample holder, previously prepared using plastic film stretched over them, which were filled with the samples up to half. The sample holders were then placed in the sample chamber, in positions according to the identifications entered in the equipment's control panel. The reading of the iron and zinc contents was performed by the XRF spectrophotometer, and the results were accessed via the Spectra EDX Launcher software from the computer associated with the equipment.

Cooking quality evaluation

The evaluation of cooking quality was carried out using the methodology proposed by Carvalho et al. (2017), with adaptations for cowpea. Two samples of 50 grains of each genotype without mechanical damage were placed in organza bags and identified. Two bags were prepared per genotype, that is, two replicates.

The bags were placed in distilled water for 60 minutes. Later, for cooking, the bags were placed at the bottom of an electric pressure cooker (Eletrolux) with a capacity of 5 liters. The water level used was 3/5 of the pot's capacity; keeping the water in which the bags were soaked. The grains were cooked for 30 minutes. After that, the samples were immediately removed from the pot and the grains placed on a counter for cooling for five minutes.

The evaluation of the percentage of cooked grains was carried out with the aid of the Mattson cooker (MATTSON, 1946). Twenty-five grains per sample were used, chosen at random and the pins placed on the grains. The number of pins that immediately drilled through the grains were recorded. The higher the percentage of grains with fully perforated pins, the higher the cooking quality. The sauce and cooking times were pre-established in preliminary tests.

Estimation of nutritional and cooking quality index

The superiority of cowpea genotypes for iron, zinc, and proteins contents and cooking quality was performed using the nutritional and cooking quality index (NCQI), which was based on the nutritional quality index adopted by Carvalho et al. (2012), with some modifications. It was established a minimum value that the genotype should have to be selected, which in the case of the present work was the general average of each characteristic; larger quantities than the general average counted positively, while smaller quantities than the general average counted negatively.

The NCQI was calculated by multiplying each value in excess (above the general average) or scarcity (below the general average) by the respective arbitrary weight. The following weights were adopted for the characteristics according to the nutritional and culinary importance of the cowpea: 4 for the protein content; 3 for iron and zinc content; and 2 for cooking quality; these were positive because they are characteristics that seek to increase the genetic improvement of the cowpea grain. The algebraic sum of each term (product between the maximum or excess and the respective weight of each characteristic) was then divided by the sum of the weights, according to the following equation:

(1) $NCQ{I}_i=\frac{\sum \left[\left(dv{m}_{i}x{p}_i\right)\right]+\dots +\left[\left(dv{m}_{n}x{p}_n\right)\right]}{P_i+\dots +P_n}$

where NCQI_i is the nutritional and cooking quality of the i-th genotype; dvm_i is the difference between the mean of the i-th genotype and the general mean for the n-th characteristic; and p_i is the arbitrary weight adopted for the n-th characteristic. The higher the NCQI, the better the genotype in terms of nutritional and cooking quality.

Statistical analysis

Data were analyzed according to a completely randomized block design, with three replications for iron, zinc and protein content and two replications for the percentage of cooked grains. Data were subjected to analysis of variances and the averages were grouped by the Scott-Knott test at the level of 5% probability. Statistical analyzes were performed using the SAS software (STATISTICAL ANALYSIS SYSTEM, 2011).

RESULTS AND DISCUSSIONS

The analysis of variance of the characteristics iron, zinc, and protein contents, and the percentage of grain cooked (cooking quality) is shown in Table 1.

Table 1
Summary of the analysis of variance of the characteristics iron, zinc, and protein contents, and the percentage of grain cooked of 100 cowpea genotypes. Teresina, PI, 2020

Variation sources	Degrees of freedom	Medium squares
		Iron content (mg 100g-1)	Zinc content (mg 100g-1)	Protein content (g 100g-1)	Percentage of cooked grains (%)
Genotypes	99	82.96**	67.84**	6.09**	1096.00**
Error		1.96	0.28	0.37	27.26
Variation coefficient (%)		3.00	1.61	2.52	7.56

• ** Significant at 1% probability by the F-test.

The genotypes showed statistically significant differences (p>0.01) for all characteristics evaluated (Table 1), showing variability between genotypes for the nutritional and cooking quality in the grain. Dias-Barbosa et al. (2021), evaluating 33 cowpea genotypes, also found genetic variability for the iron, zinc, and proteins contents and cooking time.

The mean and standard deviation of the genotypes studied for the iron, zinc, and proteins contents and the percentage of cooked grains are shown in Table 2.

Table 2
Means and standard deviation (SD) for the iron, zinc, and proteins contents and the percentage of cooked grains of 100 cowpea genotypes. Teresina, PI, 2020

Genotype	Iron content (mg 100g-1) ± SD	Zinc content (mg 100g-1) ±SD	Protein content (g 100g-1) ±SD	Percentage of cooked grains (%)
MNC11-1005E-20	4.97 ± 0.75f	2.87 ± 0.36p	23.94 ± 1.04c	98 ± 2.83a
MNC11-1005E-28	4.45 ± 0.61h	3.09 ± 0.40n	25.78 ± 0.57b	96 ± 5.66a
MNC11-1005E-37	3.79 ± 1.33j	2.71 ± 0.72r	26.60 ± 0.10a	92 ± 0.00a
MNC11-1006E-10	3.58 ± 1.52k	2.69 ± 0.84r	23.72 ± 0.60d	98 ± 2.83a
MNC11-1008E-9	4.46 ± 2.82h	2.82 ± 0.46q	24.68 ± 0.26c	94 ± 2.83a
MNC11-1012E-7	4.69 ± 0.61g	3.21 ± 0.21m	23.66 ± 0.03d	90 ± 2.83a
MNC11-1013E-18	4.83 ± 1.25f	3.89 ± 0.87f	23.32 ± 0.24d	94 ± 2.83a
MNC11-1013E-33	4.82 ± 1.14f	3.59 ± 0.53i	24.42 ± 0.23c	27 ± 9.90g
MNC11-1013E-27	4.12 ± 0.70i	2.70 ± 0.36r	26.05 ± 0.23b	96 ± 0.00a
MNC11-1013E-8	4.65 ± 1.07g	2.90 ± 0.00p	24.30 ± 0.34c	98 ± 2.83a
MNC11-1013E-16	4.66 ± 1.48g	3.49 ± 0.44j	24.55 ± 0.59c	88 ± 0.00a
MNC11-1013E-25	4.19 ± 2.00i	2.88 ± 0.21p	24.31 ± 0.08c	92 ± 5.66a
MNC11-1015E-2	5.06 ± 1.26e	2.84 ± 0.25p	22.70 ± 0.08e	94 ± 2.83a
MNC11-1015E-5	4.50 ± 1.05h	3.29 ± 0.23l	20.90 ± 1.35f	60 ± 5.66d
MNC11-1015E-7	4.35 ± 0.50h	2.97 ± 0.36º	23.62 ± 0.23d	98 ± 2.83a
MNC11-1015E-15	4.88 ± 1.72f	3.88 ± 0.60f	25.10 ± 0.17c	76 ± 5.66c
MNC11-1015E-28	4.98 ± 0.75f	3.55 ± 0.67i	23.43 ± 0.05d	68 ± 0.00c
MNC11-1015E-29	4.10 ± 0.25i	2.63 ± 0.20s	23.71 ± 0.13d	66 ± 2.83d
MNC11-1015E-35	4.59 ± 1.81g	3.41 ± 0.56k	23.61 ± 1.46d	88 ± 5.66a
MNC11-1016E-12	4.43 ± 1.05h	3.66 ± 0.17h	24.31 ± 0.31c	96 ± 0.00a
MNC11-1016E-16	5.33 ± 1.40d	3.73 ± 0.64g	24.52 ± 0.34c	72 ± 5.66c
MNC11-1017E-3	4.54 ± 0.38h	2.85 ± 0.78p	24.02 ± 0.36c	46 ± 2.83e
MNC11-1017E-8	4.44 ± 2.21h	2.96 ± 0.80o	24.64 ± 0.61c	82 ± 2.83b
MNC11-1017E-10	3.84 ± 0.35j	2.35 ± 0.31u	22.65 ± 0.31e	94 ± 2.83a
MNC11-1017E-26	4.09 ± 0.75i	3.13 ± 0.53n	24.99 ± 0.15c	86 ± 2.83b
MNC11-1017E-30	4.34 ± 1.44h	2.52 ± 0.50t	24.16 ± 0.39c	46 ± 2.83e
MNC11-1017E-31	4.68 ± 1.80g	3.20 ± 0.36m	24.30 ± 0.10c	76 ± 5.66c
MNC11-1017E-33	4.41 ± 1.25h	3.09 ± 1.02n	22.70 ± 0.09e	94 ± 2.83a
MNC11-1017E-37	3.69 ± 0.84k	2.87 ± 0.55p	26.22 ± 0.82a	86 ± 2.83b
MNC11-1018E-2	3.77 ± 1.53j	3.26 ± 0.42l	23.07 ± 0.07d	50 ± 2.83e
MNC11-1018E-4	4.17 ± 1.39i	2.89 ± 0.65p	22.79 ± 0.20e	96 ± 0.00a
MNC11-1018E-17	5.02 ± 1.11f	3.32 ± 0.70l	22.48 ± 0.23e	56 ± 5.66d
MNC11-1018E-20	4.63 ± 0.90g	2.86 ± 0.21p	25.79 ± 0.65b	62 ± 2.83d
MNC11-1019E-8	4.72 ± 1.21g	3.62 ± 0.20h	24.59 ± 0.14c	84 ± 5.66b
MNC11-1019E-12	4.28 ± 0.45i	3.51 ± 0.35j	24.75 ± 0.09c	64 ± 5.66d
MNC11-1019E-15	5.29 ± 1.17e	3.51 ± 0.64j	26.27 ± 0.36a	82 ± 2.83b
MNC11-1019E-16	4.31 ± 1.66h	3.01 ± 0.25o	23.08 ± 0.71d	90 ± 2.83a
MNC11-1019E-40	4.45 ± 1.21h	3.23 ± 0.56m	25.86 ± 1.35b	38 ± 2.83f
MNC11-1019E-46	4.65 ± 0.60g	3.25 ± 0.32l	26.24 ± 0.35a	45 ± 7.07e
MNC11-1020E-29	4.76 ± 0.15g	3.09 ± 0.65n	26.42 ± 0.34a	90 ± 8.49a
MNC11-1020E-18	4.65 ± 1.05g	3.13 ± 0.30n	24.30 ± 0.66c	28 ± 5.66g
MNC11-1020E-16	4.13 ± 2.00i	2.77 ± 0.61q	23.55 ± 0.39d	86 ± 2.83b
MNC11-1020E-5	5.14 ± 1.37e	3.17 ± 0.67m	23.29 ± 0.39d	60 ± 5.66d
MNC11-1020E-36	4.56 ± 0.23g	4.01 ± 0.21e	24.72 ± 0.50c	84 ± 5.66b
MNC11-1020E-6	4.32 ± 1.11h	3.08 ± 0.46n	24.30 ± 0.12c	56 ± 5.66d
MNC11-1021E-27	4.68 ± 1.31g	3.30 ± 0.65l	25.40 ± 0.12b	60 ± 5.66d
MNC11-1021E-17	4.18 ± 0.60i	2.78 ± 0.38q	24.77 ± 0.14c	78 ± 2.83c
MNC11-1022E-1	4.66 ± 1.68g	3.40 ± 0.61k	24.11 ± 0.10c	40 ± 5.66f
MNC11-1022E-9	5.36 ± 0.95d	4.57 ± 1.05a	25.63 ± 0.41b	49 ± 9.90e
MNC11-1022E-58	4.91 ± 2.03f	4.26 ± 0.47d	26.92 ± 0.11a	66 ± 8.49d
MNC11-1023E-28	6.06 ± 2.84a	3.45 ± 1.18j	25.67 ± 0.06b	92 ± 5.66a
MNC11-1023E-60	4.63 ± 1.76g	3.23 ± 0.38m	24.82 ± 0.41c	94 ± 2.83a
MNC11-1023E-48	4.77 ± 1.50g	3.40 ± 0.17k	24.47 ± 1.39c	75 ± 7.07c
MNC11-1023E-26	4.48 ± 0.59h	3.37 ± 0.15k	23.16 ± 1.51d	84 ± 5.66b
MNC11-1024E-18	4.05 ± 1.50i	2.51 ± 0.31t	22.35 ± 1.26e	28 ± 5.66g
MNC11-1024E-1	5.39 ± 1.59d	3.43 ± 0.70k	24.10 ± 0.80c	24 ± 5.66g
MNC11-1024E-16	4.14 ± 1.64i	3.16 ± 0.36m	26.72 ± 0.08a	24 ± 5.66a
MNC11-1026E-15	5.37 ± 2.95d	3.74 ± 0.35g	24.97 ± 0.63c	90 ± 8.49a
MNC11-1026E-5	3.91 ± 1.18j	2.89 ± 0.20p	25.53 ± 0.60b	52 ± 5.66e
MNC11-1026E-19	5.57 ± 0.67c	4.14 ± 0.60d	23.09 ± 0.81d	52 ± 5.66e
MNC11-1028E-16	5.26 ± 0.64e	3.40 ± 0.68k	24.75 ± 0.14c	94 ± 2.83a
MNC11-1028E-34	4.92 ± 1.16f	3.54 ± 0.50i	23.24 ± 0.88d	94 ± 2.83a
MNC11-1028E-95	4.43 ± 1.91h	3.23 ± 0.42m	24.71 ± 0.83c	86 ± 2.83b
MNC11-1029E-9	4.80 ± 1.71f	3.53 ± 0.25i	25.96 ± 0.14b	40 ± 0.00f
MNC11-1029E-13	5.45 ± 0.55d	3.80 ± 0.26g	25.54 ± 0.44b	34 ± 8.49f
MNC11-1029E-15	4.72 ± 1.54g	3.44 ± 0.35j	23.04 ± 0.04d	82 ± 2.83b
MNC11-1031E-5	4.64 ± 0.97g	2.60 ± 0.32s	24.88 ± 0.24c	30 ± 8.49g
MNC11-1031E-8	4.99 ± 0.61f	2.80 ± 0.61q	23.31 ± 0.55d	51 ± 7.07e
MNC11-1031E-9	4.14 ± 1.39i	3.11 ± 0.56n	22.47 ± 0.16e	90 ± 8.49a
MNC11-1031E-11	4.86 ± 0.57f	4.06 ± 1.03e	23.37 ± 0.23d	45 ± 7.07e
MNC11-1031E-13	4.41 ± 0.96h	3.79 ± 0.31g	23.60 ± 0.05d	34 ± 2.83f
MNC11-1031E-15	5.76 ± 1.22b	3.54 ± 0.35i	22.69 ± 0.49e	86 ± 2.83b
MNC11-1033E-14	4.69 ± 2.70g	2.63 ± 0.46s	24.34 ± 0.32c	47 ± 7.07e
MNC11-1033E-30	5.77 ± 1.15b	3.10 ± 0.66n	24.91 ± 0.55c	92 ± 5.66a
MNC11-1034E-1	4.55 ± 1.45h	2.99 ± 0.25o	25.70 ± 0.60b	98 ± 2.83a
MNC11-1034E-2	5.57 ± 1.13c	3.39 ± 0.06k	25.70 ± 0.36b	31 ± 7.07g
MNC11-1036E-3	4.46 ± 0.56h	3.23 ± 0.47m	25.48 ± 0.18b	34 ± 8.49f
MNC11-1036E-4	4.53 ± 0.10h	3.09 ± 0.91n	23.87 ± 2.21d	26 ± 2.83g
MNC11-1036E-5	4.85 ± 1.82f	3.56 ± 0.21i	24.33 ± 0.18c	58 ± 2.83d
MNC11-1037E-1	4.24 ± 1.72i	3.35 ± 0.57k	25.15 ± 2.00c	78 ± 2.83c
MNC11-1037E-4	4.53 ± 0.84h	2.98 ± 0.21o	24.14 ± 0.32c	46 ± 8.49e
MNC11-1037E-5	5.10 ± 1.10e	4.15 ± 0.50d	24.32 ± 0.45c	86 ± 2.83b
MNC11-1039E-4	4.26 ± 0.38i	3.09 ± 0.38n	25.11 ± 0.35c	39 ± 7.07f
MNC11-1042E-1	3.93 ± 0.75j	2.99 ± 0.32o	23.55 ± 0.31d	72 ± 5.66c
MNC11-1042E-4	5.58 ± 4.46c	4.18 ± 0.70d	25.11 ± 0.29c	80 ± 5.66b
MNC11-1043E-4	4.87 ± 0.80f	3.57 ± 1.04i	22.67 ± 0.82e	80 ± 5.66b
MNC11-1044E-8	4.01 ± 0.83i	2.97 ± 0.21o	21.39 ± 0.10f	90 ± 8.49a
MNC11-1046E-3	5.14 ± 0.60e	4.48 ± 0.32b	21.44 ± 0.07f	32 ± 5.66g
MNC11-1046E-8	4.09 ± 1.54i	3.33 ± 0.60l	22.35 ± 0.21e	58 ± 2.83d
MNC11-1046E-9	4.25 ± 1.04i	2.99 ± 0.60o	21.31 ± 0.14f	58 ± 8.49d
MNC11-1047E-4	5.20 ± 1.10e	3.97 ± 0.25e	20.82 ± 0.13f	57 ± 9.90d
MNC11-1047E-6	4.30 ± 2.14h	3.28 ± 0.71l	21.89 ± 0.27f	48 ± 0.00e
MNC11-1048E-2	4.42 ± 0.95h	2.98 ± 0.78o	20.99 ± 0.27f	82 ± 2.83b
MNC11-1052E-3	5.17 ± 0.64e	4.39 ± 0.32c	23.13 ± 0.06d	20 ± 0.00g
MNC11-1052E-4	4.47 ± 2.07h	2.82 ± 0.35q	22.43 ± 0.11e	48 ± 5.66e
MNC11-1053E-3	4.43 ± 1.14h	3.31 ± 0.38l	20.91 ± 0.15f	56 ± 0.00d
BRS Tumucumaque	5.95 ± 0.81a	4.18 ± 0.55d	23.35 ± 1.48d	96 ± 5.66a
BRS Pajeú	5.89 ± 2.05a	4.17 ± 0.80d	21.81 ± 0.18f	55 ± 7.07d
Inhuma	5.13 ± 1.07e	4.06 ± 0.45e	23.03 ± 0.35d	42 ± 2.83f
Pingo de Ouro 1-2	3.90 ± 0.06j	3.47 ± 0.46j	22.09 ± 0.06f	98 ± 2.83a
Overall mean	4.66	3.31	24.15	69.09

• Averages followed by the same capital letter in the column belong to the same group, according to the Scott-Knott grouping criterion (p>0.05).

Iron content

The iron content varied from 3.58 to 6.06 mg 100g^-1, with an overall average of 4.66 mg 100g^-1 (Table 2). Similar values were reported by Pereira et al. (2014), who assessed the bioaccessibility of iron and zinc in cowpea cultivars, found that the iron content ranged from 5.8 mg 100g^-1 to 6.4 mg 100g^-1. Gunathilake, Herath and Wansapala (2016) found values for the iron content between 2.26 mg and 3.54 mg 100g^-1 in a cowpea cultivar in Sri Lanka, contents lower than those found in the present work. In a study with mutant cowpea cultivars carried out in India, Raina et al. (2020) found higher contents between 8.17 and 9.32 mg 100g^-1.

The averages of the iron content were broken down into eleven groups by the Scott-Knott grouping (p>0.05) (Table 2), showing a great contrast for this mineral among the evaluated genotypes. According to Rocha, Damasceno-Silva and Menezes-Júnior (2017), genetic biofortification for iron content is one of the objectives of the cowpea breeding programs. Unlike food fortification, which occurs during processing, genetic biofortification occurs by increasing the micronutrient content of the plant. It benefits both farming families who produce for their own consumption, as well as urban and rural families who buy biofortified food.

Group A stood out from the others, including genotypes with high iron content: the line MNC11-1023E-28, with 6.06 mg 100g^-1 and the cultivars BRS Tumucumaque and BRS Pajeú, with 5.95 and 5.89 mg 100g^-1, respectively (Table 2). It was observed that the line MNC11-1023E-28, with 6.06 mg 100g^-1 present iron content in the grain greater than 6.00 mg 100g^-1, showing that they fall into the group of biofortified genotypes (FREIRE-FILHO, 2011).

The iron content found for the BRS Tumucumaque cultivar in the present study confirms its status as a biofortified cultivar for this mineral (COELHO et al., 2021; ROCHA; DAMASCENO-SILVA; MENEZES-JÚNIOR, 2017). These first authors, evaluating three biofortified cowpea cultivars (BRS Aracê, BRS Taumucumaque, and BRS Xiquexique), concluded that the biofortification process was effective not only in increasing the levels, but also in the bioaccessibility of iron in the grains of these cultivars.

The variation among the mineral’s contents found in cowpea can be explained by the genetic variability of the crop, edaphoclimatic conditions, and the existence of the genotype x environment interaction (SILVA et al., 2012). The genotypic difference for iron content may be associated with the additive inheritance that controls the expression of this characteristic and the genetic divergence between parents, used in the crossings that gave rise to the evaluated genotypes (SANTOS; BOITEUX, 2015).

The Resolution of the Collegiate Board (RDC) nº 269 of the National Health Surveillance Agency (AGÊNCIA NACIONAL DE VIGILÂNCIA SANITÁRIA, 2005) determines that the reference daily intake (RDI) of iron for adults is 14 mg day^-1. Considering that the average for the iron content of the genotypes analyzed in this study was 4.66 mg 100g^-1, the consumption of 100 g day^-1 of cowpea meets 33.3% of the iron RDI. Consumption of 100 g day^-1 of the best genotype, the line MNC11-1023E-28 (6.06 mg 100g^-1), meets 43.3% of the iron RDI, helping to fight anemia resulting from iron deficiency in the population.

Zinc content

The studied genotypes showed a variation for the zinc content between 2.35 mg 100g^-1 and 4.57 mg 100g^-1, with an average of 3.31mg 100g^-1 (Table 2). A similar result was found by Dias-Barbosa et al. (2020), evaluating 16 cowpea genotypes, which found an average for the zinc content of 4.17mg 100g^-1; as well as Rios et al. (2018), evaluating commercial cowpea cultivars, which had zinc content ranging from 3.17 to 5.14 mg 100g^-1; and Gunathilake, Herath and Wansapala (2016), who studied cowpea cultivars in Sri Lanka, observed zinc contents between 2.04 and 2.82 mg 100g^-1. On the other hand, Oliveira et al. (2017), evaluating the zinc content in 12 cowpea genotypes in three locations in Maranhão and Piauí, Brazil, found variation and mean of 3.66 to 5.66 mg 100g^-1, being higher than those obtained in the present study.

The genotypes were classified by the Scott-Knott test (p>0.05) in 21 groups (Table 2), showing a high genetic variability among them for the zinc content in the grain, in relation to the other characteristics evaluated in the present study. Dietary zinc deficiency is widespread globally and is particularly prevalent in low- and middle-income countries, resulting in a public health problem, and increasing the nutrient’s content in the edible parts of plants can help mitigate it (LÓPEZ-MORALES et al., 2020; SILVA et al., 2021). One of the objectives of cowpea breeding is to increase the zinc content in the grain (ROCHA; DAMASCENO-SILVA; MENEZES-JÚNIOR, 2017). Genetic variability for zinc is a condition for the development of biofortified cultivars in this mineral.

Groups A and B highlighted, with the highest zinc content, which comprised only one genotype each, respectively the lines MNC11-1022E-9, with 4.57 mg 100g^-1, and the line MNC11-1046E-3, with 4.48 mg 100g^-1 (Table 2). The cultivar BRS Tumucumaque, considered to be biofortified for zinc, had a content of 4.18 mg 100g^-1, lower than the contents observed for the lines above. Coelho et al. (2021), evaluating the zinc content in biofortified cowpea cultivars, observed a zinc content of 46.0 mg 100g^-1 for this cultivar, which was higher than that found in the present study. This zinc content is above 4.00 mg 100g^-1, higher than that presented by non-biofortified cowpea cultivars (FREIRE-FILHO, 2011).

The variation observed for the zinc content in the grains of the cultivar BRS Tumucumaque in different studies, in addition to the genotype, can be attributed to factors such as the place of cultivation and environmental factors (CARVALHO et al., 2012; PEREIRA et al., 2016), such as temperature and rainfall, which can influence the value of this characteristic.

The RDC nº 269 of the National Health Surveillance Agency determines that the zinc RDI for adults is 7.0 mg day^-1 (AGÊNCIA NACIONAL DE VIGILÂNCIA SANITÁRIA, 2005). Considering that the average for the zinc content of the genotypes analyzed in this study was 3.31 mg 100g^-1, the consumption of 100 g day^-1 of cowpea meets 47.3% of the daily zinc requirement. Consumption of 100 g day^-1 of the best genotype, the line MNC11-1022E-9 (4.57 mg 100g^-1), meets 65.3% of the zinc RDI. The adoption of this line in the population's diet represents a strategy to combat malnutrition resulting from zinc deficiency.

Protein content

Protein contents varied from 20.82 to 26.92 g 100g^-1, with a general average of 24.30 g 100g^-1 (Table 2). The Scott-Knott test (p>0.05) classified the genotypes into six groups. Group A included seven genotypes: the lines MNC11-1022E-58 (26.92 g 100g^-1), MNC11-1024E-16 (26.72 g 100g^-1), MNC11-1005E-37 (26.60 g 100g^-1), MNC11-1020E-29 (26.42 g 100g^-1), MNC11-1019E-15 (26.27 g 100g^-1), MNC11-1019E-46 (26.24 g 100g^-1), and MNC11 -1017E-37 (26.22 g 100g^-1), which highlighted in relation to the other evaluated genotypes, with the highest protein contents. This cowpea lines with high protein contents in the grains is crucial for human health, especially in the diet of the low-income population in the Brazilian semi-arid zone.

Carvalho et al. (2012), studying 30 Brazilian cowpea genotypes, found variation (17.4 to 28.3 g 100g^-1) and average (21.6 g 100g^-1) for protein content higher than those observed in the present study. Likewise, Weng et al. (2019), evaluating 173 USDA cowpea accessions, observed a variation from 22.8 to 28.9 g 100g^-1 and an average of 25.6 g 100g^-1. Several studies carried out on cowpea have found similar results for protein content to those obtained in the present study, such as the studies by Bezerra et al. (2019), with contents between 20.66 and 26.06 g 100g^-1; Gomes, Reis and Silva (2012), average content of 26.4 g 100g^-1 in whole flour; and Kanda et al. (2020), who reported an average content of 24.33 g 100g^-1.

The RDC nº 269 of the National Health Surveillance Agency (AGÊNCIA NACIONAL DE VIGILÂNCIA SANITÁRIA, 2005) determines that the RDI of proteins for adults is 50 g day^-1. Considering that the average for the protein content of the genotypes analyzed in this study was 24.15 g 100g^-1, the consumption of 100 g day^-1 of cowpea meets 48.3 g 100g^-1 of the protein RDI. Protein contents above 25 g 100g^-1 are considered quite high for legumes (ÇAKIR et al., 2019), as observed in the seven cowpea lines with higher protein content in this study. The average protein content obtained in this study is also higher than the average presented by the latest cowpea cultivars released on the market (FREIRE-FILHO, 2011).

Cooking quality

The cooking quality, assessed from the percentage of cooked grains, varied from 20 to 98% (Table 2), where samples from 72 genotypes showed good cooking quality, since when 13 of the 25 sticks pierce the grains, they are considered if the sample is cooked (MATTSON, 1946). The general average was 68.7% of cooked grains. Carvalho et al. (2017), evaluating 252 common bean progenies and three locations in Minas Gerais, used the same methodology and found an average percentage of cooked grains of 36.71%, lower than the average obtained in the present study.

The genotypes were organized into seven groups according to the Scott-Knott test (p>0.05) (Table 2). Group A comprised 32% of the genotypes, which had the highest percentage of cooked grains, constituting the group of genotypes with the best cooking quality. The lines MNC11-1005E-20, MNC11-1006E-10, MNC11-1013E-8, MNC11-1015E-7, MNC11-1034E-1, and Pingo de Ouro 1-2 showed an average of 24.5 perforated grains, equivalent to 98 % of cooked grains, constituting as the genotypes with the best cooking quality. According to Rocha, Damasceno-Silva and Menezes-Júnior (2017) and Addy et al. (2020), fast cooking has the potential to provide a highly nutritious food in less preparation time and less energy expenditure.

On the other hand, the lines allocated to group G, MNC11- 1052E-3 and MNC11- 1024E-1, with an average of five perforated grains, making up between 20 and 24% of cooked grains, presented the worst cooking quality (Table 2), indicating that there is the need for a longer cooking time for these genotypes, which is a negative aspect for the consumer. According to Addy et al. (2020), a long cooking time of cowpea leads to loss of nutrients, loss of useful time and greater expenditure of energy in the preparation of the meal.

Therefore, lines with a high percentage of cooked grain are promising for the development of new cowpea cultivars with high cooking quality. It is important to note that a fixed time was used for cooking the grains (30 minutes), so some samples were much more cooked than others, not allowing the ideal cooking time to be determined. Therefore, the grains of the genotypes that showed the highest percentage of cooking, probably have cooking time of less than 30 minutes.

Nutritional and cooking quality index

The nutritional and cooking quality indexes (NCQI) of the evaluated genotypes, based on the iron, zinc, and protein contents and the cooking quality are shown in Table 3. It is observed that the highest values of NCQI were presented by the genotypes MNC11-1023E-28 (12.48), followed of BRS Tumucumaque (10.50), MNC11-1013E-27 (9.55), MNC11-1005E-37 (9.35), and MNC11-1042E-4 (9.04). These genotypes had the best nutritional profile and culinary quality and, therefore, can be used to combat malnutrition in populations with iron and zinc deficiency, as a complementary intervention to food fortification and drug supplementation.

Table 3
Nutritional and cooking quality indexes (NCQI) of 100 cowpea genotypes, based on iron, zinc, and protein contents and cooking quality. Teresina, PI, 2020

Genotype	NCQI	Genotype	NCQI	Genotype	NCQI
MNC11-1005E-20	6.76	MNC11-1019E-8	3.81	MNC11-1031E-5	-5.21
MNC11-1005E-28	7.72	MNC11-1019E-12	7.76	MNC11-1031E-8	-5.72
MNC11-1005E-37	9.35	MNC11-1019E-15	6.16	MNC11-1031E-9	1.65
MNC11-1006E-10	5.81	MNC11-1019E-16	-0.61	MNC11-1031E-11	-6.85
MNC11-1008E-9	6.23	MNC11-1019E-40	-3.53	MNC11-1031E-13	-4.07
MNC11-1012E-7	3.53	MNC11-1019E-46	0.17	MNC11-1031E-15	0.95
MNC11-1013E-18	-9.46	MNC11-1020E-29	7.71	MNC11-1033E-14	-1.10
MNC11-1013E-33	-8.56	MNC11-1020E-18	-9.46	MNC11-1033E-30	6.92
MNC11-1013E-27	9.55	MNC11-1020E-16	-0.30	MNC11-1034E-1	7.70
MNC11-1013E-8	6.72	MNC11-1020E-5	-2.28	MNC11-1034E-2	7.78
MNC11-1013E-16	5.36	MNC11-1020E-36	4.69	MNC11-1036E-3	-7.69
MNC11-1013E-25	-0.16	MNC11-1020E-6	-3.93	MNC11-1036E-4	-9.55
MNC11-1015E-2	5.06	MNC11-1021E-27	-3.29	MNC11-1036E-5	-4.96
MNC11-1015E-5	-5.39	MNC11-1021E-17	0.26	MNC11-1037E-1	2.09
MNC11-1015E-7	5.97	MNC11-1022E-1	-7.65	MNC11-1037E-4	-5.75
MNC11-1015E-15	3.05	MNC11-1022E-9	8.60	MNC11-1037E-5	5.21
MNC11-1015E-28	-3.43	MNC11-1022E-58	8.49	MNC11-1039E-4	-5.24
MNC11-1015E-29	0.33	MNC11-1023E-28	12.48	MNC11-1042E-1	-5.65
MNC11-1015E-35	-0.88	MNC11-1023E-60	6.53	MNC11-1042E-4	9.04
MNC11-1016E-12	6.89	MNC11-1023E-48	3.01	MNC11-1043E-4	2.11
MNC11-1016E-16	-0.12	MNC11-1023E-26	-0.08	MNC11-1044E-8	0.23
MNC11-1017E-3	-5.60	MNC11-1024E-18	-15.81	MNC11-1046E-3	-9.67
MNC11-1017E-8	3.23	MNC11-1024E-1	-8.62	MNC11-1046E-8	-6.32
MNC11-1017E-10	3.03	MNC11-1024E-16	-7.23	MNC11-1046E-9	-4.61
MNC11-1017E-26	2.66	MNC11-1026E-15	7.74	MNC11-1047E-4	0.10
MNC11-1017E-30	-8.31	MNC11-1026E-5	0.06	MNC11-1047E-6	-9.99
MNC11-1017E-31	1.17	MNC11-1026E-19	7.75	MNC11-1048E-2	-0.99
MNC11-1017E-33	4.21	MNC11-1028E-16	7.73	MNC11-1052E-3	-9.85
MNC11-1017E-37	5.21	MNC11-1028E-34	6.30	MNC11-1052E-4	-3.12
MNC11-1018E-2	-8.25	MNC11-1028E-5	2.88	MNC11-1053E-3	-6.38
MNC11-1018E-4	-1.31	MNC11-1029E-9	-3.79	BRS Tumucumaque	10.50
MNC11-1018E-17	-6.33	MNC11-1029E-13	-5.78	BRS Pajeú	7.83
MNC11-1018E-20	0.87	MNC11-1029E-15	2.44	Inhuma	-7.19
				Pingo de Ouro 1-2	8.76

The result obtained in this study confirms the superiority of biofortification of the cultivar BRS Tumucumaque for iron and zinc contents (COELHO et al., 2021; ROCHA; DAMASCENO-SILVA; MENEZES-JÚNIOR, 2017) and shows that it also presents high cooking quality. These last authors highlight the BRS Tumucumaque as the cowpea cultivar with the fastest cooking time (13'23”, after soaking in water for two hours).

Carvalho et al. (2012), evaluating 30 Brazilian cowpea genotypes, used a nutritional quality index and, through this, identified genotypes with high iron, zinc, and protein contents, however, the cultivars BRS Tumucumaque and BRS Pajeú and the line Pingo de Ouro 1-2 did not present the best attributes in relation to these nutrients, when compared with the other evaluated genotypes. These differences in the behavior of these characteristics may be associated with the origin of the samples of the genotypes, which depend on the location and agricultural year of cultivation, edaphoclimatic conditions of cultivation and number of days and post-harvest storage conditions.

Among all cowpea lines evaluated, the grain of the line MNC11-1023E-28 presented the best nutritional and cooking attributes, constituting a food of great nutritional value and quick to prepare for the consumer.

CONCLUSIONS

1. Among the 100 genotypes evaluated, 83% have a high iron content and a zinc content above 30% of the reference daily intake;

2. The protein content of the genotypes supplies more than 40% of the reference daily intake, constituting an excellent source of this nutrient;

3. Most of the genotypes (72%) serve the consumer in terms of cooking quality;

4. Among the cowpea lines evaluated, MNC11-1023E-28 has the best nutritional and cooking quality profile, constituting an excellent food option for consumers who demand quick meal preparation, as well as an alternative to combat iron deficiency and zinc in the Brazilian population.

• 1
  Part of the dissertation of the first author, presented to the Graduate Program in Food and Nutrition of the Federal University of Piauí

ACKNOWLEDGMENTS

The authors would like to thank the Empresa Brasileira de Pesquisa Agropecuária (Projects 20.18.01.022.00.04 and 20.19.00.118.00.06), Agreement EMBRAPA/HARVESTPLUS/FUNARBE-4370 (IFPRI 6332 306363.006.032 - TASK 5), and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for funding this research.

REFERENCES

• ADDY, S. N. T. T. et al Genetic studies on the inheritance of storage-induced cooking time in cowpeas [Vigna unguiculata (L.) Walp]. Frontiers in Plant Science, v. 11, n. 144, p. 1-9, 2020.
• AGÊNCIA NACIONAL DE VIGILÂNCIA SANITÁRIA (BRASIL). Resolução RDC nº 269, de 22 de setembro de 2005 Regulamento técnico sobre a ingestão diária recomendada (IDR) de proteínas, vitaminas e minerais, 2005. Brasília, DF: Diário Oficial da União, 2005.
• ASSOCIATION OF OFFICIAL ANALYTICAL CHEMISTS. Official methods of analysis of the Association of Official Analytical Chemists 17 ed. Gaithersburg: AOAC International, 2008. Chapter 50, p. 15-18.
• AYENI, D. F.; IKWEBE, J.; ONYEZILI, F. N. Iron and zinc levels in Vigna unguiculata (L.) Walp under varying phosphorus and fixed nitrogen treatment conditions. Food and Energy Security, v. 7, n. 3, e00141, 2018.
• BEZERRA, J. M. et al Composição química de oito cultivares de feijão-caupi. Revista Verde de Agroecologia e Desenvolvimento Sustentável, v. 14, n. 1, p. 41-47, 2019.
• ÇAKIR, Ö. et al Nutritional and health benefits of legumes and their distinctive genomic properties. Food Science and Technology, v. 39, n. 1, p. 1-12, 2019.
• CARVALHO, A. F. U. et al Nutritional ranking of 30 Brazilian genotypes of cowpeas including determination of antioxidant capacity and vitamins. Journal of Food Composition and Analysis, v. 26, n. 1/2, p. 81-88, 2012.
• CARVALHO, B. et al New strategy for evaluating grain cooking quality of progenies in dry bean breeding programs. Crop Breeding and Applied Biotechnology, v. 17, n. 2, p. 115-123, 2017.
• COELHO, R. C. et al Expanding information on the bioaccessibility and bioavailability of iron and zinc in biofortified cowpea seeds. Food Chemistry, v. 15, n. 347, e129027, 2021.
• COMPANHIA NACIONAL DE ABASTECIMENTO (BRASIL). Acompanhamento da safra brasileira: grãos, dezembro 2020. Brasília, DF: CONAB, 2020. v. 8, n. 3, p. 12-14. Disponível em: https://www.conab.gov.br/info-agro/safras/graos/boletim-da-safra-de-graos Acesso em: 19 abr. 2021.
  » https://www.conab.gov.br/info-agro/safras/graos/boletim-da-safra-de-graos
• DIAS-BARBOSA, C. Z. M. C. et al Seleção de linhagens elite de feijão-caupi de porte semiereto biofortificadas com ferro e zinco. Brazilian Journal of Development, v. 6, n. 4, p. 19807-19814, 2020.
• DIAS-BARBOSA, C. Z. M. C. et al Selection of cowpea elite lines for iron and zinc biofortification. Current Nutrition & Food Science, v. 17, n. 1, p. 48-58, 2021.
• FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS. Biofortification: a food-systems solution to help end hidden hunger. Washington: HarvestPlus/IFPRI, 2019. 22 p. Disponível em: http://www.fao.org/3/ca8711en/ca8711en.pdf Acesso em: 3 jun. 2021.
  » http://www.fao.org/3/ca8711en/ca8711en.pdf
• FREIRE-FILHO, F. R. (ed.). Feijão-caupi no Brasil: produção, melhoramento genético, avanços e desafios. Teresina: Embrapa Meio-Norte, 2011. 84 p.
• GERRANO, A. S. et al Selection of cowpea genotypes based on grain mineral and total protein content. Acta Agriculturae Scandinavica, Section B – Soil & Plant Science, v. 69, n. 2, p. 155-166, 2019.
• GOMES, G. M. S.; REIS, R. C.; SILVA, C. A. D. T. Obtenção de farinha de feijão-caupi (Vigna unguiculata L. Walp.). Revista Brasileira de Produtos Agroindustriais, v. 14, n. 1, p. 31-36, 2012.
• GUNATHILAKE, K. T.; HERATH, T.; WANSAPALA, J. Comparison of physicochemical properties of selected locally available legume varieties (mung bean, cowpea and soybean). Potravinarstvo Eslovaca Journal of Food Sciences, v. 10, n. 1, p. 424-30, 2016.
• IQBAL, M. A. et al Forage productivity of cowpea [Vigna unguiculata (L.) Walp.] cultivars improve by optimization of spatial arrangements. Revista Mexicana de Ciencias Pecuarias, v. 9, n. 2, p. 203-219, 2018.
• KANDA, E. K. et al Nutritional yield and nutritional water productivity of cowpea (Vigna unguiculata L. Walp.) under varying irrigation water regimes. Water SA, v. 46, n. 3, p. 410-418, 2020.
• LÓPEZ-MORALES, D. et al Impact of agronomic biofortification with zinc on the nutrient content, bioactive compounds, and antioxidant capacity of cowpea bean (Vigna unguiculata L. Walpers). Agronomy, v. 10, e1460, 2020.
• MATTSON, S. The cookability of yellow peas: a colloid-chemical and biochemical study. Acta Agriculturae Suecana, v. 2, p. 85-190, 1946.
• MAZIERO, S. M.; RIBEIRO, N. D.; STORCK, L. Simultaneous selection in beans for architecture, grain yield and minerals concentration. Euphytica, v. 205, n. 1, p. 369-380, 2015.
• MOHAMMED, M.; JAISWAL, S. K.; DAKORA, F. D. Distribution and correlation between phylogeny and functional characteristics of cowpea (Vigna unguiculata L. Walp.)-nodulating microsymbionts from Ghana and South Africa. Scientific Reports, v. 8, n. 1, p. 1-19, 2018.
• OLIVEIRA, D. S. V. et al Adaptability and stability of the zinc density in cowpea genotypes through GGE-Biplot method. Revista Ciência Agronômica, v. 48, n. 5, p. 783-791, 2017.
• PEREIRA, E. J. et al Effect of different home-cooking methods on the bioaccessibility of zinc and iron in conventionally bred cowpea (Vigna unguiculata L. Walp.) consumed in Brazil. Food & Nutrition Research, v. 60, n. 1, p. 1-6, 2016.
• PEREIRA, E. J. et al Effects of cooking methods on the iron and zinc contents in cowpea (Vigna unguiculata) to combat nutritional deficiencies in Brazil. Food & Nutrition Research, v. 58, n. 1, p. 20694-20700, 2014.
• RAINA, A. et al Characterization of induced high yielding cowpea mutant lines using physiological, biochemical, and molecular markers. Scientific Reports, v. 10, n. 1, p. 1-22, 2020.
• RIOS, M. J. B. L. et al Chemical, granulometric and technological characteristics of whole flours from commercial cultivars of cowpea. Revista Caatinga, v. 31, n. 1, p. 217-224, 2018.
• ROCHA, M. M.; DAMASCENO-SILVA, K. J.; MENEZES-JÚNIOR, J. A. Cultivares. In: DoVALE, J. C.; BERTINI, C.; BORÉM, A. (ed.). Feijão-caupi: do plantio à colheita. Viçosa, MG: Editora UFV, 2017. p. 113-142.
• SANTOS, C. A. F.; BOITEUX, L. S. Genetic control and transgressive segregation of zinc, iron, potassium, phosphorus, calcium, and sodium accumulation in cowpea (Vigna unguiculata) seeds. Genetics and Molecular Research, v. 14, n. 1, p. 259-268, 2015.
• SILVA, C. A. et al Interaction genotype by season and its influence on the identification of beans with high content of zinc and iron. Bragantia, v. 71, n. 3, p. 336-341, 2012.
• SILVA, J. D. L. et al Selection for the development of black eye cowpea lines. Revista Caatinga, v. 31, n. 1, p. 72-79, 2018.
• SILVA, V. M. et al Agronomic biofortification of cowpea with zinc: variation in primary metabolism responses and grain nutritional quality among 29 diverse genotypes. Plant Physiology and Biochemistry, v. 162, p. 378-387, 2021.
• STATISTICAL ANALYS SYSTEM. SAS/STAT software 9.3 Cary, NC, USA: SAS Institute Inc., 2011.
• VAN DER STRAETEN, D. et al Multiplying the efficiency and impact of biofortification through metabolic engineering. Nature Communications, v. 11, e5202, 2020.
• WENG, Y. et al Evaluation of seed protein content in USDA cowpea germplasm. HorScience, v. 54, n. 5, p. 814-817, 2019.

Edithor-in-Article: Eng. Agr. Dra. Ana Kelly Firmino da Silva - kelly.fi [e-mail]

Publication Dates

• Publication in this collection
  06 June 2022
• Date of issue
  2022

History

• Received
  05 June 2021
• Accepted
  29 Oct 2021