Introduction

Corn is a plant species in the food and culture of Central America (^{Kato et al., 2009}). ^{Coll and Godinez (2003)} consider maize as a strategic element for the sovereignty and food security in their various forms of uses and cultural values of Mexicans, mainly for rural areas. This cereal was domesticated and revered by the Hispanic cultures, and remains the basis of Mexican food (^{Coll and Godinez, 2003}, ^{FAO, 2006}). In Mexico, corn is consumed in various forms: in corn, in tlaxcal, tamales, fermented beverages, but mainly in the form of tortilla with a per capita consumption of 100 kg of maize per year in different ways. The tortilla is a food circular flattened 10 to 30 cm in diameter and 0.2 to 0.6 cm thick, is made from different types of cooked corn with calcium hydroxide; nixtamalization process known as making more bioavailable nutrients, and waste water nixtamalization process is known as nejayote.

^{Cruz and Verdelet (2007)} indicate that the tortilla is considered a staple food for 94% of the Mexican population, especially in rural areas, where consumption is 328 g per capita per day and provides 70% of total calories, about 50% of protein and 49% calcium. This makes Mexicans are the main consumers of tortillas in the world, with production and consumption of close to 12 million tons of tortillas per year. For corn production nationwide it spends about 35% of arable land (INEGI, 2009). In the cycle 2013, corn was planted in almost every state of Mexico, with a production of approximately 23 273 million tons of corn, in an area of 7 426 million hectares with an average yield of 3.3 t ha^-1 (^{SIAP, 2014}) and is the crop that has the highest number of producers with 4 million and 3.2 million of these are ejidatarios (^{SIAP, 2012}).

Mexico is positioned between the fifth and seventh as a corn producer globally (^{FAO, 2009}), but the third as an importer of the same grain to meet domestic demand (^{SIAP, 2012)}. ^{SAGARPA (2015)} reported that in the state of Aguascalientes was destined for the production of corn for grain in spring-summer cycle 5533 ha with irrigation and 33,451 temporary. Meanwhile, the ^{INEGI (2014)} reported that 82.2% of the cultivated area in Mexico surface seeds of landraces are used, which besides being adapted to the climatic and technological conditions of producers, have characteristics that allow them to respond to their food tastes very specific populations and cultures. Planting criollo corn seeds by farmers, has generated a plant genetic resource of great biodiversity, with more than 50 recognized native breeds (^{Kato et al., 2009}).

The genetic diversity of landraces is maintained primarily to the use of this cereal in the basic food of rural and indigenous communities; which in turn, are natural promoters of conservation and in situ generation of biodiversity. However, ^{Vidal-Martinez et al. (2010)} indicate that the native maize biodiversity and plant genetic poles are threatened increasingly by factors, socioeconomic, political, commercial, biotic and abiotic. In the latter, ^{FONTAGRO (2015)} indicates that higher temperatures effect of global warming have reduced the overall yield of maize by 3.8%, equivalent to a fifth of current global reserves.

SAGARPA (2009) through the Department of Rural Development of the Directorate General of Support for Rural Development (SDRDGADS) established that the selection of landraces allows to develop varieties adapted to the natural and socio-economic conditions of producers, virtually the same resources for commercial exploitation, but with the advantage of obtaining a gradually increased performance compared to the original variety, without losing genetic diversity in this important crop, essential for food security and sovereignty of the country.

In rainfed areas where rainfall is insufficient and poorly distributed, as in the case of the state of Aguascalientes, the seeds of landraces are normally obtained by the producer after harvesting, making the selection based on morphological characteristics such as: size and shape of the cob, corn color, thin corn, among others. However, due to lack of knowledge, they do not take into account one of the most important criteria such as the nutritional composition. Therefore, the objective of this study was to analyze the nutritional composition of nixtamales, nejayotes and tortillas to 12 accessions of native maize (Zea mays L.) State of Aguascalientes, Mexico, in order to establish additional criteria for the selection of corn’s criteria and still maintain the biodiversity of this genetic material.

Materials and methods

a) Selection of material. 12 accessions of landraces of ejidatarios producers were collected; these were four ejido of El Tildio, two of Santa Rosa, five from El Retoño and one of El Terremoto, all belonging to the municipality of El Llano, Aguascalientes, Mexico, crop of spring-summer 2009. This region is considered highly marginalized and staple crops are preferably produced under rainfed conditions and with few or almost no implementation of fertilization systems.

b) Work Area. Analyses were performed in the laboratory analysis of soil, plant and water from the Autonomous University of Aguascalientes, Mexico. All samples of the same maize genotypes were collected crop cycle.

c) Analysis of physical characteristics: physical characterization of cobs, corn cobs and also the percentage of germination of 100 seeds taken from the middle of the ears was performed. The seeds were placed in sterile water with cotton dipped in Petri dishes at room temperature (24 ± 2 °C) and in total darkness, the experiment was performed in triplicate.

Analysis of protein. In analysis was performed based on the ^{AOAC (1984)} for quantifying Kjeldahl nitrogen (Tecator, Sweden) involving acid digestion of the sample and then an alkaline distillation; using the conversion factor of 6.25 for nitrogen to protein analysis was performed in triplicate.

Mineral analysis. Mineral analysis was as follows: phosphorus (AOAC 965.17), potassium (AOAC 985.35), calcium and magnesium (AOAC 968.08), sodium (AOAC 985.35), iron and manganese (AOAC 968.08), zinc (AOAC 968.08), copper boron (AOAC 968.08) by atomic absorption spectrometry f lame. It is worth mentioning that all bromatological and mineral analyzes were performed at the Laboratory of La Posta Zootecnica of the Autonomous University of Aguascalientes (UAA), analyzes were performed in triplicate.

Results and discussion

a) Physical characteristics and germination percentage. The 12 samples of accessions of landraces collected in the municipality of El Llano, Aguascalientes (Table 1) were performed measurements cobs, corn and corncobs. It was observed that the cobs had an average length of 15.16 ± 1.5 cm with an average circumference of 16.23 ± 1.13 cm, the cob with 8.68 ± 0.9 cm perimeter, and 13.33 ± 0.8 rows of grain. As seeds was found that the average weight of 100 seeds of the middle part of the cobs was 41.78 ±5.1 g, the average length of the corn was 1.3 ± 0.16 cm and the germination percentage was 81 ± 12. Importantly, the germination percentage of the 12 accessions ranged between 64 and 100%, the "T-JD" the lowest and the seeds of "Retoño-2" all germinated.

Table 1 Physical characteristics of cob, grain and cob 12 accessions of landraces cultivated in El Llano, Aguascalientes, Mexico. 

a) Peso de 100 semillas de maíz; b) Porcentaje de germinación; c) Longitud del grano de maíz (cm); y d) Perímetro del olote.

As has been reported, farmers select seed corn from the barn after harvest, considering the size of the cob, cob size and shape of the seed. However, in this study the germination percentage, additional features are reported to be considered for the selection of native seeds and ensure optimum number of plants in the field. This considering the results reported by ^{Herrera et al. (2002)} who mentioned that 76.5% of farmers use native seeds for planting, lower value with data reported by ^{INEGI (2014)}, where 82.2% of farmers select the best ears for seed, mainly considering the following characteristics: ear size (81.2%), health (69.2%), small cobs (38%), number of rows (36.9%), but did not consider producers the germination percentage of the seeds, which is an important element to consider to have the optimal number of seedlings per hectare, to avoid after the resembra, making this a preventative spending.

b) Content of minerals in nixtamal. Physical, nutritional and sensory benefits derived from the nixtamalización are enough to suggest that these were the reasons for their implementation and use in the preparation of the tortilla. In landraces nixtamalized mineral differential values (Table 2) were found. Corn nixtamalized identified as the "Retoño-6" excelled in P (0.36 mg kg^-1), the "AMET-2" showed higher content of K, Zn and B (0.39, 8.8 and 59.4 mg kg^-1, respectively) in the "AMET" higher content of Na and Fe (16.5 and 63 mg kg^-1), he found the mineral mg and Mn was higher in the "Celaya 2 criollo". The iron content, copper and zinc are greater than those reported by ^{Bressani et al. (1990)}, who report that the mineral content of corn average of five samples was 4.8, 1.3 and 4.6 mg 100 g^-1, respectively.

Table 2 Mineral content in Creole nixtamal accessions grown in El Llano Aguascalientes, Mexico. 

c) Content of minerals in tortillas to maize native. The processed corn and tortilla is transformed into food that provides significant amounts of calories, protein, fiber and minerals. Table 3 shows the mineral content is presented in tortillas to 12 accessions of landraces. The following mean values represented in mg kg^-1 all met: P (0.17 ±0.05), K (0.24 ±0.05), Ca (0.92 ±0.17), Mg (0.1 ±0.01), Na (12.13 ±1.71), Fe (38.57 ±12.03), Mg (3.61 ±1.41), Zn (6.55 ±0.94), Cu (1.18 ±0.6) y Bo (46.84 ±30.43). As you can see, the content of Fe, Zn and Bo in tortillas is highly variable from one accession corn to another. The iron content ranges from 19.9 to 54.2 mg kg^-1, the corn tortilla identified as the Retoño-7 with higher iron content (54 mg kg^-1).

Table 3 Mineral content in corn tortillas Creole accessions grown in El Llano, Aguascalientes, Mexico. 

This amount is in good proportion to supplement the minimum daily requirements in people. ^{Wyatt and Triana- Texas (1994)} state that the content of soluble Fe in tortillate is about 26% of total iron. While ^{Hurrell and Egli (2010)} considers that the bioavailability of iron has been estimated in the range of 14-18% for mixed diets and 5-12% for vegetarian diets, and dietary factors influencing iron absorption they are phytate, polyphenols, ascorbic acid and calcium. Moreover the zinc content in native corn tortillas was 4.6 to 8.1 mg kg^-1, the corn tortilla "Amet-1" with the highest content of zinc (8.1 mg kg^-1). ^{Kaur et al. (2014)} analyzed several studies on the importance of zinc, and discloses that it is one of the most important trace elements essential trace in human nutrition, its deficiency can severely affect the homeostasis of a biological system, it is essential for many physiological functions and plays an important role in a series of enzymatic action and cellular neural systems.

Similarly it can be observed a large variability in the contents for boron in each of the 12 accessions (3 to 95 mg kg^-1), the "Retoño-1" with the highest content of this microelement (95 mg kg^-1). According to ^{Nielsen (2008)} discloses that boron is a bioactive element to complete the cycle of life, and low intake of boron affects bone loss, brain function, and the immune response; therefore, low intake of boron is an important nutritional concern that diets rich in fruits, vegetables, nuts and seeds can be prevented.

d) Protein content in nixtamalized corn and tortillas. The composition and nutritional value of corn depend on the genotype, environment and agricultural management. According to ^{FAO (1993)} the average protein content of corn is 10%. In this study (Table 4) it was found that the protein content in processed corn increases slightly when transformed by nixtamalización a tortilla. Similarly, it was observed that the values of crude protein accession varies and place; the protein content of tortillas made with corn grown in the ejido The western snowy plover was 9.27 ± 4.65% in Santa Rosa was 8.23 ± 0.48%, El Retoño was 10.08 ± 0.54% and tortillas made with corn El Terremoto ejido was the lowest with 8.14%, excelling tortillas corn accession identified as the "AMET-1" with the highest protein content (10.72 g/100 tortilla).

Table 4 Protein content in nixtamales and tortilla landraces cultivated in El Llano, Aguascalientes, Mexico. 

^{Paredes et al. (2009)} indicate that there are studies that show that the quality of protein corn tortilla nixtamalized is better than white flour or refined plan of wheat. ^{Mendoza-Elos et al. (2006)} determined the body composition of whole seed of four genotypes of QPM and two varieties, and found that fat, ash and carbohydrates no significant difference, but if for protein in maize cultivars QPM was 10.38 and for yellow cultivars was 10.93. These values are very important in terms of food, considering described by ^{Jasso and Becerra (2003)} who indicate, based on information from the Survey of Income and Expenditure Survey (ENIGH), the National Institute of Statistics, geography and Informatics (INEGI), the poorest households dietary intake emphasizes the consumption of tortillas.

As can be seen, the nutrient content in native corn tortillas is important, therefore some researchers as ^{Kato et al. (2009)} recommend important to preserve not only these food materials, but also the production processes since ancient times have generated, maintained and diversified these native breeds, together with strengthening research into the issue and encourage the use of this genetic wealth task which it has been neglected in the country. To protect the genetic diversity of corn, it should support more than two million small-scale farmers or marginalized in the country, through grants, technical assistance and rural development programs.

e) Mineral content in nejayotes. The nejayote is the wastewater product of cooking maize with lime (calcium hydroxide) for the preparation of the tortilla. In most cases, the nejayote is disposed of without finding a potential use, especially tortillerías that large volumes of nejayote discarded to drain. This study found that nejayote contains an important source of macronutrients (NPK) and micronutrients such as Ca, Mg, Fe, Zn (Table 5). Is outstanding K content (79.50-252 mg L^-1) and Ca (429.4 a 6 052.1 mg L^-1), Bo content was not detected. The nejayote should be considered when preparing the tortilla. Another alternative for potential use nejayote can be as foliar fertilizer, as a humectant for animal feed, nutraceutical solution for humans or culture medium for plant tissue in vitro.

Table 5 Mineral content in nejayote of native corn grown in El Llano, Aguascalientes, Mexico. 

Conclusions

The maize native cultivated in Aguascalientes Mexico have important physical characteristics such as weight and seed germination percentage, coupled with important minerals and protein contended in nixtamalized corn and tortillas. Both criteria should be considered for cultivation and nutrition of the population; principles to continue to preserve the culture and diversification of these native breeds, together with strengthening research in culture and encourage the use of this endemic genetic wealth, considering that Mexico's rural population depends on tortillas as its main power source.