Introduction

In Mexico overweight and obesity affects 71.3% of adults and 34% of infants and adolescents (^{Barquera et al, 2013}). This among others, due to loss of balance between energy intake and energy expenditure. According to ^{Denova et al. (2010)} some of the risk factors associated with obesity, in the Mexican population, are excessive consumption of refined flour, soda and corn tortillas accompanied by foods rich in calories and fat. So one of the recommendations to prevent obesity and overweight is increasing consumption of whole grains and other high fiber grains (^{Kristensen et al, 2012}; ^{Barquera et al, 2013}).

The worldwide consumption of oat (Avena sativa L.) is associated with a nutraceutical effect (^{Daou and Zhang, 2012}); i.e., which has a favorable effect on the health of consumers by reducing low-density lipoprotein (associated with heart disease cholesterol), because of the soluble fiber grain (^{Tiwari and Cummins, 2011}). In addition, the oat has higher protein content (^{Ortiz et al, 2013}), compared to corn and wheat, which are the most consumed in Mexico. About 85% of oat proteins are globulins (^{Colyer and Luthe, 1984}), which it has higher concentration of the essential amino acid lysine, which are of greater nutritional value. So that foods with added grain or oatmeal are an option to diversify food products and offer alternatives consumer consumption. Despite the aforementioned characteristics of oat, in our country, 90% of its use is as feed, and for human consumption is 2 kg per capita, while consumption of corn and wheat, as tortillas and bread is 78.5 and 38.3 kg per capita, respectively (^{CANIMOLT, 2013}).

The process of nixtamalization makes the tortilla table have higher nutritional quality compared with the raw corn. This process involves a thermal-alkaline treatment which modifies the structure of proteins corn to make them more digestible, such that zein, which is a nutritionally poor protein reduces its solubility; while glutelin higher nutritional value, increased solubility and hence the availability of essential amino acids (^{Castillo et al., 2009}). It also, promotes significant increases in the calcium content and because resistant starch gelatinization during partial processes: cooking and steeping corn (nixtamalization); nixtamalized grinding and cooking or frying tortillas. With the aim of developing new foods with better nutritional balance, it has investigated the impact of different grains nixtamalization other maize. Thus, ^{Téllez and Arellano (2005)} obtained the optimum parameters of nixtamalization to produce bean flour, ^{Ríos and Nieves (2009)} of amaranth, ^{Garcia and Sandoval (2011)} of oat and ^{Morales (2015)} of barley.

There is a need to promote products that promote the health of Mexican consumers, so nixtamalized grain oats can be a source of excellent nutritional quality protein, fiber, calcium and resistant starch. Thus, the objective of this research was to make tortillas mixtures nixtamalized corn flour (HMN) with whole meal flour nixtamalized oats (HAVN), perform their chemical composition analysis and evaluate their sensory quality to determine the optimal mix to make tortillas table.

Materials and methods

The oat grain used was obtained from the Obsidiana variety, released by program oats National Institute of Forestry, Agriculture and Livestock (INIFAP), cultivated under rainfed conditions, in Chapingo State of Mexico, during the season spring-summer in 2011. The nixtamalization oat was performed, based on described by ^{García and Sandoval (2011)}, in the presence of 0.49% lime, 10.4 min cooking at 90 °C, then 2.9 h rested dried at 50 °C for 48 h then milling was performed in a powdery Lasser 100 mark, for whole meal oats nixtamalized (HAVN). Corn nixtamalized flour (HMN) used was brand MINSA® brands. The mixtures HAVN:HMN, treatments with two replications were 10:90, 20:80, 30:70 and 40:60% respectively.

The variables were evaluated in the mass, water absorption (%) indicating the amount of water required per 100 g and then weight (g) was measured. The moisture was carried out in 3 g of sample in an oven, brand Lumistell HTP-42, at 103 °C until constant weight and mass yield was calculated on the basis described by ^{Salinas and Vázquez (2006)} and also they were determined the luminosity (L), hue angle (Hue) and chroma using a Hunter Lab mini Scan EX plus.

For the preparation of tortillas, flour is hydrated and it was determined by touch the optimum consistency of the dough was divided into portions of 20 g, were pressed and baked tortillas on a metal griddle to 230 °C for 90 s. To evaluate the tortilla quality, the diameter (cm) and thickness (mm) was measured by a digital vernier AutoTec mark; the weight of hot tortilla (g) was determined after completion of cooking and weight of cold tortilla (g) was measured half an hour after it; the percentage of moisture in the tortilla was determined similarly as in the mass; the rollability was determined once their cooking and after being heavy hot; an omelet was wound into a cylindrical pen and based on the degree of rupture was rated on a hedonic scale, 1= breaks all tortilla, 2= 3/4 is broken, 3= breaks 1/2, 4= breaks 1/4 and 5=not broken anything. The performance of the hot and cold tortilla was calculated based on the above by ^{Cortés (2015)}.Additionally colorimetric variables, brightness, hue angle and chroma were evaluated.

The bromatological variables measured in the tortilla were: percentage of protein, which was assessed using the Kjeldahl method AACC 46-12 (1998), the crude fiber was determined in a previously defatted sample using the method 49-10 ^{AACC (2009)}, which consisted of boiling the sample in sulfuric acid 1.25%, and thereafter sodium hydroxide 1.25%, the resulting residue was constant weight, 130 °C for 2 h and subsequently calcined at 600 °C for 30 min. The ash percentage was performed according to AACC method 08 01 (1995) by incineration in a muffle furnace at 550 °C for 3 h. Quantification of calcium was carried out by the method 965.09 ^{AACC (2008)} in 1 g sample was dried for 24 h at 100 °C and subsequently calcined for 4 h at 500 °C and atomic absorption spectrophotometer set was used a cathode lamp at a wavelength of422.7 nm. Furthermore the resistant starch content tortilla was obtained based on the method ^{Goñi et al. (1996)}, by hydrolysis with pepsin at pH 1.5, followed by the breaking of digestible starch with a-amylase, after removal of the products of hydrolysis by centrifugation, the indigestible fraction, the residue was dispersed in half alkaline hydrolyzed entirely with amyloglucosidase enzyme, determining the glucose released.

To carry out sensory evaluation test and overall acceptability acceptability attributes for tortillas of each mixture was performed. The quantitative affective tests were conducted, focusing on acceptance testing using hedonic scales.

For the assignment of treatments to experimental units stayed in a complete block design at random with a repetition of each treatment; as experimental unit tortillas were considered, the SAS statistical package (^{SAS Institute, 2002}) was used and comparison of Tukey ≤ 0.05 were performed to indicate the differences between the analyzed mixtures additionally Pearson correlations were performed between sensory atributes and an analysis of main components with the properties measured in the sensory evaluation.

Results and discussion

The significant differences between the masses mixtures of HMN and HAVN, for water absorption, weight, performance, lightness, chroma and hue angle were found; except for moisture of the masses, Table 1. The water absorption was 135.8% in HMN which is consistent with that reported by ^{Flores et al. (2002)}, who reported values of 120 to 135% in different commercial flours. An increase in absorption and consequently its weight and yield of treatments with 10 and 20% was observed in HAVN; however, with 20 and 30%, these variables decreased, which may be due to the higher concentration of water-soluble polysaccharides capable of forming gums with little water. The moisture percentages ranged from 56.5 to 59.2% which is consistent with that reported by ^{Gasca and Casas (2007)}. On the other hand, was observed a decrease in the brightness of the masses as the concentration HAVN increased, impacting the same way in the hue angle which is reported yellow in HMN and brown in the mixture with 40 % of HAVN which is consistent with that reported by ^{Flores (2004)}. The brightness values for HMN match ^{González and Hernández (2012)} who reported values of 74 mass nixtamalized.

Table 1 Comparison of means features of physical and chemical mixtures of the masses of corn flour (HMN) nixtamalized flour and whole oats (HAVN). 

†Valores con la misma letra dentro de filas no son estadísticamente iguales.

For quality variables significant differences tortilla weight of the hot and cold tortilla, cold tortilla performance, brightness and hue angle were observed; while the mixtures HMN and not differentially affected HAVN the diameter, thickness, moisture, rollability, performance hot tortilla and chroma. Based on the above, the addition of HAVN not change the dimensions of diameter and thickness of the tortilla, these values match so reported by ^{González and Hernández (2012)}. Higher weight values for hot and cold tortilla were observed with the combination of 30 and 40% HAVN. On a commercial level this property represents an advantage because as many tortilla is sold with a lower percentage of raw material.

It is considered that 30% is the percentage HAVN adequate replacement for better weight of cold tortilla, the above is an advantage if marketed packaged tortilla and cold. The humidity ranged from 39.1 to 41.8% which depends on the use of raw materials spiked to HMN, which coincide with those reported by ^{Gamero and Martínez (2010)}, who found similar values with mixtures of HMN and flour nixtamalized bean. Based on values greater than 4.8 of rollability, all mixtures of HMN/HAVN were classified with good factor for this feature, similar values found ^{González and Hernández (2012)}.

The yields hot tortilla mixtures are similar to those found by ^{Téllez and Arellano (2005)} with mixtures of flour nixtamalized beans and HMN, in the case of performance cold tortilla ^{Galicia (2009)} reported values of1.4 kg, similar the treatments evaluated in this investigation. Incorporating HAVN affected the brightness of tortillas, as reflected in a decrease of 1.5, 3.4 and 7.1 units for mixtures of 20, 30 and 40%, respectively. As to, hue angle, the HMN tortillas were classified as yellow, however, with a gradual decrease trend is observed to be slightly brown with the addition with HAVN, Table 2.

Table 2 Comparison of means features of physical and chemical mixtures tortillas nixtamalized corn flour (HMN) nixtamalized flour and whole oats (HAVN). 

†Valores con la misma letra dentro de filas no son estadísticamente iguales. PTC= peso de tortilla caliente; PTF= peso de tortilla fría; RTC= rendimiento de tortilla caliente; RTF= rendimiento de tortilla fría.

The significant difference for percentage of protein, crude fiber, ash, calcium and resistant starch, Table 3, the highest for protein for HMN values were spiked with 30 and 40% were found HAVN; for crude fiber the highest value was for the combination 60% HNM and 40% HAVN, these increases is because individually the HAVN is characterized by high percentages, greater than 15% (data not shown) which is consistent with that reported by ^{Martinez et al. (2013)} and ^{Martinez et al. (2014)}, while the used HMN presented values lower than 9%. The percentage of resistant starch were higher for the HMN, which are comparable to those reported by ^{Méndez et al. (2005)}; while by adding the HAVN its concentration decreased possibly due to low nixtamalization and soak times at which the oat grain subjected. The percentage of resistant starch for the HMN was higher than HAVN with values 0.7 and 0.2%, respectively, the latter value matches mentioned by ^{Zamudio et al. (2015)}.

Table 3 Comparison of means of bromatological variables mixtures tortillas corn flour (HMN) and nixtamalized flour whole oats (HAVN). 

†Valores con la misma letra dentro de filas no son estadísticamente iguales.

The significant differences for aroma, aroma oats, overall taste, texture, rollability, thickness, chewiness, and overall acceptability were observed; while there were none for oat flavor and color, Table 4. This indicates that the incorporation of HAVN was not detected by the panelists. The overall acceptability was correlated with texture, taste, thickness, chewiness, which indicates that these characteristics are crucial to the quality of the tortilla and same texture associated with rollability and thick tortilla, same behavior showed the flavor the taste of oatmeal, and oat scent was related to the overall aroma, Table 5. The variables greater contribution to the principal component 1 were: overall acceptability, flavor and texture; while overall flavor, aroma and color oats principal component 2, Figure 1. The treatments of 100% HMN and mixtures spiked with 10 and 20% of HAVN showed better overall acceptability characteristics, taste and texture largely affected tortilla ; reverse behavior presented by those made with 30 and 40% which are also associated with scented oatmeal (Figure 1).

Table 4 Comparison of means of sensory attributes of tortillas corn flour mixtures (HMN) and nixtamalized flour whole oats (HAVN). 

Table 5 Pearson correlations between sensory attributes of tortillas corn flour mixtures (HMN) and nixtamalized flour 

ACG= aceptabilidad global.

Figure 1 Two-dimensional distribution of tortilla corn flour mixtures (HMN) and nixtamalized flour whole oats (HAVN). 0HAVN= 100%HMN; 10HAVN= 90%HMN/10%HAVN; 20HAVN= 80%HMN/ 20%HAVN; 30HAVN= 70%HMN/30%HAVN; 40HAVN= 60%HMN/40%HAVN; ACG= overall acceptability; S= taste; TX= texture; AA= smell of oats; AG= overall flavor; C= color. 

Conclusions

The tortillas made with 20% of HAVN and 80% of HMN presented tortilla quality and overall acceptability similar to 100% of cornmeal MINSA® brands, such treatment but decreased its brightness increased its percentage of protein. Adding 40% oat nixtamalized flour increased the protein content and fiber in tortillas however showed lower overall acceptability. Based on the above the use of whole grain oats, in the preparation of tortillas, favored the protein and fiber content so it can be recommended as a nutritional alternative food for the population.