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logical parameters, masa, tortilla INTRODUCTION Maize (Zea mays L.) is the most widely produced and consumed cereal in Mexico, and it is the raw material used to manufacture masa and tortilla. However, the maize plant requires nutrients like nitrogen, phosphorus, and potassium to produce high yields of seeds and grains. These nutrients may enter the soil through chemical fertilizers or manure and crop residues (Salazar et al., 2009). Pollution and the high cost of chemical fertilizers are making it necessary to use novel alternatives to fertilization. For example, the application of liquid manure to maize increases its yield and improves the balance amount of nutrients that the plant consumes and generates (Schröder et al., 2015). Likewise, nejayote is a by-product of the nixtamalization process that contains approximately 2% solids (pericarp, proteins, starch, calcium, germ, and others) (Valderrama-Bravo et al., 2012). Nejayote damages the environment because the small-scale producer disposes of it in the form of wastewater into the local drainage network. However, nejayote is an organic nutrient that contains ferulic acid, phenolic, and antioxidant compounds as well as colloids (Niño-Medina et al., 2009). Therefore, innovative and environmentally © 2020 Institute of Agrophysics, Polish Academy of Sciences M.C. VALDERRAMA BRAVO et al. 242 friendly research has been performed to reduce the pollutant load of nejayote. Examples of these activities include treatment by bioreactors and the use of chitosan to reduce biochemical oxygen demand (BOD) (López-Pacheco et al., 2019; Suarez-Meraz et al., 2016). Also, nejayote solids may be used as a substrate for fermentation with edible fungi, which has a positive influence on the content of free phenolic compounds and dietary fibre as well as its antioxidant activity, with potential use as a high added value food ingredient (Acosta-Estrada et al., 2019). Thus, nejayote treated with fermentation or composted and mixed with manure could be used as an alternative organic fertilizer. Mahmood et al. (2017) applied it as an organic nutrient source with urea, and showed that the growth and yield of maize were substantially improved by fertilizer application alongside organic manures and that the soil total organic content increased when inorganic fertilizers were applied in combination with organic manures. Zepeda-Bautista et al. (2007) applied different doses of fertilizer to maize seeds (N, P, and K); and reported that fertilization applied at 0.3 t ha of nitrogen modifies maize structure, which consequently influences the nixtamalization process. On the other hand, Vázquez-Carrillo et al. (2015) mentioned that the physicochemical, rheological, and textural properties of masa as well as the quality of the tortillas depends on the maize type used and the conditions of the nixtamalization process. Valderrama-Bravo et al. (2017) reported that tortillas processed with hard maize (hybrid H-70) had a more rigid texture. Conversely, tortillas from soft endosperm contained more swollen starch granules, which improves softness. Osorio-Díaz et al. (2011) attributed these results to a higher retrogradation rate. Santiago-Ramos et al. (2017) reported that hard maize starch showed the highest gelatinization temperature and the lowest enthalpy due to its highly compacted endosperm and high amylose content. Tortillas of intermediate and soft grains had a higher retrogradation rate than the tortillas of hard grains. Therefore, the objective of this research was to evaluate changes in flours, masa, and tortillas obtained from maize grains fertilized organically with nejayote and ovine manure. This research is based on the assumption that fertilization is decisive in the growth and development phase of the maize plant. Different regimes of nutrient application or fertilizer type produce changes in grain quality. Therefore, it is to be expected that these differences would show in the physical and chemical properties of the flours, masa, and tortillas obtained from such maize grains. MATERIALS AND METHODS Field experiments were conducted in “Laguna Seca” Ranch, Ahuazotepec, Puebla, during the spring-summer agricultural cycle of 2016. The maize hybrid AS-722 (Aspros) was sown at a density of 75 000 plants per ha. Field experiments were conducted in the “Laguna Seca” Ranch, Ahuazotepec, Puebla, during the spring-summer agricultural cycle of 2016. The maize hybrid AS-722 (Aspros) was sown at a density of 75 000 plants per ha on April 25. The experimental plot was located at 20° 01’ 51.6” N and 98° 07’ 15.6” W, at an altitude of 2268 m a.s.l. The soil is characterized as medium textured Andisol. The experiment design was carried out as a factorial with two factors and three levels: nejayote (m ha): N0 = 0, N1 = 75, and N2 = 150 m and ovine manure (t ha): A0 = 0, A1 = 25, and A2 = 50). An additional chemical fertilization treatment was established for comparison, where urea, ammonium diphosphate and potassium chloride (CO(NH2)2, (NH4)2HPO4 and KCl) were used as sources of N, P and K, respectively (Agrogen). Nejayote was obtained from the mills of the region and it was produced during a nixtamalization process, in which maize grains (50 kg) were cooked (2 h) and steeped (16 h) in alkaline conditions 0.36% Ca(OH)2, Nixtacal 1TM, Mexico) to make nixtamal, and then tortillas. On a daily basis the cooking liquid (nejayote) was collected in 30 L plastic containers. Nejayote characterization was performed by DominguezHernández et al. (2020). The experimental plots were set up as randomized blocks designed with three replicates per treatment. Each experimental unit consisted of six rows 10 m long and 0.8 m wide. The nejayote and ovine manure mixtures were composted in plastic containers for 20 days, stirring daily the first five days of nejayote collection time, and then stirring every other day the remaining time (15 days). The organic and chemical fertilizers were applied manually at 20, 40, and 60 days after sowing (Fig. 1). A physicochemical analysis (pH, organic matter, nitrogen, phosphorus and potassium) of nejayote, manure and mixtures were presented in Dominguez-Hernández et al. (2020). The harvest was carried out by hand when the formation of a black layer was observed, which indicated physiological maturity. The drying process was natural. Maize grains were cleaned by removing foreign material, impurities, and broken grains. Twenty clean grains were measured (length, diameter, and thickness) and the geometric mean diameter (Dg) was calculated according to Vilche et al. (2003) and Valderrama-Bravo et al. (2017). The hectolitre weight, flotation index and weight of 100 grains were evaluated according to Abdalaa et al. (2018). Moisture content was evaluated according to the AACC method 44-11 (AACC, 2000). Samples were prepared by cooking 500 g of maize in a solution of 1500 mL of water and 5g of food-grade calcium hydroxide (Fermont, Monterrey, Mexico). The maize samples were boiled at 90°C for 40-45 min and steeped for 12 h. The nejayote was separated, and the nixtamalized samples were washed with 750 mL of water and milled in a manually operated mill (Nixtamatic, Edo. Mex., México). The nixtamal obtained was dried by using a forced air oven, at 55°C during 24 h. The dried samples were milled using CHARACTERIZATION OF FLOURS, MASA AND TORTILLA FROM FERTILIZED MAIZE 243 a hammer mill (Pulvex 200, Mexico) with a 0.8 mm mesh. The maize flours thus obtained were packed in airtight polyethylene bags and stored at 4°C until use. Chemical analysis of maize flours, moisture content, ash, protein (N x 5.85), fat and total fibre were evaluated according to AACC methods 44-15, 08-01, 46-13, 30-25 and 32-05, respectively (AACC, 2000). The water solubility index (WSI) and swelling power (SP) were determined by applying the methodology described by Ayala-Rodríguez et al. (2009) and modified in the laboratory. Maize flour (1 g, dry base) was weighed in a 15 mL centrifuging tube. Then 10 mL of distilled water was added. The flour suspensions were heated and shaken at 30°C for 30 min in a water bath. Then they were centrifuged at 3 000 rpm for 15 min, the supernatant was decanted, and sediments were weighed to ascertain the swelling power. The supernatant was dried at 105°C for 24 h. All measurements were conducted in triplicate. The WSI and SP were calculated by Eqs (1) and (2), as: WSI = weight of dried supernatent solids weight of sample 100, (1) SP = weight of sediment paste weight of sample− weight of dried supernatent soilds . (2) The starch pasting profiles of nine water suspension samples were analysed using an Anton Paar MCR 102 Rheometer, equipped with a starch cell using the methodology proposed by Rincon-Londoño et al. (2016). The starch samples (3 g) were suspended in 18 mL of water. The suspension was heated over 5 min from 50 to 90°C; next, the suspension was maintained at a constant temperature of 90°C for 5 min and finally the samples were cooled down to 50°C for 5 min. The rotation speed of the system was 194 rpm. Maize flours were rehydrated until they reached 54% of moisture to obtain rollable masa. The colour of the masa samples were measured using a Minolta CR-300 colorimeter (Minolta, Osaka, Japan). The colour parameters CIELAB (L*, a, and b, where L* = luminosity (100 = white, to 0 = black), the a = greenish-reddish, and b*= yellowishbluish. The total colour difference was also calculated (∆E) by Eq. (3). The L* = 98.75, a = 0.72 and b = 2.58 values were evaluated with a white reference:

international agrophysics

Physicochemical characterization of flours and rheological and textural changes of masa and tortillas obtained from maize fertilized with nejayote and ovine manure