Relaxation tests and textural properties of nixtamalized corn masa and their relationships with tortilla texture

Food Bioscience 33 (2020) 100500

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Relaxation tests and textural properties of nixtamalized corn masa and their relationships with tortilla texture

T

Alfonso Topete-Betancourta, David Santiago-Ramosb, Juan de Dios Figueroa-Cárdenasa,∗ A R T I C LE I N FO

A B S T R A C T

Keywords: Corn masa Maxwell model Profile analysis Tortilla texture

The relationships among the viscoelastic and textural properties of corn masa and the texture of tortilla were studied. Six nixtamalization processes using traditional Ca(OH)2, classic (wood ashes), and potentially ecologically better compounds: CaCO3, CaSO4, CaCl2, Ca(C2H5COO)2 that are less polluting because the lower alkalinity reduces the dry matter losses, and a control were studied. Relaxation parameters showed that nixtamalization with Ca(OH)2 led to the production of a more viscous and elastic masa, while masa using the other Ca sources which had the potential to be more ecological, had a weaker and less elastic structure. Fresh tortillas derived from the potentially more ecological Ca sources were softer and more extensible than tortillas using Ca (OH)2 nixtamalization. After 48 h of storage, the inverse trend was observed. Estimated shear moduli G0, G1, G2, G3 and G and viscosity η1 and η2 from the generalized Maxwell model correlated well the cutting force, tensile strength, and extensibility of the tortillas, which were mainly affected by starch gelatinization. In masa, relaxation parameters showed better results than texture profile analysis for predicting the texture of both fresh and stored tortillas.

1. Introduction Corn tortillas are a widely consumed not only in Mexico but also in Guatemala, the United States and other countries (Román-Brito, Agama-Acevedo, Méndez-Montealvo, & Bello-Pérez, 2007). Tortillas are made from fresh nixtamalized corn masa or from reconstituted nixtamalized corn flour. Texture is one of the most important quality factors of tortillas: they should be soft, extensible, and easily rollable without cracking (Suhendro, Almeida-Dominguez, Rooney, & Waniska, 1998). Good tortilla texture is strongly correlated with an appropriate masa texture. Masa should have high values of viscosity and elasticity to be tolerant of mixing, and it should have adequate cohesiveness and adhesiveness to be easily molded into flattened round disks (RamirezWong, Sweat, Torres, & Rooney, 1993; 1994). However, the process leads to some of the problems that the masa industry needs to deal with such as large volumes of water with a high level of soluble solids (3–15%), which is discarded during the cooking and washing of the nixtamal makes it potentially highly polluting (Santiago-Ramos et al., 2018a). Consequently, the use of Ca(OH)2 as a cooking agent can result in a strongly alkaline medium with high dry matter losses. Nevertheless traditional nixtamalization has been considered a highly polluting

process (Santiago-Ramos et al., 2018a). The use of more environmentally friendly calcium sources as a substitute for lime in the nixtamalization process, including calcium salts other than Ca(OH)2, such as CaCO3, CaSO4, CaCl2, and Ca(C2H5COO)2, as well as weak acids such as acetic and propionic acids have been recommended by Figueroa, Rodríguez-Chong, and Véles-Medina (2011b). Traditional masa is considered a viscoelastic system, which is a result of the interactions among water, gelatinized and swollen starch granules, calcium-starch cross-links, calcium-protein interactions, protein aggregates, and the presence of amylose-lipid complexes (Mondragón, Mendoza-Martínez, Bello-Pérez, & Peña, 2006; Quintanar Guzmán, Jaramillo Flores, Solorza Feria, Méndez Montealvo, & Wang, 2011). Corn type and nixtamalization conditions significantly affect the textural properties of masa. Among these conditions, the most relevant could be the type of calcium compound used during cooking, because it influences pericarp hydrolysis, starch gelatinization, water and calcium absorption, lipid saponification, protein solubilization, and the formation of amylose-lipid complexes (Santiago-Ramos, Figueroa-Cárdenas, & Véles-Medina, 2018b). Texture and rheological properties of traditional corn masa have

a

Centro de Investigación y de Estudios Avanzados del IPN, Unidad Querétaro, Fracc. Real de Juriquilla, Querétaro, Querétaro, CP 76230, Mexico Programa de Posgrado en Alimentos del Centro de la República, Universidad Autónoma de Querétaro, Cerro de las Campanas S/N, Col. Las Campanas, Querétaro, Querétaro, CP 76010, Mexico ∗ Corresponding author. Cinvestav Unidad Querétaro, Libramiento Norponiente 2000, Fracc. Real de Juriquilla, Querétaro, Qro, CP 76010, Mexico. E-mail address: jfi[email protected] (J.d.D. Figueroa-Cárdenas). b

https://doi.org/10.1016/j.fbio.2019.100500 Received 4 July 2018; Received in revised form 15 November 2019; Accepted 15 November 2019 Available online 19 November 2019 2212-4292/ © 2019 Elsevier Ltd. All rights reserved.

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A. Topete-Betancourt, et al.

(Tortilladoras González, Querétaro, Qro., Mexico), to obtain tortillas that were ~1.2 mm thick and 12.5 cm in diameter. The tortillas were baked on a hot iron surface (Mabe model PMC5105N, Querétaro, Qro., México) equipment at 270 °C for 17 s on one side, for 50 s on the other side to form a thick layer, and were turned again to allow puffing for 17 s. Immediately after baking, tortillas were kept in a cloth napkin, inside a polyethylene bag, to allow cooling at room temperature for 1 h prior to doing the texture analysis. Another batch of tortillas from the same treatment was stored at 4 °C for 48 h.

been studied using instrumental methods to determined hardness and adhesiveness (Gasca-Mancera & Casas-Alencáster, 2007; Ramirez-Wong et al., 1993; 1994), and viscoelasticity has been measured using dynamic oscillatory tests as a function of the storage/elastic (G′) and loss/ viscous (G″) moduli, and the complex viscosity (η*) (Contreras-Jiménez et al., 2017; Estrada-Girón et al., 2014; Platt-Lucero et al., 2013, 2010; Santiago-Ramos et al., 2018b). However, different tests and mechanical models have not been applied to conceptualize the different patterns of viscoelasticity, and none of those studies have correlated the textural and viscoelastic properties of corn masa with tortilla texture. The stress-relaxation test is one of the important fundamental tests used to characterize wheat dough viscoelasticity. It consists of applying a constant strain, and the stress needed to maintain the deformation is measured as a function of time. The stress-relaxation data could be analyzed using several models, such as the generalized Maxwell model, which is represented by springs and dashpots combined in different ways, affording a good description of the viscoelastic behavior of polymeric materials such as doughs (Figueroa, Hernández, RayasDuarte, & Peña, 2013; Magaña-Barajas, Ramírez-Wong, Torres-Chávez, & Morales-Rosas, 2012). In this study, it was hypothesized that using lime and different Ca salts, some chemical components of masa would be changed and those changes would affect masa rheology and tortilla quality. Thus, the objective was to evaluate the masa's viscoelasticity applying Maxwell model parameters, to compare this with masa's modified texture profile analysis (mTPA) from nixtamalized corn flours obtained using several nixtamalization processes, and to determine its relationship with fresh and stored tortillas.

2.4. Degree of gelatinization and retrogradation Thermal analyses of nixtamalized flours and tortillas were carried out to determine gelatinization and retrogradation enthalpy, respectively. Four mg of sample was placed in an aluminum pan and water was added to reach 60% moisture (based on the preliminary experiments). The pan was sealed, left to stand for 1 h, and then the analysis was carried out from 30 to 130 °C, at 10 °C/min in a differential scanning calorimeter (DSC1 model 821; Mettler Toledo, Greifensee, Switzerland) previously calibrated with indium (Santiago-Ramos et al., 2017). The degree of gelatinization (DG) was calculated using the equation of Baks, Ngene, van Soest, Janssen, and Boom (2007);

DG = 1 −

ΔHgelNF x 100 ΔHgelNS

(1)

Where ΔHgelNF is the gelatinization enthalpy of the nixtamalized flour and ΔHgelNS is the gelatinization enthalpy of the raw maize starch, which was 5.9 ± 0.4 J/g on average. The degree of retrogradation (DR) was calculated using the equation of Wang, Li, Zhang, Copeland, and Wang (2016);

2. Materials and methods 2.1. Materials

DR = The white dent corn was purchased in a local market of Queretaro City, Qro, Mexico. Ashes from oak trees (Quercus spp.), consisting mainly of CaCO3, were obtained in Oaxaca City, Oax, Mexico. The Ca (OH)2, CaCO3, CaSO4, CaCl2, and Ca(C₂H₅COO)₂ were 97–99% pure and food grade (Alquímia Mexicana, Mexico City, Mexico).

ΔHrettortilla x 100 ΔHgelNF

(2)

where ΔHrettortilla is the retrogradation enthalpy of the tortilla sample and ΔHgelNF is the gelatinization enthalpy of the nixtamalized flour. Enthalpy values were calculated using the software provided with the instrument. The precision of transition temperature measurements was ± 0.2 °C. An empty aluminum pan was used as the reference. Each sample was analyzed 4 times.

2.2. Nixtamalization and flour preparation Nixtamalization was carried out according to the process used by Santiago-Ramos, Figueroa-Cárdenas, Véles-Medina, & Mariscal-Moreno (2017). One kg of corn was cooked for 35 min at 94 °C with 2 L of tap water containing 1.0% (w/w) of each calcium source. The cooked grains (nixtamal) were removed from the heat and steeped for 16 h as it went to room temperature (20 to 25 °C). The nixtamal was then separated from the cooking solution by decanting and washed twice with 2 L of tap water. The nixtamal was ground in a stone mill (M100; Fumasa, Querétaro, Qro., México) to obtain fresh masa. The masa was dried in a flash dryer (home made Cinvestav, Unit Querétaro, Qro., México) at 260 °C, passing through 4 times, for 4 s each time. The resulting flour was ground in a Pulvex grinder (Maquinaria Pulvex S.A. de C.V., Mexico City, Mexico) and sifted through a US 60 mesh (0.5 mm) screen. The dried nixtamalized flour was packed into low density polyethylene bags (Comercializadora Cantú SA de CV, Apodaca, N. L., México) and stored at 25 °C for a maximum of two wk. A treatment with no calcium added was included as a control.

2.5. Masa viscoelasticity: relaxation test The viscoelasticity of the masa was measured using a relaxation test. Masa was prepared by mixing 10 g of nixtamalized flour and distilled water to 55% moisture. The masa was manually mixed for 1 min; then, allowed to stand for 10 min in a closed polyethylene bag at 25 °C. The relaxation test was done using an ARES Rheometer (TA Instruments, Inc., New Castle, DE, USA) equipped with parallel plates 25 mm in diameter, at 25 °C, and a 2.0 mm gap. A sample of masa (3 g, 55% moisture) was compressed between the plates, the excess was removed with a putty knife, and the exposed masa surface was covered with a thin layer of mineral oil to prevent moisture loss during testing. All measurements were done in triplicate. A strain of 10% was applied and the masa was allowed to relax for 480 s. The generalized Maxwell model described by Figueroa et al. (2011a) was used to evaluate the viscoelastic behavior of the masa calculated in terms of shear modulus (G), which is proportional to stress (Fig. 1). The model consisted of three elements with a residual spring in parallel as described using the following equation:

2.3. Tortilla preparation

G (t ) = G0 + G1 e−t / τ1 + G2 e−t / τ2 + G3 e−t / τ3

Tortillas were prepared according to the method used by SantiagoRamos et al. (2017). Nixtamalized flour (200 g) was mixed with distilled water to reach 55% moisture, which was determined with a preliminary experiment, giving an appropriate consistency for all masa samples. The masa was flattened with a manual tortilla roller

(3)

and by

τi = 2

ηi ε Gi

(4)

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2.7. Tortilla texture Tortilla texture was measured in terms of extensibility, tensile strength, and cutting force using the TA-XT2 Texture Analyzer, following the method described by Arámbula-Villa, González-Hernández, & Ordorica-Falomir (2001). Extensibility and tensile strength (tearing) tests were measured on a tortilla strip. A cooked tortilla sample was cut using a metallic strip probe that gave a strip 8.6 cm long, 3.7 cm wide at each end, and 1.5 cm wide in the middle. The tortilla strip was fastened through the edges with two tension clamps (TA-96) (Texture Technologies Co; Hamilton, MA USA) with a 5.2 cm separation between them. To measure the tension force the crosshead was pulled at a speed of 2 mm s−1 until rupture occurred in the middle part of the tortilla strip. The maximum displacement of the crosshead was 1.5 cm. The cutting force was done on the same size tortilla strip. The tortilla strip was placed on a guillotine block with a heavy duty platform (TA-90) 27 mm below the initial position of the knife blade. To measure the cutting force, the crosshead with a TA-43 knife blade moved downward at 2 mm s−1 until the tortilla was cut. The maximum displacement of the crosshead was 10 mm. Each test was run with 10 tortilla samples selected randomly.

Fig. 1. Representation of a mechanical generalized Maxwell model with three elements and pure elastic spring represented in terms of shear modulus (G).

where G(t) is the relaxation shear modulus as a function of time, G0 is the equilibrium shear modulus or that for the residual spring due to the pure elastic component, Gi is the decay shear modulus of the ith Maxwell element, τi is the relaxation time of the ith Maxwell element, ηi is the viscosity of the ith Maxwell element, and ε is the strain (Figueroa et al., 2011a, 2012).

2.8. Statistical analyses All evaluations were carried out with a completely randomized design. Nonlinear regression analyses were used with OriginPro 8 SR0 (OriginLab Corp., Northampton, MA, USA). The results were analyzed using one way analysis of variance (ANOVA), means comparison with Tukey test at p ≤ 0.05, and the Pearson correlation with the Statistical Analysis System (SAS) for Windows ver. 9.0 (Cary, NC, USA) statistical software. To indicate greater significance, P ≤ 0.01 and P ≤ 0.001 were occasionally used.

2.6. Modified texture profile analysis (mTPA) of masa mTPA analysis was done with a TA-XT2 texture analyzer (Texture Technologies Corp., New York, NY, USA). A sample of 35 g masa was used to fill the cylinder probe mold and it was compressed with a weight of one kg to generate an uniformly compacted sample. The excess of masa was removed with a putty knife. The masa cylinder was removed from the mold and a sample of 51 mm in diameter and 10 mm height was obtained. The cylindrical sample was compressed in the texturometer for two cycles with a rounded TA-18 probe (diameter =1.2 cm) with 40% strain, with a speed of 1 mm s−1. The second cycle was carried out 2 s later. Hardness is defined as the force necessary to reach the 40% deformation (Gasca-Mancera & Casas-Alencáster, 2007). The mTPA of the masa was measured using the method of Bhattacharya, Narasimha, and Bhattacharya (2006) where adhesiveness = area 3; springiness = length 2/length 1; resilience = area 5/ area 4; cohesiveness = area 2/area 1; hardness = peak 1 force. (Fig. 2). Six replicates were used for each masa sample.

3. Results and discussion 3.1. Masa viscoelasticity: relaxation test The generalized Maxwell model with three elements and a residual spring in parallel fitted well with the relaxation curves (Fig. 3) with R2 > 0.9999. The estimated parameters of the Maxwell model for each masa are summarized in Table 1. Significant differences were observed among masa samples in the

Fig. 2. Generalized mTPA curve: adhesiveness = area 3; springiness = length 2/length 1; resilience = area 5/area 4; cohesiveness = area 2/area 1; hardness = peak 1 force. 3

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4

0.1a 0.3a 0.1a 0.2a 0.2a 0.1a 0.1a ± ± ± ± ± ± ± 1.7 1.6 1.6 1.7 1.8 1.7 1.7 0.1b 0.1c 0.3a 0.0cd 0.3cde 0.1ed 0.1e ± ± ± ± ± ± ± 1.9 1.5 3.5 1.4 1.3 1.1 1.0 0.8b 0.3b 0.1a 0.4bc 0.2b 0.2cb 0.3b ± ± ± ± ± ± ± 2.6 2.0 3.5 1.9 2.1 1.8 1.4 Control (No Ca used) Classic (Wood ashes) Traditional Ca(OH)2 CaCO3 CaSO4 CaCl2 Ca(C2H5COO)2

Means ± SD followed by different letters within the same column are significantly different (P ≤ 0.05). G0 = shear modulus of residual spring; G1, G2 and G3 = shear modulus of the ith Maxwell element; τ1, τ2 and τ3 = time of relaxation of the ith Maxwell element; η1, η2 and η3 = viscosity of the ith Maxwell element; η = total viscosity G=shear modulus of elasticity.

0.5a 0.8a 0.3a 1.7a 1.0a 0.2a 1.2a ± ± ± ± ± ± ± 2.3 2.3 2.3 3.3 3.1 2.3 3.4 7.3 ± 0.7b 5.8 ± 0.5c 11.1 ± 0.7a 5.4 ± 0.4dc 4.9 ± 0.8dc 4.1 ± 0.3de 3.5 ± 0.5e 0.6ab 1.2ab 0.8a 2.5ab 1.2ab 0.3b 1.1ab ± ± ± ± ± ± ± 3.1 2.8 4.9 4.0 2.7 1.5 2.3 6.0 1.1 1.0 2.5 1.1 0.3 1.1 ± ± ± ± ± ± ± 2.8 2.6 4.4 3.8 2.5 1.4 1.1 0.3b 0.5cb 0.5a 0.3cb 0.7cb 0.2c 0.1c ± ± ± ± ± ± ± 2.3 1.7 3.8 1.8 1.9 1.2 1.2 0.2b 0.2cb 0.6a 0.2cb 0.7cb 0.2c 0.2c ± ± ± ± ± ± ± 3.3 2.4 5.7 2.4 2.3 1.7 1.6 0.5a 0.8a 0.2a 1.7 a 1.0a 0.2a 1.2a ± ± ± ± ± ± ± 2.1 2.1 2.1 3.1 2.9 2.1 3.2 0.2b 0.2cb 0.2a 0.1cb 0.1cd 0.1d 0.1d ± ± ± ± ± ± ± 1.4 1.2 2.1 1.2 0.9 0.7 0.7 18 ± 3a 17 ± 5a 20 ± 2a 20 ± 5a 24 ± 5a 19 ± 2a 22 ± 3a 0.1b 0.1cb 0.2a 0.1cd 0.2cde 0.1de 0.1e

G3 (Pa) x 103 τ2 (s) G2 (Pa) x 103 τ1 (s) G1 (Pa) x 103 Spring G0 (Pa) x 103 Masa

Table 1 Estimated parameters from the generalized Maxwell model for the relaxation of nixtamalized corn masa.

τ3 (s) x 102

η1 (Pa.s) x 103

η2 (Pa.s) x 104

pure elastic component (G0), decay moduli G1, G2, and G3, viscosities η1, η2, and η3, and the shear modulus of elasticity (G). The process used to obtain the flour and the masa did not have a significant effect on relaxation times τ1, τ2, and τ3 and total relaxation time (Table 1). Shiau, Wu, and Liu (2012) mentioned that G0, and the decay parameters (G1, G2), indirectly measure the rigidity of material tested, while relaxation time (τ1, τ2) is the time that a macromolecule takes to be stretched out when it is deformed; thus, a higher decay modulus and relaxation times represent high rigidity and elasticity for viscoelastic foods, such as nixtamalized corn masa. Masa from the traditional process showed the highest magnitudes of G0, G1, G2, G3, and G. Therefore, it can be inferred that this masa was the most rigid and elastic, followed by the control masa (Table 1). On the other hand, masa using Ca (C2H5COO)2 had a less rigid and less elastic structure (Table 1). The results supported the hypothesis that in traditional masa derived from the traditional process, had higher values of G1, G2, and G3, which indicated that stronger interactions occurred between water and the flour components. Water-gelatinized starch and calcium-starch interactions could be the most important interactions, and these were possible because of the alkaline medium of the sample. The high correlation among shear moduli, especially G2 and the degree of starch gelatinization (r=0.91), suggested that strong interactions between the water added, the leached amylose, and the gelatinized and swollen starch granules exerted an influenced on the decay moduli. On the other hand, in masa using Ca(C2H5COO)2 and CaCl2 processes, the lowest values of G1, G2, and G3 could be related to the lowest degree of starch gelatinization, as well as with the lower or absence formation of calcium-starch interactions because of the acidic medium resulting from the dissociation of each salt during cooking. Shiau et al. (2012) and Yildiz et al. (2013) reported that fiber content comprises another important factor influencing the rigidity and elasticity of starch based systems. Therefore, it was hypothesized that masa from the traditional process has a rigid structure with the highest elasticity because it has the lowest fiber content. Mariscal-Moreno et al. (2015) reported that traditional tortillas had lower values for crude fiber. There was a tendency for an increase in total and insoluble fiber with CaCO3 and Ca(C₂H₅COO)₂ and also in the classic process when compared with traditional nixtamalization. In the traditional process, the OH− anions produce an alkaline medium that hydrolyzes the corn pericarp into arabinoxylans, which remain in the flour and act as hydrocolloids in the masa. On the other hand, in the rest of the flours, the whole pericarp is present in flours mostly as insoluble fiber (Santiago-Ramos et al., 2018a,b), which reduce the interaction between the water and the gelatinized starch to form a continuous phase and a strong network. In general, it was observed that only nixtamalization with Ca(OH)2 tended to increase the elasticity of masa in comparison with that of the control sample. These results were consistent with those previously reported by Santiago-Ramos et al. (2018b), where masa from

± ± ± ± ± ± ±

η3 (Pa.s) x 105

Fig. 3. Relaxation curves of masa from nixtamalized corn flours.

1.3 1.0 1.9 0.9 0.8 0.6 0.5

η (Pa.s) x 105

G (Pa) x 103

Total relaxation time (s) x 102

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Table 2 Degree of gelatinization of nixtamalized corn flour and textural properties of nixtamalized corn masa. Masa

DG (%)

Control (No Ca source used) Classic (Wood ashes) Traditional Ca(OH)2 CaCO3 CaSO4 CaCl2 Ca(C2H5COO)2

24 20 29 18 20 16 14

± ± ± ± ± ± ±

0b 1bcd 1a 1cde 2bc 1de 0e

Hardness (N)

Adhesiveness (N.s)

9 ± 1b 13 ± 1a 15 ± 3a 5 ± 1bc 4 ± 1c 4 ± 1c 6 ± 3bc

3 4 4 2 2 2 2

± ± ± ± ± ± ±

Cohesiveness x 10−1

0c 0a 1ab 0c 0c 0c 1c

3 4 3 3 5 4 4

± ± ± ± ± ± ±

Springiness x 10−1

0b 0ab 0b 0b 0a 0ab 0ab

4 4 3 5 4 4 4

± ± ± ± ± ± ±

Resilience x 10−2

0ab 0a 0b 0a 0a 0a 0a

4 5 1 4 4 4 4

± ± ± ± ± ± ±

0bc 0ab 0a 0c 0abc 0bc 0bc

Means ± SD followed by different letters within the same column are significantly different (P ≤ 0.05). DG: degree of gelatinization. Table 3 Moisture content, textural characteristics and degree of retrogradation of tortillas after 1 and 48 h of storage. Tortilla

Moisture 1 h (%)

Control (No Ca used) Classic (Wood ashes) Traditional Ca(OH)2 CaCO3 CaSO4 CaCl2 Ca(C2H5COO)2

43 43 43 44 44 43 41

± ± ± ± ± ± ±

0b 0b 0ab 1ab 1a 1ab 0c

CF 1 h (N)

16 13 14 12 12 12 13

± ± ± ± ± ± ±

1a 0bc 1b 0c 1c 0c 0bc

TS 1 h (N)

3 3 3 4 3 4 5

± ± ± ± ± ± ±

0cd 0cde 0e 01b 0de 0bc 0a

Ext 1 h (mm)

5 5 5 7 6 5 6

± ± ± ± ± ± ±

1c 0c 1c 0a 0ab 1bc 0a

Moisture 48 h (%) 42 42 42 40 40 41 39

± ± ± ± ± ± ±

1a 0ab 1ab 0bc 2abc 0abc 1c

Moisture loss 48 h (%) 1 2 2 9 8 6 5

± ± ± ± ± ± ±

1b 0b 2b 2a 5a 1ab 1ab

CF 48 h (N)

31 32 26 30 29 31 31

± ± ± ± ± ± ±

1ab 2a 1c 2abc 1bc 1ab 1ab

TS 48 h (N)

Ext 48 h (mm)

8 ± 1c 9 ± 0bc 9 ± 0b 10 ± 1ab 9 ± 1ab 10 ± 0ab 118 ± 0a

2 2 3 2 2 2 2

± ± ± ± ± ± ±

0b 0b 0a 0ab 0.1ab 0b 0b

DR 48 h (%)

30 20 28 25 34 24 12

± ± ± ± ± ± ±

0ab 4e 3bc 0cd 0a 2de 1f

Means ± SD followed by different letters within the same column are significantly different (P ≤ 0.05). CF: cutting force; TS: tensile strength; Ext: extensibility; DR: degree of retrogradation.

control processes, which had the highest degree of gelatinization, also had lower values of cohesiveness. Springiness and resilience are properties related to the capacity of a material to store energy leading the return to its original shape or position. Bhattacharya et al. (2006) reported that high values of springiness are undesirable because the thickness of the flattened sheets, such as tortillas, would increase after molding, which is undesirable. Based on this effect, masa from traditional and control processes were flattened into thinner tortillas. With respect to resilience, lower values of this property were shown by masa from CaCO3, control, CaCl2, and Ca (C2H5COO)2 when compared with masa from the traditional process. According to Valderrama-Bravo et al. (2015), fibers reduce the capacity of recuperation in dough when a force is applied. The insoluble fiber present in masa from the control and ecological processes is probably responsible for this behavior.

nixtamalization with Ca(OH)2 showed the best viscoelastic properties. The viscosities η1, η2, and η3 behaved similarly to the decay elastic components (Table 1). Masa samples with other Ca salt had lower total viscosity values, and this trend was also influenced by the degree of gelatinization, as indicated by the correlations (r = 0.50). 3.2. mTPA of masa Table 2 shows the hardness and adhesiveness in nixtamalized corn masa. The masa samples using the classic and traditional processes were the hardest and most adhesive. The hardness from masa samples using CaSO4 and CaCl2 were easily deformed and could be more easily molded into tortillas. Adhesiveness is the most important property of masa in tortilla production (Santiago-Ramos et al., 2018a,b); masa with adequate adhesiveness is required to adhere and separate properly from the rolling of the tortilla machine. All masa samples were able to be molded into tortillas; however, the lower adhesiveness of masa samples using control and other salts, mainly CaCl2 (Table 2), made it more difficult for the masa to stick to the shaping rollers. Hardness and adhesiveness were correlated with the degree of gelatinization, the higher the degree of gelatinization, the harder and more adhesive the masa (r = 0.67 and r = 0.54 respectively). Therefore, a degree of gelatinization between 20 and 30%, could be adequate to obtain the consistency necessary to mold tortillas properly. Because masa undergoes different types of forces during its handling in tortilla production, it must support higher forces before becoming deformed or brittle. The masa should be highly cohesive, tolerant to mixing and less likely to be brittle (Santiago-Ramos et al., 2018b). Masa using CaSO4 showed the highest values of cohesiveness, and no significant differences were observed between this masa and masa samples using the classic process, thus, the masa using CaSO4, CaCl2 and Ca (C2H5COO)2 were less brittle than masa from the traditional process. Cohesiveness is related to starch retrogradation. According to GascaMancera and Casas-Alencáster (2007), masa with a higher content of partially gelatinized starch granules is less cohesive because these granules function as nuclei for recrystallization during the rehydration of flour. That could be one reason why the masa from traditional and

3.3. Tortilla texture The moisture content of the tortilla after 1 h of preparation are shown in Table 3. Tortillas from the Ca(C2H5COO)2 process had the lowest moisture content. Significant differences were observed in moisture content among tortillas. As all masa samples were prepared with the same moisture content (55%) and all tortillas were prepared using the same conditions, the results indicated that tortillas using the Ca(C2H5COO)2 process lost more water during baking. The reason for this was the lower degree of starch gelatinization of the flour from which these tortillas were prepared, along with the presence of coarse particles derived from the cellulose-hemicellulose-lignin structure from the non-hydrolyzed pericarp. Both factors do not allow the interaction of water with the masa components; therefore, the majority of this water is free and could be easily released during baking. Fresh tortillas from the control process had the highest cutting force and lower values of tensile strength and extensibility (Table 3); thus, these tortillas were hard and less elastic. On the other hand, fresh tortillas from the other processes had lower values of cutting force; therefore, all of these tortillas were softer. Tortillas from the potentially more ecological processes with CaCO3 and Ca(C2H5COO)2, not only were softer, but also were more elastic, because they showed higher 5

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Table 4 Correlation coefficients among stress relaxation parameters and textural properties of masa and the tortilla quality variables. TM1h

CF1 h

TS1 h

Ext1 h

TM48 h

ML48 h

CF48 h

TS48 h

Ext48 h

G0 G1 t1 G2 t2 η1 η2 G Total relaxation time

ns ns ns ns ns ns ns ns ns

0.38* 0.41* ns 0.39* ns 0.46* ns 0.40* ns

−0.70*** −0.61*** ns −0.59*** ns −0.58** −0.47* −0.64*** ns

−0.57** −0.57** 0.37* −0.54** 0.43* −0.55** −0.39* −0.57** 0.43*

0.51** 0.50** ns 0.48** −0.43* 0.50** ns 0.51** −0.43*

ns −0.45* 0.39* −0.44* 0.38* −0.43* ns −0.44* ns

−0.63*** −0.55** 0.46* −0.50** ns −0.48* −0.41* −0.57** ns

−0.51** −0.43* ns −0.45* 0.42* −0.48* ns −0.46* 0.41*

0.43* 0.48** ns 0.41* ns 0.44* 0.43* 0.46* ns

Adhesiveness Springiness Cohesiveness Resilience Hardness

ns ns ns ns ns

ns −0.39* ns −0.38* ns

−0.42* 0.44* ns −0.54** −0.49**

−0.52** 0.46* ns −0.55** −0.64***

0.57** ns ns ns 0.45*

−0.64*** 0.38* ns −0.38* −0.57**

ns 0.38* ns ns ns

ns ns ns ns −0.38*

ns −0.39* ns ns ns

DG

ns

0.51**

−0.76***

−0.65***

0.63***

−0.48**

−0.49**

−0.64***

ns

G0 = shear modulus of residual spring; G1 and G2 = shear modulus of the ith Maxwell element; τ1 and τ2 = time of relaxation of the ith Maxwell element; η1 and η2 = viscosity of the ith Maxwell element; G= shear modulus of elasticity; DG= degree of gelatinization of nixtamalized flour; TM1h= tortilla moisture at 1 h; CF1h= cutting force at 1 h; TS1h= tensile strength at 1 h; Ext1h=extensibility at 1 h; TM48h = tortilla moisture at 48 h; ML48h=moisture loss after 48 h storage; CF48h= cutting force at 48 h; TS48h= tensile strength at 48 h; Ext48h =extensibility at 48 h; DR48h= degree of retrogradation at 48 h. *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001, ns: no significant.

understand their effects on nixtamalized corn-based products.

values of tensile strength and extensibility (Table 3). After 48 h of storage, all tortillas had a lower moisture content and were harder and more brittle than fresh tortillas (Table 3). Among the processes, stored tortillas from traditional, classic, and control processes lost less water (Table 3), but this trend was not clearly related with the tortilla texture. Loss of water is mainly due to syneresis, a common process that takes place with starch retrogradation during storage. It was observed that the degree of retrogradation (DR) negatively affected tortilla texture; the higher the DR, the softer but more brittle the tortillas (Table 3).

4. Conclusions The generalized Maxwell model with three elements was successfully used to describe the viscoelastic properties of the nixtamalized corn masa obtained with several nixtamalization processes. Masa using the traditional nixtamalization process was more elastic and viscous than masa using ecological processes. The degree of gelatinization of the nixtamalized corn flour exerts strong influences by enhancing those properties. After 1 h of baking, tortillas from ecological processes were softer and more extensible than tortillas from the traditional process. However, after 48 h of storage, tortillas from ecological processes became stale, reducing their extensibility. The pure elastic component G0, decay moduli G1, G2, and G3, the shear modulus of elasticity G, and viscosities η1 and η2 from the generalized Maxwell model correlated well with the cutting force, tensile strength, and extensibility of both fresh and stored tortillas. The results suggest that the relaxation test, especially the shear moduli parameters, is a better way than mTPA to predict masa and tortilla quality.

3.4. Correlations between masa properties and tortilla quality The pure elastic component (G0), decay moduli G1, G2, and G3, the viscosity η1, η2 and the shear modulus of elasticity (G) of the masa correlated positively with cutting force and negatively with the tensile strength and extensibility of fresh tortillas (Table 4). This implies that a more viscous, elastic, and rigid masa leads to the production of harder, more brittle, and less extensible fresh tortillas. After 48 h of storage, the inverse trend was observed. Softer and more extensible tortillas were obtained from masa samples with higher values of G0, G1, G2, G3, and G, and η1 and η2. The main factor influencing masa elasticity is the degree of gelatinization (DG), as indicated by the higher positive correlations observed between this factor and the following parameters G0, G1, G2, G3, and G, (Table 4). Additionally, shear moduli (elasticity) and DG correlated well with moisture content and loss of moisture. This behavior has important implications because tortillas made of masa by means of the traditional process lost less water and had a longer shelf life when compared with tortillas using ecological processes, which remained softer for a short time and become stale during storage. Poor correlations were observed between these properties and the texture characteristics of the tortilla. Masa samples with higher values of adhesiveness, resilience, and hardness could lead to the production of less extensible tortillas after 1 h of baking. After 48 h of storage, higher values of springiness were correlated with harder and less extensible tortillas. An important observation was that, the degree of gelatinization of the nixtamalized corn flour strongly influenced all of the rheological and textural properties of masa, as well as the textural characteristics of tortillas. Therefore, special attention must be paid to this aspect to

Declaration of competing interest The authors declare that there are no conflicts of interest. Acknowledgments This study was not supported by CONACYT that sponsored the PhD scholarships of David Santiago-Ramos and Alfonso Topete-Betancourt and Cinvestav. We thank Verónica Flores-Casamayor and José Juan Véles-Medina from Cinvestav-Querétaro for their technical support. References Arámbula-Villa, G., González-Hernández, J., & Ordorica-Falomir, C. A. (2001). Physicochemical, structural and textural properties of tortillas from extruded instant corn flour supplmented with various types of corn lipids. Journal of Cereal Science, 33, 245–252. Baks, T., Ngene, I. S., van Soest, J. J. G., Janssen, A. E. M., & Boom, R. M. (2007). Comparison of methods to determine the degree of gelatinisation for both high and low starch concentrations. Carbohydrate Polymers, 67(4), 481–490. https://doi.org/ 10.1016/j.carbpol.2006.06.016. Bhattacharya, S., Narasimha, H. V., & Bhattacharya, S. (2006). Rheology of corn dough

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