Journal of biological and health sciences http://biotecnia.unison.mx

Universidad de Sonora

ISSN: 1665-1456

Original Article

Improved Mexican Varieties of Bread Wheat: Characterization and evaluation of Physical and Viscoelastic Properties

Variedades Mexicanas Mejoradas de Trigo Panadero: Caracterización y Evaluación de Propiedades Físicas y Viscoelásticas

Dulce María Hernández Colín1 , Anayansi Escalante-Aburto2,3*

and Nestor Ponce-García1*

1 Facultad de Ciencias Agrícolas, Universidad Autónoma del Estado de México (UAEMéx), Toluca 50200, México.

2 Tecnológico de Monterrey, The Institute for Obesity Research, Monterrey 64849, México.

3 Tecnológico de Monterrey, School of Engineering and Sciences, Toluca 50110, México.

ABSTRACT

The moisture content influences the physical-mechanical and viscoelastic properties of wheat grains. A higher mois- ture content markedly reduced the hardness and elasticity of grains while increasing axial dimensions and plastic work. This research aimed to analyze wheat grains’ physical- mechanical and viscoelastic properties from four improved Mexican varieties. The small-strain uniaxial compression method was employed to achieve this, considering 12 %, 16

%, and 20 % moisture content levels. Additionally, the study sought to identify potential correlations between these pro- perties. For the viscoelastic properties, statistically significant differences were observed among the varieties in terms of total (Wt), elastic (We), and plastic work (Wp), as well as the degree of elasticity (DE). These parameters showed a gradual decrease with increasing moisture content. The study also revealed significant correlations between specific physical and viscoelastic properties. Notably, negative correlations (P < 0.05) were found between DE, thickness, and length dimensions. Furthermore, the bulk density exhibited highly significant negative correlations (P < 0.01) with Wp and highly significant positive correlations (P < 0.01) with DE. Regarding viscoelastic properties, the Z1 and X5 varieties exhibited su- perior performance, showing favorable outcomes in Wt and We and their physical-mechanical characteristics.

Keywords: Moisture content; uniaxial compression; small- strain; grain; Triticum aestivum.

RESUMEN

Las propiedades físico-mecánicas y viscoelásticas de los gra- nos de trigo están influenciadas por el contenido de hume- dad. A mayor contenido, la dureza y elasticidad de los granos reduce notablemente, e inversamente, las dimensiones axia- les y el trabajo plástico se incrementan. El objetivo de esta in- vestigación fue caracterizar las propiedades físico-mecánicas y viscoelásticas de granos de trigo de cuatro variedades mejoradas mexicanas evaluadas a diferentes contenidos de humedad: 12 %, 16 % y 20 %. Las propiedades viscoelásticas se evaluaron mediante el método de compresión uniaxial bajo pequeña deformación. Como resultado se identificaron correlaciones entre algunas propiedades físico-mecánicas y viscoelásticas. En términos de trabajo total (Wt), plástico

*Author for correspondence: Nestor Ponce-García, Anayansi Escalante-Aburto e-mail: nponceg@uaemex.mx; anayansi.escalante@tec.mx

Received: July 26, 2024

Accepted: June 18, 2025

Published: July 17, 2025

(Wp), elástico (We) y grado de elasticidad (GE), se observa- ron diferencias estadísticas significativas entre variedades. Estos parámetros mostraron una disminución gradual con el aumento del contenido de humedad. El estudio también reveló correlaciones significativas entre algunas propiedades físico-mecánicas y viscoelásticas. En particular, se observaron correlaciones negativas (P < 0.05) entre el GE y las dimensio- nes axiales grosor y longitud. La densidad aparente mostró correlaciones altamente significativas (P < 0.01), negativa con Wp y positiva con el GE. Las variedades Z1 y X5 mostraron un mejor comportamiento viscoelástico, particularmente en Wt y We, así como en sus características físicas y mecánicas. Palabras clave: Contenido de humedad; compresión uniaxial; pequeña-deformación; grano; Triticum aestivum.

INTRODUCTION

Wheat is the most widely cultivated crop globally because it is crucial in ensuring global food and nutrition security, supplying one-fifth of the world’s food calories and protein (gluten). It is the only cereal that provides optimal quality for producing well-risen bread, owing precisely to its gluten con- tent and quality (Erenstein et al., 2022). Bread wheat (Triticum aestivum L.) is the most important cereal crop worldwide. Its remarkable adaptability, versatile applications, high nutri- tional content, and significant yield make it a staple food for over one-third of the global population (Ahmad et al., 2006). According to official statistics (SEGOB, 2021), during the 2021 cycle, Mexico produced approximately 3.6 million tons of wheat, around 1.5 million tons of bread wheat; nearly half of this amount was harvested in Sonora.

1

The selection of seeds from the highest quality fruits enabled the establishment of the most advantageous geno- types in cultivated species (Listman, 2022). Wheels produc- tion and quality can be enhanced by developing new and improved varieties that yield higher outputs and perform better under diverse agro-climatic conditions. This can be ac- complished through several strategies, such as utilizing plant genetic resources, including wild relatives and landraces, and employing germplasm-assisted breeding. Wheat breeding programs should prioritize expanding the genetic diversity of wheat cultivars, with particular attention to bread wheat selection and baking quality. There is a consensus that germ-

Volume XXVII

DOI: 10.18633/biotecnia.v27.2406

plasm diversity in breeding material is essential for successful plant breeding (Khalid et al., 2023). Al Aridhee et al. (2019) suggest that wheat grain has a multi-layered and complex structure influenced by genetic traits, environmental con- ditions, and specific cultivation practices. Each structural component exhibits unique mechanical properties, such as resistance to external loads and crack formation and pro- pagation. Therefore, optimizing wheat breeding programs require thoroughly assessing grain technological quality. Although numerous methods exist to determine kernel qua- lity, many are time-consuming and expensive. Developing faster and more cost-effective measures offers the potential for new approaches to predict kernel or dough behavior.

On the other hand, grain quality evaluation begins with determining its physical properties. Additionally, the vis- coelastic evaluation of grains allows recognizing and deter- mining their potential or industrial use, serving as a more se- lective classification tool among grains with similar or related physical characteristics (Ponce-García et al., 2016; 2017). This study aimed to evaluate and characterize the main physical and viscoelastic characteristics of four improved varieties of bread wheat grains cultivated in Sonora, México. This will provide novel information to determine their main attributes and explore possible correlations between their physical and viscoelastic properties.

MATERIAL AND METHODS

Biological material

The biological material consisted of bread wheat grains (Triti- cum aestivum) from four improved varieties, cultivated in the Yaqui Valley, Sonora, México during the 2021-2022 autumn- winter agricultural cycle. These four varieties were provided by RESOURCE SEEDS INTERNATIONAL (RSI) S. DE R.L. DE C.V.

and consisted of a top-cross breeding process developed by this company. Due to confidentiality requirements, the varie- ties studied will not be named; instead, each one has been assigned a random code (Z1, J6, X5, and N3, respectively). In general, these genotypes have been determined to adapt well to the wheat-growing regions of northwestern México, are resistant to diseases such as Puccinia recondita and Pucci- nia striiformis, and possess acceptable industrial quality with good yields, exhibiting different agronomic traits.

Each grain sample was manually cleaned using alu- minum sieves with 1.98 mm (5/64”) triangular perforations (Seedburo Equipment Co., IL, USA) to remove foreign mate- rial and impurities until 2 kg of each improved variety was obtained. The cleaned samples were placed in plastic contai- ners within polyethylene bags and stored under refrigeration at 4 °C until use.

Methods

Determination of moisture content and grain conditio- ning

The moisture content of the grains was determined in tripli- cate using the ASAE Standard S352.2 (1999) method. Initially, the original moisture content of each sample was measured.

Based on these results, each sample was conditioned separa- tely to three moisture levels: 12 %, 16 %, and 20 %, according to the equation (1) proposed by Serna-Saldivar (2012), using 50 g of sample for each case. Subsequently, the physical and viscoelastic properties of the grains from each improved variety were evaluated at each moisture level.

Eq. (1)

Characterization of physical properties

Each determination was performed according to equation (1), reporting in all cases the average value of the measu- rement of 20 randomly selected grains (replicates) for each variety and moisture content, except where indicated.

Axial dimensions

The length (L), width (W), and thickness (T) of each grain were measured using a digital caliper (REXQualis). The results are reported in millimeters (mm).

Hardness (H)

This parameter was evaluated through uniaxial compression using the TA-XT2 Plus universal texture analyzer (Stable Mi- cro Systems, United Kingdom) equipped with a 2 mm SMS P/2 probe. The test involved placing each grain on the equip- ment platform with the ventral side down and compressing it until rupture (Ponce-García et al., 2013). The evaluation parameters considered were as follows: 30 % deformation (compression) and pre-test, test, and post-test speeds of 2, 3.5, and 3.5 mm/s, respectively. A force-time curve was obtai- ned for each grain, from which the corresponding maximum force (hardness) required for rupture was retrieved.

Maximum Force (Fmax) at 5 % strain

Fmax indicates the maximum compression force applied to the grain (in Newtons) at a constant deformation of 5 %. This pa-

rameter was determined simultaneously and directly during the viscoelastic analysis of each evaluated grain.

‌Individual grain weight (IGW) and thousand-grain weight (TGW)

IGW was obtained by recording the weight of individual grains in grams (g) (20 replicates) using an analytical balance (OHAUS, model BBL61, Boeco, Germany). For TGW, exactly 1,000 grains from each sample were manually counted, and their weight was reported in grams. This determination was performed in triplicate, and the average weight was reported.

Bulk Density (𝝆𝒃)

This determination followed Method 55-10, AACCI (2000) with modifications. The suggested container in the official method was replaced with a 100 mL beaker, whose exact volume was determined. The average value of 3 replicates was reported. The determination was performed following equation (2) (Bhise et al., 2014).

𝜌 = variance (ANOVA) was conducted with a significance level of

𝑏 Eq. (2)

Where: 𝜌𝑏 is the bulk density; 𝑊𝑠 is the weight of the sample in kg, and 𝑉𝑠 is the volume occupied by the sample in hectoliter (hL). Therefore, bulk density (𝜌𝑏) is expressed in kg/hL commonly referred as hectoliter weight.

Characterization of viscoelastic properties

For the evaluation of viscoelastic properties, the TA-XT2 Plus universal texture analyzer with SMS P/25 probe was used, following the method of uniaxial compression under small deformation reported by Ponce-García et al. (2017) with two modifications: the single compression mode (Return to start) was replaced with TPA mode (double compression). As a second adjustment, the deformation index increased from 3

% to 5 % during compression. The configuration parameters in the texture analyzer were as follows: compression mode, 5 % constant deformation, and pre-test, test, and post-test speeds of 1, 0.1, and 0.1 mm/s, respectively. The viscoelastic properties were determined for each sample and conditio- ning moisture levels (12 %, 16 %, and 20 %).

Total (Wt), elastic (We), and plastic (Wp) work

The viscoelastic behavior (Wt, We, and Wp) of individual gra- ins was determined from the respective load-displacement

curves obtained after compression to 5 %, following Ponce- García et al. (2013) method.

Degree of elasticity (DE)

It is the proportion of We relative to Wt after applying the load and unload cycle, expressed as a percentage (Figueroa et al., 2011).

Experimental design and statistical analysis

A completely randomized design with two factors was con- sidered to evaluate the physical and viscoelastic properties of the grains. The factors assessed were grain variety and moisture content (12 %, 16 %, and 20 %). An analysis of

95 %, and a Tukey test was performed to observe differences between treatment means (P < 0.05). Statistical analysis was conducted using SAS software, version 9.1.3 (SAS Institute, Cary, NC, USA, 2002).

RESULTS AND DISCUSSION

Tables 1 and 2 show the mean values of the physical proper- ties of the four improved wheat grain varieties at 12 %, 16 %, and 20 % moisture content.

Axial dimensions

Table 1 presents the mean values for axial dimensions. With respect to length (L), four improved varieties’ results did not show statistically significant differences (P > 0.05) among themselves at a moisture content of 12 %. However, when the moisture content of the grains was 16 % and 20 %, statis- tical differences between varieties were observed (P < 0.05). Generally, it was noted that the grains of each evaluated variety exhibited an increase in the L value directly propor- tional to the moisture content, with the Z1 variety showing the most significant increase, going from 6.6 mm to 6.9 mm to 7.0 mm when the moisture content was 12 %, 16 %, and 20 %, respectively. On average, L increased by 5 % when the moisture content of the grains rose from 12 % to 20 %.

For the width (W) parameter, statistically significant differences (P < 0.05) between varieties were observed at each of the three moisture levels. Like the grain length, the trend of increasing the W value of the grains was directly proportional to the moisture content. However, the increase in width values was proportionally less than the increase in length. At 12 % moisture content, each of the four varieties had an initial width measurement of 2 mm smaller than at 20

% moisture. Regardless of the statistical differences, the N3 and X5 varieties consistently reached the lowest and highest W values at each moisture level.

At 12 %moisture content, the grains of the four varieties showed no statistically significant differences (P > 0.05) in thickness. However, as expected, like the other two axial di-

Table 1. Mean values of axial dimensions (L, W, and T), and hardness (H) of wheat grains from four improved varieties, conditioned to 12 %, 16 %, and 20 % moisture content.

Tabla 1. Valores medios de las dimensiones axiales (L, A y G) y dureza (D) de granos de trigo de cuatro variedades mejoradas, acondicionados a 12 %, 16 % y 20

% de contenido de humedad.

± Standard deviation. In the same column, mean values with different letters are statistically different for 12 %, 16 %, and 20 % moisture content (w.b.), respectively.

L=Length; W=Width; T=Thickness; H=Hardness. n=20.

Table 2. Mean values of the physical properties of weight and density (IGW, TGW, and 𝝆𝒃) of wheat grains from four improved varieties, conditioned to 12 %, 16 %, and 20 % moisture content.

Tabla 2. Valores medios de las dimensiones axiales (PIG, PMG y 𝝆𝒃) de granos de trigo de cuatro variedades mejoradas, acondicionados a 12 %, 16 % y 20 %

de contenido de humedad

± Standard deviation. In the same column, mean values with different letters are statistically different for 12 %, 16 %, and 20 % moisture content (w.b.), respectively. IGW=Individual grain weight; TGW=Thousand grain weight; 𝝆𝒃 =bulk density. *n=20; **n=3.

mensions (length and width), as the moisture content increa- sed to 16 % and 20 %, the thickness values also increased, with statistically significant differences (P < 0.05) between varieties at both moisture contents. As shown in Table 1, the grains of the X5 variety achieved the most significant increase in thickness, gradually going from 3.3 mm to 3.5 mm and ending at 3.6 mm at 12, 16, and 20 % moisture content, respectively.

Jamali et al. (2016) examine the effect of moisture content at three levels: 10, 15, and 20 % on several physical properties of two varieties of wheat and found behaviors and trends like those in the present study, such as the axial dimensions, true density, and grain volume in both varieties, which increased with higher moisture content. Sandra et al. (2020) evaluated the physical and mechanical properties of local rice grain varieties with different moisture contents. They determined that the higher the moisture content, the greater the roundness and axial dimensions (width and thic- kness).

While the four evaluated varieties exhibited the same behavioral trend because of the increase in grain moisture content, it is worth noting that at 16 and 20 % moisture, statistical differences between varieties were observed in the three axial dimensions. In contrast, at 12 % moisture, these differences were only observed for the width parameter.

Hardness (H)

Table 1 presents mean hardness (H) values for each wheat variety at different moisture levels (12 %, 16 %, and 20 %). Hardness is another critical physical (mechanical) property used to evaluate quality and suitability for various products. According to Hourston et al. (2017), the variation in starchy endosperm texture (grain hardness) between soft wheat and hard wheat (bread wheat) significantly impacts the optimal tempering time and conditions for efficient milling due to water diffusion during tempering in individual wheat grains with varying hardness. Soft grain starchy endosperms absorb water more rapidly than hard grain types. This increased wa- ter uptake in soft grains is due to enhanced capillary forces

resulting from lower adhesion between the starch granules and the protein matrix. Additionally, bread wheat varieties typically have higher protein content and exhibit structural differences from soft wheat varieties.

Başlar et al. (2012) observe a strong correlation between protein content and rupture force, energy absorption, and hardness across all varieties and load orientations. Essentially, higher protein content results in harder grains. This associa- tion holds significance for millers and end-users involved in milling and post-milling processes. Similarly, Lullien-Pellerin (2020) pointed out that the mechanical properties of grain tissues significantly influence grain breakage behavior, the fate of various tissues, and, ultimately, the characteristics of the final product. As shown in Table 1, the J6 variety showed the highest hardness values at 12%, and 20% moisture content. A moisture content of 16 % resulted in the highest hardness for the N3 variety, although it did not show statisti- cally significant difference compared to the J6 variety. In con- trast, the Z1 variety exhibited the lowest values. To further illustrate, the average hardness at 12 % moisture was 111.6

N. When the moisture content of the grains increased to 16

%, the hardness value decreased to 84.8 N, and finally, when the moisture content increased to 20 %, the hardness further reduced to 67.7 N; on average, a 38 % decrease in hardness value when the moisture content increased from 12 % to 20

%. The limited availability of water significantly affects mois- ture migration within the kernels, which in turn impacts their breakage behavior.

Resende et al. (2013) evaluated hulled and dehulled rice grains to recognize their behavior concerning moisture content. These researchers determined that reducing the moisture content from 0.30 % to 0.12 % (dry basis) increased the breaking force of the grains. This variation in the force needed to cause breaks in the grain structure directly relates to the moisture content of the biological material and its physical resistance. Similarly, Gabrielly et al. (2019) evaluated the mechanical properties of sorghum grains subjected to compression at different moisture levels. The results de- monstrated that various factors, such as drying temperature,

moisture content, stiffness, and the grain area where the force is applied, can influence the mechanical properties of the grains. They observed that as moisture content increa- sed, the compression force needed to deform the sorghum grain decreased, depending on the grain’s moisture content; grains with higher moisture content had lower resistance to compression.

Individual grain weight (IGW) and thousand-grain weight (TGW)

Table 2 shows that the mean values of the grains’ physical properties of weight, volume, and density had a directly pro- portional behavior concerning their moisture content. There was an increase in these parameters as the moisture content increased. Each of the evaluated properties is specifically discussed below.

Concerning IGW, the four varieties did not show statis- tically significant differences (P > 0.05) among themselves at a moisture content of 12 %. However, when this increased to 16 % and 20 %, statistically significant differences (P < 0.05) were observed between varieties. In general, it was observed that the average IGW increased slightly as the moisture content increased, from 0.059 g at 12 % moisture to 0.067 g at 20 % moisture. The effect of increasing moisture content from 12 % to 20 % on IGW is more evident when comparing the value of variety N3 at 12 % moisture content (0.056g) to that of variety X5, which reached 0.073g at 20 % moisture content. The X5 variety showed the highest IGW values at all moisture levels, indicating that this cultivar produces the heaviest grains. On the other hand, the X5 and N3 varieties showed statistically significant differences in IGW at 16 and 20 % moisture levels, suggesting they may be more sensitive to moisture fluctuations. In a study by Gürzoy and Güzel (2010), the IGW of various wheat varieties was evaluated in a moisture range between 8.6 % and 9.7 %. The results revea- led that the wheat variety with the highest moisture content had the highest IGW.

Based on the results of Table 2, statistically significant differences (P < 0.05) were determined between varieties at each of the three moisture levels for TGW. In all the studied varieties, the average TGW increased as the moisture content increased, with the X5 variety reaching the highest values at all moisture levels, and in contrast, the N3 variety recorded the lowest values. TGW is an important parameter that can significantly influence the quality of wheat flour and, conse- quently, the quality of the resulting bread. Studies like that of De la Horra et al. (2012) have shown a relationship between TGW and wheat flour’s industrial quality index (ICI) of wheat flour. In this study, TGW values ranged between 47.1 g (N3 va- riety at 12 % MC) and 66 g (X5 variety at 20 % MC), indicating a variation in the sample’s weight. At 12.5 % MC, Hourston et al. (2017) reported a TGW value of 41 g for wheat grains, notably lower than the average value for 12 % MC in this study (51.6 g, Table 2). Generally, a higher TGW is associated with better flour yield, protein content, and quality, resulting in bread with greater volume and a fluffier crumb.

Bulk Density (𝝆𝒃)

The wheat varieties bulk density (hectoliter weight) value (Table 2) showed an inversely proportional trend con- cerning the moisture content. This suggested that the wheat grains exhibited lower apparent density as the moisture increased. At a moisture level of 12 %, statistically significant results were observed, with the Z1 variety having the highest bulk density values of 85.9 kg/hL. In contrast, the X5 variety recorded the lowest bulk density, with 81.7 kg/hL value. As the moisture content increased, the X5 variety reached the highest bulk density at 16 % and 20 % moisture levels, while the J6 and N3 varieties also showed statistically significant differences. In contrast, the Z1 variety exhibited the lowest bulk density values at the same moisture levels, indicating a lower apparent density of the grains than the other varieties. Differences in bulk density among four grain-varieties were notable at three moisture levels. These results demonstrate a negative correlation between 𝝆𝒃 and grain moisture content. On average, bulk density decreases by approximately 14 % when the moisture content increases from 12 % to 20 %. De la O et al. (2012) reported bulk density values like those obtained in this study (between 73 and 84 kg/hL) in Mexican wheat varieties. Similar trends were presented by Jamali et al. (2016) in wheat grains, where bulk density decreased with increased moisture content. However, the average values re- corded were lower than those in the present study (ranging between 55 and 65 kg/hL).

Maximum force at 5 % of strain (Fmax)

On the other hand, according to the ANOVA conducted,

it was established that the grains’ moisture content signifi- cantly impacted the hardness and maximum force (Fmax) of the grains from the four improved wheat varieties evaluated. Figures 1, 2, and 3 show the Fmax values at 5 % strain for different wheat varieties based on moisture content (12 %, 16 %, and 20 %, respectively). The Z1 and X5 varieties exhi- bited similar trends in their Fmax values concerning moisture content. Both reached their maximum resistance at 12 % moisture, gradually decreasing as the moisture content increased. For the Z1 variety, the maximum force decreased from 25.2 N to 18.2 N as the moisture content increased from 16 % to 20 %. Similarly, the X5 variety decreased from 27.4 N

to 22.3 N over the same moisture range.

Instead, the J6 and N3 varieties did not show statistically significant differences at 12 % moisture. However, when the moisture level was increased to 16 %, these varieties reached their maximum Fmax values, recording 23.3 N and 29.3 N, res- pectively. Nevertheless, as the moisture increased to 20 %, their Fmax values decreased to 23.1 N and 21.4 N, respectively. These results indicate that the Z1 and X5 varieties tend to lose resistance as moisture increases. In contrast, the J6 and N3 varieties show an initial increase in resistance at 16 % moisture but lose it when moisture rises to 20 %.

Despite significant advancements in the study of grain mechanical properties, few investigations have comprehen- sively addressed these aspects. By thoroughly considering

Figure 1. Viscoelastic properties of improved bread wheat varieties conditioned to 12% moisture. A. Variety Z1; B. Variety J6; C. Variety X5; and D. Variety N3. Fmax= Maxi-mum force at 5% strain; Wp =Plastic work; We =Elastic work; Wt =Total work; DE=Degree of elasticity. In the same property, different letters in parentheses indicate statistically significant differences (P<0.05).

Figura 1. Propiedades viscoelásticas de variedades mejoradas de trigo panadero acondicionadas a 12% de humedad. A. Variedad Z1; B. Variedad J6; C. Variedad X5; y D. Variedad N3. Fmax =Fuerza máxima al 5% de deformación; Wp =Trabajo plástico; We =Trabajo elástico; Wt

=Trabajo total; GE =Grado de elasticidad. En la misma propiedad, diferentes letras entre paréntesis indican diferencias estadísticamente

significativas (P<0.05).

Figure 2. Viscoelastic properties of improved bread wheat varieties conditioned to 16% moisture. A. Variety Z1; B. Variety J6; C. Variety X5; and D. Variety N3. Fmax =Maximum force at 5% strain; Wp =Plastic work; We =Elastic work; Wt =Total work; DE = Degree of elasticity. In the same property, different letters in parentheses indicate sta-tistically significant differences (P<0.05).

Figura 2. Propiedades viscoelásticas de variedades mejoradas de trigo panadero acondicionadas a 16% de humedad. A. Variedad Z1; B. Variedad J6; C. Variedad X5; y D. Variedad N3. Fmax =Fuerza máxima al 5% de deformación; Wp =Trabajo plástico; We =Trabajo elástico; Wt

=Trabajo total; GE =Grado de elasticidad. En la misma propiedad, diferentes letras entre paréntesis indican diferencias estadísticamente

significativas (P<0.05).

Figure 3. Viscoelastic properties of improved bread wheat varieties conditioned to 20% moisture. A. Variety Z1; B. Variety J6; C. Variety X5; and D. Variety N3. Fmax =Maximum force at 5% strain; Wp =Plastic work; We =Elastic work; Wt =Total work; DE = Degree of elasticity. In the same property, different letters in parentheses indicate sta-tistically significant differences (P<0.05).

Figura 3. Propiedades viscoelásticas de variedades mejoradas de trigo panadero acondicionadas a 20% de humedad. A. Variedad Z1; B. Variedad J6; C. Variedad X5; y D. Variedad N3. Fmax =Fuerza máxima al 5% de deformación; Wp =Trabajo plástico; We =Trabajo elástico; Wt

=Trabajo total; GE =Grado de elasticidad. En la misma propiedad, diferentes letras entre paréntesis indican diferencias estadísticamente

significativas (P<0.05).

the mechanical properties of grains from harvest through to final sale, minimizing losses at each stage and better maintai- ning their economic value is possible (Gao et al., 2024).

Characterization of the viscoelastic properties

The viscoelastic properties of grains are strongly influenced by their composition, especially water content. Moisture content significantly affects the viscoelasticity of grains, most notably the elastic modulus. Uniaxial compression tests on wheat have shown that as water content increases, the elastic work during compression decreases while the plastic work increases, reducing total work. An increase in moisture content leads to a decrease in the elastic modulus, reflec- ting a reduction in the material’s resistance to deformation. Thus, analyzing grain viscoelasticity is a feasible approach to understanding their fracture behavior (Ponce-García et al., 2013; Escalante-Aburto et al., 2023; Gao et al., 2024).

The average values and behavior of the total work (Wt), elastic work (We), plastic work (Wp), and degree of elasticity (DE) of the four-grain varieties at 12 %, 16 %, and 20 % mois- ture are presented in Figures 1, 2, and 3, respectively.

Total (W ), elastic (W ), and plastic (W ) work

varieties J6 and N3 had the lowest values (0.557 N·mm and 0.567 N·mm, respectively), maintaining statistical similarity between them.

As the moisture increased to 16 % (Figure 2), a signifi- cant change was evident, with a substantial increase in the average value of Wt, reaching 2.004 N·mm. However, when the moisture rose to 20 % (Figure 3), varieties J6, X5, and N3 again stood out with the highest Wt values, showing no statistical differences, however variety N3 was statistically equal to Z1. At 20 % moisture, the average Wt value for the combined varieties decreased to 1.660 N·mm compared to 16 % moisture.

Specifically, the total work peaked at different moisture levels for each variety. Varieties Z1 and X5 exhibited their best values at a moisture level of 12 %. Conversely, variety N3 showed a higher Wt value at a moisture level of 16 %. In contrast, variety J6 showed generally lower Wt levels, with its highest value recorded at 20 % moisture, suggesting it is a more rigid and less deformable material overall.

The results of dividing the total work into elastic and plastic work for the four wheat varieties evaluated at di- fferent moisture levels (12 %, 16 %, and 20 %) consistently demonstrated that We are the highest value. This finding

t e p

With 12 % moisture (Figure 1), an average value of 1.465

N·mm was obtained for Wt, with varieties Z1 and X5 exhibi- ting the highest values (2.354 N·mm and 2.380 N·mm res- pectively), which were statistically equal. On the other hand,

indicates a higher hardness of the grain endosperm, which

translates into superior quality during bread-making. Spe- cifically, varieties Z1 and X5 stand out as the most suitable options for carrying out bread-making processes optimally and effectively.

This aligns with the study by Maucher et al. (2009), which demonstrated the connection between the mechanical and viscoelastic properties of wheat grains and those of the dough. Varieties with a high elastic/plastic (E/P) ratio were observed to have greater gluten strength. These results are crucial for wheat quality in the food industry.

Concerning elastic work, varieties Z1 and X5 tend to de- crease elastic work capacity as moisture content increases. In contrast, the variety J6 exhibit an opposite trend, as its elastic work value increased with the rise in moisture content. The N3 variety exhibited an atypical behavior concerning this pa- rameter (We). Initially, as the moisture content increased from 12 % to 16 %, We increased; however, when it rose from 16

% to 20 %, it experienced a decrease. The behavior patterns in the wheat grain varieties indicate they react differently to moisture variations. This has important implications for bread-making, where Z1 and X5 are preferred options due to better gluten hydration and higher water retention at standardized moisture levels (11 % to 13 %). These characte- ristics make these varieties especially suitable for producing high-quality bread. Conversely, varieties J6 and N3, which show increased elastic work with higher moisture, may have specific applications in other areas of baking or in producing wheat products different than traditional bread.

The individual characteristics of wheat varieties and their response to moisture content are essential factors to consider when selecting the appropriate variety for bread production and other bakery products. This underscores the importance of understanding how these individual pro- perties relate to the bread-making process and how these differences can influence the quality of the final product.

On the other hand, in Figures 1, 2, and 3, it can be obser- ved that plastic work increased parallel to the rise in moisture. A directly proportional relationship was observed between Wp and moisture content, particularly evident in variety J6, where the Wp value quintupled, rising from 0.139 N·mm (12

% moisture content) to 0.711 N·mm (20 % moisture content). Variety X5 also exhibited a proportional increase, albeit to a lesser extent. Similar behavior was noted in varieties Z1 and N3, which showed a significant increase in Wp as the moisture content increased from 12 % to 16 %. However, both varieties tended to stabilize, with their Wp values slightly decreasing as the moisture content rose from 16 % to 20 %.

In a study by Ponce-García et al. (2013), the effect of moisture content on the viscoelastic properties of individual wheat grains was investigated. The uniaxial compression test under small deformation was used to evaluate the behavior of parameters such as Wt, We, Wp, and modulus of elasticity

(E). The results revealed that wheat class, moisture content,

and the interaction between cultivars significantly impacted We and Wp values, with moisture content being the most in- fluential factor. Higher moisture levels were associated with lower Wt values, indicating decreased elasticity and increased viscosity. This means that increased moisture caused grain plasticization and altered their viscoelastic properties. Su- prabha Raj et al. (2024) evaluated the effect of conditioning

time on wheat grains with different moisture contents (14 %, 16 %, and 18 %) on their mechanical and viscoelastic proper- ties, concluding that tempering moisture content notably reduced the elasticity of the wheat grains. Higher tempering moisture levels decreased elastic work while increasing plas- tic work, enhancing flour extraction. This dynamic suggests a clear inverse relationship between plastic and elastic work concerning moisture. In other words, as a material becomes more prone to plastic deformation due to increased moistu- re, its capacity for elastic work decreases.

Degree of Elasticity (DE)

A consistent trend is observed (Figures 1 to 3) in the rela- tionship between moisture content and elasticity degree. As moisture increases, DE decreases, indicating that grain varieties have a greater capacity to recover their original shape under lower humidity conditions. Among the varieties, Z1 decreases DE from 83.0 % to 70.1 % and then to 65.1 % as moisture increases from 12 % to 16 % and 20 %, respectively. On the other hand, J6 presented the lowest GE values, decre- asing from 73.2 % to 67.1 % and then to 62.1 % at the same moisture levels.

Moisture has an inverse impact on the elasticity of wheat grains due to water absorption, changes in internal structure and texture, increased brittleness, and chemical processes that alter their mechanical properties. This is important to consider for storage and processing of wheat grains, as the loss of elasticity can affect the quality and usability of wheat- derived products. Regarding the modulus of elasticity, it was found that the wheat class, moisture content, and the interaction between cultivars significantly impacted this rheological parameter. This indicates that the composition of the wheat, the moisture level, and the specific characteristics of each cultivar influenced the grain’s stiffness and resistance to deformations applied during the compression test.

Simple Correlations

A Pearson correlation analysis was conducted to identify correlations between the four improved wheat varieties’ physical-mechanical and viscoelastic properties. The results, presented in Table 3, reveal interesting correlations between these properties, providing a clearer understanding of how they relate to each other and how they can influence grain behavior. These associations are important for improving and selecting wheat varieties in future research and agricul- tural applications.

Among the most relevant findings of this correlation analysis, a significant negative correlation was observed bet- ween grain length and elasticity degree (P < 0.05), indicating that as the grain length increases, its DE decreases. Grain thickness showed a positive correlation with Wp (P < 0.05) and a negative correlation with DE (P < 0.05). This implies that as the grain thickness increases, more plastic work is done during deformation and its elasticity decreases.

Additionally, a significant correlation was observed bet- ween individual grain weight and Wp (P < 0.05), implying that

Table 3. Pearson’s simple correlations (r) between physical and mechanical properties vs. viscoelastic properties of wheat grains from improved varieties.

Tabla 3. Correlaciones simples de Pearson (r) entre propiedades físicas y

mecánicas vs propiedades viscoelásticas de granos de trigo de variedades mejoradas.

W , Total work; W , Elastic work; W , Plastic work; DE, Degree of elasticity;

The relationship between the mechanical and physical properties vs. viscoelastic properties has not been standar- dized, nor the unified mechanical determination method of grain. However, the degree of elasticity and plastic work were the viscoelastic parameters that showed the strongest correlations with the physical and mechanical properties of the grains, particularly highlighting their association with hectoliter weight and hardness.

Based on the results of this research, it is recommended that these four improved wheat varieties be further inves- tigated, particularly their functional and technological pro- perties, to assess their suitability for bread and other bakery products. This will provide valuable insights into their com- mercial applications and product development potential.

t e p

IWG, Individual grain weight; Fmáx, Maximum force at 5 % strain; ns, no

significant (P>0.05); *Significant (P < 0.05); **highly significant (P < 0.01).

a greater amount of plastic work is done during deformation as the grain weight increases. Furthermore, the bulk density of the grain exhibited a very significant negative correlation (P < 0.01) with Wp and a very significant positive correlation (P < 0.01) with the DE. This suggests that as hectoliter weight increases, a decrease in plastic work performed during de- formation is observed, while the elasticity degree tends to increase.

Regarding the mechanical properties, very significant positive correlations (P < 0.01) were found between Fmax and the respective total and elastic work. This suggests that as the Fmax increases, the work done during elastic deformation also increases. On the other hand, hardness showed a very significant negative correlation (P < 0.01) with Wp and a very significant positive correlation (P < 0.01) with the DE, indica- ting that as hardness increases, less plastic work is done and an increase in the elasticity degree is observed.

According to Warechowska et al. (2016), raising the mois- ture level of the grain mechanically strengthened the gluten network and improved its moisture absorption capacity. This treatment’s positive effect is associated with creating bread dough that absorbs water more efficiently and maintains a stable consistency during kneading.

CONCLUSIONS

The study uncovered distinct physical and mechanical cha- racteristics among the improved grain varieties. This finding is consistent with the connection between hardness alleles and mechanical behavior. This genetic variation affects hard- ness and results in differences in compressive force and total deformation energy.

Increased moisture content in grains, causes outer layers to speed up moisture transfer , causing changes in in- tercellular spacing and resulting in grain volume expansion. This expansion enhances the grain’s plasticity while reducing its hardness. At higher moisture levels, the kernels undergo plasticization, reducing the change rate in compressive force. As a result, higher moisture content leads to a significant decrease in hardness and elasticity.

ACKNOWLEDGMENTS

The authors thank RESOURCE SEEDS INTERNATIONAL S. DE

R.L. DE C.V. for generously donating the biological material used in this research.

CONFLICTS OF INTEREST

The authors declare no conflict of interest.

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