Innovation in Nixtamalization by Extrusion Using the Wet Process

Abstract

Extrusion wet milling nixtamalization (EWMN) is an innovative process that combines traditional nixtamalization with wet extrusion technology to produce high-quality corn products. As is known, wet extrusion technology is an HTST (high-temperature short-time) process and nixtamalization is an LTLT (low-temperature long-time) process. So, EWMN is the combination of these two technologies. It is used in high moisture, low temperature, low screw velocity and the corn grain is milled at 3 mm size. EWMN is based on mixing corn with water and lime, creating a homogeneous masa that is subjected to an extrusion process using a screw or double screw. The operating parameters, such as humidity, cooking time, production speed, and shear, are critical in this process and must be carefully controlled to obtain the desired product texture and characteristics. After extrusion, the product is dried to reduce humidity to safe and desirable levels for storage. This step is essential to increase the life of the final product. In summary, corn nixtamalization extrusion combines the traditional nixtamalization technique with wet extrusion, resulting in high-quality corn products, better digestibility, and efficiency compared to conventional processes. This innovative approach offers a promising solution for corn-based food production.

1. Introduction

1.1 Context of nixtamalization

The traditional nixtamalization is a centuries-old technique that involves the cooking of corn in an excess of water (3:1) and lime in a concentration of 1–3% w/w, and times from 30 min to 1 h depending on the hardness of the corn. After cooking, the grain is soaked for times from 12 to 24 h in the alkaline solution used for cooking, and a final rinsing of the cooked corn to remove cooking liquid and the pericarp of grains. The process discards the water used for cooking, which has a pH around 12. The product of nixtamalization, the cooked corn known as “nixtamal” is usually ground to create corn masa, the base for making tortillas [1]. Fresh masa is crafted in small local businesses, as well as in modern, highly efficient facilities in Mexico, and other countries of the American continent [2]. Additionally, fresh corn masa can be dried and ground to produce corn flour, which only needs to hydrate for different preparations [3]. The consumption of nixtamalized corn products also has been extended to other countries in Europe, Africa, and the Asian continent. The interest in nixtamalized products is based on their versatility and also its nutritional value, which includes calcium disponibility and important fiber content. On the other hand, industrial-scale production of nixtamalized corn flour (NCF) reduces the use of water, lime, and steeping time. It involves processing nixtamal, drying it, and subjecting it to multiple milling stages to achieve a fine particle size in the flour, resulting in a product that hydrates easily [4].

In our current context of consuming corn flour products, the traditional nixtamalization process continues to be an important method for producing corn masa, tortillas, and related items. However, industrial processes have evolved to optimize efficiency and product quality, making it more accessible to consumers. Additionally, there is a growing emphasis on sustainable and resource-efficient production methods, aligning with contemporary concerns about the environment and health.

The wet nixtamalization process represents a groundbreaking innovation in the traditional technique of nixtamalization. This modern approach involves cooking corn in a slurry of water and lime, and then using advanced extrusion technology to transform it into a versatile corn masa. This innovative method not only reduces the consumption of water but shortens processing time considerably. The resulting corn masa, rich in flavor and nutritional value, offers a sustainable alternative for producing tortillas and various corn-based products. Moreover, the fine particle size achieved through extrusion ensures that the masa hydrates easily, making it suitable for efficient large-scale production. This groundbreaking approach to nixtamalization opens the door to more resource-efficient and environmentally conscious methods of meeting the demand for corn flour products in our modern world.

2. Evolution of nixtamalization

Nixtamalization has undergone a significant evolution over the years, transitioning from a traditional technique to an innovative technologically driven process [5]. This evolution has led to the development of new methods that enhance efficiency [6], reduce resource consumption [7], and adapt to the dynamic demands of our contemporary world.

Emerging technologies addressing the environmental challenges associated with nixtamalization effluents have been introduced. Ramírez-Jiménez and Castro-Muñoz [8] have identified valuable applications for nejayote, a byproduct traditionally discarded during the washing process. Furthermore, alternative techniques, including rotary reactor with steam pressure, ohmic heating, microwave, and extrusion, which eliminates excessive water use through dry milling for starch gelatinization, have been thoroughly explored. The latter is particularly noteworthy for its ability to rapidly gelatinize starch and generate a significant amount of resistant starch, attributed to the abrupt changes experienced by starch molecules [9].

Table 1 presents various technologies proposed for use in the nixtamalization process. In contrast, the traditional method involves a high quantity of water and an extended processing time, encompassing multiple operations such as cooking, steeping, washing, and grinding. The alternative methods proposed operate at the industrial or semi-industrial level and aim to address ecological issues related to water waste and prolonged processing times, often involving modifications in the energy source.

Technology	Specifications	References
Traditional nixtamalization process	Nixtamalization at home involves cooking whole corn in a pot with a water to corn ratio of 3:1, adding 1–3% lime, and boiling for 30–60 minutes. After, cooking corn called nixtamal is steeping for 12–24 hours, and finally, it is washed and ground to create fresh masa.	[10]
	The industrial process in Mexico is also rooted in the traditional method, utilizing large kettles heated by gas to facilitate a semicontinuous process. This results in the generation of effluents typical of the traditional process. The nixtamalized corn flour industry has managed to reduce resting times to 4 hours. This reduction is attributed to the subsequent grinding of the material, inducing gelatinization through mechanical stress, followed by drying to produce instant corn flour.	[11]
Extrusion for nixtamalization with a single screw	The electrically powered equipment processes corn with lime and moisture, using minimal water for starch gelatinization and producing no effluents. It features a short residence time, a single screw mechanism with automatic feeding, simultaneous material transportation and mixing, all under controlled temperature and velocity. The final die shapes the nixtamalized masa for tortillas. Material transport and cooking occur in a heated chamber. A die induces final gelatinization, producing fresh corn masa. The process takes 1.5 to 7 minutes, with temperatures from 70 to 120°C.	[12]
Steam pressure by rotatory reactor	This method employs gas as a heat source to generate steam through combustion. The equipment includes time control to inject a steam flow, ensuring proper heat distribution in grains, with temperatures ranging from 130 to 300°C. Steam supply can be continuous or intermittent. Nixtamalization begins at 70°C and gradually increases to 90°C, inducing changes in corn grains. Additionally, there is a posttreatment step involving the cooling of nixtamalized material with water at 55°C.	[13]
Ohmic heating	Operating in batch mode with electric power, the equipment ensures temperature control through precise thermocouples and systematic power regulation. The principle involves passing an electric current through the food, rapidly heating a mixture of milling corn with minimal water and lime, resulting in the swift production of fresh masa in a matter of seconds.	[1]
Microwave oven	The kitchen-sized equipment operates in batch mode with limited processing capacity, incorporating controls for power and residence time. It utilizes electric energy to produce radiation for cooking corn grits with water and lime. A milling process follows to obtain fresh corn masa. However, this system lacks temperature control.	[14]
Low-shear transport system	This equipment is inspired by extrusion but departs from conventional screw-based transportation by utilizing rolls in the chamber. This change ensures a gentle mixing process, preventing excessive shear rates that could lead to over gelatinization. The method effectively produces fresh corn masa suitable for tortillas or chips. The raw material consists of ground corn mixed with lime and water, and the process operates at temperatures ranging from 75 to 90°C.	[15]

Table 1.

Diverse innovations in corn grain treatment: A comprehensive exploration of techniques.

Some of these methodologies are presently used in processing various foods with a few applied in industrial-level nixtamalization. However, a substantial portion of these alternatives still exists as laboratory prototypes. This is primarily attributed to technical challenges, including complexities in installation and difficulties in scaling up to an industrial or semi-industrial level. Conversely, accessible equipment, such as microwaves, is suitable for the general population, with limitations primarily related to processing capacity or accessibility in rural regions.

The methods described in Table 1 show a general overview of nixtamalization, and every technique has both advantages and disadvantages. However, of these technologies, extrusion is one of the most promising methods due to its versatility and its existence of commercial equipment in the market, which makes easier its use with different modalities of rate, moisture, particle size, die, temperature control, shear rate, and others.

2.1 Importance of innovation in the extrusion nixtamalization technology

In recent times, a groundbreaking innovation has emerged, known as “wet process extrusion nixtamalization.” This modern approach combines the principles of wet traditional nixtamalization with advanced extrusion technology. It involves cooking corn in a slurry of water and lime, and then using extrusion to transform it into a versatile corn masa. This innovation not only reduces water consumption but also significantly cuts down processing time. The resulting masa is not only efficient for large-scale production but also rich in flavor and nutritional value.

This evolution in nixtamalization aligns with our current concerns about sustainability and resource efficiency. The utilization of extrusion technology offers an environmentally conscious alternative while maintaining the authentic flavors and qualities of traditional nixtamalization. This transformation in the nixtamalization process reflects the adaptability and ingenuity of culinary traditions to meet the demands of our contemporary society. As we move forward, it is innovations, such as these that bridge the gap between tradition and innovation, ensuring that the essence of nixtamalization endures while catering to the evolving tastes and needs of our world.

3. Nixtamalization in wet extrusion grinding

3.1 Dry process vs. wet process

Nixtamalization is a traditional Mesoamerican food preparation technique used for the processing of maize (corn) into various products, most notably masa dough for making tortillas and other maize-based dishes. There are two primary methods of nixtamalization: the dry process and the wet process. These methods differ in their approach and the outcomes they yield. The differences between the two are the following:

3.1.1 Dry process

In the context of food extrusion, the “dry process” can be described as an extrusion method that relies on low water content. Maize kernels (whole or partially de-husked) are heated with a few quantity of water, but not completely dried or toasted. Therefore, we refer to dry process when humidity added is at most 30%. In the extrusion nixtamalization corn processing (ENP), dry milling is employed for size reduction, which necessitates a higher level of mechanical effort compared to the wet milling used in the traditional nixtamalization process (TNP). The elevated temperatures and reduced water content within the extruder expedite the gelatinization of starch granules [16]. Both the thermal impairment suffered by starch granules during the drying process and the mechanical damage resulting from dry milling significantly impact their functional properties. The importance of particle size in corn flour production cannot be overstated as it directly influences the gelatinization process and the ultimate quality of the product.

Dry milling is employed to produce both flour and germ, allowing for the optimal isolation of endosperm. This method exerts an abrasive force while removing the germ and pericarp layers. The resulting corn flour finds application in the production of snacks and extruded foods with semolina and various types of flour being the primary products derived from this process [17]. The isolated endosperm undergoes a size reduction process and is categorized based on particle size (coarse, medium, or fine). The moisture content is kept to a minimum, and the size reduction technique may involve various types of mills, including ball mills, hammer mills, or pin mills [18].

3.1.2 Extrusion in food using a screw

During the milling process, it is crucial to consider the type of force applied, whether it be impact, cutting, or compression. The friction generated within the mill depends on the spacing between volcanic stones and the time allocated to achieve the appropriate particle size distribution. This results in an increase in the temperature of the dough, typically ranging from 55 to 85°C, thereby promoting a secondary gelatinization process [19]. The particle size obtained, which is larger than that achieved in dry milling, allows for starch granules to be broken down or occasionally remain in their native state [20].

In contrast to the traditional nixtamalization process, where whole corn kernels undergo alkaline cooking, extrusion nixtamalization requires grinding and conditioning the corn having low moisture content lime. While this process does facilitate chemical interactions between calcium and corn components, it leads to more extensive starch damage due to the use of dry milling. The extent of starch damage depends on the specific equipment employed and the milling conditions applied as dry milling significantly disrupts the crystalline structure of starch granules.

3.1.3 Food extrusion using double screw

Food extrusion with double screws is a versatile and efficient food processing technique. It combines, cooks, and shapes ingredients simultaneously using twin screws. This process offers control over texture and expands product possibilities, making it ideal for snacks, cereals, and various food products. It is energy-efficient, adaptable for recipe customization, and allows for the addition of nutritional elements, all while ensuring consistent product quality through advanced monitoring systems [21].

3.2 Wet traditional nixtamalization process

The traditional nixtamalization is considered a wet process because it involves boiling maize kernels in an alkaline solution prepared with around three parts of water for each part of maize and using lime or ash in 1–3%. The key differences and characteristics of the wet traditional nixtamalization process include boiling in the alkaline solution, a resting of kernels in the cooking liquor (Nejayote) where through steeping time, the outer pericarp of corn grain is softened, and nutrient availability improved, such as calcium and essential amino acids [22]. Functionally, the pericarp of the corn is more easily removed during washing, and it makes it easier to grind into masa dough. All traditional nixtamalization involves a high quantity of water, which decreases the shear stress in grains and starch compared with the dry method. Besides, this wet process is extensively known in Mexico and other countries of America to produce masa with a neutral flavor profile and good machinability for applications to applications like making tortillas, or flours, as is shown in Figure 1.

Figure 1.

Traditional nixtamalization process (adapted from [10]).

During the traditional nixtamalization process, it is possible to have good-quality masa and tortillas; however, the waste of water is a big problem, as well as the loss of fiber of corn which is thrown away in nejayote. On the other hand, the functional and nutritional changes in corn grain and starch only can be reflected through a long time of cooking and steeping due to the use of whole kernels of maize [23]. The functional characteristics of corn masa obtained by nixtamalization include machinability to form the tortilla, with textural properties such as a high cohesion of corn masa, a medium hardness of corn masa, and low values of adhesiveness.

4. Operating factors and parameters in nixtamalization using extrusion

Extrusion nixtamalization in the past has been considered a process that can implicate an excess of shear stress in starch and other components of corn, which could negatively affect the quality of corn masa in terms of machinability and functionality. However, changes in the operating parameters can modify the quality of corn masa for different nixtamalized products, for example, corn chips or tortillas.

It is well knowing that the advantages of using extrusion for the nixtamalization include unit operations like mixing, transport, cooking, and forming, in addition to not generating polluting effluents. Furthermore, it leads to a reduction in space and energy requirements, minimal water consumption, and the proper mixing of ingredients [24]. On the other hand, trained personnel are required to handle the equipment, the standardization of the process, and the necessary preparation time demand careful attention. Adequate facilities are also needed [25]. Despite these challenges, the environmental and operational benefits make extrusion nixtamalization an appealing option in food production.

The challenge of applying extrusion for the nixtamalization process lies in the accessibility of the equipment, in extruders with different capacities, from home level to semi-industrial and industrial levels, acceptability of the population about the advantages of use of extrusion, and finally to find the better process parameters for production of nixtamalized products.

4.1 Nixtamalized corn masa parameters

The operating factors and parameters in corn masa composition for TNCF and ENCF include corn variety and quality. The type and quality of corn influences the flavor, texture, and nutritional value of the nixtamalized corn flour. Selecting a suitable corn variety with optimal is crucial [26, 27]. The nixtamalization process involves treating corn with an alkaline solution, usually lime (calcium hydroxide). Factors, such as lime concentration, soaking time and cooking temperature play a pivotal role in the flavor and nutritional content of nixtamalized masa [28]. Extrusion involves subjecting a whole flour of corn with a variety of particle sizes mixed with the lime in concentrations from 0.1 to 0.5% w/w and from 30 to 60% of moisture. The masa is mixed, heated, pressured, and transported with the screw and passing through a die, which implies a profile of shear forces on the corn components, mainly starch, that allow to obtain fresh corn masa. Parameters such as extrusion temperature, screw speed, and residence time impact the physicochemical changes in the masa, influencing its texture, functional properties, and flavor.

Functional properties are important parameters from a commercial point of view mainly for the instant nixtamalized corn flour industry, which demands a high-water absorption capacity of flours that increase the yield in terms of conversion from flour to corn masa for making tortillas [29]. The water absorption capacity is also related to the starch damage due to the process, and it significantly affects the textural properties such as hardness and adhesiveness of corn masa, and therefore the tortilla quality. The corn masa should have cohesiveness and low adhesiveness to ensure easier molding [30]. The grinding of nixtamalized corn is a critical step that influences the particle size and distribution in the resulting flour, functional properties, and machinability. A consistent grind ensures uniform hydration and texture in the dough. The grinding of nixtamalized corn is done through wet milling, leading to increased gelatinization and the release of hydrated granules. During this phase, water absorption primarily rises initially, facilitated by the removal of the pericarp (90%), allowing rapid calcium diffusion into the starch within the first 8 hours [31]. In the dry nixtamalization process (ENP), dry milling is employed for size reduction, requiring greater mechanical effort than wet milling used in the TNP. The starch granule undergoes thermal damage during the drying process, and mechanical damage occurs due to dry milling, significantly impacting its functional properties.

Corn kernels are cleaned and selected, and all parts, including the pericarp, are milled together. Achieving an appropriate particle size with a uniform distribution is crucial to prevent flow issues when introduced into the hopper. Dry milling is the commonly used technique for size reduction. A complete diagram of ENP is shown in Figure 2.

Figure 2.

Extrusion nixtamalization process (the authors). SS: Screw speed. FHS: Feed hopper speed. DS: Extrusion die size.

For the ENP, the selection of the base corn flour is crucial. Characteristics, such as particle size, moisture content, and starch properties, influence the extrusion process and the quality of the final product. Controlling the water content during the nixtamalization process and subsequent grinding is vital. It affects dough consistency, masa hydration, and the overall quality of the final product. Maintaining optimal moisture content in the extrusion process is essential for achieving the desired product attributes. Insufficient moisture can result in a dry texture, while excess moisture can lead to stickiness. So, the ground grain is combined with 0.3% (w/w) lime and has a moisture content ranging between 15 and 30%, depending on the purpose and operating conditions. The conditioned grain is then refrigerated for 12 hours at 5°C [9].

Another point to consider is the use of additives. Some traditional recipes include additives, such as salt, to enhance flavor or other ingredients to modify texture. Balancing these additives is crucial for achieving the desired characteristics in the nixtamalized corn flour. Some products, such as NEX-PLUS a dough conditioner available with or without bleach, facilitate a softer texture during the cooking and steeping of corn [32]. This additive extends the shelf life of the dough and tortillas without compromising taste or aroma. Its key features include preventing brittle edges, reducing sticking, and enhancing elasticity, and it does not interfere with lime. Discussing the benefits of NEX-PLUS, Enríquez-Castro and Contreras-Jiménez [33] achieved positive empirical results by using 40 to 60 g of NEX-PLUS per 25 kg of nixtamalized corn grain for producing “gorditas” (a type of corn tortillas filled with food or stews) in a commercial food establishment. Although the puffing grade was not measured, the clerk confirmed the achievement of a softer tortilla. The use of this additive is recommended all year long but is particularly beneficial during dry seasons, where almost all of the corn grain is produced through rainfed farming, especially in countries, such as Mexico.

In 2022 and 2023, the northern states, responsible for nearly 90% of corn grain production, experienced limited rainfall, approximately 27 mm according with the National Water Council of México. Consequently, this has led to a reduced corn yield, resulting in the production of older and harder grains, which are then sold to the corn and masa industry [34]. Incorporating specific additives, such as emulsifiers or stabilizers, can influence the rheological properties of the extruded nixtamalized corn flour. These additives may alter viscosity, elasticity, and overall dough behavior. Depending on the desired product, additives, such as emulsifiers, stabilizers, and fortifiers, may be included during the extrusion process. These additives influence the texture, shelf life, and nutritional content of the extruded nixtamalized corn flour.

Proper cooling and drying after extrusion are critical to set the final texture and prevent moisture-related issues. Careful control of these parameters ensures the stability and quality of the extruded product. In both traditional nixtamalized corn flour and extruded nixtamalized corn flour productions, a comprehensive understanding and control of these operating factors and parameters are essential for achieving consistent and high-quality results. The rate at which the extruded dough is cooled post-extrusion is crucial. It affects the setting and final rheological properties of the product. Proper cooling ensures the development of the desired texture [26].

Figure 3 displays two extruded corn pellets obtained with the same formulation but with different water content. This indicates that starch with lower moisture levels may undergo greater dextrinization and a darker coloration, which can affect the quality indicators of the ENCF. This type of flours exhibit reduced particle size, facilitating rapid water absorption into molecules. Several researchers attributed increased water absorption capacity in nixtamalized flours to the combined effects of milling and the extrusion cooking process [1, 25]. Thermal processing, a variable contributing to heightened damaged starch content, promotes resistant starch formation due to the loss of crystallinity during extrusion cooking [26]. Temperature fluctuations lead to significant resistant starch formation through hydrolysis and retrogradation. The amylose-amylopectin ratio in corn starch, and the impact of moisture content and temperature, play crucial roles in influencing the functional properties of nixtamalized flour, showcasing a high dependence on these factors in evaluating physical and rheological properties [18].

Figure 3.

A detailed image featuring two varieties of dried extruded corn pellets, each with the same composition but different moisture content (the authors).

4.2 Rheological properties

4.2.1 Traditional nixtamalization process (TNP)

Corn flour in TNP is intricately tied to the variables of time and temperature. The duration of the cooking process (8–12 h) and the temperature range (90–96°C) during nixtamalization significantly impact the rheological properties of the resulting dough. These properties, closely linked to viscoelastic parameters, such as elastic modulus and viscous modulus, play a crucial role in determining the quality of the final product [2].

Optimal conditions are paramount to ensuring the proper gelatinization of starch and protein interactions. The corn-to-water ratio during nixtamalization (1:3) directly influences the hydration of starch and proteins, thereby affecting the rheological behavior of the dough. The steeping step is a critical consideration; without proper attention, extended cooking times and prolonged steeping can lead to an increase in gelatinized starch and lower enthalpy values [35]. Allowing the nixtamalized corn masa to rest after preparation is essential for optimal rheological development. This resting period allows for hydration and relaxation of the masa structure. This, in turn, raises the gelatinization temperature and results in a more reorganized starch molecule, contributing to a higher degree of crystallinity retrogradation, shortening, and syneresis [28].

The particle size distribution following the grinding of nixtamalized corn is a key factor influencing dough viscosity and texture. The particle size distribution obtained in the traditional nixtamalization process generates particles ranging from medium to coarse. This allows for the presence of starch granules in their native structure, in contrast to dry corn milling, where the content of fine particles is higher, potentially causing greater damage to the internal conformation of the starch molecule. A more uniform grind generally leads to improved rheological properties. The theoretical expertise of the operator is particularly crucial in achieving optimal granulometry, as seen in Figure 4.

Figure 4.

Detailed image showcasing the milling and conditioning process of corn masa (with Tortillería Aguanaval permitted authorization).

4.2.2 Extrusion nixtamalization process

One of the factors that significantly impacts the process is the rise in temperature, as an elevated temperature entails a greater heat flow through conduction. This increase accelerates the fusion rate, resulting in a consequent reduction in the material’s viscosity, and consequently, the starch structure can be modified [9].

Extrusion is performed with low moisture levels (<30%), emphasizing that starch transformation relies more on the mechanical stress inside the extruder than on moisture. Moisture levels below 30% promote granule fragmentation and dextrinization, resulting in heightened extrudate expansion at the cost of crucial functional properties such as rheological, structural, and physicochemical characteristics. Notably, this includes impacts on solubility and water absorption rates [35]. According to Palanisamy et al. [36], an increase in barrel temperature and feed moisture leads to a reduction in the material viscosity within the extruder, directly affecting die pressure. In this scenario, the protein content played a significant role in influencing the response of the extruder.

The screw configuration significantly impacts melting efficiency, with three sections—feeding, transition, and metering. To minimize friction, a simple screw design with a large blade angle is crucial. The length-to-diameter ratio (L/D), measuring the enclosed screw portion, typically falls between 24:1 and 30 or 32:1. However, the appropriate ratio depends on the specific process and application. This ratio correlates with starch granule damage, with a higher L/D ratio causing more thermo-mechanical impact [37]. Figure 5 presents the sections of a single screw extruder used in the elaboration of foods and cereals.

Figure 5.

Sections of a single screw extruder (https://www.globalseafood.org [38]).

Three regions are located inside the extruder: transport, increase in volume (swelling), and melting/degradation. This third stage is where the greatest damage to the starch structure is generated. The effect produced by the use of heat combined with the application of mechanical stress weakens the structure of the starch granules, favors gelatinization, and increases the water absorption capacity [39, 40]. Another factor to consider is the moisture content used. Unlike wet milling that uses excess water, dry milling uses little water, which eliminates the protective effect of water [18]. Understanding and optimizing these operating factors and parameters are essential for achieving the desired rheological properties in both TNP and ENP. This knowledge is fundamental for ensuring consistent quality and meeting specific product requirements.

5. Relationship between nixtamalization and wet extrusion

5.1 Benefits of combining techniques

Utilizing nixtamalization in conjunction with extrusion enhances the bioavailability of calcium and niacin, facilitating the gelatinization of starch and the absorption of these compounds [41]. The extrusion nixtamalization process (ENP) reduces water activity, thereby extending the stability and shelf life of the products. The ENP achieves a more homogeneous and soft texture. Enríquez-Castro et al. [9] conducted a study comparing the texture of tortillas produced through two distinct processes. The measurements were taken at intervals of 2, 24, and 48 h. Surprisingly, there was no discernible difference in texture between the two processes at these time points, indicating that consumers did not perceive variations in palatability between the products. Notably, an important observation emerged after the initial measurement period. Extruded tortillas, when stored in the refrigerator, exhibited greater flexibility compared to their traditionally nixtamalized counterparts. This increased flexibility persisted for up to 7 days, highlighting the potential impact of extrusion on the extended shelf life of tortilla products (unpublished data). Importantly, there was no decomposition of the extruded tortillas within this timeframe, underscoring the significance of extrusion not only in maintaining texture but also in enhancing the overall durability and quality of the product over an extended period.

Extrusion is a rapid and efficient process that enables high-scale production, offering potential benefits to the food industry in terms of cost-effectiveness and enhanced performance. The combination of these two processes allows for the adjustment and personalization of corn masa properties, including texture, flavor, and nutritional profile, in line with consumer preferences. The study conducted by Platt-Lucero et al. [25] on the production of tortillas using ENCF revealed that various factors significantly influence the ultimate quality of the product. Among these factors, particle size, the milling process, and water absorption capacity play crucial roles. It is evident that the starch molecules, when subjected to successive milling, result in increased damage to the inner structure. This damage has a direct impact on the texture of the final product, highlighting the intricate relationship between these processing variables and the overall quality of the tortillas. Another advantage of using this technology is the reduction of mycotoxin levels in corn grain and the potential elimination of other pathogenic agents. Extrusion provides greater control over the production process, resulting in a more uniform corn masa with respect to both physical and nutritional characteristics.

5.2 Difference between HTST process and LTLT process

Extrusion cooking is a high-temperature short-time (HTST) method that utilizes temperature, pressure, and shear force to transform damp starchy and proteinaceous raw materials in low-density products with unique physicochemical characteristic [42].

In extrusion processing, HTST principles can be applied by subjecting the product to a rapid and intense heat treatment for a short duration. The extruder uses high temperatures, often exceeding 100°C, and the product spends only a brief time in the extrusion chamber. This approach is effective for achieving microbial reduction and ensuring food safety while preserving the sensory qualities of the product [43]. Conversely, LTLT principles in extrusion involve using lower temperatures during the extrusion process but extending the processing time. This allows for a more gradual heat application, potentially impacting the flavor, color, and texture of the final extruded product.

Choton et al. [44] conducted a study involving diverse extrusion treatments, revealing a direct correlation between the phenolic compounds content (TPC) and finger millet, as well as sorghum. Their findings indicated that by adjusting processing parameters such as feeder speed, moisture content, screw speed, and temperature, higher TPC levels could be achieved for both flours. Specifically, they reported values of 966.32 mg FE/100 g dw for finger millet and 506.71 mg FE/100 g dw for sorghum. This observation aligns with the conclusions drawn by other researchers, including Neder-Suárez et al. [45], Escalante-Aburto et al. [46], and Menchaca-Armenta et al. [47] who similarly identified the impact of processing parameters on the anthocyanin content in nixtamalized blue corn flour.

5.2.1 Impact on product quality in extrusion

HTST extrusion is commonly favored when maintaining the original characteristics of the product is crucial. It helps retain flavors, colors, and nutritional content, making it suitable for applications where sensory attributes are a priority. The extrusion process does not produce effluent, such as cooking liquor called nejayote. So, valuable compounds are retained, producing a whole corn flour to produce nixtamalized products. Enríquez-Castro et al. [9, 42] proved instrumental information in assessing and contrasting the texture and palatability of tortillas crafted from ENCF in comparison to commercially available corn flour and traditionally processed corn flour. Remarkably, the researchers identified no significant differences between the two products, noting consistent values in terms of texture and rollability across varying time intervals—specifically at 2, 24, and 48 hours.

The LTLT approach in extrusion may be chosen when a longer processing time at lower temperatures is acceptable or desired. It is crucial to recognize that prolonged exposure to heat can exert a significant impact on the quality of the product, potentially leading to variations in flavor profiles or textures. Additionally, when low-shear extrusion dominates the processing conditions within the extruder and is not appropriately established, there is a heightened likelihood of increased starch damage, ultimately yielding dextrinized starch. This underscores the importance of meticulously managing and optimizing extrusion parameters to ensure the desired product attributes and prevent undesirable alterations in starch composition [15].

5.3 Applications in extrusion

HTST extrusion is suitable for a range of heat-sensitive products, such as cereal-based snacks, where preserving the original attributes of the product is essential. LTLT extrusion may find applications in products where a more prolonged heat treatment is acceptable or where achieving specific textural or flavor modifications is desirable. The preconditioning phase of corn, undertaken prior to the extrusion process, proves highly effective in elevating the texture and rheological properties of the flour. This preparatory step is crucial as it sets the foundation for the subsequent transformation into masa, eventually leading to the production of tortillas [2]. The preconditioning stage in corn processing closely resembles the traditional steeping phase in nixtamalization. However, it deviates by utilizing a reduced amount of calcium, effectively eliminating the subsequent risk of contamination or discharge of cooking. Employing this meticulous technique not only optimizes the final texture of the product but also minimizes starch damage, resulting in a superior-quality end product.

The selection between HTST and LTLT principles in extrusion depends on the desired final product goals. HTST is favored for its efficient microbial reduction without compromising product quality, while LTLT is considered when extended processing time at lower temperatures aligns with the desired product characteristics. Adherence to regulatory standards and careful consideration of sensory attributes are paramount in making informed decisions, mirroring best practices in food processing.

In recent years, significant innovations in food extrusion and nixtamalization have emerged, revolutionizing the production landscape. A key focus has been on the development of novel products, cleaner production processes, and energy-efficient operations. One notable innovation lies in the creation of new food products through extrusion and nixtamalization. Researchers and food technologists have explored diverse raw materials and formulations, resulting in a wide array of extruded and nixtamalized products with enhanced nutritional profiles, textures, and flavors. These advancements have expanded the possibilities for offering consumers unique and healthier alternatives.

Cleaner production processes have also become a priority in the field. Efforts have been made to minimize environmental impact by optimizing resource utilization, reducing waste generation, and incorporating sustainable practices. Innovations in cleaning-in-place (CIP) systems, waste recovery, and efficient water and energy usage have contributed to a more environmentally friendly approach in both extrusion and nixtamalization processes.

Energy efficiency has become a central theme in the evolution of these technologies. Researchers have developed new extrusion and nixtamalization systems that maximize energy utilization while minimizing waste. This not only reduces operational costs but also aligns with the global push toward sustainable and eco-friendly practices in the food industry.

One groundbreaking development is the integration of nixtamalization and extrusion as a novel wet process for producing nixtamalized products. This combined approach leverages the benefits of both techniques, enhancing the nutritional quality and sensory attributes of the final products [48]. The synergy between nixtamalization and extrusion allows for more efficient processing, reduced cooking times, and improved textural characteristics, ultimately providing consumers with products that maintain traditional flavors while meeting modern dietary preferences [49].

Extrusion nixtamalization has been managed with a maximum of 30%, resulting in increased starch dextrinization due to the inflicted thermo-mechanical damage. Therefore, tests have been conducted to reduce the speed (rpm) while increasing the moisture percentage. This approach achieves maximum cooking, enhancing protein digestibility. Such extruded products may be ideal for formulating third-generation foods for fish, pets, pasta, and snacks. However, ongoing efforts are directed toward making it more suitable for the production of nixtamalized products. Additionally, implementing this technique in twin-screw extruders allows its use in producing high-protein meat analogs. When handling “chunked” corn kernels, the particle size is larger than that used in traditional nixtamalization. In this manner, broken corn kernels are processed, even though the moisture content can increase up to 45%, and cooking cycles may be repeated up to two or three times. Simultaneously, the equipment gradually reduces the temperature, requiring less water and lime than those used in the traditional process [50].

6. Conclusion

The continuous innovations in food extrusion and nixtamalization reflect a commitment to developing healthier products, adopting cleaner production processes, and achieving energy efficiency. The integration of nixtamalization and extrusion as a wet process further exemplifies the industry’s dedication to pushing the boundaries of traditional food processing, offering exciting possibilities for the future of food technology. The integration of extrusion and nixtamalization processes plays a pivotal role in transforming raw ingredients into a diverse range of food products. The choice between dry and wet processes, coupled with meticulous attention to dough composition, influences the quality and characteristics of the final extruded products. Various factors, including temperature, moisture content, and screw speed, significantly impact the efficiency of the extrusion process. Furthermore, in the corn and masa industry, a nuanced comprehension of the HTST and LTLT methods is indispensable. Each method offers specific advantages tailored to the unique requirements and desired outcomes of corn-based products. The intricacies of these techniques directly influence the quality, safety, and shelf life of masa, ensuring that the industry meets stringent standards and consumer expectations. Altogether, these considerations underscore the multifaceted nature of extrusion and nixtamalization in the food industry, highlighting their paramount importance in shaping the sensory, nutritional, and safety attributes of the end products.

Acknowledgments

The authors extend their thanks to all the people of the Food Industry Engineering Department of TECNM Campus Zacatecas Norte who provided support for this work. Also, thanks to Tortillería Aguanaval in Río Grande, Zacatecas, Finally, the authors extend their acknowledgment to TIA Food (Technology in Food Ingredients S.A De C.V) for supporting some of the investigations conducted.