Changes in the thermal and structural properties of maize starch during nixtamalization and tortilla-making processes as affected by grain hardness

The objective of this work was to evaluate the changes in the thermal and structural properties of maize starch during nixtamalization and the tortilla-making process and their relationship with grain hardness. Three maize types with varying hardness (hard, intermediate, soft) were processed by three nixtamalization processes (classic, traditional and ecological). Starch from the three maize types showed an A-type pattern and two endotherms corresponding to gelatinization and melting of the Type I amylose-lipid complexes. After cooking and steeping, in intermediate and soft grains the partial gelatinization and the annealing affected the starch properties and promoted the formation of amylose-lipid complexes. These effects were not observe in hard grains. The increase in melting enthalpy and the intensity of the peak 2θ∼20° from nixtamal to tortillas demonstrated the formation of amylose-lipid complexes. A third endotherm above 114 °C in some treatments of nixtamal and tortilla starch demonstrated the transformation of some amylose-lipid complexes in a most ordered structures (Type II complexes). The V-type polymorph structure found in native starch, nixtamal, and tortilla corresponds to a coexistence of Type I and Type II complexes. Formation of amylose-lipid complexes in tortillas had a partial effect on decreasing starch retrogradation (r = −0.47, P < 0.05).     

Corn proteins solubility changes during extrusion and traditional nixtamalization for tortilla processing: A study using size exclusion chromatography

Changes in the solubility of corn proteins occurring during traditional nixtamalization and extrusion processes used to produce tortillas were studied using size exclusion chromatography, SDS-PAGE and the Dumas method to measure 50% propanol-insoluble protein. Size exclusion chromatography (HPL-SEC) studies furthered the understanding of protein solubility changes during both processes. Extrusion caused more protein aggregation in tortilla intermediate and final products than traditional nixtamalization. Mixing during extrusion and in the intermediate step of masa production in the traditional nixtamalization process was critical in reducing protein solubility. Baking tortillas also considerably reduced the protein solubility for the traditional nixtamalization process. Baking produced aggregation that could not be disrupted with a reducing agent.     

Effect of the nixtamalization with calcium carbonate on the indigestible carbohydrate content and starch digestibility of corn tortilla

There is a growing interest for an environment-friendly nixtamalization process. Nixtamalization with calcium salts generates a minimum level of polluting residues. The effect of a nixtamalization process with calcium carbonate (NCC) on the indigestible carbohydrate content and starch digestibility of tortillas was evaluated. Traditional and NCC tortillas showed lower moisture content than commercial tortillas. Similar protein, ash, and carbohydrate content were found for the three tortillas, but NCC tortillas showed the highest lipid content. The NCC tortilla had the highest dietary fiber content, with the highest insoluble dietary fiber level. Fresh and stored (96 h) NCC and traditional tortillas showed similar resistant starch content. Fresh traditional tortilla showed the highest slowly digestible starch (SDS), but upon storage the rapidly digestible starch (RDS) content of NCC tortilla decreased. Fresh traditional and NCC tortillas had lower predicted glycemic index (pGI) than commercial tortillas, and upon storage, the three tortillas presented lower pGI values than their fresh counterparts. Consumption of tortillas produced with the NCC can produce positive effects in the human health.     

Antioxidant Capacity and Antimutagenic Activity of Anthocyanin and Carotenoid Extracts from Nixtamalized Pigmented Creole Maize Races (Zea mays L.)

Nixtamalization process is the first step to obtain maize based products, like tortillas; however, in both the traditional and commercial processes, white grain is generally preferred. Creole maize races, mainly pigmented varieties, have increasingly attention since these are rich in anthocyanins and carotenoids. The aim of this investigation was to evaluate the antioxidant and antimutagenic activity of rich anthocyanins and carotenoids extracts from creole maize races before (grain) and after (masa and tortilla) the nixtamalization process. Most anthocyanins and carotenoids were lost during nixtamalization. Before nixtamalization, blue and red genotypes contained either higher antioxidant capacity and anthocyanin contents (963?±?10.0 and 212.36?±?0.36 mg of cyanidin-3-glucoside eq/100 g, respectively) than the white and yellow genotypes. However, the highest carotenoid levels were displayed by red grains (1.01?±?0.07 to 1.14?±?0.08 μg of β-carotene eq/g extract). Anthocyanins losses were observed when the blue grains were processed into masa (83 %) and tortillas (64 %). Anthocyanins content correlated with antiradical activity (r?=?0.57) and with 2-aminoanthracene -induced mutagenicity inhibition on TA98 and TA100 (r?=??0.62 and r?=??0.44, respectively). For white grains, nixtamalization also reduced carotenoids (53 to 56 %), but not antioxidant activity and 2-Aa-induced mutagenicity. Throughout the nixtamalization process steps, all the extracts showed antimutagenic activity against 2-aminoanthracene—induced mutagenicity (23 to 90 %), displaying higher potential to inhibit base changes mutations than frameshift mutations in the genome of the tasted microorganism (TA100 and TA98, respectively). The results suggest that even though there were pigment losses, creole maize pigments show antioxidant and antimutagenic activities after nixtamalization process.     

Effect of annealing from traditional nixtamalisation process on the microstructural,thermal, and rheological properties of starch and quality of pozole

Eleven maize landraces were evaluated for pozole quality. The microstructural, thermal and rheological properties of annealed starch granules determine most of the quality of pozole. Annealed starch in traditional nixtamalisation has an important role in increasing gelatinisation onset (To), peak (Tp) and final (Tf) temperatures; peak, setback and final viscosity as well as the stability of the starch granule, all of which significantly affect pozole quality. Annealed starch in Cacahuacintle nixtamal (pozole end-use) increased temperatures To, Tp and Tf by >5.2, >3.8 and >4.1 °C respectively, and narrowed the range Tf − To from 13.78 to 12.62 °C. The enthalpy was reduced from 6.76 to 5.85 J/g, while the nixtamal starch in tortilla maize landraces presented fewer annealing effects. The annealing effect in nixtamal starch seems to stabilize the starch granules and avoid their collapse, compared to native starch, as shown by the X-ray diffraction peak intensity and pattern that is similar to unprocessed maize. Starch in nixtamal changes from Type A to Type V pattern in pozole. Kernel physical parameters, although important, affected the quality to a lesser extent, with the exception of the flotation index. Cacahuacintle maize landrace showed the best quality and yield as well as a short pozole cooking time.     

Effect of annealing from traditional nixtamalisation process on the microstructural,thermal, and rheological properties of starch and quality of pozole

Eleven maize landraces were evaluated for pozole quality. The microstructural, thermal and rheological properties of annealed starch granules determine most of the quality of pozole. Annealed starch in traditional nixtamalisation has an important role in increasing gelatinisation onset (To), peak (Tp) and final (Tf) temperatures; peak, setback and final viscosity as well as the stability of the starch granule, all of which significantly affect pozole quality. Annealed starch in Cacahuacintle nixtamal (pozole end-use) increased temperatures To, Tp and Tf by >5.2, >3.8 and >4.1 °C respectively, and narrowed the range Tf − To from 13.78 to 12.62 °C. The enthalpy was reduced from 6.76 to 5.85 J/g, while the nixtamal starch in tortilla maize landraces presented fewer annealing effects. The annealing effect in nixtamal starch seems to stabilize the starch granules and avoid their collapse, compared to native starch, as shown by the X-ray diffraction peak intensity and pattern that is similar to unprocessed maize. Starch in nixtamal changes from Type A to Type V pattern in pozole. Kernel physical parameters, although important, affected the quality to a lesser extent, with the exception of the flotation index. Cacahuacintle maize landrace showed the best quality and yield as well as a short pozole cooking time.     

Rheological and thermal properties of masa as related to changes in corn protein during nixtamalization

Traditional nixtamalization process produces a masa (dough) with appropriate cohesiveness and adhesiveness. Masa is considered as a network of solubilized starch polymers with dispersed, uncooked and swollen starch granules, cell fragments, proteins and lipids. In this work, the influence of proteins on the masa viscoelastic behavior was studied in corn kernels under different nixtamalization conditions. Scanning electron microscopy, SDS-PAGE, differential scanning calorimetry and rheological analysis were used to characterize the corn samples. The micrographs showed that the nixtamalization modified the shape of the starch granules and protein bodies, but no changes in appearance were observed when protein was removed. SDS-PAGE showed that corn proteins polymerized during cooking. Lime promoted both calcium–protein and protein–calcium–protein interactions mainly by calcium bridges, which were difficult to disrupt and increased the protein thermo-resistance. In the absence of lime, corn proteins polymerized mainly by disulfide bond cross-linking. Thermal analysis (DSC) indicated that the gelatinization temperature increased in lime-treated samples compared to control samples. Rheological studies showed that the corn protein exhibited greater influence on gel strength by enhancing the elastic character of the samples (G′). These results suggested that polymerized corn proteins stabilized the gel structure, which in consequence influenced the viscoelastic behavior of masa.     

Physicochemical, Rheological and Structural Characteristics of Starch in Maize Tortillas

Fresh and stored maize (white and blue) tortillas were evaluated for physicochemical, rheological and structural characteristics assessed by calorimetry, x-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, dynamic viscoelastic tests, and high-performance size-exclusion chromatography. Two endotherms were found in studies of fresh and stored tortillas. The low temperature endotherm (50–56 °C) was due to reorganized (retrograded) amylopectin, while the high temperature endotherm (105–123 °C) was attributed to retrograded amylose. The enthalpy value for the lower temperature transition was minor than that of the high temperature transition. Fresh tortillas showed an amorphous starch arrangement by x-ray diffraction study. Stored samples showed the presence of peaks at 2θ = 17o and 23o, indicating re-crystallization of starch components. FTIR results confirmed the development of higher levels of starch crystals during storage. Differences in the viscoelastic parameters were also observed between fresh and stored samples. At the longest storage times, white tortillas were more rigid than blue tortillas. Molar mass values for starch increased for both white and blue tortillas as storage time progressed, though relatively higher values were obtained for white tortillas. More starch reorganization occurred in white tortillas, in accordance to calorimetric, x-ray diffraction, FTIR and rheological results. These results corroborate that changes occurring in tortillas during storage are related to reorganization of starch components, and the maize variety more than the color plays an important role.     

Gelation characteristics of Mesona chinensis polysaccharide-maize starches gels: Influences of KCl and NaCl

An investigation was conducted into the effects of potassium chloride (KCl) and sodium chloride (NaCl) on the gelation properties of maize starch-Mesona chinensis polysaccharide (MCP) gels. Waxy maize starch (WS), normal maize starch (NS), and high amylose maize starch (HS) were used to compare the effects of different amylose contents on the gel properties of maize starch-MCP gels. The results showed that KCl and NaCl have similar effects on the gelation, rheological, and structural properties of maize starch-MCP gels. The addition of KCl and NaCl increased the pasting viscosity, breakdown values, setback values, dynamic modulus, and apparent viscosity of maize starch-MCP gels, especially for HS-MCP gels. LF-NMR (Low-field nuclear magnetic resonance) showed that salts reduced bound water content while increasing the free water content of maize starch-MCP gels. CLSM (Confocal laser scanning microscopy) results also indicated that salt can restrict the expansion and maintain the integrity of starch granules, especially for WS-MCP gels.     

Production of nixtamalized flour and tortillas from amarantin transgenic maize lime-cooked in a thermoplastic extruder

The potential use of quality protein transgenic maize (genetically modified maize with the cDNA of amarantin) for preparation of flour and tortillas through an extrusion lime cooking process was investigated. Tortillas from extruded transgenic maize flour had similar physicochemical and sensory properties than those from the commercial brand MASECA™; however, the former had the highest (P < 0.05) protein content (12.91 vs 8.93%, db), essential amino acids content, calculated protein efficiency ratio (C-PER; 2.27 vs 0.90) and protein digestibility corrected amino acid score (PDCAAS; 55.54 vs 30.18%) and therefore they were nutritionally better. The use of transgenic maize for flour and tortilla preparation through an extrusion lime cooking process may have a positive impact on the nutritional status of people from countries where maize is the basic staple food. It also represents an alternative process to nixtamalization that requires little energy and water, it does not generate wastewater, and all components of the maize kernel are retained.     

Stability of anthocyanins of blue maize (Zea mays L.) after nixtamalization of seperated pericarp-germ tip cap and endosperm fractions

Most naturally occurring foods that are sources of anthocyanins are often processed under severe temperature, pressure, and pH conditions that may extensively alter the naturally occurring pigments with loss of their potential antioxidant properties. It is desirable that anthocyanins present in pigmented maize not be completely destroyed when producing processed products. In the present study, the effect of different concentrations of calcium hydroxide used in the nixtamalization after fractionation process on the stability of the pigments found in blue maize was evaluated. The anthocyanin profile was analyzed using HPLC. The total anthocyanin content as well as that of acyl-type anthocyanins decreased during the cooking process and as the concentrations of calcium hydroxide used increased (P<0.001). More anthocyanin was retained in the nixtamalization after fractionation process with 0.5% calcium hydroxide than in the traditional nixtamalization process. In maize cooked and nixtamalized with up to 1.5% calcium hydroxide, only 16.1% of the acyl-type anthocyanin remained, compared to between 32 and 38% in the original uncooked maize. Conversely, the cyanidin and pelargonidin anthocyanin content increased.     

Effect of Lime and Wood Ash on the Nixtamalization of Maize and Tortilla Chemical and Nutritional Characteristics

The objective of the study was to obtain information on the chemical composition, functional properties, sensory quality and protein value of tortillas made from the nixtamalization of maize using either lime or wood ashes. The Ca, K, Mg, Fe, and Zn content of lime and wood ashes showed lime to be high in Ca content while wood ash contained more K and about 71% of the Ca content of lime. Both contained relatively high levels of Mg, Fe and Zn, but more so in the wood ashes. The level of reagent for nixtamalization was set at 0.8% of the maize weight. All other processing conditions were kept constant. The pH of the cooking solution was 12.0 for lime and 10.9 for wood ash. The moisture content of maize at 60 min of cooking was 45.8% for both treatments, however after 12 h of soaking, moisture level was 51.0% for the lime treatment and only 46.8% for the ash treatment. Solids (2.4%) in the lime cooking liquor were higher than in the wood ash liquor (1.0%). Chemical composition changes were similar between treatments in masa and tortilla; however, both masa and tortillas absorbed relatively high levels of all minerals including Fe and Zn from the wood ash treatment. The different treatment influenced functional properties particularly hardness and color. Tortilla characteristics were also similar. Protein quality of both alkali cooked products was lower than that of raw corn, more so the product from the wood ash treatment. Although some differences were observed in the sensory studies, human subjects did not dislike the wood ash made tortillas.     

Pasting,thermal and rheological properties of octenylsuccinylate modified starches from diverse small granule starches differing in amylose content

Waxy maize (a standard starch of normal granule size) and five small granule starches from different botanical sources (rice, wheat B type, oat, quinoa and amaranth) were subjected to 2-octenyl-1-succinic anhydride (OSA) modification. Changes of pasting, gel texture, thermal and rheological properties were investigated. Different small granule starches showed quite different property changes after OSA modification. Pasting viscosity was generally increased in OSA starches, among which OSA oat starch had notably high peak and breakdown viscosity but low setback viscosity. Gel hardness of rice, wheat B type, oat and quinoa starches was reduced by OSA treatment, whereas that of waxy maize and amaranth starches was increased. Amylose content was considered to be the major factor influencing pasting, gel and thermal property of OSA starches. Esterification increased pseudoplastic flow behavior of all starches, while OSA oat starch uniquely had reduced flow consistency coefficient. The dynamic rheological properties were also changed differentially among OSA starches. Viscoelastic properties of rice, wheat B type, oat and quinoa starches were increased after OSA treatment, whereas those of waxy maize and amaranth starches were decreased. This study showed that diverse functionalities from OSA small granule starches may fulfil different demands in product development.     

Production of bioethanol from steam-flaked sorghum and maize

The aim was to study the effect of steam-flaking of sorghum and maize on bioethanol production and the performance of their ground meals during liquefaction, saccharification and yeast fermentation. A bifactorial experiment with a level of confidence of P < 0.05 was designed to study differences between sorghum and maize and the effectiveness of steam-flaking. Grains were steam-flaked to increase starch bioavailability and disrupt the protein matrix that envelopes starch granules. The steam-flaked sorghum had significantly higher and faster starch hydrolysis compared to the regular kernel during liquefaction. This hydrolysate contained about 33% more reducing sugars compared to the untreated counterpart and similar amounts compared to both maize treatments. At the end of saccharification, the sorghum spent grains contained more residual starch compared to the maize counterparts. Steam-flaking significantly reduced residual starch especially in steam-flaked sorghum. The final glucose concentration in steam-flaked sorghum was similar to the concentration obtained in both maize mashes and 26.5% higher compared to the untreated sorghum. The yield of ethanol in steam-flaked sorghum was 44.2% higher compared to the untreated counterpart and similar to both maize treatments. Therefore, steam-flaking is a treatment useful to increase ethanol production especially in sorghum due to the higher starch bioavailability.     

Effect of zein extrusion and starch type on the rheological behavior of gluten-free dough

Previous research has shown that zein, above its glass transition temperature, may adopt molecular structures that are able to form doughs with viscoelastic properties comparable to those of wheat gluten. It is hypothesized that extrusion can promote molecular changes in zein and favor interactions with starch that enhance dough viscoelasticity. Thus, the effects of extruding zein at 90–160 °C on the rheological properties of doughs prepared with potato, rice, and maize starches were determined.Formulations were optimized to provide similar mixing profiles to that of a standard wheat dough. For all zein samples, creep-recovery tests demonstrated that doughs prepared with maize and potato starches were less elastic when compared to doughs prepared with rice starch. Zein doughs produced using rice starch were comparable to wheat-dough. Extensional tests showed that zein extruded at 160 °C provided a larger increase in strain-hardening behavior, which is important for bread production. These samples also exhibited larger extensional stresses. Gel electrophoresis of zein extruded at 160 °C revealed an increase in protein aggregates and the presence of smaller peptides when compared to samples subjected at lower extrusion temperatures.Scanning electron micrographs of doughs containing zein showed starch granules embedded within an amorphous material and fibrous structures, which is attributed to elongated zein.     

Carotenoid composition and antioxidant activity of tortillas elaborated from pigmented maize landrace by traditional nixtamalization or lime cooking extrusion process

Mexican pigmented maize (Zea mays L.) landrace kernels have been scantily evaluated regarding potential as functional food. In this study, eight Mexican pigmented (yellow and red) maize accessions of Tuxpeño, Tabloncillo and Chapalote landraces collected in the northwestern region of Mexico were processed into tortilla to determinate carotenoid profiles, as well as their Oxygen Radical Absorbance Capacity for Lipophilic extract (ORAC-L). The total carotenoid content ranged from 3.66 to 5.56 mg LE/kg DW in the yellow maize and from 1.49 to 3.49 mg LE/kg DW in the red maize among all raw genotypes. Lutein and zeaxanthin were major carotenoids in all pigmented maize, accounting for ∼85% of total carotenoids. The traditional nixtamalization and lime-cooking extrusion process significantly (p < 0.05) decrease total carotenoid and ORAC-L assays when compared to raw kernels. Traditional tortillas retained among 72.0–87.6% and 65.1–78.8% of total carotenoids and ORAC-L levels respectively, compared to 68.8–79.5% and 60.3–75.5% assayed in extruded tortillas. Interestingly, traditional and extruded tortillas maintained more 72.7 and 60%, respectively; of the lutein concentration associated with raw grains. Our results suggest that yellow maize landrace could be considered for the elaboration of nixtamalized food products with nutraceutical potential.     

Effect of instantaneous controlled pressure drop (DIC) on physicochemical properties of wheat, waxy and standard maize starches

Standard maize starch (SMS), waxy maize starch (WMS) and wheat starch (WTS) were hydrothermally treated by the Instantaneous Controlled Pressure Drop (DIC) process. This process consists in a short pressurisation obtained by the injection of saturated steam at fixed pressure during a predetermined time followed by a sudden pressure drop towards vacuum. The effects of DIC conditions on thermal characteristics, enzyme susceptibility, pasting (Brabender) and rheological properties of treated starches were investigated. For treated starches, an increase of transition temperatures (T_o and T_p), a narrowing of the width of gelatinization endotherms and a decrease of the gelatinization enthalpies (ΔH) were observed as the severity of processing conditions increased. WMS, SMS and WTS showed a significant increase in enzymatic hydrolysis after treatment. The saccharification yield showed an increase from 19% (native) to 44%, 21% (native) to 59% and 55% (native) to 79% for SMS, WMS and WTS, respectively. The study suggests that the structural modifications due to the previous DIC treatment influence the in-vitro hydrolysis and the access to the ultrastructure of starch granules; the susceptibility to hydrolysis increases from SMS to WMS and WTS. For all treated starches, the decrease in peak viscosity and in apparent viscosity was related to the processing conditions.     

Simulating the formation of bread crust in a DMTA rheometer

Water evaporates very fast from the surface layers of dough, enhanced by high heating rates at the beginning of baking. The rheological properties of the surface layers play an important role during the baking process, especially in local and overall expansion and water loss. The aim of this study was to determine the rheological properties of bread dough in the heat-moisture dynamics of the baking process, especially in surface drying and delayed drying conditions. The DMTA method was used in tensile mode in order to expose the samples to fast dehydration to simulate real bread crust. The degree of starch gelatinization was demonstrated by the disappearance of the “Maltese cross” (polarized light microscopy). Temperature and water content were monitored during baking. The modulus evolution depended on both the heat and moisture evolution (i.e. immediate or delayed in the present study). In contrast to reports in the literature, starch gelatinization was observed even under drying conditions. Nevertheless, comparison between samples under drying and under delayed drying conditions suggested that water content prevailed in the rheological changes.     

Phenolic Acids Profiles and Cellular Antioxidant Activity in Tortillas Produced from Mexican Maize Landrace Processed by Nixtamalization and Lime Extrusion Cooking

Phenolic acids profiles, chemical antioxidant activities (ABTS and ORAC), as well as cellular antioxidant activity (CAA) of tortilla of Mexican native maize landraces elaborated from nixtamalization and lime cooking extrusion processes were studied. Both cooking procedures decreased total phenolics, chemicals antioxidant activity when compared to raw grains. Extruded tortillas retained 79.6–83.5%, 74.1–77.6% and 79.8–80.5% of total phenolics, ABTS and ORAC values, respectively, compared to 47.8–49.8%, 41.3–42.3% and 43.7–44.4% assayed in traditional tortillas, respectively. Approximately 72.5–88.2% of ferulic acid in raw grains and their tortillas were in the bound form. Regarding of the CAA initially found in raw grains, the retained percentage for traditional and extruded tortillas ranged from 47.4 to 48.7% and 72.8 to 77.5%, respectively. These results suggest that Mexican maize landrace used in this study could be considered for the elaboration of nixtamalized and extruded food products with nutraceutical potential.     

Microstructural changes in the maize kernel pericarp during cooking stage in nixtamalization process

The microstructural changes in the maize pericarp during the critical lime-cooking step of a traditional nixtamalization process are reported. Scanning Electron Microscopy at low vacuum (SEM-LV) images and Energy Dispersive Spectrometry (EDS) were used to study the evolution of the pericarp transformation during lime-cooking and the CaCO₃ formation on the pericarp. Moisture content in cooked maize kernels and calcium content in the pericarp were used as physicochemical criteria in order to establish the end of the cooking step. For the first time, the cooking step was analyzed in situ by using a differential photoacoustic cell (DPC), in order to associate photoacoustic amplitude signals of nixtamalized pericarp with its structural modifications. X-ray diffraction patterns of nixtamalized pericarp showed an increase in the peak intensity of the crystalline fraction compared with the native pericarp. These results were supported by SEM images and amplitude signals obtained through the use of the photoacoustic technique.