Assessing Degree of Cook During Corn Nixtamalization: Impact of Processing Variables

Nixtamalization involves cooking and steeping corn in a lime solution, washing the corn (nixtamal), and stone grinding nixtamal to form a corn dough or masa. Masa is used to produce nixtamalized products (corn tortillas, tortilla chips, corn chips, taco shells, etc.) by forming and baking or deepfat frying. The degree of corn kernel cook determines the quality and texture of masa. Response surface methodology (RSM) was used as an experimental design to study the impact of process variables (cook temperature, cook time, initial steep temperature, and steep time) on the degree of cook measured using a Rapid Visco Analyser (RVA) and differential scanning calorimetry (DSC). RSM data exhibited significant (P < 0.005), although not predictive, linear models for RVA peak viscosity (r² = 0.63), setback (r² = 0.61), final viscosity (r² = 0.61), and peak time (r² = 0.57), indicating a dependence of these parameters on nixtamalization conditions. Peak viscosity, setback, and final viscosity increased linearly with steep time. DSC enthalpy (r² = 0.83) and peak temperature (r² = 0.89) of freezedried masa also exhibited significant (P < 0.0001) linear regression models with processing variables. DSC enthalpy increased with an increase in steep time, suggesting that starch is annealed during steeping. This study demonstrated that fundamental starch properties were altered on extended steeping during nixtamalization.     

Nixtamalized Instant Flour from Corn (Zea mays L.) Meal: Optimization of Nixtamalization Conditions

The present investigation provides a new method for the nixtamalization process wherein corn endosperm fractions (corn meal) are treated in an alkaline solution that yields quality masa or instant masa flour like traditional nixtamalization process (alkaline cooking of corn with lime). The objective of this work was to determine the best combination of nixtamalization process variables for producing nixtamalized instant flour (NIF) from corn meal. Nixtamalization conditions were selected from factorial combinations of process variables including nixtamalization time (NT 8–22 min) and cooking temperature (CT 78–88°C). A central composite rotable experimental design was chosen. Lime concentration was 1% (10 g of Ca(OH)₂/L of water) and ratio of corn meal to cooking medium was 1:4. At the end of each cooking, each treatment was steeped for 5 hr at room temperature (25°C). Nixtamalized corn meal was dried (55°C/12 hr) and milled to pass through 80 U.S. mesh to obtain NIF. Response surface methodology (RSM) was applied as an optimization technique over four response variables: masa firmness (MF), masa adhesiveness (MA), tortilla cutting force (CF), and tortilla tensile strength (TS). Predictive models for response variables were developed as a function of process variables. Conventional graphic methods were applied to obtain response variable values similar to the control (MASECA). Contour plots of each response variable applied superposition surface methodology to obtain a contour plot for observation and for selecting the best combination of nixtamalization time (NT 15 min) and cooking temperature (CT 83°C) for producing an optimized NIF from corn meal. Values of MF, MA, CF, and TS obtained from the predictive models were compared with those derived from experimental tests; a close agreement (coefficient of variance < 10%) between both values was observed.     

Effects of Resistant Starch and Fiber from High‐Amylose Non‐Floury Corn on Tortilla Texture

A high‐amylose, non‐floury corn, a floury corn, and a 1:1 blend were made into masa and then tortillas. The masa flour made with the high‐amylose corn had a greater amount of resistant starch (RS 28.8%) and a greater amount of total dietary fiber (TDF 42.1%) than that with the floury corn (RS 2.9%, TDF 9.6%), producing a high‐fiber tortilla. The masa was evaluated for pasting properties using a Rapid ViscoAnalyser (RVA). The high‐amylose masa slurry gelatinized little at 95°C. The floury masa had the greatest peak viscosity, whereas the 1:1 blend was intermediate in value. Sensory evaluations of the tortillas for the textural attributes showed the floury tortillas to be chewier, more rollable, and grittier than the high‐amylose tortillas, whereas the blend tortillas were intermediate for most attributes. The cutting force of the high‐amylose tortillas, measured on a texture analyzer, was very low; the blend and floury tortillas required more force. Chewiness was correlated to rollability (r = 0.99, P = 0.05). The %RS and %TDF were correlated to rollability (r = –0.99), and cutting force (r = 0.99). The floury and blend tortillas had firm textures expected of desirable tortillas, whereas the high‐amylose tortillas broke under little force, and would not roll. The high‐amylose tortillas had high amounts of RS and TDF but poor texture. The blend tortillas retained most floury tortilla textural properties, making them suitable products for consumer use.     

Isolation and Characterization of a Soluble Branched Starch Fraction from Corn Masa Associated with Adhesiveness

A water‐soluble starch fraction isolated from corn masa and identified by HPSEC as predominantly fragmented amylopectin was highly correlated in amount to both masa adhesiveness (r = 0.890, P < 0.01) and cook time (r = 0.957, P < 0.01). The molecular weight of the component ranged from approximately 6.4 × 10⁵ to 1.2 × 10⁶, based on HPSEC column calibration with pullulan standards. Debranching with isoamylase illustrated that the structure of the soluble masa starch component was highly branched with a similar debranched profile to native amylopectin. Further analysis revealed that a minor amount of amylose was present in the second half of the broad HPSEC peak containing the fragmented amylopectin component. There was a high second‐order correlation (r = 0.998, P < 0.01) between the absorbance at the wavelength of maximum absorbance (λ_max) of the soluble fraction from masa (527–532 nm) and masa adhesiveness, indicating that a rapid assay for masa adhesiveness could easily be developed. Increasing the shear at the stone mill by reducing the gap setting between the stones, increased the amount of fragmented amylopectin. The high correlation between the amount of fragmented amylopectin and masa adhesiveness suggests that this fraction is the main determinant of masa adhesiveness. The amount of fragmented amylopectin can be controlled by cook time and gap between the stone plates of the mill.     

Extrusion of Cross‐Linked Hydroxypropylated Corn Starches I. Pasting Properties

A series of cross‐linked (0, 0.014, 0.018, 0.024, and 0.028% POCl₃, dry starch basis) hydroxypropylated (8%) corn starches were extruded using a Leistritz micro‐18 co‐rotating extruder. Process variables included moisture, barrel temperature, and screw design. Differential scanning calorimetry and X‐ray diffraction studies showed the level of starch crystallinity decreased with increasing severity of extrusion conditions. Pasting properties of the extruded starches were examined using a Rapid Visco Analyser. Pasting profiles of starches extruded at different conditions displayed different hot paste viscosity and final viscosity. Increasing starch moisture content during extrusion and level of cross‐linking increased starch viscosity (P < 0.0001), whereas increasing extrusion temperature and shear decreased starch viscosity (P < 0.0001). Interactions were found between level of cross‐linking and screw design and between extrusion temperature and starch moisture content (P < 0.0001).     

An Improved Process for Isolation of Corn Fiber Gum

Sequential alkaline extraction and alkaline hydrogen peroxide (AHP) bleaching have been used to prepare corn fiber gum in yields ranging from 21 to 40%, depending on the pH of the extraction medium. The pH was adjusted by using different ratios of NaOH and Ca(OH)₂ The whitest product was obtained after AHP bleaching of the extract obtained using the lowest pH value. In order for the product gum to give its characteristic clear and low viscosity solutions, it was necessary to remove starch from the corn fiber substrate using α-amylase. The water-insoluble hemicellulose A fraction, a minor component, was removed by neutralizing AHP-treated extracts before ethanol precipitation of the useful hemicellulose B (corn fiber gum) fraction. At ambient temperature, AHP bleaching was near optimal after ≈2 hr under the processing conditions used. High ratios of arabinose (39%) to xylose (50%) were present in the corn fiber gum extracted under various alkaline conditions, and the H₂O₂ processing step did not significantly alter these ratios. The same low levels of galactose (7%) and glucuronic acid (4%) were present regardless of the extraction conditions. Molecular mass of the corn fiber gum preparations ranged from 2.78 × 10⁵ for the material extracted with Ca(OH)₂ to 3.94 × 10⁵ for the material extracted with NaOH. Molecular mass was unaffected by the H₂O₂ present in the second processing step. As expected for a carbohydrate polymer with a rather low uronic acid content, solution viscosities were unaffected by the presence of salt.     

Evaluation of Bacterial Effects on Folic Acid Loss in Fortified,Nixtamalized Corn Masa Flour

Many Mexican women are deficient in folic acid. Fortification of the corn tortilla could be an effective way to help increase the folic acid levels among the Mexican population. Previous studies have shown significant folic acid losses in the masa dough as it is held before baking. This loss in folic acid could be owing to utilization by lactic acid bacteria naturally present in the masa. The objective of this study was to determine the effect of bacteria native to corn masa on the folic acid content in masa. Bacteria in dough samples from six mills in Guadalajara, Mexico, were isolated and identified. Bacterial isolates were inoculated into sterile fortified corn masa flour, which was converted to masa and held at 56°C for 0, 3, and 6 h, replicating the conditions of freshly milled masa as held before baking. All samples, including the control, showed losses of folic acid between 66 and 79% w/w in the first 3 h of incubation. Because folic acid degradation in the sterile control sample was not different than the inoculated sample results, the decline in folic acid was not owing to bacteria (mainly Streptococcus spp.) present in the masa flour but appeared to be a chemical degradation related to time and temperature.     

Alkaline Processing (Nixtamalization) of White Mexican Corn Hybrids for Tortilla Production: Significance of Corn Physicochemical Characteristics and Process Conditions

Five white corn hybrids were processed (nixtamalized) using 10 different processing conditions; tortillas were prepared to establish relationships between corn composition, physical characteristics, and nixtamalization process or product properties. Corn hybrids were characterized by proximate analysis and by measuring Stenvert hardness, Wisconsin breakage, percent floaters, TADD overs, thousand‐kernel weight, and test weight. Corn characteristics were correlated with process and product variables (effluent dry matter loss and pH; nixtamal moisture and color; masa moisture, color, and texture; and tortilla moisture, color, and rollability). Process and product variables such as corn solid loss, nixtamal moisture, masa texture, and tortilla color were influenced not only by processing parameters (cook temperature, cook time, and steep time) but also depended on corn characteristics. Significant regression equations were developed for nixtamalization dry matter loss (P < 0.05, r² = 0.79), nixtamal moisture (P < 0.05, r² = 0.78), masa gumminess (P < 0.05, r² = 0.78), tortilla texture (P < 0.05, r² = 0.77), tortilla moisture (P < 0.05, r² = 0.80), tortilla calcium (P < 0.05, r² = 0.93), and tortilla color a value (P < 0.05, r² = 0.87).     

Kinetic Approach to Nixtamalization of Corn Pericarp

The nixtamalization of the pericarp isolated from grains of corn was studied with 2, 5, 10, 20 and 40% Ca(OH)₂ based upon the mass of the pericarp. For 2 and 5% Ca(OH)₂ a small loss of the mass of the pericarp takes place quickly which is accompanied by an abrupt fall of the concentration of the OH^‐ ions. A suitable kinetic model for the decrease of the mass of the pericarp is a two phases exponential equation. The second phase is the slowest and it depends on the quantity of Ca(OH)₂ employed.     

Addition of Sodium Stearoyl Lactylate to Corn and Sorghum Starch Extrudates Enhances the Performance of Pregelatinized Beer Adjuncts

Double mashing for wort production is a time‐consuming process that can be reduced if pregelatinized adjuncts are used. Optimal extruding conditions were determined to obtain brewing adjuncts from corn and sorghum starch. For corn starch extrusion, a Box–Behnken design was devised in which moisture, screw speed, temperature of the barrel, and concentrations of sodium stearoyl lactylate (SSL) were varied, and sorghum starch was extruded according to a 2³ model in which the modified variables were moisture, SSL concentration, and temperature. The aim was to maximize starch damage and minimize resistant starch and final viscosity as determined with a Rapid Visco Analyzer. The treatments that satisfied these requirements were mashed, and wort extract yield was determined. Glucose, maltose, and maltotriose concentrations in the resulting worts were determined by HPLC with a refractive index detector. Feedstock tempering and SSL content were the most important factors affecting the response; for corn starch, treatments with lower moisture (20%) and middle levels of SSL (0.5%) or with high levels of both moisture (40%) and SSL (1%) produced the most desirable samples for mashing, whereas for sorghum starch the best treatment was tempering to 20% moisture and containing middle levels of SSL (0.5%). No statistical differences were found between these experimental treatments and the control.     

Comparison of Solubility of Corn Proteins in Propanol,Ethanol, and tert‐Butyl Alcohol Solutions on the Tortilla Process Samples

To find the best solvent of those reported and to study changes in protein aggregation during corn processing to obtain tortillas, extractability of corn proteins with three alcoholic solutions (70% ethanol, 50% propanol, and 60% tert‐butyl alcohol) was compared in corn, nixtamal, masa, and tortillas. Relative solubility was assessed through size‐exclusion chromatography, SDS‐PAGE, and insoluble polymeric protein determination using the Dumas procedure. Differences in the behavior of solvents in the samples indicate that different protein interactions are promoted during each of the processing steps. All the three alcoholic solutions can be used to study changes in corn proteins, but the best solvent was 50% propanol. Ethanol (70%) extracted the lowest amounts of corn proteins in tortilla process samples.     

Effects of Waxy Rice Moisture Content and Rate of CO2 Injection on Characteristics of Extruded Pellets and Vacuum‐Puffed Yukwa (a Korean Traditional Snack)

Extrusion with CO₂ injection was developed to simplify the process of producing vacuum‐puffed yukwa (rice snacks). The effects of feed moisture content and CO₂ injection on the characteristics of extruded pellets (maximum viscosity and degree of gelatinization) and vacuum‐puffed yukwa (expansion ratio, bulk density, hardness, and color) were investigated. Higher feed moisture increased the size of vacuum‐puffed yukwa and the degree of gelatinization, whereas the maximum viscosity decreased. Maximum viscosity and gelatinization degree of extruded pellets were highly correlated with expansion ratio, bulk density, hardness, and color values of vacuum‐puffed yukwa. Increasing feed moisture content significantly increased expansion ratio but decreased bulk density and hardness. CO₂ injection decreased bulk density and hardness of vacuum‐puffed yukwa.     

Coagulation Behavior and Floc Properties of Dosing Different Alkaline Neutralizers into the Fenton Oxidation Effluent

Neutralization is the necessary operation to ensure the Fenton effluent pH. In situ coagulation can be induced during neutralization. In this study, three types of alkaline neutralizers (Ca(OH)₂, NaOH, and Ca(OH)₂?+?NaOH) were added into the Fenton oxidized PSE to control the effluent pH of 6 to 9. The coagulation behavior, floc structure, and properties were investigated. The results indicated that the coagulation with the adding of three neutralizers can remove 9.68 to 24.02% of the TOC. Ca(OH)₂ exhibited the highest TOC removal efficiency at the dosage of 0.4 g/L. Charge neutralization ability was in the following order: Ca(OH)₂?>?Ca(OH)₂?+?NaOH?>?NaOH. Ca(OH)₂ and Ca(OH)₂?+?NaOH showed the increase of floc growth rate with the increase of agent dosage, especially for Ca(OH)₂?+?NaOH. Moreover, D_f of NaOH flocs was higher than that of Ca(OH)₂ and Ca(OH)₂?+?NaOH, indicating the floc formed by NaOH was more compact than that of Ca(OH)₂. The main coagulation process of three neutralizers was different, and it was also affected by the agent dosage (or pH). When the dosage was 0.35 g/L (pH 6–7.5), the complexation, adsorption, and bridging were the predominant processes while charge neutralization gradually became the main coagulation process for Ca(OH)₂ and Ca(OH)₂?+?NaOH with the increase of dosage (pH 7.5–9).     

Quality,Decontamination, and Energy Use Considerations During Radiant‐Heat and Tempering Treatments of Shelled Corn

Infrared (IR) heating of corn followed by tempering treatments has potential to decontaminate corn of microbes without adverse effects on the overall corn quality. However, it is vital to determine the optimal processing parameters that maximize throughput and microbial load reduction and minimize drying energy without affecting overall corn quality. This study investigated effects of IR heating and tempering treatments on mold load reduction, corn color change, and drying energy requirements. Freshly harvested corn samples with initial moisture contents (IMCs) of 20, 24, and 28% wet basis were dried with a laboratory‐scale IR batch dryer in one and two drying passes. The dried samples were then tempered for 2, 4, and 6 h at 50, 70, and 90°C. Results showed that mold load reduction ranged from 1 to 3.8 log colony forming units per gram of corn (log CFU/g) for one‐pass treatments and from 0.8 to 4.4 log CFU/g for two‐pass treatments as tempering temperature and tempering duration increased. Compared with the control, treatments resulted in reduction of the corn color parameter (ΔE ) (P < 0.05). Energy expended to dry the corn varied between 1.7 and 2.5 MJ/kg for one‐pass treatments and between 4.1 and 6.1 MJ/kg for two‐pass treatments. This work showed that IR heating of corn has the potential to significantly decontaminate microbes on corn. The IR process may help producers combat mycotoxin issues in corn that result from mold contamination.     

Development of Laboratory Techniques to Mimic Industrial‐Scale Nixtamalization

A laboratory nixtamalization process was developed to imitate larger scale cooking/steeping conditions. Corn (45 kg) was cooked in a pilot plant gas‐fired cook/steep tank and temperature was monitored every 30 sec. Cooling and heating rates were mimicked in the laboratory using a digital temperature programmable hot plate that adjusted grain‐water‐lime temperature changes at a specified rate. A Response Surface Central Composite Design was used to model pasting and thermal properties of nixtamal and masa as a function of cooking temperature (86–96°C), cooking time (20–40 min), and steeping time (3–11.77 hr). Nixtamal and masa moisture, dry matter loss, nixtamal and masa RVA peak temperature, shear thinning, nixtamal peak viscosity, masa final viscosity, nixtamal and masa DSC enthalpy peak and end temperatures, and nixtamal onset temperature were explained by the same regression terms for results obtained using both processes conditions. The intercept and slopes of the fitted models for the pilot plant and laboratory responses were not significantly different (P < 0.05). The laboratory method can be used to mimic larger scale processing over a wide range of nixtamalization conditions.     

Molecular Characteristics of Corn Fiber Gum and Their Influence on CFG Emulsifying Properties

The molecular characteristics of two purified arabinoxylan fractions derived from corn kernels, corn fiber gum-1 and -2 (CFG-1 and -2), have been studied and correlated with emulsifying properties. CFG-1 and -2 fractions were isolated from different corn fiber sources by 1) a sequential alkaline extraction and H₂O₂ bleaching to produce CFG-1; and 2) additional H₂O₂ treatment of the alkali-extracted residue at pH 11.5, yielding CFG-2. Multiangle laser light-scattering and online viscosity were used to measure the molar mass, polydispersity, structure compactness, and intrinsic viscosity of the generated CFG fractions. Emulsification properties in an oil-in-water emulsion system with 10:1 oil-to-gum ratio was investigated by measuring turbidity of an aliquot from the bottom of the diluted emulsion over 10 days. The isolated CFG-2 from each fiber source was higher in weight-average molar mass (M_w) polydispersity) (M_w/M_n) and structure compactness, and also lower in solution weight-average intrinsic viscosity (η_w) than the corresponding CFG-1. Average M_w and η_w values were 244–491 kDa and 1.35–1.84 dL/g, respectively. The emulsion stabilizing capacity of CFG-2 from each fiber source was superior to the corresponding CFG-1.     

Absorption of potassium,sodium, calcium,and phosphorus by two date palm cultivars and the effect of Gibberellin treatment

Experiments were conducted to avaluate the K, Na, Ca, and P uptake by seedlings of two date palm (phoenix dactylifera L.) cultivars, Khedhri and Sekkeri as well as the effect of gibberellin (GA₃) treatment, Khedhri cultivar showed a typical hyperbolic curve of absorption of K,N, end low concentration of Ca (up to 5mM) but at higher Ca concentration, there seems to be another phase of absorption. Sekkeri cultivar exhibited similar but lower absorption rate of K and Ca while Na seems to be extruded at lower substrate concentration. The rate of P uptake by Sekkeri was irregular. Applied GA₃ slightly stimulate Na uptake by Sekkeri cultivar but at 10^–4M GA₃ enhancement of both Ca and P accummulation in both cultivars was observed.     

Effects of Annealing and Concentration of Calcium Salts on Thermal and Rheological Properties of Maize Starch During an Ecological Nixtamalization Process

The objective of the present work was to study the effect of annealing and concentration of Ca(OH)₂ (lime) and calcium salts on the thermal and rheological properties of maize starch during an ecological nixtamalization process. Thermal and rheological properties of maize starch changed during the ecological nixtamalization process because of three main causes: the annealing phenomenon, type of calcium salt, and calcium salt concentration. In all treatments thermal properties (T_o, T_p, and T_f) of nixtamal starch increased owing to the annealing process, whereas the type of salt or lime increased thermal properties and decreased pasting properties in this order: CaCl₂ > CaSO₄ > Ca(OH)₂ ≈ CaCO₃. This behavior was because of the dissociation of each salt or lime in water. Anions (OH⁻) can penetrate much more easily into the starch granule and start the gelatinization process by rupturing hydrogen bonds. Additionally, amylose‐lipid complexes were formed during the nixtamalization processes, as indicated by an increasing peak at 4.5 Å in X‐ray diffraction patterns.     

Evaluation of Nutrient Release in Salt‐Saturated Soils

Abstract

The effects of irrigating with saline water on native soil fertility and nutrient relationships are not well understood. In a laboratory experiment, we determined the extent of indigenous nutrient [calcium (Ca), magnesium (Mg), potassium (K), manganese (Mn), and zinc (Zn)] release in salt-saturated soils. Soils were saturated with 0, 75, and 150 mmolc L^?1 sodium chloride (NaCl) solution and incubated for 1, 5, 10, and 15 days. The saturation extracts were analyzed for pH, ECe, and water‐soluble Ca, Mg, K, Mn, and Zn, and the remainder soil samples were analyzed for exchangeable forms of these elements. In a subexperiment, three soil types (masa, red‐yellow, and andosol) were saturated individually either with 100 mmolc L^?1 of NaCl, sodium nitrate (NaNO₃), or sodium sulfate (Na₂SO₄) salt. These salts were also compared for nutrient release. Soils treated with NaCl released higher amounts of water‐soluble than exchangeable nutrients. Except for Zn, the average concentrations of these nutrients in the soil solution increased significantly with time of incubation, but concentrations of the exchangeable forms varied inversely with time of incubation. The masa soil exhibited the highest concentrations of Ca and Mg, whereas K was highest in andosol. The extract from soils treated with NaCl contained greater amounts of soluble cations, whereas soils treated with Na₂SO₄ produced the lowest concentration of these elements irrespective of the type of soil used.     

Boron availability to plants from coal combustion by-products

Agronomic use of coal combustion by-products is often associated with boron (B) excess in amended soils and subsequently in plants. A greenhouse study with corn (Zea mays L.) as test plant was conducted to determine safe application rates of five fly ashes and one flue gas desulfurization gypsum (FDG). All by-products increased soil and corn tissue B concentration, in some cases above toxicity levels which are 5 mg hot water soluble B (hwsB) kg^?1 soil and 100 mg B kg^?1 in corn tissue. Acceptable application rates varied from 4 to 100 Mg ha^? for different by-products. Leaching and weathering of a high B fly ash under ponding conditions decreased its B content and that of corn grown in fly ash amended soil, while leaching of the same fly ash under laboratory conditions increased fly ash B availability to corn in comparison to the fresh fly ash. Hot water soluble B in fly ash or FDG amended soil correlated very well with corn tissue B. Hot water soluble B in fly ash amended soil could be predicted based on soil pH and B solubility in ash at different pH values but not so in the case of FDG. Another greenhouse study was conducted to compare the influence of FDG and Ca(OH)₂ on B concentration in spinach (Spinacia oleracea L.) leaves grown in soil amended with the high B fly ash. The Ca(OH)₂ significantly decreased tissue B content, while FDG did not affect B uptake from fly ash amended soil.