Revising the role of pH and thermal treatments in aflatoxin content reduction during the tortilla and deep frying processes.

Naturally aflatoxin-contaminated corn (Zea mays L.) was made into tortillas, tortilla chips, and corn chips by the traditional and commercial alkaline cooking processes. The traditional nixtamalization (alkaline-cooking) process involved cooking and steeping the corn, whereas the commercial nixtamalization process only steeps the corn in a hot alkaline solution (initially boiling). A pilot plant that includes the cooker, stone grinder, celorio cutter, and oven was used for the experiments. The traditional process eliminated 51.7, 84.5, and 78.8% of the aflatoxins content in tortilla, tortilla chips, and corn chips, respectively. The commercial process was less effective: it removed 29.5, 71.2, and 71.2 of the aflatoxin in the same products. Intermediate and final products did not reach a high enough pH to allow permanent aflatoxin reduction during thermal processing. The cooking or steeping liquor (nejayote) is the only component of the system with a sufficiently high pH (10.2-10.7) to allow modification and detoxification of aflatoxins present in the corn grain. The importance of removal of tip, pericarp, and germ during nixtamalization for aflatoxin reduction in tortilla is evident.     

Assessment of Corn Quality for Nixtamalization: Development of a Convenient Bench‐Top Cooking Method

A convenient small‐scale laboratory method that can be used to simultaneously analyze multiple samples was developed to rapidly assess suitability of corn for nixtamalization. This new 100 g method was developed based on a previously reported 500 g laboratory process that has been shown to mimic the industrial nixtamalization process. The two methods were compared for nixtamal moisture, dry matter loss, degree of pericarp removal, and gelatinization properties of the cooked corn. The heating and cooling profiles of the 100 g method were developed using the 500 g method, by monitoring temperature every 30 s during cooking and steeping. Nixtamalization was conducted with a 1:4 corn/water ratio, with 1% lime. A response surface central composite design was used to model a wide range of processing conditions for the two methods: cook temperature (80–95°C), cook time (3–40 min), and steep time (2–12 h). Parameter estimates and response surfaces were compared, and predictive models were fitted. The response surface models for the two methods were not significantly different for nixtamal moisture, dry matter loss, and gelatinization enthalpy; there was an overlap of the 90% Bonferroni confidence intervals (P < 0.05, r ² > 0.7). The bench‐top 100 g nixtamalization process can successfully mimic the 500 g method over a wide range of processing conditions.     

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.     

Effect of processing conditions on phytic acid, calcium, iron, and zinc contents of lime-cooked maize

Tortillas are made by cooking maize in a lime solution during variable times and temperatures, steeping the grain for up to 12 h, washing and grinding it to a fine dough, and cooking portions as flat cakes for up to 6 min. The effects of the main processing steps on the chemical composition, nutritive value, and functional and physicochemical characteristics have been areas of research. The present work evaluates the effect of lime concentration (0, 1.2, 2.4, and 3.6%) and cooking times (45, 60, and 75 min) on phytic acid retention of whole maize, its endosperm, and germ, as well as on the content of calcium, iron, and zinc on the same samples. The effects of steeping time and temperature and steeping medium on the phytic acid of lime-cooked maize were also studied. Finally, phytic acid changes from raw maize to tortilla were also measured. The results indicated that lime concentration and cooking time reduce phytic acid content in whole grain (17.4%), in endosperm (45.8%), and in germ (17.0%). Statistical analyses suggested higher phytic acid loss with 1.2% lime and 75 min of cooking. Cooking with the lime solution is more effective in reducing phytic acid than cooking with water. Steeping maize in lime solution at 50 degrees C during 8 h reduced phytic acid an additional 8%. The total loss of phytic acid from maize to tortilla was 22%. Calcium content increased in whole maize, endosperm, and germ with lime concentration and cooking and steeping times. The increase was higher in the germ than in the endosperm. The level, however, can be controlled if steeping of the cooked grain is conducted in water. Iron and zinc contents were not affected by nixtamalization processing variables but were affected in steeping.     

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.     

Fate of fumonisins during the production of fried tortilla chips.

The fate of fumonisin B(1) (FB(1)), a mycotoxin found in corn, during the commercial manufacture of fried tortilla chips was studied. FB(1) and hydrolyzed FB(1) (HFB(1)) concentrations in four lots of corn and in the masa, other intermediates, liquid and waste byproducts, and fried chips were determined by HPLC. FB(1) concentrations in the masa and chips were reduced significantly, up to 80% in the fried chips, compared to that in the raw corn. HFB(1) was also found in the masa and chips, but at low concentrations compared to FB(1). LC-MS analyses corroborated HPLC findings and further showed the presence of partially hydrolyzed FB(1) (PHFB(1)), which, like HFB(1), was formed during the nixtamalization (cooking/steeping the corn in alkaline water to make masa) step and found predominantly in the cooking/steeping liquid and solid waste. No significant amounts of N-(carboxymethyl)-FB(1) or N-(1-deoxy-D-fructos-1-yl)-FB(1), indicative of fumonisin-sugar adduct formation, were found. Thus, FB(1) is removed from corn and diverted into liquid and waste byproducts during the commercial production of fried tortilla chips. Nixtamalization and rinsing are the critical steps, whereas grinding, sheeting, baking, and frying the masa had little effect.     

Study of Calcium Ion Diffusion in Nixtamalized Quality Protein Maize as a Function of Cooking Temperature

In this report, the effect of temperature on the calcium content of Quality Protein Maize (QPM H-368C) during the nixtamalization process as a function of the steeping time for three cooking temperatures (72, 82, and 92°C) is presented. Also, for the first time, we report in physico-chemical terms the end of the cooking stage during the nixtamalization process that was established when the moisture content in corn kernels reached a value of 36% (w/w) with a lime concentration of 1% (w/v), independent of the cooking temperature. Atomic absorption spectroscopy was used to determine the calcium concentration in the whole kernel and in its different anatomical components (pericarp, endosperm, and germ) as well as in 10% of the outermost layers, the next 10%, and the remaining 80% of the endosperm as a function of the steeping time. It was found that if the cooking temperature increases, the calcium content increases also. For steeping times in the range of 5–7 hr, a relative maximum was found in the calcium contents of 0.24, 0.21, and 0.18% (w/w) in QPM H-368 flours at 92, 82, and 72°C, respectively. Calcium was found in the most external layers in the endosperm and minimum diffusion occurs in the internal 80%. Phosphorous was measured by using UV spectroscopy and the results showed that it remains constant at 0.24% throughout the process. Scanning electron microscopy analysis was used to explain the calcium ion diffusion in the kernel. The physical changes in the pericarp govern the calcium diffusion process.     

Effect of nixtamalization (Alkaline cooking) on fumonisin-contaminated corn for production of masa and tortillas

Studies were undertaken to determine the fate of the mycotoxins, fumonisins, during the process of alkaline cooking (nixtamalization), using normal-appearing corn that was naturally contaminated with fumonisin B(1) (FB(1)) at 8.79 ppm. Corn was processed into tortillas, starting with raw corn that was cooked with lime and allowed to steep overnight; the steeped corn (nixtamal) was washed and ground into masa, which was used to make tortillas. Calculations to determine how much of the original fumonisin remained in the finished products took into consideration that FB(1) will be converted to hydrolyzed fumonisin B(1) (HFB(1)) by the process of alkaline cooking. All fractions, including steeping and washing water, were weighed, and percent moisture and fumonisin content were determined. Tortillas contained approximately 0.50 ppm of FB(1), plus 0.36 ppm of HFB(1), which represented 18.5% of the initial FB(1) concentration. Three-fourths of the original amount of fumonisin was present in the liquid fractions, primarily as HFB(1). Nixtamalization significantly reduced the amount of fumonisin in maize.     

Effect of Temperature and Steeping Time on Calcium and Phosphorus Content in Nixtamalized Corn Flours Obtained by Traditional Nixtamalization Process

This report shows the effect of temperature (72, 82, and 92°C) during the cooking stage and steeping time (0, 1, 3, 5, 7, 9, 11, 13, and 15 hr) on calcium and phosphorus contents in nixtamalized corn flours obtained by the traditional nixtamalization process (NCF). In addition, calcium and phosphorus contents in industrial nixtamalized corn flours were analyzed for comparative purposes. Atomic absorption spectroscopy and UV‐vis spectroscopy methods were used to study the calcium and phosphorus contents as well as the Ca²⁺/P ratio in NCF and industrial nixtamalized corn flours. Additionally, deposition and identification of calcium compounds in the nixtamalized corn pericarp were analyzed by low‐vacuum scanning electron microscopy, energy dispersive spectrometry, and X‐ray diffraction techniques. Dry matter loss in NCF is also reported. As the temperature increased, Ca²⁺ content was enhanced, while the phosphorus content decreased with statistical differences (P ≤ 0.05) between thermal treatments. Ca²⁺ content in industrial nixtamalized corn flours was significantly lower (P ≤ 0.05) than that of NCF. On the other hand, no statistical differences (P ≤ 0.05) were found between phosphorus content in commercial nixtamalized corn flours and NCF. Calcium compounds, identified as calcite, were detected in corn pericarp. Statistical differences (P ≤ 0.05) were observed in phosphorous content in NCF obtained at different cooking temperatures. In addition, a decrease in phosphorus levels significantly correlated with the steeping time at 92°C (r = –0.91). At 72, 82, and 92°C, the average Ca²⁺/P ratio in NCF was 0.45 ± 0.03, 0.61 ± 0.05, and 0.82 ± 0.05, respectively, indicating a correlation between this parameter and the cooking temperature. However, no correlation was found between the Ca²⁺/P ratio and the steeping time. This behavior is attributed to calcium attached to corn kernel. In commercial nixtamalized corn flours, the Ca²⁺/P ratio was significantly lower (P ≤ 0.05) than that of NCF. There was a significant correlation (P ≤ 0.01) between dry matter loss and steeping time (r = 0.99) in NCF, this fact influenced the Ca²⁺/P ratio due to the calcium attached to pericarp. At 82 and 92°C, maximum values of Ca²⁺/P ratio were detected in NCF at 7 hr of steeping time and at 9 hr at 72°C. These results can be used with industrial purposes to assess a maximum calcium‐to‐phosphorus ratio, and at the same time, to avoid the loss of pericarp to increase the functional properties of NCF.     

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).     

Influence of Kernel Damage on Corn Nutrient Composition,Dry Matter Losses,and Processability During Alkaline Cooking

The nutrient losses of corn containing 0–30% damaged kernels that occurred during alkaline cooking into tortillas were examined. Samples from different stages during processing were tested for chemical composition and protein fractionation. The most prevalent type of kernel damage was mechanical, followed in decreasing order by molds, insects, heat, and rodent damage. Corn with higher content of damaged kernels was susceptible to overcooking, resulting in cracked or fully open nixtamal kernels and sticky masa that were difficult to handle during processing. Nutrient losses increased with increasing levels of kernel damage. Most nutrient losses from sound corn kernels occurred during washing as the pericarp and attached solids were removed. During simmering, damaged corn kernels were fully cooked into physically opened kernels with more nutrients being extracted into the water. About 15% of total solids and 50% of both crude fiber and fat were lost during cooking of corn with 30% kernel damage. The greatest losses were consistently observed for albumins and globulins from both sound and damaged kernels at all stages of cooking. Appropriate control of kernel damage level is required to improve yield of product with consistent quality. The susceptibility to overcooking of excessively damaged corn increases the complexity to consistently meet product quality specifications. Excess dry matter losses in the cooking liquor can significantly increase the risk of environmental contamination and cost of sewage water treatment.     

Changes in Nixtamalized Corn Flour Dependent on Postcooking Steeping Time

We studied the effect of steeping time on various physical and chemical properties of maize flour prepared by the traditional nixtamalization process as well as in oversaturated calcium ion conditions. The calcium content of the corn flour was measured by atomic absorption spectroscopy and was correlated with X‐ray diffraction, viscosity, and pH measurements. Calcium content of the flour showed a nonlinear dependence on steeping time, with a local calcium maximum occurring at ≈7 hr. The pH level of the corn flour increased with steeping time, thus roughly following the time trend shown by the steeping time dependence of the calcium content. Flour crystallinity and peak viscosity of water suspensions of the flour reached maximal values at ≈7–9 hr of steeping, in agreement with manufacturing experience showing that these are appropriate steeping times to prepare tortillas with the desirable rheological and organoleptic properties.     

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.     

Study of Calcium Ion Diffusion in Components of Maize Kernels During Traditional Nixtamalization Process

Our report shows the calcium ion diffusion process through the different parts of maize kernels (pericarp, endosperm, and germ) during the traditional nixtamalization process as a function of steeping time (t) 0–24 hr. The cooking step of the nixtamalization process used 3 kg of maize kernels in 6L of water and 2% calcium hydroxide (w/w). The cooking temperature was 92°C for 40 min. The calcium content of the samples was measured using atomic absorption spectroscopy. We found that the whole instant corn flour, pericarp, endosperm, and germ, had a nonlinear relationship to steeping time, showing a local maximum at 9 hr. Analysis of the different parts of the nixtamalized kernels showed that in short steeping times (0–5 hr) calcium diffusion took place mainly in the pericarp. Calcium diffusion in the endosperm and germ occurred gradually over longer steeping times. However, the physical state of the kernels (broken kernels) accelerated the diffusion process. Calcium diffusion occurred first in the pericarp, followed by the endosperm and germ. Immediately after cooking (t = 0 hr), we found a 1.148% calcium content in the pericarp, 0.007% in the germ, and 0.028% in the endosperm. After 24 hr of steeping, the calcium contents were 2.714% in the pericarp, 0.776% in the germ, and 0.181% in the endosperm. In another study, the calcium content in the endosperm was measured by first separating the 10% from the outermost, followed by another 10% from the next endosperm tissue, and concluding with the remaining 80%. Calcium ions were present mainly in the outermost layers of the endosperm. The damaged kernels steeped for more than 5 hr showed greater calcium concentrations than the undamaged counterparts.     

Effect of Micronutrient Fortification on Nutritional and Other Properties of Nixtamal Tortillas

Nixtamalization is the process of steeping dried corn in hot water with calcium hydroxide (lime) with subsequent removal of all or most of the pericarp through washing. The resulting product is called nixtamal. Approximately 60% of corn tortillas in Mexico are produced from nixtamal, with the remainder prepared from nixtamalized corn flour. Nixtamal was fortified with micronutrient premix containing iron, zinc, folic acid, niacin, riboflavin, and thiamin. Premix composition followed a proposed Mexican regulation for corn flour fortification, adjusted for moisture. Effects of premix on masa adhesiveness, hardness, and pH, as well as tortilla sensory properties, stretchability, rollability, and color were measured. Micronutrient levels were tested in the dry corn, nixtamal, masa, and tortillas. There were no significant differences in masa texture or pH, tortilla rollability, or consumer acceptance of tortillas when comparing unfortified control and fortified treatments. Added thiamin was almost entirely degraded during processing. Folic acid and riboflavin decreased 26 and 45%, respectively, through the masa‐tortilla manufacturing process. Niacin showed no significant loss. Despite processing losses, fortification resulted in significant nutrient increases compared with control tortillas. Folic acid increased 974%, riboflavin increased 300%, niacin increased 141%, iron increased 156%, and zinc increased 153% in fortified tortillas.     

Analysis of Quality Protein Changes in Nixtamalized QPM Flours as a Function of the Steeping Time

This study showed the protein changes in Quality Protein Maize (QPM H‐368C) during the traditional nixtamalization process as a function of the steeping time from 0 to 15 hr. Protein content (N × 6.25), pH, protein fractionation, reactive lysine, essential amino acids, and protein digestibility were analyzed to explain the protein quality modifications in nixtamalized corn flours (NQF). The thermoalkaline process increased significantly (P ≤ 0.05) the protein content (5.57 ± 0.86%) in NQF obtained at 3, 5, 7, 9, 11, 13, and 15 hr of steeping time compared with native corn or corn without treatment (NC). The pH values of NQF were not proportional to the steeping time and significantly different (P ≤ 0.05) between them. At 5 hr critical steeping time, the total lysine and reactive lysine content decreased severely (36 and 32%, respectively) with statistical differences (P ≤ 0.05) compared with NC. On the other hand, the tryptophan content decreased significantly (P ≤ 0.05) at steeping times of 5–15 hr (38.70 ± 6.7%) compared with NC. The changes in the lysine and tryptophan content were not proportional to the steeping time. The protein recovery in the albumin and globulin fraction diminished (P ≤ 0.05) with respect to raw corn. The protein recovery for γ‐zeins, glutelin‐like proteins, glutelins, and residue increased. A significant (P ≤ 0.05) decrease was found in the essential amino acids in NQF with 3–7 hr of steeping time compared with NC. Equally important was the reduction in protein digestibility observed in NQF steeped at long steeping times (11–15 hr) with significant (P ≤ 0.05) differences compared with NC. The protein solubility distribution along the steeping step and the essential amino acids location, specifically lysine in corn kernel, could explain partially the protein quality changes observed in this research. Finally, these results contribute to reconciling discrepancies associated with the protein quality modifications in nixtamalized corn reported previously in literature.     

Effect of Broken Corn Levels on Water Absorption and Steepwater Characteristics

Broken corn created by grounding sound corn kernels was added back at levels of 0, 4, 8, 12, or 16%, by weight, to whole kernels of three corresponding hybrids: FR27 × FRMo17 (a soft endosperm corn), FR618 × FR600 (amedium‐hard endosperm corn), and FR618 × LH123 (a hard endosperm corn). The samples had been dried from 28% moisture content to 15% moisture content either by using ambient air at ≈25°C or at 110°C. Samples were steeped for 36 hr at 52°C in 0.15% sulfur dioxide and 0.5% lactic acid steeping solution. The steepwater characteristics, such as water absorption, solids and protein content in the steepwater, and steepwater pH, were measured by periodic sampling and analyzed. Broken corn level has a significant effect on the amount of solids released during steeping and steepwater protein content for all samples. Both steepwater solids and protein content increased linearly as broken corn content increased. Corn drying temperature, kernel hardness, and interactions between drying temperature and kernel hardness has a significant effect on steepwater solids and protein content and steepwater pH in both broken and unbroken corn. Corn dried at low temperature released more soluble solids and protein into the steepwater than corn dried at high temperature. Soft endosperm and medium‐hard endosperm corn released more soluble solids and protein into the steepwater than hard endosperm corn. Soft endosperm corn resulted in a higher steepwater pH than medium‐hard and hard endosperm corn. No significant effect of broken corn content on final moisture content of steeped corn and steepwater pH was observed.     

Response to lime and P by several genetic sources of corn (Zsa mays L.) on a low pH and P soil in the greenhouse 1

The objective of this study was to investigate the response of 16 different genetic sources of corn (Zea mays L.) to lime and P application on a low pH and P Parsons silt loam soil in the greenhouse. A highly significant lime x P interaction was found for both dry matter production and P concentration. Phosphorus increased both dry matter production and P content of plant tissues with or without lime application. However, liming produced a detrimental effect when P was applied but no effect when no P was applied. Corn genetic sources showed a highly significant interaction with P treatment, but not with lime for both dry matter production and P concentration. The results suggest that improvement in corn growth could be achieved in a low P soil environment by genetic selection.     

Effects of fertilizer factory effluent on soil and crop productivity

Laboratory experiments were conducted to evaluate the impact of various concentrations (2.5, 5, 10, 25, and 50%) of fertilizer factory effluent on certain physico-chemical properties of soil, and germination, growth, photosynthetic pigments, and dry matter productions of corn (Zea mays L.) and rice (Oryza sativa L.). The effluent was highly alkaline and contained high amounts of N⁺, Ca²⁺, Na⁺, Cl^?, CO _in3 ^su? , HCO _in3 ^su? and suspended and dissolved solids. Its BOD value was also high. The effluent treatment to soil resulted in a significant increase in the water soluble salts, electrical conductivity, cation exchange capacity, pH, N, Ca, Na, and Cl content of the soil for effluent concentrations of 10% and above. The effluent in the lower concentrations of 2.5 and 5 % enhanced the growth and development of corn and rice. Higher concentrations of effluent (10% and above), however, inhibited the percentage of seed germination and caused deleterious effects on the dry matter production, yield (quantitative and qualitative) and the photosynthetic pigments of both test crops.     

A Radioisotopic Study of the Entry of Calcium Ion into the Maize Kernel During Nixtamalization

The entry of calcium ions from the nixtamalization solution into maize kernels over time was followed in model experiments using radiolabeled calcium ions, with autoradiographic evaluation of the kernels after different cooking and steeping times. Calcium ions immediately entered the pericarp and were rapidly fixed at the outer boundary of the endosperm, especially at the external surface of the germ. Entry of calcium into the endosperm occurred gradually after long steeping times, except in the case of broken kernels, for which massive invasion by calcium was observed. After extended steeping times, a moderate amount of calcium‐45 was evident in the germ. Specific perforation of the outer layers of the grains provided a defined route of facilitated entry of calcium into the endosperm. No fundamental difference with respect to penetrability by calcium ion was seen in a comparison between flint‐type grains and grains containing only floury endosperm.