Analysis of Headspace Volatiles of Corn Gluten Meal

Corn gluten meal is the high‐protein fraction from wet milling of corn. Although protein, minerals, and fat compositions have been reported, minor components that cause unpleasant flavor and taste are not known. The objective of this study was to determine the compounds present in headspace of corn gluten meal and wet cake (dryer feed). A solid‐phase microextraction device with a polyacrylate coating was used to collect volatiles for 1 hr at 25 and 100°C above a stirred water slurry of corn gluten meal or wet cake. The absorbed compounds were desorbed onto the inlet injector of a gas chromatograph equipped with a mass selective detector. Compound identification was done using a Wiley library and confirmed by retention time of pure compounds in the gas chromatograph. Twenty‐nine compounds were identified. Knowledge concerning volatiles of corn gluten meal may lead to improvement of flavor and taste, and increased utilization of this material, produced over 1 million metric tons per year in the United States.     

Pilot-Plant Wet-Milling Process for Producing Corn Gluten Meal

A pilot-plant wet-milling process was specially used to produce corn gluten meal (CGM) with a relatively high protein content (49.8% from Pioneer 3394 and 53.7% from Wilson D110). The protein content of the CGM obtained from a starch table in our pilot-plant procedure was similar to the results obtained by using the hydrocyclone method. Wilson D110 has a higher protein content in its corn kernels, producing higher yield and protein content gluten than the Pioneer 3394, which has lower protein content in the corn. The effects of drying method and temperature on the color of CGM were also discussed.     

Effect of Hydrophilic Plasticizers on Thermomechanical Properties of Corn Gluten Meal

The glass transition temperature and rheological moduli of plasticized corn gluten meal (CGM) were determined with dynamic mechanical thermal analysis (DMTA). The tested plasticizers were water, glycerol, polyethylene glycols (PEG) 300 and 600, glucose, urea, diethanolamine, and triethanolamine, at concentrations of 10–30% (dwb). The glass transition temperature (T_g) of CGM, measured at 188°C when unplasticized, was lowered by >100°C at 30% plasticizer content, except by PEG 600 and glucose, which showed limited compatibility with CGM proteins. The highest plasticizing efficiency, on a molar basis, was measured with PEG 300 and was attributed to the large number of hydrophilic groups and the high miscibility of this compound with CGM proteins. The change in T_g due to the plasticizing effect was modeled with the Gordon and Taylor equation, but a better fit of the experimental data was obtained with the Kwei equation.     

Corn Gluten Meal Odorants and Volatiles After Treatment to Improve Flavor

Production of corn gluten meal (CGM), a high‐protein coproduct from wet milling of corn, is increasing as production of fuel ethanol from corn increases. Unpleasant taste and odor have limited the use of CGM in human food. Adjustment of pH and extraction with water have been reported to reduce the off‐flavor of CGM but the improvement is not enough for substantial addition of CGM to the human diet. More study of CGM is needed. In this study, volatile compounds released under different conditions of pH, water extraction, and temperature were identified and compared using solid‐phase microextraction‐gas chromatography‐mass spectrometry (SPME‐GC‐MS). The water‐extractable portion, which improves the taste of CGM by its absence, was dried and analyzed by SPME‐GC‐MS. In addition, materials extractable from CGM with methylene chloride were identified by gas chromatography‐mass spectrometry (GC‐MS). Further, the spontaneous generation of a CGM‐like odor accompanied by a change in physical appearance of the CGM sample was described. Flavors and odors known to be associated with the identified CGM compounds were listed. Some possible origins of the volatiles, from degradation of corn constituents or as fermentation products of the corn steeping process, were noted.     

Factors Affecting Yield and Composition of Zein Extracted from Commercial Corn Gluten Meal

Twelve corn gluten meal samples obtained from six wet-milling plants were processed into zein. Zein was extracted using 88% aqueous isopropyl alcohol at pH 12.5, followed by chilling. Protein recovery ranged from 21.3 to 32.0%, and protein purity ranged from 82.1 to 87.6%. Protein recovery increased as the protein purity increased (r = 0.76) (P < 0.01). One of the major factors influencing extraction yield was protein composition; especially α-zein content, which ranged from 53.4 to 64% of the total protein in the corn gluten meal samples. The intensity of red color of the corn gluten meal was negatively correlated with protein recovery and zein purity (r = -0.66 and -0.72, respectively) (P < 0.02).     

Effects of Lysine on Growth of Tilapia Fed Diets Rich in Corn Gluten Meal

Tilapia is a warmwater fish with mild flavor. Nearly 8.6 million kg are produced domestically, and ≈22.7 million kg are imported. Corn gluten meal (60% protein fraction) is a product obtained from wet-milling of corn. Diets (36% protein) containing 36–44% corn gluten meal with different levels of lysine and fish meal were formulated and fed to tilapia in aquaria for 12 weeks. Weight gain (WG) of tilapia fed diets containing the highest level of lysine (7.4% protein) with 4% fish meal was equal to that of fish fed a commercial control diet. Diets with lower lysine resulted in lower WG. The feed conversion ratio (FCR) and protein efficiency ratio (PER) of tilapia fed experimental diets containing adequate levels of essential amino acids and fish meal were the same as for fish fed the commercial control diet (also containing fish meal). Fish fed diets containing lower lysine levels had less favorable FCR and PER. This study shows that corn gluten meal is utilized at high levels in tilapia diets, particularly if essential amino acids are provided in adequate amounts.     

Corn Gluten Meal as a Thermoplastic Resin: Effect of Plasticizers and Water Content

Corn gluten meal (CGM) was studied to investigate the effect plasticizers and water have on its melt processing, and how this melting affects its mechanical properties. GCM containing varying amounts of water were mixed with 23% (w/w) plasticizers; (glycerol, triethylene glycol (TEG), dibutyl tartrate, and octanoic acid in a Haake bowl mixer at 80°C. The amount of water in the CGM affected the amount of torque produced in the Haake mixer. This increase in torque was correlated with how well the CGM melted in the mixer. SEM images of CGM melted in the mixer showed a more uniform homogenous structure when processed at its optimum moisture content. Glycerol, TEG, and dibutyl tartrate produced the greatest torque when the CGM contained <1% water. Octanoic acid produced the greatest torque when the CGM was processed at 8% moisture. CGM plasticized with TEG and octanoic acid were mixed at either their optimum moisture or at 9.6% moisture and then compression molded into tensile bars. The tensile strengths of the bars that were mixed at their optimum moisture content were significantly greater than the bars mixed at 9.6% moisture. The tensile properties of the CGM samples were affected by relative humidity (rh). The tensile strength decreased and elongation increased as relative humidity increased. CGM plasticized with TEG saw a greater changes in its tensile properties due to relative humidity than did octanoic acid plasticized CGM.     

Effects of Extrusion and Starch Removal Pretreatment on Zein Proteins Extracted from Corn Gluten Meal

In this study, the structure and selected properties of zeins extracted from corn gluten meal (CGM) pretreated by extrusion and removal of starch were investigated. The structure and properties of the zeins from pretreated CGM changed significantly. Pretreatments can decrease the extraction yields of zeins and change the granule shape and size of zein aggregates. The studies indicated that extrusion and removal of starch can significantly decrease the thermal enthalpy (ΔH₁ and ΔH₂) of zein from 1.94 ± 0.20 to 0.19 ± 0.10 and from 107.20 ± 0.80 to 78.62 ± 2.30 and J/g, respectively. The SDS‐PAGE results confirmed that the molecular weight of zeins from CGM was 24,000 and 27,000, and the molecular weight of zeins did not change with the pretreatment. On the other hand, the circular dichroism spectroscopy results showed that the processing of extrusion and removal of starch can change the secondary structure content of β‐sheets and β‐turns; these results indicated that extrusion and removal of starch can significantly break the secondary structure of zeins. Furthermore, extrusion and removal of starch can change the sulfhydryl content of zeins. The obtained results provided some fundamental information that is useful for further modification of CGM to improve its functional properties and industrial applications.     

Improved Isolation of Zein from Corn Gluten Meal Using Acetic Acid and Isolate Characterization as Solvent

An improved means of isolating zein is needed to develop new uses for corn zein. We have measured the yield of zein and evaluated the ability of acetic acid to remove zein from corn gluten meal, distillers dried grains, and ground corn using acetic acid as solvent. Acetic acid removed zein more quickly, at lower temperatures, and in higher yields when compared with alcoholic solvents. After 60 min at 25°C, ≈50% of the zein in corn gluten meal was removed. A step change in yield from 43 to 50% occurs as the extraction temperature is increased from 40 to 55°C after mixing for 30 min at 25% solids. The protein composition of the zein removed from corn gluten meal using acetic acid is very similar to that of commercial zein by SDS‐PAGE. The zein obtained from corn gluten meal using acetic acid had higher amounts of fatty acids and esters according to IR analysis, leading to slightly lower protein content. Films made from zein extracted from corn gluten meal using acetic acid had lower tensile strength (≈60% lower) than films produced from commercial zein. Fibers with very small diameter (0.4–1.6 μm) can be produced by electrospinning using the AcOH solution obtained after corn gluten meal extraction.     

Development of New Method for Extraction of α‐Zein from Corn Gluten Meal Using Different Solvents

A modified procedure for the extraction of α‐zein from corn gluten meal was developed and compared against a commercial extraction method. The modification involved raising the concentration of alcohol in solvent and removing the precipitate by centrifugation. Five organic solvent mixtures were compared using the modified extraction procedure developed along with the reductant sodium bisulfite and NaOH. The modified procedure precipitated most of the non‐α‐zein protein solids by increasing the concentration of alcohol. The supernatant had α‐zein‐rich fraction, resulting in higher yield of α‐zein than the commercial method when cold precipitated. The commercial extraction procedure had a zein yield of 23% and protein purity of 28% using 88% 2‐propanol solvent. The three best solvents, 70% 2‐propanol, 55% 2‐propanol, and 70% ethanol, yielded ≈35% of zein at protein purity of 44% using the modified extraction procedure. Zeins extracted using the novel method were lighter in color than the commercial method. Densitometry scans of SDS‐PAGE of α‐zein‐rich solids showed relatively large quantities of α‐zein with apparent molecular weights of 19,000 and 22,000 Da. The α‐zein‐rich solids also had small amounts of δ‐zein (10,000 Da) because it shares similar solubility properties to α‐zein. A solvent mixture with 70% 2‐propanol, 22.5% glycerol, and 7.5% water extracted significantly less zein (≈33%) compared to all other solvents and had α‐zein bands that differed in appearance and contained little to no δ‐zein.     

Gluten Enhances Cooking,Textural, and Sensory Properties of Oat Noodles

Whole grain oats are widely regarded as conferring significant health benefits. Composite flour of whole grain oat flour, wheat flour, and tapioca starch in the ratio 1:1:0.16 was formulated to make oat noodles with the addition of gluten at various levels. The influence of gluten on pasting and gelling properties of composite flour, and on cooking, textural, and sensory properties of salted oat noodles was evaluated. Addition of gluten decreased the paste viscosity, reduced hardness and springiness of gel, reduced cooking yield, cooking loss, and broken ratio during cooking, and increased the tensile strength and firmness of cooked noodles. Scanning electron microscopy showed that gluten tightened the network of protein in the noodles by forming oriented fibrils. Addition of gluten had little effect on the color of raw and cooked oat noodles, which were somewhat yellow. Sensory evaluation indicated that addition of gluten could enhance the overall acceptability of cooked oat noodles. This study may stimulate further interest in using functional whole grain cereal ingredients in developing healthy staple foods.     

Mixograph Responses of Gluten and Gluten‐Fortified Flour for Gluten Produced by Cold‐Ethanol or Water Displacement of Starch from Wheat Flour

The total protein of gluten obtained by the cold‐ethanol displacement of starch from developed wheat flour dough matches that made by water displacement, but functional properties revealed by mixing are altered. This report characterizes mixing properties in a 10‐g mixograph for cold‐ethanol‐processed wheat gluten concentrates (CE‐gluten) and those for the water‐process concentrates (W‐gluten). Gluten concentrates were produced at a laboratory scale using batter‐like technology: development with water as a batter, dispersion with the displacement fluid, and screening. The displacing fluid was water for W‐gluten and cold ethanol (≥70% vol, ‐12°C) for CE‐gluten. Both gluten types were freeze‐dried at ‐10°C and then milled. Mixograms were obtained for 1) straight gluten concentrates hydrated to absorptions of 123–234%, or 2) gluten blended with a low protein (9.2% protein) soft wheat flour to obtain up to 16.2% total protein. The mixograms for gluten or gluten‐fortified flour were qualitatively and quantitatively distinguishable. We found differences in the mixogram parameters that would lead to the conclusion of greater stability and strength for CE‐gluten than for W‐Gluten. Differences between the mixograms for these gluten types could be markedly exaggerated by increasing the amount of water to the 167–234% range. Mixograms for evaluation of gluten have not been previously reported in this hydration range. Mixograms for fortification suggest that less CE‐gluten than W‐gluten would be required for the same effect.     

Farinograph Responses for Wheat Flour Dough Fortified with Wheat Gluten Produced by Cold‐Ethanol or Water Displacement of Starch

The objective of this research was to identify and define mixing characteristics of gluten‐fortified flours attributable to differences in the method for producing the gluten. In these studies, a wheat gluten concentrate (W‐gluten) was produced using a conventional process model. This model applied physical water displacement of starch (dispersion and screening steps), freeze‐drying, and milling. W‐gluten was the reference or “vital” gluten in this report. An experimental W‐concentrate was produced using a new process model. The new model applied coldethanol (CE) displacement of starch (dispersion and screening steps), freeze‐drying, and milling. Freeze‐drying was used to eliminate thermal denaturation and thereby focus on functional changes due only to the separation method. The dry gluten concentrates were blended with a weak, low‐protein (9.2%), soft wheat flour and developed with water in a microfarinograph. We found that both water and cold‐ethanol processed gluten successfully increased the stability (St) and improved mixing tolerance index (MTI) to create in the blended flour the appearance of a breadbaking flour. Notably, in the tested range of 9–15% protein, the St for CE‐gluten was always higher then the St for W‐gluten. Furthermore, the marginal increase in St (slope of the linear St vs. protein concentration) for the CE‐gluten was ≈57% greater than that for the W‐gluten. The slope of the MTI vs. protein data was lower for the CE‐gluten by 24%. Flour fortified with CE‐gluten exhibited higher water absorption (up to 1.8% units at 13.5% P) than flour fortified with W‐gluten.     

Influence of Particle Size on the Twin-Screw Extrusion of Corn Meal

Effects of particle size (50–1,622 μm), screw speed (200–400 rpm), and feed moisture content (19–22%) on twin-screw extrusion of corn meal were investigated using a full-factorial design. Torque, specific mechanical energy, and product temperature generally showed no change within the commonly used particle-size range (100–1,000 μm), but each value dropped significantly as the particle size increased >1,000 μm. Die pressure was influenced by the three-way interaction of particle size, screw speed, and feed moisture content. The highest moisture level (22%), largest particle size (1,622 μm), and two lowest screw speeds (200 and 300 rpm) were the only conditions where the starch was <97.5% of transformation (gelatinization). Consequently, these two conditions also showed the least expansion and hardest product.     

Effects of Calcium Hydroxide and Processing Conditions on Corn Meal Extrudates

The effects of added calcium hydroxide (0.0, 0.15, 0.25, and 0.35%) and processing conditions, feed moisture content (mc) (16, 18, and 20%) and barrel temperature (130 and 150°C) on characteristics of corn meal extrudates were studied. Extruder screw speed was maintained at 130 rpm. Corn meal was extruded with a single-screw extruder (Brabender model GNF 1014/2) with a screw compression ratio of 3:1. The highest values (P < 0.05) for radial expansion and the lowest values for density and breaking force of extrudates were found for the treatment with 0.00% calcium hydroxide extruded at 16% feed mc and 130°C barrel temperature. This treatment was statistically different from the other treatments. Best values for radial expansion of samples extruded with added calcium hydroxide were for the samples with 0.15% calcium hydroxide at 18% feed mc and 130°C barrel temperature, followed by the sample with 0.35% calcium hydroxide at 16% feed mc and 130°C barrel temperature. Water absorption index and water solubility index were affected by calcium hydroxide and extrusion conditions evaluated. Extrudates had large numbers of flattened and sheared granules. Increases in calcium hydroxide increased extrudate yellowness. The combined action of calcium hydroxide and extrusion conditions completely modified the organized structure of the starch and suggest the formation of a starch-calcium complex (crystalline region). The texture of the extruded products was crispy after puffing.     

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.     

Effect of Iron Source on Color and Appearance of Micronutrient‐Fortified Corn Flour Tortillas

Iron deficiency anemia is a widespread occurrence. Consequently, iron is commonly added in cereal fortification programs. However, many iron sources cause undesirable sensory changes, especially color changes, in the food being fortified. This study evaluated the effect of different iron sources on CIE L*a*b* color values and sensory color perception in fortified corn tortillas. Corn masa flour was fortified with micronutrient premix containing vitamins, zinc, and one of eight iron compounds. Iron sources included ferrous fumarate (F), ferrous sulfate (S), ferric orthophosphate (OP), ferrous lactate (L), ferrous gluconate (G), ferric pyrophosphate (PP), sodium iron (III)‐EDTA, and A‐131 electrolytic iron (E), with addition levels adjusted based on bioavailability. Control (Ct) samples were prepared with all micronutrients except iron. All iron‐fortified tortillas had lower L* values and were significantly darker than control tortillas. Based on instrumental color values and Mexican regulatory recommendations, five treatments were selected for further testing. A difference‐from‐control sensory test was conducted comparing PP, E, OP, F, and S with Ct tortillas. Sensory rankings were C t > E = PP > OP > F > S. A‐131 electrolytic iron is recommended for fortification of corn tortillas due to minimal effect on color and significantly lower cost than other iron sources evaluated.     

Combining Maltogenic Amylase with CMC or Wheat Gluten to Prevent Amylopectin Recrystallization and Delay Corn Tortilla Staling

Antistaling properties of a bacterial maltogenic amylase, sodium carboxymethylcellulose (CMC), and vital wheat gluten on quality of corn tortillas were evaluated during 14 days of storage. Amylopectin recrystallization was the driving force behind the staling of corn tortillas. Increasing levels of recrystallized amylopectin measured by differential scanning calorimetry (DSC) correlated significantly with increased tortilla stiffness (r = 0.43) and reduction in tortilla pliability (r = ‐0.42) during storage. Maltogenic amylase (275–1,650 activity units) made tortillas less stiff but did not preserve pliability and extensibility as effectively as CMC (0.25–0.5%). The combination of 825 MANU of maltogenic amylase (to interfere with intragranular amylopectin recrystallization) and 0.25% CMC (to create a more flexible intergranular matrix than retrograded amylose and amylopectin) produced less stiff, equally flexible, and less chewy tortillas than did 0.5% CMC. Vital wheat gluten was not as effective as CMC in preserving tortilla flexibility or as good as the maltogenic amylase in reducing stiffness. Further research is required to optimize the addition of maltogenic amylases in continuous processing lines that use fresh masa instead of nixtamalized corn flour (NCF) and to determine how these amylases interfere with amylopectin recrystallization.     

Water Solubility and Macromolecular Properties of Corn Meal Extrudates as Affected by Epichlorohydrin

Degermed corn meal adjusted to 18% moisture content (db) with epichlorohydrin (ECH) content at 0, 0.5, 1, or 2% (w/w) were extruded with a twin-screw laboratory extruder at a screw speed of 140 rpm. Compression and metering barrel zones were set at 100, 120, or 140°C. Water solubility (WS) of ground extrudates ranged from 7.6 ± 1.1% to 14.3 ± 1.3%. ECH content had a significant (P < 0.01) negative effect on WS, while barrel temperature and the interaction between barrel temperature and ECH content were not significant (P > 0.05). Presumably, ECH reduced WS of extrudates through cross-linking between hydroxyl groups on starch and protein molecules. Gel-permeation chromatography patterns for both 100 and 140°C barrel temperatures showed that high molecular weight carbohydrates in the extrudates decreased with increasing ECH content without a simultaneous increase in low molecular weight carbohydrates. This suggested that the decrease in high molecular weight fractions was due to insolubilization by cross-linking rather than degradation. SDS-PAGE revealed that two protein bands of ≈29 and 17.5 kDa disappeared, and a new band appeared at 45 kDa with increasing ECH content. This indicated that, most likely, ECH reacted with protein in addition to reacting with starch. However, glycoprotein and starch-protein complexes were not identified with electrophoresis.     

Stability of Native Folate and Added Folic Acid in Micronutrient‐Fortified Corn Masa and Tortillas

Degradation of added folic acid and native folates in micronutrient‐fortified corn masa and tortillas was evaluated using masa prepared from either nixtamalized corn flour or fresh nixtamal. Variations in masa pH, masa holding time at an elevated temperature, and iron source failed to show significant differences in folate loss in corn flour masa prepared in the laboratory. Masa was subsequently prepared from fresh nixtamal in a commercial mill in Mexico, and fortified with one of two different micronutrient premixes containing iron, zinc, B‐vitamins, and either unencapsulated or lipid‐encapsulated folic acid. Folate loss in commercial masa increased significantly with prebake masa holding time for both premixes. Unencapsulated folic acid showed a 73% loss after 4 hr of holding, compared to 60% loss for encapsulated. The difference was statistically significant, indicating a protective effect from the lipid coating. No significant differences in folate levels were found between prebake masa and baked tortillas. Holding baked tortillas for up to 12 hr also had no effect on folate levels. Native folate showed no significant losses throughout the process. Results from the commercial tortilla mill indicate that most of the loss in added folic acid occurs during prebake holding of masa, possibly from microbial degradation.