A 10‐g Laboratory Wet‐Milling Procedure for Maize and Comparison With Larger Scale Laboratory Procedures

A very small scale laboratory procedure (≈10 g) is needed to test wet‐milling characteristics of corn when amounts of corn available for testing are quite limited. The objective of this study was to downscale 100‐g laboratory wet‐milling methods already widely used to measure wet‐milling properties of 10 g of corn. A Standard 100‐g procedure, a Modified 100‐g procedure, and an Experimental 10‐g procedure were compared using three corn hybrids with known differences in wet‐milling properties. All three procedures ranked most fraction yields (all except for germ) of the three hybrids the same. Germ separation was conducted differently for each procedure and probably accounts for these differences. Flotation and screening methods were likely affected by germ density and germ size, and hand‐picking the germ was efficient in recovering a pure germ fraction. The two 100‐g procedures were performed very similarly except for fiber recovery. The Modified 100‐g procedure was more efficient in recovering fiber because of intensive washing. Hybrid effects on the starch/gluten separation were more pronounced when the Experimental 10‐g procedure was used, which may allow for more discrimination among hybrids. Although most fraction yields are too small to run replicates for analytical tests, the Experimental 10‐g procedure will be useful in measuring milling efficiency of early generations of corn hybrids where limited samples are available, such as when valuable recombinant proteins are expressed for therapeutics and industrial enzymes.     

Wet‐Milling and Dry‐Milling Properties of Dent Corn with Addition of Amylase Corn

A transgenic corn (amylase corn) has been developed that produces an endogenous α‐amylase that is activated in the presence of water and elevated temperature (>70°C). Wet‐ and dry‐milling characteristics of amylase corn were evaluated using laboratory wet‐ and dry‐milling procedures. Different amounts of amylase corn (0.1–10%) were added to dent corn (with the same genetic background as the amylase corn) as treatments. Samples were evaluated for wet‐ and dry‐milling fraction yields using 1‐kg laboratory procedures. Milling yields for all amylase corn treatments were compared with the control treatment (0% amylase corn or 100% dent corn). No significant differences were observed in wet‐ and dry‐milling yields between the control and the 0.1, 1, and 10% amylase corn treatments. Most of the amylase activity (77%) in wet‐milling fractions was detected in the protein fraction. In dry‐milling, amylase activity (68.8%) was detected in endosperm fractions (fines, small grits, and large grits).     

Compositional,Physical, and Wet‐Milling Properties of Accessions Used in Germplasm Enhancement of Maize Project

Forty‐nine accessions used in the Germplasm Enhancement of Maize (GEM) project, two commercial hybrids (Pioneer Brand Hybrids 3394 and 3489), and two Corn Belt inbreds (B73 and Mo17) were evaluated for compositional, physical, and wet‐milling properties. GEM accessions had lower starch contents (65.9–69.1% vs. a mean of 72.2% for the commercial hybrids) and greater protein contents (12.0–14.4% vs. a mean of 8.2% for the commercial hybrids) than did the improved Corn Belt material. Absolute densities were consistently higher for the GEM accessions compared with the commercial hybrids (1.320 vs. 1.265 g/cm³, respectively). The wet‐milling characteristics of the GEM accessions were not nearly as good as for the commercial hybrids. Mean starch yields were only 54.3% for the GEM accessions versus 64.8% for the commercial hybrids. Residual protein levels in the starches recovered from the GEM accessions were much greater (0.45–2.03%) than for commercial corn hybrids (<0.3%).     

Effect of Stress Cracks on Corn Wet‐Milling Yields

U.S. No. 2 yellow dent corn was randomly probe‐sampled from rail cars being shipped to a wet‐milling plant from a Corn Belt local elevator. The probe samples were blended together and kernels were sorted into four levels of stress cracks (0, 1, 2, or multiple). Each level of stress cracking was then laboratory wet‐milled in triplicate. The only statistically observed differences were in total fiber and in protein content of the gluten meal fraction. The starch yield difference between zero stress cracked corn and multiple stress cracked corn was smaller (0.8%) than would be expected if stress cracking were an indicator of damage to the wet‐milling characteristics of the corn.     

Physical,Compositional, and Wet‐Milling Characteristics of Mexican Blue Maize (Zea mays L.) Landrace

Mexico has the largest diversity of genetic resources for maize in the world, with about 59 different landraces. However, little is known about their wet‐milling characteristics. The aim of this study was to determine whether 15 Mexican blue maize (Zea mays L.) genotypes of Elotero de Sinaloa landrace collected in the northwestern region of Mexico have suitable wet‐milling properties. Great variability of physical, compositional, and wet‐milling characteristics among these blue maize genotypes was observed. The FAUAS‐457 and FAUAS‐488 maize genotypes had similar starch yield and starch recovery as reported for the wet‐milling industry, which indicated that they may be useful as a source of extractable starch. Residual protein levels in the starch fractions were in the range of 0.39–0.68%, and total solids recovery exhibited a mean value of 98.8%, indicating acceptable efficacy of the wet‐milling process. This process afforded starches from blue maize genotypes with low protein contents. Wet‐milling fractions correlated with the physical and chemical properties of the kernels. Our results indicate that Mexican blue maize genotypes contain characteristics that make them appropriate and utilizable at the industrial level, and they can also be valuable for improving wet‐milling characteristics of maize through breeding programs.     

Study of a Small‐Scale Laboratory Wet‐Milling Procedure for Wheat

The objectives of this research were to study the effects of slurry specific gravity, starch table slope, slurry pumping rate, and their interactions on starch recovery and purity; and to propose a small‐scale laboratory wet‐milling procedure for wheat. First‐order and second‐order response surface regression models were developed to study the effects and interactions of slurry specific gravity, starch table slope, and slurry pumping rate on starch and gluten separation for a 100‐g wheat wet‐milling procedure. The starch and starch protein content data fit the first‐order models (R² = 0.99 and 0.96) better than the second‐order models (R² = 0.98 and 0.93). Regression results from the first‐order models indicated that specific gravity, table slope, pumping rate, and their interactions all had a significant effect on starch yield and purity. However, these effects could be simplified as the effect of the resident time of starch and gluten slurry on the starch table and the specific gravity. Starch yield increased as resident time increased and specific gravity decreased. Protein content in starch decreased as the resident time decreased and the specific gravity increased. The separation condition with specific gravity of 3 Bé, table slope of 1.04 cm/m, and pumping rate of 50 mL/min was recommended. Under this condition, starch recovery was 85.6% and protein content of starch was 0.42%, which was similar to the 1.5‐kg laboratory methods in starch recovery. Total solids recovery was 98.1%, which is similar to that from 1.5‐kg laboratory methods. These results indicated that precision of the 100‐g wheat wet‐milling procedure was similar to that of the 1.5‐kg laboratory methods.     

Wet‐Milling Characteristics of 10 Lines from Germplasm Enhancement of Maize Project Compared with Five Corn Belt Lines

The use of corn (Zea mays L.) hybrids with high grain yield and starch extractability has steadily increased in the processing industry. In light of widespread corn seed industry participation in the Germplasm Enhancement of Maize Project (GEM), which seeks to enhance exotic germplasm, future hybrids may contain more exotic sources in genetic backgrounds. It is necessary to establish and monitor physical, compositional, and milling characteristics of the new exotic breeding materials to determine the processing value. The present study was conducted to determine the wet‐milling characteristics of a set of GEM lines compared with typical Corn Belt lines. Ten GEM lines introgressed with exotic materials from Argentina, Chile, Cuba, Florida, and Uruguay and previously identified as having different starch yields, three commercial inbred lines, and two public inbred lines (B73 and Mo17) were analyzed using both near‐infrared transmittance (NIT) and a 100‐g wet‐milling procedure. There were statistical differences (P < 0.05) in the yield of wet‐milled fractions (starch, fiber, gluten, and germ). The GEM lines AR16035:S19‐227‐1‐B and CUBA117:S1520‐562‐1‐B had similar or better starch yield and starch recovery than B73 and the other adapted inbred lines, indicating that they may be useful in improving the proportion of extractable starch present in kernels of hybrids. Residual protein levels in the starch and gluten fractions were 0.26–0.32% and 38–45%, respectively. The starch yield of GEM lines from wet milling correlated positively with starch content from NIT and was negatively correlated with protein content of the corn kernels. Oil content in the germ varied from 50 to 60%. Our results indicate that incorporating GEM lines in a breeding program can maintain or even improve wet‐milling characteristics of Corn Belt materials if lines with appropriate traits are used.     

Relationship Between Wheat (Triticum aestivum L.) Grain Hardness and Wet‐Milling Quality

Grain hardness variation has large effects on many different end‐use properties of wheat (Triticum aestivum). The Hardness (Ha) locus consisting of the Puroindoline a and b genes (Pina and Pinb) controls the majority of grain hardness variation. Starch production is a growing end‐use of wheat. The objective of this study was to estimate the differences in starch yield due to natural and transgenically conditioned grain hardness differences. To accomplish this goal, a small‐scale wet‐milling protocol was used to characterize the wet‐milling properties of two independent groups of isogenic materials varying in grain hardness and in Pin expression level. The first group of lines consisted of hard/soft near‐isogenic lines created in cultivars Falcon or Gamenya in which lines carried either the Pina‐D1a (functional) or the Pina‐D1b (null) alleles of Pina. The second group of lines consisted of Pina, Pinb, or Pina and Pinb overexpressing lines created in Hi‐Line, a hard red spring wheat. Soft near‐isogenic lines had higher starch extractability than the hard Pina null counterparts. This difference in starch extractability was more pronounced between Hi‐Line and its transgenic isolines, with highest levels of extractable starch observed in the transgenic isoline with intermediate grain texture. The results demonstrate that the Ha locus and puroindoline expression are both linked to wet‐milling starch yield and that selection for increased Ha function increases starch yield through the enhanced separation of starch granules and the protein matrix during wet milling.     

Nitrogen and Sulfur Concentrations and Flow Rates of Corn Wet-Milling Streams

Nitrogen (N) and sulfur (S) concentrations can affect the market value of coproducts from corn wet-milling. The composition of parent streams would be expected to affect composition of the resulting coproducts but there are few published data available to examine this relationship. Concentration and flow data are needed to determine which streams are important in modifying N and S coproduct concentrations. The objective was to measure concentrations and flows of N and S in corn wet-milling streams. Samples were taken from 21 process streams from 3 wet-milling plants during two periods of three weeks each; N and S concentrations of each sample were determined. There were large differences in N and S concentrations among processing streams; within most streams, N and S concentrations were similar among plants. Concentrations of N and S were related inversely to flow rates. Steepwater and gluten streams contained most of the N and S flow and provide an opportunity for modification. The process water stream carried large quantities of N and S and represents another opportunity for improving process efficiency and coproduct value.     

Effects of Maturity on Grain Quality and Wet‐Milling Properties of Two Selected Corn Hybrids

The effects of maturity on grain quality and wet‐milling properties were investigated for two hybrids of corn. Significant differences for hybrid and maturity were observed for all grain quality parameters. Test weight, absolute density, and thousand‐grain weight all increased as the corn matured. Kernel hardness increased and breakage susceptibility varied with increased maturity. Water uptake parameters decreased with maturity of the grain. The starch yield results from wet milling showed that the starch yield increased significantly within each cultivar in the early stages of grain maturity, but there were no significant differences between hybrids. Mathematical models using selected grain quality parameters accurately predicted trends in starch yield for the immature and mature corn samples in this study.     

Pasting Properties and Surface Characteristics of Starch Obtained from an Enzymatic Corn Wet‐Milling Process

Recently, we reported the development of an enzymatic corn wet‐milling process that reduces or eliminates sulfur dioxide requirements during steeping, considerably reduces steep time, and produces starch yields comparable to that of conventional corn wet‐milling. The best results so far, using the enzymatic corn wet‐milling procedure, were achieved when a particular protease enzyme (bromelain) was used. In this study, pasting properties and surface characteristics of starch obtained from six different enzyme treatments (three glycosidases [β‐glucanase, cellulase, and xylanase] and three proteases [pepsin, acid protease, and bromelain]) using the enzymatic corn wet‐milling procedure were evaluated and compared with those from starch obtained using the conventional corn wet‐milling procedure. Significant effects from enzymatic milling were observed on all the three starch pasting properties (peak, shear thinning, and setback). The setback viscosities of starch from all enzyme treatments were significantly lower compared with those of the control sample, indicating that starch polymers from enzymatic corn wet‐milling do not reassociate to the same extent as with the control. Comparison between bromelain treatment and the control sample showed that starch samples obtained from bromelain treatment are very similar to control starch in water‐binding capacity, molecular breakdown, and time to swell when cooked in water. Significant effects from enzymatic milling were observed on the surface characteristics of starch granules. The glycosidase treatments, especially the β‐glucanase samples, showed holes in the starch granules. No visual differences were observed in starch granules between bromelain and control samples.     

Use of Proteases to Reduce Steep Time and SO2 Requirements in a Corn Wet‐Milling Process

To eliminate the diffusion barriers associated with enzyme addition during conventional steeping, we have developed a two‐stage milling procedure to evaluate the effects of enzyme addition on corn wet milling. The current study compares the effects of the addition of commercially available enzyme preparations during conventional steeping to their comparable addition in the two‐stage procedure. Results are presented in terms of yields of fiber, starch, germ, and gluten. The results demonstrate that the application of enzymes to the normal steeping step of wet milling is not an effective means of decreasing the steeping time or sulfur dioxide usage. Only when specific enzymes are added to the hydrated ground corn, using the modified two‐stage procedure, are enzymes effective in decreasing the steeping time and sulfur dioxide requirements. The overall steeping time with the two‐stage modified procedure ranges from 6 to 8 hr, representing a 67–83% reduction over the conventional process. The modified process greatly decreases, and possibly eliminates, the need for sulfur dioxide addition, while producing starch yields and quality equivalent to that from the conventional process.     

Effect of Steeping with Sulfite Salts and Adjunct Acids on Corn Wet‐Milling Yields and Starch Properties

Two corn hybrids (3394 and 33R87) were steeped with three sulfite salts and five acids to test the effect of sulfur dioxide (SO₂) source and acid sources on wet‐milling yields and starch properties. Milling yields from each treatment were compared with a control sample that was steeped with 2,000 ppm of SO₂ (using sodium metabisulfite) and 0.55% lactic acid. Sulfur dioxide sources were potassium sulfite, sodium sulfite, and ammonium sulfite; acids were acetic, hydrochloric, oxalic, phosphoric, and sulfuric. Starch yields were affected by the SO₂ source and steep acids but the effects were hybrid‐dependent. Different steep acids gave different starch yields when wet milled at the same pH. Among the acids tested, weak acids (lactic and acetic) tended to give higher starch yields compared with strong acids (hydrochloric, sulfuric, phosphoric, and oxalic). Some differences were observed with different sulfite salts and acids on starch pasting properties; however, there were no clear trends.     

Roller Milling of Canadian Hull‐less Barley: Optimization of Roller Milling Conditions and Composition of Mill Streams

Roller milling of hull‐less barley generates mill streams with highly variable β‐glucan and arabinoxylan (AX) content. For high β‐glucan cultivars, yields >20% (whole barley basis) of a fiber‐rich fraction (FRF) with β‐glucan contents >15% can be readily obtained with a simple short mill flow. Hull‐less barley cultivars with high β‐glucan content require higher power consumption during roller milling than normal β‐glucan barley. Recovery of flour from high β‐glucan cultivars was greatly expedited by impact passages after grinding, particularly after reduction roll passages. Pearling before roller milling reduces flour yield and FRF yield on a whole unpearled barley basis, but flour brightness is improved and concentration of β‐glucan in fiber‐rich fractions increases. Pearling by‐products are rich in AX. Pearling to 15–20% is the best compromise between flour and FRF yield and flour brightness and pearling by‐products AX content. Increasing conditioning moisture from 12.5 to 14.5% strongly improved flour brightness with only a moderate loss of flour yield on a whole unpearled barley basis. As moisture content was increased to 16.5%, flour yield declined without a compensating improvement in brightness, but the yield of fiber‐rich fraction continued to increase and concentration of β‐glucan in FRF also increased.     

Condensed Tannins in Traditional Wet‐Cooked and Modern Extrusion‐Cooked Sorghum Porridges

The profile and quantities of condensed tannins (CT) in foods are affected by processing due to their highly reactive nature, which may affect their antioxidant activity and the nutritional value of the foods. The objective was to compare the quantity and profile of condensed tannins in traditional wet‐cooked and modern ready‐to‐eat extrusion‐cooked sorghum porridges. CT were analyzed using normal‐phase HPLC with fluorescence detection and their content was compared to CT and total phenols determined with standard colorimetric assays. Both the traditionally prepared and instant porridges had significantly reduced CT polymers (DP > 8), with retentions of 38 and 9%, respectively, of the CT present in the whole grain. Oligomer (DP 2–8) and monomer (DP 1) contents in traditional porridges were not significantly different from those of grain. In extruded porridges, the oligomers were reduced and the monomer content was increased. The extractable CT oligomers and monomers in the extrusion‐cooked sorghum porridges may be more biologically available because extrusion appears to increase their availability.     

Maize Proximate Composition and Physical Properties Correlations to Dry‐Grind Ethanol Concentrations

Dry‐grind ethanol plants incur economic losses because of seasonal variations in ethanol yields. One possible cause associated with ethanol yield variability is incoming grain quality. There is little published information on factors causing variation in dry‐grind ethanol concentrations. The objective of this study was to determine relationships between rapidly measurable corn quality attributes (physical parameters and chemical composition) and dry‐grind ethanol concentrations. Corn samples obtained from a Midwestern ethanol plant were analyzed for physical quality parameters (test weight, kernel weight, true density, percent stress cracks, and moisture content) and composition (starch, protein, oil, and soluble sugars contents) and then processed with a laboratory‐scale dry‐grind procedure. There were significant (P < 0.05) variations in corn quality parameters and ethanol concentrations. Correlation coefficients were significant (P < 0.05) but low (–0.50 < r < 0.50) between starch content and final ethanol concentrations (72 h) and total soluble sugar content and ethanol concentrations at 72 and 48 h. Ethanol concentrations (at 24, 48, and 72 h) were predicted as a function of a combination of grain quality factors using multiple regression methods; however, the R² values obtained were low. Variations in ethanol concentrations were not related to physical and chemical composition quality factors. Other factors, such as structural and physiologic attributes of corn grain, need to be evaluated.     

Effects of Selected Harvest Moistures and Frozen Storage Times on Selected Yellow Dent Corn: Wet‐Milling Yields and Starch Pasting Properties

The effects of harvest moistures and frozen storage times on corn wet‐milling yields and the pasting properties of the resulting starch were studied. Pioneer hybrid P‐0916‐XR harvested at three moisture contents (49, 35, and 21% wb) were stored frozen for three days or for five months, followed by wet‐milling. The pasting properties of the resulting starch were evaluated with a Rapid Visco Analyzer. The yields of starch and germ increased by 1.2 and 1.9 percentage points, respectively, when harvest moisture decreased from 49 to 21% wb, whereas the yields of steep water solids, total fiber, and gluten decreased by 2.1, 0.7, and 0.6 percentage points, respectively. The frozen corn had lower coarse fiber yields but higher cellular fiber yields. The starch pasting properties showed that peak and breakdown viscosities decreased by 8% (3,824 ± 36 versus 3,520 ± 38 cP) and 13% (2,336 ± 47 versus 2,029 ± 60 cP), respectively, when harvest moisture decreased from 49 to 21% wb, whereas peak time increased by 5% (6.32 ± 0.06 versus 6.62 ± 0.07 min). The setback and final viscosities of starch from long‐term frozen storage (five months) were 14% (1,574 ± 65 versus 1,828 ± 79 cP) and 8% (3,063 ± 27 versus 3,317 ± 101 cP) lower, respectively, than that from control (unfrozen) corn.     

Viscoelastic Properties of Gelatinized Dispersions of Maize Starch Modified by Solid‐State Milling

Solid‐state milling is an effective physical modification method applied to improve functional properties of starch. In this work the effect of solid‐state milling on the viscoelastic characteristics of maize starch gelatinized dispersions (gels) was investigated by using oscillatory squeeze film rheometry. The relaxation spectrum of the samples under study was calculated from the data obtained. It was found that solid‐state milling resulted in a decrease of the storage (G′) and loss (G″) moduli; meanwhile, loss tangent (tan δ) increased. At a starch milling time more than 10 h, G″ > G′ and the gelatinized starch dispersions behaved as liquid‐like systems. The relaxation maxima shifted to shorter relaxation times, and the heights of the maxima decreased with increasing milling time. The relationship between the complex viscosity η* and steady‐shear viscosity η gradually altered from η* > η to η* < η as the milling time increased. The results can be used to determine the processing conditions of milled starch.     

Correlations between Kinetic Parameters of Phosphate Uptake and Internal Phosphorus Concentrations in Maize Plants: Making it Possible to Estimate the Status of Phosphate Uptake according to Shoot Phosphorus Concentrations

Abstract

The relationship between internal phosphorus (P) concentration [P] and kinetics of phosphate (Pi) uptake was investigated in maize seedlings grown hydroponically at different Pi concentrations (0.1–1,000 µM) and in the phase of Pi deprivation (0–10 d). The results indicated when the internal [P] was higher than 85 µmol g^?1 dw, apparent K_m, C_min, and V_max were significantly (P<0.01) related to [P]s in shoots and roots; when the internal [P] was lower than 85 µmol g^?1 dw, K_m and C_min were small and only V_max was significantly related (P<0.01) to internal [P]s. Three equations were deduced from the linear regressions of the kinetic parameters and [P]s in shoots. Using these equations, the values of apparent K_m, C_min, and V_max of Pi uptake of seedlings grown in different circumstances were calculated according to [P]s in shoots. In all the circumstances involved, for K_m and C_min, there was a parallel relationship between the values estimated by [P]s in shoots and by the Pi‐depletion technique; for V_max, the values estimated by [P]s in shoots were consistent with those obtained from Pi‐depletion experiments except the period of supplying Pi to the Pi‐starved seedlings over several days. These results indicated it is possible to estimate the Pi‐uptake status according to shoot P concentrations in maize plants under experimental conditions, which might be helpful to estimate in‐season status of Pi uptake of maize plants in the field.     

Measuring Water-Extractable Phosphorus in Manures to Predict Phosphorus Concentrations in Runoff

Water-extractable phosphorus (WEP) in manures can influence the risk of phosphorus (P) losses in runoff when manures are land applied. We evaluated several manure handling and extraction variables to develop an extraction procedure for WEP that will minimize pre-analysis manure-sample-handling effects on WEP measurements. We also related manure WEP determinations to runoff dissolved reactive phosphorus (DRP) concentrations found in previously conducted field simulated rainfall experiments using the same manures to evaluate WEP as a predictor of P runoff losses. Dairy and poultry manure WEP concentrations increased with manure-to-water extraction ratio and shaking time. Relative to fresh manures, drying and grinding dairy manures before analysis usually decreased WEP concentrations, while WEP in poultry manures was often increased. Pre-analysis handling effects on WEP were minimized at the 1:1000 extraction ratio with a 1-h shaking time. Relationships between manure WEP and runoff DRP concentrations were strongly influenced by season of year and WEP extraction procedure. The best prediction of DRP concentration in spring runoff experiments was with manure WEP concentration at the 1:1000 extraction ratio. With fall runoff studies, DRP concentrations were best predicted with WEP application rate rather than concentration. These seasonal differences can be explained by the greater percentage of rainfall that ran off in the fall compared to the spring. For all studies, runoff DRP concentrations were strongly related (r² = 0.82) to the ratio of runoff to rainfall volumes, confirming that models need to take runoff hydrology into account as well as manure WEP in P-loss risk assessments.