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.     

Variation Among Physical,Compositional, and Wet‐Milling Characteristics of the F1 Generation of Corn Hybrids of Introgressed Exotic and Adapted Inbred Lines

Hybrids with high grain yield and higher starch, protein, or oil content are available to corn growers; however, they result from crossing adapted Corn Belt inbred lines that rarely include exotic germplasm. This study was conducted to determine whether Corn Belt lines introgressed with exotic materials from Argentina, Chile, Uruguay, Cuba, and Florida have appropriate wet‐milling characteristics in their hybrids. Ten lines from the Germplasm Enhancement of Maize (GEM) project with different starch contents were crossed to three adapted inbred lines used as testers. The B73×Mo17 hybrid was used as a control. The F₁ generation of these 30 experimental hybrids was analyzed using both near‐infrared transmittance (NIT) technology and a 100‐g modified wet‐milling procedure, and measuring test and 1,000‐kernel weight. There was great variation among physical, compositional, and wet‐milling characteristics of the experimental hybrids, suggesting that exotic germplasm can be used to improve wet‐milling characteristics of Corn Belt hybrids.     

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.     

Variability in Starch Acetylation Efficiency from Commercial Waxy Corn Hybrids

Raw material variability is common for starch processors and is responsible for increased processing costs. In this study, variability of starch acetylation due to hybrid influence was quantified. Six waxy corn (maize) hybrids from 1998 and five waxy corn hybrids from 1999 were wet‐milled in the laboratory. Starch obtained from each hybrid was modified according to a laboratory‐scale acetylation procedure. To evaluate reaction efficiency, reaction rate, acetyl content, pH, and amount of NaOH used were recorded for each reaction. After modification, a Rapid Visco Analyser (RVA) was used to characterize modified starches and determine differences in modified starches from different hybrids. Using the same acetylation protocol, reaction efficiencies were observed at 47–73%. Reaction efficiencies were significantly lower for 1998 hybrids (50.0%) compared with the efficiency observed for the same hybrids grown in 1999 (62.7%). Acetylated starch from 1999 had increased peak, trough and final viscosities and increased reaction efficiency as compared with acetylated starch from 1998. Differences in setback were observed among 1998 hybrids for acetylated samples. Differences in trough and final viscosity were observed among 1999 hybrids for acetylated and native (unmodified) samples. Differences in breakdown among 1999 hybrids also were observed for native samples.     

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.     

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.     

Ethanol Production from Modified and Conventional Dry‐Grind Processes Using Different Corn Types

Different corn types were used to compare ethanol production from the conventional dry‐grind process to wet or dry fractionation processes. High oil, dent corn with high starch extractability, dent corn with low starch extractability and waxy corn were selected. In the conventional process, corn was ground using a hammer mill; water was added to produce slurry which was fermented. In the wet fractionation process, corn was soaked in water; germ and pericarp fiber were removed before fermentation. In the dry fractionation process, corn was tempered, degerminated, and passed through a roller mill. Germ and pericarp fiber were separated from the endosperm. Due to removal of germ and pericarp fiber in the fractionation methods, more corn was used in the wet (10%) and dry (15%) fractionation processes than in the conventional process. Water was added to endosperm and the resulting slurry was fermented. Oil, protein, and residual starch in germ were analyzed. Pericarp fiber was analyzed for residual starch and neutral detergent fiber (NDF) content. Analysis of variance and Fisher's least significant difference test were used to compare means of final ethanol concentrations as well as germ and pericarp fiber yields. The wet fractionation process had the highest final ethanol concentrations (15.7% v/v) compared with dry fractionation (15.0% v/v) and conventional process (14.1% v/v). Higher ethanol concentrations were observed in fractionation processes compared to the conventional process due to higher fermentable substrate per batch available as a result of germ and pericarp fiber removal. Germ and pericarp yields were 7.47 and 6.03% for the wet fractionation process and 7.19 and 6.22% for the dry fractionation process, respectively. Germ obtained from the wet fractionation process had higher oil content (34% db) compared with the dry fractionation method (11% db). Residual starch content in the germ fraction was 16% for wet fractionation and 44% for dry fractionation. Residual starch in the pericarp fiber fraction was lower for the wet fractionation process (19.9%) compared with dry fractionation (23.7%).     

Steady and Dynamic Shear Rheological Properties of Starch and Decolorized Hsian‐tsao Leaf Gum Composite Systems

Rapid Visco Analyser (RVA) and dynamic rheological measurements were performed on a mixture of decolorized hsian‐tsao leaf gum (dHG) and starch as a function of starch‐to‐gum ratio (S/G 0:6, 1:5, 2:4, 3:3, 4:2, 5:1, and 6:0), starch type (wheat, corn, and tapioca), and total solid content (2, 3, and 4%). Under S/G of 5:1, 4:2 and 3:3, dHG interacted with starch synergistically, which resulted in a marked increase in viscosity during cooling. The storage modulus of the resulting mixed gel was higher than the loss modulus, and both moduli were almost frequency‐independent throughout the frequency range tested, indicating that the composite gels could be classified rheologically as elastic gels. Mixed systems with tapioca starch showed higher pseudo‐gel viscosity in the RVA test, but lower storage modulus in the dynamic test than those with wheat or corn starch. Such results implied that tapioca starch contributed a more viscous property but wheat and corn starch contributed a more elastic property to the mixed systems.     

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).     

Rheological Properties of Starch‐Oil Composites with High Oil‐to‐Starch Ratios

Many applications have been developed for aqueous dispersions of jet‐cooked starch‐oil composites prepared by excess steam jet cooking. Previous formulations have typically contained 20–50% oil by weight based on the weight of starch. To expand the range of potential applications, new preparation methods were investigated to increase the oil content to as high as four times the weight of starch. High‐amylose corn starch was cooked in an excess‐steam jet cooker in the presence of oleic acid, and soybean oil was added to form the starch‐oil composites. Amylose is removed from solution by forming helical inclusion complexes with the oleic acid and, if the materials are cooled sufficiently quickly, the helical inclusion complexes only form small aggregates and shells around the oil droplets. Depending on the composition and preparation method, a wide range of stable, high‐oil materials from low‐viscosity liquids to smooth pastes can be formed. The flow, textural, and structural properties of these materials are shown. The materials can be used in a wide range of applications, including spray lubricants, lotions, and for fat delivery in cake mixes.     

Effect of Oil Content and pH on the Physicochemical Properties of Corn Starch‐Soybean Oil Composites

Starch‐lipid composites are a new category of fat replacers. The physicochemical properties of reconstituted corn starch and soybean oil composites (CSSBOC) were evaluated and compared with the properties of reconstituted jet‐cooked corn starch (JCCS). Gel firmness, thermal properties, and hot pasting properties at two pH levels and two oil content levels were studied. Amylose content of CSSBOC was unaffected by processing. Buffer pH significantly affected the firmness of the gels made with JCCS. Gels appeared to have a more ordered structure and were firmer at pH 3.4 than at pH 6.0. The firmness of gels made with CSSBOC was not affected by pH or oil content. Retrogradation enthalpy of the gels made with JCCS was significantly affected by pH. Differences in the thermal characteristics of gels made with CSSBOC were attributed to pH and oil content. Peak viscosity, cold paste viscosity, and breakdown viscosity changed significantly when CSSBOC pastes were reconstituted in different pH buffers. Only hot paste viscosity and cold paste viscosity changed significantly when JCCS pastes were reconstituted in different pH buffers. Results establish critical parameters for processing decisions and for the understanding of the behavior of CSSBOC in food system models in which pH is an important factor.     

Effect of Steeping Corn with Lactic Acid on Starch Properties

Pasting and thermal properties of starch from corn steeped in the presence of lactic acid and at different steeping times (8, 16, 24, 32, and 40 hr) were investigated. Corn kernels were steeped at 52°C with 0.2% (w/v) SO₂ and with and without 0.5% (v/v) lactic acid. The isolated starch obtained by corn wet‐milling was characterized by determining starch recoveries, retrogradation, and melting transition properties of the lipid‐amylose complex by differential scanning calorimetry (DSC), and pasting properties by the Rapid Visco Analyser (RVA). Damaged granules and the starch granule size were determined by using microscopic techniques. Starches from corn steeped in the presence of lactic acid (LAS) were compared with control starch (CS) steeped without lactic acid. Greater starch recoveries were obtained for LAS samples than for CS samples, and practically no damaged starch was present in the former preparations. The presence of lactic acid affected the RVA profiles and steeping time affected the viscosities of the starch suspensions. In general, the RVA parameters of LAS suspensions were lower than those of CS suspensions. No great modification of the thermal properties was observed; only a slight decrease in amylopectin retrogradation and in the melting enthalpy of the amylose‐lipid complex was observed. Hydrolysis of the starch during steeping seems the most probable explanation to the starch modifications produced by lactic acid addition.     

Physicochemical and Structural Characteristics of Flours and Starches from Waxy and Nonwaxy Wheats

A waxy spring wheat (Triticum aestivum L.) genotype was fractionated into flour and starch by roller and wet‐milling, respectively. The resultant flour and starch were evaluated for end‐use properties and compared with their counterparts from hard and soft wheats and with commercial waxy and nonwaxy corn (Zea mays L.) starches. The waxy wheat flour had exceptionally high levels of water absorption and peak viscosity compared with hard or soft wheat flour. The flour formed an intermediate‐strength dough that developed rapidly and was relatively susceptible to mixing. Analysis by differential scanning calorimetry and X‐ray diffractometry showed waxy wheat starch had higher gelatinization temperatures, a greater degree of crystallization, and an absence of an amylose‐lipid complex compared with nonwaxy wheat. Waxy wheat and corn starches showed greater refrigeration and freeze‐thaw stabilities than did nonwaxy starches as demonstrated by syneresis tests. They were also similar in pasting properties, but waxy wheat starch required lower temperature and enthalpy to gelatinize. The results show analogies between waxy wheat and waxy corn starches, but waxy wheat flour was distinct from hard or soft wheat flour in pasting and mixing properties.     

Effects of Amylose,Corn Protein,and Corn Fiber Contents on Production of Ethanol from Starch‐Rich Media

The effects of amylose, protein, and fiber contents on ethanol yields were evaluated using artificially formulated media made from commercial corn starches with different contents of amylose, corn protein, and corn fiber, as well as media made from different cereal sources including corn, sorghum, and wheat with different amylose contents. Second‐order response‐surface regression models were used to study the effects and interactions of amylose, protein, and fiber contents on ethanol yield and conversion efficiency. The results showed that the amylose content of starches had a significant (P < 0.001) effect on ethanol conversion efficiency. No significant effect of protein content on ethanol production was observed. Fiber did not show a significant effect on ethanol fermentation either. Conversion efficiencies increased as the amylose content decreased, especially when the amylose content was >35%. The reduced quadratic model fits the conversion efficiency data better than the full quadratic model does. Fermentation tests on mashes made from corn, sorghum, and wheat samples with different amylose contents confirmed the adverse effect of amylose content on fermentation efficiency. High‐temperature cooking with agitation significantly increased the conversion efficiencies on mashes made from high‐amylose (35–70%) ground corn and starches. A cooking temperature of ≥160°C was needed on high‐amylose corn and starches to obtain a conversion efficiency equal to that of normal corn and starch.     

Effects of Pollination Method and Growing Location on Starch Thermal Properties of Corn Hybrids

Starch gelatinization and retrogradation properties of corn were studied to determine the effect of controlled (self) pollination versus noncontrolled pollination on analytical determinations, and the potential to eliminate the expensive and time-consuming step of self-pollinating before research screening of corn genotypes. Twenty-four hybrids were grown in two Iowa locations, Story City and Ames. At Story City, all hybrids received three pollination treatments: self-pollination; small-plot, openpollination (representing corn from small test plots); and large-plot, openpollination (representing corn from a farmer's field). Self-pollinated and small-plot, open-pollinated corn were grown in replicated two-row plots, whereas large-plot, open-pollinated corn was grown in unreplicated plots of 12.8 m × 8 rows. At Ames, the small-plot, open pollination treatment was not done. Starch was extracted from samples of corn harvested from each plot, and gelatinization and retrogradation properties were determined using differential-scanning calorimetry (DSC). Hybrids exhibited different starch gelatinization and retrogradation properties. Significant differences (P ≤ 0.05) in starch gelatinization and retrogradation properties occurred among pollination methods and between locations. Pollination method did not influence gelatinization enthalpy values, but onset temperature values for gelatinization, and range values for retrogradation differed significantly among pollination methods. At Ames, treatments gave different values for retrogradation enthalpy and percentage of retrogradation. Because of differences in some starch characteristics associated with pollination methods, self-pollination is recommended when growing samples in small plots for research purposes.     

气氛条件对玉米淀粉辐射改性的影响

为提高玉米淀粉的使用性能,采用⁶⁰Co-γ射线在氧气、空气和氮气条件下对玉米淀粉进行辐照处理,辐照剂量分别为1、3、5、7、10 kGy,测定玉米淀粉的粘度、羧基含量,并采用傅里叶红外(FTIR)和扫描电镜(SEM)进行表征分析。结果表明,随着辐照剂量的增加,玉米淀粉粘度逐渐下降,而羧基含量逐渐升高,其中,辐照剂量为1~5 kGy时,粘度下降较快,最大达到70%以上;辐照剂量为5~10 kGy时,粘度降低减缓。不同气氛条件辐照对玉米淀粉粘度的降低速度和羧基含量的增加速度有明显影响,且其影响程度按照氮气、空气和氧气次序逐渐增强,辐照为5 kGy时,与充氮辐照组相比,充氧辐照组玉米淀粉粘度值降低12.0%,而羧基含量相对增加比率达到107.7%;与原淀粉相比,在3种气氛条件下经5、10 kGy剂量辐照处理后,玉米淀粉分子结构和表面颗粒形貌皆无可见变化,但表征淀粉有序结构的FTIR量化指标1 047 cm^-1/1 022 cm^-1比值总体上呈下降趋势。综合考虑,辐照引起淀粉分子结构的变化主要发生在无定型区域,而氧气对此有促进作用,氧含量的增加有利于增强该区域内淀粉大分子的辐射裂解与氧化。通过调节辐射剂量和气氛条件,可以节约辐照加工成本,制备性能优良的变性淀粉,从而促进辐照技术在淀粉改性上的推广应用。     

Influence of Stenocarpella maydis Infected Corn on the Composition of Corn Kernel and Its Conversion into Ethanol

Widespread epidemics of Stenocarpella ear rot (formerly Diplodia ear rot) have occurred throughout the central U.S. Corn Belt in recent years, but the influence of S. maydis infected grain on corn ethanol production is unknown. In this study, S. maydis infected ears of variety Heritage 4646 were hand‐harvested in 2010 from a production field in central Illinois and segregated into one of five levels of ear rot severity based upon visual symptoms. The concentration of ergosterol, a sterol produced by fungi but not plants, was observed to increase with the severity of ear rot (127–306.5 μg/g), and none was detected in the control corn. Corn test weight declined with progression of the disease and was 42.6% lower for the most severely rotted grain from ears infected early in their development. Accompanying changes in composition were also apparent. Crude fat and oil contents decreased (from 4.7 to 1.5%) and fiber increased (from 6.6 to 9.6%), but starch content remained largely invariant. Oil composition also varied among the infected samples. Control and infected corn samples were subjected to ethanol fermentation with a laboratory‐scale corn dry‐grind ethanol process. Ethanol yields for control and infected samples were similar on an equivalent weight basis (2.77–2.85 gal/bu). In comparison with the control, S. maydis infection altered the distillers dried grains with solubles (DDGS) properties, wherein the crude protein was significantly higher and oil significantly reduced, and ash, fiber, and yield per ton were not significantly different. Based upon these results, we conclude that Stenocarpella ear rot has the potential to affect DDGS composition but not ethanol yield on an equivalent weight basis.     

Effect of Steeping Conditions (Sulfur Dioxide,Lactic Acid,and Temperature) on Starch Yield,Starch Quality,and Germ Quality from the Intermittent Milling and Dynamic Steeping Process (IMDS) for a Brazilian Corn Hybrid

Effect of lactic acid, SO₂, temperature, and their interactions were assessed on the dynamic steeping of a Brazilian dent corn (hybrid XL 606) to determine the ideal relationship among these variables to improve the wet‐milling process for starch and corn by‐products production. A 2×2×3 factorial experimental design was used with SO₂ levels of 0.05 and 0.1% (w/v), lactic acid levels of 0 and 0.5% (v/v), and temperatures of 52, 60, and 68°C. Starch yield was used as deciding factor to choose the best treatment. Lactic acid added in the steep solution improved the starch yield by an average of 5.6 percentage points. SO₂ was more available to break down the structural protein network at 0.1% than at the 0.05% level. Starch‐gluten separation was difficult at 68°C. The lactic acid and SO₂ concentrations and steeping temperatures for better starch recovery were 0.5, 0.1, and 52°C, respectively. The Intermittent Milling and Dynamic Steeping (IMDS) process produced, on average, 1.4% more starch than the conventional 36‐ hr steeping process. Protein in starch, oil content in germ, and germ damage were used as quality factors. Total steep time can be reduced from 36 hr for conventional wet‐milling to 8 hr for the IMDS process.     

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.     

Effect of Lactic Acid on Protein Solubilization and Starch Yield in Corn Wet‐Mill Steeping: A Study of Hybrid Effects

To better understand the role of lactic acid (LA) in corn wet‐milling, steeping studies were performed on different yellow dent corn hybrids using four different solutions containing LA, sulfur dioxide (SO₂), a combination of LA and SO₂, or no added chemicals. Although there was variation in protein solubilization among the hybrids, protein release was consistently higher when LA was included in the steepwater than when it was excluded (both with and without SO₂). Several groups have reported that starch recoveries are improved when steepwater contains LA. To explore the relationship between protein solubilization and starch yield as effected by LA, several yellow dent hybrids were steeped in 0.20% SO₂ and 0.50% LA‐0.20% SO₂ solutions and milled to recover starch by a 100‐g laboratory corn wet‐milling procedure. In all instances, both starch yields and protein solubilization were enhanced in solutions containing LA. These results support the hypothesis that direct dissolution of the endosperm protein matrix by LA contributes to the improved starch recoveries.