Solvent Extraction of Zein from Dry‐Milled Corn

Batch extraction of zein from dry‐milled whole corn with ethanol was optimum with 70% ethanol in water, an extraction time of 30–40 min, and temperature of 50°C. High yields (60% of the zein in corn) and high zein contents in the extracted solids (50%) were obtained at a solvent‐to‐solids ratio of 8 mL of 70% ethanol/g of corn. However, zein concentration in the extract was higher at lower ratios. Multiple extraction of the same corn with fresh ethanol resulted in a yield of 85% after four extractions, whereas multiple extractions of fresh corn with the same ethanol resulted in high (15 g/L) zein concentration in the extract. Optimum conditions for batch extraction of zein were 45°C, with 68% ethanol at a solvent‐to‐solids ratio of 7.8 mL/g for an extraction time of 55 min. Column extractions were also best at 50°C and 70% ethanol; a solvent ratio of 1 mL/g resulted in high zein concentrations in the extract (17 g/L) but yields were low (20%).     

Corn Dry‐Milled Grit and Flour Fractions Exhibit Differences in Amylopectin Fine Structure and Gel Texture

Corn starch amylopectin (AP) fine structure and gel textural properties of dry‐milled grit and flour fractions were investigated in 10 corn cultivars. Amylopectin was isolated by fractionating the starch derived from these two milled fractions using size‐exclusion chromatography (SEC). Fine structure was characterized by SEC after thorough debranching with pullulanase. SEC revealed three major fractions of debranched AP from the grit and flour portion. Amylopectin in the grit portion had a significantly higher proportion of long chains (DP_n 70–75) and a postulated lower extent of chain branching than its flour counterpart. Texture profile analysis showed that flour gels from the grit fraction had significantly higher values for hardness, gumminess, and springiness compared with gels from the floury fraction. Trends were similar for starch gels of the two dry‐milled fractions, though only springiness was significantly different. The finding that differences in AP fine structure in dry‐milled fractions relate to gel textural differences suggests that dry millers may be able to produce flours of different functionalities that would be suited for different end uses. Additionally, mixing the dry‐milled flour fraction with a grit‐derived flour would result in different product properties.     

Laboratory Measurement of Yield and Composition of Dry‐Milled Corn Fractions Using a Shortened,Single‐Stage Tempering Procedure

The objective was to describe a laboratory‐scale dry‐milling procedure that used single‐stage tempering and determine the effect of hybrid on yields and fraction compositions in milled corn. Samples of 11 commercially available hybrids were processed through a laboratory dry‐milling procedure that used 1 kg samples of corn to produce milling fractions of large grits, small grits, fines, germ, and pericarp. Compositions of milling fractions (protein, neutral detergent fiber, ash, and crude fat) were determined. The procedure used a single‐stage tempering step that increased corn moisture from 15 to 23.5% wb during an 18‐min tempering period. Germ were separated from endosperm particles using a roller mill followed by screening over a sieve with 1.68‐mm openings. Coefficients of variability were small, indicating acceptable repeatability. Overall yield means were 39.2, 25.3, 13.8, 78.2, 14.3, and 6.8 g/100 g (db) for large grits, small grits, fines, total endosperm, germ, and pericarp, respectively. There were effects due to hybrid (P < 0.05) on fraction yields and compositions of milling fractions. Correlations (r) among endosperm fractions (large grits, small grits, and fines) ranged from 0.54 to |–0.92|. Correlations among endosperm fractions and germ and pericarp were <0.68. The developed dry‐milling method estimated milling yields among hybrids with low standard deviations relative to the means and should be a useful tool for research and industry in measuring dry‐milling characteristics.     

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).     

Enzymatic Process for Corn Dry‐Grind High‐Solids Fermentation

A modified dry‐grind process that combined the use of conventional amylases (glucoamylase [GA]), phytase, and granular starch hydrolyzing enzymes (GSHE) to achieve low liquefaction viscosities and low glucose concentrations during simultaneous saccharification and fermentation (SSF) with a high slurry solids content (>33% w/w) was developed. Doses of GSHE and GA were optimized for the modified process. At 35% solids content, the modified process had 80% lower slurry viscosity, 24% lower peak glucose concentration, 7.5% higher final ethanol concentration, and 51% higher fermentation rate compared with the conventional dry‐grind process. At 40% solids content, the modified process had lower viscosities, lower peak and residual glucose concentrations, and higher ethanol concentrations than the conventional process; however, the results were in contrast to those for 35% solids content. At 40% solids content, SSF did not run to completion for conventional or modified processes, and more than 2.5% w/v of residual glucose was left in the fermentation broth. Final ethanol concentration achieved with the modified process at 40% solids content was 19.5% v/v, similar to the ethanol concentration achieved with the modified process at 35% solids content. At 35% slurry solids content, a GSHE level of 1.25 μL/g db of corn and a GA level of 0.25 μL/g db of corn were selected as optimum enzyme doses for the modified process.     

Dry‐Grind Processing of Corn with Endogenous Liquefaction Enzymes

An amylase corn has been developed that produces an α‐amylase enzyme that is activated in the presence of water at elevated temperatures (>70°C). Amylase corn in the dry‐grind process was evaluated and compared with the performance of exogenous amylases used in dry‐grind processing. Amylase corn (1–10% by weight) was added to dent corn (of the same genetic background as the amylase corn) as treatments and resulting samples were evaluated for dry‐grind ethanol fermentation using 150‐g and 3‐kg laboratory procedures. Ethanol concentrations during fermentation were compared with the control treatment (0% amylase corn addition or 100% dent corn) which was processed with a conventional amount of exogenous α‐amylase enzymes used in the dry‐grind corn process. The 1% amylase corn treatment (adding 1% amylase corn to dent corn) was sufficient to liquefy starch into dextrins. Following fermentation, ethanol concentrations from the 1% amylase corn treatment were similar to that of the control. Peak and breakdown viscosities of liquefied slurries for all amylase corn treatments were significantly higher than the control treatment. In contrast, final viscosities of liquefied slurries for all amylase corn treatments were lower than those of the control. Protein, fat, ash, and crude fiber contents of DDGS samples from the 3% amylase corn treatment and control were similar.     

Development of an Ethanol Yield Procedure for Dry‐Grind Corn Processing

In 2008, the United States produced ethanol at a rate of 39.5 billion L/year; an additional 8.5 billion L/year capacity was under construction. Kernel composition and physical properties are not correlated with ethanol yield. A procedure that measured the potential of hybrids to produce ethanol would benefit corn seed companies, corn producers, and ethanol processors. The objective was to develop a laboratory procedure to measure ethanol yield from corn samples and evaluate the developed procedure for accuracy and precision. To determine parameters for routine analyses, effects of mill type, dry solids, and yeast addition were investigated separately followed by effects of fermentation time (T_f), glucoamylase dose, and yeast addition. Measurement of ethanol using HPLC and gravimetric (change in weight due to CO₂ loss) methods were compared. Using the procedure developed, ethanol yields for five diverse hybrids (dent, waxy, white, high oil, and high amylose) were measured. Effects of mill type, dry solids, T_f, glucoamylase dose, and yeast addition were significant (P < 0.05). The gravimetric method estimated higher yields (428 ± 10 L/tonne) than HPLC (405 ± 15 L/tonne) and had a higher level of precision. Both methods had coefficients of variations of <4% and gave similar conclusions. In the final procedure, we used corn (25 g/batch) liquefied with α‐amylase (60 min at 90°C) in 75 mL of distilled water. Simultaneous saccharification and fermentation was used (64 hr at 32°C) with glucoamylase and yeast. Gravimetric and HPLC methods measured differences in ethanol yield for the five hybrids (158–435 L/tonne). The method is suitable for routine testing of ethanol yield potential and as a reference method for verifying more rapid measurement techniques.     

Phenolic Content and Antioxidant Activity of Pearled Wheat and Roller‐Milled Fractions

Wheat contains phenolic compounds concentrated mainly in bran tissues. This study examined the distribution of phenolics and antioxidant activities in wheat fractions derived from pearling and roller milling. Debranning (pearling) of wheat before milling is becoming increasingly accepted by the milling industry as a means of improving wheat rollermilling performance, making it of interest to determine the concentration of ferulic acid at various degrees of pearling. Eight cultivar samples were used, including five genotypes representing four commercial Canadian wheat classes with different intrinsic qualities. Wheat was pearled incrementally to obtain five fractions, each representing an amount of product equivalent to 5% of initial sample weight. Wheat was also roller milled without debranning. Total phenolic content of fractions was determined using the modified Folin‐Ciocalteau method for all pearling fractions, and for bran, shorts, bran flour, and first middlings flour from roller milling. Antioxidant activity was determined on phenolic extracts by a method involving the use of the free radical 2,2‐diphenyl‐l‐picrylhydrazyl (DPPH). Total phenolics were concentrated in fractions from the first and second pearlings (>4,000 mg/kg). Wheat fractions from the third and fourth pearlings still contained high phenolic content (>3,000 mg/kg). A similar trend was observed in antioxidant activity of the milled fractions with ≈4,000 mg/kg in bran and shorts, ≈3,000 mg/kg in bran flour, and <1,000 mg/kg in first middlings flour. Total phenolic content and antioxidant activity were highly correlated (R² = 0.94). There were no significant differences between red and white wheat samples. A strong influence of environment (growing location) was indicated. Pearling represents an effective technique to obtain wheat bran fractions enriched in phenolics and antioxidants, thereby maximizing health benefits associated with wheat‐based products.     

Pretreatment of Wet‐Milled Corn Fiber to Improve Recovery of Corn Fiber Oil and Phytosterols

The phytosterol‐containing oil in the corn fiber (corn fiber oil) has potential use as a natural low‐density lipoprotein (LDL) lowering nutraceutical but its low concentration (1–3%) makes it difficult and expensive to extract. Pretreatment of corn fiber with dilute acid or glucosidases removed nonlipid components of fiber, producing oil‐enriched fractions that should be more amenable to efficient and inexpensive oil extraction. Acid, as well as enzymes, significantly increased the content of corn fiber oil and its phytosterol compounds by hydrolyzing (and removing) the starch and nonstarch (cell wall) polysaccharides from the wet‐milled corn fiber. Dual treatment of the fiber with acid and enzyme greatly increased the concentrations of corn fiber oil and its phytosterol components, compared with acid or enzyme treatments alone. Depending on the treatment, the oil concentration in the residual solids increased from 0.3 to 10.8% (21–771% increase in conc.) and the total phytosterol concentration increased from 19.8 to 1256.2 mg/g of fiber (11–710% increase in conc.) compared with untreated fiber.     

Evaluation and Strategies to Improve Fermentation Characteristics of Modified Dry‐Grind Corn Processes

New corn fractionation technologies that produce higher value coproducts from dry‐grind processing have been developed. Wet fractionation technologies involve a short soaking of corn followed by milling to recover germ and pericarp fiber in an aqueous medium before fermentation of degermed defibered slurry. In dry fractionation technologies, a dry degerm defiber (3D) process (similar to conventional corn dry‐milling) is used to separate germ and pericarp fiber before fermentation of the endosperm fraction. The effect of dry and wet fractionation technologies on the fermentation rates and ethanol yields were studied and compared with the conventional dry‐grind process. The wet process had the highest fermentation rate. The endosperm fraction obtained from 3D process had lowest fermentation rate and highest residual sugars at the end of fermentation. Strategies to improve the fermentation characteristics of endosperm fraction from 3D process were evaluated using two saccharification and fermentation processes. The endosperm fraction obtained from 3D process was liquefied by enzymatic hydrolysis and fermented using either separate saccharification (SS) and fermentation or simultaneous saccharification and fermentation (SSF). Corn germ soak water and B‐vitamins were added during fermentation to study the effect of micronutrient addition. Ethanol and sugar profiles were measured using HPLC. The endosperm fraction fermented using SSF produced higher ethanol yields than SS. Addition of B‐vitamins and germ soak water during SSF improved fermentation of 3D process and resulted in 2.6 and 2.3% (v/v) higher ethanol concentrations and fermentation rates compared with 3D process treatment with no addition of micronutrients.     

Distribution of Fusarium Molds and Fumonisins in Dry-Milled Corn Fractions

The distribution of Fusarium molds and fumonisins was determined in commercial and experimental dry-milled corn fractions. Fusarium infection of the commercial whole corn samples ranged from 10 to 28%; F. moniliforme was the predominant species. Fusarium counts in corn fractions were <100 colony-forming units (CFU)/g in flaking grits, <100 - 6.4 × 10⁴ CFU/g in bran, <100 − 1.6 × 10⁴ CFU/g in germ, and <100 − 2.7 × 10³ CFU/g in flour. Fumonisin concentrations were ≤0.1 μg/g in flaking grits, 0.2–1.1 μg/g in flour, 0.1–2.0 μg/g in germ, and 1.5–3.2 μg/g in bran. Yellow, blue, and white dent corns naturally contaminated with varying levels of fumonisins (25.4, 3.9, and 0.3 μg of fumonisin B₁ per gram) and Fusarium molds (3.9 × 10⁶, 8.0 × 10⁵, and 2.6 × 10⁴ CFU/g) were experimentally dry milled with a horizontal drum degermer. Number 5 grits contained significantly lower Fusarium counts and fumonisin concentrations than the whole kernel corn. Fusarium counts and fumonisins increased as grit size decreased, and high Fusarium counts and fumonisin concentrations were found in germ, bran, and fines.     

Comparison of Modified Dry‐Grind Corn Processes for Fermentation Characteristics and DDGS Composition

Three different modified dry‐grind corn processes, quick germ (QG), quick germ and quick fiber (QGQF), and enzymatic milling (E‐Mill) were compared with the conventional dry‐grind corn process for fermentation characteristics and distillers dried grains with solubles (DDGS) composition. Significant effects were observed on fermentation characteristics and DDGS composition with these modified dry‐grind processes. The QG, QGQF, and E‐Mill processes increased ethanol concentration by 8–27% relative to the conventional dry‐grind process. These process modifications reduced the fiber content of DDGS from 11 to 2% and increased the protein content of DDGS from 28 to 58%.     

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%).     

High‐Starch and High‐β‐Glucan Barley Fractions Milled with Experimental Mills

This study focused on the performance of two hulless barley cultivars (Doyce and Merlin) and one commercial husked (hulled) sample using experimental milling. The purpose was to use experimental milling as a preliminary indicator of the milled streams with potential use for fuel ethanol production and fractions that could be used in food products. Experimental mills designed for flour production evaluation from wheat were Chopin CD1 Auto, Quadrumat Sr, Buhler, and an experimental Ross roller mill walking flow. Results indicate that the shorts had the highest levels of β‐glucan from all the mills. However, the β‐glucan content in the break flours was highest with the roller mill walking flow and the Chopin CD1 for the hulless cultivars. The lowest β‐glucan content in the break flour was found with the Buhler for Doyce. Break flour and, to a slightly lesser extent, reduction flour from all cultivars tested on all mills contained the highest starch content (up to 83%) and are therefore most appropriate for use as feedstock for fuel ethanol production. Conversely, bran and shorts from all cultivars and mills were lowest in starch (as low as 25%), making them ideal as low‐starch food ingredients.     

Hydrolysis and Fermentation of Pericarp and Endosperm Fibers Recovered from Enzymatic Corn Dry‐Grind Process

A modified dry‐grind corn process has been developed that allows recovery of both pericarp and endosperm fibers as coproducts at the front end of the process before fermentation. The modified process is called enzymatic milling (E‐Mill) dry‐grind process. In a conventional dry‐grind corn process, only the starch component of the corn kernel is converted into ethanol. Additional ethanol can be produced from corn if the fiber component can also be converted into ethanol. In this study, pericarp and endosperm fibers recovered in the E‐Mill dry‐grind process were evaluated as a potential ethanol feedstock. Both fractions were tested for fermentability and potential ethanol yield. Total ethanol yield recovered from corn by fermenting starch, pericarp, and endosperm fibers was also determined. Results show that endosperm fiber produced 20.5% more ethanol than pericarp fiber on a g/100 g of fiber basis. Total ethanol yield obtained by fermenting starch and both fiber fractions was 0.370 L/kg compared with ethanol yield of 0.334 L/kg obtained by fermenting starch alone.     

Influence of Temper Duration and Weight Distance on System Output in the Corn Dry‐Milling Process

Initial uniform distribution of moisture in the corn kernel is transformed into nonuniform distribution through tempering to facilitate easy fractionation of corn components. Proper temper duration is essential for effectiveness of the tempering process: a short temper time is insufficient to cause necessary nonuniformity; a long temper duration may allow moisture to redistribute uniformly. Untempered corn suffers from lack of beneficial swelling stress and therefore produces lower yields of flaking grits, coarse grits, and germ. For tempered corn, the system throughput exponentially decreases with temper duration and then stabilizes; the period of stabilization is dependent on weight distance. Throughput values are lower at longer weight distances. At a temper duration of 0.066 m, throughput was ≈33–50% at 0.053 m weight distance. Tail stock fraction rapidly and nonlinearly decreases with increase in temper duration; the rate of decrease is higher at longer weight distance. The peak values of flaking grits can exceed 50% at some combinations of weight distance and temper duration. Coarse grit yields were 9–19% and 16–24% for the shorter and longer weight distances, respectively. Germ recovery improved due to tempering, and differed only by ≈0.5% at the two weight distances. Tempering lowered the oil content of flaking grit, but the temper duration did not have much influence on moisture content of various fractions.     

Yield and Phytosterol Composition of Oil Extracted from Grain Sorghum and Its Wet‐Milled Fractions

Corn fiber contains an oil with high levels of three potential cholesterol‐lowering phytosterol compounds. Little information is available about the levels and types of phytosterols in sorghum. In this study, phytosterols were evaluated in grain sorhgum and its wet‐milled fractions and were compared with the phytosterols in corn. The study showed that sorghum kernels can provide a significant source of two phytosterol classes, free phytosterols (St) and fatty acyl phytosterol esters (St:E). Most of these phytosterols are concentrated in the wet‐milled fiber fraction followed by the germ fraction. In addition to phytosterols, other lipid classes such as wax esters and an aldehyde (50% C28 and 50% C30) are also present in the sorghum oil. Comparison of sorghum and corn kernels show that corn has 72–93% more phytosterols than sorghum.     

Comparison of Raw Starch Hydrolyzing Enzyme with Conventional Liquefaction and Saccharification Enzymes in Dry‐Grind Corn Processing

In a conventional dry‐grind corn process, starch is converted into dextrins using liquefaction enzymes at high temperatures (90–120°C) during a liquefaction step. Dextrins are hydrolyzed into sugars using saccharification enzymes during a simultaneous saccharification and fermentation (SSF) step. Recently, a raw starch hydrolyzing enzyme (RSH), Stargen 001, was developed that converts starch into dextrins at low temperatures (<48°C) and hydrolyzes dextrins into sugars during SSF. In this study, a dry‐grind corn process using RSH enzyme was compared with two combinations (DG1 and DG2) of commercial liquefaction and saccharification enzymes. Dry‐grind corn processes for all enzyme treatments were performed at the same process conditions except for the liquefaction step. For RSH and DG1 and DG2 treatments, ethanol concentrations at 72 hr of fermentation were 14.1–14.2% (v/v). All three enzyme treatments resulted in comparable ethanol conversion efficiencies, ethanol yields, and DDGS yields. Sugar profiles for the RSH treatment were different from DG1 and DG2 treatments, especially for glucose. During SSF, the highest glucose concentration for RSH treatment was 7% (w/v), whereas for DG1 and DG2 treatments, glucose concentrations had maximum of 19% (w/v). Glycerol concentrations were 0.5% (w/v) for RSH treatment and 0.8% (w/v) for DG1 and DG2 treatments.