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%.     

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.     

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.     

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%).     

Use of Pigmented Maize in Both Conventional Dry‐Grind and Modified Processes Using Granular Starch Hydrolyzing Enzyme

In the dry‐grind ethanol process, distillers dried grains with solubles (DDGS) is the main coproduct, which is primarily used as an ingredient in ruminant animal diets. Increasing the value of DDGS will improve the profitability of the dry‐grind ethanol process. One way to increase DDGS value is to use pigmented maize as the feedstock for ethanol production. Pigmented maize is rich in anthocyanin content, and the anthocyanin imparts red, blue, and purple color to the grain. It is reported that anthocyanin would be absorbed by yeast cell walls during the fermentation process. The effects of anthocyanin on fermentation characteristics in the dry‐grind process are not known. In this study, the effects of anthocyanin in conventional (conventional starch hydrolyzing enzymes) and modified (granular starch hydrolyzing enzymes [GSHE]) dry‐grind processes were evaluated. The modified process using GSHE replaced high‐temperature liquefaction. The ethanol conversion efficiencies of pigmented maize were comparable to that of yellow dent corn in both conventional (78.4 ± 0.5% for blue maize, 74.3 ± 0.4% for red maize, 81.2 ± 1.0% for purple maize, and 75.1 ± 0.2% for yellow dent corn) and modified dry‐grind processes using GSHE (83.8 ± 0.8% for blue maize, 81.1 ± 0.3% for red maize, 93.5 ± 0.8% for purple maize, and 85.6 ± 0.1% for yellow dent corn). Total anthocyanin content in DDGS from the modified process was 1.4, 1.9, and 2.4 times of that from the conventional process for purple, red, and blue maize samples, respectively. These results indicated that pigmented maize rich in anthocyanin did not negatively affect the fermentation characteristics of the dry‐grind process and that there was a potential to use pigmented maize in the dry‐grind process, especially when using GSHE.     

Use of Phytases in Ethanol Production from E‐Mill Corn Processing

Effects of phytase addition, germ, and pericarp fiber recovery were evaluated for the E‐Mill dry grind corn process. In the E‐Mill process, corn was soaked in water followed by incubation with starch hydrolyzing enzymes. For each phytase treatment, an additional phytase incubation step was performed before incubation with starch hydrolyzing enzymes. Germ and pericarp fiber were recovered after incubation with starch hydrolyzing enzymes. Preliminary studies on phytase addition resulted in germ with higher oil (40.9%), protein (20.0%), and lower residual starch (12.2%) contents compared to oil (39.1%), protein (19.2%), and starch (18.1%) in germ from the E‐Mill process without phytase addition. Phytase treatment resulted in lower residual starch contents in pericarp fiber (19.9%) compared to pericarp fiber without phytase addition (27.4%). Results obtained led to further investigation of effects of phytase on final ethanol concentrations, germ, pericarp fiber, and DDGS recovery. Final ethanol concentrations were higher in E‐Mill processing with phytase addition (17.4% v/v) than without addition of phytase (16.6% v/v). Incubation with phytases resulted in germ with 4.3% higher oil and 2.5% lower residual starch content compared to control process. Phytase treatment also resulted in lower residual starch and higher protein contents (6.58 and 36.5%, respectively) in DDGS compared to DDGS without phytase incubations (8.14 and 34.2%, respectively). Phytase incubation in E‐Mill processing may assist in increasing coproduct values as well as lead to increased ethanol concentrations.     

Laboratory Yields and Process Stream Compositions from E‐Mill and Dry‐Grind Corn Processes Using a Granular Starch Hydrolyzing Enzyme

In dry‐grind corn processing, the whole kernel is fermented to produce ethanol and distillers dried grains with solubles (DDGS); the E‐Mill process was developed to generate coproducts in addition to DDGS. Compositions of thin stillage and wet grains obtained from the E‐Mill process will be different from the dry‐grind process. Knowledge of thin stillage compositions will provide information to improve coproducts from both processes. Laboratory dry‐grind and E‐Mill processes that used granular starch hydrolyzing enzymes (GSHE) were compared and process yields determined. Two methods, centrifugation and screening, were used to produce thin stillage and wet grains from the laboratory processes. Compositions of process streams were determined. In the dry‐grind process using GSHE, solids contents of beer, whole stillage, and wet grains were higher compared to the same fractions from the E‐Mill process using GSHE. Solids contents of mash for both processes were similar. Total solids, soluble solids, and ash contents of thin stillage were similar for the two processes. Fat content of thin stillage from E‐Mill was lower than that from the dry‐grind process; protein content of E‐Mill thin stillage was higher than that from dry‐grind thin stillage. Removal of germ and fiber before fermentation changed composition of thin stillage from the E‐Mill process. The screening method produced higher thin stillage and lower wet grains yields than using a centrifugation method. The screening method was less time consuming but resulted in limited wet grains material for additional analyses or processing. The centrifugation method of thin stillage separation removed more solids from thin stillage than the screening method.     

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.     

Pericarp Fiber Separation from Corn Flour Using Sieving and Air Classification

In the dry‐grind process, starch in ground corn (flour) is converted to ethanol, and the remaining corn components (protein, fat, fiber, and ash) form a coproduct called distillers dried grains with solubles (DDGS). Fiber separation from corn flour would produce fiber as an additional coproduct that could be used as combustion fuel, cattle feed, and as feedstock for producing valuable products such as “cellulosic” ethanol, corn fiber gum, oligosaccharides, phytosterols, and polyols. Fiber is not fermented in the dry‐grind corn process. Its separation before fermentation would increase ethanol productivity in the fermenter. Recently, we showed that the elusieve process, a combination of sieving and elutriation (air flow), was effective in fiber separation from DDGS. In this study, we evaluated the elusieve process for separating pericarp fiber from corn flour. Corn flour remaining after fiber separation was termed “enhanced corn flour”. Of the total weight of corn flour, 3.8% was obtained as fiber and 96.2% was obtained as enhanced corn flour. Neutral detergent fiber (NDF) of corn flour, fiber, and enhanced corn flour (dry basis) were 9.0, 61.5, and 5.7%, respectively. Starch content of corn flour, fiber, and enhanced corn flour (dry basis) were 68.8, 23.5, and 71.3%, respectively. Final ethanol concentration from enhanced corn flour (14.12% v/v) was marginally higher than corn flour (13.72% v/v). No difference in ethanol yields from corn flour and enhanced corn flour was observed. The combination of sieving and air classification can be used to separate pericarp fiber from corn flour. The economics of fiber separation from corn flour using the elusieve process would be governed by the production of valuable products from fiber and the revenues generated from the valuable products.     

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.     

Separation of Fiber from Distillers Dried Grains with Solubles (DDGS) Using Sieving and Elutriation

A process was developed to separate fiber from distillers dried grains with solubles (DDGS) in a dry‐grind corn process. Separation of fiber from DDGS would provide two valuable coproducts: 1) DDGS with reduced fiber, increased fat, and increased protein contents; and 2) fiber. The process, called elusieve process, used two separation methods, sieving and elutriation, to separate the fiber. Material carried by air to the top of the elutriation column was called the lighter fraction and material that settled to the bottom of the column was called the heavier fraction. We evaluated the compositions of fractions produced from sieving and elutriation. Two commercial samples of DDGS were obtained from two dry‐grind corn plants. Sieving over four screens (869, 582, 447, and 234 μm openings) created five size categories. The two smallest size categories contained >40% (w/w) of the original DDGS and had reduced fiber and increased protein and fat contents relative to the original DDGS. Elutriation of the remaining three size categories increased protein and fat contents and reduced fiber contents in the heavier fractions. Elutriation at air velocities of 1.59–5.24 m/sec increased the protein content of the heavier fraction by 13–41% and increased the fat content of the heavier fraction by 4–127% compared with the bulk fractions of each size category. This process was effective in separating fiber from both DDGS samples evaluated. Elusieve process does not require changes in the existing dry‐grind process and can be implemented at the end of the dry‐grind process.     

Effect of Harvest Moisture Content on Selected Yellow Dent Corn: Dry‐Grind Fermentation Characteristics and DDGS Composition

Efficiently utilizing the nongrain portion of the corn plant as ruminant food and the grain for ethanol will allow the optimization of both food and fuel production. Corn and corn stover could be more effectively used if they were harvested earlier before dry down. Corn harvested at different moisture contents (MCs) may exhibit different processing characteristics for the ethanol industry, because of differences in physical and chemical properties. Therefore, the objective of this study was to investigate the effect of corn harvest MC on dry‐grind fermentation characteristics and dried distillers grains with solubles (DDGS) composition. Pioneer hybrid 32D78 was harvested at seven different dates from August 21 to November 23, 2009, with harvest MCs ranging from 73 to 21% (wb). The corn samples with different harvest MCs were evaluated by a conventional dry‐grind process. Final ethanol concentration from the corn with harvest MC of 54% (kernel dent stage) was 17.9% (v/v), which was significantly higher (0.5–1.2 percentage points) than the mature corn with lower harvest MCs (P < 0.05). Ethanol conversion efficiencies for the corn with harvest MCs of 73 and 54% (wb) were 98.5 and 93.2%, respectively, whereas ethanol conversion efficiencies for the corn with lower harvest MCs were significantly lower (P < 0.05), ranging between 83.2 and 88.3%. For DDGS composition, with corn harvest MC decreasing from 73 to 21% (wb), the residual starch concentration increased from 7.7 to 15.2%, the crude protein concentration decreased from 29.4 to 24.9%, and the neutral detergent fiber concentration decreased from 26.6 to 20.6%.     

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.     

Fate of Bt Protein and Influence of Corn Hybrid on Ethanol Production

Corn hybrids were compared to determine the fate of recombinant Bt protein (CRY1Ab from Bacillus thuringiensis) in coproducts from dry grind and wet‐milled corn during production of fuel ethanol. Two pairs of Bt and non‐Bt hybrids were wet milled, and each fraction was examined for the presence of the Bt protein. Bt protein was found in the germ, gluten, and fiber fractions of Bt hybrids. In addition, one set of Bt and non‐Bt hybrids were treated by the dry‐grind ethanol process and Bt protein was monitored during each step of the process. The Bt protein was not detected after liquefaction. Subsequent experiments determined that the Bt protein is rapidly denatured at liquefaction temperatures. Finally, five hybrids were compared for ethanol yield after dry grinding. Analysis of fermentation data with an F‐test revealed the percent of total starch available for conversion into ethanol varied significantly among the hybrids (P < 0.002), indicating ethanol yield is not exclusively dependent on starch content. No difference, however, was observed between Bt and non‐Bt corn hybrids for either ethanol productivity or yield.     

Effect of Alternative Milling Techniques on the Yield and Composition of Corn Germ Oil and Corn Fiber Oil

The effects of alternative corn wet‐milling (intermittent milling and dynamic steeping (IMDS), gaseous SO₂ and alkali wet‐milling) and dry grind ethanol (quick germ and quick fiber with chemicals) production technologies were evaluated on the yield and phytosterol composition (ferulate phytosterol esters, free phytosterols, and fatty acyl phytosterol esters) of corn germ and fiber oil and compared with the conventional wet‐milling process. Small but statistically significant effects were observed on the yield and composition of corn germ and fiber oil with these alternative milling technologies. The results showed that the germ and fiber fractions from two of the alternative wet‐milling technologies (the gaseous SO₂ and the IMDS) had, for almost all of the individual phytosterol compounds, either comparable or signficantly higher yields compared with the conventional wet‐milling process. Also, both of the modified dry grind ethanol processes (the quick germ and quick fiber) with chemicals (SO₂ and lactic acid) can be used as a new source of corn germ and fiber and can produce oils with high yields of phytosterols. The alkali wet‐milling process showed significantly lower yields of phytosterols compounds in germ but showed significantly higher yield of free phytosterols, fatty acyl phytosterol esters and total phytosterols in the fiber fraction.     

Quick Fiber Process: Effect of Mash Temperature,Dry Solids,and Residual Germ on Fiber Yield and Purity

Preliminary calculations showed that recovery of fiber before fermentation in the dry grind ethanol facilities known as the Quick Fiber process increases fermenter capacity and reduces ethanol production cost by as much as 4 ¢/gal. The objective of the current research was to evaluate the effect of mash temperature, dry solids, and residual germ on fiber yield and purity when using the quick fiber process. Fiber was recovered by flotation and skimming, while maintaining a specified temperature, dry solids, and residual germ in the mash. Varying temperature and dry solids in the mash resulted in a statistically significant effect on the fiber yield, neutral detergent fiber (NDF) content, and weight of NDF/100 g of dry corn. Varying residual germ in the mash resulted in statistically significant differences for NDF through dilution and the weight of NDF/100 g of dry corn. The highest fiber yield was 10.9% at 45°C, 23% dry solids, and 15% residual germ; the highest NDF was 50.9% at 30°C, 21% dry solids, and 0% residual germ. The highest weight of NDF/100 g of dry corn was observed at 45°C, 23% dry solids, and 0% residual germ.     

Methods for Characterization of Residual Starch in Distiller's Dried Grains with Solubles (DDGS)

The objective of this study was to establish methods for determining the content and components of residual starch in distiller's dried grains with solubles (DDGS), a coproduct from dry‐grind corn ethanol production. Four DDGS prepared in our laboratory and one DDGS obtained from a commercial ethanol manufacturer were used for the study. Quantitative analysis of total residual sugar (TRS) in DDGS was performed by determining d ‐glucose produced by enzymatic hydrolysis of oligosaccharides and residual starch remaining in hexane‐defatted DDGS after being dispersed in 90% DMSO. The TRS consisted of free glucose, oligosaccharides, and residual starch. The commercial manufacturer's DDGS contained more TRS (15.8%, w/w db) than the laboratory‐processed DDGS (2.4–2.9%, w/w db). The content of residual starch remaining in the commercial DDGS (5.5% w/w db) was also larger than the laboratory‐processed DDGS (1.9–2.5% w/w db). Analyses of molecular weight distribution showed that the residual starch in DDGS consisted of short‐chain amylose and amylopectin, respectively, as the major and minor components. The short‐chain amylose molecules constituted 86.5–94.1% of the residual starch. The major population of the short‐chain amyloses had an average degree of polymerization (DP) of 85, closely resembling the length of enzyme‐resistant fragments of amylose‐lipid complexes.     

Improvement of Dry‐Fractionation Ethanol Fermentation by Partial Germ Supplementation

Ethanol fermentation of dry‐fractionated grits (corn endosperm pieces) containing different levels of germ was studied with the dry‐grind process. Partial removal of the germ fraction allows for marketing the germ fraction and potentially more efficient fermentation. Grits obtained from a dry‐milling plant were mixed with different amounts of germ (2, 5, 7, and 10% germ of the total sample) and compared with control grits (0% germ). Fermentation rates of germ‐supplemented grits (2, 5, 7, and 10% germ) were faster than control grits (0% germ). Addition of 2% germ was sufficient to achieve a high ethanol concentration (19.06% v/v) compared with control grits (18.18% v/v). Fermentation of dry‐fractionated grits (92, 95, and 97% grits) obtained from a commercial facility was also compared with ground whole corn (control). Fermentation rates were slower and final ethanol concentrations were lower for commercial grits than the control sample. However, in a final experiment, commercial grits were subjected to raw starch hydrolyzing (RSH) enzyme, resulting in higher ethanol concentrations (20.22, 19.90, and 19.49% v/v for 92, 95, and 97% grits, respectively) compared with the whole corn control (18.64% v/v). Therefore, high ethanol concentrations can be achieved with dry‐fractionated grits provided the inclusion of a certain amount of germ and the use of RSH enzyme for controlled starch hydrolysis.     

Protease Treatment to Improve Ethanol Fermentation in Modified Dry Grind Corn Processes

To improve fractionation efficiency in modified dry grind corn processes, we evaluated the effectiveness of protease treatment in reducing residual starch in endosperm fiber. Three schemes of protease treatment were conducted in three processes: 1) enzymatic milling or E‐Mill, 2) dry fractionation with raw starch fermentation or dry RS, and 3) dry fractionation with conventional fermentation or dry conv. Kinetics of free amino nitrogen production were similar in both dry and wet fractionation (E‐Mill), indicating that proteolysis was effective in all three schemes. At the end of fermentation, endosperm fiber was recovered and its residual starch measured. Using protease treatment, residual starch in the endosperm fiber was reduced by 1.9% w/w (22% relative reduction) in dry conv and 1.7% w/w (8% relative reduction) in dry RS, while no reduction was observed in the E‐Mill process. Protease treatment increased ethanol production rates early in fermentation (≤24 hr) but final ethanol concentrations were unaffected in both dry RS and E‐Mill. In dry conv, the addition of protease resulted in a decline in final ethanol concentration by 0.3% v/v, as well as a higher variability in liquefaction product concentration (higher standard deviations in the glucose and maltose yields). Protease treatment can be used effectively to enhance modified dry grind processes.     

Economics of Fiber Separation from Distillers Dried Grains with Solubles (DDGS) Using Sieving and Elutriation

Separation of fiber from distillers dried grains with solubles (DDGS) provides two valuable coproducts: 1) enhanced DDGS with reduced fiber, increased fat and increased protein contents and 2) fiber. Recently, the elusieve process, a combination of sieving and elutriation was found to be effective in separating fiber from two commercial samples of DDGS (DDGS‐1 and DDGS‐2). Separation of fiber decreased the quantity of DDGS, but increased the value of DDGS by increasing protein content and produced a new coproduct with higher fiber content. Economic analysis was conducted to determine the payback period, net present value (NPV), and internal rate of return (IRR) of the elusieve process. The dependence of animal foodstuff prices on their protein content was determined. Equipment prices were obtained from industrial manufacturers. Relative to crude protein content of original DDGS, crude protein content of enhanced DDGS was higher by 8.0% for DDGS‐1 and by 6.3% for DDGS‐2. For a dry‐grind plant processing corn at the rate of 2,030 metric tonnes/day (80,000 bushels/day), increase in revenue due to the elusieve process would be $0.4 to 0.7M/year. Total capital investment for the elusieve process would be $1.4M and operating cost would be $0.1M/year. Payback period was estimated to be 2.5–4.6 years, NPV was $1.2–3.4M, and IRR was 20.5–39.5%.