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

Radhakrjshnan Srinivasan, 1 Robert A. Moreau, 2 Kent D. Rausch,' Ronald L. Belyea,3M. E. Tumbleson,' and Vijay Singh "45

ABSTRACT Cereal Chem. 82(5):528-533

A process was developed to separate fiber from distillers dried grainswith solubles (DDGS) in a dry-grind corn process. Separation of fiberfrom DDGS would provide two valuable coproducts: 1) DDGS withreduced 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 thetop of the elutriation column was called the lighter fraction and materialthat settled to the bottom of the column was called the heavier fraction.We evaluated the compositions of fractions produced from sieving andelutriation. Two commercial samples of DDGS were obtained from twodry-grind corn plants. Sieving over four screens (869. 582, 447, and 234 Jimopenings) created five size categories. The two smallest size categories

In a dry-grind corn plant, starch is fermented to ethanol. Remain-ing components in the corn (protein, fiber, fat, unconverted starch,and ash) form a coproduct known as distillers dried grains withsolubles (DDGS). DDGS is defined as the product obtained afterremoval of ethyl alcohol by distillation from the yeast fermentationof a grain or a grain mixture by condensing and drying at least75% of the resultant whole stillage (AAFCO 2002). Currently,dry-grind corn plants produce about 70% of fuel ethanol in theUnited States. Ethanol production in the United States is expectedto increase in the future (RFA 2004); DDGS supply will increaseproportionately. Supply and demand of DDGS will play an impor-tant role in the economics of ethanol production. In the currentscenario of rapidly increasing DDGS supply. there is a need for en-hancing the value of DDGS. Separation of fiber from DDGS couldresult in two products: 1) DDOS with reduced fiber, increased fat,and increased protein contents; and 2) fiber.

DDGS with reduced fiber content could be used in nonrumi-nant animal diets. DDGS with increased protein and fat contentwill enhance nutritional value and could increase market value.DDGS with high fat (13%) and high protein (33%) is worth about$5-20/ton more from a nutrient content basis than DDOS withlower fat (11%) and lower protein (28%) (Belyea et at 2004).Fiber produced from the elusieve process would be an additionalcoproduct of the dry-grind plants. Corn fiber could be used tomake valuable products such as corn fiber oil, corn fiber gum,bioethanol, and xylitol (Grohmann et at 1997; Moreau et at 1999:Anonymous 2002; Buchanan 2002).

Singh et at (2002) investigated air aspiration as a method toseparate fiber front DDGS. They showed limited success for aspir-ation in recovering fiber from DDGS and in recovering phytosterolcompounds. In the present study, we used a combination of two

Department of Agricultural and Biological Engineering, University of Illinois atUrbana-Champaign, Urbana, IL 61 801.2 Lead scientist, Crop Conversion Science and Engineering Research Unit, Eastern

Regional Research Center. ARS, USDA, Wyndmoor, PA 19038.Professor of animal sciences, University of Missouri. Columbia, MO 65211.

'Assistant professor, Department of Agricultural and Biological Engineering.University of Illinois at Urbana-Champaign, Urbana. IL 61801.

'Corresponding author. Phone: 217-333-9510. Fax: 217-244-0323. E-mail:vsingh@uiuc.edu

001:10.1094/ CC-82-0528© 2005 AACC International, Inc.

528 CEREAL CHEMISTRY

contained >40% (w/w) of the original DDGS and had reduced fiber andincreased protein and fat contents relative to the original DDGS. Elu-triation of the remaining three size categories increased protein and fatcontents and reduced fiber contents in the heavier fractions. Eluiriat ion atair velocities of 1.59-5.24 rn/sec increased the protein content of theheavier fraction by 13-41% and increased the fat content of the heavierfraction by 4-127% compared with the bulk fractions of each size cate-gory. This process was effective in separating fiber from both DDGSsamples evaluated. Elusieve process does not require changes in theexisting dry-grind process and can he implemented at the end of the dry-grind process.

separation methods, sieving and elutriation, to separate fiber fromDDGS. This process is referred to as the elusieve process. Elu-triation is defined as the separation of particles by means of anupward flowing stream of fluid. Aspiration is defined as "the actor the result of removing, carrying along, or drawing by suction"(McGraw-Hill 1978). The term aspiration is commonly used in thecereal processing industry to refer to the separation of particles bymeans of a stream of air, regardless of the method used to generatethe flow of fluid. In this study, a blower was used to produce anupward stream of air: hence, elutriation is used here instead ofaspiration. Equipment such as aspirators and cyclones may beused for industrial applications of this process.

Sieving is used to separate particles based on the difference insize. Elutrtation by air is used to separate the particles in DDGSbased on combined effects of density, shape, and size characteris-tics. In the dry-milling process, fiber is separated from other com-ponents of corn based on its lower density. Fiber would be lessdense than nonfiber components in DDGS. When air is passedthrough DDGS. fiber would be carried away. Some nonfiber alsowould get carried with the air because nonfiber particles that aremore dense and have smaller size would experience the same forceas fiber particles that are less dense and have larger sizes.

Fiber in the original DDGS spans a wide range of sizes; hence.elutriation of DDGS would selectively remove fiber with a sizethat can be carried by the air at the operating velocity. At high airvelocities, air would carry fiber of all sizes, but the carry over ofnonfiber material would be high. Hence, it could be effective tofirst sieve the DDGS into various size categories and then elutriatethe material in each size category at appropriate velocities toseparate fiber from each size category. Objectives of this studywere to I) determine the composition and other nutritional charac-teristics of fractions produced after sieving and elutriation steps:and 2) assess the effect of velocity of air on composition and yieldof lighter fractions.

MATERIALS AND METHODS

DDGS samples (20 kg) were obtained from two dry-grind cornplants in the United States. The dry-grind corn plants used onlycorn as their feedstock. DDGS-1 was produced from a flash-drying process. DDGS-2 wasproduced from a ring-drying process.In a flash dryer, the wet feed is dried by transporting it for a fewseconds in a hot gas stream. Ring dryers contain a centrifugal

classifier in the flash-drying loop that recirculates larger, wetterparticles back for further drying.

SievingA vibratory screen (model LS188333. Sweco Vibro-Energy Sep-

arator, Los Angeles. CA) was used to sieve DDGS samples intosize categories. The screens were 24T (869 pm), 34T (582 urn),35M (447 urn), 60M (234 urn), and pan. The letters "M" and "T"refer to market-grade cloth and tensil bolt cloth. The size categoriesof material retained on these screens are referred to as 24T, 34T,35M, 60M, and Pan, based on their respective screen labels.Material (1 kg) was sieved on each screen for 2 hr. The comple-tion of sieving was ensured by measuring the weight change inthe receiving container. The material passing through the sieve witha larger opening was collected and then fed to the next smallersieve size. Only one sieve was used at a time.

ElutriationAn elutriation apparatus (Fig. 1) was developed for separating

fiber from DDGS. It consisted of an elutriation column, an airblower for supplying air to the elutriation column, a surge boxmechanism for controlling airflow, a vibratory feeder for feedingmaterial into the column, and collection vessels for receiving thelighter and heavier fractions. Material elutriatcd by the air wascalled the lighter fraction. Material that settled to the bottom ofthe elutriation column was called the heavier fraction. The elu-triation column was constructed using transparent perspex materialto be able to visualize the separation process. The internal diameterof the column was 63 mm and the distance from the powder inletto the air inlet nozzle was 360 mm. The distance of the lighterfraction collection vessel from the powder inlet was 1,100 mm.The lighter fraction collection vessel (300 x 300 x 300 mm) wasconstructed of transparent Perspex material and had a hole 66 mmin diameter in the center of the bottom plate to insert the vesselonto the elutriation column. During operation, the open top wascovered to 95% of its area using a wooden sheet. The velocity ofairflow was measured by inserting a hotwire anemometer (model8355, TSI Velocicaic, St. Paul, MN) into the powder inlet nozzle,with a set time constant of 10 sec. The anemometer was calibratedusing a wind tunnel (model 8390, TSI). Air inlet diameter was 63mm and powder inlet diameter was 19 mm.

The air was supplied using a blower (model 2C701. Dayton.Chicago, IL). Airflow was controlled by a sliding plate arrange-ment on top of a cubical wooden box that was used as a surgevessel for the air supply. The air flow through the elutriationcolumn is in the turbulent regime for the range of flow rate usedin this study. DDGS material was fed into the elutriation columnby a vibratory feeder (model 3090. Powdertec sample mill.Germany) at a rate of 1.0 g/min.

Experimental ProcedureElutriation of each size category was conducted at four differ-

ent velocities. The velocity range was selected such that the yieldof lighter fraction was a minimum of 15% and a maximum of 90%.Air velocities were 1.59-5.24 mlscc, depending on DDGS materialcharacteristics and size category.

Analytical TestsChemical analyses were conducted at a commercial analytical

laboratory. Protein was reported as 6.25 x total nitrogen. Sampleswere analyzed for crude protein (Method 990.03. AOAC 2003),crude fat (Method 920.39). ash (Method 942.05), crude fiber(Method 962.09), and acid detergent fiber (Method 973.18).Neutral detergent fiber (NDF) content was determined by the pro-cedure outlined by Van Soest et al (1991). Crude fiber is the residueremaining after extraction by acid and alkaline hydrolysis; NDF isa measure of the cellulose, hemicellulose, and lignin contents:while acid detergent fiber (ADF) is a measure of cellulose, aciddetergent insoluble nitrogen, acid insoluble ash, and lignin con-tents (Van Soest et al 1991). Sample moisture contents were deter-mined using the two-stage convection oven method (ApprovedMethod 44-18, AACC International 2000). Total digestible nutrients(TDN%) was calculated using digestive factors of 0.78, 1.90,0.57. and 0.85 for protein, fat, fiber, and nitrogen free extract, res-pectively, and was calculated as (NRC 1982): TDN% = ((% crudeprotein x 0.78) + (% crude fat x 1.90) + (% crude fiber x 0.57) +(% nitrogen free extract x 0.85)}. Metabolizable energy (ME..Mcal/kg) was calculated as: ME = (0.96 - (0.00202 x % crudeprotein)} x TDN x 0.02/0.4536: net energy gain (NEg. Mcal/kg)was calculated as: NEg = ((0.00786 x % TDN) - 0.0511/0.4536.

ci [LighterDIII fraction

flDGSI0

a0:0000

.a

aa

feeder

Air inletml I

HeavierBoxfraction

IE-IIJ-1 Blower63 mm

Fig. 1. Schematic of clutriation apparatus.

TABLE IWeight Percent of Material Retained on Each Screen

Mesh Category24T34T35M6DMPan

Opening(pm)Referred to as

86924T

58234T

44735M

2346DM0 Pan

DDC,S-1

(%w/v.) Retained on Screen27.019.413.320.120.2

I)DGS-2(%w/w) Retained on Screen

12.716.913.330.127.0

Vol. 82, No. 5, 2005 529

Crude Protein% (H)29.3*33.035.641.235.526.9*32.033.134.935.53 1.2*35.436.236.537.1

Crude Fat% (H)

12.513.014.215.516.411.3*12.613.816.216.310.9*13.113.314.115.4

, Values at 0 rn/sec denote initial bulk material: NDF, neutral detergent fiber: H, heavier fraction: L, lighter fraction.

Size Category

241 (size> 869 Mm)

341 (582 pm < size < 869 pm)

35M (447 pm <size < 582 pm)

Velocity (rn/see)Yield% (1)0*2.47 17.203.35 27.804.45 43.305.24 61.680*2.22 23.132.55

33.402.85 52.823.86 82.300*1.84 19.302.03 31.802.22 47.102.60 75.98

NDF Separation FactorNDF separation factor for elutriation is defined as the ratio of

the NDF%/Non-NDF% of the lighter fraction to the NDF%INon-NDF% of the heavier fraction. It is calculated as: [NDF%/(100 -NDF%)] L ,ghtcr irac iionl{NDF%/( 100 - NDF%)l Heavier fracuori' NDF sepa-ration factor indicates the selectivity of air in carrying fiber ratherthan nonfiber at the operating air velocity.

A high NDF separation factor indicates that the selectivity ofair in carrying fiber is high. NDF separation factor is analogous tosolvent selectivity in liquid extraction and relative volatility in di-tillation (Treybal 1980).

Statistical AnalysesThe repeatability of the elutriation experiments was verified.

Elutriation of DDGS-1 24T size category was done five times atan air velocity of 2.47 rn/sec and powder feeding rate of I g/min.Mean yield of lighter fraction obtained was 16.7% with a coeffi-cient of variation of ±2.5%.

Elutriation of DDGS-2 35M size category was done five timesat air velocity of 1.59 rn/sec and powder feeding rate of I g/min.Mean yield of lighter fraction obtained was 16.8% with a coeffi-cient of variation of ±9.9%. All composition values are reported asthe mean of two determinations taken from the same material lot.

RESULTS AND DISCUSSION

SievingThe two smallest size categories, 60M (234 - 447 pm) and Pan

(<234 Mm), which were produced by sieving of the original DDGSsamples, comprised 40% of the mass of the original DDGS forDDGS- I and 57% of the mass of the original DDGS for DDGS-2(Table 1). Size categories 60M and Pan contained lower fiber andhigher protein contents with respect to the original DDGSsamples (Tables 11 and III).

For DDGS-1, the original material contained 33.6% protein and32.5% NDF; the 60M size category contained 37.5% protein and29.3% NDF. The Pan size category contained 42.2% protein and19.0% NDF (Table H). For DDGS-2, the original material con-tained 32.9% protein and 33.6% NDF the 60M size categorycontained 33.6% protein and 29.7% NDF. The Pan size categorycontained 40.1% protein and 27.9% NDF (Table III). These twosize categories (60M and Pan) of DDGS- t and DDGS-2 were notsubjected to elutriation due to low fiber and high protein contents.

Elutriation and Fiber SeparationTo determine yields of lighter fraction at each velocity and

compositions of lighter and heavier fractions, the three largest size

TABLE 11Composition (db) of Original Material and Size Categories for DDGS-1 After Sieving

Nominal ParticleCrudeCrude Crude NEgMESize Category Size (pm)Protein%Fat%TDN%Ash%NDF%Fiber%ADF% (Meal/kg) (Meal/kg)Original material All 33.612.590.73.9532.511.518.71.463.57241 >86929.312.589.53.9533.411.515.21.463.5734T 58210 86926.911.388.84.1537.89.2515.31.433.5535M 447 to 58231.210.989.84.1433.610.117.11.463.5560M 234 to 44737.511.389.74.3329.37.7519.61.463.51Pan <23442.212.990.94.5719.06.1214.31.483.51

TDN, total digestible nutrients: NDF, neutral detergent fiber; ADF, acid detergent fiber; NEg, net energy gain; ME, metabolizable energy.

TABLE IIIComposition (db) of Original Material and Size Categories for DDGS-2 After Sieving

Nominal ParticleCrudeCrude Crude NEgMESize Category Size (pm)Protein%Fat%TDN%Ash%NDF%Fiber%ADF% (Meal/kg) (Meal/kg)Original materialAll 32.913.291.04.5333.68.9013.91.483.5924T >869 21.213.190.34.0939.012.6015.51.463.6634T 582to869 24.111.990.03.3040.110.7015.91.463.6435M 447 to 582 27.512.790.34.3234.58.6013.41.463.6260M 234 to 447 33.612.589.34.8029.78.5511.51.463.51Pan <234 40.113.390.94.7027.94.3510.81.483.53"TON, total digestible nutrients; NDF, neutral detergent fiber; ADF, acid detergent fiber; NEg, net energy gain; ME, metabolizable energy.

TABLE IVComposition (db) of Fractions from Elutriation of DDGS-1 Demonstrating Separation of Fibera

NDF% (L)

62.853.346.84.2:3

62.758.748.141.3

56.051.444.339.3

NDF% (H)334*31.432.624.227.637.8*34.532.431.626.233.6*27.628.326.925.8

530 CEREAL CHEMISTRY

categories, 24T (>869 pm). 34T (583-869 .ini). and 35M (447-583 fini) were each subjected to air elutriation at different veloci-ties. High NDF in the lighter fractions in conjunction with highprotein and fat content in the heavier fractions signify effectiveseparation of fiber from the bulk of each size category subjectedto elutriation. For both DDGS samples, elutriation using air waseffective in separating fiber from the bulk material of each sizecategory (Table IV for DDGS-1 and Table V for DDGS-2). Forexample, for the bulk material in the 35M size category of DDGS-1 and air velocity of 2.03 mlsec, NDF increased from 33.6 to 51.4%in the lighter fraction, protein increased from 31.2 to 36.2% in the

heavier fraction, and fat increased from 10.9 to 13.3% in theheavier fraction (Table IV). For the bulk material in the 34T sizecategory of DDGS-2 and air velocity of 2.55 in/sec, NDF increasedfrom 40.1 to 54.6% in the lighter fraction, protein increased from24.1 to 32.7% in the heavier fraction, and fat increased from 11.9to 18.8% in the heavier fraction (Table V).

The relative values of NDF, protein, and fat contents in thefractions at each air velocity signify the separation of fiber, at allair velocities: NDF% (lighter fraction) > NDF% (bulk) > NDF%(heavier fraction); protein% (heavier fraction) > protein% (bulk) >protein% (lighter fraction) and fat% (heavier fraction) > fat% (bulk)

TABLE VComposition (db) of Fractions from Elutriation of DDGS-2 Demonstrating Separation of Fiber'

Size Category Velocity (m/sec)Yield% (L)Crude Protein% (H)Crude Fat% (H)NDF% (L)

24T (size> 869 pm) 0* . . . 21.2 13.12.5521.20 25.6 17.1 66.23.3545.82 26.7 20.1 50.04.4568.52 25.5 24.7 45.24.8089.44 24.9 24.7 45.3

34T (52 urn < si/c < 869 tm) 0* 24.1* 1 l.92.0921.22 29.6 13.8 67.12.5541.93 32.7 18.8 54.62.8558.45 31.4 18.6 50.93.6088.21 29.9 27.0 43.8

35M (447 pm < size < 582 .im)O ... 27.5* 12.71.5918.22 32.1 13.4 61.22.0340.10 33.7 15.1 55.82.2246.30 33.6 15.3 52.42.7288.40 32.8 18.1 41.9

aValues at 0 rn/sec denote initial bulk material: NDF, neutral detergent fiber: H. heavier fraction: 1., lighter fraction.

TABLE VIOther Characteristics (db) of Fractions from Elutriation of DDGS-P

SizeVelocityCrude Protein% Crude Fat%Crude Fiber% ADF%

Category(mlsec)(L) (L) H I. H

L

H

24T 2.4713.0 5.28 5,95 14.816.8

16.5

91.4

3.3519.3 7.05 7.70 12.818.0

19.4

91.9

4.4523.214.90 7.00 11.522.5

20.6

92.6

5.2426.110.20 4.55 9.618.0

15.6

95.134T 2.2212.2 5.66 8.70 13.418.2

18.4

90.0

2.5515.5 6.45 10.60 15.618.8

18.3

90.5

2.8521.7 7.93 9.15 11.617.2

18.0

92.8

3.8626.210.30 11.50 9.620.9

18.8

81.835M 1.8416.5 8.46 7.10 13.718.9

17.3

90.4

2.0323.0 8.30 8.40 10.818.3

18.7

90.0

2.2225.3 9.19 6.80 11.117.7

19.0

91.5

2.6028.810.40 6.50 9.714.6

17.9

92.6

ADF. acid detergent fiber: TDN. total digestible nutrients: H, heavier fraction: L. lighter fraction.

NDF% (H)39,0*32.237.237.733.440.1*35.232.729.325.734,5*28.532.729.726.7

TDN %

82.584.492.588.183.083.185.187.785.685.586.287.6

TABLE VI (continued)Other Characteristics (db) of Fractions from Elutriation of DDGS-13

ME (Meal/kg)

H L

3.62 3.40

3.593.44

3.593.73

3.73 3.53

3.55 3.42

3.573.42

3.643.44

3.223.53

3.553.5!

3.533.44

3.573.46

3.623.48

Size Ash% NEg (McaI/kg)

Category H L H L

24T 3.87 3.53 1.48 1.32

3.98 3.62 1.48 1.34

4.56 3.83 1.50 1.50

3.93 3.69 1.54 1.4134T 4.23 3.85 1.46 1.32

4.31 3.78 1.46 1.32

4.884.04 1.50 1.37

4.804.19 1.32 1.4135M 4.663.89 1.46 1.37

4.744.17 1.46 1.37

4.554.13 1.48 1.39

4.904.30 1.50 1.41

NEg, net energy gain: ME, metabolizable energy: H. heavier fraction: L. lighter fraction.

Vol. 82, No. 5, 2005 531

TABLE ViiOther Characteristics (db) of Fractions from Elutriation of DDGS2a

Size VelocityCrude Protein% Crude Fat%Crude Fiber% ADF%Category(mlsec)(L) (L) H L H241 2.55 10.7 4.8 12.6 16.5

3.35 18.5 7.1 14.5 12.14.4520.7 8.0 12.5 13.44.8021.811.9 7.35 8.9

34T 2.0911.5 5.4 9.20 15.92.55 17.5 7.3 7.90 12.62.8520.5 8.4 7.35 14.13.6024.810.9 9.40 11.6

.59 12.3 6.0 6.70 12.72.03 18.6 8.3 6.55 12.02.2220.8 9.0 6.00 10.52.7226.511.4 4.90 8.3

• \ 0 . AC I i ICI eiecn 6 her: TDN. total (hgestihlc nutrients: H. hc:i icr fraction: L. lighter fraction.

FUII.l. \ LI coiitiiiiit'il)Other Characteristics (db) of Fractions from Elutriation of t)DGS.2

OF

13.918.217.516.514.414.813.717.311.812.415.416.7

TDN %

H

17.5

93.9

81.4

16.2

96.2

84.3

16.3

101.0

85.7

15.6

103.0

89.9

18.3

90.7

81.9

18.7

95.9

84.5

16.6

95.8

84.9

16.5

104.0

87.7

17.1

91.2

84.0

15.0

92.8

85.5

15.7

92.9

86.6

15.4

96.4

89.3

NEg (MeaL/kg)

H L

1.52 1.301.57 1.341.65 1.371.68 1.461.48 1.301.57 1.34.541 .37

1.70 1.411.48 1.341.50 1.371.50 1.391.57 1.43

Site Ash %

Category H

24 I

4.46

3.89

4.67

4.07

4.98

4.03

4.43

4.29

4.89

4.07

5.16

3.98

5.17

4.20

5.32

4.4635M

4.47

3.34

4.62

4.21

4.89

3.99

4.61

4.01

ME (Meal/kg)

H

L

3.77

3.37

3.86

3.44

4.08

3.48

4.17

3.64

3.62

3.40

3.79

3.44

3.79

3.44

4.14

3.53

3.62

3.46

3.66

3.48

3.66

3.53

3.81

3.57NEg. net energy gain: ME. ntetaholizable energy: H, heavier fraction: L. lighter fraction.

> fat% (lighter fraction) (Tables TV-Vu). Higher NDF content inthe lighter fraction and higher protein and fat contents in theheavier fraction indicates that the combination of sieving andelutriation was effective in separating fiber from DDGS producedby two different drying methods (flash drying and ring drying).There were corresponding increases in protein and fat contents inthe heavier fractions from DDGS-1 and DDGS-2.

Elutriation and Effect of Air Velocityon Fiber Separation

An increase in air velocity increased the mass of lighterfraction and reduced the mass of heavier fraction. Correspond-ingly, protein and fat were higher in the heavier fraction and NDFwas lower in the lighter fraction because higher air velocitiescarried the denser nonfiber components into the lighter fraction(Tables IV and V). In general, an increase in air velocity reduced theNDF separation factors obtained by elutriating the size categories,which signifies reduced selectivity of the air in carrying fiberbecause of the ability of air to carry the denser nonfiber com-ponents at higher velocities (Fig. 2).

In general, protein contents of heavier fractions exhibited anincreasing trend with increasing air velocity except for some sizecategories of both DDGS- I and DDGS-2. Protein contents ofheavier fractions tended to become constant or reduce at high airvelocities (Tables IV and V). The fat contents of heavier fractionsfor all size categories showed an increasing trend as air velocitywas increased (Tables IV and V).

In a dry-grind corn plant. the economic optimum air velocitiesftr each size category will be governed by the dependence of fiberalue on fiber purity and the dependence of the value of remaining

532 CEREAL CHEMISTRY

DDGS on protein and fat contents. At low air velocities, fiberseparated from the bulk material would have high NDF% (highpurity of fiber), but the remaining DDGS would have lower proteinand fat contents. At high air velocities, fiber separated from thebulk material would have low NDF% (low fiber purity), but theremaining DDGS would have higher protein and fat contents.

Decrease in size of particles fed to the elutriation column wasexpected to decrease the air velocity needed to produce a specificyield of lighter fraction as the force needed to carry smallerparticles would be lower, density and shape would remain con-stant. Results from Tables IV and V confirm this. As the size ofbulk material fed to the elutriation column decreased, operatingair velocity needed to produce the same yield of lighter fractiondecreased. For the size category >869 pm of DDGS-1, the yield oflighter fraction at air velocity of 2.47 rn/sec was 17.2 17c (Table IV).For the size category 447-582 ini of DDGS- I, the air velocityneeded to produce a similar yield (19.3%) was 1.84 rn/see (TableIV), which was lower than the operating air velocity for 24T sizecategory.

Elutriation and Other Characteristicsof Fractions

Crude fiber in the lighter fractions decreased as air velocityincreased, exhibiting a trend similar to that of NDF. while ADFvalues did not follow any specific trend (Tables VI and VII). TDNin the heavier fractions increased with increasing air velocity,exhibiting a trend similar to those of protein and fat contents inthe heavier fractions, while there was no specific trend observedin the ash content, NEg (net energy gain), and ME (metabolizableenergy) values for heavier as well as lighter fractions.

4.50

T, DOGS-2

LTC 3.00

LL 201

1.04)1.522.533.544.555.5

Air Velocity (misec)

Fig. 2. Neutral detergent fiber (NDF) separation factors at different elu-triation air velocities for elutriation of 241 34T. and 35M size categoriesof distillers dried grains with solubles (DDGS- I and DDGS-2).

CONCLUSIONS

The elusieve process was effective in separating fiber fromDDGS. Sieving alone produced two size categories that containedreduced fiber and increased contents of protein and fat. Elutriationof screened fractions resulted in increased contents of protein andfat and reduced fiber in the heavier fractions. Higher protein andfat content will increase market value of these DDGS fractionsand decreased fiber content would increase the inclusion levels ofDDGS in nonruminant diets. Fiber produced from the process isan additional coproduct and will further increase revenues becauseof its potential use in ruminant diets, production of corn fibergum, corn fiber oil. phytosterols, xylitol, and bioethanol.

Thus, the elusieve process and its products would benefit dry-grind corn processors, especially important in the current scenarioof rapidly increasing ethanol production. This separation processdoes not call for changes in the existing dry-grind corn processand facilitates easy implementation in existing plants. An economicfeasibility study of elusieve process is underway.

ACKNOWLEDGMENTS

We thank Larry Pruiett for technical assistance in assembling the elu-triation apparatus and Nilesh Garasia for technical assistance in the elutri-ation of samples. This study was funded in part by Illinois Council forFood and Agricultural Research (C-FAR). Grant No. IDA CF 04E-072- I.

LITERATURE CITED

AACC International. 2000. Approved Methods of the American Associ-ation of Cereal Chemists, 10th Ed. Method 44-18. The Association: St.Paul, MN.

AAFCO. 2002. Official publication of the Association of American FeedControl Officials Incorporated. The Association: Oxford, IN.

Anonymous. 2002. Microbial production of xylitol from corn fiber. Indus.Bioprocessing 24:5.

AOAC. 2003. Official Methods of the Association of Official AnalyticalChemists, 17th Ed. The Association: Gaithersburg, MD.

Belyea, R. L., Rausch, K. D., and Tumbleson. M. E. 2004. Compositionof corn and distillers dried grains with solubles from dry grind ethanolprocessing. Biores. Technol. 94:293-298.

Buchanan, C. M. 2002. High value products from corn fiber. Indus.Bioprocessing 24:3-4.

Grohmann, K.. and Bothast. R. J. 1997. Saccharitication of corn fiber bycombined treatment with dilute sulphuric acid and enzymes. ProcessBiochem. 32:405-415.

McGraw-Hill. 1978. McGraw-Hill Dictionary of Scientific and TechnicalTerms. 2nd Ed. McGraw-Hill: New York.

Moreau, R. A., Norton, R. A.. and Hicks. K. B. 1999. Phytosterols andphytostanols lower cholesterol. INFORM 10:572-577.

NRC. 1982. United States-Canadian tables of Feed Composition. 3rdRev. Nat. Acad. Press: Washington. DC.

RFA. 2004. U.S. fuel ethanol production capacity. www.cthanolrfa.org/eth_prodjac.html. Renewable Fuels Association: Washington, DC.

Singh, V., Moreau, R. A., Hicks. K. B., Belyca, R. L.. and Staff, C. H.2002. Removal of fiber from distillers dried grains with solubles(DDGS) to increase value. Trans. ASAE 45:389-392.

Treybal, R. E. 1980. Mass-Transfer Operations. 3rd Ed. McGraw-Hilt:New York.

Van Soest. P. J.. Robertson. J. B.. and Lewis B. A. 1991. Methods fordietary fiber, neutral detergent fiber and non-starch polysaccharides inrelation to animal nutrition. J. Dairy Sci. 74:3583-3597.

[Received January 31, 2005. Accepted May 13, 2005.]

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