Effect of die dimension on extrusion processing parameters (animal feed)

Effect of Die Dimensions on Extrusion Processing Parametersand Properties of DDGS-Based Aquaculture Feeds

Nehru Chevanan,' Kasiviswanathan Muthukumarappan, 2 ' 3 Kurt A. Rosentrater, 4 and James L. Julson3

ABSTRACT

Cereal Chem. 84(4):389-398

The goal of this study was to investigate the effect of die nozzledimensions, barrel temperature profile, and moisture Content on DDGS-based extnidate properties and extruder processing parameters. An In-gredient blend containing 40 17'e. distillers dried grains with solubles(DDGS), along with soy flour, corn flour, fish meal, whe y, mineral andvitamin mix, with a net protein content adjusted to 28 0/c was extruded in asingle-screw laboratory extruder using seven different die nozzles. In-creasing moisture content of the ingredient mix from 15 to 25% resultedin a 2.0. 16.0, 16.3, 22.9. 18.5. 32.5. and 63.7% decrease, respectively, inbulk density, water-solubility index, sinking velocity, L 5 . 6*. mass flowrate, and absolute pressure, as well as 11.6. 16.2, and 7% increases, res-pectively, in pellet durability, water-absorption index, and a. Increasing

Distillers dried grains with solubles (DDGS) typically containhigh amounts of protein (23-29%) and low levels of' starch (l--2%)and are thus a possible alternative protein source for aquaculturefeeds (Chin et al 1989; Lee et al 1991: Wu et al 1994. 1996). De-pending on the species, aquaculture feeds generally require proteincontents of 26-50% (Lovell 1989). Consequently, these formulatedfeeds can contain high quantities of both protein and starch.Floatability of the extrudates is an important quality parameter foraquaculture feeds (Bandyohadhyay and Ranjan 2001: RolI'e et al2001). The unit density of extrudates, which affects the floatahility,depends on the extent of expansion obtained during extrusioncooking. Expansion can he controlled by changing the type andnature of ingredients used, and by changing the processing con-ditions in the extruder. In the extrusion industry, starch-based in-gredients are often used to obtain puffed products, while protein-based ingredients are often used to obtain texturized products(Kokini et al 1992). During extrusion processing of starch-basedproducts, the extent of gelatinization occurring inside the barrelplays an important role in determining final extrudate properties.Depending on the extent of gelatinization, the ingredient mix isturned into an elastic melt inside the barrel (Case et al 1992; Sokheyet al 1994; Ihanoglu et al 1996; Ilo et al 1996; Lin et al 2000). Whenthe elastic melt exits through the die, expansion occurs due to theflashing of water vapor, which occurs due to the sudden drop inpressure (Alves et al 1999; Lam and Flores 2003). During theextrusion processing of protein-based products, on the other hand,the ingredient mix becomes more of a plastic melt inside thebarrel. The protein can be denatured due to the heat, which resultsin modifications in the peptide bonds and amino acid chains.When the material exits through the die, it is in a plastic, homo-genous state, and a more porous, fibrous textured product generallyresults, often due to the voids formed by the steam generated during

Graduate research assistant, South Dakota State University, Brookings, SD 57007.2 Professor, South Dakota State University, Brookings, SD 57007.

Corresponding author. Phone: 605-688-5661. Fax: 605-688-6764, E-mail address:[email protected] Engineer, North Central Agricultural Research Laboratory, USDA, ARS,Brookings, SD 57006. Mention of a trade name, propriety product or specific equip-ment does not Constitute a guarantee or warranty by the United States Departmentof Agriculture and does not imply approval of a product to the exclusion of othersthat may be suitable,Professor, South Dakota State University, Brookings, SD 57007.

doi:1 0.1 094/CCHEM-84-4-0389© 2007 AACC International, Inc.

the temperature from 101) to 140°C resulted in 17.0. 5.9. 35.4. 50.6. 28.8.33.9, and 33.9% decreases, respectively, in unit density, pellet durability.sinking velocity, absolute pressure. specific mechanical energy, torque, andapparent viscosity, but a 49.1 and 16.9% increase, respectively, in doughtemperature and water-absorption index. Increasing the LID ratio of thedie nozzle resulted in an increase in bulk density. L* , o*, and torque, but adecrease in unit density, pellet durability, water-absorption index, sinkingvelocity, h, mass flow rate. dough temperature, and apparent viscosity.As demonstrated in this study, the selection of an appropriate die geometry,in addition to the selection of suitable temperature and moisture contentlevels, are critical for producing DDGS-based extrudates with optimumproperties.

sudden pressure drop (Gwiazda et al 1987; Singh et al 1991; Sandraand Jose 1993). Operation of extruders depends on many factors,including the pressure developed inside the die, slip at the barrelwall, and the degree to which the screw is filled. The combinationof these variables, along with the type and composition of rawingredients used, will affect operational capabilities (Mercier et al1989). The extruder die plays an important role in affecting the pro-cessing conditions as well. For circular dies, nozzle dimensions(i.e., nozzle diameter and length) will affect process conditions andperformance (Chinnaswarny et al 1987). The how of dough insidea circular shaped die (Q) is directly proportional to the pressuredeveloped inside the die (AP). and inversely proportional to theapparent viscosity (id) of the dough inside the die. This can bemathematically expressed as

Q =K(AP/ ud ) ( I)

where K is a proportionality factor, which, for a circular die witha nozzle radius of R and nozzle length of L, can be expressed as(Sokhey et al 1997)

K=.irR4I8L (2)

The rheological and thermodynamic processes occurring insidethe die during forming and stretching have decisive effects on thefinal quality of extruded products (Mercier et al 1989). Apparentviscosity is the most important rheological property that affectsfinal product properties. During extrusion of biologically basedl'eed materials, ingredients often transform into a pseudoplasticmelt. And the moisture content of the ingredients, as well as cook-ing temperature, often significantly affect the apparent viscosityand thus the final extrudate properties (Harper 1981; Rosentrateret al 2005; Shukla et al 2005).

Therefore, the objective of this study was to investigate theeffect of the die nozzle dimensions, barrel temperature profile,and moisture content on the DDGS-based extrudate properties, andextruder processing parameters.

MATERIALS AND METHODS

Sample PreparationAn ingredient blend containing 40% DDGS, along with appro-

priate quantities of soy flour, corn flour, Menhaden fish meal, whey,vitamin and mineral mix, with the net protein adjusted to 28%was prepared following Chevanan et al (2005a,b). DDGS wasprovided by Dakota Ethanol LLC (Wentworth, SD) and was

Vol. 84, No. 4, 2007 389

ground to a particle size of 100 pm using a laboratory grinder(S500 disc mill, Genmills, Clifton, NJ). Corn flour was providedby Cargill Dry Ingredients (Paris, IL), and soy flour was providedby Cargill Soy Protein Solutions (Cedar Rapids, IA). The ingre-dients were mixed in a laboratory-scale mixer (N50 mixer, HobartCorporation, Troy, OH) for 10 mm, and then stored overnight atrefrigerated conditions (10 ± 1°C) for moisture stabilization. Themoisture content of the ingredient mix was adjusted by addingrequired quantities of water during mixing.

Experimental DesignThe extrusion studies were conducted using a single-screw ex-

truder (Brahender Plasti-Corder. model PL 2000. South Hacken-sack, NJ), which had a barrel of 317.5 mm. with a length to diameterratio of 20:1. The die assembly had an internal conical sectionand a length of 101.6 mm. A screw with a uniform pitch of 9.05rnni was used in the experiments. The screw had variable flutedepth, with the depth at the feed portion of 9.05 mm, and near thedie of 3.81 mm. The compression ratio achieved inside the barrelwas 3:1. The speed of the screw and the temperature inside thebarrel were controlled by a computer control system. The extruderbarrel's band heaters allowed the temperature of the feed lone.transition zone in the barrel, and the die section to be controlled.Compressed air cooling was provided in the barrel section as well,but the die section was not cooled. The extruder had a 7.5 HPmotor, and the computer system could control the speed of thescrew at 0-2 10 rpm (0-22 rad/sec).

Experiments were conducted with a full-factorial design usingthree levels of moisture content (MC) (IS, 20. and 25%, wh);three levels of temperature gradient in the barrel (90-100-100°C,90-120-120, and 90-140-140'C) hereafter referred to as temper-atures of 100, 120, and 140°C. respectively: and seven levels ofdie geometry with various nozzle length to diameter ratios. The di-mensions of the seven different dies used in the experiments aregiven in Table I.

Measurement of Extrudate PropertiesUnit density (UD). Extrudates were cut with a razor blade into

20-mm lengths. UD was determined as the ratio of mass to the cal-culated volume of each piece by assuming cylindrical shapes foreach extrudate according to Jamin and Flores (1998).

Bulk density (BD) was measured using a standard bushel tester(Seedburo Equipment Co., Chicago. IL) following the method pre-scribed by the USDA (1999).

Pellet durability (PD) was determined following ASAE standardmethod S269.4 DEC01 (1996); 200 g of the extrudates was tum-bled inside a pellet durahilty tester (Seedhuro) for 10 min and thenhand-sieved through a No. 6 screen. PD was calculated as

PD = (Mass of pellet after tumbling/Mass of pellet before (3)rumbling) x too

Water absorption index (WAI) was determined according to Joneset a! (2000). To determine WAI, 2.5 g of finely ground samplewas suspended in 30 mL of distilled water at 30°C in a 50-mi,tarred centrifuge tube. The content was stirred intermittently over

TABLE 1Dimensions of Dies Used in Study

Diameter of Length ofDie No. Nozzle (mm) Nozzle (mm) LID Ratio

3.0 10.0 3.3

6.0 20.0 3.3

4.0 13.7 3.4

2.7 13.0 4.8

3.0 17,5 5.8

2.0 14.5 7.3

3.0 30.0 10.0

390 CEREAL CHEMISTRY

30 min and then centrifuged at 3,000 x g for 10 mm. The super-natant water was transferred into tarred aluminum dishes. The massof the remaining gel was weighed, and WA! was calculated as theratio of gel mass to the sample mass.

Water-solubility index (WSJ) was determined as the water-solu-ble fraction in the supernatant, expressed as percent of dry sample(Jones et al 2000). The WSI was determined from the amount ofdried solids recovered by evaporating the resulting supernatant inan oven at 135°C for 2 hr; it was determined as the mass of solidsin the extract to the original sample mass (%).

Sinking velocit y (SV) was measured following the method adop-ted by Hiinadri et a! (1993). SV was measured by recording thetime takeii for an extrudate 20 mm long to travel from the surfaceof water to a depth of 425 min a 2,000-mL graduated cylinder.

Color of the extrudates was determined using a spectrophoto-meter (portable model CM 2500d, Minolta Corporation, Ramsey,NJ) using the L-a-b opposable color space. where L* quantifiesthe brightness, a quantifies redness/greenness, and h* quantifiesyellowness/blueness.

Extrusion Processing ParametersThe temperature of the ingredient melt at the end of the barrel

(TB) was measured with a Type J thermocouple with a range of0-400°C. The absolute pressure (P) inside the die was recordedwith pressure transducer that had it of 0-68.9 MR The terii-perature of the melt in the die (TD) was recorded with a therriio-couple that was integral to the pressure transducer. The net torque() was measured with a torque transducer that had a range of 0-40,000 m-g. During experimentation, the extrudate samples werecollected for 30-sec intervals, and the mass flow rate (MFR) wasthen calculated (g!nirn). Based on the torque and the mass howrate data, the various processing variables were then determined.

Specific mechanical energ y ( SME) (J/g) was calculated accord-in- to Harper (1981) and Martelli (1983) as

SME = (* W *60)/ fl7(4)

where Q is the net torque exerted on the extruder drive (N-rn), wis the angular velocity of the screw (rad/sec), and ,n,,.,.,, is the massflow rate (g/min).

Apparent viscosity (ii) of the dough in the extruder (Pa-see) wascalculated by approximating the barrel and screw as a concentriccylinder viscometer. and then incorporating corrections for taperedscrew geometry (Rogers 1970; Lo and Moreira 1996; Konkoly1997; Lam and Flores 2003; Rosentrater et al 2005). The apparentviscosity was determined as the ratio of shear stress (t,) at screw(N/ni 2 ) to the shear rate (y,) at the screw (I /sec) calculated fromEquations 5 and 6

7. =)/(2*)r*(cor)2 */) =C5 Q (5)

= (2o) *r2)/(,.2 (r 2 ) = w (ôa)

wherer, -,rr i s the radius correction due to frustum value

re, +T.ffJ ? JJ2 +r(, 2 )/3 ,(m) (6b)

where r is the effective radius including the screw root radiusand half of flight height (in), L is the screw length in the axialdirection (,n), C,, is a correction factor for shear stress (5675.4 forthe screw used), 'y, is the shear rate at the screw (]/see), r5 is thebarrel radius (m), and C., is the correction factor for shear rate(6.31 for the screw used).

Statistical AnalysisThe measurements were completed in triplicate for all extru-

date properties and extrusion processing parameters, except forpellet durability, which was measured in duplicate. The data were

then analyzed with Proc GLM to determine the main and interac-tion effects and LSD using a = 0.05 for comparison, with SAS v.8software (SAS Institute, Cary, NC). To determine the effect ofnozzle length (L), nozzle diameter (D), and length to diameterratio (L/D) on individual response variables, multiple linearregression analysis was conducted with linear quadratic models

Response =Ii + a * D + 02 MC + a 1 * T+a4 * I) * T+ a D * (7)MC+a(, * 1 * MC+a 7 */)2+a5 MCI +a972

Response = 12 + b, * L + h2 MC + h 3 * T + b4 * L * T+ b5 * L (8),MC+h6iMC+b7L2+b5 MCI +h911

Response =/+c 1 *(lJD)+c 2 *MC+csT+c4* (lJD)*/+cs' (9)(liD) MC+c5* T * MC+c7 *(IJD)2+c5MCI +

The Proc Reg procedure in SAS was used to determine thecoefficients for each of the terms, and only statistically significantterms were included in the final model using a step-wise selectionmethod. In Equations 7, 8. and 9. J, '2, and 13 are the interceptvalues; Oi - a. b 1 - h9 , and c 1 - c9 are the regression coefficientsfor respective terms; D. L. LID. MC . and T represent the diameter(mm), length (mm). length-to-diameter ratio of the die nozzle (-),moisture content (%, wb) of the blend, and temperature (°C),respectively.

RESULTS AND DISCUSSION

Changing the levels of temperature, moisture content, and diedimensions were each found to have significant effects on all theextrudate properties studied, except for UD, where the effect ofmoisture content was not significant (Table II). Temperature,moisture content, and die dimensions also significantly affectedall extrusion processing parameters as well (Table Ill). Addition-ally, the interaction effects were also significant (P < 0.05) for allthe extrudate properties. except for die*rnoisture content and die*moisture content*temperature for UD, and temperature* moisturecontent for WSI. The interaction effect of temperature, moisturecontent, and die dimensions were also significant for all the ex-trusion processing variables studied.

With regression, it was determined that LID, moisture content,and temperature (using Equation 9) predicted all extrudate prop-erties and the extrusion processing parameters with high R 2 valuescompared with L or D alone as the primary geometric parameters(Equations 7 and 8). Hence, regression modeling using L/D as thedie geometry parameter was pursued for all subsequent analysis.

Extrudate PropertiesUnit density (UD), which affects floatahility of extrudates, is a

very important quality parameter for aquaculturc feed materials.

II

TABLE IIMain Treatment Effects on the Ph ysical Properties of Extrudates'

Unit Bulk Pellet Water Water SinkingDensity Density Durability Absorption Solubility Velocity

Parameter (g/cm3) (g/cm3) (%) Index Index (%) (m/sec)

Temp profile ("C)90-100-I 00 1.03a 0.45h 95.75a 2.63c 17.71 it 0.l0a90-120-120 l.00b 0.45a 94.6Ib 2.90h 17.70a 0.09b90-140-140 0.88c 0.42c 87.19c 3.13a 16.95a 0.07c

Moisture content ('T)15 0.96a 0.44a 86,95c 2,73c 18.33a 0.09a20 0,96a 0.44h 92.40h 2.88b 17.57b

0.08b

25 0.99a 0.44b 97.04a 101a I6,66c 0.08cL/D (-) D (mm)

3.33 3.0 0.98ah 0.43d 94.55c 2.99a 17.03c 0.08d3.33 6.0 0.95b 0,48a 85.06e 2.85h 17.45h

0.12a3.43 4.0 0.99c 0.45b 87.17d 2.96a 16.44d

0. lOb

4.81 2.7 0.97ab 0.43d 95.06h 2.86h 17,61h

0.07e5.83 3.0 0.98ah 0.42f 95.21h 2.95a 18.30a 0.08c7.25 2.0 101a 0.42e 97.99a 2.84h 17,34hc 0.07f10.00 3.0 1.02a 0.44c 94.23c 2.78c 17.99a 0.08d

Values with the same letter in a column for a given factor are not significantly different (P < 0.05).

Color

L a' b'

40,92h 4.30c I 3.98th

41.39a 4,37h 14,06a

39.65c 4.51a 13.91b

4-4.41a 4.26c 15.12a

42.39h 4.32b 14.33h

36.1 3c 4.56a 12,76c

39.28c 4.35cd

13.36e

41,30b

4.38bcd

l4,62a

40,78h 4.46b 14.13b

41.27b

4.15e 13.7 Id

41,32h 4.31d l3.90c

38.09d 4.67a I 3.76cd

42,l3a 4.4lbc l4,17h

TABLE IIIMain Treatment Effects on Extrusion Processing Parameters-'

Mass Flow Apparent Absolute Dough Temp Dough TempParameter Rate (g/min) Torque (N-m) SME (Jig) Viscosity (Pa-sec) Pressure (MPa) (Barrel) (°C) (Die) (°C)

Temp profile (°C)90-100-100 139.3c 74.04a 430.52a 4894.37a90-120-120 141.6b 62.89b 360.34b 4157.66h90-140-140 144.8a 55.24c 306.66c 3651.55c

Moisture content (%)IS 165.Ia 62.07b 307.24b 4103.00b20 153.4b 89.12a 476.70a 5890.98a25 11 1.5c 41.03c 305.24b 2712.31c

UD (-) D (mm)

3.33 3.0 126.2g 59.05d 364.65c 3903.20d

3.33 6.0 149.2a 54.67e 301.91e 3614.00e

3.43 4.0 145.6b 56.41de 312.73e 3728.80de

4.81 2.7 140.6e 65.06c 367.66c 4300.80c

5.83 3.0 138.5f 57,26de 330.83d 3784.90de

7.25 2.0 144.1c 80.06a 467.51a 5292.00a

10.00 3.0 143.Od 74.47b 471.89b 4922.40b

Values with the same letter in a column for a given factor are not significantly different (P < 0.05).

10.91a 102.85c 104.09c

7.71b 1l6.82h 131.14b

5.38c 127.12a 155.19a

12.82a 116.31a 126.44c

8.02b I l5.64h 129.25b

4.65c 1t4.43c 132.84a

4.01f 117.05b 136.60a

3.94f 105.25d 126.88e

5.05c I l7.58ab 130.77c

9.32c 118.l5a 132.05b

7.91d 114.89c 126.82e

11.88b 1t7.55ab 128.82d

13.87a t17.84a 12805d

Vol. 84, No. 4, 2007 391

Increasing the moisture content of the ingredient mix had nosignificant effect (P > 0.05) on the UD of the extrudates. How-ever, increasing the temperature from 100 to 140°C resulted in asignificant decrease (17%) in UD of extrudates. Many researchershave observed that temperature has an inverse relationship withthe apparent viscosity of the ingredient melt inside the barrel anddie (Harper et al 1981; Bhattacharya and Hanna 1986), and thathigher temperatures typically result in lower apparent viscosity ofthe melt. When the ingredient melt (at lower viscosities) exitsthrough the die, extrudates tend to expand more and, thus, havereduced UD. Regression analysis for UD resulted in an R2 value0.65 using LID as the geometric parameter. Model equation 10predicts the UD of extrudates with L/D. MC, and T (Table V). Thenegative value for the term containing L/D, within the bounds ofthe experiment, indicated that there was a general trend of de-crease in UD as the LID ratio was increased.

Bulk density (BD) is another key property, as it influences storagespace required at the processing plant, during shipping, and atanimal production facilities. BD depends on the size, shape, andthe extent of expansion during extrusion. Increasing temperaturehad a significant effect on the BD (P < 0.05). The lowest BD(0.319 g/cm 3 ) was recorded at a Tof 140°C, MC of 25%, and L/Dof 7.25. The highest RD (0.509 g/cm) was recorded at a T of120°C, MC of 20%, and L/D of 3.33 (Table IV). Changing theMC of ingredient mix also had a significant effect on the BD (P <0.05): increasing MC from 15 to 25% resulted in a 2% decrease inBD. The R2 value of the linear quadratic model with L/D as thegeometric parameter was 0.62. Model equation 11 predicts BD usingL/D, MC, and T (Table V). A positive coefficient for the L/D and(LID ) 2 terms in the model indicate that there was general increas-ing trend in BD as the L/D ratio was increased.

Pellet durability (PD), which is an important quality parameterof feed materials (Rosentrater et al 2005), can indirectly assess themechanical strength of extrudates. Increasing T resulted in a sig-nificant decrease in the PD (P <0.05). The PD at Tof 100°C was9.8% higher compared with the PD at T 140°C (Table II). Chang-ing the MC of the ingredient mix also had a significant effect onthe PD of the extrudates; and PD at 25% MC was 11.9% highercompared with the PD at 15% MC. At higher MC, the tempera-ture of dough at the die was significantly higher as well (TableIII). The mechanical strength of extrudates depends on the extentof heat treatment and the relative degree of starch gelatinizationthat occurs during processing (Colonna et al 1989). Increasing theMC and T synergistically resulted in a higher extent of heat treat-ment and gelatinization, which resulted in higher PD. The R2 valueof the linear quadratic model using liD as the geometric parameterwas 0.69. Model equation 12 predicts PD with L/D, MC, and T(Table V). A negative coefficient for the L/D, LID *MC, and (LID)2terms in the model indicated that there was, in general, a decreas-ing trend in PD as the LID ratio was increased. The higher PD atlower T is indicated by the negative coefficient of (1.11 - 0.04*MC) for the T term, while the higher PD at higher MC is sum-marized by the positive coefficient of (0.04 * 7' - 2.31) for the MCterm.

Water-absorption index (WAI) is related to the extent of starchthat has maintained integrity during extrusion processing, and tothe molecular breakdown of starch and protein components. WAIis also indirectly related to water-holding capacity, which thusaffects product storage stability. T had a significant effect on theWAI (P <0.05); the WAI was 16.9% higher at a T of 140°C com-pared with the WAI at a Tof 100°C (Table 11). A similar trend wasobserved by Anderson et al (1969) with extruded corn grits.

TABLE IVTreatment Combination Effects on the Extrudate Properties'

Die Diameter 90-100-1001C 90-120.120°C

Property (mm) LID (.) 15% 20% 25% 15% 20% 25%

Unit density (glcm3)3.06.04.02.73.02.03.0

Bulk density (g/cm3)3.06.04.02.73.02.03.0

Pellet durability (%)3.06.04.02.73.02.03.0

Water absorption index (-)3.06.04.02.73.02.03.0

na 0.97612 1.19120.958- 14 0.95614 1.1115087 12.17 0.8911-17 08114171.00 1 ' l.02'' 119'0 .994 ( 20.95 7.13 1.12'1.1116 1.03 3- 1.17 1-41,05 1.09' 1.17'

na na 0.490.47460466.8 0.490.41 21-22 04219.21 0.480 . 43 15 - 17 0 . 42 1 6. 20 0.4930.42 16-20 0.4226.2( 0.465-70 ,467.10 0459.12 0.4023240431315 0.451' 0.49

na 93.601516 98.0083 . 352397.96 99.06"87 .982292.1316.79 9364'5169601 9.129665510 96.5661194 7313.15 96 , 098.1298.42'9942 1.299.411.2 9974(29545(0(4 97.80 99.09

na 2.642226 2.7618232 . 6926.242. 6926.24 2.5175-292 . 6826.2.7916.22 2.9201624927.29 2 . 1229 2.6423272 .6223.27 2 . 82 15.20 2.8912182 .4627.29 2 . 51 2529 2.5724292 .6521.25 2.5026.29 2.7319.23

no 1.0I1' 0929.160994.12 l.02'' 1.01"'0.96` 30.99412 1.001'1.00 1 ' 0.948(5 0,94801.00 1 ' 0.9812 0.9942

1.08 1-8I.03'°1.03 3-101.0431() 1.014-11

no na 0.412(230.51 1.2 0.511 0.50230.47' 0.45900.44 11130467.8 0.4315'

na 0.431518 0.4315200.4580.459-12 0.441214045112 0.46 04316.20

no 93.0016.18 96.9088 . 162290.772021 96.5l691 .70 18.20 92 . 68 16.18 97.10

95.2411-1493.3617 97743.6na 91.36 19-20 95.27'°'

99.771 97494.7 97.6l95 . 989292.05 17-20 95.0712(4

na 2801621 3.093.102 . 6323.27 2.8912-18 2.99902.86 14-19 3.13 3.20252 .6726.2430'J8-13 3.02'2 .731923 2.9111-17 3.3122.76 17-23 3.02713 3.162 .4028 2.65 22-26 2.8116.20

90-140.140°C

15% 20% 25%

no 0.92 0.8512O. 80 00.79 16-17 0939.150.75 17 0929.16 0.99101'0 .939 6o.8911 17 0.83 13-1

na 0.89 0.9480.99' 0.929- 16 0.75'0985120.91' 0.85''

no 0.421821 0.4022.230466.80457(0 0.460.43 [4-16 04411' 046°0.44 1214 0.402223 03726

na 0.3923 0.3823042 1620 0.4313-14 0.32270.42°° 0.412223 03924.25

na 88.3822 97444.840 . 372675.8024 93.66°'44042587.3022 98.019263 161991.1320.21 96.24712

na 91.61 19-20 99.00'96 . 56&1935415.16 98.362489 . 882188,3822 9439(4.15

na 3143.8 3.4912 . 93 I63.12 3192.63.02 7-13 3.05'' 3.037132 . 91 1.83.2923 3.62'

na 3.2824 3046.123 . 085102,9610.15 3.027-112 .88 1 3 . 19 3.1536 3.29

(continued on next page)

3.33.33.44.85.87.3

10.0

3,33.33.44.85.87.3

10.0

3.33,33.44.85.87.3

10.0

3.33.33.44.85.87.3

10.0

Values with the same superscript numbers for a given property are not significantly different (P <0.05); na, data not available.


L

14.0615-1814.5210-1514.3812-1613.4719-2114.5210-1.514.2713014.0415-18

1265222614.24''13.8916-19

13.1420-2213.6218.2012.2724-28127122.25

Changing the MC of the ingredient mix also had a significanteffect on the WAI (P < 0.05). Increasing the MC from 15 to 25%resulted in a 16.2% increase in the WAI. Anderson (1982)observed that higher temperatures and higher moisture contentscould result in greater starch breakdown and thus increased forma-tion of an expansible matrix, resulting in higher water-holdingcapacity, which could lead to an increased extrudate WAI. In thisstudy also, higher T and higher MC resulted in higher WAI of theextrudates. The R2 value for the linear quadratic model with L/Das the geometric parameter was 0.65. Regression equation 13 pre-dicts WAI with L/D, MC, and T (Table V). The negative coef-ficient for the L/D term in the model indicated that there was ageneral decreasing trend in WAI as L/D ratio increased. HigherWAI at higher MC and higher T are indicated by the positivecoefficients for MC and T terms in the model.

Water-solubilitv index (WSJ) is directly related to the extent ofstarch gelatinization that occurs inside the extruder (Harper 1981).Generally, WSJ increases as the temperature increases, due to starchdepolymerization, which leads to reduced length of amylose andaniylopectin chains (Anderson et a! 1982). In our experimentsusing DDGS. changing T did not result in significant changes inthe WSJ of the extrudates. But changing MC did have a signi-licant effect. William et al (1977) observed drier conditions of theingredients affected the extent of dextrinization of starch, whichresulted in higher extrudate WSJ. Similarly, in this study the WSJ

at 15% MC was 16.0% higher compared with the WSI at 25% MC.The R2 value with LID as the geometric parameter in the linearquadratic model was 0.41. Model equation 14 predicts WSI withL/D, MC, and T (Table V). The very low R2 value for the resultingmodel indicated that WSI may be controlled by various otherfactors such as residence time, extent of shear, etc., in addition todie dimensions, MC, and Tduring processing.

Sinking velocity (SV) depends on the extent of expansion and,thus, the biochemical changes occurring inside the barrel. Extru-date expansion affects density of extrudates as well. Moreover,the extent of biochemical changes affect the water-absorptioncapacity and structural integrity of extrudates, which also affectthe SV. The SV of the extrudates significantly (P < 0.05) decreased(35.4%) at higher T, indicating that the extrudates had a decreasedUD and better buoyancy. Even though changing the MC of theingredient mix had no significant effect on the UD of the extru-dates, the SV of the extrudates obtained at 25% MC was signifi-cantly lower (16.3%) compared with the extrudates at 15% MC(Table II). The R2 value using L/D as the geometric parameter in thelinear quadratic model was 0.84. Model equation IS predicts SVwith L/D, MC, and T (Table V). The negative value for terms con-taining liD, within experimental boundaries, indicated that therewas, in general, a decreasing trend in SV as the L/D ratio increased.Lower SV at higher MC and higher T is indicated by the negativecoefficient for the MC and T terms in the model equation.

Water solubility index (%)3.06.04.02.73.02.03.0

Sinking velocity (mis)3.06.04.02.73.02.03.0

L8(-)3.06.04.02.73.02.03.0

3.06.04.02.73.02.03.0

na 17.16'° 0 16.43132219 . 51 2418.37-57 17.1690174971416.6713 20 16.541422I9.07 18.3330 17.50'19 .63 2417,16ho118 17.99610

18.21 17.387-1117.986017 . 8461!19,662.4 14.0523

nit 0.091113 0.111-10 . 12 20,121.2 0.113-1'0 , 106.90.1 0.10 . 09000.0911' 0.01690 .09 1200.091316 0.1069008 19.22 0.081822 0.0719.230 . 09 100 0.092 13 0,109.12

na 43.31712 35.622527

45.29 42658.14 399016.1944954.7 43357.11 36.9622.2344 . 615 84404610 33.7027.2846.08 s 4348710 36.4023.26

38.94 18-22 43,357.11 33.0428.29

47.22' 46.38 31.6129

na 4Q719.25 4.66"4.29'' 4.19 16-22 4.0220.26

4.18 16-22 4.1417.22 4091825

4 . 01 2126 3.86 25-27 47369

422 15.21 4.0220.26 43312.17

5.23 2377' 4.63113 .902327 3.962227 5Q92.4

na 17.96 6-10 1674122017 . 946 II) 17.4470 16.65 13-2117 . 02 1019 16261622 15.6221 2218.25 17121019 17.23"2016 1217.676' 16.72°°18 . 03 31017131018 16.32162221.14' 19.9323 18644.6

na 0.0914-19 0.0720.24

0.13' 0022.3 0.12240.10' 0.108-11 00913.16009 13.18 0.08 17-21 0.0629320.0913-15 0.08 14-19 0.0810.220 .08 19.22 0.062529 0.07 21-250.09 1.1 ' 0091' 0062630

na 43.856)0 37.05222546 . 162544435.9 40.51'"46 .292543996.10 390618.7145 .523641.841 1-16 347926.28

45.62' 42700.13 35.82242640.65 14-18 40.5915 8 32.8628.29

48.70' 42.8 1 8-13 34.562(28

na 4.25 15-20 4.27''4.28 13-1 4.0021.27 4.1018-25

4.29 13 ' 4.141 7.22 4.1317-23

38924.27 43113.18 4.46004. 1017-24 43312.18 4.65"4914.6 44311153 . 8026.27 5.272

90-140-140°C

15% 20% 25%

na 17.61613 16.26162217 , 308.1616.51 14-22 1614192216 . 75 12211 15.5822 16.07 19-2218 , 055.1016.8011.10 16.21 17-22

na 19.45 3 5 17636.13

17.37° 17636.13 16.0719.2217 . 786 1117.05") 15.85 20-22

na 0.0723.27 0.040 . 12240,116.9 0.l0'°0 . 109200815' 0.072025

0.08" 0.053032 0.09cia 0.07 22-26 00624.28

0.06 27-30 0.06 29-31 0.060.0816-20 0.0631.32 0

na 41391216 344526.28

38.721 8-22 38.721822 35372527

39.31 17-20 36.052326 37.0921 .2446.88' 42.15'°° 37.9219.22

na 41.15 13-17 39171720

42.25 10-15 41.1 1317 35.2825.2747,771.2 42.449- 15 37.65 20-23

na 4.15 17-22 4.7069

4.63'' 4.80 5152.34 , 855.85.521 4.764.27'' 4 00 1 " 4.3212.18

na 4.25)520 4,539.11

4 . 28 14.19 4 50'° 13 4.50 10-143 . 8022743912.16 4,519.12

TABLE IV (con:inuedfro,n previous page)Treatment Combination Effects on the Extrudate Propertiesa

Die Diameter 90-100-100°C 90-120-120°C

Property (mm)

15% 20% 25% 15% 20% 25%

3.33.33.44.85.87.3

10.0

3.33.33.44.85.87.3

10.0

3.33.33,44.85.87.3

10.0

3.33.33.44.85.87.3

10.0b*()

3.0 3.3 na 14.4911.15 12.45 22-27 na 13.91 16-19 12.6122.27 na

6.0 3.3 15.541-314.822 13.82' 15.80' 14.67 13.7717-1914.3812- 16

4.0 3.4 l5.09 14.501 1-15 12 o927-28 15.65' 14.0611- 16 12.862224 14699.13

2.7 4.8 14.961' 14.15 14-18 12.11 25-28 14,885.12 140415.18 11.8827-28 147383

3.0 5.8 15.5114 14.4711-1.512.25 25-28 15.25 13.90169 12.34 13-28 na

2.0 7.3 15.05 14.50-15 11.8328 15.29' l4.18' 12.4 123-28 14.751- 13

3.0 10.0 15.4215 l4.94" 12 o927-28 15.40' 15,331.6 12.95 21-23 14.629-

with the same superscript numbers for a given property are not significantly different (P < 0.05); na, data not available.

Vol. 84, No. 4, 2007 393

Color change in extrusion processing is mostly due to Maillardreactions (Mercier et al 1989). In fact, significant losses of lysine(an important ammo acid required for fish growth) during"sion processing (Bjorck and Asp 1983) have been observed due toMaillard reactions. Extrudates obtained at a T of 140°C had lowerbrightness (L) and yellowness (b) values, but had a higher red-ness (a) value (Table II). A similar trend was observed by Shuklaet al (2005) during extrusion experiments with raw materials thatalso contained DDGS. This may have been due to Maillardreactions, which resulted in the browning of extrudates at highertemperatures. Increasing the MC from 15 to 25% resulted in a22.9 and 18.5% decrease, respectively, in brightness and yellow-ness, hut a 7.0% increase in the redness of the extrudates. Ingeneral. extrudates obtained with higher MC had lower brightnessand yellowness values and higher redness values. This might havebeen due to the higher resulting temperature of the ingredientmelt at the die (Table Ill), which may have contributed to thebrowning. Changing the die dimensions also had a significanteffect on resulting color values: model equations 16, 17. and 18(Table V) predict the color of the extrudates with L/D. MC, and T(R2 for I. = 0.70, R 2 for a = 0.29, and R 2 for b* = 0.76). Withinthe scope of the experiment, the positive value for the term contain-ing L/D in the model indicated that there was a general increasing(rend in L as the L/D ratio was increased. Similarly, a positivevalue for the term containing L/D in the model indicated thatthere was an increase in a as the LID ratio was increased. On theother hand, the negative coefficient for the L/D term in the modelfor b* indicated that there was a decrease in h as the L/D ratiowas increased.

Extrusion Processing ParametersMass flow rate (MFR) in a single-screw extruder depends on

the drag flow developed by screw rotation and the pressure flowdeveloped due to the restriction of the die (Mercier et al 1989). Inthis study. increasing T from 100 to 140°C resulted in a signifi-cant increase (3.9%) in the MFR (P < 0.05). On the other hand,increasing the MC from 15 to 25% resulted in a 32.5% decreasein the MFR. The R2 value using LID as the geometric parameterin the linear quadratic model was 0.87. Regression equation 19predicts MFR using L/D, T, and MC (Table V). A negative coeffi-cient for LID in the model indicated that there was a decreasingtrend in MFR as the L/D ratio was increased. The decrease inMFR with higher MC is explained by the coefficient (18.42_O.6*MC) for MC term in the model. The higher MFR at higher Tcanhe explained by the positive coefficient for Tin the resulting model.

Dough TemperatureThe temperature development inside the barrel depends on

thermal gradients, thermal conductivity, thermal diffusivity, degreeof mixing, velocity of flow, etc., and ultimately affects the extru-sion process as well as the resulting extrudate properties. IncreasingT from 100 to 140°C resulted in a 23.60% increase in TB, whichcompared with a 49.1% increase in TD. In the extruder used, thedie section did not have a compressed air cooling system, whichcontributed to the increase in TD. The pressure and shear devel-oped inside the die may also have contributed to the higher TD.Increasing MC of the ingredient mix resulted in a significant (P <0.05) decrease in TB, while the reverse was observed for ID(Table LII). The R2 value of the Linear quadratic model with L/D asthe geometric parameter in the TB prediction model was 0.73.The R 2 value to predict TD was 0.97. The resulting TB predictionequation 20 uses L/D, MC. and T (Table V). The negative valuefor the L/D terms indicated that there was, in general, a decreasingtrend in TB as the L/D increased. A negative coefficient for MC inthe model indicated that the TB decreased as the MC was in-creased, whereas a positive coefficient for the T term indicated thatthe TB increased as Tincreased.

Regression equation 21 predicts ID with LID. MC , and T(TahleV). A negative coefficient for the IJD term in the model indicatedthat there was a general decreasing trend in TD as the LID ratiowas increased. On the other hand, a positive coefficient for theMC and T terms in the model indicated that there were generalincreasing trends in TD as the MC and T were increased. In ourexperiment, we observed that increasing the temperature profile inthe barrel resulted in increased TD and TB (Table IL!) leading to areduction in UD, BD. PD, SV. L, and an increase in WAI and a*of the extrudates (Table II). However, increasing the moisturecontent of the ingredient mix resulted in reduced TD but increasedTB of the molten dough.

Absolute Pressure (P)The pressure developed inside the die depends on various

parameters such as rheological properties of the ingredient blendand pumping characteristics, in addition to the die dimensionsused in the extruder. The biochemical conversions occurring insidethe barrel depend on the extent of pressure developed inside theextruder, in addition to the extent of thermal and mechanicalenergy available for chemical reactions, and ultimately affects theextrudate properties. Increasing the T resulted in a significant de-crease in the P developed in the die (P < 0.05). In foct, increasingT from 100 to 140°C resulted in a 50.6% decrease. Moreover, at

TABLE VRegression Models for Extrudate Properties and Extrusion Processing Parameters Using Moisture Content (MC),

Barrel Temperature (T), and Length-to.Diameter Ratio of I)ie (L/D)a

Regre.ssion Model

1.141+0003 *(IJD)-0.025 * MC +0.018 * T-O.003 *(LJD)*MC-0.63 + 0.0104 * (UD) + 0.022 * MC + 0.01 6 * T+ 0.002 * (LID)2 - 0.003MC2t39.78- l4.93 *(UD)-2.3t *MC- lIT *T_0.33*(IJD)*MC+004*T*MC_054*(LID)20.99-0.02 * (LID) + 0.03 * MC + 0.01 * T12.41 +0.57 *(IJD)-0.25 *MC+0.14 *T+0.002(1JD) T-0.017 *(UD)* MC+0.002 * T*MC0.934-0.084 * (UD) - 0.005 * MC - 0.002 * T + 0.006 * (LID)216.62 + 1.77 *(UD)+ 3.21 * MC -0.03 * T- 0.09 *(LID) * MC -0.09 *(MC)22.42 + 0.14 * (LID)- 0.03 * MC + 0.02 * T- 0.003 * (LID) * T+ 0.0l * (L/D) * MC27.86-0.03 * (LID) -0.67 * MC -0.07 T + 0.004 * T MC3.95-0.20 *(tJD)+ 18.42 * MC + 0.17 * T-0.60 * MC260.t4 - 0.710 * (L/D)- 0.229 * MC + 0.390 * T- 0.04 * (UD) * T- 0.259 * (L/D)2-30.38-0.41 *(LID)+ 0.48 * MC+ 1.27 * T173.7- 0.64 * (LID)- 1.27 * MC - 14.0 * T- 0.03 *(L/D) * MC+0.09 * T* MC -3.0 * (JJTJ)2-2 t 90 + 58.3 * (LID) + 282.6 * MC - 3.16 * T - 3.03 * (LID)2 - 7.04 * MC2-447.9 + 3.26 * (L/D)+ 59.6 * MC -0.47 * T- 1.53 * MC2-34049 + 1134.9 * (LID) +4049 * MC- 18.8*T_2 .2 * (LID) * T- t53*(LJD) * MC-26.5 * (lJrJ)2_ 102.3 * MC2

Eq Property

to

UDBD

t2

PD13

WAI14

wsIl5

sv16

L*17 a *l819

MFR20

TB21

TD22

P23

SME2425

R2 SE CV(%)

0.65

0.098 10.0

0.62

0.025

5.7

0.69

6.87

7.4

0.65

0.176

6.?

0.4 I

t.to

6.3

0.84

0.044 15.4

0.70

2.36

5.7

0.29

0362

8.2

0.76

0.520

3.7

0.87

9.33

6.6

0.73

6.43

5.6

0.97

3.98

3.1

0.86

1.58

19.2

0.56

tO 1.8

27.7

0.71

15.3

23.8

0.71

101.7

23.8UD, unit density, BD, bulk density; PD, pellet durability; WAL, waier-soluble index; WSI, water-soluble index; SV, sinking velocity; L* . brightness. a*, redness,b* , yellowness, MFR, mass flow rate; TB, temperature of dough at the barrel; TD, temperature of dough at die; P, pressure developed in the die; SME, specificmechanical energy; Q. torque; ii, viscosity of dough.


SME (Jig)3.0 3.36.0 3.34.0 3.42.7 4.83.0 5.82.0 7.33.0 10.0

Apparent viscosity (Pa-sec)3.0 3.36.0 3.34.0 3.42.7 4.83.0 5.82.0 7.33.0 10.0

Absolute pressure (MPa)3.0 3.36.0 3.34.0 3.42.7 4.83.0 5.82.0 7.33.0 10.0

Dough temp barrel (°C)3.0 3.36.0 3.34.0 3.42.7 4.83.0 5.82.0 7.33.0 10.0

A,. i°C\

na 563.0"

247 . 8 2(25501.6'

291 , 8 18.22 520.868

381 . 7) 2.14570.9'

352.5'''' 547.8'

338.8''' 576.3'

485 . 8810596.9'

na 6788.0'na 6298.9'

5367.5 11 7087.1 1-43862 . 3 1518 6658.7'

4948.5" 7623.9'

4509.0°" 6888.324

6073 . 4677l09.7"

na 8.10144922125 5.16 20

I3.07 6.67''l9.2 I18.93 10,47)112

, 39479 15.3556

27.68' 17.14

na 102.82124

J01.6 23 25 10172325

104 . 9 19.2 ) 103.121-24

108 . 1) 7 ( 8102.92)24

105.5 19-20 102.522-24

106 . 8 1819102.92124

108 . 8 .18103.2 21 23

90-140-140°C

15% 20% 25%

na 140.6 ° II47(9.21

172.2 1 ' 155.87 ' 130.4°'

176.1 5 161.1312 123.616 1

I 56.7' 153,9814 110 19.24

°

na 147.311-14 l6.622

°

177 . 0( 2163.22 1 104,62025

169.0" 161.8 ' 11661722

flU

42.9212),46.42024

n 694)2(467.1 ''

n 203.2 25- 27215.2 24 27289.5)7.21

n 319.915-18324.3°' (8

112.6' 247.81922

63.6 14-175.99 (253.6 17-209435.891.16-7

653.6'250.31' -25322 5°'°402.9' '-'297.2(0.20471 .8' '°459.8' '°

25.9311

30.7 28-1030 9281))32.120.1))34 1273838.1 2 .2937.4 24-29

184.6191 .926 27203 .911-27

237.3 24-27238.423 . 26

297.6 16-20262.3''

na 744l.1" 1716.00

2832 . 921263157.1 19-22 2026.82030

3672.7" 5020.5'' 2122.82830

3068 . 22023 4206.8'"' 2040.72830

4585.8° " 6234.4 5-6 2520.123.28

no 35444)7.20 2250.927.30

4438.0' -' 6023 , 60.72476.724.29

na 4332225 1.18'2 .6827.30 1.363072 0.94323 . 91 2327 2.142932 1.3 131-32

10.431 1-12 6.55'" 2.902529

na 3.882327 53032

12 .799109.92i2 4.922)'25

15.92 I0.15° " 5491922

na 136.8' 124.8

100 , 824.27 93.529 110.116.17

133. 12-4 132. 1 2-5 132.32.5133 . 92l32.9 132.22.5

na 131.638 130. 11-6

133 . 524131.63.6 129.66

13372 3 131446 13144.6

154. 947152.078155.7155.2l55.7'152.468150.30.9

170.7'156.1153.05.8158.523160.22159.32147.49

Vol. 84, No. 4, 2007 395

higher T, the apparent viscosity of the ingredient melt decreased(Table 111). Thus the ingredient melt at lower viscosity might haveresulted in decreased P inside the die. Lam and Flores (2003) ob-served a similar trend during extrusion of fish feed. Increasing theMC of the ingredient mix also had a significant effect on the Pdeveloped in the die. The P at 15% MC was 63.7% higher com-pared with the P at 25% MC. The R 2 value using L/D as the geo-metric parameter in the linear quadratic model was 0.86. Modelequation 22 predicts P with L/D, MC, and T (Table V). Within thebounds of the study, the coefficient for (LID )2 in the model wassignificant indicating that P had a nonlinear relationship with

LID. The reduced P inside the die at higher T is indicated by the

negative value for the terms containing T in the model. Increasingthe temperature profile in the barrel as well as increasing the mois-ture content of the ingredient blend resulted in reduced P (TableIll) leading to decreasing trends in UD, BD, PD, SV, L*, andincreasing trends in WAI and a (Table 11).

Specific Mechanical Energy (SME)In extrusion processing, the amount of biochemical reactions

occurring inside the barrel depends on the thermal and mechan-ical energy available. To induce optimum conversion of the ingredi-ents to obtain extrudates of high quality, appropriate combinationsof shear and thermal energy are very important. The amount of

DieProperty (mm)

Mass flow rate (g/min)3.06.04.02.73.02.03.0

Torque (N-rn)3.06.04.02.73.02.03.0

TABLE VITreatment Combination Effects on the Extrusion Parameters'

90-100-100°C 90-120-120°C

LID (-) 15% 20% 25% 15% 20% 25%

3.3 ia 1 48.9° 940252s na 157.45 11 1()1.821-21

3.3 158.8" 55 7.14 31.21" 165.079 152 4814 121 I620

34 163.529 I57.9'13 81.326 I70,9'' I56.3"° I l9.9'"°

4.8 173.71-4153,30.14 99.62425 158.7'' 157.5' 1 104.02125

5.8 158.0 ° 553711 109,52024 I50.9''' 151.8814 II

0A' 163.4''° 100.221156.0 146212.14 115.819-22

0.0 154.4''° 147,11114 100,572.25 166.118 144.01215 127.916 8

3.3 Ila 102.7-1-429.6"° no 4941922 34 ITh'

3.3 48.21922 95 345 30.12830 50,818.21 7331113 730H

34 58.415- 1 R 100 745 29.72830 53916.19 88.160 3592529

4.8 81.2811 107.214 41,322.27 61,9117 95.0156 3532829

5.8 68.212-14 104.22141,622.27 34.12730 83.97-938.32328

73 74.9'0 11 115.3' III 313 68.214 104.42-444.62125

10.0 91 90.7 107.6' 441 , 422.27 82,181 105.524 46,120.24

256.82024 no 256.3 20 21 273.41823

187 , 5 27251,42(1.25 392.8' 2-3 490.88)0

298 . 5( 20257.52024 460.1 9 10 244322.25

°'

338.8'' 318.4 1 °' 492.5' '° 277.4(7.23

310.5 15-1 194.6 45I.10' 264.51924

626 . 2 2 .3 357.2''° 624.62.3 314.3 15-18

3359(512 4035' 12 597.831

1954.3 29 10 no 3266.0(9.22 2253.627.31)

"°

1991.52830 3357,91821 4846.4 14828.5'"°

2728 , 422.224091.6°' 6280.456 2336.020.29

1965 , 228303563.1

"

17.20 5822.6 2371.425.29

7359.8 4511.112.14 6898 . 4242946.5225

2753. 122 21 2255 . 827.305544.O' 2533.42328

2733 . 822275427 .08 ( 06970, 4243049.021.24

4 . 052326 flu3,942327 2.44283)

2 . 882629 6.9211- 18 3.62 23-28 6.75 16-193.37 24-29 8 l5'' 4752)25 2.0929.32

629)8.20 3,7979 8.97 4.08 23-266 .04 1821 10.34° 7.72'' 4.31 22-25

°14.961-714.3968 13.5589 7.07'

8.02'' 20,572 12.8290 6,97(5(8

103 , 920.22 na 117.1(0.14 I l6.9°'

9932628 110.816 115.91214 113.5°

101 , 423.26 118.611-11 I 17 . 3 (014 11561315

97 .928 119.88.9 118.01- ° 117.79-1199 . I 27118.38-11 I l6.7°' 115,314.15

101 , 623.27 119.38.10 117.410- 1 I5.7°'°

99.65 25-28 120.0' 116.91 1l5.515

Ong Un.. 5

3.0 3.3 na 104.42123 109.3' na 136.811 143.4" na

60 3.3 101,223.27 102 . 1 232799.82 127.1(6 128.513(6 123.617 151.58

4.0 3.4 102,422.27 103,12226 105,220.22 129.8)1.16 130.312-15141.410 156.1'

2.7 4.8 l04.3223 106,719.21 107.8'° I30.8°'' 131.412' 138.01' 155.9

3.0 5.8 101 923 .27 103921.24 104.521.23 128.91-1-t6129.3' 129.913.16 na

2.0 7.3 101,025.27 102 . 62227103.62225 127.2 16 127.715-16 152.7

30 10.0 100.62627 102 , 922.2) 114.418 127.08 128.414-16130.5(2.15 150.9

Values with the same superscript numbers for a given property are not significantly different (P < 0.05); na. data not available.

TABLE VIICorrelation Coefficients for All Multivariate Extrusion Data,h

DLLDTMCUDWAIwsIBE)PDsv

MFRSMEii

a.

I,TBTI)

D

0.174-0.541'

0.007-0.028-0.177

0.011-0.0900.509'

-0.405'0.676'3234'0.1170.270*

-0.1930.116

-0.0390.257

-0.43)'-0.318'-0.042

IM

0.716*-0.001-0.076

0.128-0.164

0.2260.105

-0.0360.0870.0980.0950.0730.1100.1730.0290.1820.337*

-0.062-0.087

LI)

-0003-0.057

0.242*-0.1640.242'

-0.247'0.255*

-0.380'0.274'0.021(1.272*0.243*0.0380.096

--0.0)00.60Y0.150

-0.053

T

0.0280.489*0.693*

_0,223*-0.368'-0.332'-0.499'0.277*0.089

-0.316'-0.231 *-0.112

0. 203 *-0.022-0.392'0.813'0,976*

MC

0.0740.383*

-0.492'4)0887

0.380*-0.221-0.345'-0.875'-0.017-0.294°_0.76l*0.298'

-0.839"4)567*-4)0630.12)

LSJJJ

4)414*0.16)0.372'0.459*1)1620)77

-0.1220.249'0.141

-0.0240.0)3

-0.0620,314*

-0339'-0.471'

WAL

473*-0.334'41.1250.48l*

-0.387'-0.287'_0,299*4)333*-0.387'

0.211*-4)384'-0.5660.552'0.727*

wsI

0.0070.020.0990.307'0,380*0.1860.283*0.531*

-0.308'11.480'0.498'

-0.084-0.282'

BD

-0.0680.715'

-0.0380.064

-0.078-0.056

0.0790.0470.188

-0.048-0.462'-0.389'

PD

-0.255'0.111

-0.3840.210'0.077

-0.096-0.156-4)272'0.2)7

-0.033-0.278*

(continued on next page)D. diameter of die nozzle. 1.. length of (lie nozzle; liD. liD ratio of die nozzle; T. temperature: MC, moisture content of ingredient mix; UD. twit density: WAI,water-absorption index, WSI, water-solubility index: BD, hulk density: PD. pellet durability: SV, sinking velocity: Q. torque: MFR. mass flow rate; SME.specific mechanical energy. t. apparent viscosity: I. e. brightness; a. redness; 6'. yellowness; P. absolute pressure in the die; TB, temperature of ingredient nixat the barrel; TD, temperature of the ingredient mix at die.'. Significant at P <0.01.

mechanical energy applied to the ingredient mix is measured interms of SME. SME is the net amount of energy utilized by theextruder to produce unit mass flow rate of the material. In single-screw extrusion, it is very difficult to control the SME because thematerial is transported by friction between the screw and barrelsurfaces and the material. At higher T, SME decreased; increasingT from 100 to 140°C resulted in a 28.8% decrease in the SME.The reduced SME consumption at higher temperature profile inthe barrel resulted in decreasing trends in UD, BD, PD, SV, L*,and increasing trends in WAI and a' value. The MC also hadsignificant effect. The highest SME (653.6 JIg) was observed at20% MC, while the lowest SME (184.6 JIg) was observed at 15and 25% MC (Table VI). As expected, die dimensions also had asignificant effect. The R2 value with L/D as the geometric param-eter in the linear quadratic model was 0.56. Model equation 23predicts SME with LID, MC, and T (Table V). The (LID) 2 term inthe model indicated that there was a nonlinear trend betweenSME consumption and LID ratio. A negative coefficient for T inthe model indicated that there was a decrease in SME as T wasincreased. MC also exhibited a nonlinear relationship with SME,as indicated by the MC 2 term in the model.

Torque (U)In general, most food and feed materials exhibit pseudoplastic

behavior. As the screw speed increases, viscosity decreases,which affects the torque requirement. Reduced viscosity at highershear rates affects the mass flow rate as well. Mass flow rate alsoaffects the torque requirement. Hence, U is an important param-eter in extrusion processing, and ultimately affects the quality ofextrudate properties. Increasing T resulted in a decrease (P <005) in the U required to operate the extruder (Table Ill). In fact,increasing T from 100 to 140°C resulted in a 33.9% decrease inU. This behavior occurred, at least in part, because increasing Tresulted in a reduced apparent viscosity (Ti) of the dough, whichthus required less torque to rotate the screw. The decreased torquerequirement at higher temperature profile in the barrel resulted inreduced UD, BD, PD, SV, L*, and increased WAI and a' values(Table III). Changing the MC also had a significant effect on theU required to operate the extruder. Maximum U was required at


20% MC, and increasing or decreasing the moisture content from20% resulted in reduced U. Changing the die dimensions also hada significant effect on U. The R2 value with L/D as the geometricparameter in the linear quadratic model was 0.71. Model equation24 predicts U with LID, MC, and T (Table V). A positive coeffi-cient for the L/D term in the model indicated that there was, ingeneral, an increasing trend in U requirement as L/D increased. Anegative coefficient for T in the model indicated that the U require-ment decreased as the temperature was increased.

Apparent Viscosity (i)Viscosity development inside the barrel depends on ingredient

composition, constituent molecular weights, processing temper-atures, pressures developed, and thermomechanjcal history, andaffects the final product properties (Gagos and Bhakuni 1992).Apparent viscosity can reveal several of these parameters and thusis often used to monitor product quality online. Increasing T from100 to 140°C resulted in a 33.9% decrease in the r inside thebarrel. Due to this decreased r], there was a decreasing trend inextrudate properties such as UD, BD, PD, SV, and an increasingtrend in WAI and a' value was observed (Table II). As expected,changing the MC of the ingredient mix also had a significant effecton i Maximum Ti was observed at 20% MC. Changin g the diedimensions had significant effect on ii as well. The R2 value topredict Ti with L/D was 0.71. Model equation 25 predicts Ti usingL/D, MC, and T (Table V). The negative coefficient for the T termin the model indicated that there was a decrease in apparentviscosity as Tincreased. The (LID)2 and (MC) 2 terms in the modelwere also significant, indicating that the LID of the die and MChad a nonlinear relationship with Ti of the ingredient melt insidethe barrel.

Correlation AnalysisAfter examining individual treatment effects, as well as treat-

ment combination effects, the multivariate data were subjected tocorrelation analysis to further examine relationships between thevariables. The Pearson correlation coefficient r provides the strengthof linear relationship between two variables (Rao 1997). In thisstudy, high correlation coefficients occurred between some a priori

0.4680.8900.956*0,464

_0.284*0.398*0.575°

-0.095.0350*

0.0740.409*0.721*.0.205*0.844*0.414°0.119

-0.018

TABLE VII (continued from previous page)Correlation Coefficients for All Multivariate Extrusion Dataa

sV

ri MFR

SME

a TB

TD

DLLDTMCUDWA!WslBDPDsv

MFRSME11L5ab5PTBTD

-00060.143

-0.0330.0080.233*

-0.1490.288*

-.1)027-0.643*-0.532'

0.9l6 I0.186 0.462k I

.40236* _0.347* -.0,672*0.055 0.354° 0.832°0.453° 0.530* 0.531

-0.156 4)070 0.066.0356* .0299* -.0.202*

-0.226° I.40323° 0.454° I

0.016 0.025 -0.1290.229° -0.132 -0463° 0799°

D. diameter of die nozzle: L. length of die nozzle; LID. LID ratio of die nozzle; T. temperature; MC, moisture content of ingredient mix; 1.JD, unit density; WA!,water-absorption index; WSI. water-solubility index: BI). hulk density: PD. pellet durability; SV. sinking velocity; D, torque: MFR. mass flow rate, SME, specific

mechanical energy: r, apparent viscosity; l.°. brightness; a°, redness: h* . yellowness: P. absolute pressure in the die; TB. temperature of ingredient inix at the

barrel: TD, temperature of the ingredient mix at die.. Significant at P <0.01.

expected pairs of responses; some were not anticipated, however.The temperature profile in the barrel was adjusted to control theextent of heat treatment applied to the dough during processing.The nature of thermo/cheinical/mechaflical changes occurring inthe ingredient mix affects the viscosity of the dough that develops,which thus affects the extrusion processing parameters. Hence,we expected strong correlations between barrel and dough temper-ature, between die and dough temperature, and between apparentviscosity, torque, and SME. As anticipated, several of these corre-lation coefficients exhibited very strong relationships, with absoluter values >0.90 (P < 0.01) (Table VII). The independent variablescontrolled in our experiments will affect the extruder processingconditions, which in turn will affect the extrudate properties.Hence, we expected good correlations between the processing con-ditions and extrudate properties. As anticipated, mass flow rate andmoisture content, WAI, and dough temperature at the die, sinkingvelocity, and dough temperature at the barrel, apparent viscosity,and die pressure, sinking velocity, and dough temperature at thedie, and bulk density and die diameter had correlation coefficientswith an absolute value >0.70. It was also anticipated that correla-tions between extrudate properties such as bulk density, unit den-sity, sinking velocity, and color would occur. As expected, the cor-relation between bulk density and sinking velocity, unit density,and sinking velocity, L* and a* had correlation coefficients withabsolute values >0.70. Additionally, the color of the extrudates ex-hibited correlation with extrusion processing parameters: mass flowrate and L*, mass flow rate and b*, water-solubility index and L*,die pressure and L* all were significant, with correlation coeffi-cients with absolute values > 0.6. These correlations may have thepotential for predicting extrusion processing conditions and extru-date properties and should be further investigated.

CONCLUSIONS

The goal of this study was to investigate the effect of die nozzledimensions, barrel temperature profile, and moisture content onDDGS-based extrudate properties and extruder processing param-eters. All of these factors had significant effects on extrudate

properties such as unit density, bulk density, pellet durability,water absorption index, water solubility index, sinking velocity,and color, and extrusion process ingparameterS such as the massflow rate, dough temperature, absolute pressure, specific mechani-cal energy, torque, and apparent viscosity. Increasing the moisturecontent from 15 to 25% resulted in decreases of 2.0, 16.0, 16.3,22.9, 18.5, 32.5, and 63.7%, respectively, in bulk density, watersolubility index, sinking velocity, L*, b*, mass flow rate, and abso-lute pressure, but an 11.6, 16.2, and 7.0% increase, respectively,in pellet durability, water absorption index, and a* . On the otherhand, increasing temperature from 100 to 140°C resulted in de-creases of 17.0, 5.9. 35.4, 50.6, 28.8, 33.9, and 33.9%, respectively,in unit density, pellet durability, sinking velocity, absolute pressure,specific mechanical energy, torque, and apparent viscosity, but a49.1 and 16.9% increase, respectively, in dough temperature andwater absorption index. It was also determined that, using a linearquadratic model, the L/D ratio of the die, along with moisture con-tent and temperature of the transition and die sections, predictedwell most of the extrudate and extrusion properties studied. Theaim of this study was to investigate extrusion processing of a 40%DDGS aquaculture feed blend on a laboratory scale, as a precursorto scaling up to commercial equipment.

Ultimately, production of these types of feeds on a largerextruder may change the interactions observed with this study, butwe have examined a wide range of parameter settings, which willbe useful for scale-up purposes. Future studies will examine otherlevels of DDGS as well.

ACKNOWLEDGMENTS

We thankfully acknowledge the financial support provided by theAgricultural Experiment Station, South Dakota State University, Brook-ings, SD, and the North Central Agricultural Research Laboratory, USDA,ARS, Brookings, SD.

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[Received September 21, 2006. Accepted March 22, 2007.]
