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Abstract

1. Introduction

skin, important component of pomace, is source of lyco-pene. Lycopene is an excellent natural food color and also

serves as a functional ingredient with important health ben-

Dietary ber has received increased attention recently.As consumers become more concerned about eating foodwith health benets, barley, which is naturally healthy, eas-ily available and inexpensive crop is strongly favored forincreased incorporation into human diet (Czuchajowska,Klamczynski, Paszczynska, & Baik, 1998). The dietary

* Corresponding author. Tel.: +90 342 3172309; fax: +90 342 3601105.E-mail address: maskan@gantep.edu.tr (M. Maskan).

Journal of Food Engineering 8Tomato (Lycopersicon esculentum) is one of the mostpopular vegetables and an integral part of human dietworldwide. Signicant amounts are consumed in the formof processed products such as juice, paste, puree, ketchup,sauce and salsa. During tomato processing a by-product,known as tomato pomace, is generated. This by-productrepresents, at most, 4% of the fruit weight (Del Valle,Camara, & Torija, 2006). Tomato pomace consists of thedried and crushed skins and seeds of the fruit (Tadeu-Pon-tes, Carvalheiro, Roseiro, & Amaral-Colloco, 1996). The

ets beyond basic nutrition (Kaur, Sogi, Gary, & Bawa,2005). A diet rich in lycopene is related to a decreased riskof certain cancers, particularly cancers of the digestivetract, prostate cancer and pancreatic cancer due to protec-tive eect of lycopene against oxidative damage (Johnson,2000). It also was found that tomato pomace signicantlyreduced cholesterol level in liver and heart by 15% and18%, respectively (Bobek, Ozdin, & Hromadova, 1998).The use of tomato processing by-products could providegaining valuable substances and at the same time reducethe waste disposal problem.Blends of barley our and tomato pomace were processed in a co-rotating twin-screw extruder. Experimental design with die temper-ature (140160 C), screw speed (150200 rpm) and tomato pomace level (210%) as independent variables produced 20 dierent com-binations that were studied using response surface methodology to investigate the eect of these variables on system parameters (SME,die melt temperature and die pressure) and product responses (expansion, bulk density, water absorption and solubility indices, textureand color). Extrudate from ve experiments within 20 samples was selected for sensory evaluation in terms of color, texture, taste, o-odor and overall acceptability. Regression equations describing the eect of each variable on the system parameters and productresponses were obtained. The system parameters and product responses were most aected by changes in temperature, pomace leveland to a lesser extent by screw speed. Extrudates with 2% and 10% tomato pomace levels extruded at 160 C and 200 rpm had higherpreference levels for parameters of color, texture, taste and overall acceptability. The results suggest that tomato pomace can be extrudedwith barley our into an acceptable and nutritional snack. 2007 Elsevier Ltd. All rights reserved.

Keywords: Extrusion cooking; Barley; Tomato pomace; Response surface methodologyEvaluation of snack foods fromby extrusio

Aylin Altan a, Kathryn L. MaDepartment of Food Engineering, Univers

bDepartment of Food Science and Technology, One Shields Avenu

Received 15 March 2007; received in revisAvailable onl0260-8774/$ - see front matter 2007 Elsevier Ltd. All rights reserved.doi:10.1016/j.jfoodeng.2007.05.014barleytomato pomace blendsprocessing

arthy b, Medeni Maskan a,*

f Gaziantep, Gaziantep TR-27310, Turkey

niversity of California Davis, Davis, CA 95616, United States

orm 14 May 2007; accepted 15 May 200718 May 2007

www.elsevier.com/locate/jfoodeng

4 (2008) 231242

d Eber content of barley contributes to its nutritional value,making it a highly desirable cereal grain today.

Extrusion cooking is an important and popular foodprocessing technique classied as a high temperature/shorttime process to produce ber-rich products (Gaosong &Vasanthan, 2000; Vasanthan, Gaosong, Yeung, & Li,2002). In the extruder, the food mix is thermomechanicallycooked to high temperature, pressure and shear stresswhich are generated in the screw-barrel assembly. Thecooked melt is then texturized and shaped in the die(Arhaliass, Bouvier, & Legrand, 2003). The thermome-chanical action during extrusion brings about gelatiniza-tion of starch, denaturation of protein and inactivationof enzymes, microbes and many anti-nutritional factors;all this occurs in a shear environment, resulting in a plasti-cized continuous mass (Bhattacharya & Prakash, 1994).

In recent years, there is an increasing demand for con-version of fruit and vegetable wastes into useful products.The primary motivation is to minimize environmentalimpact of these by-products and to utilize valuable constit-uents that remain, such as lycopene and dietary ber. Oneviable method for utilization of fruit and vegetable by-products into useful products is extrusion processing dueto its versatility, high productivity, relative low cost, energyeciency and lack of euents. Successful incorporation oftomato pomace into extruded products that deliver physi-ologically active components represents a major opportu-nity for food processors providing the consumer ahealthy barley-based product to choose from which is cur-rently lacking in the marketplace. Therefore, the objectiveof this research was to investigate processability of barleyour with the combination of tomato pomace to producesnack food in a twin-screw extruder. The eect of the vari-ables such as tomato pomace content, extrusion die tem-perature and screw speed on system parameters andphysical properties of extrudates were evaluated by usingresponse surface methodology. Sensory properties weredetermined in terms of color, texture, taste, o-odor andoverall acceptability for selected extrudate samples.

2. Materials and methods

2.1. Materials

Barley our was obtained from Bobs Red Mill NaturalFoods (Milwaukie, OR, USA). The particle size distribu-tion of the barley our was 12.1% (on mesh 40); 42.9%(on mesh 60); 38.9% (on mesh 80); 5.5% (on mesh 100);0.4% (on mesh 120) and 0.2% (mesh 120). Barley ourwas stored at 4 C until use. Tomato pomace, tomato-pro-cessing by-product, was obtained from the ConAgra Foodstomato processing plant located in Oakdale (California,USA). The pomace, obtained from the paste line, had amoisture content of 46.4% (w.b.). It was dried at 50 Covernight in a forced-air drier (Model # R-4, Commercial

232 A. Altan et al. / Journal of FooDehydrator System, Inc., Eugene, OR, USA). The driedtomato pomace was coarsely ground and passed on sievewith mesh size of 20. Then, the sieved tomato pomacewas nely ground and stored in polyethylene bags at20 C for further usage. The moisture content of driedtomato pomace was 2.43 0.2% (w.b.).

2.2. Sample preparation

Blends were prepared by mixing barley our and tomatopomace in the ratios of 100:0, 98:2, 94:6, 90:10 and87.27:12.73 on a dry-to-dry weight basis. These blends werechosen according to preliminary tests without jamming ofextruder and for acceptable products physical characteris-tics. The blended samples were conditioned to 2122%(w.b.) moisture by spraying with a calculated amount ofwater and mixing continuously at medium speed in a mixer(Model F-30T, Blakeslee, Chicago, IL, USA). The sampleswere put in buckets and stored at 4 C overnight. The feedmaterial was then allowed 3 h to equilibrate at room tem-perature prior to extrusion. This preconditioning proce-dure was employed to ensure uniform mixing andhydration and to minimize variability in the state of thefeed material. Moisture content of samples was determinedby halogen moisture analyzer (Model HR83 and HR83P,Mettler-Toledo GmbH, Greifensee, Switzerland) at 105 C.

2.3. Extrusion cooking

A laboratory-scale co-rotating twin-screw extruder(APV, Staordshire, England) with a System9000 torquerheometer (Haake Buchler, Paramus, NJ) that providedcomputer control and data acquisition was used. The slitdie (Haake Buchler, Paramus, NJ, USA) had dimensionsof 1.47 mm 20 mm 150 mm. The barrel diameter andits length to diameter ratio (L/D) were 30 mm and 13:1,respectively. The MPC/V-30 had a clamshell barrel consist-ing of three independent temperature zones controlled byelectrical heating and compressed air cooling. A computer-ized data acquisition system was used to control ve settemperatures and rotor speed and to record ve melt tem-peratures, pressure at the slit die and torque data. Dataacquisition rate was every 6 s. The barrel zone tempera-tures were set at 30, 60, 100 and 130 C throughout theexperiments. The actual extruder screw speed is 2.5 timesthe rotor speed. The screws were composed of screw ele-ments and lope-shaped paddles which could be assembledon the hexagon-shaped shafts to give dierent screw cong-urations. The screw conguration used is shown in Fig. 1.The screw conguration had three pieces of 1.5D twin leadfeed screws, two 1D twin lead feed screws, nine kneadingelements oriented at 30 feed forward, one 1D single leadfeed screw followed by nine kneading elements orientedat 30 feed forward and 1D discharge screw. Barley ourand tomato pomace blends were fed into extruder with aK-tron Type T-20 twin-screw volumetric feeder (K-TronCorp., Pitman, NJ, USA) at a rate of 2.11 0.042 kg/h.

ngineering 84 (2008) 231242Extrudate was collected when the operation conditionwas at steady state identied by torque value that vary less

formed for sensory data to determine dierences betweentreatments by using SPSS.

2.5. System parameters

Specic mechanical energy, the mechanical energy inputper unit mass of the extrudate, was calculated by dividingthe net power input to the screw by the extrudate ow rate.SME input was calculated by the following equation(Chang, Martinez-Bustos, Park, & Kokini, 1999; Fan,Mitchell, & Blanshard, 1996; Sokhey & Chinnaswamy,1992):

SME Wh kg1 screw speed s1 torque Nm

mass flow rate kg h1 :

Fig. 1. Schematic representation of screw conguration.

A. Altan et al. / Journal of Food Engineering 84 (2008) 231242 233than 5%. The samples were dried at 52 C overnight in aforced-air drier (Model # R-4, Commercial DehydratorSystem, Inc., Eugene, OR, USA). The nal dried samplescontained a maximum of 5.5% (w.b.) moisture. Dried sam-ples were stored in polyethylene bags at room temperatureand used for further analysis.

2.4. Experimental design and data analysis

The central composite design for three independent vari-ables was performed. The independent variables consideredwere die temperature (X1), screw speed (X2) and pomacelevel (X3). The independent variables and variation levelsare shown in Table 1. The levels of each variable wereestablished according to literature data and preliminary tri-als. The outline of experimental design with the coded andactual levels is presented in Table 2. Dependent variableswere specic mechanical energy (SME), die melt tempera-ture, die pressure as system parameters and sectionalexpansion index (SEI), bulk density, water absorptionand solubility indices, color and texture as productresponses. Response surface methodology was applied forexperimental data using a commercial statistical package,Design-Expert version 6.0.6 (Statease Inc., Minneapolis,MN, USA) for the generation of response surface plots.The same software was used for statistical analysis ofexperimental data. The results were analyzed by a multiplelinear regression method which describes the eects of vari-ables in rst order, a two-factor interaction (2FI) and sec-ond order polynomial models. Experimental data weretted to the selected models and regression coecientsobtained. Statistical signicance of the terms in the regres-sion equation was examined by analysis of variance(ANOVA) for each response. A Pearsons correlationmatrix on product responses and system parameters wascarried out using SPSS 11.0 (SPSS Inc., Chicago, IL,USA) in order to determine correlation coecientsbetween parameters. Duncans multiple range test was per-Table 1Process variables used in the central composite design for three indepen-dent variables

Code Variable level codes

1.682 1 0 1 1.682Die temperature (C) X1 133.18 140 150 160 166.82Screw speed (rpm) X2 133 150 175 200 217Pomace level (%) X3 0 2 6 10 12.731Torque was recorded every 6 s for at least 12 min and SMEwas calculated and averaged for each processing condition.Die pressure was measured using a Dynisco pressure trans-ducer (PT-412, Dynisco, Franklin, MA, USA). Readingswere recorded every 6 s for at least 12 min and average val-ues were expressed as kPa. Die melt temperature was also

Table 2Experimental design for extrusion experiment with coded and actualvariable levels

Run Coded levels Actual levels

X1 X2 X3 Dietemperature(C)

Screwspeed(rpm)

Pomacelevel (%)

1 1 1 1 140 150 22 1 1 1 160 150 23 1 1 1 140 200 24 1 1 1 160 200 25 1 1 1 140 150 106 1 1 1 160 150 107 1 1 1 140 200 108 1 1 1 160 200 10

9 1.682 0 0 133.18 175 610 1.682 0 0 166.82 175 611 1 1.682 0 150 133 612 1 1.682 0 150 217 613 0 0 1.682 150 175 014 0 0 1.682 150 175 12.7315 0 0 0 150 175 616 0 0 0 150 175 617 0 0 0 150 175 618 0 0 0 160 175 619 0 0 0 150 175 620 0 0 0 150 175 6

d Engineering 84 (2008) 231242measured by thermocouple and monitored for every 6 s bya computerized data acquisition system.

2.6. Product responses

2.6.1. ExpansionExpansion of extrudates was evaluated as sectional

expansion. The width and thickness of 15 pieces of extru-date taken at random were measured with a digital caliperand the average calculated. The sectional expansion index(SEI) was calculated using the equation proposed by Alva-rez-Martinez, Kondury, and Harper (1988):

SEI SeSd W eheW dhd

; 2

where Se and Sd are the cross-sectional areas of the extru-date and the die; We and he are the width and thickness ofthe extrudate andWd and hd are the width and thickness ofthe die, respectively.

2.6.2. Bulk density

Bulk density was determined by measuring the volumeof extrudate by glass bead displacement (Hwang & Hayak-awa, 1980; Sokhey, Ali, & Hanna, 1997). Glass beads witha diameter range of 1.001.18 mm were used as displace-ment medium. Bulk densities of the extrudates were calcu-lated as

qb W exW gb

qgb; 3

where qb is the bulk density using glass bead displacementmethod (g/cm3), Wex is the extrudate mass (g), Wgb is themass of glass beads displaced (g) and qgb is the density ofthe glass beads (g/cm3). The values were average of fourmeasurements.

2.6.3. Water absorption and solubility indices

The water absorption index (WAI) is the weight of gelobtained per gram of dry ground sample. The WAI ofextrudates was determined according to the AACC method5620 (AACC, 1995). The ground extrudate was suspendedin water at room temperature. After standing for 10 min,gently stirred during this period, samples were centrifugedfor 15 min at 1000g (AllegraTM 6 Centrifuge, BeckmanCoulter Inc., Palo Alto, CA, USA). The supernatant wasdecanted into a tarred aluminum pan. The WAI was calcu-lated as the weight of sediment obtained after removal ofthe supernatant per unit weight of original solids as drybasis. The water solubility index (WSI) is the percentageof dry matter recovered after the supernatant is evaporatedfrom the water absorption determination. The supernatantwas dried in a vacuum oven at 84.4 C and 2024 mmHggauge pressure for 24 h and weighed. The WSI was theweight of dry solids in the supernatant expressed as a per-centage of the original weight of sample on dry basis (Jin,

234 A. Altan et al. / Journal of FooHsieh, & Hu, 1995). WAI and WSI determinations werereplicated four times.2.6.4. Texture

The hardness of samples was measured with a TA-XT2iTexture Analyzer (Texture Technologies Corp., Scarsdale,NY, USA). Hardness in N was determined by measuringthe maximum force required to break the extruded samples(42 mm long) using three point bend test with a sharp-bladed probe (55 mm wide, 40 mm high, 9 mm thick).The test speed was 2 mm/s and the distance between twosupports was 22 mm. A forcetime curve was recordedand analyzed by Texture Exponent 32 software program(version 3.0). Elevan measurements were performed oneach sample and averaged.

2.6.5. ColorHunterLab LabScan XE (Hunter Associates Labora-

tory, Inc., Reston, VA, USA) was used to determine colorvalues of the raw materials and ground extruded in termsof the L, a and b as measures of lightness, redness and yel-lowness, respectively. The measuring head was equippedwith 51 mm diameter viewing port and used the systemof diuse illumination with 10 viewing geometry. Theilluminant was D65. The colorimeter was calibratedagainst a standard white tile (L = 91.43, a = 0.74,b = 0.25). The extrudates were ground in a laboratorygrinder and passed through a 60 mesh sieve prior to coloranalysis. For each sample, four measurements were takenand averaged. The total color change (DE) was calculatedas

DE L L02 b b02 a a02

q; 4

where the subscript 0 indicates initial color values of theraw material.

2.7. Sensory evaluation

A semi-trained panel of 34 students and faculty fromFood Engineering Department evaluated the extrudedsnacks for color, texture and overall acceptability on a 7-point hedonic scale (from 1 = extremely dislike to7 = extremely like), while taste in terms of bran, tomatoavor and bitterness and o-odor was rated on a 7-pointscale (from 1 = none to 7 = very high). Panelists rinsedtheir mouths with water after tasting each sample.

3. Results and discussion

Figures for die pressure, expansion, WAI, L, a and bwere not given for the sake of simplicity.

3.1. Diagnostic checking of tted model and surface plots for

various responses

3.1.1. Specic mechanical energy

A regression analysis were carried out to t mathemati-

cal models to the experimental data. The predicted model

eect of screw speed and tomato pomace level on SME isshown in Fig. 2. Increasing tomato pomace level in theblends increased the SME input in extrusion cooking sig-nicantly (P < 0.05). This eect could be explained by add-ing tomato pomace to barley our gives a more viscousmelt requiring a higher torque and cause an increase inSME input. The observed eect of tomato pomace onSME was similar to that reported by Hsieh, Hu, Lue,and Stringer (1991) in extrusion of sugar beet ber andcorn meal. They reported that less water was availablefor starches in corn meal in the presence of sugar beet ber.Because the viscosity of the starch-water system increaseswith decreasing water content, torque and specic energyincreased with increasing sugar beet ber. Statistical analy-sis revealed that SME was positively correlated with diepressure (R = 0.564, P < 0.01) (Table 4). The measureddie melt temperature in extrusion cooking of barley ourand tomato pomace blends ranged from 129.55 to150.19 C. Die melt temperature was negatively correlated

d Engineering 84 (2008) 231242 235for specic mechanical energy (SME) can be described bythe following equation in terms of coded values:

SME 268:89 28:10X 1 35:95X 2 16:45X 3 14:01X 21 11:50X 23 19:93X 1X 3 17:03X 2X 3: 5

The signicance of coecients of tted quadratic model(Eq. (5)) was evaluated by using the F-test and P-value.Temperature (X1) had highly signicant negative linear ef-fect (P < 0.001) while screw speed (X2) and pomace level(X3) had a signicant positive linear eect on SME atP < 0.001 and P < 0.05 followed by a positive quadratic ef-fect of temperature X 21 (P < 0.05) and pomace level X 23(P < 0.05). The interaction of temperature and pomace le-vel (X1X3) had a signicant negative eect (P < 0.05)whereas the interaction of screw speed and pomace level(X2X3) had a signicant positive eect (P < 0.05) on SME.

The analysis of variance (ANOVA) for SME of qua-dratic model (Eq. (5)) is given in Table 3. Regression model

Table 3Analysis of variance results for tted models

Response Source df Sum ofsquares

Meansquares

F-value

P-value

SME Regression 9 46169.46 5129.94 13.37 0.0002*

Lack-of-t 5 610.87 122.17 0.19 0.9541Pure error 5 3225.64 645.13Residual 10 3836.51 383.65

Total 19 50005.97

P Regression 6 3.820 107 6.367 106 15.07 0.05).

The measured SME in extrusion cooking of barley ourand tomato pomace blends ranged from 163.37 to372.13 W h/kg. SME decreased with increasing tempera-ture and decreasing screw speed. Similar results wereobserved by other authors (Dogan & Karwe, 2003; Koksel,Ryu, Basman, Demiralp, & Ng, 2004; Ryu & Ng, 2001).Increase in temperature suggests reduction in viscositywhich ultimately leads to reduced SME (Chang et al.,1999; Hsieh, Mulvaney, Hu, Lue, & Brent, 1989). Anincrease in screw speed increased SME input. The increaseof SME with screw speed is evident from Eq. (5) whichshows that SME is proportional to the screw speed. Baik,Powers, and Nguyen (2004) reported that increasing thescrew speed causes increases in SME input attributed tothe increase in shear rate with increased screw speed. The(R = 0.533, P < 0.05) with SME (Table 4). One mightexpect that as the product temperature in the melting zoneincreased, the viscosity of the dough would decrease which,in turn, would reduce torque and SME (Hsieh et al., 1991).Ryu and Ng (2001) reported that melt temperature in thedie exit aected SME input and decreased with the increasein melt temperature for both wheat our and wholecornmeal.

3.1.2. Die pressure

The regression analysis results indicate that die pressure(P) was highly signicant (P < 0.001) on linear term of tem-perature (X1) and interaction term of temperature andpomace level (X1X3). The regression equation obtainedfor die pressure was as follows:

P 3806:71 1446:37X 1 1065:77X 1X 3: 6

217.80247.02276.24305.46334.68

SM

E (W

h/kg)

150.0 162.5

175.0 187.5

200.0

2.04.0

6.08.0

10.0

Screw speed (rpm) Pomace level (%) Fig. 2. Response surface plot for specic mechanical energy (SME) as afunction of screw speed and pomace level at a temperature of 150 C.

2*

3ns

8*

3ns

8**

inde

d EThe negative coecient of the rst order term of tempera-ture (X1) (Eq. (6)) indicated that die pressure increased withdecrease of temperature. Meanwhile, negative coecient ofinteraction term (X1X3) of temperature and pomace levelalso resulted in decrease of die pressure. ANOVA for the2FI model as tted to experimental results (Table 3) showssignicance (P < 0.05). The coecient of determination(R2) for die pressure was 0.8743. Die pressure modelshowed signicant (P < 0.05) lack-of-t. The measureddie pressure in extrusion cooking of barley our and toma-to pomace blends ranged from 786.45 to 6106.29 kPa. Thepressure at the die exit was decreased upon increase in tem-perature. Decrease in die pressure with the increase in tem-perature may be attributed to decrease in viscosity of themelt (Ryu & Ng, 2001; Singh & Smith, 1997) due to degra-dation of gelatinized starch granules (Cai, Diosady, & Ru-bin, 1995; Singh, Sekhon, & Singh, 2007). A negative

Table 4Correlation coecients between product responses and system parameters

SEI BD WAI WSI L a

SEI 1 0.219ns 0.149ns 0.149ns 0.502* 0.51BD 1 0.212ns 0.542* 0.106ns 0.11WAI 1 0.184ns 0.508* 0.54WSI 1 0.462* 0.43L 1 0.98a 1b

DEH

SMEP

T

SEI: sectional expansion index; BD: bulk density; WAI: water absorptionP: die pressure; T: die melt temperature.ns Not signicant.* Signicant at P < 0.05.** Signicant at P < 0.01.

236 A. Altan et al. / Journal of Foocorrelation was found between die pressure and melt tem-perature (R = 0.777, P < 0.01) (Table 4). It was observedthat increasing pomace level with increasing temperaturedecreased die pressure.

3.1.3. Expansion

The regression equation for expansion as sectionalexpansion index (SEI) at any temperature (X1) and pomacelevel (X3) was

SEI 1:59 0:25X 1 0:18X 3 0:14X 21 0:073X 23 0:099X 1X 3: 7

It was observed that temperature (X1) and pomace level(X3) had highly signicant negative linear eect(P < 0.001) on SEI followed by a negative quadratic eectof temperature X 21 (P < 0.001) and a positive quadraticeect of pomace level X 23 (P < 0.05). The interaction oftemperature and pomace level (X1X3) had a signicant po-sitive eect (P < 0.05) on SEI (Eq. (7)). ANOVA for qua-dratic model of SEI is given in Table 5. Regressionmodel tted to experimental results of SEI showed highercoecient of determination (R2 = 0.9557). Table 5 showsthat the F-value for SEI was signicant with a signicantlack-of-t (P < 0.05).

The measured SEI of barley our and tomato pomaceblend extrudates varied between 0.893 and 2.014. Whenextrusion-cooked melts exit the die, they suddenly gofrom high pressure to atmospheric pressure. This pressuredrop causes a ash-o of internal moisture and the watervapor pressure, which is nucleated to form bubbles in themolten extrudate, allows the expansion of the melt(Arhaliass et al., 2003). SEI decreased when temperaturewas increased. The lowest values for expansion werefound with temperature of 166.8 C. Expansion decreaseat higher extruder temperatures can be attributed toincrease dextrinization and weakening of structure (Men-donca, Grossmann, & Verhe, 2000). Launay and Lisch

b DE H SME P T

0.441ns 0.236ns 0.282ns 0.382ns 0.754** 0.494*0.180ns 0.376ns 0.925** 0.152ns 0.351ns 0.644**

0.543* 0.269ns 0.397ns 0.133ns 0.188ns 0.091ns0.476* 0.309ns 0.467* 0.782** 0.488* 0.618**

0.974** 0.721** 0.031ns 0.271ns 0.089ns 0.296ns0.992** 0.722** 0.038ns 0.212ns 0.080ns 0.296ns1 0.752** 0.110ns 0.240ns 0.171ns 0.364ns

1 0.319ns 0.131ns 0.235ns 0.323ns1 0.134ns 0.444ns 0.637**

1 0.564** 0.533*1 0.777**

1

x; DE: total color change; H: hardness; SME: specic mechanical energy;

ngineering 84 (2008) 231242(1983) proposed that the corn extrudate longitudinaland diametral (sectional) expansions depended on themelt viscosity and elasticity. They reported that anincreased water content or temperature would yield alower melt viscosity and increased longitudinal expansionwhile the melt elasticity would be lowered and a decreasein diametral expansion would be observed. This result isin agreement also with the works of other researchers(Dogan & Karwe, 2003; Ilo, Liu, & Berghofer, 1999).Several researchers have demonstrated that the expansionratio of extruded cereals depends on the degree of starchgelatinization (Case, Hanna, & Scwartz, 1992; Chinnasw-amy & Hanna, 1988). However, increasing level oftomato pomace resulted in decrease in SEI of extrudates.This may be attributed to dilution eect of pomace onstarch. Screw speed had no signicant eect (P > 0.05)on expansion of extrudates. Increasing level of pomacewith increasing temperature decreased expansion. Sec-tional expansion index was correlated with die melt tem-perature (R = 0.494, P < 0.05) and pressure (R = 0.754,P < 0.001). Sokhey et al. (1997) concluded that radial

uar

3

3

d ETable 5Analysis of variance results for tted models

Response Source df Sum of sq

SEI Regression 9 1.71Lack-of-t 5 0.071Pure error 5 7.913 10Residual 10 0.079

Total 19 1.78

BD Regression 9 0.50Lack-of-t 5 0.033Pure error 5 7.699 10Residual 10 0.041

Total 19 0.54

WAI Regression 3 0.76Lack-of-t 11 0.46Pure error 5 0.15Residual 16 0.60

Total 19 1.36

WSI Regression 3 44.94Lack-of-t 11 8.47Pure error 5 0.67

A. Altan et al. / Journal of Fooexpansion (sectional expansion) depended directly on thepressure at the die nozzle that correlates our results.

3.1.4. Bulk density

The quadratic model obtained from regression analysisfor bulk density (BD) in terms of coded levels of the vari-ables was developed as follows:

BD 0:53 0:15X 1 0:093X 21 0:085X 1X 3: 8Bulk density of barley our and tomato pomace extrudatewas signicantly aected (P < 0.001) by the linear and qua-dratic terms of temperature (X1 and X

21) but was not signif-

icantly (P > 0.05) dependent on screw speed (X2) andpomace level (X3). The interaction term of temperatureand pomace level (X1X3) was found to be signicant(P < 0.001). ANOVA for bulk density of quadratic model(Eq. (8)) is given in Table 5. Regression model tted toexperimental results of bulk density showed good correla-tion coecient (R2 = 0.9244). Table 5 shows that the F-va-lue for bulk density was signicant (P < 0.05), whereaslack-of-t was not signicant (P > 0.05).

The expansion ratio and bulk density of extrudates seekto describe the degree of pung undergone by the dough asit exits the extruder. Sectional expansion index considers

Residual 16 9.14

Total 19 54.08

H Regression 9 742.88Lack-of-t 5 9.34Pure error 5 0.053Residual 10 9.39

Total 19 752.27

* Signicant at P < 0.05, df: degrees of freedom.es Mean squares F-value P-value

0.19 23.95

holding capacity when the ratio of ber/corn starchincreased in extrusion of corn ber and corn starch blend.In addition, Singh et al. (2007) observed a decrease in WAIwith addition of pea grits in extrusion of rice. Theyexplained that a decrease in WAI was due to the dilutionof starch in rice pea blends.

The WSI ranged from 7.08% to 12.99% for the barleyourtomato pomace extrudates. The eect of temperatureand screw speed on WSI of extrudates is shown in Fig. 4.The WSI increased signicantly (P < 0.001) with increasingscrew speed and tomato pomace level and decreasing tem-perature. The increase in WSI with increasing screw speedwas consistent with the results reported for corn meal andcorn and wheat extrudates (Jin et al., 1995; Mezreb, Goul-lieux, Ralainirina, & Queneudec, 2003). Mezreb et al.(2003) reported that the increase of screw speed induceda sharp increase of specic mechanical energy, the highmechanical shear degraded macromolecules, and so themolecular weight of starch granules decreased and hence

d Engineering 84 (2008) 231242WAI 6:54 0:12X 1 0:18X 3; 9WSI 9:66 1:15X 1 1:03X 2 0:98X 3: 10The negative coecients of the linear terms of temperature(X1) and pomace level (X3) (Eq. (9)) indicated that WAI de-creases with increase of these variables while positive coef-cients (Eq. (10)) of the linear terms of screw speed (X2)and pomace level (X3) resulted increase in WSI. ANOVAfor models of WAI and WSI is given in Table 5. As indi-cated in ANOVA table, rst order model for WAI andWSI was found to be signicant (P < 0.05). However, thelack-of-t was not signicant (P > 0.05) for WAI but sig-nicant for WSI (P < 0.05). The coecients of determina-tion (R2) for water absorption and solubility indices were0.5569 and 0.8310, respectively.

0.3670.4840.6020.7190.836

140.0145.0

150.0155.0

160.0 2.0 4.0

6.0 8.0

10.0

Temperature (C) Pomace level (%)

B

ulk

dens

ity (g

/cm3 )

Fig. 3. Response surface plot for bulk density (BD) as a function ofpomace level and temperature at a screw speed of 175 rpm.

238 A. Altan et al. / Journal of FooThe WAI measures the volume occupied by the granuleor starch polymer after swelling in excess water. While theWSI determines the amount of free polysaccharide or poly-saccharide released from the granule after addition ofexcess water (Sriburi & Hill, 2000). The WAI ranged from6.10 to 7.03 g/g for the barley ourtomato pomace extru-dates. Increasing temperature signicantly (P < 0.05)decreased the WAI of extrudates. Similar results werereported by Guha, Ali, and Bhattacharya (1997), Pelembe,Erasmus, and Taylor (2002) Ding, Ainsworth, Plunkett,Tucker, and Marson (2006). A decrease in WAI withincreasing temperature was probably due to decompositionor degradation of starch (Pelembe et al., 2002). Ding et al.(2006) also stated that the WAI decreases with increasingtemperature if dextrinization or starch melting prevailsover the gelatinization phenomenon. The WAI decreasedsignicantly (P < 0.01) as the percentage of tomato pomaceincreased. This may be attributed to relative decrease instarch content with addition of pomace and competitionof absorption of water between pomace and availablestarch. This result is in agreement with those of Artz, War-ren, and Villota (1990). They reported a decrease in waterincreased WSI. In this study, it was observed that WSIwas positively correlated with SME (R = 0.782, P < 0.01),die pressure (R = 0.488, P < 0.05) and bulk density(R = 0.542, P < 0.05) but negatively correlated with diemelt temperature (Table 4). Temperature was found beinginversely proportional to WSI; that is, the higher the extru-sion temperatures, the lower the WSI values. Similar nd-ings were achieved by Gutkoski and El-Dash (1999) inextruded oat products.

3.1.6. TextureThe quadratic model for hardness (H) in terms of coded

levels of the variables was developed as follows:

H 7:70 5:79X 1 0:67X 2 4:13X 21 1:93X 1X 3: 11Hardness of the barley our and tomato pomace extrudatewas signicantly aected by linear terms of temperature

7.488.579.66

10.7411.83

W

SI (%

)

140.0 145.0

150.0 155.0

160.0

150.0162.5

175.0187.5

200.0

Temperature (C)Screw speed (rpm) Fig. 4. Response surface plot for water solubility index (WSI) as afunction of temperature and screw speed at a pomace level of 6%.

(X1) and screw speed (X2) at P < 0.001 and P < 0.05,respectively. Temperature had also signicant quadratic ef-fect (P < 0.001) on hardness of extrudates. The interactionterm (X1X3) between temperature and pomace level wassignicant, so that high values of hardness were found athigh level of pomace, dependent on temperature. Regres-sion model (Eq. (11)) tted to experimental results of hard-ness showed higher coecient of determination(R2 = 0.9875). Table 5 shows that the F-value for hardnesswas signicant with a signicant lack-of-t (P < 0.05).

The textural property of barley our and tomato pom-ace extrudate was determined by measuring the forcerequired to break the extrudate (Singh, Hoseney, & Fau-bion, 1994). The higher the value of maximum peak forcerequired in gram, which means the more force requiredto breakdown the sample, the higher the hardness of thesample to fracture (Li, Zhang, Tony Jin, & Hsieh, 2005).The eect of temperature and tomato pomace level on

3.1.7. Color

Color is an important quality factor directly related tothe acceptability of food products, and is an importantphysical property to report for extrudate products. Theregression equations for color parameters (L, a and b val-ues) and total color change (DE) at any temperature (X1)and pomace level (X3) were

L 69:95 3:23X 3 0:79X 23; 12a 9:88 3:21X 3 0:92X 23; 13b 22:89 0:32X 1 2:88X 3 0:17X 21 0:86X 23; 14DE 8:90 0:31X 1 0:69X 3 0:80X 23: 15Tomato pomace level (X3) was an important variable in theresponse surface models (Eqs. (12)(15)) of product colorparameters, as its linear and quadratic terms were signi-cant at P < 0.01 and P < 0.001, respectively. The colorparameter b of barley our and tomato pomace extrudatewas signicantly (P < 0.01, P < 0.05) aected by linearand quadratic terms of temperature (X1). Temperaturehad also signicant (P < 0.05) eect on DE of extrudates.ANOVA results for models of L, a and b color parametersand DE are given in Table 6. As indicated in ANOVA ta-ble, quadratic model for L, a, b color parameters and totalcolor change, DE was found to be signicant (P < 0.05).However, the lack-of-t was not signicant (P > 0.05) for

A. Altan et al. / Journal of Food Ehardness of extrudates is shown in Fig. 5. Response surfaceplot showed that a decrease in die temperature withincreasing level of tomato pomace increased the producthardness. Hardness of barley our and tomato pomaceextrudate varied between 5.64 and 29.75 N. A decrease indie temperature increased the product hardness giving amaximum at about 133.18 C, 175 rpm screw speed and6% tomato pomace level. This result is in line with densitywhere an increase in density was observed. High densityproduct naturally oers high hardness evident by high cor-relation between product density and hardness (R = 0.925,P < 0.01) (Table 4). Similar eect of temperature has beenobserved while extruding yam and wheat our (Ding et al.,2006; Sebio & Chang, 2000). Increasing screw speedslightly decreased the hardness of the barley ourtomatopomace extrudate, particularly at higher temperatures.Liu, Hsieh, Heymann, and Hu (2000) found that thehardness of the extruded oatcorn our increased as thescrew speed decreased.

4.748.60

12.4716.3320.20

140.0145.0

150.0155.0

160.0 2.0 4.0

6.0 8.0

10.0

Temperature (C) Pomace level (%)

Har

dnes

s (N)Fig. 5. Response surface plot for hardness (H) as a function of pomacelevel and temperature at a screw speed of 175 rpm.Table 6Analysis of variance results for tted models

Response Source df Sum ofsquares

Meansquares

F-value

P-value

L-value Regression 9 139.17 15.46 36.91

(R2) for L, a, b color parameters and DE were 0.9708,0.9949, 0.9928 and 0.8605, respectively.

The non-extruded blend of barley our and tomatopomace with a percentage of 0, 2, 6, 10 and 12.73 pomacehad color values of the ranges: L: 70.7979.17; a: 2.029.22;b: 11.3819.09, whereas the barley ourtomato pomaceextrudates had color values of the ranges: L, 65.8576.32;a, 2.7012.66; b, 16.1025.63. Among the color parameters,the L and a values showed marked changes due to additionof tomato pomace only. An increase in tomato pomacelevel decreased the L value of the samples and increasedthe a value of samples as expected due to the lycopene pig-ment in the tomato pomace. Statistical analysis showedthat there was a negative correlation between L and a val-ues of samples (R = 0.988, P < 0.01) (Table 4). Similarresult was found by Ilo and Berghofer (1999). The L valuewas positively correlated with SEI (R = 0.502, P < 0.05)and WAI (R = 0.508, P < 0.05) but negatively correlated

color. Extrudates B and D had higher preference valuesfor the parameter of texture. There were no signicant dif-ferences (P > 0.05) in bran avor, bitterness and o-odorscores among extrudates. Tomato avor score changed asa result of increasing percentage of tomato pomace. How-ever, tomato avor was perceived as weak (3.02) by panel-ists for highest level of pomace. The overall acceptability ofthe barley our and tomato pomace extrudate ranged low-est (3.94) in extrudate A and highest (5.23) in extrudate D.

4. Conclusion

The system parameters and product responses werefound to be most dependent on temperature and pomacelevel. The results showed that varying levels of tomatopomace could be incorporated into an extruded barleysnack depending on the desired texture of the nal product.Extrudates with 2% and 10% tomato pomace levels

240 A. Altan et al. / Journal of Food Ewith WSI (R = 0.462, P < 0.05). On the other hand, avalue was negatively correlated with SEI (R = 0.512,P < 0.05) and WAI (R = 0.548, P < 0.05). An increasein expansion gives more bright color in extrudates due toair cells rather than dull color. The change in yellowness(b value) decreased with increasing temperature which isin agreement with the results of Ilo and Berghofer (1999).They reported that the changes in yellowness during extru-sion cooking of yellow maize induced by the eects of twodierent reactions: the non-enzymatic browning and pig-ment destruction. They also concluded that some of thecaratenoids might have been damaged by the thermal treat-ment and some browning might have made up the colorloss. Increasing tomato pomace content resulted in a signif-icant (P < 0.001) increase in the extrudate b value and DE.The b value was positively correlated with a value(R = 0.992, P < 0.01) and WSI (R = 0.476, P < 0.05),whereas negatively correlated with L value (R = 0.974,P < 0.01) and WAI (R = 0.543, P < 0.05) (Table 4).

Temperature (C)

7.347.918.489.049.61

140.0145.0

150.0155.0

160.0 2.0 4.0

6.0 8.0

10.0

Pomace level (%)

EFig. 6. Response surface plot for total color change (DE) as a function ofpomace level and temperature at a screw speed of 175 rpm.Total color change in extruded products ranged between5.56 and 9.99. The eect of temperature and pomace levelon total color change of extrudates is shown in Fig. 6.Results of regression analysis show that color change wasmost dependent on tomato pomace content (P < 0.001).It was observed that DE was negatively correlated with Lvalue (R = 0.721, P < 0.01) and positively correlated witha value (R = 0.722, P < 0.01) and b value (R = 0.752,P < 0.01) (Table 4).

3.2. Sensory evaluation

Five extrudate samples were selected out of 20 extrudatesamples with respect to textural property and dierent pom-ace level for sensory evaluation. The mean values of sensorypanel ratings of extrudates are presented in Table 7. Extru-dates with dierent level of tomato pomace had better scorethan that of extrudate with 0%. Extrudate D with 10%tomato pomace had the highest level of acceptance for

Table 7Sensory evaluation scores of extrudates produced at dierent conditions

Extrudates

AA B C D E

Color 3.64a 4.70bc 4.85bc 5.08c 4.23ab

Texture 3.91a 5.32b 4.58c 5.26b 3.44a

TasteBran avor 3.67a 3.79a 3.23a 3.44a 3.82a

Tomato avor 1.67a 1.50a 2.70b 2.50b 3.02b

Bitterness 1.85a 1.61a 1.94a 1.88a 2.00a

O-odor 1.79a 1.79a 1.70a 1.58a 1.88a

Overall acceptability 3.94a 4.85b 4.94b 5.23b 4.08a

A: 0% pomace level, 150 C, 175 rpm; B: 2% pomace level, 160 C,200 rpm; C: 6% pomace level, 150 C, 217 rpm; D: 10% pomace level,160 C, 200 rpm; E: 12.73%, 150 C, 175 rpm.A Means within a row with dierent superscripts are signicantly dif-ferent (P < 0.05).

ngineering 84 (2008) 231242extruded at 160 C and 200 rpm had higher preference lev-els for parameters of color, texture, taste and overall

The inuence of specic mechanical energy on cornmeal viscosity

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Ding, Q. B., Ainsworth, P., Plunkett, A., Tucker, G., & Marson, H.(2006). The eect of extrusion conditions on he functional and physicalacceptability. Such extrusion would also provide anotheravenue for tomato pomace utilization.

Acknowledgements

This research project was supported by the University ofGaziantep (Turkey) and Center for Advanced Materials,Methods and Processing, supporting the mission of theRobert Mondavi Institute for Wine and Food Science, Uni-versity of California, Davis. Special thanks are extended toMr. Jannes Vandeven for assistance with extrusion process-ing and Mr. Ken Shaw, principal mechanician, Departmentof Food Science and Technology, UC Davis.

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Evaluation of snack foods from barley-tomato pomace blends by extrusion processingIntroductionMaterials and methodsMaterialsSample preparationExtrusion cookingExperimental design and data analysisSystem parametersProduct responsesExpansionBulk densityWater absorption and solubility indicesTextureColor

Sensory evaluation

Results and discussionDiagnostic checking of fitted model and surface plots for various responsesSpecific mechanical energyDie pressureExpansionBulk densityWater absorption and solubility indicesTextureColor

Sensory evaluation

ConclusionAcknowledgementsReferences