Single-Screw Extrusion Processing of Distillers Dried Grains with Solubles (DDGS)-Based Yellow Perch (Perca flavescens) Feeds

Transcription

1 e-xtr* Single-Screw Extrusion Processing of Distillers Dried Grins with Solubles (DDGS)-Bsed Yellow Perch (Perc flvescens) Feeds Ferouz Y. Aydi, 1 Ksiviswnthn Muthukumrppn, 1 Kurt A. Rosentrter, 2,3 nd Michel L. Brown 4 ABSTRACT Cerel Chem. 88(2): This study ws conducted to investigte the production of blnced diets for juvenile yellow perch (Perc flvescens) feeds. Six isocloric ( 3.21 kcl/g), isonitrogenous (30.1 ± 0.4% db) ingredient blends were formulted with 0, 10, 20, 30, 40, nd 50% distillers dried grins with solubles (DDGS), nd pproprite mounts of soyben mel, fish mel, vitmins, nd minerls. Extrusion cooking ws performed using lbortory-scle single-screw extruder t constnt brrel temperture profile of C, nd constnt screw speed of 230 rpm (24.1 rd/sec). The mss flow rte ws determined during processing; it generlly incresed with progressively higher DDGS content. Additionlly, moisture content, wter ctivity, unit density, expnsion rtio, compressive strength, compressive modulus, pellet durbility index, wter stbility, nd color were extensively nlyzed to quntify the effects of DDGS content on the physicl properties of the resulting extrudtes. Significnt differences (P < 0.05) between blends were observed for color nd wter ctivity for both the rw mteril nd extrudtes, respectively, nd for the unit density of the extrudtes. There were significnt chnges in brightness (L), redness (), nd yellowness (b) mong the finl products when incresing the DDGS content of the blends. Expnsion rtio nd compressive strength of the extrudtes were low. On the other hnd, ll blends showed high pellet durbility (PDI 96.18%). Overll, it ws scertined tht DDGS could be successfully included t rtes of <50%, nd tht ech of the ingredient blends resulted in vible, high qulity extrudtes. Aquculture is one of the fstest growing sectors in the food producing industries. It incresed from per cpit supply of 0.7 kg in 1970 to 7.8 kg in With n nnul growth rte of 6.9%, it exceeded by fr the nnul growth rte of the world s popultion, which hs risen from 3.7 billion in 1970 to 6.6 billion in 2006, nd reched pek growth rte of 2%/yer during (FAO 2009: ftp.fo.org/docrep/fo/011/i0250e/i0250e.pdf) (PRB 2008: prb.org/ pdf06/06worlddtsheet.pdf) (UN 2007: org/es/popultion/publictions/wpp2006/wpp2006_highlights_ rev. pdf.). Compring quculture production in the erly 1950s to tht in 2006, it grew from 1 million tonnes per yer to over 51 million tonnes, with vlue of over 78 billion US dollrs. The world s incresing demnds for sefood lso results in incresing needs for fish feed. Commonly, high mounts of fish mel re used in these diets to provide fish with proteins tht re essentil for their metbolism nd growth. Fish mel hs become highly questioned commodity in recent yers, due to high cost nd declining supplies. Investigtors hve begun looking for lterntive protein sources. Much reserch hs been pursued to find resonble, cost efficient, nd comptible lterntives. For exmple, God et l (2007) found tht equivlent effects on growth rte nd feed utiliztion could be chieved by totlly replcing fish mel with poultry by-product mels (PBM) in diets for Africn ctfish. However, the composition nd qulity of PBM vries becuse it is initilly wste product. Accordingly, in similr trils, where PBM ws used s the exclusive protein source in feeding humpbck grouper, Shpwi et l (2007) observed lower growth rte compred to fish mel, which might hve been due to n insufficient mino cid blnce in the PBM. *The e-xtr logo stnds for electronic extr nd indictes tht Figs. 1 nd 2 pper in color online. 1 South Dkot Stte University, Agriculturl & Biosystems Engineering, Brookings, SD USDA-ARS, North Centrl Agriculturl Reserch Lbortory, 2923 Medry Ave., Brookings, SD Corresponding uthor. Phone: Fx: E-mil: krosentr@ ngirl.rs.usd.gov 4 South Dkot Stte University, Wildlife & Fisheries Sciences, Brookings, SD doi: /cchem This rticle is in the public domin nd not copyrightble. It my be freely reprinted with customry crediting of the source. AACC Interntionl, Inc., Bcteril protein mel (BPM) is nother potentil feed ingredient. BPM hd been ble to replce high-qulity fish mel up to 25% in diets for juvenile fresh wter Atlntic slmon (Storebkken et l 2004), nd of levels 25 27% for rinbow trout (As et l 2006; Øverlnd et l 2006). Compred to fish mel, BPM contins lower lysine but higher concentrtions of tryptophn; hence, combintion with fish mel or other protein sources is required to chieve blnce (Storebkken et l 2004). Other undesirble side effects hve been reported regrding reduced digestibility of nitrogen, lipid, nd energy when incresing the level of BPM compred to fish mel (As et l 2006). A specil focus of reserch in recent yers hs been on plnt protein sources, which re mostly inexpensive in price, esy to obtin, nd hve reltively consistent composition compred to met or poultry by-products (Dvies nd Arbold 2000; Smoch et l 2004). For exmple, prtil replcement trils hve been conducted using cottonseed mel, penut lef mel, corn gluten mel, pe protein concentrte, lflf, nd mny other plnt mterils (Ali et l 2003; Grduño-Lugo nd Olver-Novo 2008; Guimrães et l 2008; Øverlnd et l 2009). Becuse of its high protein content, stbility on the mrket, nd reltively low price, soyben mel (SBM) hs become one of the most widely used fish mel substitutes in fish feed (Thompson et l 2008). Webster et l (1992) scertined tht optiml growth of blue ctfish could be chieved for diet including 48% SBM by the supplementtion of 13% fish mel. In erlier studies, Wilson nd Poe (1985) observed tht growth nd protein efficiency rtios of fingerling chnnel ctfish were reduced by rw nd improperly heted soyben mel. These rtios could only be enhnced by reducing the trypsin inhibitor ctivity (Wilson et l 1985), one of the primry ntinutritionl fctors in soyben mel (Frncis et l 2001). A totl replcement of fish mel by soyben mel is only possible for preprocessed (Arndt et l 1999) nd mino cid supplemented SBM blends to ensure feed efficiency, pltbility, digestibility, nd optiml growth (Viol et l 1981; Floreto et l 2000; El-Sidy nd Gber 2002). Another lterntive for fish mel my be distillers dried grins with solubles (DDGS), the residul leftover of corn kernel fermenttion during fuel ethnol mnufcturing. The ethnol industry hs been growing rpidly due to chnges in energy policies (RFA 2009: (Voc et l 2009), therefore incresing mounts of DDGS hve become vilble. Vol. 88, No. 2,

2 The U.S. production of distillers grins hs risen from 2.3 million tonnes in 1999 to 30.5 million tonnes in 2009 (RFA 2009: For over century now, DDGS hs been fed to ruminnt nimls (USDA GIPSA 2006: In contrst to corn, DDGS contins pproximtely three times the mount of nutrients such s ft, protein, fiber, nd minerls resulting from the fermenttion process (Jcques et l 2003). In ddition, DDGS contins no ntinutritionl fctors compred to SBM (U.S. Grins Council 2008: org/imges/stories/ddgs_user_hndbook/ddgs%20hndbook% 20FULL.pdf). Preceding reserch with DDGS, which usully contins 27 33% protein nd 5 12% crude fiber (Rosentrter nd Muthukumrppn 2006) s prtil replcement for fish mel, showed effective nd economicl growth for tilpi (Coyle et l 2004) nd for chnnel ctfish (Webster et l 1991). Cheng nd Hrdy (2004) determined tht DDGS could replce 50% of fish mel in fish feed for rinbow trout nd then improved the substitution 75% by dding supplementl lysine nd methionine. Furthermore, successful trils hve been conducted with both prtil nd totl replcement of fish mel by combintions of DDGS nd SBM for freshwter prwn (Tidwell et l 1993). Yellow perch (Perc flvescens) is smll-sized, low-ft fish in growing demnd, especilly ner the Gret Lkes re of the U.S. (González et l 2006). Diet formultions tht re generlly recommended hve been bsed upon the requirements for trout nd slmon, which often contin minimum of 36% crude protein (Brown et l 1996). This occurred becuse there hve only been few nutritionl studies undertken for yellow perch. Rmseyer nd Grling (1998) determined tht protein levels of g/kg of dry diet, with pproprite contents of mino cids nd crbohydrtes, should be suitble for yellow perch insted of higher nd commonly used mounts of 400 g/kg of dry diet. So fr, reserch for lterntive protein sources in diets for yellow perch hs only been performed by Ksper et l (2007), who concluded tht yellow perch were ble to effectively utilize diets contining solventextrcted, dehulled, expelled or extruded soyben mel, with conservtive protein recommendtion of 300 g/kg of diet. Fish mel protein ws successfully replced in their feeds. Some studies hve been conducted on processing DDGS-bsed tilpi feeds. In previous studies, Chevnn et l (2007,b,c, 2008, 2009, 2010), Rosentrter et l (2009,b), nd Knndhson et l (2009,b, 2010) investigted how die dimensions, screw speeds, nd brrel tempertures of the extruder, nd ingredient moisture nd DDGS content of vrious tilpi feed blends ffected the resulting extrudte physicl properties nd extrusion processing TABLE I Ingredient Components (% db) nd Nutrient Compositions (% db) of the Feed Blends Dry Weight of Ingredients (% db) in Diets Ingredients DDGS Soyben mel Fish mel (menhden) Vitmin mix Minerl mix Soyben oil Celufil CMC Menhden oil Totl Feed Blend Composition (% db) Totl moisture (% wb) Totl dry mtter (% wb) Crude protein (% db) Crude ft (% db) All blends were formulted on dry bsis, db. prmeters from both the single-screw nd twin-screw extruders. Chevnn et l (2008) showed tht ingredient moisture content nd screw speed hd significnt effects on extrudte durbility, color, nd extruder throughput; DDGS could be included t 40% in the blend nd still produced vible extrudtes. In twin-screw studies, Chevnn et l (2007b) chieved vible pellets t DDGS inclusion levels t 60%; s DDGS incresed, the extrudtes exhibited higher moisture content, unit density, fiber, nd ft content but decresed durbility nd expnsion rtio. To dte, however, no trils of prtil or complete fish mel replcement using DDGS for yellow perch feeds hve been conducted. Industril-scle extrusion cooking of niml feeds begn between 1955 nd 1960 (Moscicki nd vn Zuilichem 1983) nd is commonly pplied in commercil processing of qufeeds to produce cost-effective, floting feeds (Tudor 1996; Opstvedt et l 2003). Extrusion is performed t high tempertures, for short residence times, with high pressures nd high sher forces. Extrusion results in modifying nd texturizing the food ingredients. Additionlly, it cn inctivte severl ntinutritionl fctors such s oxidtive nd other deteriortion enzymes (Cheftel 1986). More informtion bout extrusion processing cn be found in Mercier et l (1989), Chng nd Wng (1998), Riz (2000), nd other literry sources. The objectives of this study were 1) to produce feed pellets for juvenile yellow perch (Perc flvescens) using DDGS s n lterntive protein source, nd 2) to exmine the effects of vrying DDGS content on the resulting physicl properties of extrudtes nd on extruder processing prmeters. MATERIALS AND METHODS Feed Blend Preprtion Six isocloric ( 3.21 kcl/g) ingredient blends (Tble I) were djusted to similr protein content of 30% db, similr ft content of 17% db, nd similr moisture content of 19% wb. With different DDGS levels (0, 10, 20, 30, 40, nd 50% db), vrying mounts of soyben mel, soyben oil, nd celufil, but constnt level of fish mel, menhden oil, cellulose gum, vitmin, nd minerl mix, these ingredients were used to prepre nutritionlly blnced diets for juvenile yellow perch. DDGS ws provided by Dkot Ethnol (Wentworth, SD) nd soyben mel ws obtined from Dkotlnd Feeds (Huron, SD). These were ground with Wiley mill (model 4, Thoms Scientific, Swedesboro, NJ) to flour with n verge prticle size of 500 μm. Soyben oil ws purchsed from Consumers Supply Distributing (Sioux City, IA); celufil ( nonnutritive filler) ws obtined from USB Corportion (Clevelnd, OH); menhden fish mel from The Scoulr Compny (Minnepolis, MN); menhden fish oil from Omeg Protein (Houston, TX); cellulose gum (sodium crboxy methyl cellulose used s binder) from Akzo Nobel Functionl Chemicls (Netherlnds); vitmin mix nd minerl mix from Rngen (Buhl, ID). Components were mixed for 10 min, combined with the soyben nd menhden oil nd stirred for nother 15 min in mixer (Kushln Products, Goldendle, WA). After ll ingredients were thoroughly combined, ech blend ws djusted to desired preextrusion moisture content of 60 65% by dding dequte mounts of wter during mixing using lbortory scle mixer (N50, Hobrt Corportion, Troy, OH). Rw Ingredient Properties Ech rw blend ws nlyzed for moisture content, wter ctivity, therml conductivity (k), therml diffusivity (α), nd color (Hunter L,,b vlues). Rw mteril from ech blend ws plced in 250-mL beker. The sensor needle of the therml properties nlyzer (KD2, Decgon Devices, Pullmn, WA) ws inserted into the medium, nd the therml conductivity nd therml diffusivity were mesured three times on three different positions (n = 3) in the mteril t room temperture (20 ± 1 C). 180 CEREAL CHEMISTRY

3 Extrusion Processing The extrusion processing of ech blend ws performed using single-screw extruder (model PL 2000 Plsti-Corder, Brbender South Hckensck, NJ) with compression rtio of 3:1, screw length-to-dimeter rtio of 20:1, nd brrel length of mm. The center of the die ssembly ws conicl nd tpered from n initil dimeter of 6.0 mm to dimeter of 2.95 mm t the dischrge opening. The length of the die ws mm, which resulted in die length-to-dimeter rtio of A 7.5 HP (5.5 kw) motor ws connected to the extruder. The screw speed ws djusted to 230 rpm during extrusion. The temperture of the feed zone ws controlled nd mintined t 40 C, tht of the trnsition zone t 90 C, nd tht of the die zone t 100 C during ll trils. Rw blends were mnully funneled into the extruder in constnt quntities to void jmming t the brrel throt. The mss flow rte (MFR) ws determined by collecting extrudte smples t 30-sec intervls during extrusion, weighing the collected quntity on n electronic blnce (PB 5001, Mettler Toledo, Switzerlnd), nd then ccounting for moisture losses t the die exit (Rosentrter et l 2005). During extrusion processing, the moisture content t the die (% db) ws monitored, nd the temperture ( C) of the extrudtes exiting the extruder ws mesured with n infrred thermometer (model 42540, Extech Instruments, Wlthm, MA). Physicl Properties After the prepred blends were cooked in the extruder nd then dried for 24 hr t room temperture (20 ± 1 C), they were nlyzed in terms of moisture content (% db), wter ctivity (-), unit density (kg/m 3 ), expnsion rtio (-), compressive strength (MP), compressive modulus (MP), pellet durbility index (%), wter stbility (min), color (-), nd nutrient compositions (% wb, %db). Moisture content (MC). According to Approved Method (AACC Interntionl 2010), the moisture content of the rw mteril nd extrudte smples for ech blend were determined using lbortory oven (Thelco Precision, Jovn, Winchester, VA) t 135 C for 2 hr. The sme methodology ws used for smples collected t the die. Wter ctivity ( w ). Wter ctivity ws mesured for rw mteril nd extrudte smples from ech tretment with wter ctivity meter (Sprint TH-500, Novsin, Pfäffikon, Switzerlnd). A smple bowl ws filled with ech smple nd then plced into the mesuring chmber of the preclibrted instrument. Unit density (UD). The extrudtes were cut to pieces 25.4 mm long, weighed on n nlyticl blnce (Adventurer, Ohus, Pine Brook, NJ), then mesured with digimtic cliper (model CD- 6 C, Mitutoyo, Tokyo, Jpn) to determine the dimeter. According to Rosentrter et l (2005) the unit density (UD, kg/m 3 ) ws clculted s the rtio of the mss M (kg) to the volume V (m 3 ) of ech mesured nd weighed extrudte smple, ssuming cylindricl shpe for ech extrudte: UD = M/V (Eq. 1) Expnsion rtio (ER). The rtio of the dimeter of the extrudte for ech blend, mesured with digimtic cliper (model CD- 6 C, Mitutoyo, Tokyo, Jpn), to the dimeter of the die nozzle (2.95 mm) ws used to quntify the rdil expnsion rtio. Compressive strength nd modulus. For ech tretment, the extruded smples were cut into pieces 25.4 mm long nd tested for compressive strength nd modulus (stiffness) using compression testing mchine (model 5564, Instron, Cnton, MA). Pellet durbility index (PDI). The pellet durbility index ws determined ccording to ASAE Method S269.4 (2004). Extrudtes ( 100 g) from ech blend were mnully sieved (U.S.A. stndrd testing, ASTM E-11 specifiction, Digger, Vernon Hills, IL) for 10 sec to remove initil fines nd then tumbled in pellet durbility tester (model PDT-110, Seedburo Equipment, Chicgo, IL) for 10 min. Afterwrds, smples were gin sieved for 10 sec, nd weighed on n electronic blnce (Explorer Pro, model EP 4102, Ohus, Pine Brook, NJ). For blends 1 4, sieve No. 7 (2.80 mm) ws used, but for blends 5 nd 6 sieve No. 8 (2.36 mm) ws used. PDI = (M /M b ) 100 (Eq. 2); where M ws the mss (g) fter tumbling nd M b ws the smple mss (g) before tumbling. Wter stbility. Wter stbility is defined s the mount of time for pellet to begin to brek prt fter it hs been plced in wter. For extrudtes of ech blend, 1-g smple ws plced in 200 ml of distilled wter nd gently stirred with mgnet stirrer (PMC No. 524C, Brnsted Interntionl, Dubuque, IA) until the extrudtes broke, to determine the stirred wter stbility. For still wter stbility, the sme process ws used without stirring. Color. A spectrophotometer (LbScn XE, HunterLb, Reston, VA) ws used to determine extrudte color, where L quntified the brightness/drkness, referred to the redness/greenness, nd b referred to the yellowness/blueness of the smples. Likewise, the color ws tested on the rw mteril blends. Nutrient nlysis. For ech diet single replicte (n = 1) of extrudte smples ws nlyzed for totl moisture, totl dry mtter, crude protein, nd crude ft following officil Method 990.3, , , nd (AOAC 2003), respectively. Dt Anlysis Ech blend ws extruded twice. For ech extrusion run, three replictes (n = 3) were mesured for ll physicl properties except for compressive strength, compressive modulus, unit density, nd expnsion rtio, where 10 mesurements (n = 10) were tken, nd except for wter stbility (both stir nd still), where one replicte (n = 1) ws tken. All dt were nlyzed using SAS v.8.0 softwre (SAS Institute, Cry, NC) with Type I error rte of 0.05, by nlysis of vrince (ANOVA), nd then post hoc LSD for the vribles tht exhibited significnt differences. RESULTS AND DISCUSSION Rw Blend Anlysis Physicl properties of the rw blends re provided in Tble II. Averge moisture content cross ll blends ws ± 0.37%. Owing to the high moisture content, wter ctivity ws lso high (0.89 ± 0.00). Averge therml conductivity ws 0.10 W/(m C) ± 0.01 W/(m C), nd verge therml diffusivity ws 0.11 mm 2 /sec ± 0.01 mm 2 /sec. The therml conductivity expresses the bility of mteril to trnsfer het by conduction. Therefore, in this study, the vlues were low t W/(m C); they decresed insignificntly when incresing the DDGS content in the blend. Low therml conductivity indictes poor het trnsfer in mteril. Therml dif- TABLE II Physicl Properties of Rw Feed BlendsBefore Extrusion Processing Diet (DDGS % db) Properties MC (% db) (0.56) (0.05) (0.70) (0.36) 58.02b (0.20) 59.21b (0.33) w (-) b 0.89c 0.87d 0.86e k (W/m C) α (mm 2 /sec) Hunter L (1.58) (1.45) (2.86) 38.35bc (0.35) 40.37b (0.80) 36.54c (1.11) Hunter 8.41 (0.26) 8.39 (0.38) 9.18b (0.49) 9.56bd (0.06) 10.85c (0.24) 10.00d (0.16) Hunter b (1.15) (1.48) (0.98) (0.27) (0.57) 33.41b (0.59) Mens followed by the sme letters within row re not significntly different t P < 0.05, LSD. Vlues in prentheses re stndrd devition. MC, moisture content; w, wter ctivity; k, therml conductivity; α, therml diffusivity; L,,b, Hunter color prmeters. Vol. 88, No. 2,

4 fusivity, on the other hnd, is defined s the rtio of the therml conductivity to the volumetric het cpcity. It is the prmeter tht governs time-dependent unstedy-stte het trnsfer (Bouguerr et l 2001) nd is n indictor of therml performnce (Kwski nd Kwi 2006). Becuse therml diffusivity ffects the rte of het trnsfer in mteril, it my ffect cooking nd shering processes in the extruder. Thus, the resulting moleculr structure of the finl extrudtes my be ffected. The therml diffusivity for ll rw blends ws mesured t constnt level of 0.11 mm 2 /sec. Therefore, it ppers tht the DDGS level did not interfere with the het trnsfer in the extruder during processing. Therml conductivity nd diffusivity re relted to the het trnsport efficiency (Arámbul-Vill et l 2007). Due to low vlues of the blends in this study, the heting nd cooling of the rw mterils requires more time, which cn hve negtive effect on the extrusion process. On the other hnd, the process is less sensitive to externl therml influences, which mkes the process more stble. Regrding color of the rw blends, Hunter L vlues were ± 1.11 to ± 1.45; Hunter vlues were 8.39 ± 0.38 to ± 0.24; b vlues were ± 0.27 to ± As DDGS incresed, brightness (Hunter L) decresed, redness (Hunter ) incresed, wheres yellowness (Hunter b) remined lmost stedy. These chnges were due to the color of the DDGS prticles. Extrusion Processing Prmeters Tble III provides the processing prmeter dt during extrusion, including extrudte mss flow rte (MFR), nd the resulting processing tempertures (in reltion to set points). Incresing the DDGS content from 0 to 10% yielded decrese in MFR from to g/min. Subsequently, stedy increse in MFR from to g/min (n increse of 144%) ws observed by rising the DDGS content from 10 to 30%. An increse from 30 to 40% DDGS content yielded slight drop in MFR of 24.4%. Using similr ingredients, Chevnn et l (2008) observed n increse in extruder throughput when rising the DDGS content of the blends from 20 to 30% nd decrese in extruder throughput when rising the DDGS content from 30 to 40%, s well. An increse of DDGS from 40 to 50% yielded further 50.3% increse in MFR nd resulted in the highest mss flow rte for ll blends, t level of g/min. Overll, it ppered tht incresing the DDGS in the blend led to n increse in MFR, which cn be relted to n increse in density with higher DDGS level. Vrince from this trend ws probbly due to either experimentl error or instbility in the extruder. The mss flow rte is one wy to quntify the performnce of the extruder during processing. It cn be influenced by the screw speed, dimeter of the die (Knndhson et l 2009c), sher rte, TABLE III Tretment Effects on Extrusion Processing Prmeters Diet (DDGS % db) Prmeter MFR (g/min) (11.02) b (23.18) b (2.31) c (28.00) (25.06) d (7.02) Processing temperture ( C) Feed (n = 40) b (0.82) 40.60c (0.52) 40.20cd (0.42) 40.60c (0.70) 40.00d Trnsition (n = 90) (0.74) 89.80b (0.42) 90.90c (0.88) 89.80b (0.79) 90.30c (1.06) 89.30b (0.67) Die (n = 100) Dischrge product (2.73) (28.82) 64.42b (3.39) 62.52b (4.16) (0.79) 63.57b (3.33) (0.48) 65.08b (2.86) (0.48) 72.09c (1.62) Mens followed by similr letters within row re not significntly different t P < 0.05, LSD. Vlues in prentheses re stndrd devition. MFR, mss flow rte. blend composition, level of DDGS, moisture content, nd viscosity of the dough melt (Chevnn et l 2008). Rosentrter et l (2009) nd Knndhson et l (2009b) observed g/min nd g/min, respectively, s the highest MFR, both using screw speed of 200 rpm for DDGS-bsed extrusion studies. Compred to these results, MFR determined in this study ppered to be higher. Furthermore, it is pprent tht the MFR ws ffected by DDGS level. In terms of processing tempertures, ll observed vlues for the vrious extruder zones (feed, trnsition, die) were close to the set points. DDGS level did not pper to hve cler effect. The sme pplied to product temperture t the die dischrge. Extrudte Properties Tble IV provides the physicl properties including moisture content, wter ctivity, unit density, expnsion rtio, compressive strength, pellet durbility, wter stbility, nd color dt of the resulting extrudtes. Moisture content. The moisture content (MC) of the ingredient blends typiclly hs significnt effects on extrudte properties such s wter stbility, pellet durbility, nd color. In ddition, the initil MC lso ffects the extrusion processing prmeters including mss flow rte through the extruder (Chevnn et l 2007). For the finl product, MC will impct texture nd the resistnce to externl pplied forces; t higher MC, pellets re less brittle nd less frgile (Mzumder et l 2007). An initil moisture content of the rw mterils hd been set t high levels (60 65%) to chieve softer nd more wter stble extrudtes. Thus, no cler pttern of chnges in MC ws observed when incresing the DDGS level. Adding 10% of DDGS to the rw ingredient blend yielded decrese from 1.26 to 0.82% in finl extrudte moisture content, nd therefore resulted in the lowest MC of ll blends. The increse of the DDGS content from 20 to 40% did not show significnt effects on pellet MC, which incresed by 4.1%. However, n increse from 40 to 50% DDGS level showed highly significnt effect nd resulted in n increse from 1.5 to TABLE IV Tretment Effects on Resulting Extrudte Physicl Properties Diet (DDGS % db) Property MC (% db) 1.26 (0.21) 0.82b (0.19) 1.45 (0.13) 1.31 (0.10) 1.51 (0.09) 5.33c (0.22) w (-) b 0.04c 0.05b 0.18d UD (kg/m 3 ) b b bc c (83.88) (66.39) (53.86) (60.29) (45.56) (34.93) ER (-) 1.09 (0.03) 1.09 (0.05) 1.04b (0.04) Comp S (MP) 3.15 (1.21) 3.06 (0.60) 3.36 (0.73) 3.64b (0.85) 3.54 (0.46) 4.28b (0.53) Comp M (MP) (30.34) (31.06) (37.30) (31.01) (30.28) (29.79) PDI (%) (0.55) 97.63b (0.29) 96.43c (0.29) 96.83bc (0.28) 97.29bc (0.28) (1.05) WS stir (min) bd >30c 24.00d 27.00b >30c (2.12) (1.41) WS still (min) (0.71) >30 >30 >30 >30 >30 Hunter L (-) (0.70) (0.55) 42.77b (0.17) 41.33c (0.41) 38.59d (0.69) 38.36d (0.94) Hunter (-) 6.23 (0.14) 6.98b (0.09) 7.03b (0.08) 7.67c (0.12) 8.02d (0.05) 8.27e (0.14) Hunter b (-) (0.23) 31.18b (0.12) 29.85c (0.06) 30.29d (0.33) 29.74c (0.29) 28.67e (0.32) Mens followed by similr letters within row re not significntly different t P < 0.05, LSD. Vlues in prentheses re stndrd devition. MC, moisture content; w, wter ctivity; UD, unit density; ER, expnsion rtio; Comp S, compressive strength; Comp M, compressive modulus; PDI, pellet durbility index; WS, wter stbility; L,,b, Hunter color prmeters. 182 CEREAL CHEMISTRY

5 5.3% in MC. Therefore, the blend contining 50% DDGS hd the highest extrudte MC. In previous studies using DDGS nd whey, Chevnn et l (2009) showed similr result when incresing the DDGS content from 20 to 40%, nd determined n increse of 5.8% in the finl MC of the extrudtes. Compred to the rw mterils, the extrudte MC ws, s expected, much lower. This reduction in the mount of wter cnnot only scribed to the stem flshing t the die exit, but lso becuse the extrudtes were cooled nd dried t room temperture for 24 hr (Rosentrter et l 2009). In the extrusion process, the sudden drop from high pressure to tmospheric pressure t the die exit cuses extensive wter flshing-off nd llows the expnsion of the melt. Additionlly, the rdil expnsion influences the internl structure of the expnding melt nd therefore determines the texture of the finl extrudtes (Arhliss et l 2003). Wter ctivity. Wter ctivity, unlike moisture content, mesures the free wter existing in the mteril tht is not bound to molecules. It influences the shelf life of product becuse it provides microorgnisms such s bcteri, molds, nd yest with wter tht supports growth; the higher the w, the greter the risk of rpid spoilge. Wter ctivity is defined s the rtio of wter pressure in the mteril to the wter pressure of pure wter under the sme environmentl condition. It specifies equilibrium reltive humidity nd the scle extends from 0 (completely dry) to 1.0 (pure wter) (Food Science Austrli 2005: csiro.u/wter_fs.htm). In generl, w <0.6 is considered to provide shelf-stble product with long storge stbility (Lowe nd Kershw 1995). The wter ctivity of the rw blends ws nd showed no significnt differences between ll blends. This ws nticipted, s ll blends were formulted to the sme trget moisture level. Likewise, w vlues for the rw blends were, s expected, high due to the initil djusted moisture content. In terms of the extruded product, incresing the DDGS content from 10 to 50% resulted in significnt increse for w from 0.02 to Even so, the vlues for the wter ctivity of ll extrudtes were very low, nd the finl product ws extremely dry. This cn be ttributed to the fct tht extrudtes were thoroughly ir-dried fter extrusion. Unit density. Unit density is n importnt spect of fish feed. It is inversely relted to the expnsion rtio (Ilo et l 1999); the more compct (dense) pellet, the less expnsion. Unit density thus governs product flotbility, which is importnt for quculture feed (Chevnn et l 2007d). The unit density of the extrudtes ws kg/m 3, which ws n increse of 17.3%. Overll, s DDGS incresed, unit density incresed. There ws significnt increse in unit density (11.0%) when DDGS content incresed from 10 to 20%. Chevnn et l (2009) nd Knndhson et l (2009b) found tht incresing DDGS levels to 20 40% resulted in no significnt chnges in extrudte unit density. In this study, ll extrudtes with DDGS level of 0 30% hd density below tht of wter (1,000 kg/m 3 ). Even so, they did not flot well nd snk slowly to the beker bottom. This cn be trced bck to the reltively porous structure of the pellets (Figs. 1 nd 2), which rpidly bsorbed the wter. Unlike other cultured fish species, yellow perch re slow feeders (Webster nd Lim 2002). Becuse they feed on or ner the bottom, even in open wters (Perse nd Achtenberg 1920), flotbility of the pellets is not necessrily required. Expnsion rtio. The level of extrudte expnsion upon exiting the die impcts the resulting unit density, s well s the frgility nd hrdness of the extrudtes (Rosentrter et l 2009). As shown in Tble IV, expnsion levels were nd showed no significnt differences, except for the tretment with 20% DDGS content. All expnsion rtios were very low nd this difference could be ttributed to experimentl error. Expnsion rtio is relted to the unit density (Ilo et l 1999). Expnsion depends on the flshing of wter vpor nd the flow properties of the molten dough t the die exit (Mercier et l 1989). DDGS nturlly hs low strch content (often %) nd high fiber content (Rosentrter nd Muthukumrppn 2006). Thus, the higher the DDGS level in the blend, the lower the strch, nd higher the fiber content. Even though these chnges hve the potentil to hinder expnsion, this did not seem to occur in this study. Compressive strength nd compressive modulus. Compression tests provide informtion bout the cpcity of pellets to resist forces without breking or deforming. The vlues for compressive strength in this study were MP. The blend with 50% DDGS hd the highest compressive strength of 4.28MP, which ws significntly different from the other blends, except the blend with 30% DDGS. The higher resistnce ginst forces my be relted to the significntly higher moisture content of the 50% blend. It cn be ssumed tht the components were more closely bonded to ech other. This is reflected in the higher unit density for this blend s well. Mzumder et l (2007) observed incresing forces pplied on redy-to-et corn blls when incresing the ingredient moisture content from 2 to 10%, but this ws due to the high strch content of corn. Strch, in combintion with the high wter content nd het, is redily geltinized (Avérous nd Hlley 2009). All compressive strength vlues were low, which indicted tht the extrudtes hd frgile structure nd broke reltively esily. This my be scribed to the reltively low strch content of the DDGS nd the rw blends. Compressive modulus is mesure of structurl stiffness. There were no significnt differences for the compressive moduli cross the blends, which my be due to the high stndrd devition for ll vlues (i.e., we were not ble to resolve differences). The mens for compressive moduli were MP, lthough no trends with incresing DDGS levels were observed. These highly vrible dt cn be explined by the fct tht extrudtes re complex in structure; the texture is not homogenous (Figs. 1 nd 2), nd they hd different sized prticles tht induced different rections when externl forces were pplied. Pellet durbility index. Pellet durbility index (PDI), nother physicl qulity prmeter of feed pellets, is mesured by the mount of fines generted under stndrdized conditions. The qulity of extruded fish feed is decisive fctor for the fish production expense. During shipping nd storge, pellets re subject to brekge nd ttrition, which results in fines in the feed. Extrudtes should hve high level of resistnce to fines genertion (Thoms nd vn der Poel 1996; Hnsen nd Storebkken 2007). No cler pttern of chnges in PDI ws observed when incresing the DDGS levels. Chnging the levels of DDGS yielded only minor chnges in PDI. The blend including 10% DDGS yielded the highest PDI (97.63%) nd resulted in 1.5% higher PDI thn the blend without DDGS. In ccordnce with the results from Chevnn et l (2007b), who conducted studies on twin-screw extrusion, n increse of the DDGS content from 20 to 40% did not result in significnt chnges in extrudte durbility. The durbility vlues for blends including DDGS were %, indicting high pellet durbility indices for ll blends nd hence, very good resistnce ginst destructive forces tht occur during trnsporttion nd storge. Wter stbility. Besides flotbility, stbility in wter plys decisive role for fish feed becuse it determines the dissolving period nd thus the loss of extrudte nutrients once they re plced in wter. Physicl properties, blend compositions, processing methods, nd the type of binders used could ffect wter stbility of extrudtes. Furthermore, the required durtion of wter stbility depends on the time tht fish need to consume their rtions (Lim nd Cuzon, 1994). The time for lmost ll extrudtes to dissolve in still wter ws >30 min; only the extrudtes without DDGS strted dissolving erlier t 29.5 min. The times tht extrudtes strted dissolving in stirred wter were lower t 14.5 min for the blend without DDGS Vol. 88, No. 2,

6 nd 24 to >30 min for the extrudtes contining DDGS. Overll, ll blends exhibited dequte wter stbility. Color. The color of n qufeed generlly plys no decisive role for the sles mrket, but it cn be used to ssess potentil dmge of protein in these processed products (Björck et l 1984). Lysine, n importnt component in fish feed, is the most rective mino cid in the Millrd rection, which is cused by high tempertures in combintion with low wter content, nd it often occurs in extrusion cooking (Björck nd Asp 1983). A significnt decrese of 14.0% in extrudte brightness (Hunter L) ws observed when incresing the DDGS content from 0 to 50%; the lower the L vlue, the drker the smple. For the rw blends, no discernble trends in brightness were evident. Regrding the chnges in extrudte redness (), ll Hunter vlues resulted in significnt differences. Incresing the DDGS content from 0 to 50% resulted in stedy increse in Hunter by 32.7%. Prllel behvior ws seen in the rw blends (Tble II). Similr conclusions for Hunter were scertined by Chevnn et l (2007b) for twin-screw extrusion trils using DDGS. DDGS is drk yellow-brown; n increse in DDGS content cn be expected to result in drker nd more brownish extrudtes. As the DDGS content ws incresed from 0 to 50%, the extrudte brightness (Hunter L) decresed by 14%, redness (Hunter ) incresed by 33%, nd yellowness (Hunter b) decresed by 10.2%. For the blend contining 30% DDGS, Hunter b ws ctully higher thn for the blend contining 20% DDGS. This vlue ws higher thn expected nd might be ttributed to the high vlue for stndrd devition for this tretment. Compring the chnge in color of the rw mterils to the extrudtes, brightness (Hunter L vlue) decresed (becme drker) 5.3%, redness (Hunter vlue) decresed (becme greener) from 16.8 to 26.1%, nd yellowness (Hunter b vlue) decresed (becme bluer) between 6.3 nd 17.3% due to extrusion processing. Thus, it ppers tht the chnges in color were not only ffected by chnges in DDGS content nd ingredient composition, Fig. 1. Extrudtes produced in this study were cylindricl in shpe. Fig. 2. Cross-sections of resulting extrudtes (60X). 184 CEREAL CHEMISTRY

7 but were lso prtilly ffected by processing conditions, probbly relting to the Millrd rection. Property Correltions Person liner correltion nlysis results cn be found in Tbles V, VI, nd VII. Among the vrious properties, 25 correltions hd r vlues > 0.80, nd 28 correltions hd r vlues < 0.8. Most of these strong liner reltionships were nticipted bsed on results of previous reserch (e.g., Chevnn et l 2007b; Knndhson et l 2009). In this study, severl color prmeters were highly correlted, but these hve lredy been discussed. Extrudte moisture content nd compressive strength hd n r vlue > Likewise, compressive strength showed strong positive reltion to the mss flow rte (r > 0.86). It cn be ssumed tht the less wter ws evported, the higher the mss flow rte. Hence, the moisture content ws higher in the extrudtes, which required higher forces to brek the finl product. Severl strong correltions existed between the therml conductivity of the rw blends nd extrudte TABLE V Liner Correltions Among All Independent nd Dependent Vribles for Extrudte, Processing, nd Rw Properties DDGS MC UD ER Comp S Extrudte properties DDGS 1 MC UD ER Comp S Comp M w WS stir WS still PDI L b Processing properties MFR T feed T trnsition T die T dischrge Rw properties MC w k α L b DDGS, distillers dried grins with solubles; MC, moisture content; UD, unit density; ER, expnsion rtion; Comp S, compressive strength; Comp M, compressive modulus; w, wter ctivity; WS, wter stbility; PDI, pellet durbility index; L,,b, Hunter color prmeters; MFR, mss flow rte; T, temperture; k, therml conductivity; α, therml diffusivity. TABLE V (continued) Liner Correltions Among All Independent nd Dependent Vribles for Extrudte, Processing, nd Rw Properties Comp M w WS stir WS still PDI L b Extrudte properties Comp M 1 w WS stir WS still PDI L b Processing properties MFR T feed T trnsition T die T dischrge Rw properties MC w k α L b Comp M, compressive modulus; w, wter ctivity; WS, wter stbility; PDI, pellet durbility index; L,,b, Hunter color prmeters; MFR, mss flow rte; T, temperture; MC, moisture content; k, therml conductivity; α, therml diffusivity. Vol. 88, No. 2,

8 TABLE VI Liner Correltions Among All Independent nd Dependent Vribles for Processing Properties nd Rw Properties MFR T feed T trnsition T die T dischrge Processing properties MFR 1 T feed T trnsition T die T dischrge Rw properties MC w k α L b MFR, mss flow rte; T, temperture; MC, moisture content; w, wter ctivity; k, therml conductivity; α, therml diffusivity; L,,b, Hunter color prmeters. TABLE VII Liner Correltions Among All Independent nd Dependent Vribles for Rw Properties MC w k α L b Rw properties MC 1 w k α L b MC, moisture content; w, wter ctivity; k, therml conductivity; α, therml diffusivity; L,,b, Hunter color prmeters. properties. The therml conductivity ws very strongly nd negtively correlted to the DDGS content, with r < A strong positive correltion between therml conductivity nd moisture content nd wter ctivity of the rw blends ws observed with r > These could be scribed to therml conductivity of wter, which hs n verge vlue of 0.6 W/(m C), which is higher thn the vlues determined in the rw blends. CONCLUSIONS This study ws conducted with the gol of producing wterstble feeds for juvenile yellow perch by enhncing the mount of DDGS, with constnt protein content (30.1%), using similr feed moisture content (60 65%), nd constnt extruder settings. Chnging the levels of DDGS hd significnt effects on extrudte unit density, wter ctivity, color (Hunter L,,b), nd on the rw mteril wter ctivity nd color. The mss flow rte generlly incresed when rising the DDGS content of the blends. The expnsion rtio of ll blends ws low, s expected, due to the low strch content of the DDGS nd high moisture of the feed blends. The extruded mterils hd low compressive strength. In contrst, the PDI vlues were high, nd thus the pellets were highly resistnt to destructive forces. The combintion of low compressive strength nd high PDI provides pellets with excellent trnsport properties tht re esily consumble s feed for the fish. Moreover, results showed very good wter stbility; it took t lest 30 min before the extrudtes would dissolve in wter. All pellets showed significnt chnges in color fter extrusion due to the processing conditions; this ws prtilly ttributble to the chnges in the composition of the rw mterils before processing. In summry, the investigtion yielded high qulity extrudtes. Continuing work is focusing on testing of cceptbility in ctul fish diets nd resulting growth performnce, but those results re reported elsewhere. ACKNOWLEDGMENTS We thnk the Agriculturl Experiment Sttion, South Dkot Stte University, nd the North Centrl Agriculturl Reserch Lbortory, USDA ARS, Brookings, SD, for funding, fcilities, equipment nd supplies. Furthermore, the coopertion nd ssistnce of Shron Nichols, Christine Keierleber, Steve Schcht, Trvis Scheffer, nd Vnj Jurisic is gretly pprecited. Their contributions hve helped bring this project to completion. LITERATURE CITED Ali, A., Al-Asgh, N. A., Al-Ogily, S. M., nd Ali, S Effect of feeding different levels of lflf mel on the growth performnce nd body composition of Nile tilpi (Oreochromis niloticus) fingerlings. Asin Fish. Soc. 16: AOAC Officil Methods of Anlysis of the Assocition of Officil Anlyticl Chemists Interntionl, 17th Ed. The Assocition: Githersburg, MD. Arámbul-Vill, G., Guitiérrez-Áris, E., nd Moreno-Mrtínez, E Therml properties of mize ms nd tortills with different components from mize grins, nd dditives. J. Food Eng. 80: Arhliss, A., Bouvier, J. M., nd Legrnd, J Melt growth nd shrinkge t the exit of the die in extrusion-cooking process. J. Food Eng. 60: Arndt, R. E., Hrdy, R. W., Sugiur, S. H., nd Dong, F. M Effects of het tretment nd substitution level on pltbility nd nutritionl vlue of soy deftted flour in feeds for Coho slmon, Oncorhynchus kisutch. Aquculture 180: ASAE Engineering prctices nd dt stndrds of the Americn Society of Agriculturl Engineers. The Society: St. Joseph, MI. Avérous, L., nd Hlley, P. J Biocomposites bsed on plsticized strch. Biofuels Bioprod. Biorefining 3: Björck, I., nd Asp, N.-G The effects of extrusion cooking on nutritionl vlue A literture review. J. Food Eng. 2: Björck, I., Asp, N.-G., nd Dhlqvist, A Protein nutritionl vlue of extrusion-cooked whet flours. Food Chem. 15: Bouguerr, A., Aït-Mokhtr, A., Amiri, O., nd Diop, M. B Mesurement of therml conductivity, therml diffusivity nd het cpcity 186 CEREAL CHEMISTRY

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D Digestibility of dry mtter, protein, lipid, nd orgnic mtter of two fish mels, two poultry by-product mels, soyben mel, nd distiller s dried grins with solubles in prtil diets for sunshine bss, Morone chrypsops M. sxtilis. J. World Aquc. Soc. 39: Tidwell, J. H., Webster, C. D., Yncey, D. H., nd D Abrmo, L. R Prtil nd totl replcement of fish mel with soyben mel nd distillers by-products in diets for pond culture of the freshwter prwn Vol. 88, No. 2,