This article is from the

January-February 2014 issue of

published by

AACC International, Inc.

For more information on this and other topics related to cereal science,

we invite you to visit AACCnet at www.aaccnet.org

Vol. 91, No. 1, 2014 79

Characteristics of Vegetable-Based Twin-Screw Extruded Yellow Perch (Perca flavescens) Diets Containing Fermented High-Protein Soybean Meal

and Graded Levels of Distillers Dried Grains with Solubles

Parisa Fallahi,1 Kurt A. Rosentrater,2,3 Kasiviswanathan Muthukumarappan,1 and Michael L. Brown4

ABSTRACT Cereal Chem. 91(1):79–87

A twin-screw extrusion study was performed in replicated trials to produce vegetable-based feeds for juvenile yellow perch. Two iso-caloric (3.06 kcal/g) experimental diets were balanced to contain 20 and 40% distillers dried grains with solubles (DDGS) and a constant amount (20%) of fermented high-protein soybean meal (PepSoyGen) as the fishmeal protein replacers; crude protein content was targeted at 40%. A fishmeal-based diet was used as a control. Extrusion condi-tions included conditioner steam (0.11–0.16 kg/min), extruder water (0.11–0.19 kg/min), and screw speed (230–300 rpm). Increasing DDGS from 0 to 40% led to a considerable rise in bulk density, light-

ness (L*), yellowness (b*), and unit density but to decreases in water activity (aw) and expansion ratio by 12.6, 14.4, 23, 21, 31, and 13%, respectively. The lowest unit density of 791.6 kg/m3 and highest bulk density of 654.5 kg/m3 were achieved with diets containing 20 and 40% DDGS, respectively; changes in DDGS content did not affect extrudate moisture, absorption index, or thermal properties. Raising DDGS from 0 to 40% resulted in an increase in water solubility and redness (a*) by 13.4 and 35%, respectively. All extrudates had high durability (>98%), and low aw of less than 0.5. Overall, this study yielded viable feeds for yellow perch.

Over the past few decades, concern about the production of

enough nutritious food to feed the global human population has been growing dramatically. World population has been predicted to reach 10 billion by 2083 (UN 2010), bringing to the forefront the issue of whether agricultural products are sufficient to provide nutritious food required by the global human population for the next several decades. Many researchers believe that aquaculture is the most promising future food protein source for humans (Watanabe 2002; FAO 2006; Duarte et al 2009). Statistics have shown that aquaculture production increased by about 6.5% annu-ally from 1970 to 2008, whereas the world population growth rate was only about 1.6% per year during this period.

However, issues such as limited fresh water supplies and risk of environmental pollution restrict further development in this agri-food industry (UN 2010). Also, of particular concern is the high cost of farm production. Feed expenses contribute to the high cost of aquaculture production, and the protein in fish diets is the most expensive ingredient (Watanabe 2002). Therefore, it is vital to solve these issues in a practical, economical, and environmentally friendly manner.

Fish meal is the main protein source for most traditional aqua-feeds, and it supplies essential proteins, fatty acids, minerals, and phospholipids for fish metabolism. The high demand for fish meal in recent years has resulted in depletion of sources of wild fish stocks, which were once considered endless but are not sustaina-ble any more (Naylor et al 2000). Therefore, finding alternative protein sources for fish diets is vitally important to minimize the amount of wild fish used as protein, lower dietary expenses, and reduce nutrient levels in effluent waste caused by aquaculture activities.

Considerable research has been conducted to investigate alter-native protein sources for fish meal. Poultry by-product meals, bacterial protein meals, and plant protein meals have excellent potential as feed ingredients (Samocha et al 2004; Storebakken et al 2004; Aas et al 2006; Shapawi et al 2007). Although these al-ternative protein sources can reduce the cost of fish diets, poten-tial undesirable side effects because of their imbalanced content of essential amino acids, such as lysine (Ayadi et al 2011c), and some antinutritional factors, such as trypsin inhibitors and lectin, are the major issues that affect their viability (Aas et al 2006).

Among these alternative protein sources, plant-based proteins are the most readily available and the cheapest sources that can replace fish meal (Samocha et al 2004). Recently, partial and total replacement with these materials has been extensively investi-gated. For instance, a combination of soybean meal and corn glu-ten meal was successfully used to replace fish meal protein in shrimp diets (Amaya et al 2006); Khan et al (2003) and El-Saidy et al (2002) replaced 100% of the fish meal with soybean meal in diets of rohu and Nile tilapia, respectively. Because of the pres-ence of antinutritional factors, low palatability, and lack of some amino acids, high inclusion levels of many plant-derived proteins in aquafeeds can be achieved only with amino acid supplementa-tions (Francis et al 2001; Ayadi et al 2011b, 2011c, 2011d). The antinutritional effect of trypsin inhibitor activity that exists in soybean meal is the drawback of this plant-based protein source.

Distillers dried grains with solubles (DDGS), the nonfer-mented coproduct of corn ethanol processing, is the other large-scale plant-based protein and energy source most commonly used by the livestock industry (Rosentrater and Muthukumarap-pan 2006). The high price of fossil fuels, worldwide emphasis on environmental concerns, and political instability in some oil-producing countries have kindled interest in the United States in renewable biofuel production. Among several potential sources for alternative fuel production, production of crop-based fuels such as ethanol has been rapidly growing over the last decade and may provide the majority of the renewable fuels. Recent available statistical data have shown that nearly 50% of the world’s ethanol is produced in the United States (RFA 2012) and is based on corn. Because of this massive expansion of fuel ethanol recently, the annual production of its coproduct, DDGS, is now significant in the United States. Usage of DDGS has increased from 21.62 million tons in 2007 to 33.07 million tons

* The e-Xtra logo stands for “electronic extra” and indicates that Figure 1 appearsin color online.

1 Agricultural and Biosystems Engineering, South Dakota State University, Brook-

ings, SD, 57007, U.S.A. 2 Agricultural and Biosystems Engineering, Iowa State University, Ames, IA,

50011, U.S.A. 3 Corresponding author. Phone: (515) 294-4019. E-mail: karosent@iastate.edu 4 Department of Natural Resources Management, South Dakota State University,

Brookings, SD, 57007, U.S.A.

http://dx.doi.org/10.1094 / CCHEM-08-12-0100-R © 2014 AACC International, Inc.

e-Xtra*

80 CEREAL CHEMISTRY

in 2011 and is expected to reach more than 40 million tons by 2014 (AgMRS 2012).

DDGS is a source of protein (27–33%) and fiber (5–12%), but its starch content is low (Rosentrater and Muthukumarappan 2006). Ethanol production uses only the starch from corn and grain sor-ghum, so that the remaining nutrients (i.e., protein, fiber, fat, and minerals) remain in the coproducts of the fermentation process. In fact, the nutrient amounts in DDGS are almost triple those of raw corn (Jacques et al 2003) because of the yeast metabolism. In addition, DDGS phosphorous content is much lower than that of fish meal, so substituting DDGS for fish meal in aquaculture diets can minimize the total phosphorous level in the diet formula; there-fore, the level of phosphorous entering the aqua farm discharge water can be reduced. According to the U.S. Grains Council (USGC 2012), inclusion of DDGS in aquaculture diets is increas-ing globally, not only because of its moderately high protein con-tent, relatively low phosphorous content, and low cost but also because it does not contain antinutritional factors found in other plant-derived protein sources such as soybean meal (Shiau et al 1987) or cottonseed meal (gossypol) (Jauncey and Ross 1982).

Several studies have been conducted on use of DDGS in fish diets over the past few decades. Because the dietary protein con-tents, aquaculture diets are strongly dependent on the species and age and can vary 25–55% (NRC 1993), the optimum inclusion level of DDGS also depends on the type of DDGS and other in-gredients present in the diet, as well as fish species and age. Data for typical dietary inclusion rates of DDGS obtained from differ-ent research studies are presented in Table I (USGC 2012). Nutri-ent contents of DDGS can vary based on the initial corn quality and ethanol production processing techniques. Lightness and yel-lowness of color in the DDGS is a reasonable sign of its protein quality, which can be evaluated by lysine digestibility measure-ment. Theoretically, a shorter heating process can improve the lysine availability of DDGS; however, there is a lack of information regarding this particular subject. Essential amino acids such as lysine and methionine still need to be supplemented when DDGS is used as the protein source (Stone et al 2005; Metts et al 2007). Among the species, salmonids require the highest amount of pro-tein at 40–50% (Hardy 1996). Reis et al (1989), Abdel-Tawwab et al (2010), and Ahmed et al (2011) reported that dietary protein demands for channel catfish, Nile tilapia, and rainbow trout are 32–35, 35–45, and 42%, respectively. The effect of DDGS inclu-sion with and without lysine supplementation on growth perfor-mance of several species has been investigated, and promising results were observed: for instance, 30% DDGS in channel catfish diet (Tidwell et al 1990); 70% DDGS and 4% lysine (Webster et al 1991; Zhou et al 2010); soybean meal and DDGS combination in juvenile prawns diet (Tidwell et al 1993); 22.5% DDGS and lysine-methionine supplementation in rainbow trout feed (Cheng and Hardy 2004a, 2004b); and 29% DDGS in Nile tilapia diets resulted in higher weight gains compared with fish fed a commer-cial feed (Wu et al 1994).

To date, few studies have been done on fish meal replacement for yellow perch diets. Using ≤50 and ≥75% DDGS in yellow perch feed blends resulted in the lowest and the highest growth performance, respectively (A. Von Eschen et al, unpublished); Schaeffer et al (2009) observed the highest growth performance at less than 50% inclusion of DDGS and soybean meal. Brown et al (1993, 1996) suggested that dietary protein required for yellow perch is close to that of trout (i.e., 21–27%). This high demand for protein can lead to high dietary costs for yellow perch, just as for salmon and trout.

The nutrient composition of diets is important, but the physical properties of diets are critical as well, as all these affect the growth rate and production efficiency. Many factors impact the physical and chemical qualities of aquafeeds. The most important physical properties are floatability, mechanical strength, and wa-ter stability (Rolfe et al 2001; Chevanan et al 2009). Generally, the basic goal in aquafeed processing is to obtain floatable and water-stable pellets that result in few losses of feed and nutrients when placed in water (Vens-Cappell 1984).

The physical properties of fish feeds are strongly related to the chemical composition of the diet ingredients and the processing conditions used (Thomas et al 1999). Among these ingredients, starch and protein are key constituents. Floatability and sinking velocity are highly affected by the extent of starch gelatinization and protein denaturation occurring during production (Case et al 1992; Thomas et al 1999).

Extrusion processing is the primary technique for production of floating, sinking, and slow-sinking aquaculture feed (Opstvedt et al 2003). High pressure and high shear forces that develop inside this bioreactor can improve the physical quality, digestibility, palatability, functionality, and shelf life of the feed. This proc-essing can also be effective for detoxification and sterilization of feed ingredients (Cheftel 1986). Antinutritional factors such as trypsin inhibitors and oxidative enzymes can be inactivated during extrusion processing (Romarheim et al 2005). Extrusion can thus enhance dietary efficiency and utility (Kiang 1998). Single-screw and twin-screw extruders are the most common types used in the food and feed industries. Choosing a proper extruder configura-tion depends on the type of ingredients and final properties of the product and plays an important role in achieving an optimal extru-sion process (Tran et al 2008).

Several studies have been conducted on extrusion processing of DDGS-based aquaculture diets. Chevanan et al (2007a, 2007b) studied the effect of DDGS inclusion and single-screw extruder processing parameters, such as temperature and die dimension, on final quality of feed for Nile tilapia. They could produce viable feed with less than 60% DDGS inclusion and found that with increasing DDGS both durability index and float-ability of the products significantly decreased. In a later study, Chevanan et al (2008) investigated the effect of ingredient mois-ture content on the physical properties of Nile tilapia diets pro-duced by a single-screw extruder. They observed that as the DDGS inclusion level increased, the physical quality of the final product decreased considerably. In their next study, they im-proved product quality with the incorporation of 5% whey pro-tein as a binder (Chevanan et al 2009). Later on, they also at-tempted to quantify the processing behavior of the DDGS-based blends for Nile tilapia by measuring processing parameters such as mass flow rate, net torque required, specific mechanical en-ergy consumption, and apparent viscosity (Chevanan et al 2010). Rosentrater and Tulbek (2010) and Fallahi et al (2011) carried out other research to evaluate the effects of conditioner steam, extruder water, and screw speed on the properties of DDGS-based Nile tilapia feeds by using a twin-screw extruder. Ayadi et al (2011b) achieved high-quality DDGS-based extrudates for yellow perch at inclusion levels of less than 50% by using a sin-gle-screw extruder. In their next study, they found that by in-creasing the inclusion level of DDGS in juvenile yellow perch

TABLE I Maximum Recommended Dietary Inclusion Rates of DDGS

for Various Species of Fish and Shellfishz

Species

Maximum DDGS Inclusion (%)

Catfish <30 Prawns <40 Salmon <10 Shrimp <10 Tilapia (without additional amino acids) <35 Tilapia (with additional amino acids) <82 Trout (without additional amino acids) <15 Trout (with additional amino acids) <22.5

z Based upon USGC (2012). DDGS = distillers dried grains with solubles.

Vol. 91, No. 1, 2014 81

diets, mass flow rate and processing temperature decreased sig-nificantly (Ayadi et al 2011d).

So far, only limited studies have examined optimal extrusion processing conditions for the production of DDGS-based aquacul-ture feeds for yellow perch. Microbial fermented soybean meal is another promising ingredient. It is rich in protein, is very low in antinutritional factors, and thus is highly digestible. The majority of the antinutritional factors are removed during the fermentation process. To our knowledge, only Fallahi et al (2012) have studied the effect of microbial-fermented soybean meal inclusion on ex-truded yellow perch diet physical properties.

Thus, the objectives of this study were 1) to produce vegetable-based protein feeds for juvenile yellow perch (Perca flavescens) by using graded levels of DDGS along with a fermented high-protein soybean meal as the protein source using twin-screw extrusion, and 2) to evaluate the physical properties of these ex-trudates.

MATERIALS AND METHODS

Blend Preparation. Two isocaloric (3.06 kcal/g) experimental diets containing two levels of DDGS (20 and 40%) and a constant amount of microbial-fermented high-protein soybean meal (Pep-SoyGen, 20%), in combination with appropriate amounts of other required ingredients including corn gluten meal, wheat flour, menhaden fish meal, vitamin mix, minerals, and essential amino acids, were formulated to contain a net protein content of approxi-mately 40% (Table II). DDGS was provided by Dakota Ethanol (Wentworth, SD, U.S.A.) and was ground to a fine particle size of approximately 100 μm with a laboratory-scale grinder (S500 disc mill, Glenmills, Clifton, NJ, U.S.A.). The ingredients were first mixed with a laboratory-scale mixer (model 600, Hobart Corpora-tion, Troy, OH, U.S.A.) for 3 min, and the vitamin premix was added to the rest of the ingredients; the blend was then mixed with a twin-shell dry blender (Patterson-Kelly, East Stroudsburg, PA, U.S.A.) at 60 rpm for 10 min to obtain homogenous blends. The resulting blends were then stored at ambient temperature overnight.

Extrusion Processing. Experimental extrusions were carried out with a semi-industrial twin-screw extruder (TX-52, Wenger, Sabetha, KS, U.S.A.) with a 30 hp motor and throughput of 50–250 kg/h. The extruder was self-wiping with two corotating, fully intermeshing screws, a dry-feed system, and a continuous precon-ditioner that was equipped with steam and water injection ports. The dry feed blends were transferred to the feed hopper and were then conveyed into the preconditioner, where steam was injected at a rate of 0.11–0.16 kg/min. After being adjusted to the desired moisture content and temperature inside the preconditioner, the blends were transferred into the extruder at a feed rate of 20 kg/h, and the conditioner’s screw speed was kept constant. The barrel of the extruder had a length-to-diameter ratio of 25.5/1, and its twin screws each had a diameter of 52 mm. The screws used in this experiment had 25 individual sections (Fig. 1), and the configura-tion (from the feeding section to the die section) was composed of four conveying screws, three shear locks, one conveying screw, one conveying screw backward, three conveying screws, one con-veying screw backward, four conveying screws, one shear lock, one interrupted flight conveying screw, one conveying screw, one interrupted flight conveying screw, one conveying screw, one in-terrupted flight conveying screw, one shear lock, and finally a screw with a cone-shaped endpoint. This configuration was rec-ommended by the manufacturer. Moreover, the barrel was com-posed of eight temperature zones, which were set at 25–90°C. Even though each was kept at a constant temperature, the tem-perature profile of the barrel varied depending on the actual tem-perature of each zone because of friction. The amount of water added to the extruder was maintained at 0.11–0.19 kg/min. The extruder had two die nozzles, each with a circular diameter of

3 mm. The exiting extrudates were cut into desired lengths with a rotating three-blade cutter mounted at the end of the dies.

Measurement of Extrusion Processing Parameters. Tem-peratures (T) of the raw material in the hopper, at the conditioner exit, and at the external die exit (which was unheated) were all monitored by a portable infrared thermometer (model 42540, Extech Instruments, Waltham, MA, U.S.A.).

Measurement of Extrudate Physical Properties. After proc-essing, the extrudates were cooled for 72 h at ambient tempera-ture (24 ± 1°C) and then dried in an oven (TAH-500, Grieve, Round Lake, IL, U.S.A.) for 24 h at 45°C. The extrudates were then subjected to extensive physical property analyses, including moisture content, water activity (aw), thermal conductivity (k), thermal resistivity (R), thermal diffusivity (α), expansion ratio, unit density, bulk density, water absorption and water solubility indices, pellet durability index, and color.

Moisture Content. Moisture content of the extruded samples was determined according to AACC International Approved Method 44-19.01.

Water Activity (aw). Water activity of the extrudates was meas-ured with a water activity meter (AW Sprint TH-500, Novasina, Pfäffikon, Switzerland). Before measurement, the system was calibrated according to the specified procedure of the manufacturer.

Thermal Properties. Thermal conductivity (k), thermal diffusiv-ity (α), and thermal resistivity (R) were determined with a thermal

TABLE II Ingredient Components (g/100 g) and Nutrient Compositions (db)

of the Feed Blends

Componentsz Control Diet 1 Diet 2

Ingredients, dry weight (g/100 g) DDGS 0.00 19.88 39.13 PepSoyGen soybean meal 0.00 20.97 20.64 Menhaden fish meal 45.90 5.13 5.05 Corn gluten meal 28.07 21.07 10.86 Whole wheat flour 22.47 22.58 13.84 Carboxyl methyl cellulose 0.76 2.82 3.05 Vitamin premix 0.63 0.56 0.55 Mineral mix 0.00 0.11 0.11 Oils … … …

Supplements (g/100 g) Total 2.17 6.83 6.77 Stay-C vitamin C 0.63 0.06 0.06 Choline 0.00 0.23 0.22 Phytase 0.00 0.04 0.04 DVAqua supplement 0.16 0.07 0.14 Arginine 0.00 0.28 0.28 Lysine 0.00 0.85 0.83 Isoleucine 0.00 0.06 0.06 Histidine 0.00 0.11 0.11 Glycine 0.00 0.56 0.55 Methionine 0.00 0.23 0.22 Taurine 0.00 0.00 0.00 Sodium chloride 0.63 1.13 1.11 Potassium chloride 0.76 0.90 0.89 Magnesium oxide 0.00 0.06 0.06 Calcium phosphate 0.00 2.25 2.21

Total 100.00 100.00 100.00

Feed blend composition (% db) Protein 39.96 39.05 37.87 Moisture 9.51 6.22 5.45 Fat 16.0 4.81 5.51 Crude fiber 0.36 1.99 2.43 Ash 2.03 8.54 9.54

z Sources: distillers dried grains with solubles (DDGS), Dakota Ethanol (Wentworth, SD, U.S.A.); PepSoyGen fermented soybean meal, Nutraferma (Sioux City, IA, U.S.A.); menhaden fish meal, Omega Protein (Houston, TX,U.S.A.); corn gluten meal, Consumers Supply Distributing Company (SiouxCity, IA, U.S.A.); whole wheat flour, Bob’s Red Mill Natural Foods (Milwaukie, OR, U.S.A.); carboxyl methyl cellulose, USB Corporation(Cleveland, OH, U.S.A.); and vitamin and mineral premixes, Lortscher AgriService (Bern, KS, U.S.A.).

82 CEREAL CHEMISTRY

properties analyzer (KD2, Decagon Devices, Pullman, WA, U.S.A.).

Expansion Ratio. Expansion ratio is expressed as the diametral expansion of the extrudate, which was determined as the ratio of the extrudate diameter to the diameter of the die nozzle (3 mm); both were measured with a digital caliper (Digimatic Series 293, Mitutoyo, Tokyo, Japan), following Conway and Anderson (1973), Colonna et al (1989), and Van Zuilichem et al (1975).

Unit Density. Assuming cylindrical shapes for the extruded samples, unit density was determined as the ratio of mass to volume for 10 randomly chosen extrudates, following Jamin and Flores (1998) and Rosentrater et al (2005). The mass of each ex-trudate (M) was measured with an analytical balance (Adventurer AR1140, Ohaus, Pine Brook, NJ, U.S.A.); the diameter of each extrudate was measured with a digital caliper (Digimatic Series 293, Mitutoyo), and volume (V) was calculated from diameter. Unit density was calculated as

)kg/m(densityunit 3

V

M=

Bulk Density. Bulk density was measured with a standard bushel tester (Seedburo Equipment, Chicago, IL, U.S.A.). Bulk density (g/cm3) was defined as the ratio of the mass of the extru-dates (g) occupying a given bulk volume to the volume of the bulk (cm3), according to the method recommended by USDA (2009).

Water Absorption and Water Solubility Indices. These two physi-cal characteristics were determined following Anderson et al (1969) and Jones et al (2000).

Pellet Durability Index. Pellet durability index was determined following ASAE standard method S269.4 (2004): 200 g of an extruded sample was tumbled inside a pellet durability tester (PDT-110, Seedburo Equipment) for 10 min and then sieved man-ually with a number 6 screen to remove fines. Thereafter, pellet durability index was calculated with the following equation, where Ma and Mb are the mass (g) of the extrudates after tumbling and before tumbling, respectively:

100(%) index durabilitypellet ×=b

a

M

M

Color (L*, a*, b*). Color included L* (brightness/darkness), a* (redness/greenness), and b* (yellowness/blueness) and was meas-ured with a spectrophotometer (Lab Scan XE, Hunter Lab, Reston, VA, U.S.A.).

Compositional Analysis. The extrudates were air-dried and pro-tein, moisture, fiber, fat, and ash contents were determined fol-lowing AOAC official method 990.03, AACCI Approved Method

44-19.01, and AOAC official methods 978.10, 920.39, and 920.48, respectively (AOAC International 2012). Each chemical constituent was determined in duplicate (n = 2) for all raw ingre-dient blends.

Statistical Analysis. All collected data were analyzed with Ex-cel 2010 (Microsoft, Redmond, WA, U.S.A.) and SAS version 9.0 software (SAS Institute, Cary, NC, U.S.A.) using a type 1 error rate (α) of 0.05, by analysis of variance to find significant differ-ences among the control diet and the treatments. Additionally, if significant differences were found, then post hoc LSD tests were used to determine where the significant differences occurred.

RESULTS AND DISCUSSION

Extrusion Processing Parameters. Temperatures During Proc-essing (T). Temperatures at three points of the process were moni-tored (Table III). As depicted, increasing DDGS level from 0 to 20% led to a 6.9% increase in processing temperature at the con-ditioner section; further increasing DDGS did not impact the con-ditioner temperature (Tc). In terms of processing temperature at the die exit (Td), extrudates produced with higher DDGS content had lower temperature upon exiting the die section. Hence, the highest temperature at the die exit was observed for the control diet. Temperature increased proportionately along the extruder barrel, because of heat addition as well as frictional heating. The highest temperature at the die zone apparently resulted from the lower moisture content and consequently higher frictional forces between the cooked dough and internal surface of the die walls (Ayadi et al 2011d) for the control blend. The higher temperature at the die zone for the control diet might also be related to the heat of the water releasing energy to the surroundings at the die exit, which may be related to compositional changes in the diet blends: greater fiber content generally leads to greater water ab-sorption and binding (Ayadi et al 2011d). Temperature at the die zone was higher for the control blend than for the experimental diets.

Extrudate Physical Properties. Table IV provides the physical properties of the final products, including moisture content, water activity, thermal properties, expansion ratio, unit density, bulk density, water absorption and water solubility indices, pellet dura-bility index, and color.

Moisture Content. As depicted in Table IV, the highest moisture content was observed for the extrudates of the control blend, which could be because of higher moisture content of the control diet; however, changing DDGS levels from 0 to 40% did not in-fluence the moisture content of the extrudates significantly, which could be because of the high standard deviations obtained for the moisture content of diet 1. These observations were in good agree-ment with what Ayadi et al (2011b, 2011d) reported.

Fig. 1. Screw configuration used in the extruder.

Vol. 91, No. 1, 2014 83

By definition, water content of biological materials can exist in two forms (bound and unbound). Unbound water, or free moisture content (i.e., water activity), is the moisture that is higher than the equilibrium moisture content and can be removed by drying or by placing in storage at a specific relative humidity. Moisture content (especially free water, discussed subsequently) of biological prod-ucts influences their resistance to microbial spoilage and thus their shelf life. All the produced extrudates in this study had mois-ture content of less than 9% (db).

Physical interactions among water and food constituents such as polysaccharides, fat, and protein affect the texture of the bio-material (Molnar 1983; Fennema 1985; Walstra 2003). Generally, in extrusion processing, reduced moisture content of a raw blend causes higher die pressure (Moscicki and Zuilichem 2011). On the other hand, interactions between the heat transfer and shearing forces developing inside the barrel of the extruder influence the reaction between the water and other key ingredients such as starch and protein. As a result, the water in the dough evaporates and flashes into the vapor phase, which changes the structure of the melted dough and positively affects the expansion of the ex-trudates (Miller 1985; Lee et al 2000; Riaz 2000). In this study, the water content of the blend was adjusted through both direct water addition and steam injection to obtain a stable process and to maintain uniformity of expansion. Furthermore, variation in water content of the blend during the process can result in no-ticeable changes in extrudate properties, such as durability, cohe-siveness, and water absorption and solubility indices. It is well documented that structure of extruded products highly depends on protein denaturation and starch gelatinization because of in-teractions among water, pressure, temperature, and shear in the evaporation process (Friesen et al 1992).

Water Activity (aw). Using DDGS in the diet formula led to a decrease in aw of the extrudates compared with that of the control diet, but increasing DDGS levels from 20 to 40% did not show significant impact on aw of the products (Table IV). Overall, as the DDGS content increased, water activity of the extrudates de-creased significantly from 0.48 to 0.34, which was in contrast to what Ayadi et al (2011b) and Chevanan et al (2007a) observed.

Water activity, a measure of free water, is the ratio of water pressure in a material to that of pure water at the same condition (Koop et al 2000) and is temperature dependent, owing to changes in water binding and water solubility (Bettina et al 2007). Water activity is the most important factor in controlling spoilage, be-cause it indicates the lowest limit of available water for microbial growth. It is also a major factor affecting the activity of enzymes, vitamins, color, and ultimately the shelf life of the product during storage. The lower the water activity, the lower the chance of spoil-age. Lowe and Kershaw (1995) and Chirife and Buera (1994) proved that water activity of less than 0.6 can guarantee a long shelf life for most food products. The low water activity of the extrudates produced (<0.5) in this extrusion trial implies high storage stability and microbial resistance of the products. Also, it

can be related to protein denaturation and crosslinking at high temperature and pressure happening during the extrusion cooking process (Fennema 1985; Walstra 2003).

Thermal Properties. As shown in Table IV, the thermal proper-ties of the extrudates produced from diets containing DDGS were not changed compared with those of the control diet, indicating that DDGS inclusion had no impact on the thermal properties (conductivity, resistivity, and diffusivity) of the products.

Thermal properties of a material can be explained by three key physical characteristics. Thermal conductivity (k), which indicates a material’s potential to transfer heat by conduction, depends on temperature, composition, and molecular structure of a material. If a material is denatured during a heating process, its thermal conductivity decreases (Heldman 2003). Thermal resistivity (R) is the ability of a material to prevent the transfer of heat through that material; it depends on the temperature difference across the ma-terial and the thickness of the material (Arámbula-Villa et al 2007). Thermal diffusivity (α) indicates a material’s capability of heat storage versus heat transfer (Kawasaki and Kawai 2006). According to Arámbula-Villa et al (2007), substances with higher thermal diffusivity can adjust their temperatures in a shorter time because they conduct heat rapidly in comparison to their volu-metric heat capacity. Moreover, a material with a higher thermal diffusivity does not require as much energy from its surroundings to reach thermal equilibrium (www.calce.umd.edu/TSFA/laser_ flash/Results.pdf). In addition, when the molten starch component is leaving the extruder, a rapid water evaporation can occur, which leads to expansion and cooling of the extrudates. The speed of cooling at this point is directly related to thermal conductivity of the extrudates. In this study, however, there were no significant differences among the extrudates, even though there were some expansion differences.

Expansion Ratio. The effects of DDGS on the expansion ratios are provided in Table IV. Extrudates produced from diet 1 and

TABLE III Treatment Effects on Extrusion Processing Parametersz

Treatment

Parameter Control Diet 1 Diet 2

Processing temperature (°C) Feeder zone 25.44a 24.76a 25.33a (0.21) (0.50) (0.29) Conditioner zone 30.76a 32.89b 32.38b (0.56) (1.01) (1.59) Die zone 46.02a 44.94ab 43.98b

(1.10) (1.38) (0.78)

z Parentheses indicate ±1 standard deviation; means followed by similar lettersfor a given dependent variable are not significantly different at P < 0.05 among treatments.

TABLE IV Treatment Effects on Extrudate Physical Propertiesz

Treatment

Property Control Diet 1 Diet 2

Moisture content (% db) 8.32a 7.49a 7.24a (0.12) (1.59) (0.72) Water activity (aw, –) 0.48a 0.38b 0.34b (0.01) (0.10) (0.02) Thermal conductivity (k, W/m°C) 0.06a 0.06a 0.06a (0.01) (0.01) (0.01) Thermal resistivity (R, m°C/W) 18.47a 17.57a 17.47a (0.90) (1.51) (1.82) Thermal diffusivity (α, mm2/s) 0.16a 0.16a 0.15a (0.01) (0.02) (0.02) Expansion ratio (–) 1.18a 1.10b 1.03c (0.08) (0.08) (0.11) Unit density (kg/m3) 731.70a 791.60ab 886.55b (102.85) (153.55) (160.48) Bulk density (kg/m3) 572.15a 607.93ab 654.50b (1.30) (95.74) (55.68) Water absorption index (–) 3.48a 3.66a 3.48a (0.06) (0.53) (0.58) Water solubility index (%) 14.81ab 12.73b 15.56a (0.24) (2.85) (1.13) Pellet durability index (%) 99.46a 98.74b 98.91ab (0.05) (0.54) (0.63) Brightness/darkness (L*, –) 22.36a 25.59b 26.12b (0.21) (2.23) (0.36) Redness/greenness (a*, –) 5.51a 8.48c 7.86b (0.10) (0.69) (0.30) Yellowness/blueness (b*, –) 9.00a 11.69b 11.74b (0.21) (1.51) (0.31)

z Parentheses indicate ±1 standard deviation; means followed by similar letters for a given dependent variable are not significantly different at P < 0.05 among treatments.

84 CEREAL CHEMISTRY

diet 2 had a lower expansion ratio compared with that of the con-trol diet. At 20 and 40% incorporation of DDGS, expansion ratio decreased by 6.8 and 12.7%. Thus, as DDGS increased, expan-sion decreased.

Expansion ratio is one of the most critical physical properties for aquafeeds, because it affects density, floatability, and fragility of the extrudates, which are also important for aquafeeds (Oliveira et al 1992; Rosentrater et al 2009a, 2009b). For example, yellow perch species feed on or near the bottom of the pond, so a sinking feed may be more appropriate for this species (Webster and Lim 2002). Our observations indicated that the floatability of DDGS-based extrudates decreased as the DDGS content increased. This observation was in agreement with the decreasing trend of expan-sion ratio of the DDGS-based extrudates (Table IV). Theoreti-cally, extrudate expansion is defined by the ratio between extru-date diameter and die diameter (Conway and Anderson 1973; Van Zuilichem et al 1975), but Launay and Lisch (1983) believed that volumetric expansion (i.e., both longitudinal and diametral expan-sion) should be considered. Fan et al (1994) suggested that the molten dough expansion at the die occurs as two phases: an ex-pansion phase followed by a shrinkage phase. Therefore, the in-ternal structure of the melt is affected by expansion during die exit and results in extrudates with different textures (Arhaliass et al 2003). The extent of expansion is dependent on factors such as composition of the blend (Bouzaza et al 1996), temperature and rheological behavior of the dough, mass flow rate, residence time in the extruder (Fan et al 1994; Mitchell et al 1994), and die ge-ometry (Bouzaza et al 1996). In this study, temperature, screw speed, and residence time were kept constant, and the effect of DDGS as a proteinaceous ingredient on the expansion ratio of the extrudates was examined. Future work with varying levels of extrusion parameters is required to better understand the combi-nation effects of extrusion parameters and DDGS inclusion on DDGS-based yellow perch diets. According to Nielsen (1976), extruded materials with higher starch content can exhibit greater expansion because of starch gelatinization, which leads to for-mation of an elastic melt inside the barrel; on the other hand, those with higher protein content show a limited degree of expan-sion owing to formation of a plastic melt and protein denatura-tion. The degree of starch gelatinization affects the expanded shape and air cell structure as well (Chinnaswamy and Bhattacharya 1983, 1986; Bhattacharya and Hanna 1987; Lee et al 2000). Launay and Lisch (1983) postulated that viscosity and elastic properties of the melted starch were the main reasons for volu-metric expansion phenomena in extrusion processing. As was expected, increasing levels of DDGS resulted in extrudates with a lower expansion ratio because of the higher fiber content (Table II), lower starch contents of the blends (because most of the starch component of corn had been utilized during the fermentation process of ethanol production), and consequently lower degree of gelatinization. Low expansion of the products could also be be-cause of the low processing temperature during this extrusion study. In general, dough does not expand at a temperature of less than 100°C. High-temperature extrusion decreases the dough viscosity and provides more vapor pressure release. But at low-temperature extrusion, the starch component of the dough is only partially gelatinized and results in unexpanded or minimally ex-panded products (Ding et al 2005). In the extrusion studies carried out by Ayadi et al (2011b, 2011d) on production of DDGS-based diets for yellow perch, with both single-screw and twin-screw extruders, they did not observe any noticeable change in the ex-pansion ratio of the extrudates.

Unit Density. The main effects of DDGS on the unit density of the extruded products are presented in Table IV. Diets with 20 and 40% DDGS content had higher unit density than that of the control diet, leading to increases of 8.2 and 21% in unit density when in-creasing DDGS from 0 to 20 to 40%, respectively. In general, unit density is inversely related to the expansion ratio (Colonna et al

1989; Bhatnagar and Hanna 1996). In aquafeeds, unit density is a key parameter related to the floatability of the feeds, because floata-bility is directly related to the expansion ratio. In this study, as the expansion ratio increased, the unit density decreased, which was in agreement with this concept. In another single-screw extrusion study for production of DDGS-based yellow perch diets, an in-crease of 17% in extrudate unit density values was observed when DDGS was increased from 10 to 50% (Ayadi et al 2011b); no no-ticeable difference was found among the unit density of the yellow perch diets containing 10, 20, and 30% DDGS that were extruded in the twin-screw extruder, however (Ayadi et al 2011d). Using a twin-screw extruder, Chevanan et al (2007b) obtained a 159% rise in unit density of DDGS-based fish feed when raising DDGS con-tent from 20 to 60%. However, the microbial-fermented soybean meal used in this study may have an impact on unit density of the extrudates owing to addition of different types of proteins.

Bulk Density. The main effects of DDGS inclusion on the bulk density of the extrudates are summarized in Table IV. As shown, inclusion of 20% DDGS resulted in a 6% rise in bulk density of the extrudates in comparison to the control diet. Further increas-ing the DDGS level to 40% raised the bulk density from 607.9 to 654.5 kg/m3, or nearly 7%. Raising DDGS content reduces the expansion ratio and thus increases the unit density and bulk den-sity values of the extrudates. Gujska and Khan (1991) reported that protein-enriched extrudates have a bulk density of up to 600 kg/m3. Our observations for bulk density of the DDGS-based yellow perch extrudates were in good agreement with their re-ported value.

Bulk density is defined as the ratio of the mass of a bulk of ex-trudates to the volume of a specific container; therefore, products with higher bulk density occupy smaller space for a given mass. From a commercial point of view, this makes the bulk density an important physical property, because it influences the required storage space either at the processing plant or during shipping (Guy 2001). Hence, the higher the bulk density, the lower the packaging, storage, and transportation costs for a given mass. Several parameters such as die design, processing parameters (such as extruder water and conditioner steam), and diet composi-tion affect the bulk density of the extrudates resulting from the extent of expansion (Ayadi et al 2011a; Fallahi et al 2011). As expansion impacts bulk density, so temperature, pressure, and feed composition affect this property as well.

Water Absorption and Water Solubility Indices. Increasing lev-els of DDGS from 0 to 20 to 40% did not result in any significant impact on the water absorption index of the extrudates (Table IV). However, increasing DDGS from 0 to 20 to 40% led to a 14% decrease and a 13.4% increase in water solubility index values of the extrudates, respectively. The diet containing 20% DDGS ex-hibited the lowest water solubility index value of 12.73%, whereas the highest water solubility index value of 15.56% was obtained for the diet containing 40% DDGS; increasing the DDGS level from 20 to 40% increased water solubility index by nearly 22%.

Water absorption index of a material is a measure of the volume occupied by the swollen starch component in the product after exposing it to water (Mason and Hoseney 1986). In extrusion processing, water absorption index is an indicator of that portion of starch that was not affected by processing and still is in its na-tive structure (Kirby et al 1988). Any change in water absorption index can be due to structural modifications of the blend composi-tion, such as starch gelatinization and protein denaturation (Badrie and Mellowes 1991; Rosentrater et al 2009a, 2009b).

On the other hand, water solubility index indicates the degrada-tion of the macromolecule components of a blend and that they are more soluble in water (Colonna and Mercier 1983; Govindasamy et al 1996); thus, the larger molecules (i.e., those with higher mo-lecular weight) exhibit a lower water solubility index. In extrusion cooking, water solubility index is an indicator of that part of

Vol. 91, No. 1, 2014 85

starch that was converted. Menegassi et al (2011) observed that extrusion processing can increase water solubility index. Changes in water solubility index observed in this study were likely the consequence of the changes in the composition of the feed blends, not just the DDGS level but the levels of all other ingredients as well. Some ingredients were higher in starch versus other struc-tural carbohydrates, and as the composition changed, a curvilinear response in water solubility index was observed.

Pellet Durability Index. The main effect of DDGS level on pel-let durability index is illustrated in Table IV. Increasing DDGS content from 0 to 20 to 40% caused a curvilinear decrease in pel-let durability index. However, all the extrudates exhibited very high durability of more than 98%, indicating their high resistance and mechanical durability.

Pellet durability index is another important physical property of extrudates, especially for aquafeeds. It indicates the mechanical strength of the extruded products. The higher the pellet durability index, the more stable the extrudates will be during storage, feed-ing, and handling processes. It is believed that the extent of heat treatment, along with the level of starch transformation and water content, influence the pellet durability of the extrudates (Rosen-trater 2009a, 2009b). Similarly, Ayadi et al (2011b, 2011d) could achieve highly durable DDGS-based feeds for yellow perch using both single-screw and twin-screw extruders.

Color (L*, a*, b*). The effects of each diet on color of the ex-trudates are provided in Table IV. As shown, increasing DDGS contents in the blend significantly raised the color values of the extruded blends (L*, a*, and b*). The lightest and darkest extru-dates, with L* values of 26.12 and 22.36, were observed for 40 and 0% DDGS inclusion, respectively. The control diet (0% DDGS) showed the lowest yellowness (b*) value of 9.0 and was the least red (a* of 5.51). Although increasing DDGS levels raised the yellowness value of the extrudates, no significant dif-ferences between the b* values of the diets containing 20 and 40% DDGS were observed. These results are similar in nature to results by Ayadi et al (2011b, 2011d), which found that color changes among extrudates were primarily a function of dietary ingredients, at least under moderate processing temperatures. They found that processing temperatures greater than approxi-mately 90°C can lead to darkening of the extrudates because of protein denaturation.

CONCLUSIONS

This study was intended to produce complete, nutritionally via-ble feeds for juvenile yellow perch by increasing the levels of DDGS, along with a constant amount of fermented high-protein soybean meal and other ingredients, using a twin-screw extruder. Moisture content and aw of the extrudates substantially decreased with increasing DDGS content of the blend. Water activities of the extrudates were low, which indicated that the extrudates had high shelf life. Higher inclusion of DDGS increased water solu-bility index, although it did not have any effect on water absorp-tion index; extrudates produced from the blends containing 40% DDGS appeared to be more water soluble. Increasing DDGS re-sulted in a significant increase in unit density and bulk density while simultaneously inducing a decrease in expansion ratio of all the extrudates, as expected. In addition, all extrudates exhibited high durability indices of more than 98%, which is important to retaining their physical structure during transportation and stor-age. Extrudates with a higher L* value were detected for the diets with higher DDGS inclusion as well. Thus, physically high-qual-ity extrudates were achieved in this study. In a parallel study by another research group, the extrudates were then fed to actual juvenile yellow perch, with the intention of evaluating the accept-ability and growth performance of these feeds (A. Von Eschen et al, unpublished). Future studies should concentrate on further investigating the effects of extrusion processing, using graded

levels of different types of DDGS and graded levels of microbial-fermented soybean meal, on resulting processing parameters and properties of DDGS-based diets for yellow perch, as well as feed digestibility and growth performance.

ACKNOWLEDGMENTS

The authors thank the Agricultural Experiment Station, South Dakota State University, and the North Central Agricultural Research Laboratory, USDA-ARS, Brookings, South Dakota, for funding, facilities, equipment, and supplies. Furthermore, the cooperation and assistance of Sharon Nichols, Christine Wood, Mike Barnes, Mehmet Tulbek, and Riley Morgan are greatly appreciated.

LITERATURE CITED

AACC International. Approved Methods of Analysis, 11th Ed. Method 44-19.01. Moisture—Air-oven method, drying at 135°. AACC International: St. Paul, MN. http://dx.doi.org/10.1094/AACCIntMethod-44-19.01

Aas, T. S., Hatlen, B., Grisdale-Helland, B., Terjesen, B. T., Bakke- McKellep, A. M., and Helland, S. J. 2006. Effects of diets containing bacterial protein meal on growth and feed utilization in rainbow trout (Oncorhynchus mykiss). Aquaculture 261:357-368.

Abdel-Tawwab, M., Ahmad, M. H., Khattab, Y. A. E., and Shalaby, A. M. E. 2010. Effect of dietary protein level, initial body weight, and their in-teraction on the growth, feed utilization, and physiological alterations of Nile tilapia, Oreochromis niloticus (L.). Aquaculture 298:267-274.

Agricultural Marketing Resource Center (AgMRS). 2012. Estimated U.S. dried distillers grains with solubles (DDGS) production & use. Available at: www.extension.iastate.edu/agdm/crops/outlook/dgsbalancesheet.pdf

Ahmed, A., Rab, A., Khan, F., Afzal, M., and Mehdi, M. R. G. 2011. Formulation of balance and low cost feeds for rainbow trout fingerlings at Mountain Agricultural Research Centre, PARC, Juglote, Gilgit Paki-stan. Adv. Environ. Biol. 5:71-73.

Amaya, E. A., Davis, D. A., and Rouse, D. B. 2006. Plant proteins ef-fectively replace fishmeal in shrimp feed trial. Global Aquacult. Ad-vocate (Nov./Dec.): 50-51. Available at: http://pdf.gaalliance.org/pdf/ GAA-Amaya-Nov06.pdf

American Society of Agricultural Engineers (ASAE). 2004. American Society of Agricultural Engineers—Standards, Engineering Practices, and Data. ASAE: St. Joseph, MI.

Anderson, R. A., Conway, H. F., Pfeifer, V. F., and Griffin, L. E. 1969. Gelatinization of corn grits by roll and extrusion cooking. Cereal Sci. Today 14:4-7.

AOAC International. 2012. Official Methods of Analysis. Available at: www.eoma.aoac.org. AOAC International: Gaithersburg, MD.

Arámbula-Villa, G., Guitiérrez-Árias, E., and Moreno-Martínez, E. 2007. Thermal properties of maize masa and tortillas with different compo-nents from maize grains, and additives. J. Food Eng. 80:55-60.

Arhaliass, A., Bouvier, J. M., and Legrand, J. 2003. Melt growth and shrinkage at the exit of the die in the extrusion-cooking process. J. Food Eng. 60:185-192.

Ayadi, F. Y., Fallahi, P., Muthukumarappan, K., and Rosentrater, K. A. 2011a. Single-screw extrusion modeling effects on extrusion proc-essing parameters and physical properties of DDGS-based Nile tilapia (Oreochromis niloticus) feeds. Paper No. 1110885, ASABE Annual In-ternational Meeting 2011, August 7–10, Louisville, KY.

Ayadi, F. Y., Muthukumarappan, K., Rosentrater, K. A., and Brown, M. L. 2011b. Single-screw extrusion processing of distillers dried grains with solubles (DDGS)-based yellow perch (Perca flavescens) feeds. Cereal Chem. 88:179-188.

Ayadi, F. Y., Muthukumarappan, K., Rosentrater, K. A., and Brown, M. L. 2011c. Twin-screw extrusion processing of rainbow trout (Oncorhyn-chus mykiss) feeds using various levels of corn-based distillers dried grains with solubles (DDGS). Cereal Chem. 88:363-374.

Ayadi, F. Y., Rosentrater, K. A., Muthukumarappan, K., and Brown, M. L. 2011d. Twin-screw extrusion processing of distillers dried grains with solubles (DDGS)-based yellow perch (Perca flavescens) feeds. Food Bioproc. Technol. 5:1963-1978.

Badrie, N., and Mellowes, W. 1991. Effect of extrusion variables on cas-sava extrudate. J. Food Sci. 56:1334-1337.

Bettina, H., Kurtmann, L., Carlsen, C. U., Ratjen, J., Först, P., Skibsted, L. H., Kulozik, U., and Risbo, J. 2007. Impact of water activity, tem-perature, and physical state on the storage stability of Lactobacillus

86 CEREAL CHEMISTRY

paracasei ssp. paracasei freeze-dried in a lactose matrix. Biotechnol. Prog. 23(4):794-800.

Bhatnagar, S., and Hanna, M. A. 1996. Starch-based plastic foams from various starch sources. Cereal Chem. 73:601-604.

Bhattacharya, M., and Hanna, M. A. 1987. Textural properties of extru-sion cooked corn starch. LWT—Food Sci. Technol. 20:195.

Bouzaza, D., Arhaliass, A., and Bouvier, J. M. 1996. Die design and dough expansion in low moisture extrusion-cooking process. J. Food Eng. 29:139-152.

Brown, P. B., Griffin, M. E., and White, M. R. 1993. Experimental and practical diet evaluations with juvenile hybrid striped bass. J. World Aquacult. Soc. 24:80-89.

Brown, P. B., Dabrowski, K., and Garling, D. L. 1996. Nutrition and feed-ing of yellow perch (Perca flavescens). J. Appl. Ichthyol. 12:171-174.

Case, S. E., Hamann, D. D., and Schwartz, S. J. 1992. Effect of starch gelatinization on physical properties of extruded wheat- and corn-based products. Cereal Chem. 69:401-404.

Cheftel, J. C. 1986. Nutritional effects of extrusion-cooking. Food Chem. 20:263-283.

Cheng, Z. J., and Hardy, R. W. 2004a. Effects of microbial phytase sup-plementation in corn distiller’s dried grains with solubles on nutrient digestibility and growth performance of rainbow trout (Oncorhynchus mykiss). J. Appl. Aquacult. 15:83-100.

Cheng, Z. J., and Hardy, R. W. 2004b. Nutritional value of diets contain-ing distiller’s dried grain with solubles for rainbow trout (Oncorhyn-chus mykiss). J. Appl. Aquacult. 15:101-113.

Chevanan, N., Muthukumarappan, K., Rosentrater, K. A., and Julson, J. L. 2007a. Effect of die dimensions on extrusion processing parameters and properties of DDGS-based aquaculture feeds. Cereal Chem. 84:389-398.

Chevanan, N., Rosentrater, K. A., and Muthukumarappan, K. 2007b. Twin-screw extrusion processing of feed blends containing distillers dried grains with solubles (DDGS). Cereal Chem. 84:428-436.

Chevanan, N., Rosentrater, K. A., and Muthukumarappan, K. 2008. Effect of DDGS, moisture content, and screw speed on physical properties of extrudates in single-screw extrusion. Cereal Chem. 85:132-139.

Chevanan, N., Muthukumarappan, K., and Rosentrater, K. A. 2009. Ex-trusion studies of aquaculture feed using distillers dried grains with solubles and whey. Food Bioproc. Technol. 2:177-185.

Chevanan, N., Rosentrater, K. A., and Muthukumarappan, K. 2010. Ef-fects of processing conditions on single screw extrusion of feed ingre-dients containing DDGS. Food Bioproc. Technol. 3:111-120.

Chinnaswamy, R., and Bhattacharya, K. R. 1983. Studies on expanded rice: Optimum processing conditions. J. Food Sci. 48:1604-1608.

Chinnaswamy, R., and Bhattacharya, K. R. 1986. Pressure-parboiled rice: A new base for making expanded rice. J. Food Sci. Technol. 23:14-19.

Chirife, J., and Buera, P. M. D. 1994. Water activity, glass transition and microbial stability in concentrated/semi moist food systems. J. Food Sci. 59(5):921-927.

Colonna, P., and Mercier, C. 1983. Macromolecular modifications of manioc starch components by extrusion-cooking with and without lip-ids. Carbohydr. Polym. 3:87-108.

Colonna, P., Tayeb, J., and Mercier, C. 1989. Extrusion cooking of starch and starchy products. Pages 247-319 in: Extrusion Cooking. C. Mer-cier, P. Linko, and J. M. Harper, eds. American Association of Cereal Chemists: St. Paul, MN.

Conway, H. F., and Anderson, R. A. 1973. Protein-fortified extruded food products. Cereal Sci. Today 18:94-97.

Ding, Q., Ainsworth, P., Plunkett, A., Tucker, G., and Marson, H. 2005. The effect of extrusion conditions on the physicochemical properties and sensory characteristics of rice base expanded snacks. J. Food Eng. 66(3):283-289.

Duarte, C. M., Holmer, M., Olsen, Y., and Soto, D. 2009. Will the oceans help feed humanity? Bioscience 59:967-976.

El-Saidy, D. M. S. D., and Gaber, M. M. A. 2002. Complete replacement of fish meal by soybean meal with dietary L-lysine supplementation for Nile tilapia Oreochromis niloticus (L.) fingerlings. J. World Aquacult. Soc. 33:1119-1127.

Fallahi, P., Rosentrater, K. A., Muthukumarappan, K., and Tulbek, M. 2011. Effects of conditioner steam, extruder water and screw speed on physical properties of DDGS-based extrudates in twin-screw extrusion. Paper No. 1110887, ASABE Annual International Meeting 2011, Au-gust 7–10, Louisville, KY.

Fallahi, P., Muthukumarappan, K., and Rosentrater, K. A. 2012. Twin-screw extrusion processing of vegetable-based protein feeds for yellow perch (Perca flavescens) containing distillers dried grains, soy protein

concentrate, and fermented high protein soybean meal. J. Food Res. 1(3):230-246.

Fan, J., Mitchell, J. R., and Blanshard, J. M. V. 1994. A computer simula-tion of the dynamics of bubble growth and shrinkage during extrudate expansion. J. Food Eng. 23:337-356.

Fennema, O. R. 1985. Food Chemistry, 2nd Ed. Marcel Dekker: New York, NY.

Food and Agriculture Organization (FAO). 2006. State of world aquacul-ture: FAO Fish Tech Paper 500. FAO: Rome. Available at: www.fao.org/ docrep/009/a0874e/a0874e00.htm

Francis, G., Makkar, H. P. S., and Becker, K. 2001. Anti-nutritional fac-tors present in plant-derived alternate fish feed ingredients and their ef-fects in fish. Aquaculture 199:197-227.

Friesen, K. G., Nelssen, J. L., Behnke, K. C., and Goodband, R. D. 1992. Ingredient processing: Improving pig feed by extrusion. Feed Manage. 43:33-38.

Goedeken, D. 1991. Single-screw extrusion-cooking of corn starch with se-lected proteins. Master’s thesis. University of Nebraska: Lincoln, NE.

Govindasamy, S., Campanellab, O. H., and Oatesa, C. G. 1996. High moisture twin-screw extrusion of sago starch: 1. Influence on granule morphology and structure. Carbohydr. Polym. 30:275-286.

Gujska, E., and Khan, K. 1991. Functional properties of extrudates from high starch fractions of navy and pinto beans and corn meal blended with legume high protein fractions. J. Food Sci. 59:431-435.

Guy, R. 2001. Extrusion Cooking: Technologies and Applications. Wood-head/CRC Press: Cambridge, U.K. p. 89.

Hardy, R. W. 1996. Alternate protein sources for salmon and trout diets. Anim. Feed Sci. Technol. 59(1-3):71-80.

Heldman, D. R. 2003. Encyclopedia of Agricultural Food and Biological Food Engineering. CRC Press: Boca Raton, FL. p. 1004.

Jacques, K. A., Lyons, T. P., and Kelsall, D. R. 2003. The Alcohol Text-book. University Press: Nottingham, U.K. p. 379.

Jamin, F. F., and Flores, R. A. 1998. Effect of separation and grinding of corn dry-milled streams on physical properties of single-screw low-speed extruded products. Cereal Chem. 75:775-779.

Jauncey, K., and Ross, B. 1982. A Guide to Tilapia Feeds and Feeding. University of Stirling, Institute for Aquaculture: Stirling, U.K. p. 111.

Johnsen, P. B., and Dupree, H. K. 1991. Influence of feed ingredients on the flavor quality of farm-raised catfish. Aquaculture 96:139-150.

Jones, D., Chinnaswamy, R., Tan, Y., and Hanna, M. 2000. Physiochemi-cal properties of ready-to-eat breakfast cereals. Cereal Foods World 45:164-168.

Kawasaki, T., and Kawai, S. 2006. Thermal insulation properties of wood-based sandwich panel for use as structural insulated walls and floors. J. Wood Sci. 52:75-83.

Khan, M. A., Jafri, A. K., Chadha, N. K., and Usmani, N. 2003. Growth and body composition of rohu (Labeo rohita) fed diets containing oilseed meals: Partial or total replacement of fish meal with soybean meal. Aquacult. Nutr. 9:391-396.

Kiang, M. J. 1998. Principles of aquaculture feed production by cooking extruder. Pages 107-113 in: Advances in Extrusion Technology. Tech-nomic: Lancaster, PA.

Kirby, A. R., Ollett, A. L., Parket, R., and Smith, A. C. 1988. An experi-mental study of screw configuration effects in the twin screw extrusion cooking of maize grits. J. Food Eng. 8:247-272.

Koop, T., Luo, B., Tsias, A., and Peter, T. 2000. Water activity as the determinant for homogeneous ice nucleation in aqueous solutions. Na-ture 406:611-614.

Launay, B., and Lisch, J. M. 1983. Twin-screw extrusion cooking of starches: Flow behavior of starch pastes, expansion and mechanical properties of extrudates. J. Food Eng. 2:259-280.

Lee, E. Y., Lim, K. I., Lim, J., and Lim, S.-T. 2000. Effects of gelatiniza-tion and moisture content of extruded starch pellets on morphology and physical properties of microwave-expanded products. Cereal Chem. 77:769-773.

Lim, C. E., and Aksoy, M. 2008. Distillers dried grains with solubles as an alternative protein source in fish feeds. Pages 67-82 in: Proceedings of the 8th International Symposium on Tilapia in Aquaculture, October 12–14, 2008, Cairo, Egypt.

Lowe, J. A., and Kershaw, S. J. 1995. Water activity-moisture content relationship as a predictive indicator for control of spoilage in commer-cial pet diet components. Anim. Feed Sci. Technol. 56:187-194.

Mason, W. R., and Hoseney, R. C. 1986. Factors affecting the viscosity of extrusion-cooked wheat starch. Cereal Chem. 63:436-441.

Menegassi, B., Pilosof, A. M. R., and Arêas, J. A. G. 2011. Comparison

Vol. 91, No. 1, 2014 87

of properties of native and extruded amaranth (Amaranthus cruentus L. – BRS Alegria) flour. LWT—Food Sci. Technol. 44:1915-1921.

Metts, L. S., Thompson, K. R., Xiong, Y., Kong, B., Webster, C. D., and Brady, Y. 2007. Use of alfalfa hay, compared to feeding practical diets containing two protein levels, on growth, survival, body composition, and processing traits of Australian red claw crayfish, Cherax quadri-carinatus, grown in ponds. J. World Aquacult. Soc. 38:218-230.

Miller, R. C. 1985. Low moisture extrusion: Effects of cooking moisture on product characteristics. J. Food Sci. 50:249-253.

Mitchell, J. R., Fan, J., and Blanshard, J. M. V. 1994. The shrinkage do-main. Extrusion Communiqué, March 1994, 10-12.

Molnar, P. J. 1983. A theoretical model to describe food quality. J. Food Qual. 12:1-11.

Moore, D., Sanei, A., Van Hecke, E., and Bouvier, J. M. 1990. Effect of ingredients on physical/structural properties of extrudates. J. Food Sci. 55:1383-1387.

Moscicki, L., and Zuilichem, D. J. 2011. Extrusion cooking techniques: Applications, theory and sustainability. In Extrusion-Cooking and Re-lated Techniques. L. Moscicki, ed. Wiley-VCH: Wienheim, Germany.

National Research Council (NRC). 1993. Nutrient Requirements of Fish. National Academy Press: Washington, D.C. Available at: www.nap.edu/ catalog.php?record_id=2115

Naylor, R. L., Goldburg, R. J., Primavera, J. H., Kautsky, N., Beveridge, M. C. M., Clay, J., Folke, C., Lubchenco, J., Mooney, H., and Troell, M. 2000. Effect of aquaculture on world fish supplies. Nature 405:1017-1024.

Nielsen, E. 1976. Whole seed processing by extrusion cooking. J. Am. Oil Chem. Soc. 53:305-309.

Oliveira, M. A., Moller, H. S., Haaland, H., and Rosenlund, G. 1992. The effect of process parameters on expansion of extruded fish feed. Pages 693-709 in: Food Extrusion Science and Technology. J. L. Kokini, C. T. Ho, and M. V. Karwe, eds. Marcel Dekker: New York, NY.

Opstvedt, J., Nygard, E., Samuelsen, T. A., Venturini, G., Luzzana, U., and Mundheim, H. 2003. Effect on protein digestibility of different processing conditions in the production of fish meal and fish feed. J. Sci. Food Agric. 83:775-782.

Reis, L. M., Reutebuch, E. M., and Lovell, R. T. 1989. Protein-to-energy ratios in production diets and growth feed conversion and body compo-sition of channel catfish, Ictalurus punctatus. Aquaculture 77:21-27.

Renewable Fuels Association (RFA). 2012. Statistics. Washington, D.C. Available at: www.ethanolrfa.org/pages/statistics

Riaz, M. N. 2000. Extruders in Food Applications. Technomic: Lancaster, PA. pp. 1-2, 19, 27, 82-85.

Riaz, M. N., Muhammad, A., and Rashida, A. 2009. Stability of vitamins during extrusion. Crit. Rev. Food Sci. Nutr. 49:361-368.

Rolfe, L. A., Huff, H. E., and Hsieh, F. 2001. Effects of particle size and processing variables on the properties of an extruded catfish feed. J. Aquatic Food Prod. Technol. 10:21-33.

Romarheim, O. H., Aslaksen, M. A., Storebakken, T., Krogdahl, A. S., and Skrede, A. 2005. Effect of extrusion on trypsin inhibitor activity and nutrient digestibility of diets based on fish meal, soybean meal and white flakes. Arch. Anim. Nutr. 59:365-375.

Rosentrater, K. A., and Muthukumarappan, K. 2006. Corn ethanol coprod-ucts: Generation, properties, and future prospects. Int. Sugar J. 108:648-657.

Rosentrater, K. A., and Tulbek, M. 2010. Extrusion of aquafeeds contain-ing corn distillers dried grains with solubles (DDGS) for Nile tilapia. Aquaculture America, March 1–5, San Diego, CA.

Rosentrater, K. A., Richard, T. L., Bern, C. J., and Flores, R. A. 2005. Small-scale extrusion of corn masa by-products. Cereal Chem. 82:436-446.

Rosentrater, K. A., Muthukumarappan, K., and Kannadhason, S. 2009a. Effects of ingredients and extrusion parameters on aquafeeds contain-ing DDGS and potato starch. J. Aquacult. Feed Sci. Nutr. 1:22-38.

Rosentrater, K. A., Muthukumarappan, K., and Kannadhason, S. 2009b. Effects of ingredients and extrusion parameters on properties of aqua-feeds containing DDGS and corn starch. J. Aquacult. Feed Sci. Nutr. 1:39-43.

Samocha, T. M., Davis, D. A., Saoud, I. P., and DeBault, K. 2004. Substi-

tution of fish meal by coextruded soybean poultry by-product meal in practical diets for the Pacific white shrimp, Litopenaeus vannamei. Aquaculture 231:197-203.

Schaeffer, T. W., Brown, M. L., and Rosentrater, K. A. 2009. Performance characteristics of Nile tilapia (Oreochromis niloticus) fed diets contain-ing graded levels of fuel-based distillers dried grains with solubles. J. Aquacult. Feed Sci. Nutr. 1:78-83.

Shapawi, R., Ng, W. K., and Mustafa, S. 2007. Replacement of fish meal with poultry by-product meal in diets formulated for the humpback grouper, Cromileptes altivelis. Aquaculture 273:118-226.

Shiau, S. Y., Chuang, J. L., and Sun, G. L. 1987. Inclusion of soybean meal in tilapia (Oreochromis niloticus × O. aureus) diets at two protein levels. Aquaculture 65:251-261.

Stone, D. A. J., Hardy, R. W., Barrows, F. T., and Cheng, Z. J. 2005. Ef-fects of extrusion on nutritional value of diets containing corn gluten meal and corn distiller’s dried grain for rainbow trout, Oncorhynchus mykiss. J. Appl. Aquacult. 17:1-20.

Storebakken, T., Baeverfjord, G., Skrede, A., Olli, J. J., and Berge, G. M. 2004. Bacterial protein grown on natural gas in diets for Atlantic salmon, Salmo salar, in freshwater. Aquaculture 241:413-425.

Thomas, M., Huijnen, P. T. H. J., van Vliet, T., van Zuilichem, D. J., and van der Poel, A. F. B. 1999. Effects of process conditions during ex-pander processing and pelleting on starch modification and pellet qual-ity of tapioca. J. Sci. Food Agric. 79:1481-1494.

Tidwell, J. H., Webster, C. D., and Yancey, D. H. 1990. Evaluation of distillers grains with solubles in prepared channel catfish diets. Trans. Kentucky Acad. Sci. 51:135-138.

Tidwell, J. H., Webster, C. D., Yancey, D. H., and D’Abramo, L. R. 1993. Partial and total replacement of fish meal with soybean meal and dis-tiller’s by-products in diets for pond culture of the freshwater prawn, Macrobrachium rosenbergii. Aquaculture 118:119-130.

Tran, Q. D., Hendriks, W. H., and van der Poel, A. F. 2008. Effects of extrusion processing on nutrients in dry pet food. J. Sci. Food Agric. 88:1487-1493.

United Nations (UN). 2010. World population prospects: The 2010 re-vision database. Available at: http://esa.un.org/wpp/Other-Information/ faq.htm#q1

United States Department of Agriculture (USDA). 2009. Practical proce-dures for grain handlers. Available at: www.gipsa.usda.gov/publications/ fgis/ref/primer.pdf

U.S. Grains Council (USGC). 2012. Use of DDGS in aquaculture diets. In: DDGS User Handbook. Available at: www.grains.org/images/stories/ DDGS_user_handbook/2012/Chapter-25.pdf

Van Zuilichem, D. J., Lamers, G., and Stolp, W. 1975. Influence of process variables on the quality of extruded maize. Pages 380-406 in: Engineering and Food Quality: Proceedings of the 6th European Food Symposium. International Union of Food Science and Technol-ogy, European Federation of Chemical Engineering: Cambridge, U.K.

Vens-Cappell, B. 1984. The effects of extrusion and pelleting of feed for trout on the digestibility of protein, amino acids and energy and on feed conversion. Aquacult. Eng. 3:71-89.

Walstra, P. 2003. Physical Chemistry of Foods. Marcel Dekker: New York, NY.

Watanabe, T. 2002. Strategies for further development of aquatic feeds. Fisheries Sci. 68:242-252.

Webster, C. D., and Lim, C. E. 2002. Percids. Page 237 in: Nutrient Re-quirements and Feeding of Finfish for Aquaculture. C. D. Webster and C. E. Lim, eds. CABI: Wallingford, U.K.

Webster, C. D., Tidwell, J. H., and Yancey, D. H. 1991. Evaluation of distillers grains with solubles as a protein source in diets for channel catfish. Aquaculture 96:179-190.

Wu, Y. V., Rosati, R. R., Sessa, D. J., and Brown, P. B. 1994. Utilization of protein-rich ethanol co-products from corn in tilapia feed. J. Am. Oil Chem. Soc. 71:1041-1043.

Zhou, P., Davis, D., Lim, C. E., Akshoy, M., Paz, P., and Roy, L. A. 2010. Pond demonstration of production diets using high levels of distiller’s dried grains with solubles with or without lysine supplementation for channel catfish. North Am. J. Aquacult. 72:361-367.

[Received August 23, 2012. Accepted August 19, 2013.]