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Physicochemical Properties of Quinoa Extrudates H. Dogan and M. V. Karwe Food Science and Technology International 2003; 9; 101 DOI: 10.1177/1082013203009002006 The online version of this article can be found at: http://fst.sagepub.com/cgi/content/abstract/9/2/101

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Physicochemical Properties of Quinoa Extrudates H. Dog˘an1 and M.V. Karwe2,* 1

TUBITAK Marmara Research Center, Food Science and Technology Research Institute, P.O. Box 21, Gebze/Kocaeli, 41470, Turkey 2 Food Science Department, Rutgers University, 65 Dudley Road, New Brunswick, NJ, 08901 USA Response surface methodology (RSM) was used to analyse the effect of temperature, screw speed, and feed moisture content on physicochemical properties of quinoa extrudates. A three-level, three-variable, Box-Behnken design of experiments was used. The experiments were run at 16–24% feed moisture content, 130–170 C temperature, and 250–500 rpm screw speed with a fixed feed rate of 300 g/min. Second order polynomials were used to model the extruder response and extrudate properties as a function of process variables. Responses were most affected by changes in feed moisture content and temperature, and to a lesser extent by screw speed. Calculated specific mechanical energy (SME) values ranged between 170– 402 kJ/kg which were lower than those observed for other cereals, most likely due to high (7.2%) fat content of quinoa. High levels of feed moisture alone, and in combination with high temperature, resulted in poor expansion. The best product, characterised by maximum expansion, minimum density, high degree of gelatinization and low water solubility index, was obtained at 16% feed moisture content, 130 C die temperature, and 375 rpm screw speed, which corresponds to high SME input. It was demonstrated that the pseudo-cereal quinoa can be used to make novel, healthy, extruded, snack-type food products. Key Words: quinoa, extrusion cooking, physico-chemical properties

INTRODUCTION Quinoa (Chenopodium quinoa Willd.) is a disc shaped small seed that looks like a cross between sesame seed and millet. It is a crop that has been grown in South American countries for centuries and has many potentially beneficial properties such as resistance to cold (Becker and Hanners, 1990; Coulter and Lorenz, 1991a; Prakash et al., 1993). It can be grown in poor soil and at high altitude (Ng et al., 1994). The edible seed of the quinoa plant has been called both a pseudo-cereal and a pseudo-oilseed because of its unique nutritional profile. It has been recently identified to have promising potential to overcome world’s food shortage (Ahamed et al., 1996). The seeds have protein quality comparable to that of whole dry milk in terms of balanced amino acid composition (Ng et al., 1994). Quinoa protein is rich in lysine, methionine and cysteine (Becker and Hanners, 1990). Thus, it is a good complement for legumes, which are often low in methionine and cysteine. Some types of wheat come close to matching protein content of quinoa, but cereals such as corn and rice generally have less than half the protein content of quinoa. In addition, quinoa is a relatively good source

*To whom correspondence should be sent (e-mail: [email protected]). Received 11 July 2002; revised 18 December 2002. Food Sci Tech Int 2003;9(2):0101–14 2003 Sage Publications ISSN: 1082-0132 DOI: 10.1177/108201303033940

of vitamin E, and several of the B vitamins (Ruales and Nair, 1993; Ahamed et al., 1996). It also has desirable fatty acid composition, and high levels of calcium, iron and phosphorous (Ruales and Nair, 1993; Przybylski et al., 1994) which make it a unique food source. The Aztecs and Incas credited quinoa with medicinal properties including lowering blood cholesterol, improving glucose tolerance and reducing insulin requirements (Guzman-Maldonado and Paredes-Lopez, 1998). In recent years, scientific information supporting the health benefits of quinoa has accumulated (GuzmanMaldonado and Paredes-Lopez, 1998). Quinoa contains significant amounts of flavonoids and phenolic acids, and a number of structurally diverse saponins (Ridout et al., 1991; Gee et al., 1993; Ng et al., 1994; Masterbroek et al., 2000). Saponins can help lower cholesterol blood levels, inhibit growth of cancer cells, eliminate digestive toxins, and strengthen the immune system (Arditi et al., 2000). Phenolic derivatives act as natural antimicrobial agents. They have been proven to be very good antioxidants, scavenging free radicals and providing metal chelating activities. Polyphenols have been implicated in health benefits, such as prevention of cancer and cardiovascular diseases. This unique added chemical composition makes quinoa an ideal candidate to be further studied for establishing it as a functional food. Processing of traditional grains like quinoa into products that deliver nutritive as well as physiologically active components represents a major opportunity for food processors catering to the health-food market. Extensive studies on extrusion processing of cereals, such as corn and wheat, to generate ready-to-eat 101


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M.V. KARWE

breakfast cereals and snacks, have been carried out (Chinnaswamy and Hanna, 1990; Case et al., 1992; Cai and Diosady, 1993; Guha et al., 1997). The only study reported in literature on extrusion of quinoa (Coulter and Lorenz, 1991a, b) is about the nutritional, sensory and physical characteristics of quinoa-corn grit blends (up to 30 : 70 ratio) extruded at 15–25% feed moisture content, 100–150 C, 100–200 rpm screw speed, and at 1 : 1 and 3 : 1 compression ratios on a Brabender Plasticorder single-screw extruder. Although the products extruded at 15% moisture content and a 3 : 1 compression ratio had a greater expansion, lower density and lower shear strength, addition of quinoa to corn grit resulted in a general decrease in product quality and an increase in extrusion rate under all processing conditions. In our research we focused on the investigation of processability of quinoa flour by twin-screw extrusion and the evaluation of physicochemical properties of extruded quinoa in comparison to unprocessed grains. This paper treats the effect of feed moisture content, die temperature, and screw speed on process and product responses during twin-screw extrusion of quinoa flour.

MATERIALS AND METHODS Material Quinoa seeds (Chenopodium quinoa Willd) were obtained from Quinoa Corporation (Torrance, CA) and milled into flour using a Fitz Mill (Model D). Proximate Analysis For the proximate composition analysis of quinoa flour the following methods were used (AACC, 1984). Moisture: oven drying at 103 C (method no. 44–15A). Ash: calcination at 550 C (method no. 08–01)

Lipids: defatting in a soxhlet apparatus with petroleum ether (method no. 30–10) Protein: micro Kjeldahl (N 6.25) (method no. 46–13) CHOþfiber: by the difference. Amylose content was determined by the method proposed by Chrastil (1987). The method is based on spectrophotometric measurement of the intensity of blue color formed due to complex formation between amylose and iodine. Extrusion Extrusion experiments were carried out on a twinscrew extruder (ZSK-30, from Krupp Werner & Pfleiderer, Ramsey, New Jersey). The extruder has two co-rotating, self-wiping screws (30.7 mm diameter, 4.7 mm channel depth, and 878 mm processing length; L/D ¼ 28.6) in a steel barrel with five zones. Each zone is heated by resistive electric heaters and the temperature of each zone can be controlled independently. The screw configuration used in extrusion experiments consisted of forward conveying elements, mild mixing elements, kneading elements and reverse elements (Table 1). Die pressure was measured using a Dynisco pressure transducer (TPT463E, Dynisco, Sharon, MA). The die had two circular orifices (3 mm diameter, 5 mm long). Quinoa flour was metered into the feed section of the extruder with a volumetric feeder (K-Tron Corp., Pitman, NJ). Water was injected into the feed section of the extruder immediately after the feed port using a triple action piston pump (US Electric Co., Milford, CT). Both the feeder and the pump were calibrated prior to extrusion runs to determine the set points required for desired mass flow rates of quinoa flour and water, respectively. Throughput or the total mass flow rate (flour þ water) was kept constant at 300 g/min for all experiments. Temperatures at zones I, II, and III were set to room temperature, 80 and 120 C, respectively, while the temperatures at zones IV and V were adjusted such that the desired die temperatures could be maintained.

Table 1. Screw configuration used for quinoa extrusion. Extrusion zones* Feed zone (84 mm)

Zone I (196 mm)

Zone II (210 mm)

Zone III (178 mm)

Zone IV (98 mm)

Zone V (84 mm)

Die zone (28 mm)

SK 42/42 SK 42/42

42/21 T 42/42 42/42 42/21 IGEL 42 28/28

28/28 28/28 IGEL 42 28/28 28/28 KB 45/5/28 28/14 28/14

28/14 KB 45/5/14 20/20 20/20 20/20 20/20 20/20 KB 45/5/20 20/10 LH 20/10 20/10

20/10 20/10 KB 45/5/20 20/10 LH 20/10 20/10 14/14 14/14

KB 45/5/14 KB 45/5/14 LH 14/14 14/14 14/14 14/14

14/14 14/14

*IGEL: mild kneading element. KB: kneading block. LH: left handed (reverse) element. SK: feed element.T: transition element.


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Experimental Design Response surface methodology was used to investigate the effects of extrusion conditions on the product and process responses of quinoa. Results from preliminary trials were used to select suitable extruder operating window. The independent variables considered in this study were feed moisture content (16–24% w.b.), die temperature (130–170 C), and screw speed (250–500 rpm). A three-variable, threelevel, Box-Behnken design (Table 2) was employed to determine the extrusion conditions. Experiments were randomized in order to minimize the systematic bias in the observed responses due to extraneous factors. Preparation of Samples Samples were collected under steady state conditions of pressure, torque and temperature. Immediately after extrusion, extrudates were cooled, packed into glass jars, flushed with nitrogen gas, sealed and kept refrigerated (5 C) until analysis.

The drive motor has a rated power of 9.1 kW at a rated screw speed of 500 rpm. The friction torque was measured with screws attached to the drive and the barrel empty. The determination of specific energy delivered (SED) to the extrudate is based on the energy balance (Figure 1) between the inlet and just before the exit at the die of the extruder under steady state conditions computed from the following equations, mf Cpi Ti þ QH QC þ ME ¼ mf Cpo Tp

ð2Þ

QH QC ME þ ¼ Cpo Tp Cpi Ti mf mf

ð3Þ

SME and SED were measured from experimental conditions and STE was calculated from Equation (4). STE þ SME ¼ SED

ð4Þ

Process Responses The ZSK-30 extruder is equipped with a torque indicator which shows % torque which is proportional to the current drawn by the drive motor. A reading of 100% torque corresponds to the max allowable torque of 172 Nm. The specific mechanical energy (SME) was calculated from the measured torque reading as follows (Godavarti and Karwe, 1997): SME ðkJ=kgÞ ¼ ðTotal torque (%) Friction torque (%)ÞN ð9:1Þ ð100Þ ð500Þmf ð1Þ Table 2. Experimental design for extrusion of quinoa. Coded Levels

Actual Levels

X1

X2

X3

M (% wb)

T ( C)

S (rpm)

þ1 þ1 1 1 0 0 0 0 þ1 þ1 1 1 0 0 0

þ1 1 þ1 1 þ1 þ1 1 1 0 0 0 0 0 0 0

0 0 0 0 þ1 1 þ1 1 þ1 1 þ1 1 0 0 0

24 24 16 16 20 20 20 20 24 24 16 16 20 20 20

170 130 170 130 170 170 130 130 150 150 150 150 150 150 150

375 375 375 375 500 250 500 250 500 250 500 250 375 375 375

Negative value of specific thermal energy (STE) indicates net cooling at the barrel. Product Responses Extrudate samples used for determination of the degree of gelatinization (DG), water solubility index (WSI), and water absorption index (WAI), were dried at 45 C overnight to 4–5% moisture. Dried samples were ground and passed through 28-mesh sieve (590 mm opening), and the flour samples were placed in glass jars and sealed. The method proposed by Birch and Priesty (1973) was used for determination of the DG. The method was based on the monitoring of the complexation of iodine with amylose released due to starch gelatinization. The results reported are the mean of five measurements for each extrudate sample. Water solubility index and water absorption index of both unprocessed quinoa and extrudate samples were determined by the method of Anderson et al. (1969) with

Figure 1. Schematic diagram showing the barrel of extruder and various energy flows.


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some modifications. WSI was calculated as follows:

WSI ¼

g water soluble matter g dry sample

ð5Þ

For the calculation of WAI the total solids in the original sample were corrected for the loss of solubles in the supernatant and WAI was expressed as, WAI ¼

g water absorbed g dry sample ð1 soluble fractionÞ

ð6Þ

Product density (e) was measured by volumetric displacement method as described by Hiçs as maz and Clayton (1993). Glass beads of 0.5 mm diameter (Biospec Products, Inc., Bartlesville, OK) were used as displacement medium. Density of glass beads was determined as 1550 kg/m3, then the density of extrudates was calculated as

e ¼

We gb Wgb

M.V. KARWE

for dark and 100 for bright, a represents the extent of green colour in the range from 100 to 0 and red in the range 0 to 100, b quantifies blue colour in the range from 100 to 0 and yellow in the range from 0 to 100. The total colour change (E ) was then calculated as

E ¼

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ðLÞ2 þðaÞ2 þðbÞ2

ð8Þ

where L ¼ L – L0, ia ¼ a – a0, and b ¼ b – b0; the subscript ‘‘0’’ indicates initial colour values before processing. Analysis of Data Process responses (SME, SED, STE, SME/SED) and product responses (iE, e, WAI, WSI, DG, SEI, LEI, VEI, hardness and breaking strength) obtained as a result of the proposed experimental design were subjected to regression analysis in order to assess the effects of feed moisture content, extrusion temperature and screw speed. Second-order polynomials of the form

ð7Þ yi ¼ b0 þ

The e values were obtained from five random samples for each extrusion condition, with three replications. The sectional expansion index (SEI) of extrudate was measured as the ratio of the diameter of the extrudate to that of the die. The extrudate diameter was measured with a digital Vernier caliper and the results were expressed as the average of hundred measurements on each condition. The longitudinal (LEI) and volumetric expansion (VEI) indices were calculated according to Alvarez-Martinez et al. (1988). Textural properties of extrudates were measured using TA-XT2 texture analyser (Stable Micro Systems, UK). A three-point bend rig with a support length (bridge) of 30 mm and a rounded plate probe (15 mm 5 mm, D ¼ 5 mm) exerting force in the middle of bridge were used to test extrudates in the bend mode (Zasypkin and Lee, 1998). The test speed was 2 mm/s and the full load scale was 50 kg. Data were processed with an XT-RA Dimension software package (Stable Micro Systems, Haslemere, Surrey, UK). The hardness of dry extrudates was measured as the peak force offered by the sample during cutting. Breaking strength (N/mm2) was calculated as the peak breaking force (N) divided by the cross-sectional area (mm2) calculated for each extrudate sample. The reported values are the averages of 15 measurements. The color of ground unprocessed quinoa and extrudate samples was measured in triplicate using Minolta Chroma Meter (CR-210) in terms of Hunter Lab values (L, a, b), where L represents lightness with 0

3 X

bi Xi þ

i¼1

3 X 3 X

bij Xi Xj

ð9Þ

i¼1 j¼i

were fitted to the independent variables and were computed by using SAS (version 8.1) statistical package, where Xi, XiXi and XiXj are linear, quadratic, and interaction effect of the input variables which influence the response y, respectively, and b0, bi, and bij are the model constants to be determined. All crosscorrelations between the process and product responses themselves were also assessed. The response surface plots for these models were plotted as a function of two variables, while keeping the third variable constant at its intermediate value.

RESULTS AND DISCUSSION Composition of grain could vary with variety and growing conditions, even though experimental results for composition (Table 3) agreed with previous data (Becker and Hanners, 1990; Coulter and Lorenz, 1990; GuzmanMaldano and Paredes-Lopez, 1998; Koziol, 1992; Prakash et al., 1993; Ruales and Nair, 1993). The quinoa seeds used in this study have high crude protein, crude fat and ash than common cereals, such as rice and corn. Extrudates of widely different physical structure were obtained by twin-screw extrusion of quinoa flour at different combinations ofprocessing parameters (Table 2). Regression analyses of the physicochemical properties of quinoa extrudates (Table 4) indicated that all the second


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Quinoa Extrudates

Table 3. Proximate composition and some properties of unprocessed quinoa flour. Quinoa Flour Characteristics Proximate composition (g/100 g) Moisture Protein Lipid Ash CHO þ fiber Colour L a b Water absorption index (g H2O/g dry sample) Water solubility index (g water soluble matter/g dry sample) Amylose content (%)

Mean ± SD (n ¼ 3) 10.96 ± 0.06 11.95 ± 0.12 7.19 ± 0.02 2.15 ± 0.02 67.75 87.27 ± 0.30 0.48 ± 0.03 11.94 ± 0.41 1.69 ± 0.11 0.073 ± 0.003 11.1 ± 0.04

order polynomial models correlated well with the measured data and were statistically significant ( p < 0.05). Process Responses Calculated SME values ranged between 170 and 402 kJ/kg. The regression analysis results (Table 4) revealed that temperature (T ), feed moisture content (M ) and screw speed (S ) had linear and significant ( p

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