Propiedades Fisico Quimicas Quinoa

8/12/2019 Propiedades Fisico Quimicas Quinoa

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Food Science and Technology International

DOI: 10.1177/1082013203009002006

2003; 9; 101Food Science and Technology InternationalH. Dogan and M. V. Karwe

Physicochemical Properties of Quinoa Extrudates

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Physicochemical Properties of Quinoa Extrudates

H. Dog an1 andM.V. Karwe2,*

1TUBITAK Marmara Research Center, Food Science and Technology Research Institute,P.O. Box 21, Gebze/Kocaeli, 41470, Turkey

2Food 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 1624% feed moisture content,

130170C temperature, and 250500 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 poten-

tially 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 athigh 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 worlds 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 andrice generally have less than half the protein content of

quinoa. In addition, quinoa is a relatively good source

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; Przybylsk

et al., 1994) which make it a unique food source.

The Aztecs and Incas credited quinoa with medicina

properties including lowering blood cholesterol, improv-

ing 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 (Guzman

Maldonado 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 havebeen 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 o

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-ea

*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):010114 2003Sage PublicationsISSN: 1082-0132DOI: 10.1177/108201303033940

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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 1525% feed moisture

content, 100150C, 100200 rpm screw speed, and at1 : 1 and 3 : 1 compression ratios on a Brabender

Plasticorder single-screw extruder. Although the pro-

ducts 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 103C (method no. 4415A).

Ash: calcination at 550C (method no. 0801)

Lipids: defatting in a soxhlet apparatus with petro-

leum ether (method no. 3010)

Protein: micro Kjeldahl (N 6.25) (method no. 4613)

CHOfiber: 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 twin-

screw 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 878mm processing length;

L/D 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 trans-

ducer (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 massflow rates of quinoa flour and water, respectively.

Throughput or the total mass flow rate (flour 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 120C, 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

(84mm)

Zone I

(196mm)

Zone II

(210mm)

Zone III

(178mm)

Zone IV

(98mm)

Zone V

(84mm)

Die zone

(28mm)SK 42/42 42/21 T 28/28 28/14 20/10 KB 45/5/14 14/14

SK 42/42 42/42 28/28 KB 45/5/14 20/10 KB 45/5/14 LH 14/14

42/42 IGEL 42 20/20 KB 45/5/20 14/14

42/21 28/28 20/20 20/10 LH 14/14

IGEL 42 28/28 20/20 20/10 14/14

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

28/14 20/20 14/14

28/14 KB 45/5/20 14/14

20/10 LH

20/10

20/10

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

102 H. DOGAN AND M.V. KARWE

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Experimental Design

Response surface methodology was used to investi-

gate the effects of extrusion conditions on the product

and process responses of quinoa. Results from pre-

liminary trials were used to select suitable extruder

operating window. The independent variables con-

sidered in this study were feed moisture content(1624% w.b.), die temperature (130170C), and

screw speed (250500 rpm). A three-variable, three-

level, 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(5C) until analysis.

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 kJ=kg

Total torque (%) Friction torque (%) N 9:1

100 500mf

1

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 conditionscomputed from the following equations,

mfCpiTi QH QC ME mfCpo Tp 2

QH QC

mf

ME

mf Cpo Tp CpiTi 3

SME and SED were measured from experimenta

conditions and STE was calculated from Equation (4).

STE SME SED 4

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 45% moisture. Dried samples wereground and passed through 28-mesh sieve (590mm

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

Table 2. Experimental design for extrusion of quinoa.

Coded Levels Actual Levels

X1 X2 X3 M(% wb) T(C) S (rpm)

1 1 0 24 170 375

1 1 0 24 130 375

1 1 0 16 170 375

1 1 0 16 130 375

0 1 1 20 170 500

0 1 1 20 170 250

0 1 1 20 130 500

0 1 1 20 130 250

1 0 1 24 150 500

1 0 1 24 150 250

1 0 1 16 150 500

1 0 1 16 150 250

0 0 0 20 150 375

0 0 0 20 150 375

0 0 0 20 150 375Figure 1. Schematic diagram showing the barrel oextruder and various energy flows.

Quinoa Extrudates 103



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some modifications. WSI was calculated as follows:

WSI g water soluble matter

g dry sample 5

For the calculation of WAI the total solids in the

original sample were corrected for the loss of solubles inthe supernatant and WAI was expressed as,

WAI g water absorbed

g dry sample 1 soluble fraction 6

Product density (e) was measured by volumetric

displacement method as described by Hicsasmaz 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 We

Wgbgb 7

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

30mm and a rounded plate probe (15 mm 5mm,

D 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 calcu-

lated 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

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

Effiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffiffiL 2 a 2 b 2

q 8

where L LL0, ia aa0, and b bb0; 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 theeffects of feed moisture content, extrusion temperature

and screw speed. Second-order polynomials of the form

yi b0 X3i1

biXi X3i1

X3ji

bijXiXj 9

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 themodel 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 forcomposition (Table 3) agreed with previous data (Becker

and Hanners, 1990; Coulter and Lorenz, 1990; Guzman-

Maldano 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

differentcombinations ofprocessingparameters (Table2).

Regression analyses of the physicochemical properties of

quinoa extrudates (Table 4) indicated that all the second




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order polynomial models correlated well with the mea-

sured 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


7/15

Table 4. Results of regression analysis (calculated on coded levels where all independent variables a

Levels

Degree of

Geltn

Density

(kg/m3)

Sectional

Expansion

Index

Longitudinal

Expansion

Index

Volumetric

Expansion

Index

Water

Solubility

Index

(g/g)

Water

Absorption

Index

(g/g) iE

Hardness

(N)

Breaking

Strength

(N/mm2)

Spe

Mecha

Ene

(kJ/

C 0.781*** 246.7*** 2.75*** 0.630** 4.78*** 0.202*** 6.03*** 21.35*** 3.62*** 0.068*** 258.

M 0.046*** 88.1*** 0.43*** 0.090ns 1.67*** 0.025*** 0.57*** 1.88*** 0.19ns 0.041*** 37.9

T 0.058*** 30.4*** 0.73*** 0.650*** 0.99** 0.017*** 0.14** 0.84** 1.04*** 0.028*** 59.3

S 0.034*** 38.0*** 0.15* 0.010ns 0.61ns 0.021*** 0.20*** 0.53ns 0.17ns 0.016** 51.

M M 0.033** 57.9*** 0.24** 0.296ns 0.33ns 0.026*** 0.33*** 1.49** 0.46* 0.017* 15.6

T T 0.037*** 34.6** 0.39*** 0.711** 0.96ns 0.031*** 0.15* 2.67*** 0.62** 0.021** 23.

S S 0.041*** 38.2** 0.04ns

0.364ns

0.77ns

0.009** 0.19** 0.25ns

0.34ns

0.001ns

9.M T 0.015ns 4.0ns 0.17ns 0.218ns 0.92ns 0.002ns 0.53*** 0.10ns 0.07ns 0.017* 11.

M S 0.015ns 18.8ns 0.10ns 0.038ns 0.05ns 0.003ns 0.02ns 0.76ns 0.32ns 0.006ns 9.

T S 0.009ns 26.8** 0.02ns 0.098ns 0.66ns 0.011** 0.06ns 0.10ns 0.15ns 0.004ns 7.

R2 0.98 0.98 0.98 0.90 0.89 0.99 0.98 0.96 0.94 0.97 0.

F 28.28 28.68 24.65 5.25 4.59 102.6 27.13 13.97 9.48 16.14 21.

Sig. F 0.001 0.001 0.001 0.041 0.052 0.000 0.001 0.005 0.012 0.003 0.

C: model constant; M , Tand S: linear effects of moisture content, die temperature and screw speed, respectively. M M, T Tand S S: quadratic effects of moistrespectively;.M T, M S and T S: interaction effects of moisture content and die temperature, moisture content and screw speed, and die temperature and screw**significant at p


8/15

(T), screw speed (S) and moisture (M), and the

quadratic effects of screw speed (S S) and tempera-

ture (T T) had the highest impact, significant at

p


9/15

In general, low feed moisture and high product

temperature have been found to increase the DG in

extrusion of starchy materials (Bhattacharya and

Hanna, 1987; Cai and Diosady, 1993). However, in the

presence of lipids, extrusion temperature required for

maximum DG was in the intermediate range. Lower

temperatures compensated for the decrease in melt

viscosity due to lipids (Dog an, 2000). In high lipidcontaining cereals like quinoa, excessive feed moisture

acts as a secondary lubricant which prevents the

achievement of appropriate development or cooking of

dough by shear induced disruption. In this study, DG

was found to be highly correlated (0.81, p


10/15

decreased with increasing temperature (Figure 5), which

can be explained by the negative effect of temperature

on the elasticity of extrusion cooked melts (Launay and

Lisch, 1983). This result is in agreement also with the

work of Ilo et al. (1999). On the other hand, longitudinal

expansion appeared to be extensively favored by lower

melt viscosity at higher temperature and higher moisture

level (Figure 6).Volumetric expansion index, the multiplication pro-

duct of SEI and LEI, was affected only by feed moisture

content (p


11/15

giving a minimum value at about 140C die tempera-

ture, 19.1% feed moisture, and 425 rpm screw speed.

The mechanical properties of extruded products can

be described either by compressive deformation or by

breaking strength (Colonna et al., 1989). Breaking

strength is the measure of the strength of cell wall

which is expected to affect the texture and sensory

crispiness of the extruded product (Chen et al., 1991).Breaking strength was found to be highly correlated

with SEI (0.85,p


12/15

feed moisture content due to the fact that high thermal

and mechanical energy inputs favour starch dextriniza-

tion (Figure 9). Low WSI values were observed at

intermediate to low temperature levels at all processing

conditions. The increase in WSI with increasing

temperature was consistent with the results reported

for oat extrudates (Singh and Smith, 1997). The

WSI decreased with the increase in moisture. Similareffects of decreasing moisture on WSI have been

reported earlier for starch, maize grits, wheat and pea

flour (Della Valle et al., 1994; Kirby et al., 1988).

Minimum WSI of 0.186 g/g was achieved at 18.3% feed

moisture content, 140C die temperature, and 192 rpm

screw speed.

The poor correlation between WSI and most of the

process and product responses (Table 5) may be

explained by the fact that WSI includes the opposing

effects of starch dextrinization and the molecular level

interactions between degraded components, which may

not be favoured at the same condition. An increase in

the amount of dextrinized starch during extrusion

cooking results in an increase in WSI. However

molecular interactions between degraded starch, pro

tein, and lipid components, which in turn lead to anincrease in molecular weight, may decrease the solubi-

lity, thus WSI. Moreover, according to the mode

proposed by Gomez and Aguilera (1984) for starch

degradation during extrusion cooking, three pure states

i.e., raw, gelatinized, and dextrinized, of starch exis

together. Due to different states in which starch is found

in extrudates, some granules may be underprocessed

while some others may be overprocessed or dextrinized

According to the same model, dextrinization can be

considered to take place together with or right after

adequate gelatinization. According to our experimental

results, thermal and mechanical input seemed to be

enough for sufficient starch gelatinization but not severeenough to favour starch dextrinization. SME values

were not high enough to cause dextrinization, which in

turn increases WSI. This is also evident by the high

correlation coefficient between SME and DG (0.81

p 0.10).

Water absorption index depends on the availability of

hydrophilic groups and on the gel formation capacity of

the macromolecules (Gomez and Aguilera, 1983). It is a

measure of damaged starch together with protein

denaturation and new macromolecular complex forma-

tions. WAI of extrudates ranged between 4.45 and

6.72 g/g which was significantly higher than that o

(1.69g/g) unprocessed quinoa. The regression analysis

(Table 4) showed that the linear effect of feed moisture

content (M), and the interaction effect of die tempera-

ture and moisture content (T M) were highly sig

nificant on WAI. Singh and Smith (1997) reported an

increase in WAI with the increase in moisture and

temperature during extrusion of oats, which is in

agreement with our experimental results (Figure 10)

WAI had poor correlations with almost all process and

product responses except product density (Table 5). This

is an expected result since it includes the effect of starch

gelatinization, protein denaturation and molecular levelcrosslinking reactions which are not always favoured at

the same conditions.

Colour

Colour is an important quality parameter since i

reflects the extent of chemical reactions and degree of

cooking or degradation that take place during extrusion

cooking. In this study, E represents the total colour

difference compared to the colour of unprocessed

quinoa. Higher E means darker products with more

Figure 9. Effect of feed moisture content, die tem-perature and screw speed on water solubility index(WSI, g soluble matter/g dry sample).




13/15

intense yellow and red colour. The total colour change

in extruded products ranged between 15.5 and 23.7

(Table 4). Quadratic effect of temperature (T T) and

the linear effect of feed moisture content (M) were

found to have the highest contribution to total colour

change. Low feed moisture content and high tempera-

ture increased the total colour change possibly due toincreased extent of browning reactions under this

condition (Figure 11). Although, the screw speed was

not a significant parameter (Table 4), at low screw

speeds a slight increase in colour change observed due to

longer residence times which might increase the extent of

chemical reactions.

In summary, because the high lipid and low amylose

contents, extrusion cooking of quinoa required proces-

sing conditions that provide high shear environ-

ment indicated by high SME values which disrupts

starch granules. Extrusion cooking conditions that

produced quinoa products with desirable expansion

characteristics were at low moisture, low temperature

and medium screw speed within the range of our process

variables.

NOMENCLATURE

Cp heat capacity (kJ/kg.K)

LEI longitudinal expansion index (dimensionless)

ME rate of mechanical energy input (dissipa-

tion) (W)

mf total mass flow rate (kg/s)

N screw speed (rpm)

QC rate of energy removal by the cooling sys-

tem (W)

QH rate of heat generation (W)

SED specific energy delivered (kJ/kg)

SEI sectional expansion index (dimensionless)

Figure 10. Effect of feed moisture content, dietemperature and screw speed on water absorptionindex (WAI, g H2O/g dry sample).

Figure 11. Effect of feed moisture content, die

temperature and screw speed on total color change(E).




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SME specific mechanical energy (kJ/kg)

STE specific thermal energy (kJ/kg)

Ti inlet temperature of the product (C)

To outlet temperature of the product (C)

Td die temperature or product temperature (C)

VEI volumetric expansion index (dimensionless)

WAI water absorption index (g water absorbed/g dry

sample)We weight of extrudate (kg)

Wgb weight of glass beads displaced by the extru-

dates (kg)

WSI water solubility index (g water soluble matter/g

dry sample)

E total colour change

e density of extrudate (kg/m3)

gb density of glass beads (kg/m3)

ACKNOWLEDGEMENTS

This is publication No. D 01544-01-01 of the NewJersey Agricultural Experiment Station supported by

State funds and the Center for Advanced Food

Technology (CAFT). The Center for Advanced Food

Technology is a New Jersey Commission on Science

and Technology Center. Author H. Dog an acknowl-

edges the financial support from TUBITAK Marmara

Research Center, Food Science and Technology Res-

earch Institute, Turkey.

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