Effect of sprouting conditions on functional and dynamic rheological properties of wheat

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Eect of sprouting conditions on functional and dynamic rheological properties of wheat Hardeep Singh a , Narpinder Singh a, * , Lakhwinder Kaur a , S.K. Saxena b a Department of Food Science and Technology, Guru Nanak Dev University, Amritsar, Punjab 143005, India b Food Research and Analysis Center, New Delhi, India Received 15 October 1999; accepted 30 May 2000 Abstract Studies were undertaken to see the eect of sprouting conditions (soaking duration, sprouting temperature and sprouting du- ration) on functional and dynamic rheological properties of wheat. Falling number and water absorption index (WAI) decreased and water solubility index (WSI) increased with the increase in sprouting. The cultivar PBW-343 showed the greatest changes in these parameters while PDW-233 showed the least under similar sprouting conditions. The elastic modulus (G 0 ) decreased with the increase in soaking and sprouting duration, however, the sprouting duration showed a greater eect. The viscous modulus (G") showed an increase with increase in soaking duration and a decrease with the increase in sprouting duration. The tan d value im- proved with the soaking and sprouting of wheat. Ó 2000 Elsevier Science Ltd. All rights reserved. Keywords: Sprouting; Falling number; Water solubility; Water absorption; Rheology 1. Introduction Untimely rains during harvesting of wheat lead to sprouting of grain and bring about an increase in en- zymatic activity along with several other chemical changes in the grain. The extent of these changes de- pends upon a number of factors such as soaking dura- tion, temperature, variety and sprouting duration, etc. The degree of sprouting had an important bearing on the eective utilization of wheat in dierent products. The starch in wheat grain during sprouting gradually degraded and the values for free sugars increased, as this progressive process was due to the activity of amylase (Lorenz, 1980). The extent of starch degradation de- pends upon the length of sprouting time. The adverse eect of sprouting on bread, cake, noodles and spaghetti making properties of wheat have been extensively studied (Finney, Natsuaki, Bolte, Mathewson, & Pom- eranz, 1981; Edwards, Ross, Mares, Ellison, & Tom- linson, 1989; Sekhon, Singh, & Nagi, 1992; Sekhon, Singh, Kaur, & Nagi, 1995). The sprouting has been reported to adversely aect the rheological properties measured using Farinograph and Visco-amylograph (Singh, Sekhon, & Nagi, 1987; Sekhon et al., 1992; Singh, Singh, & Kaur, 1998). The present study was undertaken to get compre- hensive information on the eect of sprouting conditions on the functional and dynamic rheological properties of wheat. 2. Material and methods 2.1. Preparation of samples Two bread wheat cultivars PBW-343, PBW-373 and one durum wheat cultivar PDW-233 were obtained from Punjab Agricultural University, Ludhiana from 1998 harvest. Wheat (2 kg) was soaked in water (10 l) for 2, 6 and 10 h at 20°C. The excess water was drained o and superficial water present on the grains was removed with filter paper. The soaked samples were sprouted for 12 and 24 h at 20°C, 30°C and 40°C in a temperature controlled incubator. Wheat samples after sprouting were immediately dried to 14% moisture in a hot air cabinet drier at 40°C. Wheat samples were ground to pass through 50 mesh sieve in a Hammer mill. The milled samples were sealed in polyethylene bags and kept in a refrigerator at 5°C for further use. Journal of Food Engineering 47 (2001) 23–29 www.elsevier.com/locate/jfoodeng * Corresponding author. Tel.: +91-258802; fax: +91-183-258820. E-mail address: [email protected] (N. Singh). 0260-8774/00/$ - see front matter Ó 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 0 - 8 7 7 4 ( 0 0 ) 0 0 0 9 4 - 7

Transcript of Effect of sprouting conditions on functional and dynamic rheological properties of wheat

Page 1: Effect of sprouting conditions on functional and dynamic rheological properties of wheat

E�ect of sprouting conditions on functional and dynamic rheologicalproperties of wheat

Hardeep Singh a, Narpinder Singh a,*, Lakhwinder Kaur a, S.K. Saxena b

a Department of Food Science and Technology, Guru Nanak Dev University, Amritsar, Punjab 143005, Indiab Food Research and Analysis Center, New Delhi, India

Received 15 October 1999; accepted 30 May 2000

Abstract

Studies were undertaken to see the e�ect of sprouting conditions (soaking duration, sprouting temperature and sprouting du-

ration) on functional and dynamic rheological properties of wheat. Falling number and water absorption index (WAI) decreased

and water solubility index (WSI) increased with the increase in sprouting. The cultivar PBW-343 showed the greatest changes in

these parameters while PDW-233 showed the least under similar sprouting conditions. The elastic modulus (G0) decreased with the

increase in soaking and sprouting duration, however, the sprouting duration showed a greater e�ect. The viscous modulus (G")showed an increase with increase in soaking duration and a decrease with the increase in sprouting duration. The tan d value im-

proved with the soaking and sprouting of wheat. Ó 2000 Elsevier Science Ltd. All rights reserved.

Keywords: Sprouting; Falling number; Water solubility; Water absorption; Rheology

1. Introduction

Untimely rains during harvesting of wheat lead tosprouting of grain and bring about an increase in en-zymatic activity along with several other chemicalchanges in the grain. The extent of these changes de-pends upon a number of factors such as soaking dura-tion, temperature, variety and sprouting duration, etc.The degree of sprouting had an important bearing onthe e�ective utilization of wheat in di�erent products.The starch in wheat grain during sprouting graduallydegraded and the values for free sugars increased, as thisprogressive process was due to the activity of amylase(Lorenz, 1980). The extent of starch degradation de-pends upon the length of sprouting time. The adversee�ect of sprouting on bread, cake, noodles and spaghettimaking properties of wheat have been extensivelystudied (Finney, Natsuaki, Bolte, Mathewson, & Pom-eranz, 1981; Edwards, Ross, Mares, Ellison, & Tom-linson, 1989; Sekhon, Singh, & Nagi, 1992; Sekhon,Singh, Kaur, & Nagi, 1995). The sprouting has beenreported to adversely a�ect the rheological propertiesmeasured using Farinograph and Visco-amylograph

(Singh, Sekhon, & Nagi, 1987; Sekhon et al., 1992;Singh, Singh, & Kaur, 1998).

The present study was undertaken to get compre-hensive information on the e�ect of sprouting conditionson the functional and dynamic rheological properties ofwheat.

2. Material and methods

2.1. Preparation of samples

Two bread wheat cultivars PBW-343, PBW-373 andone durum wheat cultivar PDW-233 were obtained fromPunjab Agricultural University, Ludhiana from 1998harvest. Wheat (2 kg) was soaked in water (10 l) for 2, 6and 10 h at 20°C. The excess water was drained o� andsuper®cial water present on the grains was removed with®lter paper. The soaked samples were sprouted for 12and 24 h at 20°C, 30°C and 40°C in a temperaturecontrolled incubator. Wheat samples after sproutingwere immediately dried to 14% moisture in a hot aircabinet drier at 40°C. Wheat samples were ground topass through 50 mesh sieve in a Hammer mill. Themilled samples were sealed in polyethylene bags andkept in a refrigerator at 5°C for further use.

Journal of Food Engineering 47 (2001) 23±29

www.elsevier.com/locate/jfoodeng

* Corresponding author. Tel.: +91-258802; fax: +91-183-258820.

E-mail address: [email protected] (N. Singh).

0260-8774/00/$ - see front matter Ó 2000 Elsevier Science Ltd. All rights reserved.

PII: S 0 2 6 0 - 8 7 7 4 ( 0 0 ) 0 0 0 9 4 - 7

Page 2: Effect of sprouting conditions on functional and dynamic rheological properties of wheat

2.2. Analysis

WSI and WAI were measured as described earlier byAnderson, Conway, Pfei�er, and Gri�n (1969). Fallingnumber value of meal samples was determined withfalling number apparatus (Perten, Sweden) using AACCmethod (1995).

2.3. Preparation of dough

Wheat meal samples (5 g) were mixed with 3.2 ml ofdistilled water in a 100 ml beaker with the help of aspatula into a smooth dough and rested for 3 min beforeplacing between cone and plate.

2.4. Rheological properties

Rheological measurements of samples milled fromPBW-343 variety soaked for 2, 6 and 8 h and sproutedfor 0, 12 and 24 h at 30°C were performed with a Carri-Med CSL rheometer (TA Instrument, Surrey, England)equipped with 4 cm 1.59° steel cone geometry. Thedough was placed between the cone and the plate andthe minimum gap was adjusted to 1 mm. The excessdough was trimmed with a small knife and the edgeswere coated with lubrication grease to reduce the loss ofwater from the dough. The instrument was set at 20°C.Rheological properties such as elastic modulus (G0) andviscous modulus (G") were measured at 1% strain andfrequency of 0±250 rad/s.

2.5. Statistical analysis

The second-order polynomials were computed byregression analysis using Minitab Statistical software(Minitab, USA). Soaking duration, sprouting tempera-ture and duration were used as independent variables.These variables had values of X1 (soaking duration), 2, 6and 10; X2 (sprouting temperature), 20°C, 30°C and40°C and X3 (sprouting duration) 0, 12 and 24 h. All theobservations of 27 experiments were included in thedesign. The data for all the parameters were the averageof three replications. The polynomials were ®tted tomeasure dependent variables (y1) such as falling num-ber, WSI and WAI. The equation used was as follows:

yi � B0 �X3

i�1

Bi Xi �X3

i�1

X3

j�1

BijXi Xj:

3. Results and discussion

3.1. WSI

WSI increased with the increase in soaking andsprouting duration in all wheat cultivars. WSI increased

with the increase in sprouting temperature upto 30°Cand further increase in sprouting temperature to 40°Ccaused a decrease in WSI in all cultivars (Figs. 1±3). Theregression analysis in Table 1 revealed that sproutingtemperature had the most pronounced e�ect on WSI ofwheat followed by soaking and sprouting duration. Allthese factors showed signi®cant e�ect on WSI of wheatboth in linear and squared terms, however, soaking andsprouting durations showed signi®cant e�ect at slightlyhigher P value. Sprouting duration and temperatureinteracted signi®cantly in a�ecting WSI. The increase in

Fig. 1. Contour response surface plot showing the e�ect of soaking

duration and sprouting temperature on WSI (%) of PBW-343 after 12 h

of sprouting.

Fig. 2. Contour response surface plot showing the e�ect of soaking

duration and sprouting temperature on WSI (%) of PBW-373 after 12 h

of sprouting.

Fig. 3. Contour response surface plot showing the e�ect of soaking

duration and sprouting temperature on WSI (%) of PDW-233 after

12 h of sprouting.

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WSI with the increase in soaking and sprouting dura-tions may be attributed to an increase in amylolytic andproteolytic activity (Kulp, Roewe-Smith, & Lorenz,1983; Singh et al., 1987; Sekhon et al., 1992). The e�ectof sprouting duration on WSI was observed to be de-pendent on soaking duration (Figs. 4±6). Highest WSIwas observed in samples sprouted at 30°C which may beattributed to their highest amylase activity as indicatedby lowest falling number value. Soaking for 2, 6 and10 h and subsequent sprouting for 24 h at 30°C resultedin WSI of 11.05%, 12.95% and 13.87%, respectively, inPBW-343 and 7.4%, 8.7% and 10.2%, respectively, inPBW-373 in contrast with WSI of 6.95%, 7.25% and7.90%, respectively, in PDW-255 under similar condi-tions of sprouting. PBW-343 wheat cultivar showedgreatest change in WSI and PDW-233 wheat cultivarshowed the least change under similar sprouting condi-tions. This may be attributed to higher a-amylase

activity in PBW-343 as indicated by lower falling num-ber value as compared to PDW-233 (Figs. 12 and 13).

3.2. WAI

Figs. 7±10 illustrate the e�ect of soaking duration,sprouting temperature and sprouting duration on WAIof wheat. Among sprouting temperature, soaking du-ration and sprouting duration, the regression analysis inTable 2 revealed that sprouting temperature had themost pronounced e�ect followed by sprouting durationand soaking duration. Sprouting temperature and du-ration showed signi®cant e�ect on WAI both in linearand squared terms. However, soaking duration showedsigni®cant e�ect in linear term only. Sprouting andsoaking duration interaction e�ect on WAI was alsohighly signi®cant (Figs. 7 and 8). WAI decreased withthe increase in soaking duration. WAI decreased withthe increase in sprouting temperature upto 30°C andfurther increase caused an increase in WAI (Figs. 9 and10). An increase in sprouting temperature also caused adecrease in WAI. PDW-233 showed higher WAI ascompared to PBW-373 and PBW-343 under similarsprouting conditions. WAI of PDW-233, PBW-373 andPBW-343 wheat sprouted for 24 h at 30°C after soaking

Fig. 4. Contour response surface plot showing the e�ect of sprouting

duration and soaking duration on WSI (%) of PBW-343 after

sprouting at 30°C.

Fig. 5. Contour response surface plot showing the e�ect of sprouting

duration and soaking duration on WSI (%) of PBW-373 after

sprouting at 30°C.

Fig. 6. Contour response surface plot showing the e�ect of sprouting

duration and soaking duration on WSI (%) of PDW-233 after

sprouting at 30°C.

Table 1

Coe�cients of regression models for WSIa

Term PBW-343 PBW-373 PDW-233

Constant 3.07116 3.36427 4.82329

X1 0.40132b 0.01427 0.00979

X2 0.37854c 0.23483b 0.09607b

X3 )0.07074d )0.06993d )0.05574c

X1 ´ X1 )0.01660d )0.00286 0.00056

X2 ´ X2 )0.00641c )0.00414b )0.00169b

X3 ´ X3 0.00379b 0.00221 0.0026c

X1 ´ X2 0.00056 0.00184 0.00073

X1 ´ X3 0.00163 0.00519b 0.00139d

X2 ´ X3 0.00133d 0.00120d 0.00057d

Model P

value

0.00 0.000 0.000

R2 92.4% 86.6% 94.7%

a X1�Soaking duration, X2�Sprouting temperature, X3� Sprouting

duration.b P < 0.02.c P < 0.002.d P < 0.2.

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for 10 h was 2.07%, 1.90% and 1.95%, respectively. Thedecrease in WAI with the increase in soaking andsprouting duration may be attributed to decrease indamaged starch content. A decrease in damaged starchcontent with sprouting of wheat has been reported ear-lier (Willm, 1977; Singh et al., 1987).

3.3. Falling number

Falling number value is used to evaluate a-amylaseactivity in cereal ¯ours. Falling number value, which is

more or less varietal characteristic, was commensuratewith the extent of sprouting. A comparison between thee�ect of soaking duration, sprouting temperature andsprouting duration on falling number revealed sproutingtemperature as the most prominent factor (Table 3). Inall wheat cultivars falling number decreased with theincrease in soaking and sprouting duration. The fallingnumber values corroborate the WSI results. The sampleswith lower falling number value showed higher WSI andvice versa. The decrease in falling number value duringsprouting provides an indication of degradation ofstarch and/or an increase in enzyme activity (Lorenz &Valvano, 1981). An increase in sprouting temperaturefrom 20°C to 30°C also caused a decrease in fallingnumber and further increase in sprouting temperature to40°C resulted in an increase in falling number value(Figs. 11±13). These changes may be attributed to thevariation in the extent of sprouting at di�erent temper-atures. The optimum temperature for sprouting ofwheat has been reported to fall between 20°C and 30°C

Fig. 8. Contour response surface plot showing the e�ect of sprouting

duration and soaking duration on WAI of PDW-233 after sprouting at

30°C.

Fig. 7. Contour response surface plot showing the e�ect of sprouting

duration and soaking duration on WAI of PBW-373 after sprouting at

30°C.

Fig. 10. Contour response surface plot showing the e�ect of sprouting

temperature and soaking duration on WAI of PDW-233 after

sprouting at 30°C.

Fig. 9. Contour response surface plot showing the e�ect of sprouting

temperature and soaking duration on WAI of PBW-373 after

sprouting at 30°C.

Table 2

Coe�cients of regression models for WAIa

Term PBW-343 PBW-373 PDW-233

Constant 2.4196 2.53651 2.86789

X1 )0.0144b 0.01548b )0.00982

X2 )0.0227c )0.02371d )0.02542d

X3 )0.0069b 0.00141 )0.00261

X1 ´ X1 )0.00017 )0.00173b )0.00046

X2 ´ X2 0.00038c 0.00041d 0.00041d

X3 ´ X3 0.00012b )0.00021c )0.00023c

X1 ´ X2 )0.00009 )0.00011 0.00005

X1 ´ X3 0.00064d )0.00012 )0.00013

X2 ´ X3 )0.00003 )0.00011b )0.00005

Model P

value

0.000 0.000 0.000

R2 83.4% 94.5% 97.1%

a X1�Soaking duration, X2�Sprouting temperature, X3�Sprouting

duration.b P < 0.2.c P < 0.02.d P < 0.002.

26 H. Singh et al. / Journal of Food Engineering 47 (2001) 23±29

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(Lorenz, 1980). Sprouting temperature showed highlysigni®cant e�ect both in linear and squared terms onfalling number, while soaking and sprouting durationsalso showed signi®cant e�ect, however, at higher P

value. Sprouting and soaking durations interacted sig-ni®cantly in a�ecting the falling number value of wheat.PDW-223 showed higher falling number value as com-pared to PBW-373 and PBW-343 under similar sprout-ing conditions. A good correlation between fallingnumber and amylase activity has been reported earlier(Derrick & Every, 1990).

3.4. Rheological properties

The e�ect of soaking and sprouting of PBW-343wheat at 30°C on the dynamic rheological properties ofdough was studied. The G0 and G" of dough from wheatsoaked and sprouted under di�erent conditions in-creased with the frequency of oscillation. The rheologi-cal properties of dough were measured with the increasein frequency of oscillation at 1% strain. Figs. 14±16 il-lustrate the dynamic rheological properties of doughprepared from sound and sprouted wheat. Dough

Fig. 14. E�ect of soaking duration and sprouting duration on elastic

modulus G0.

Table 3

Coe�cients of regression models for falling number valuea

Term PBW-343 PBW-373 PDW-233

Constant 1189.16 738.24 819.38

X1 )22.75 )19.89b )6.74

X2 )51.26c )15.56d )25.67d

X3 4.49 )11.58d 5.19b

X1 ´ X1 1.38 0.72 )0.08

X2 ´ X2 0.85c 0.24b 0.42d

X3 ´ X3 )0.48d )0.12 )0.32d

X1 ´ X2 0.04 0.06 0.15

X1 ´ X3 )0.44b 0.10 0.44b

X2 ´ X3 )0.07 )0.04 )0.20d

Model P

value

0.000 0.00 0.00

R2 90.7 97 95.5

a X1�Soaking duration, X2�Sprouting temperature, X3� Sprouting

duration.b P < 0.2.c P < 0.002.d P < 0.02.

Fig. 12. Contour response surface plot showing the e�ect of sprouting

temperature and soaking duration on falling number value(s) of

PBW-373 after sprouting for 12 h.

Fig. 13. Contour response surface plot showing the e�ect of sprouting

temperature and soaking duration on falling number value(s) of

PDW-233 after sprouting for 12 h.

Fig. 11. Contour response surface plot showing the e�ect of sprouting

temperature and soaking duration on falling number value(s) of

PBW-343 after sprouting for 12 h.

H. Singh et al. / Journal of Food Engineering 47 (2001) 23±29 27

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prepared from sprouted wheat showed lower G0 and G"as compared to sound wheat. This shows that the elas-ticity (strength) of dough decreased with sproutingwhich may be due to increase in proteolytic activityduring sprouting. Miller and Hoseney (1999) reportedthat the dough from stronger wheat ¯our has higher G0

than those from weaker wheat ¯our. Similar weakeninge�ects of sprouting on dough strength studied usingFarinograph have been reported by Singh et al. (1987)and Sekhon et al. (1992). The decreased strength ofdough was attributed to increased activity of the pro-teolytic enzymes which hydrolyzed the gluten and pro-tein disul®de reductase developed during sprouting(Singh et al., 1987; Sekhon et al., 1992). The analysis of

variance of the data for G0, G" and tan d measured at 125rad/s frequency revealed a signi®cant e�ect of bothsoaking and sprouting duration on G0. However, thee�ect of sprouting was greater. The G0 decreased withthe increase in soaking while G" and tan d increased withsoaking. Soaking and sprouting interaction e�ect on G0

was also signi®cant. The G0 and G" decreased with theincrease in sprouting duration. The changes in theseparameters were soaking duration dependent. The tan dprogressively increased with increase in sprouting du-ration. This suggests that the relative contribution of theelastic character (G0) decreased with sprouting. He andHoseney (1991) and Jensesen, van Vliet, and Vereijken(1996) suggested that the higher tan d of the doughÕsmade from poor quality ¯ours resulted either from fewerentanglements or entanglements that were easily disso-ciated. This may be true in the present study because ofincrease in proteolytic activity. The results clearlyshowed that dough with higher WSI had higher tan dvalue and were less elastic (had higher G0). The increasein water soluble fraction make the dough more ÔslackerÕ.The tan d values observed in the present study agree withthe reported values of Abdelrahman and Spies (1986)and Miller and Hoseney (1999).

It could be concluded that the functional and rhe-ological properties which are more or less varietal char-acteristic were commensurate with the extent ofsprouting. PBW-343 showed the greatest change in WSI,WAI and falling number value and PDW-233 showedthe least under similar sprouting conditions. Sproutingled to a decrease in both viscous (G") and elastic modulus(G0). Sprouting temperature had most signi®cant e�ecton functional properties in all the three wheat cultivars.

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