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* Corresponding author: P. LinyDepartment of Chemical Engineering, MVJCE , Whitefield, Bangalore,Karnataka, 560067, India

ISSN: 0976-3031

RESEARCH ARTICLEREHYDRATION BEHAVIOR OF BLACKGRAM

*Liny. P., Manish S. Khodwe and M.Shashikala

Department of Chemical Engineering, MVJCE , Whitefield, Bangalore,Karnataka, 560067, India

ARTICLE INFO ABSTRACT

Kinetics of hydration behavior of blackgram with seed coat was analyzed at different

temperatures (30, 40, 50, 60, 70, and 80C) andwas modeled with Pelegs equation. Study

indicated with the increase in temperature (30 to 80C) Peleg rate constant K1 and capacityconstant K2 significantly decreased from 2.147 to 0.022 s % d.b.

-1 and from 0.018 to 0.030%d.b.-1 respectively. Decrease in K1 and K2 indicates that the water absorption rate and waterabsorption capacity increased with time and temperature. Peleg model was fitted to correlatewater absorption of blackgram with soaking time and temperature. Gelatinization

temperature of black gram from Pelegs model was found around 70C. Arrhenius equationsuited well for the temperature dependence of the rate constant. Swelling of grains was dueto water sorption which is slightly less than the volume of water imbibed. This loss is related

to the energy of activation of water sorption process. Equilibrium moisture content (EMC)on soaking at different temperature of the blackgram was evaluated.

INTRODUCTION

Food legumes decreased frequency of several diseases, suchas cancer, cardiovascular diseases and diabetes (Bhathena et

al., 2002).Black gram is one of the important grain legumeswith the sources of protein, energy, vitamins and minerals.

Black gram is a good source of phosphorus. It has significantlipid lowering action. Studies showed that black grampolysaccharide had the highest fiber content compared to thatof cellulose and maximum hypocholesterolemic effect (Indiraet al., 2003). In the different system of traditional medicines, it

has been recognized as the treatment of different diseases andailments of human beings (Anupriya Pandey et al., 2011). Thebiological value improves greatly, when wheat or rice is

combined with black gram because of the complementaryrelationship of the essential amino acids such as arginine,leucine, lysine, isoleucine, valine, phenylalanine etc.

Rehydration of dry legumes is done by soaking in water orother pre-treatments before further processing. Studiesindicated the soaking time of various seeds can be shortenedby increasing the temperature of the soaking medium will

accelerate water uptake by various seeds. In determining thecooking time, appearance and the extent of proteindenaturation and starch gelatinization of legumes, hydration

prior to cooking have an important role (Quast et al., 1977;Ekpenyong et al., 1980; Davis et al., 1982). Many attemptshave been made to reduce the soaking process which has been

characterized as a time consuming step (Rocklandet al., 1967;Kon et al., 1973). It is necessary to characterize and optimize

the soaking conditions as it varies depending upon the legumeunder study. Hence, water absorption during soaking needs tobe predictable as a function of time and temperature.

Rehydration of legume grains normally involves the operationssuch as steeping, blanching, cooking and washing of grainswhere the grain is either contacted with liquid water or withthe saturated water vapor. In designing of proper rehydration

process and related equipment, it is desirable if the extent ofwater gain could be predicted as a function of time andtemperature. Earlier studies of wheat (Becker, 1960), corn andsorghum and paddy (Bandopadhyay et al., 1976) found thatgrain water uptake is a diffusion controlled process which

followed the Beckers equation (Becker, 1960, Engels et al.,1986). Studies on legumes indicate that water sorption couldbe described with a non-linear diffusion model. The hydration

analyses were based on the laws of diffusion (Hayakawa 1974)which involve numerous functions and parameters. The non-exponential two-parameter empirical Pelegs equation is used

to simplify the mode of water absorption kinetics in foodmaterials (Peleg 1988). In general, the Peleg model shows thesame or better fit than the models that are used in the water

absorption analyses. It has the effect on the physical, chemical,biological activity of the material.

Hydration phenomenon in red kidney beans in blanched andunblanched form at four temperatures and hydration data was

fitted to Pelegs equation. Because of the plasticitydevelopment in the seed coat of kidney beans while blanching,Pelegs equation was applied more adequately in the blanched

beans compared to un-blanched beans (Vasudeva et al.,(2010). Sopade et al., (1990) studied sorption behavior ofsoybean, cow pea and peanuts at low, room and hightemperatures and reported that Pelegs constant K1 varied with

temperature while Pelegs constant K2 was not affected. In thepresent study, the blackgram is hydrated before use and their

hydration behavior was studied at different temperatures. Thisstudy is important as it led to a water sorption model other than

Available Online at http://www.recentscientific.com

International Journal

of Recent Scientific

ResearchInternational Journal of Recent Scientific ResearchVol. 4, Issue, 6, pp.1036 1040, July, 2013

Article History:

Received 16th, June, 2013

Received in revised form 28th, June, 2013

Accepted 17th, July, 2013

Published online 30th July, 2013

Copy Right, IJRSR, 2013, Academic Journals. All rights reserved.

Key words:Legume, blackgram, Pelegs model, Hydration

behavior, EMC

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International Journal of Recent Scientific Research, Vol. 4, Issue, 7, pp. 1036 - 1040, July, 2013

1037

liquid diffusion. Peleg model was used in knowing thehydration behavior on the black gram and to characterize the

equation constants and to determine the suitable conditions ofrehydration.

MATERIAL AND METHODS

Materials

Blackgram was procured from the local market and the studywas conducted on it. Seeds were examined visually; only

sound grains were used after removing foreign materials anddamaged seeds. The average diameter was found to be 2.679mm using screw gauge. Seeds were considered for hydration

behavior. EMC at different temperatures and modeling ofhydration behavior were studied. The moisture content ofrandomly selected grains was determined in dry basis at 105C

using the AOAC method (AOAC 2002). Initial moisturecontent (Mo) of the sample was found to be 11.11% (d.b.).

Water absorption determination during soaking

Twenty grams of black gram seeds were soaked in water in the

ratio of 1:20 at different temperatures such as 30, 40, 50, 60,70 and 80C. Glass beakers of 500ml capacity were consideredto which 400ml of water was added, it was then placed in thetemperature controlled water bath. When the water attains the

bath temperature, 20g of black gram sample was added andwas covered to avoid to loss of heat. At different timeintervals, the seeds were quickly removed and the seeds were

gently wiped with the filter paper to remove excess water andthe surface moisture and weight was checked (M (t)). Moisturecontent data were used to model with Pelegs equation for

water absorption characteristics of blackgram. Tests were donein two replicates.

Kinetic model for sorptionModeling of black gram absorption as a function of time

The water absorption kinetics of dry legumes during soakingwas analysed using Peleg (Jideani & Mpotokwana 2009).

Peleg (1988) proposed a two-parameter sorption equation andtested its prediction accuracy during water vapor adsorption ofmilk powder and whole rice, and soaking of whole rice. This

empirical equation is used to describe the water absorptionbehavior of various legumes:

( ) =

(1)

Where ( ) is moisture content at time t in % d.b.

is initial moisture content in % d.b.is the Peleg rate constant in s % d.b

.-1;

is the Peleg capacity constant in % d.b-1.

One differentiation of (1) , the rate of sorption (R) can beobtained

R = = ( )

(2)

At t= to Peleg rate constant K1 relates to sorption rate at theinitial condition (Ro)

Ro= = 1/K1 (3)

to

The Peleg capacity constant K2 relates to maximum (orminimum) attainable moisture content. As t , Equation (1)

gives the relation between Equilibrium Moisture Content(EMC or Me) and K2:

= (4)

The relation of K1 and K2 to the rate and equilibriumconditions is expressed by equation (2) and (4).

RESULTS AND DISCUSSIONS

Swelling of the grains and a small but definite leaching ofsolids was associated with water sorption. The rate of watergain, leaching of solids and volume increase with the increase

in temperature of the soaking medium but the rate ofabsorption decreases gradually. Mass leached being fullysolvated should be associated with relatively higher amount of

water. Since whole grain could retain most of the leachablefraction, it could assume higher moisture, the effect is morepronounced for higher values of contact time.

Water absorption characteristics of black gram duringsoaking

Legume grains are soaked before cooking to provide sufficientamount of moisture for gelatinization of starch and/or gelationof protein. It can be achieved either through conditioning

below the gelatinization temperature and then cooking abovethe gelatinization temperature, or through direct cooking abovethe gelatinization temperature. The mean moisture contents of

soaked blackgram at 30, 40, 50, 60, 70 and 80C wereillustrated in Figure 2.

y = 0.018x + 2.147

R = 0.990

0

5

10

15

20

25

0 200 400 600 800 1000 1200

t/(M(t)-Mo)

Time(min)

t/(M(t)-Mo) v/s time at 30oC

y = 0.024x + 0.849

R = 0.991

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 50 100 150 200

t/(M(t)-Mo)

time(min)


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1038

Figure 1: Linearization of moisture sorption curves

y = 0.025x + 0.137R = 0.997

0

1

2

3

4

5

6

0 50 100 150 200

t/(M(t)-Mo)

time(min)


y = 0.027x + 0.083

R = 0.992

0

0.5

11.5

2

2.5

3

3.5

4

4.5

5

0 50 100 150 200

t/(M(t)-Mo)

time (min)


y = 0.035x + 0.38

R = 0.989

0

12

3

4

5

6

7

0 50 100 150 200 250

t/(M(t)-Mo)

time(min)


y = 0.030x + 0.022

R = 0.993

0

0.5

1

1.5

2

2.5

3

3.5

4

0 20 40 60 80 100 120 140

t/(M

(t)-Mo)

time(min)


0

10

20

30

40

50

60

0 200 400 600 800 1000 1200 1400

Moisturecontent(%)

Time(min)

Moisture content v/s time at 30oC

30C

Peleg Model

0

5

10

15

20

25

30

35

40

45

0 50 100 150 200 250

Mo

issturecontent(%)

time(min)


40C

Peleg Model

0

5

10

15

20

25

30

35

40

45

0 50 100 150 200 250 300

Moisturecontent(%)

time(min)


50C

Peleg Model

05

10

15

20

25

30

35

40

0 100 200 300 400

Moisturecontent(%)

time(min)


80C

Peleg

Model

05

1015

2025303540

45

0 100 200 300

Moisturecontent(%)

time(min)


60C

Peleg Model

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1039

Figure 2 Means of experimental and predicted moisture contents of black

gram at different temperatures

Initial moisture content of the black gram 11.11 % (d.b.) andthe equilibrium moisture content was evaluated (table 1)With the increase in temperature and time the moisture content

of black gram during soaking also increased significantly(Figure 1 and 2). Rate of increase in moisture content was

higher during the early stages of soaking but lower in the latesoaking periods. Blackgram water absorption curves arecharacterized by an initial phase of rapid water pickupfollowed by an equilibrium phase, during which the blackgram

approaches its full soaking capacity. The rate of waterabsorption increased with increasing temperature as suggestedby the slopes of the absorption curves getting steeper withincreased temperature.

Modeling of black gram water absorption as a function of

time

The parameters Me, K1 and K2 were estimated by using the

non-linear regression analysis of Equations 1-4 (Table 1).

The path of the hydration was fitted by Pelegs nonlinear

equation with coefficients, shows that the seed water content

increases with soaking time at all temperatures. K1 values ofthe Peleg model decreased from 2.147 to 0.022 s % d.b. -1 with

increasing temperature from 30 to 80 C. Similarly, K2decreased from 0.018 to 0.030% d.b.

-1for black gram as the

temperature increased from 30 to 80C (Table 1). Change of

K2 value of black gram with change in temperature was due tothe differences in solid losses at different temperatures and Mecould be different and K2 would be dependent upon the

temperature (Table 1). The equilibrium moisture content ofblack gram decreased from 57.78 to 35.56 % d.b.

-1with

increase in temperature from 30 to 80C. The Peleg model was

successfully fitted to correlate water absorption of black gramwith soaking time and temperature (R

2= 0.989-0.997).

Modeling of blackgram water absorption as a function of

time and temperature

Arrhenius equation (5) was used for modeling the dependence

of Peleg rate constant (K1) on temperature in order to find theeffect of temperature on water absorption of black gram, it hasbeen used to describe the temperature dependent hydrationkinetics of legumes (Abu-Ghannam and McKenna 1997;

Turhan et al., 2002):=

(5)

= ln (6)

where, Kref-reference hydration rate constant in s % d.b.-1;

Ea - Activation energy in kJ mol-1

;R - Ideal gas constant in 8.314 x10

-3kJ mol

-1K

-1; and

T - Soaking temperature in K-1, respectively.

Arrhenius plot for blackgram was superposed in Figure 3. In

the graph, the activation energy Ea is related to the slope, andis analytical of the temperature dependence of K1. For soakedblack gram, a break seemed to occur at a certain soak

temperature in the Arrhenius curve.

Figure 3 Change in K1 with temperature

The estimated natural log of rate constant K1 was fitted to alinear model with break point and the break temperature was

found to be around 70C which indicates the start ofgelatinization. From the Figure 3, the linearity shows anArrhenius relationship for this model. The activation energyvalues were predicted based on the Arrhenius equation (6) was

applied to the values of K1 for temperatures below and abovebreak points i.e., 70C. The activation energy values of soakedblackgram below and above 70C for this model was found as

31.452 kJ mol-1

and 16.85 kJ mol-1

respectively.

CONCLUSION

For blackgram the water absorption rate significantly increasedwith increasing of soaking time, temperature. K1 for atemperature range of 20-80C decreased from 2.147 to 0.022 s

% d.b.-1 due to increasing of water absorption. Peleg modelwas successfully fitted to correlate water absorption withsoaking time and temperature. Average gelatinization

0

5

10

15

20

25

30

35

40

0 50 100 150 200 250 300

Moisturecontent(%)

time(min)


70C

Peleg Model

Temperature :30-70oC

y = -3783.x + 12.15

R = 1

Temperature from 70-800C

y = -2027.x + 6.514R = 0.843

-1

-0.5

0

0.5

1

1.5

2

0.0028 0.0029 0.0030 0.0031 0.0032 0.0033 0.0034ln(1/K1)(s/%d.b.)

1/T (K-1)

ln(1/K1) v/s (1/T)

Table 1 Values of parameters from Peleg model for different temperatures of black gram during soaking

TemperatureK1 (s/%d.b) K2 (%d.b1) R2 1/Temp (1/T) Me= +

(oC) ( K)

30 303 2.147 0.018 0.99 0.0033 -0.332 57.78

40 313 0.849 0.024 0.991 0.0032 0.071 43.89

50 323 0.137 0.025 0.997 0.0031 0.863 42.22

60 333 0.083 0.027 0.992 0.0030 1.081 39.26

70 343 0.38 0.035 0.989 0.0029 0.420 30.79

80 353 0.022 0.030 0.993 0.0028 1.658 35.56

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temperature of black gram from the water absorption modelwas found as 70C. The dependence of constant (K1) on

temperature was modeled using the Arrhenius equation indescribing the temperature dependent hydration kinetics ofblackgram.Activation energy (Ea) value of blackgram was

found 31.452 kJ mol-1

for below 70C and 16.85 kJ mol-1

forabove 70C.

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Sopade, P.A., Obekpa, J.A. (1990). Modelling water absorption insoybean, cowpea and peanuts at three temperatures using

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