This article was downloaded by: [Linnaeus University]On: 06 October 2014, At: 21:29Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

International Journal of Food PropertiesPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/ljfp20

Modeling Effective Moisture Diffusivity ofOrange Slice (Thompson Cv.)Shahin Rafiee a , Mohammad Sharifi a , Alireza Keyhani a , MahmoudOmid a , Ali Jafari a , Seyed Saeid Mohtasebi a & Hossain Mobli aa Agricultural Machinery Engineering Department, Faculty of Bio-systems Engineering , University of Tehran , Karaj , IranPublished online: 13 Jun 2012.

To cite this article: Shahin Rafiee , Mohammad Sharifi , Alireza Keyhani , Mahmoud Omid , AliJafari , Seyed Saeid Mohtasebi & Hossain Mobli (2010) Modeling Effective Moisture Diffusivityof Orange Slice (Thompson Cv.), International Journal of Food Properties, 13:1, 32-40, DOI:10.1080/10942910802144345

To link to this article: http://dx.doi.org/10.1080/10942910802144345

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the“Content”) contained in the publications on our platform. However, Taylor & Francis,our agents, and our licensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor & Francis. The accuracy of the Contentshould not be relied upon and should be independently verified with primary sourcesof information. Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilities whatsoever orhowsoever caused arising directly or indirectly in connection with, in relation to or arisingout of the use of the Content.

This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

International Journal of Food Properties, 13: 32–40, 2010Copyright © Taylor & Francis Group, LLCISSN: 1094-2912 print / 1532-2386 onlineDOI: 10.1080/10942910802144345

32

MODELING EFFECTIVE MOISTURE DIFFUSIVITY OF ORANGE SLICE (THOMPSON CV.)

Shahin Rafiee, Mohammad Sharifi, Alireza Keyhani, Mahmoud Omid, Ali Jafari, Seyed Saeid Mohtasebi, and Hossain MobliAgricultural Machinery Engineering Department, Faculty of Bio-systems Engineering,University of Tehran, Karaj, Iran

The present study was conducted to compute effective moisture diffusivity and activationenergy of orange slices during convection drying. The thin-layer drying experiments werecarried out at five air temperatures of 40, 50, 60, 70, and 80ºC, three air velocities of 0.5,1.0, and 2.0 m/s and three orange slice thicknesses of 2, 4, and 6 mm. Results indicated thatdrying took place in the falling rate period. Moisture transfer from orange slices wasdescribed by applying the Fick’s diffusion model. The effective diffusivity values wereincreased from 6.27 × 10-10 to 3.50 × 10-9 m2/s for the temperature range used in this study.An Arrhenius relation with an activation energy value of 16.47 to 40.90 kJ/mol and thediffusivity constant value of 7.74 × 10-7 to 3.93 × 10-3 m2/s were obtained. It was found thatwith increasing the temperature and air velocity the effective diffusivity increases whileslice thickness showed no considerable changes on the effective diffusivity.

Keywords: Orange, Activation energy, Thin layer, Page model.

INTRODUCTION

Drying, as a complex process involving heat and mass transfer phenomena andfrEq.uently used in food processing industries,[1] is probably the main and the most expen-sive step in postharvest treatment. It improves the product shelf life without the addition ofany chemical preservative and reduces both the size of package and transport costs. Math-ematical modeling and simulation of drying curves under different conditions is importantto obtain a better control of this unit operation and an overall improvement of the qualityof the final product. Models are often used to study the variables involved in the process,predict drying kinetics of the product and to optimize the operating parameters and condi-tions.[2] Drying process of food materials mostly occurs in the falling rate period.[3] Topredict the moisture transfer during the falling rate drying period, several mathematicalmodels have been proposed using Fickian’s diffusion, as shown in Eq. (1), as a basis todescribe the moisture transport process.[4–10] Moisture transfer during drying is controlledby internal diffusion:[8]

Received 7 May 2007; accepted 22 April 2008.Address correspondence to Shahin Rafiee, Agricultural Machinery Engineering Department, Faculty of

Bio-systems Engineering, University of Tehran, Karaj, Iran. E-mail: shahinrafiee@ut.ac.ir

Dow

nloa

ded

by [

Lin

naeu

s U

nive

rsity

] at

21:

29 0

6 O

ctob

er 2

014

EFFECTIVE MOISTURE DIFFUSIVITY OF ORANGE SLICE 33

where D is effective moisture diffusivity in m2/s; t is time in second; and M is moisturecontent of the product in kg water/kg dry solid. The effective moisture diffusivity is repre-senting the conductive term of all moisture transfer mechanisms. This parameter is usuallydetermined from experimental drying curves.[4,10] The diffusion coefficient of a foodproduct is a material property and its value depends upon the conditions within the mate-rial.[11,12] Effective moisture diffusivity describes all possible mechanisms of moisturemovement within the product, such as liquid diffusion, vapor diffusion, surface diffusion,capillary flow and hydrodynamic flow.[13,14] Moisture transport which involves diffusionof moisture in solid foods is a complex process. Temperature dependence of the effectivediffusivity has been shown to follow an Arrhenius relationship:[9–17]

where D0 is The diffusion constant, and the pre-exponential factor of the ArrheniusEquation in m2/s; Ea is the activation energy in kJ/mol; R is the universal gas constant invalues 8.3145 kJ/mol K; and Ta is the absolute air temperature in K. The activation energycan be determined from the slope of the Arrhenius plot of ln (D) versus 1/T. The tempera-ture used in the Arrhenius analysis is the ambient temperature of drying, thus assumingthat the temperature of the material being dried is also that of the surrounding drying envi-ronment. Therefore, the isothermal assumption has been applied in both determining theeffective diffusivity and the activation energy. Potatoes and carrots have shown to developnegligible porosity during drying,[18] and thus will be representative hygroscopic, non-porous materials. No published literature is available on effective diffusivity data fororange slices during drying. A knowledge of effective moisture diffusivity is necessary fordesigning and modeling mass transfer processes such as dehydration, adsorption anddesorption of moisture during storage. The aim of this work was to determine the effectivemoisture diffusivity and activation energy of orange (Thompson variety) slices duringdrying process and its dependence on factors such as air temperature, air velocity andthickness of orange that essentially influence the drying rate.

MATERIAL AND METHODS

Orange slices were considered as an infinite slab because the thickness of the slice(2, 4 and 6 mm) was much less than its diameter (about 85 mm). The moisture diffusivityfor an infinite slab was therefore calculated by Eq. (3) proposed by Crank (1975)[19]

considering assumptions mentioned hereunder:[15,20] a) Moisture is initially distributeduniformly throughout the mass of a sample; b) Mass transfer is symmetric with respect tothe center; c) Surface moisture content of the sample instantaneously reaches Eq.uilibriumwith the condition of surrounding air; d) Resistance to the mass transfer at the surface isnegligible compared to internal resistance of the sample; e) Mass transfer is by diffusiononly; f) Diffusion coefficient is constant and shrinkage is negligible; and g) Me is omitteddue to high initial moisture content of juicy fruits[27]:

¶¶M

tD Meff= ⎡⎣ ⎤⎦∇ ∇( ) , (1)

D DE

RTa

a

= −⎛⎝⎜

⎞⎠⎟0 exp , (2)

Dow

nloa

ded

by [

Lin

naeu

s U

nive

rsity

] at

21:

29 0

6 O

ctob

er 2

014

34 RAFIEE ET AL.

where MR is the moisture ratio; L is the thickness of slice (m); and n is a positive integer.Only the first term of Eq. (3) is used for long drying times: [16]

The slope (k0) is calculated by plotting ln (MR) versus time according to Eq. (5):

Sample Preparation

In this research, a thin layer laboratory dryer is used which has recently beendesigned and built in the Department of Agricultural Machinery at University of Tehran.Schematic diagram of the dryer system is shown in Fig. 1. A portable, 0–15 m/s range dig-ital anemometer (TESTO, 405-V1) was used to occasionally measure air flow velocity of

MRM

M n

n Dt

Ln

= =−

−−⎛

⎝⎜⎞

⎠⎟∑

0

8 1

2 1

2 1

42 2

2 2

21p

p

( )exp

( )

=

∞(3)

MRDt

L= −

⎛

⎝⎜⎞

⎠⎟8

42

2

2p

pexp . (4)

kD

L0

2

24=p

. (5)

Figure 1 Schematic diagram of the drying system for measurement of the thin-layer parameters of orange slices.1. PC; 2. microcontroller; 3. digital balance; 4. fan; 5. heating elements; 6. duct and tunnel; 7. trays; 8. tempera-ture sensor; 9. relative humidity sensor.

Dow

nloa

ded

by [

Lin

naeu

s U

nive

rsity

] at

21:

29 0

6 O

ctob

er 2

014

EFFECTIVE MOISTURE DIFFUSIVITY OF ORANGE SLICE 35

air passing through the system. The airflow was adjusted by means of a variable speedblower. The heating system was consisted of four heating elements placed inside the duct.A simple control algorithm was used to control and adjust the drying tunnel temperature.The opening side on the right was used to load or unload the tunnel and to measure dryingair velocity. The trays were supported by lightweight steel rods placed under the digital bal-ance.[21] Measured variables were air temperature, air velocity, relative humidity (RH), andloss of sample mass during drying. Specifications regarding the measurement instrumentsincluding their rated accuracy are summarized in Table 1. After turning on the computer,fan, scale, elements and data acquisition system, the essential velocity for the fan was set. Amanual TESTO 405-V1 model sensor was used to measure the velocity. The control soft-ware was implemented and the rEq.uired temperature for the experiment was adjusted.Experiments were carried out 30 minutes after the system was turned on to reach to itssteady state condition. Then, the tray holding the samples was carefully put in the dryer.

At first, a foreign Thompson orange (Novel) cultivar was selected. Being seedlessmakes the sliced product suitable for drying. Oranges were washed and sliced perpendicularto the major diameter in thicknesses of 2, 4, and 6 mm using a slicing machine. The uniformthickness of t ± 0.01 mm was prepared by adjusting the opening of the slicer with a verniercaliper having a least count of 0.01 mm. About 150 g of orange slices were weighed and uni-formly spread in a tray and kept inside the dryer. The orange moisture content of 5.5–7.1 kgwater/kg dry solid was obtained by drying the sample in an oven at 105°C for 24 h.

RESULTS AND DISCUSSION

Drying rates were calculated from the drying data by estimating the change in mois-ture content, which occurred in each consecutive time interval and was expressed as kgwater/(kg dry matter hr). The variations of the drying rates as against moisture content areshown in Fig. 2. As shown in Fig. 2, since at the start of drying period, moisture accumulateson the slice surface and the surface temperature becomes low, part of the drying air energy isused to warm up the product surface instead of moisture removal. Getting warmed up, thedrying rate of orange slices increased up to a certain level. Then, due to advancement ofdrying front and the corresponding lower diffusivity, a barrier to moisture transfer of insidelayers is created. Therefore, the drying rate slows down as the moisture content is reduced.

The accelerated drying rates may be attributed to internal heat generation. Theabsence of a constant drying rate period may be due to the thin layer of product that didnot provide a constant supply of water in the specified period of time. Also, some resis-tance to water movement may exist due to shrinkage of the product on the surface, whichreduces the drying rate considerably. The relationship between the drying rate and themoisture content was obtained by regression analysis. For temperature 40°C and 50°C therelationship was found to be linear while for 60°C, 70°C and 80°C it was of the seconddegree polynomial form.

Table 1 Specifications of measurement instruments including their rated accuracy.

Instrument Model Accuracy Make

Digital balance GF3000 ± 0.02 g A&D, JapanT-sensor LM35 ± 1° C NSC, USARH-sensor Capacitive ± 3% PHILIPS, UKV-sensor 405-V1 ± 3% TESTO, UK

Dow

nloa

ded

by [

Lin

naeu

s U

nive

rsity

] at

21:

29 0

6 O

ctob

er 2

014

36 RAFIEE ET AL.

Table 2 illustrates the linear and nonlinear relationships between drying rate andmoisture content obtained from regression analysis. The values for the coefficient ofdetermination R2 were in the range of 0.9891–0.9935. Results show that the thin layer dry-ing of orange slices occurs entirely in the falling rate period. However, the drying rateappears to be slow and gradually receding for the low level of temperature and wasobserved to increase at higher levels (Fig. 2). An increase in drying rates with an increasein temperature has been reported in earlier studies by Pathare and Sharma[3] for onionslice, Akpinar et al.[22] for red pepper slice, Mohapatra and Rao[23] for parboiled wheat,Doymaz[24] for green bean, Madamba et al.[25] for garlic slice.

The effective moisture diffusivity D was calculated using Eq. (5) and is shown inTable 3. The effective diffusivity values of dried samples at 40–80ºC were varied in therange of 6.27 × 10−10 to 3.50 × 10−9 m2/s. It can be seen that D values increased greatlywith increasing temperature. Drying at 80ºC gave the highest D values. Effective diffusivityvalues for orange skin was reported as 0.81 × 10−10 to 5.11 × 10−9 m2/s in the temperaturerange of 30 to 90ºC by Garau et al.[26] Based on the independent variables thickness (TK),drying air temperature and air velocity, using the multivariate regression technique, the

Figure 2 Influence of temperature on drying rate of orange slices at five temperatures of , 40°C, , 50°C,, 60°C, , 70°C, , 80°C and air velocity of 2 m/s and slice thickness of 6mm.

Table 2 Values of constants and coefficients of linear and nonlinear model for differenttemperatures.

Temperature (ºC) a b c R2

801 −0.0903 1.0889 −0.0459 0.9891701 −0.0537 0.7368 0.0103 0.9938601 −0.0485 0.7472 −0.2900 0.9898502 0.2783 −0.0156 0.9935402 0.2408 −0.0589 0.9926

1DR = aM2 + bM + c.2DR = bM + c2.

Dow

nloa

ded

by [

Lin

naeu

s U

nive

rsity

] at

21:

29 0

6 O

ctob

er 2

014

EFFECTIVE MOISTURE DIFFUSIVITY OF ORANGE SLICE 37

effective diffusivity with R2 of 0.815 was estimated. A multiple regression Equation as afunction of temperature, air velocity and sample thickness was found to be:

The relationship of the effective moisture diffusivity and temperature follows the Arrhe-nius Equation as shown by Eq. (2). The activation energy (Ea) and diffusion constant weredetermined from the slope of the Arrhenius plot, ln (D) vs 1/T, and given in Table 4. Theln (D) as a function of reciprocal of absolute temperature (T) is plotted in different conditionsof drying in Fig. 3. Results show linear relationships except for Fig. 3e and f corresponding toair velocity of 1 and 2 m/s in 4 mm thickness. The activation energy of all sampleswas less than 41.00 kJ/mol, ranging from 16.47–40.90 kJ/mol, similar to valuesreported by several authors for different fruits and vegetables. For example, 36.40 kJ/molin orange skin;[26] 32.94 kJ/mol, for untreated tomato;[27] and 24.70–28.40 kJ/mol ingreen peas. [17] Activation energy of orange slice showed slightly higher compared to

Table 3 Effective diffusivity of orange slice in different drying conditions.

Effective diffusivity (×10−10 m2/s)

Slice thickness (mm) Drying air velocity (m/s) 40 °C 50 °C 60 °C 70 °C 80 °C

2 0.5 6.57 7.83 12.7 16.3 20.12 1.0 8.26 10.4 17.2 23.5 31.52 2.0 9.87 11.2 18.6 23.8 32.14 0.5 7.52 8.48 14.7 23.4 35.04 1.0 8.76 17.2 22.0 24.0 26.84 2.0 10.4 18.0 23.3 24.9 26.56 0.5 6.27 7.72 12.4 14.8 19.86 1.0 6.83 8.42 13.3 17.1 22.46 2.0 7.90 8.97 14.4 18.3 23.9

D a bTK cV dT

a 1 1 419 1 b 7 88395 1 and

c 2 36

9 11

= + + +

= − × = − ×

=

− −

,

. , . ,

.

0 0 0

8854 1 d 4 65791 11 11× = ×− −0 00 , . . (6)

Table 4 Diffusivity constant and activation energy for orange slice (Thompson) for different slicethinness’s and air velocities.

Thickness (mm) Velocity (m/s)Diffusion constant,

D0 ((×10-5 m2/s)Activation energy,

Ea (kJ/mol)

2 0.5 1.69 × 10−5 26.461.0 1.72 × 10−4 32.002.0 6.71 × 10−5 29.20

4 0.5 3.93 × 10−3 40.901.0 1.82 × 10−6 18.982.0 7.74 × 10−7 16.47

6 0.5 1.82 × 10−5 26.781.0 3.31 × 10−5 28.172.0 2.59 × 10−5 27.26

Dow

nloa

ded

by [

Lin

naeu

s U

nive

rsity

] at

21:

29 0

6 O

ctob

er 2

014

38 RAFIEE ET AL.

Figure 3 Arrhenius type relationship between effective diffusivity and temperature.

a-Air velocity at 0.5m/s and thickness slice at 2 mm b-Air velocity at 1.0m/s and thickness slice at 2 mm

c-Air velocity at 2.0m/s and thickness slice at 2 mm d-Air velocity at 0.5m/s and thickness slice at 4 mm

e-Air velocity at 1.0m/s and thickness slice at 4 mm f-Air velocity at 2.0m/s and thickness slice at 4 mm

g-Air velocity at 0.5m/s and thickness slice at 6 mm h-Air velocity at 1.0m/s and thickness slice at 6 mm

i-Air velocity at 2.0m/s and thickness slice at 6 mm

-In(D) = –0.2969/T + 21.462R2

= 0.9758

-In(D) = –0.3113/T + 21.107R2

= 0.9756

-In(D) = –0.0918/T2 + 21.526

R2 = 0.9753

-In(D) = –0.2948/T + 21.495R2

= 0.9803-In(D) = –0.3081/T + 21.433

R2 = 0.9872

-In(D) = –0.2929/T + 21.303R2

= 0.9764

-In(D) = –0.0831/T2 – 0.7178T + 21.291

R2 = 0.9865

-In(D) = –0.4089/T + 21.542R2

= 0.9741

-In(D) = –0.4089/T + 21.542R2

= 0.9741

Dow

nloa

ded

by [

Lin

naeu

s U

nive

rsity

] at

21:

29 0

6 O

ctob

er 2

014

EFFECTIVE MOISTURE DIFFUSIVITY OF ORANGE SLICE 39

carrots (16.00 kJ/mol)[28] and lower than red chilli drying (41.95 kJ/mol)[29] and okra(51.26 kJ/mol).[24] Using the regression method, one can estimate ln(D) by knowing 1/Twith high R2 of 0.9741 to 0.9881. As can be seen from Fig. 3, for 4-mm thickness andair velocities of 1 and 2 m/s, the relationship is second degree polynomial while forthe rest it is linear.

CONCLUSIONS

Effective moisture diffusivity increased with increase in drying air temperature. Thehighest effective diffusion was found to be 3.50 × 10−9 m2/s in air temperature, air velocityand slice thickness of 80ºC, 0.5 m/s, and 4 mm, respectively. The lowest effective diffu-sion was 6.27 × 10−10 m2/s in air temperature, air velocity and slice thickness of 40ºC,0.5 m/s, and 6 mm, respectively. The highest activation energy value of orange slice wasdetermined as 40.90 kJ/mol at slice thickness of 4 mm and drying air velocity of 0.5 m/s,and the lowest value was 16.47 kJ/mol at slice thickness of 4 mm and drying air velocityof 2 m/s. The diffusion constant value of orange slice was attained as 3.93 × 10−3 m2/s atthe slice thickness of 4 mm and drying air velocity of 0.5 m/s and the lowest value was7.74 × 10−7 m2/s at the slice thickness of 4 mm and drying air velocity of 2 m/s.

ACKNOWLEDGMENTS

This research was supported by Bio-systems engineering faculty of University of Tehran.

REFRENCES

1. Cohen, J.S.; Yang. T.C.S. Progress in food dehydration. Trends in Food Science and Technology1995, 6, 20–25.

2. Karathanos, V.T.; Belessiotis V.G. Application of a thin layer Equation to drying data fresh andsemi-dried fruits. Journal of Agricultural Engineering Research 1999, 74, 355–361.

3. Jumah, R.; Banat, F.; Al-Asheh, S.; Hammad, S. Drying kinetics of tomato Paste. InternationalJournal of Food Properties 2004, 7 (2), 253–259.

4. Doymaz, I. Thin-layer drying behaviour of mint leaves. Journal of Food Engineering 2006, 74,370–375.

5. Gou, P.; Comaposada, J.; Arnau. J. content and temperature effects on moisture diffusivity inthe gluteus medius muscle of pork jam. Meat Science 2003, 63 (1), 29–34.

6. Maskan, A.; Kaya S.; Maskan M. Hot air and sun drying of grape leather (pestil). Journal ofFood Engineering 2002, 54 (1), 81–88.

7. Sablani, S.; Rahman, S.; Al-Habsi, N. Moisture diffusivity in foods-an overview. In DryingTechnology in Agriculture and Food Sciences; Mujumdar, A.S.; Ed.; Enfield, NH: SciencePublishers, Inc., 2000; 35–59.

8. Saravacos, G.D.; Charm, S.E. Effect of surface-active agents on the dehydration of fruits andvegetables. Journal of Food Technology 1962, 16 (1), 91–93.

9. Sacilik, K. Effect of drying methods on thin-layer drying characteristics of hull-less seed pump-kin (Cucurbita pepo L.). Journal of Food Engineering 2007, 79, 23–30.

10. Srikiatden, J.; Roberts, J.S. Measuring moisture diffusivity of potato and carrot (core and cor-tex) during convective hot air and isothermal drying. Journal of Food Engineering 2006, 74,143–152.

11. Maroulis, Z.B.; Saravacos, G.D.; Panagiotou, N.M.; Krokida, M.K. Moisture diffusivity datacompilation for foodstuffs: effects of material moisture content and temperature. InternationalJournal of Food Properties 2001, 4 (2), 225–237.

Dow

nloa

ded

by [

Lin

naeu

s U

nive

rsity

] at

21:

29 0

6 O

ctob

er 2

014

40 RAFIEE ET AL.

12. Rafiee, S., Sharifi, M., Keyhani, A., Jafari, A. and Mobli, H. 2007. Modeling Effective MoistureDiffusivity of Thompson Variety Orange. International Journal of Food Properties. 2008, 11,223–232.

13. Roberts, J.S.; Tong, C.H. Drying kinetics of hygroscopic porous materials under isothermal con-ditions and the use of a first-order reaction kinetic model for predicting drying. InternationalJournal of Food Properties 2003, 6 (3), 355–367.

14. Kim S.S.; Blowmilk S.R. Effective moisture diffusivity of plain yoghurt undergoing microwavevacuum drying. Journal of Food Engineering 1995, 24, 137–148.

15. Pathare, P.B.; Sharma, G.P. Effective Moisture Diffusivity of Onion Slices undergoing InfraredConvective Drying. Journal Biosystems Engineering 2006, 93 (3), 285–291.

16. Lopez, A.; Iguaz, A.; Esnoz, A.; Virseda, P. Thin-layer drying behaviour of vegetable wastefrom wholesale market. Drying Technology 2000, 18 (4&5), 995–1006.

17. Simal, S.; Mulet, A.; Tarrazo, J.; Rossello, C. Drying models for green peas. Food Chemistry1996, 55 (2), 121–128.

18. Zogzas, N.P.; Maroulis, Z.B.; Marinos-kouris, D. Moisture diffusivity data compilation in food-stuffs. Drying Technology 1996, 14 (10), 2225–2253.

19. Crank, J. Mathematics of diffusions, 2nd ed.; Oxford University Press: London, 1975.20. Sharma, G.P.; Verma, R.C.; Pankaj, P. Mathematical modeling of infrared radiation thin layer

drying of onion slices. Journal of Food Engineering 2005, 71, 282–286.21. Yadollahinia, A. A Thin Layer Drying Model for Paddy Dryer, M. Sc. Thesis, Faculty of Bio-

systems Engineering, University of Tehran, Karaj, Iran, 2006.22. Akpinar, E.K.; Bicer Y.; Yildiz, C. Thin layer drying of red pepper. Journal of Food Engineer-

ing 2003, 59, 99–104.23. Mohapatra, D.; Rao, P.S. A thin layer drying model of parboiled wheat. Journal of Food

Engineering 2005, 66, 513–518.24. Doymaz, I. Drying behaviour of green beans. Journal of Food Engineering 2005, 69, 161–165.25. Madamba, P.S.; Driscoll, R.H.; Buckle, K.A. The thin layer drying characteristics of garlic

slices. Journal of Food Engineering 1996, 29, 75–97.26. Garau, M.C.; Simal, S.; Femenia, A.; Rossello, C. Drying of orange skin: drying kinetics model-

ing and functional properties. Journal of Food Engineering 2006, 75, 288–295.27. Doymaz, I. Air-drying characteristics of tomatoes. Journal of Food Engineering 2007, 78,

1291–1297.28. Reyes, A.; Alvarez, P.I.; Maquardt, F.H. Drying of carrots in a fluidized bed. Effects of drying

conditions and modelling. Drying Technology 2002, 20 (7), 1463–1483.29. Gupta, P.; Ahmed, J.; Shivhare, U.S.; Raghavan, G.S.V. Drying characteristics of red chilli.

Drying Technology 2002, 20, 1975–1987.

Dow

nloa

ded

by [

Lin

naeu

s U

nive

rsity

] at

21:

29 0

6 O

ctob

er 2

014