Drying Kinetics of Nephelium Lappaceum (Rambutan) in a Drying Oven

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Procedia - Social and Behavioral Sciences 195 ( 2015 ) 2734 – 2741

Peer-review under responsibility of Istanbul Univeristy. doi: 10.1016/j.sbspro.2015.06.383

ScienceDirect

World Conference on Technology, Innovation and Entrepreneurship

Drying Kinetics of Nephelium Lappaceum (Rambutan) in a

Drying Oven

Syarifah Nor Faizah Syed Abdul Rahman

a

, Radziah Wahid

a

, Norazah Ab Rahman

a,b

*

a_{Faculty of Chemical Engineering, Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia}

b_{CoRe of Frontier Materials & Industry Applications, Universiti Teknologi MARA, 40450 Shah Alam, Selangor Darul Ehsan, Malaysia}

Abstract

Nephelium Lappaceum (Rambutan) is a local seasonal fruit that has a short storage life. In this study, the effects of temperature

on the drying of Nephelium Lappaceum samples were investigated. The present investigation was conducted at drying temperatures of 40ºC, 50ºC, 60ºC, 70ºC and 80ºC for 24 hours, and the drying kinetics of Nephelium Lappaceum were evaluated. The experimental data were fitted to five thin layer mathematical models, including the Lewis, Page, Handerson and Pabis, logarithmic and two-term model. These models were evaluated by comparing the coefficient of determination (R2_{), chi square}

Ȥ2), reduced sum square error (SSE) and root mean square error (RMSE). The logarithmic model best fit the experimental data. The effective diffusivity, Deff, was calculated using Fick’s diffusion equation, and the value of Deffvaried from 1.34 x 10-10to

4.36 x 10-10_m2_{/s. The activation energy, E}

a, and diffusivity constant, D0, were 24.99 kJ/mol and 2.23 x 10-6m2/s, respectively.

Keywords: Drying kinetics; Rambutan; Nephelium Lappaceum; thin layer model; mathematical modelling

1. Introduction

Nephelium lappaceum (Rambutan) is a seasonal fruit and a member of the Sapindaceae family. Nephelium lappaceum consists of a seed, edible white pulp and hairy rind (Chooi, 2004; Diczbalis, 2002) and can be found in humid tropical countries such as Malaysia, Thailand and Indonesia (Chooi, 2004; Radha & Mathew, 2007). Nephelium lappaceum is abundant during its growing season, which often leads to fruit overproduction. Nephelium

* Corresponding author. Tel.:+603-55436307; fax:+603-55436300.

E-mail address: noraz695@salam.uitm.edu.my

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lappaceum undergoes a rapid loss of moisture and darkening of the rind after it is harvested, leading to wasted fruit. The dehydration and darkening process of the fruit is followed by rind cracking and exposure of the juicy part of the fruit to pathological damage (S. Mohamed & E. Othman, 1988). Normally, fresh Nephelium Lappaceum can be stored for 4 to 5 days at ambient temperature and relative humidity (Landrigan et al., 1996; O'Hare et al., 1994; Yingsanga et al., 2008). Therefore, Nephelium Lappaceum must be preserved to prolong its shelf life.

Drying is the oldest preservation technique used in various industries because it is a cost-effective and practical means of preservation (Lewicki, 1998; Ramaswamy & Marcotte, 2006). Previously, studies on the drying of a variety of fruits such as apple (Kaya et al., 2007), longan (Varith et al., 2007), litchi (Janjai et al., 2010), kiwi (Allaeddini & Emam-Djomeh, 2004; Ceylan et al., 2007) and banana (Dandamrongak et al., 2002; Karim & Hawlader, 2005; Ceylan et al., 2007) have been performed. Many drying methods are used in the drying of fruits and vegetables, such as solar drying, microwave drying, spray drying, freeze drying and hot air drying (Guiné et al., 2011). However, hot air drying offers more uniform and hygienic production of dried fruit (Doymaz, 2004).

Various studies on the drying kinetics of fruits and vegetables have been reported, including those on grape seeds (Roberts et al., 2008), strawberry (Doymaz, 2008), banana (Ceylan et al., 2007), mulberry (Doymaz, 2004) and carrot (Krokida et al., 2003). However, information on the drying kinetics of Nephelium lappaceum has not yet been published.

The objectives of the present research were to (1) study the effects of temperature on the drying characteristics of Nephelium Lappaceum, (2) determine a suitable thin layer mathematical model that describes its drying behaviour and (3) evaluate the corresponding diffusivity and activation energy.

2. Materials and Methods

2.1. Sample Preparation

Fresh Nephelium Lappaceum was obtained from a local market in Selangor and was deseeded, cleaned and cut into 2.5 cm x 2.5 cm pieces with a thickness of 0.4 cm-0.6 cm. The moisture content and weight of the samples were recorded, and the samples were placed into a drying chamber. A pre-treatment process was not performed on the samples prior to drying.

2.2. Drying Method

Nephelium Lappaceum samples were dried in an oven (UFE 500, Memmert) at 40o_{C for 24 hours. The weight of}

the samples was recorded at different time intervals, and the moisture content of the dried samples was determined after 24 hours. The experiment was repeated at temperatures of 50ºC, 60ºC, 70ºC and 80ºC, and each experiment was repeated in triplicate. The data were subsequently analysed to study the drying kinetics.

2.3. Data Analysis

The drying characteristics were analysed using semi-theoretical drying models. Five mathematical drying models were used to evaluate the drying kinetics of Nephelium Lappaceum, as shown in Table 1. The moisture ratio of the samples was calculated using Equation (1):

(1) where MR is the dimensionless moisture ratio, M is the moisture content at time t of the drying process (g/g dry solid), M0is the initial moisture content (g/g dry solid) and Me is the equilibrium moisture content (g/g dry solid).

e e

M

MR

0

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Me was assumed to be 0 g/g dry solid because it is relatively small compared to M and M0 (Al-Muhtaseb et al.,

2010; Roberts et al., 2008). Thus, Equation (1) was simplified to:

(2) Non-linear regression analysis was performed using Microsoft Excel. The coefficient of determination (R2_{), chi}

VTXDUHȤ2), reduced sum square error (SSE) and root mean square error (RMSE) of each mathematical model were calculated, and a suitable drying model was chosen based on the highest value of R2 _{and lowest value of SSE,}

RMSE DQGȤ2_.

Table 1. Mathematical models applied to the drying curves.

Model Name Mathematical Equation References

Lewis MR = exp(-kt) Ceylan, 2007; Guiné et al., 2011 Page MR = exp(-ktn₎ _{Ceylan, 2007; Guiné et al., 2011}

Henderson and Pabis MR = a exp(-kt) Ceylan, 2007; Guiné et al., 2011 Logarithmic MR = a exp(-kt) + c Ceylan, 2007; Guiné et al., 2011 Two-Term MR = a exp(-k0t) + b exp(-k1t) Ceylan, 2007; Guiné et al., 2011

3. Results and Discussion

3.1. Drying Curves

The drying curves of Nephelium Lappaceum at different temperatures are shown in Figure 1. The drying temperature significantly affected the drying rate of Nephelium Lappaceum. This finding is in agreement with those obtained by Vega-Galvez et al. (2012), who studied the effect of temperature and air velocity on the drying kinetics of apple slices, and found that the drying rate of apples increased with an increase in temperature. At high drying temperatures, the drying rate is faster due to the excitation of molecules in the samples (Jamali et al., 2006). As the temperature increases, water molecules inside the sample move faster, which increases the distance between molecules and indirectly reduces the attractive forces between them. Thus, an increase in the drying temperature increases the amount of moisture removed from the samples.

Fig. 1. Drying curves of Nephelium Lappaceum dried in an oven at different temperatures.

0

M

MR

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Based on the results shown in Figure 2, samples dried at 40ºC, 50ºC, 60ºC, 70ºC and 80ºC showed a falling rate period. These results were in accordance with those obtained by Hii et al. (2009), Lemus-Mondaca et al. (2008) and Evin (2012) and Doymaz (2008), who observed a falling rate period in their studies on the drying of fruit products. As shown in Figure 1 and Figure 3, in the early stages of the drying process, a rapid loss of moisture was observed due to moisture loss at the surface of samples and capillary action, which transported unbound water to the surface through the capillaries of the samples. As the drying time increased, the surface layer of water slowly receded below the surface, and hot air filled the voids left by moisture removed from the samples. Moisture was continuously removed until there was insufficient water left to maintain a continuous film across the pores. At this stage, the limiting step in the drying process was the rate of water vapour diffusion in the pores because liquid water had to evaporate and move to the surface in the gas phase. This phenomenon explains the observed decrease in the drying rate at longer drying times (Geankoplis, 2003; Perre et al., 2007).

Fig. 2. Normalised drying rate (NDR) versus moisture ratio (MR) curves of Nephelium Lappaceum dried at different drying temperatures.

Fig. 3. Plot of NDR versus drying period. 3.2. Mathematical Modelling

The moisture ratio (MR) was calculated using Equation 3, and regression analysis was performed using Microsoft Excel. Table 2 shows the calculated data for the selected thin layer drying model.

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Compared to other mathematical models, the Logarithmic model was the best model for all of the drying WHPSHUDWXUHV EHFDXVH WKH ORZHVW 506( 66( DQG Ȥ2 were observed (Table 3). The results were confirmed by plotting the graph of the experimental MR versus the predicted MR (Figure 4). All of the R2_{values were greater}

than 0.99, which indicates that the fit was good.

Table 2. Mathematical drying model constants.

T (ºC) Model Name Model Constants Lewis k = 0.1831

Page n = 1.0670, k = 0.1650 40 Handerson and Pabis a = 1.0473, k = 0.1949

Logarithmic a = 1.0489, c = -0.0075, k = 0.1907

Two-Term a = 0.5236, b = 0.5236, k0= 0.1949, k1= 0.1949

Lewis k = 0.3081

Logarithmic a = 1.1650, c = 0.0061, k = 0.3690

Two-Term a = 0.5793, b = 0.5793, k0= 0.3605, k1= 0.3605

Lewis k = 0.3434

Logarithmic a = 1.0868, c = 0.0133, k = 0.3906

Two-Term a = 0.5344, b = 0.5344, k0= 0.3685, k1= 0.3685

Lewis k = 0.4236

Logarithmic a = 1.2028, c = 0.0085, k = 0.5141

Two-Term a = 0.5902, b = 0.5902, k0= 0.4937, k1= 0.4937

Lewis k = 0.6402

Logarithmic a = 0.9258, c = 0.0116, k = 0.6282

Two-Term a = 0.4378, b = 0.4378, k0= 0.5748, k1= 0.5748

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Table 3. Statistical results for thin layer mathematical modelling with different drying temperatures.

T (ºC) Model Name RMSE SSE Ȥ2 R2

Lewis 0.01164 0.00014 0.00014 0.99951

Page 0.00647 0.00004 0.00004 0.99952

40 Handerson and Pabis 0.00597 0.00004 0.00004 0.99933

Logarithmic 0.00550 0.00003 0.00003 0.99955

Two-Term 0.00597 0.00004 0.00004 0.99933

Lewis 0.01982 0.00039 0.00041 0.99630

Page 0.00855 0.00007 0.00008 0.99766

Logarithmic 0.00450 0.00002 0.00002 0.99923

Two-Term 0.00528 0.00003 0.00003 0.99707

Lewis 0.01152 0.00013 0.00014 0.99840

Page 0.01035 0.00011 0.00011 0.99860

Logarithmic 0.00635 0.00004 0.00004 0.99929

Two-Term 0.00874 0.00008 0.00008 0.99929

Lewis 0.01542 0.00024 0.00025 0.99628

Page 0.00877 0.00008 0.00008 0.99436

Logarithmic 0.00433 0.00002 0.00002 0.99831

Two-Term 0.00615 0.00004 0.00004 0.99559

Lewis 0.01012 0.00010 0.00011 0.99651

Page 0.00694 0.00005 0.00005 0.99697

Logarithmic 0.00503 0.00003 0.00003 0.99729

Two-Term 0.00809 0.00007 0.00007 0.99114

3.3. Effective Diffusivity and Activation Energy

Fick’s second law of diffusion was used to evaluate the effective diffusivity of Nephelium Lappaceum because all of the samples showed a falling rate period in their drying characteristics. Samples used in the present study were analysed in slab geometry form; thus, the effective diffusivity of the samples was determined by writing Equation 3 in terms of a linear equation (Equation 4).

As the drying temperature increased, the value of Deffalso increased. Samples dried at 40ºC presented the lowest

Deff, which was 1.34 x 10-10m2/s, and samples dried at 80ºC had the highest Deff, which was 4.36 x 10-10m2/s. These

results are within the range of effective diffusivities of agriculture products reported by several researchers (Table 4).

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(4) The Arrhenius equation (Equation 5) was used to describe the relationship between the effective diffusivity and drying temperature (Roberts et al., 2008). The estimated diffusivity constant, D0, and activation energy, Ea, were

2 2 2

4 )

(

exp

)

8 (

L

D

MR

S

eff

S

2 2 2

4 )

(

)

8 ln(

)

ln(

L

D

MR

S

eff

S

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2.23 x 10-6_m2_{/s and 24.99 kJ/mol, respectively. These values were determined using the relationship shown in}

Figure 5. The value of Ea was within the range of Ea values reported in previous studies, which varied from 12.32

kJ/mol to 51.26 kJ/mol (Hii et al., 2009; Senadeera et al., 2003).

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Table 4. Effective diffusivities of dried Nephelium Lappaceum and other agriculture products.

Agriculture Material Effective Diffusivity, Deff(m2/s) References

Nephelium Lappaceum (40ºC) 1.34 x 10-10 _{Current work}

Apple 0.483 x 10-10_{– 2.019 x 10}-10 _{Kaya et al., 2007}

Strawberry 4.95 x 10-10_{– 1.42 x 10}-9 _{Doymaz, 2008}

Celery 3.43 x 10-11_{– 1.714 x 10}-10 _{Evin, 2012}

Cocoa 8.01 x 10-11_{– 4.84 x 10}-10 _{Hii et al., 2009}

Figure 5. Plot of ln Deff vs. 1/T during the oven drying of Lappaceum Nephelium.

4. Conclusion

The drying of Nephelium Lappaceum was carried out using an oven at five different drying temperatures (40ºC, 50ºC, 60ºC, 70ºC and 80ºC) for 24 hours. Based on the present results, the drying temperature significantly affects the drying rate of Nephelium Lappaceum. Moreover, a falling rate period was observed for all of the samples during the drying process. According to the R2

Ȥ2, SSE and RMSE values, the logarithmic model best fit the experimental data. The effective diffusivities varied from 1.34 x 10-10_m2_{/s to 4.36 x 10}-10_m2_{/s. The diffusivity constant, D}

0, and

RT

E

D

a eff

)

(

exp

0

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activation energy, Ea, were estimated using the Arrhenius equation, and the values were 2.23 x 10-6m2/s and 24.99

kJ/mol, respectively.

Acknowledgement

The authors gratefully acknowledge the Ministry of Higher Education of Malaysia for FRGS grant (600-RMI/st/FRGS5/3/Fst(276/2010), the Faculty of Chemical Engineering and Universiti Teknologi MARA (UiTM).

References

Al-Muhtaseb, A. A. H., Al-Harahsheh, M., Hararah, M., & Magee, T. R. A. (2010). Drying characteristics and quality change of unutilized-protein rich-tomato pomace with and without osmotic pre-treatment. Industrial Crops and Products, 31(1), 171-177.

Allaeddini, B., & Emam-Djomeh, Z. (2004). Formulation and quality improvvement of dried kiwifruit slices using an osmotic pre-treatment. Paper presented at the 14th Internationaal Drying Symposium (IDS 2004), Sao Paulo, Brazil.

Ceylan, I., Aktas, M., & Dogan, H. (2007). Mathematical Modelling of Drying characteristics of tropical fruits. Aplied Thermal Engineering, 27, 1931-1936.

Chooi, O. H. (2004). Buah: Khasiat Makanan dan Ubatan (4th ed., pp. 124-126). Utusan Publications & Distributors Sdn Bhd, Kuala Lumpur. Dandamrongak, R., Young, G., & Mason, R. (2002). Evaluation of various pre-treatments for the dehydration of banana and selection of suitable

drying models. Journal of Food Engineering, 55, 139-146.

Diczbalis, Y. (2002). Rambutan: improving yield and quality. Rural Industries Research and Development Corporation, Queensland. Doymaz, I. (2004). Drying Kinetics of White Mulberry. Journal of Food Engineering, 61, 341-346.

'R\PD]ø&RQYHFWLYHGU\LQJNLQHWLFVRIVWUDZEHUU\Chemical Engineering and Processing: Process Intensification, 47(5), 914-919. Evin, D. (2012). Thin layer drying kinetics of Gundelia tournefortii L. Food and Bioproducts Processing, 90(2), 323-332.

Geankoplis, C. J. (2003). Transport Processes and Separation Process principles, Includes Unit Operations (4th ed., pp. 576-580). Prentice Hall, Hew Jersey.

Guiné, R. P. F., Pinho, S., & Barroca, M. J. (2011). Study of the convective drying of pumpkin (Cucurbita maxima). Food and Bioproducts

Processing, 89(4), 422-428.

Hii, C. L., Law, C. L., Cloke, M., & Suzannah, S. (2009). Thin layer drying kinetics of cocoa and dried product quality. Biosystems Engineering, 102(2), 153-161.

Jamali, A., Kouhila, M., Mohamed, L. A., Idlimam, A., & Lamharrar, A. (2006). Moisture adsorption–desorption isotherms of Citrus reticulata leaves at three temperatures. Journal of Food Engineering, 77(1), 71-78.

Janjai, S., Mahayothee, B., Lamlert, N., Bala, B. K., Precoppe, M., Nagle, M., & Müller, J. (2010). Diffusivity, shrinkage and simulated drying of litchi fruit (Litchi Chinensis Sonn.). Journal of Food Engineering, 96(2), 214-221.

Karim, M. A., & M. N. A. Hawlader. (2005). Mathematical modelling and experimental investigation of tropical fruits drying. International

Journal of Heat and Mass Transfer, 48, 4914-4925.

Kaya, A., Aydin, O., & Demirtas, C. (2007). Drying Kinetics of Red Delicious Apple. Biosystem Engineering, 96(4), 517-524.

Landrigan, M., Morris, S. C., Eamus, D., & McGlasson, W. B. (1996). Postharvest Water Relationships and Tissue Browning of Rambutan Fruit.

Scientia Horticulture, 66(3-4), 201–208.

Lemus-Mondaca, R., Betoret, N., Vega-Galvez, A., & Lara, E. (2008). Dehaydration characteristics of papaya (Carica Pubenscens): determination of equilibrium moisture content and diffusion coefficient. Journal of Food Process Engineering, 32(5), 645-663.

Lewicki, P. P. (1998). Effect of pre-drying treatment, drying and rehydration on plant tissue properties: A review. International Journal of Food

Properties, 1(1), 1-22.

O'Hare, T. J., Prasad, A., & Cooke, A. W. (1994). Low temperature and controlled atmosphere storage of rambutan. Postharvest Biology and

Technology, 4(1–2), 147-157.

Perre, P., Remond, R., & Turner, I. W. (2007). Modern drying technology (Vol. 1: computational tools at different scales). WILEY-VCH, Germany.

Radha, T., & Mathew, L. (2007). Fruit crops- horticulture science series (Vol. 3). New India Publishing Agency, New Delhi Ramaswamy, H., & Marcotte, M. (2006). Food processing: principle and applications. Taylor & Francis, New York

Roberts, J. S., Kidd, D. R., & Padilla-Zakour, O. (2008). Drying kinetics of grape seeds. Journal of Food Engineering, 89(4), 460-465.

Mohamed, S. & Othman, E. (1988). Effect of packaging and modified atmosphere on the shelf life of rambutan (Nephelium lappaceum) I.

Pertanika, 11(2), 217-228.

Senadeera, W., Bhandari, B. R., Young, G., & Wijesinghe, B. (2003). Influence of shapes of selected vegetable materials on drying kinetics during fluidized bed drying. Journal of Food Engineering, 58(3), 277-283.

Varith, J., Dijkanarukkul, P., Achariyaviriya, A., & Achariyaviriya, S. (2007). Combined microwave-hot air drying of peeled longan. Journal of

Food Engineering, 81(2), 459-468.

Vega-Gálvez, A., Ah-Hen, K., Chacana, M., Vergara, J., Martínez-Monzó, J., García-Segovia, P.,Lemus-Mondaca,R., Di Scala, K. (2012). Effect of temperature and air velocity on drying kinetics, antioxidant capacity, total phenolic content, colour, texture and microstructure of apple (var. Granny Smith) slices. Food Chemistry, 132(1), 51-59.

Yingsanga, P., Srilaong, V., Kanlayanarat, S., Noichinda, S., & McGlasson, W. B. (2008). Relationship between browning and related enzymes (PAL, PPO and POD) in rambutan fruit (Nephelium lappaceum Linn.) cvs. Rongrien and See-Chompoo. Postharvest Biology and