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1 This article was downloaded by: [The University of Nottingham ( Malaysia Campus )] On: 6 October 2008 Access details: Access Details: [subscription number ] Publisher Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: Registered office: Mortimer House, Mortimer Street, London W1T 3JH, UK Drying Technology Publication details, including instructions for authors and subscription information: Drying Kinetics, Texture, Color, and Determination of Effective Diffusivities During Sun Drying of Chempedak Chien Hwa Chong a ; Chung Lim Law a ; Michael Cloke a ; Luqman Chuah Abdullah b ; Wan Ramli Wan Daud c a Faculty of Chemical and Environmental Engineering, The University of Nottingham, Malaysia Campus, Semenyih, Selangor, Malaysia b Faculty of Engineering, University Putra Malaysia, Serdang, Selangor Darul Ehsan, Malaysia c Faculty of Chemical Engineering, Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia Online Publication Date: 01 October 2008 To cite this Article Chong, Chien Hwa, Law, Chung Lim, Cloke, Michael, Abdullah, Luqman Chuah and Daud, Wan Ramli Wan(2008)'Drying Kinetics, Texture, Color, and Determination of Effective Diffusivities During Sun Drying of Chempedak',Drying Technology,26:10, To link to this Article: DOI: / URL: PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.

2 Drying Technology, 26: , 2008 Copyright # 2008 Taylor & Francis Group, LLC ISSN: print/ online DOI: / Drying Kinetics, Texture, Color, and Determination of Effective Diffusivities During Sun Drying of Chempedak Chien Hwa Chong, 1 Chung Lim Law, 1 Michael Cloke, 1 Luqman Chuah Abdullah, 2 and Wan Ramli Wan Daud 3 1 Faculty of Chemical and Environmental Engineering, The University of Nottingham, Malaysia Campus, Semenyih, Selangor, Malaysia 2 Faculty of Engineering, University Putra Malaysia, Serdang, Selangor Darul Ehsan, Malaysia 3 Faculty of Chemical Engineering, Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia Sun drying of chempedak (Artocarpus integer) was carried out on different sample sizes to investigate the effects on product quality. Fick s second law model was used to determine the effective diffusivities of sun dried chempedak slabs based on the drying rate versus moisture content plots. In addition, texture degradation and total color changes were investigated. The texture and color changes of dried chempedak were relatively significant (p < 0.05) compared to fresh chempedak. There was an increase in dried fruit hardness and chewiness but a decrease in springiness and cohesiveness during drying. Keywords Chempedak; Color; Effective diffusivities; Sun drying; Texture INTRODUCTION Depletion of fossil fuel energy and economical and environmental problems have brought forth many alternative drying methods such as indirect dryers, rotary dryers, fluidized-bed dryers, drum dryers, spray dryers, freeze dryers, microwave-dielectric dryers, solar dryers, conveyor dryers, spouted-bed dryers, impingement dryers, infrared dryers, superheated steam dryers, and pneumatic flash, hot air dryers and forced hot air dryers. [1] However, sun drying is widely used to dehydrate cocoa, fruit, vegetables, and crops of all varieties in food processing. [2] Drying kinetics are generally affected by drying temperature, relative humidity, and product sizes. [3 7] Thus, many studies on the drying characteristics and kinetics of various vegetables and fruits such as apricots, [8] sultana grapes, [9] figs, [10] white mulberry, [11] and ciku [3] have been conducted. However, research on the drying kinetics of chempedak is rather scarce, with studies on the kinetics Correspondence: Chien Hwa Chong, Faculty of Chemical and Environmental Engineering, The University of Nottingham, Malaysia Campus, Broga Road, Semenyih, Selangor, Malaysia; chongchienhwa@hotmail.com of nutrient destruction but fewer studies on the texture and color changes, even though texture is one of the major sensory evaluations determining the quality of most food. According to Bourne, [12] texture is the response of the tactile senses to physical stimuli that results from contact between some parts of the body with food products. This sensory evaluation is very important because people like to attain great enjoyment from eating food that possesses certain texture properties. Texture degradation of thermally processed biomaterials is closely related to enzymatic and nonenzymatic changes in pectin (a cell wall polysaccharide). Enzymatic degradation of cell wall pectin is catalyzed by different pectinases, such as pectinmethylesterase (PME) and polygalacturonase (PG). [13] Hardness, springiness, cohesiveness, and chewiness that occur during processing were measured, as these are valuable insights in understanding the changes of texture. During the drying of solids, some undesired chemical and physical changes like color changes or browning occur simultaneously. [14,15] The objective of this study was to investigate the drying kinetics and drying characteristics of sundried chempedak and to evaluate the texture degradation and color changes of chempedak slabs. In addition, the effective diffusivities during chempedak drying were determined. METHODOLOGY Preparation of Samples Chempedak (Artocarpus integer) was purchased from a local fruit supplier. The chempedak fleshy arils were cut into dimensions of 2.0 cm 3.0 cm 0.3 cm, 3.0 cm 3.0 cm 0.3 cm, and 4.0 cm 3.0 cm 0.3 cm by using a stainless steel knife. Different dimensions of samples were placed on a perforated tray fully covered by fishing net. A typical diagram of the perforated dryer and ciku slabs is shown in Fig. 1. Sun-drying experiments were performed 1286

3 SUN DRYING OF CHEMPEDAK 1287 Effective Diffusivities Fick s second law equation was applied to describe the effective diffusivity of sundried chempedak slabs at the product size tested. Moisture ratio (MR) is used as a dependent variable as described in Eq. (4), which relates the initial moisture content ðm i Þ, equilibrium moisture content ðm e Þ, and moisture in actual time ðm t Þ. The effective diffusivity ðd eff Þ is determined by using the analytical solution of Fick s second law (Eq. (5)). [16] FIG. 1. Schematic diagram of solar dryer and ciku slabs. during the period of June to November 2007 in Selangor ( N and E), Malaysia. Samples were sundried from 10:00 am to 4:00 pm and tempered from 4:00 pm to 10:00 am. The same procedures were repeated for day 2 until no measurable weight loss was observed. The weight losses of samples were recorded using an electronic balance (Adventure OHAUS, AR3130, Pine Brook, NJ, USA) with range g with a system error of g at 15-min intervals for 3 h, followed by hourly intervals. Thereafter, provision was also made to record the relative humidity, temperature using a Hygrometer (HygroFlex, RS232, Huntington, NY, USA), and air velocity using Hygrolog (Rotronic, D5-U-2, Huntington, NY, USA). The average velocity recorded was 1.65 m=s. Three replicates were carried out in this study. The moisture content (M) and drying rate (DR) for the chempedak slabs during drying experiments were calculated using the following equation: M ¼ M f M t M f DR ¼ M t M tþdt ð2þ Dt A Area of the fruit was calculated using the following equation and assume to be constant in this study: A ¼ xy þ 2ðxzÞþ2ðyzÞ ð1þ ð3þ MR ¼ M t M e ð4þ M i M e MR ¼ 8 p 2 e D Ltðp=2lÞ 2 þ 1 9 e 9D Ltðp=2lÞ 2 þ e 25D Ltðp=2lÞ þ ð5þ Equation (5) assumes uniform distribution of moisture at initial stages of drying. The first term in Eq. (5) is used if the drying time is sufficiently long. [17 19] Thus, Eq. (5) is simplified to Eq. (6). MR ¼ 8 p 2 e D eff tðþ 2l p 2 ð6þ By applying natural logarithm on both sides, Eq. (7) is obtained: ln MR ¼ ln 8 p 2 D p 2t eff ð7þ 2l If ln MR is plotted versus drying time, t, a straight line is obtained. The slope of the line is p 2 Slope ¼ D eff 4l 2 ð8þ The effective diffusivity, D eff, can be obtained once the slope of ln MR versus t plot is obtained and the intersection is ln 8=p 2, which is Compression Test The length, width, and thickness of fresh and dried chempedak were measured. Each sample was aligned horizontally from the stem end to the apex on the platform and deformation on only one side of the chempedak slab was assumed. Three measurements were taken on each sample. Texture analyzer (TA.XT Plus, Stable Micro System, Surrey, U.K.) fitted with a cylindrical puncture probe of 2.0 mm diameter was used. The texture analyzer was programmed so that the downward movement began at 10 mm above the surface of the sample. The probe was moved from the surface of the fruit to a depth of 10 mm (chempedak slabs total thickness are 30 mm) with a trigger force 5.0 g at a pretest, test, postspeed of 1.0, 5.0, and 5.0 mm=s, respectively. Three replicates were performed in this study. Two compression cycles were

4 1288 CHONG ET AL. of (a ) corresponds to more redness. Equations (13) (15) were used to calculate the total color change shown in Eq. (16). DL ¼ L L o Da ¼ a a o Db ¼ b b o The total color change was determined by Eq. (16): ð13þ ð14þ ð15þ DE ¼½ðDL Þ 2 þðda Þ 2 þðdb Þ 2 Š 1 2 ð16þ FIG. 2. Typical force-time diagram of texture profile analysis (TPA). used in the texture profile analysis, [20] where the fruit was compressed up to the maximum force twice continuously. The second maximum force is kept at the same position and the decline in force was recorded. After the second cycle, the probe returned to its initial position. From the two-cycle compression curve, parameters such as maximum load of first cycle ðf 1 Þ, maximum load of second cycle ðf 2 Þ,area under first curve ða 1 Þ, area under second curve ða 2 Þ,time elapsed from area 1 above positive y axis ðt 1 Þ, and time elapsed from area 2 above positive y axis ðt 2 Þ were extracted for the quality analysis. Sensory attributes that are used to describe texture quality of solid fruits are given in Eqs. (9) (12) and shown in Fig. 2. Hardness; H ¼ F 1 Springiness; S ¼ T 2 T 1 Cohesiveness; C ¼ A 2 A 1 Chewiness; CW ¼ H:C:S ð9þ ð10þ ð11þ ð12þ Hardness, springiness, cohesiveness, and chewiness were automatically computed from each curve using texture analyzer software macro (Texture Exponent 32 Stable Micro [4, 21 23] System, Texture Profile Analysis). Color Analysis The color of fresh and dried chempedak was determined in terms of stimulus color parameters based on Commission Internationale de I Eclairage (CIE) using color meter (AccuProbe, HH06, Salem, MA, USA) Lightness (L ) is 0 (black) to 100 (white); greenness or redness (a ) is 60 (greenness) to 60 (redness); and blueness or yellowness (b )is 60 (blueness) to 60 (yellowness). Lightness (L ) indicates brightness and higher positive value of (b ) correspond to more yellowness, while higher positive value Statistical Analysis All quality experiments were analyzed in triplicate by using completely randomized design. Analysis of variance was performed by SAS statistical package (SAS Institute Inc, SAS=STAT 9.1). Means were compared by Tukey s Studentized range (HSD) test at p < RESULTS AND DISCUSSION The average variation of relative humidity and temperature during sun drying of chempedak slabs is shown in Fig. 3. During the drying experiments, the ambient relative humidity and temperature were measured and both were in the range of 51.9 to 87.6% and 24.6 to 32.5 C, respectively. From Fig. 3 it can be observed that the temperature increased gradually from 29.6 to 31.7 C from 10:00 am to 11:00 am and then started to fluctuate in the range of 31.2 Cto32 Cfrom 11:00 am to 12:30 pm. It attained a maximum value between 12:30 pm to 3:00 pm, where temperature was in the range of 32.0 to 32.5 C. Then, the temperature started to decrease from 31.4 to 32.0 C during 3:00 pm to 4:00 pm. The temperature profile on day 2 was similar. The ambient relative humidity is inversely proportional to the ambient temperature, and the relative humidity decreased gradually from 64.8 to 54.5% from 10:00 am to 12:30 pm and then the lowest relative humidity can be seen fluctuating around 1:00 pm to 3:00 pm, which was in the range of 52.5 to 55.7% due to the high ambient temperature. In addition, tempering period temperature and relative humidity were recorded in this study as it was an unavoidable period for natural sun drying process during nighttime, where it was in the range of 24.6 to 31.2 Cand60.9to87.6%, respectively. Effects of Samples Dimensions The drying kinetics of chempedak slabs (dried in two sunny days) with different product size are as shown in Figs. 4 and 5. The initial transient period (day 1) occurred in the first 45 min, where temperature and relative humidity were in the range of 29.6 to 31.7 C and 57.8 to 64.8%, respectively. The highest drying rates were generally observed at moisture content of 2.05 g H 2 O=g DM to

5 SUN DRYING OF CHEMPEDAK 1289 FIG g H 2 O=g DM because the moisture content is still high and the temperature of the sample starts to increase at this stage (region 1). Then, the drying rates of chempedak slabs were nearly constant at region 2, where the temperature and relative humidity fluctuate in the range of 31.3 to 32.0 C and 54.5 to 59.1%, respectively, from 90 to 135 min. min. Furthermore, the drying rates enhanced noticeably from 135 to 360 min because of the drying condition (region 3), where temperature and humidity were in the range of 32.0 to 32.5 C and 52.5 to 55.7%, respectively. Average ambient temperature and relative humidity. Tempering period (region 4) drying rates (0.013 to g H 2 O=g DMm 2 s) was relatively low compared to other region D1, D2, and D3 because of the drying condition (low temperature and high relative humidity). The drying rates were in the range of to g H 2 O=g DMm 2 s, to g H 2 O=g DMm 2 s, and to g H 2 O=g DMm 2 s, for the three dimensions tested (2.0 cm 3.0 cm 0.3 cm, 3.0 cm 3.0 cm 0.3 cm, and 4.0 cm 3.0 cm 0.3 cm). It can be clearly seen from Figs. 4 and 5 that smaller product drying rates was higher. FIG. 4. Drying curves of different dimensions of chempedak slabs (2.0 cm 3.0 cm 0.3 cm, 3.0 cm 3.0 cm 0.3 cm, and 4.0 cm 3.0 cm 0.3 cm) obtained from sun drying.

6 1290 CHONG ET AL. This is because of the bigger surface-to-volume ratio of the sample, the higher the rate of heat and mass transfer. These are in agreement with observations reported by Gong et al., [24] Panchariya et al., [25] Giraldo-Zuniga et al., [26] and Demirel and Turhan [27] in drying of other fruit and vegetables. FIG. 5. Drying rate versus time of different dimensions of chempedak slabs (2.0 cm 3.0 cm 0.3 cm, 3.0 cm 3.0 cm 0.3 cm, and 4.0 cm 3.0 cm 0.3 cm) obtained from sun drying. Determination of Effective Diffusivities The drying kinetics of sundried chempedak were separated into six different regions based on Fig. 4 drying kinetics for each dimensions (4.0 cm 3.0 cm 0.3 cm, 3.0 cm 3.0 cm 0.3 cm, 2.0 cm 3.0 cm 0.3 cm), which are initial transient, first falling rate period (D1), second falling rate period (D2), third falling rate period (D3), tempering period (D4), and fourth falling rate period (D5). The effective diffusivities were determined by the slope of a straight line obtained from the natural logarithm of moisture ratio values, ln (MR) versus drying time (t) plot as shown in Fig. 6. Effective diffusivities of sundried FIG. 6. ln MR versus time plots of chempedak slabs dried at different product sizes: (a) 4.0 cm 3.0 cm 0.3 cm, (b) 3.0 cm 3.0 cm 0.3 cm, (c) 2.0 cm 3.0 cm 0.3 cm under sun drying.

7 SUN DRYING OF CHEMPEDAK 1291 TABLE 1 Effective diffusivities of sundried chempedak slabs Region, D Average ambient temperature ( C) Average relative humidity (%) Product size Effective diffusivities (m 2 =s) 4.0 cm 3.0 cm 0.3 cm cm 3.0 cm 0.3 cm cm 3.0 cm 0.3 cm The values indicate mean standard deviation from three replications. chempedak slabs for different dimensions calculated based on Eq. (8) are shown in Table 1. It was in the range of to m 2 =s, to m 2 =s and to m 2 =s for different product size tested (2.0 cm 3.0 cm 0.3 cm, 3.0 cm 3.0 cm 0.3 cm, and 4.0 cm 3.0 cm 0.3 cm). These values are in agreement with the fruit and vegetable effective diffusivities range reported in most food materials reports (Table 2). Moisture transfer increases as a result of the drop at relative humidity due to increase of ambient temperature (Fig. 3), which in turn causes an increase in the effective diffusivities (Table 1). Tempering period (D4) effective diffusivities were in the range of to m 2 =s. These values were low compared to other falling rate period effective diffusivities owing to the moisture distribution in the samples and the ratio of sample diffusive to the surroundings is relatively small (sealed in 4.0 cm 5.0 cm plastic bag). Texture Analysis Table 3 shows the texture analysis of fresh and dried chempedak slabs. Based on the results, hardness, cohesiveness, and chewiness values were significantly changed (p < 0.05) during sun drying but not springiness (p > 0.05). Dried chempedak hardness and chewiness were found to be higher (p < 0.05) compared to fresh chempedak. However, cohesiveness and springiness were relatively low compared to fresh chempedak. Hardness is an important parameter used to investigate case-hardening in dried fruits. The softer the dried fruits, the higher the quality of the dried product. Fresh chempedak is soft where the hardness is 9.18 g but after sun drying the hardness of the samples increased to g. Hardness increased significantly (p < 0.05), which could be due to the depolymerization of cell wall constituents such as pectin, after exposure to heat in the drying process. This was in agreement with the findings of Yang et al. [28] in the study of storage temperature on textural properties of Chinese bayberry fruit. TABLE 2 Effective diffusivities of other fruit and vegetables Fruits Effective diffusivity (m 2 =s) References Hot air dried grape [32] Hot air dried mulberry [33] Hot air dried prune [34] Sundried tomato [35] Vacuum-assisted solar-dried tomato [35] TABLE 3 Hardness, springiness, cohesiveness, and chewiness of fresh and dried chempedak Original Hardness (g) Springiness Cohesiveness Chewiness (g) Fresh chempedak a a a a Dried chempedak b a b b The values indicate mean standard deviation from three replications. Values within the same column with similar letters are not significantly different.

8 1292 CHONG ET AL. TABLE 4 Color parameters (L, a, b ) of fresh and dried chempedak Original L a b Fresh chempedak a a a Dried chempedak b b b The values indicate mean standard deviation from three replications. Values within the same column with similar letters are not significantly different. However, these results are comparable to hot air and freeze drying of apple slices, where texture strengths were g and g, respectively. [29] Springiness (S ) depends on the gelling agent in the fruits in most agriculture products. This quality is important as it measures the elastic behavior of the treated samples and how much the samples structure is broken by the initial penetration. The fresh and dried chempedak samples springiness were not significant (p > 0.05), at and 0.605, respectively. Springiness of the dried chempedak is lower than fresh chempedak, which could be due to dehydration reducing the elasticity of the fruit. This is in agreement with the findings of Sirisomboon et al. [30] in texture studies of Japanese pear, where hardening indicated a decrease of fruit elasticity. The cohesiveness (C) measures the rate at which the material disintegrates under mechanical action. Table 3 shows that the fresh chempedak slabs (0.602) were relatively higher in cohesiveness compared to the dried samples (0.475). This could be because of the cell membrane structure of chempedak slabs being altered during drying, thus causing the pectin substances to redistribute. Chewiness (CW) is measured in terms of the energy required to masticate a solid food, which is defined in Eq. (12) as the product of hardness, cohesiveness, and springiness. Evaluation on the chewiness of the dried chempedak slabs is the major consideration for consumers as it affects the oral cavity mouth feel. The chewiness of fresh and dried chempedak were 3.65 g and g, respectively. The statistical significance in the difference between fresh and dried samples for the compression test is shown in Table 3. There is a significant difference between fresh and dried samples (p < 0.05). Total Color Changes The changes in color of sundried chempedak slabs compared to fresh chempedak slabs are shown in Table 4. It was observed that the lightness, L and b values of the samples decreased from to and to 33.03, respectively, while the parameter a increased from 2.57 to This result shows that the sundried chempedak slabs were significantly darker (p < 0.05) than the fresh chempedak because of the enzymatic browning effect. The total color change value for sundried chempedak slabs is Dried chempedak slabs tended to exhibit significant difference (p < 0.05) in color change compared to fresh samples because of the long drying duration (two sunny days). However, the sundried samples total color changes were low compared to cabbages (24.66 to 35.68) [24] and in the range of okra drying, which is [31] CONCLUSIONS It was found that the effective diffusivities of sun drying are comparable to the D eff obtained from other drying methods, where the values are in the range of 10 9 to m 2 =s except in the tempering period. In terms of quality, it was observed that the color and texture change of dried chempedak was relatively significant compared to fresh chempedak. However, the results obtained were in the accepted range of dried fruit products with regard to quality, drying, and diffusion rates found in this study, it can be concluded that Malaysia weather conditions are suitable for sun drying of fruits in general and chempedak in particular. NOMENCLATURE A Area A 1 Area under first curve A 2 Area under second curve a a Value (CIE) a o Initial a value (CIE) b b Value (CIE) a o Initial b value (CIE) C Cohesiveness CIE Commission Internationale de I Eclairage CW Chewiness D1 Region 1 D2 Region 2 D3 Region 3 D4 Region 4 D5 Region 5 D eff Effective diffusivity (m 2 =s) DM Dry matter DR Drying rate (g H 2 O=g DMm 2 s) DE Total color change E a Activation energy (kj=mol) F 1 Maximum load of first cycle (g) Maximum load of second cycle (g) F 2

9 SUN DRYING OF CHEMPEDAK 1293 H L L o l M M e M f M i MR M t R 2 S T a T 1 T 2 Dt x y z Hardness (g) L value (CIE) Initial L value (CIE) Thickness of the slab (m) Moisture content (g H 2 O=g DM) Equilibrium moisture content (g H 2 O=g DM) Final moisture content (g H 2 O=g DM) Initial moisture content (g H 2 O=g DM) Moisture ratio Moisture content at actual time, t (g H 2 O=g DM) Coefficient of determination Springiness Air temperature (K) Time elapsed from area 1 (above positive y axis) Time elapsed from area 2 (above positive y axis) Time difference (s) x Axis of ciku slabs y Axis of ciku slabs z Axis of ciku slabs ACKNOWLEDGEMENTS The authors acknowledge the support given by the Ministry of Science and Technology and Innovation through the allocation under e-science fund ( SF0001). REFERENCES 1. Mujumdar, A.S. Handbook of Industrial Drying, 3rd Ed; CRC Press: UK Murthy, M.V.R. A review of new technologies, models and experimental investigations of solar driers. 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