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1 DRYIG CHARACTERISTICS OF SWEET ORAGE PEEL Sankalpa, K.B., Ramachandra, C.T., Udaykumar idni, Sharanaguda Hiregudar, Beladhadi, R.V & Dinesha, B.L. Department f Prcessing and Fd Engineering, Cllege f Agricultural Engineering, University f Agricultural Sciences, Raichur , Karnataka, India. Crrespnding authrs ABSTRACT The aim f this wrk is t investigate the drying characteristics f sweet range peel in three different drying methds i.e., slar tunnel drying, ht air drying and dehumidified air drying. The drying study shwed that the times taken fr drying f sweet range peel in three different drying methd. The drying data were fitted t 5 thin-layer drying mdels, viz.,ewtn, Page, Hendersn-Pabis, Lgarithmic and Midilli-Kucuk mdels The perfrmances f these mdels were cmpared using the determinatin f cefficient (R ), reduced chi-square (χ ) and rt mean square errr (RMSE) between the bserved and predicted misture ratis. Amng the five tested mdel Midilli-Kucuk mdel described the best fit t the experimental data. KEYWORDS: Dehumidified air Drying, Ht air drying, Drying characteristics, Drying mdels and Sweet range peel. ITRODUCTIO Sweet range (Citrus sinensis Osbeck) belngs t sub family Aurantideae which is categrised under family Rutaceae (Milind and Dev, 01). In sweet range 16-0% is cmpsed f peel and it is main by-prduct btained frm sweet range fruit juice prcessing industries. It is the highly perishable and if nt prcessed the peel becme waste and in turn may becme a pssible surce f envirnmental pllutin. By-prduct recvery frm fruit wastes can imprve the verall ecnmics f the prcessing units and the prblem f envirnmental pllutin als can be reduced cnsiderably (Kumar et al., 011). Arund the wrld, 3100 tnnes f range and ther citrus fruits are annually prcessed ut f which the estimated annual waste is 15.6 millin MT (Djilas, 009). These are mainly used fr animal feeds, due t their high fibre cntent; they culd represent an interesting surce f dietary fibre (Larrauri et al., 1997). Since the fruit byprduct has high misture cntent it need efficient drying methd t cnvert wet sweet range peel int dry frm. Slar tunnel drying is an imprved methd ver the pen yard sun drying since the farmer results in shrter drying time and safer prduct. wadays ht air drying is quite cmmn in many industries due t easing f peratin, lw investment and peratin cst cmpare t ther advanced technique. Dehumidified air drying is ne f the imprved drying methds which dry the sample at relatively less temperature and humidity. Garau et al. (006) cnducted experiments n drying kinetics, mdelling and functinal prperties f range skin, Silva et al. (011) prpsed cmbined apprach t ptimize the drying prcess f flavnid-rich leaves using thin layer mdelling, Pnkham et al. (01) cnducted experiment n thin layer mdelling f cmbined farinfrared radiatin and air drying f a ring shaped pineapple, Galvez et al. (010) determined the effective misture diffusivity and mathematical mdelling f the drying curves fr the live-waste cake. In all the stated studies they cnsidered thin layer drying mdels viz., ewtn, Page, Hendersn and Pabis, lgarithmic and Midilli Kucuk mdels. There are n studies shwing drying characteristics f sweet range peel. S in present study effrts were undertaken t describe the drying characteristics f sweet range peel with respect t three drying (slar tunnel drying, ht air drying and dehumidified air drying) by cnsidering the abve said mdels. MATERIAL AD METHODS Sample preparatin Fresh sweet range (cv. Sathgudi) were selected unifrmly accrding t maturity, clur, size and freshness. The fruits were washed, weighed and peeled by using knife. Then peels were cut int small pieces (0mm 10mm), after that it was washed using ht water at 90 C fr 5 min. After that peel surface misture was remved by using muslin clth then it was fllwed by three drying methds with bed thickens f 5mm. Drying prcess and mathematical mdeling Sweet range peel was dried using three drying methds till cnstant weight is btained. In ht air drying, ht air drying at 60 ±1 C was selected accrding t results f Garau et al. (007) in case f dehumidified air drying 45 ±1 C at 15 ±1% RH was selected which is less than ht air drying temperature. In slar tunnel drying, the average temperature recrded was 5 C when average ambient temperature was 37 C. The mathematical mdels namely, ewtn, Page, Hendersn-Pabis, Lgarithmic and Midilli- Kucuk mdels were selected n their ability t best fit the experimental data. The mdels are; ewtn mdel: = exp (-Kθ)...(1) 171

2 Drying traits f sweet range peel Page mdel: = exp (-Kθ n)...() Hendersn- Pabis mdel: = a*exp (-Kθ)...(3) Lgarithmic mdel: = a*exp ( Kθ) + c...(4) Midilli-Kucuk mdel: = bθ + a*exp ( Kθ n )...(5) = Misture rati M-M e The misture rati () is dented by...(6) M-Me M e = equilibrium misture cntent, (% d.b.) M = misture cntent at any time, θ (% d.b.) M = initial misture cntent (% d.b.) K, n, a, b and c = drying rate cnstants θ = drying time (min) Drying rate was calculated accrding t methdlgy explained by Chakraverty Amunt f misture remved Drying Rate...(7) Ttal bne dry weight f sample in gm Time taken 100 The drying parameters f all the mdels were estimated by using Matlab versin 7.0 sftware. The fit quality f the prpsed mdels n the experimental data was evaluated using linear regressin analysis using curve fitting tl in MATLAB. The statistical parameters standard square errr (SSE) and rt mean square errr (RMSE) were calculated emplying the fllwing equatins. 100 P i0 - i=0 RMSE = df 1 SSE =( - ) P p...(8)...(9) p...(10) i=1 ( p ) i1 z...(11) = bserved misture rati P = predicted misture rati df = degrees f freedm =. f data pints z =. f cnstants RESULTS & DISCUSSIO Drying behaviur f sweet range peel Irrespective f drying methd, an increasing trend was bserved in the reductin f misture cntent in beginning f the drying. As the drying prceeded, the lss f misture in sweet range peel decreased with drying time. The reductin in misture cntent, drying rate and misture rati with respect t drying time is given in Table 1. TABLE 1: Final Misture cntent, average drying rate and drying time fr drying f sweet range peel in three drying methds Sl.. Dehumidified air drying Ht air drying slar tunnel drying 1 Drying time, h Final Misture cntent, % d.b Average drying rate, g f water/min. per 100 gm f bne dry materials

3 Fig. 1 shws the influence f drying air temperature n drying rate with respect t drying time. It can be seen that, the drying prcess mainly cnsisted f three drying perids i.e., heating up, cnstant rate and falling rate perid. Ht air drying at temperature f 60±1 C shwed nly the falling rate perid, which was due t mderate temperature f drying. In ht air drying, the drying rate started frm 0.33 t 0.01 g f water/min. Per 100 g f bne dry materials at 60 ±1 C. Cnstant rate f drying was nt bserved in the drying perid, this might be due t thin layer arrangement and t rapid heating f peel, similar bservatin was bserved by Giri and Prasad (007) during micrwave and ht air drying f mushrm. Drying rate [gm f water/ min 100 gm f bne dry material] Average drying time (h) FIGURE 1: Drying rate curve fr different drying methds with respect t drying time Abbreviatin: STD, slar tunnel drying; HD, ht air drying; DD and dehumidified drying DD HD ST D In dehumidified air drying prcess at temperature f 45 ±1 C and 15 ±1% RH, nly falling rate perid was detected and the drying rate was bserved frm 0.51 t 0.0 g f water/min. per 100g f bne dry materials, due t lwer RH f drying air. Drying rate curves shwed a fast increase at the beginning f the prcess ( i.e., 0.51 g f water/min. per 100 gm f bne dry materials) due t rapid sample heating and a subsequent decrease f the drying rate ( i.e., 0.0 g f water/min. per 100 gm f bne dry materials). The results f present research are in agreement with previus studies dealing with drying f range peel in micrwave drying (Ghanem et al., 01) and similar result was als bserved fr drying f nin in dehumidified air dryer (Guda et al., 014). TABLE : Cnstants f drying mdels Sl.. Mdel Cnstants Drying methd STD TD DD 1 ewtn k Page k Hendersn- Pabis 4 Lgarithmic 5 Midilli- Kucuk n a k a c k a b k n The drying rate f sweet range peel varied frm 0.19 g f water/min. per 100 g f bne dry materials in the initial stage f drying t 0.01 g f water/min. per 100 gm f bne dry materials in final stage f drying in slar tunnel drying. In this drying, the drying rate was mainly dependent n varying drying temperature. Here, the temperature varied accrding t the climatic cnditin. Frm the data btained during investigatin, it was bserved that, the cnstant rate perid f drying was absent during the entire perid f drying and the drying tk place under the falling rate perid in all drying methds. Similar type f results were bserved in the case f range peel dried in ht air dryer (Garau et al., 007), micrwave drying f three citrus peel (Ghanem et al., 01), cabinet drying f pmegranate peel (gueira et 173

4 Drying traits f sweet range peel al., 01) and fr thin layer drying fr apple slices (Mabruk et al., 01). Mathematical mdelling f drying f sweet range peel in different drying methds The drying data btained during thin layer drying was fitted int five different drying mdels viz., ewtn, Page, Hendersn-Pabis, lgarithmic and Midilli-Kucuk mdels. The values f misture rati were determined fr all drying methds. Drying cnstants and estimated values f statistical parameters f all five mdels were given in Tables and 3, respectively. TABLE 3: Estimated values f statistical parameters f ewtn, Page, Hendersn-Pabis, Lgarithmic and Midilli-Kucuk mdels used fr fur drying methds Sl.. Parameter Methd Mdel ewtn Page Hendersn- Pabis Lgarithmic Midilli- Kucuk 1 R HD STD DD STD SSE HD DD STD Adjusted-R HD DD STD RMSE HD DD STD P (%) HD DD STD.679E E E E E χ HD.3301E E E E E-004 DD.3466E E E E E-004 The Midilli-Kucuk mdel successfully described the relatinship between misture rati and drying time with the highest R value and lwer χ, P, SSE and RMSE values. The experimental and predicted drying curves f dried sweet range peel are given in Fig.. Similar result was fund fr drying f nin (Guda et al. 014). Present result is als similar t the value (R =0.99) f Garavand et al. (011) fr thin layer drying f tmat and they als reprted Midilli-Kucuk mdel as a gd estimatin mdel fr drying prcess. The results btained are als in line with the value f Mirzaee et al. (011), fr thin layer drying f aprict and they reprted Midilli-Kucuk is the best mdel with highest R value f Misture rati [(M-Me)/M-Me)] DD actual HD actual STD actual DD predicted HD predicted STD predicted Drying time (h) FIGURE : Experimental and midilli-kucuk mdel predicted misture rati fr different drying methds (Abbreviatin: STD, slar tunnel drying; HD, ht air drying; and DD dehumidified drying) 174

5 COCLUSIO Amng three drying techniques dehumidified air drying required less drying time (3.5 h) with lwest misture cntent (6.5 % d.b.). Experimental results shw that dehumidified drying is the best methd t dry the fresh sweet range peel. Amng the five drying mdels tested namely, ewtn, Page, Hendersn-Pabis, Lgarithmic and Midilli-Kucuk, the Midilli-Kucuk mdel described the best fit f the experimental data with higher R value and lwest SSE, χ, RMSE and P values. REFERECES Chakraerty, A. (1981) Pst harvest technlgy f cereals, pulses and ilseeds. 3 rd editin. Oxfrd and IBH publishing C. Pvt. Ltd. ew Delhi. Djilas, S. (009) By-prducts f fruits prcessing as a surce f phytchemicals- A review. Chem. Ind. Chem. Eng. Q. 15 (4): Galvez, A.V., Miranda, M., Diaz, L.P., Lpez, L., Rdriguez, K. and Scala, K.D. (010) Effective misture diffusivity determinatin and mathematical mdelling f the drying curves f the live-waste cake. Biresurce Technl. 101, Garau, M.C., Simal, S., Femenia, A. & Rssell, C. (006) Drying f range skin: drying kinetics mdelling and functinal prperties. J. Fd Engg. 75, Garau, M.C., Simal, S., Rssell, C. and Femenia, A. (007) Effect f air-drying temperature n physicchemical prperties f dietary fibre and antixidant capacity f range ( Citrus aurantium v. Canneta) byprducts. J. Fd Chem. 104 (3), Garavand, A.T., Rafieea, S. and Keyhani, A. (011) Mathematical mdeling f thin layer drying kinetics f tmat influence f air dryer cnditins. Int. T. J. Eng. (), Ghanem,., Mihubi, D., Kechau,. and Mihubi,. B. (01) Micrwave dehydratin f three citrus peel cultivars: Effect n water and il retentin capacities, clur, shrinkage and ttal phenls cntent. J. Ind. Crps Prd. 40, Giri, S.K. and Prasad, S. (007) Drying kinetics and rehydratin characteristics f micrwave-vacuum and cnvective ht-air dried mushrms. J Fd Eng. 78, Guda, G.P., Ramachandra, C.T. and idni, U. (014) Dehydratin f Onins with Different Drying Methds. Curr. Trends Tech. Sci. 3, Kumar, A.K., arayani, A., Subanthini, D. and Jayakumar, M. (011) Antimicrbial activity and phytchemical analysis f citrus fruit peels-utilizatin f fruit waste. J. Sci. Technl. 3 (6), Larrauri, Rupbrez, P., Brav, L. and Calixt, S.F. (1997) High dietary fibre peels: assciated pwders frm range and lime plyphenls and antixidant capacity, Fd Res. Int. 9 (8), Mabruk, S.B., Benali, E. and Queslati, H. (01) Experimental study and numerical mdelling f drying characteristics f apple slices, Fd Biprd. Prcess. 94 (4), Milind, P. and Dev, C. (01) Orange: Range f benefits: A review. Int. Res. J. Pharm. 3 (7): Mirzaee, E., Rafiee, S. and Keyhani, A. (011) Evaluatin and selectin f thin-layer mdels fr drying kinetics f aprict (cv. asiry). Agric Eng Int: CIGR J. 1 (), gueira, R.I., Paim, D.R.F., Crnej, F.E.P., Marian, E. S., Barret, A.S. and Freitas, S.P. (01) Drying kinetics f pmegranate (Punica granatum) peels, Pster presented in internatinal cnference n agricultural engineering held at valencia, Spain during July 8-1, paper. P1765. Pnkham, K., Mees,., Spnrnnarit, S. and Siriamrnpun, S. (01) Mdeling f cmbined far - infrared radiatin and air drying f a ring shapedpineapple with/withut shrinkage. Fd Biprd. prcess. 90, Silva, E.M., Silva, J.S., Pena, R.S. and Rgez, H. (011) A cmbined apprach t ptimize the drying prcess f flavnid-rich leaves ( Inga edulis) using experimental design and mathematical mdelling. Fd Biprd prcess. 89,