PADDY DRYING IN A VIBRATION-ASSISTED VACUU INFRARED DRYER Jiraporn Sripinyowanich JONGYINGCHAROEN1, Sahawa THANIKARN2 and *Paarachai VICHAIYA 1 1 Curriculum of Agriculural Engineering, Faculy of Engineering, King ongku s Insiue of Technology Ladkrabang Ladkrabang, Bangkok 10520, Thailand 2 Agriculural echanizaion Deparmen, Rajamangala Universiy of Technology Srivijaya Thungsong, Nakorn Sri Thamaraj 80110, Thailand Corresponding auhor: Jiraporn Sripinyowanich JONGYINGCHAROEN. E-mail: kjjirapo@kmil.ac.h 265 PT-14 ABSTRACT This sudy aimed o invesigae he effec of vibraion-assised vacuum infrared (VVIR) drying on drying characerisics and qualiy of dried paddy of 12% (w.b.). The remoisened paddy of RD 47 variey wih 25% (w.b.) and 10-mm grain bed deph was used in his sudy. The infrared inensiies were 734, 853 and 952 W/m 2. The comparison of VVIR drying wih vacuum infrared (VIR) drying and ho air (HA) drying (45-120 C) was also conduced. The resuls showed ha VVIR drying a he infrared inensiy of 734 W/m 2 provided high percenage of head rice yield (HRY) (38.31%), which was close o he HRY obained by HA drying a 45 C (44.07%). However, he VVIR drying provided higher maximum drying rae and ook shorer drying ime (108 ± 003 g/g dry maer min, 25 min) han hose of he HA drying (018 ± 004 g/g dry maer min, 360 min). VVIR and VIR drying also generaed low paddy emperaure of 40-50 C. Keywords: Paddy; Infrared drying; Infrared radiaion; Vibraion; Vacuum drying INTRODUCTION Rice is a global saple food and has been considered as a significan agriculural produc for Thai economy. The key discussion of rice pos-harvesing is ypically relaed o qualiy maximizaion. Harvesed paddy has a moisure conen in he range of 18 o 43% (d.b.). The drying process mus be employed for a safe sorage. However, his process has a considerable influence on developmen of inernal cracking in he endosperm of he rice kernel which consequenly resuls in kernel breakage during rice processing [1]. Hence, proper drying of paddy is necessary in order o maximize he rice yield and qualiy. Alhough many research has been done on paddy drying, research on new and/or hybrid drying sysems for paddy drying is sill required. Far-infrared (FIR) drying has been reviewed as a poenial mehod for drying various agriculural producs such as fruis, vegeables and cereal grains.under FIR drying, maerial can be dried direcly by absorpion of FIR radiaion. Peneraion of FIR radiaion provides more uniform heaing han hea ransferred by ho air. Hence, moisure gradien and sress developmen in rice kernels during drying are reduced [2, 3]. However, peneraion deph of FIR radiaion, i.e. 1-2 mm ino grains, limis is abiliy o only surface heaing applicaion [3, 4]. echanical sysem like vibraion would be useful o agiae rice grains in he bed o allow he grains o receive he radiaion uniformly [5, 6]. Das and Bal found ha he bed deph of paddy insignificanly affeced he drying rae when drying he paddy in a vibraion aided infrared dryer [4]. In addiion, vacuum condiion in he dryer leads o a lower boiling poin of waer. Drying a lower emperaure is desirable and leads o prevenion of a hea damage during he drying process. Therefore, his sudy combined he advanages of vibraion, vacuum drying and infrared radiaion for paddy drying. Drying characerisics and qualiy of dried paddy undergoing VVIR drying were invesigaed and compared wih hose of he paddy subjeced o VIR and HA drying. ATERIALS AND ETHODS Paddy Sample Paddy of RD47 variey was used as a sample of his sudy. Before using in each experimen, he paddy of 12% (w.b.) was
remoisened o he moisure conen of 25% (w.b.) and kep a 4-5 C for 5-7 days o ensure uniform moisure hroughou he kernels. The paddy was allowed o come o room emperaure before drying. Experimenal Dryer Figure 1 shows he experimenal se-up of he VVIR dryer. A sainless seel drying chamber wih inner dimensions of 21 29 3 cm 3 was equally divided ino six channels and covered wih empered glass. Type-K hermocouple was embedded on each channel of he drying chamber o measure he emperaure of he paddy bed surface. An FIR heaer (220 V, 700 W) was insalled over he drying chamber o be operaed a he infrared inensiies of 734, 853 and 952 W/m 2 a he bed surface. An aluminum cover was placed on op of he FIR heaer as an infrared reflecor. The vibraion sysem consised of an eccenric join wih a speed-conrolled moor (SF-JR, kw, isubishi, Thailand) and four helical springs. The drying chamber was vibraed a 800 rpm during operaion. A vacuum pump (VE-290, Value, Zhejiang, China) was used o mainain absolue pressure of 5 kpa in he drying chamber during operaion. Fig.1 Schemaic diagram of he VVIR dryer Drying Procedure and Daa Analysis The VVIR drying experimens were performed a infrared inensiies of 734, 853 and 952 W/m2, vibraion of 800 rpm and absolue pressure of 5 kpa. Before running each experimen, he infrared heaer was allowed o sabilize for 5 min. The paddy of 10-mm grain bed deph (500 g) was hen fed ino he drying chamber and dried unil is final moisure conen reached abou 12% (w.b.) For he VIR drying, no vibraion was applied in he drying sysem. For comparison purposes, he convenional drying mehod, i.e. HA drying, was also conduced a emperaures of 45, 60, 266 90 and 120 C in a HA oven (UL 500, emmer GmbH+Co.KG, Schwabach, Germany). During he process of drying, he dried paddy was sampled a predeermined inervals o measure is moisure conen by HA drying a 130 C for 24 h [7]. The dimensionless moisure raio () and drying rae (DR) were calculaed as follows: DR i d e e d (1) (2) where i,, e and +d are moisure conen (g/g dry maer) a iniial, specific ime, equilibrium and +d, respecively; and is drying ime (min). As prolonged radiaion yields burn paddy, i was reasonable o omi e for VVIR and VIR drying [8]. The values of e for HA drying of paddy samples were deermined using he following equaion [9]: e 1 1 ln(1 RH ) C2 100 C1Tabs (3) where RH is relaive humidiy (decimal); Tabs is absolue emperaure ( K); and C1 and C2 are equaion consans, which are -3.146 10-6 and 2.464 for paddy, respecively. The e of he paddy samples subjeced o HA drying a 45 and 60 C were 017 and 015 g/g dry maer respecively while HA drying a he emperaures of 90 and 120 C boh provided he e of zero g/g dry maer. Deerminaion of illing Qualiy of Dried Paddy HRY and whieness were deermined. Head rice is defined as milled rice having a kernel lengh a leas 80% of is original lengh. To measure HRY, 250 g of paddy was dehusked by a rubber roll huller (THU-35A, Saake Engineering Co., Ld., Osaka, Japan), milled by a rice polisher (T05, Saake Engineering Co., Ld., Osaka, Japan) and graded o obain whole grains and head rice by a rice grader (TRG 05A, Saake Engineer-ing Co., Ld., Osaka, Japan). Whieness of milled rice was calculaed using Equaion (4). Color of milled rice in he CIE L* (lighness o darkness), a* (redness o greenness), b* (yellowness o blueness) sysem was obained from a
specrocolorimeer (iniscan XE Plus, Huner Associaes Laboraory, Inc., Virginia, USA) Whieness 100 2 2 (100 L*) a* b * 2 1/ 2 (4) Saisical Analysis All experimens were riplicae. The daa were analyzed using he analysis of variance in a compleely randomized design. Signifi-can difference among reamen was deermi-ned using Duncan s muliple range es a 95% confidence inerval. RESULTS AND DISCUSSION Drying Characerisics Figures 2-4 illusrae he change in of paddy wih ime by VVIR, VIR and HA drying, respecively. As proposed by Toyoda [10], a paddy kernel could be considered o consis of wo componens, husk and a brown rice kernel, which are assumed o funcion as waer anks. During drying, he husk is mainly dried in he firs shor period. In he second longer period, brown rice kernel is principally dried and waer ransfer from brown rice o he air slows down. However, as seen in hese figures, i is obvious ha infrared radiaion provided more uniform moisure ransfer han ho air. I should be because of he absorpion of infrared radiaion inside he paddy kernel which promoes he migraion of moisure from inside o surface of he kernel [2, 3]. As shown in Table 1, drying ime decreased and maximum DR increased wih increasing eiher infrared inensiy or ho air emperaure (Table 1). I appears ha maximum DR of VVIR and VIR reamens were insignificanly differen. They were also saisically he same as he maximum DR obained by HA drying of paddy a he emperaure of 120 C. VVIR drying a 952 W/m 2 provided he highes maximum DR of 160 g/g dry maer min, which was abou 9 imes higher han he lowes maximum DR of HA drying a 45 C. Shorer drying ime and higher maximum DR of VVIR drying can be explained by uniform radiaion creaed by a vibraion sysem [5, 6]. Effec of vibra-ion was more pronounced a he lowes infrared inensiy of 734 W/m 2 as he larges difference beween he drying imes of VVIR and VIR drying a his infrared inensiy was observed. 0 10 20 30 Fig. 2 Drying curves of VVIR drying of paddy a differen infrared inensiies 734 W/m2 853 W/m2 0 10 20 30 40 50 Fig. 3 Drying curves of VIR drying of paddy a differen infrared inensiies 734 W/m2 853 W/m2 952 W/m2 45 C 60 C 90 C 120 C 0 100 200 300 400 500 Fig. 4 Drying curves of HA drying of paddy a differen drying emperaures Final emperaures of paddy during drying are shown in Table 2. Final emperaure of he paddy undergoing VVIR drying was slighly higher han ha of he paddy undergoing VIR drying. I should be due o he effec of vibraion which provided well-disribued radiaion. I was also observed ha infrared radiaion could promoe high value of maximum DR while generaed low paddy emperaure in he range of 40-50 C. 267
Drying condiion Drying ime (min) aximum DR (g/g dry maer min) 734 W/m 2 25 108±003 abc 853 W/m 2 20 134±008 ab 952 W/m 2 15 160±004 a 734 W/m 2 40 098±010 abc 853 W/m 2 25 102±011 abc 952 W/m 2 20 151±016 a 45 C 360 018±004 d 60 C 150 036±017 cd 90 C 70 064±010 bcd 120 C 40 104±097 abc significanly differen (p 5). Table 2 Final emperaures of dried paddy under- going VVIR, VIR and HA drying Final emperaure of Drying condiion dried paddy ( C) 734 W/m 2 44.50±1.97 f 853 W/m 2 49.67±1.51 d 952 W/m 2 48.33±3 de 734 W/m 2 43±1.94 g 853 W/m 2 47.33±1.86 e 952 W/m 2 46.83±1.47 e 45 C 42.50±1 g 60 C 56.00±1 c 90 C 80.12±5 b 120 C 107.38±8 a 734 W/m 2 44.50±1.97 f 853 W/m 2 49.67±1.51 d 952 W/m 2 48.33±3 de 734 W/m 2 43±1.94 g 853 W/m 2 47.33±1.86 e 952 W/m 2 46.83±1.47 e 45 C 42.50±1 g 60 C 56.00±1 c 90 C 80.12±5 b 120 C 107.38±8 a significanly differen (p 5). illing Qualiy of Paddy The milling qualiy of dried paddy in erms of HRY and whieness are shown in Table 3. The higher drying condiion (eiher infrared inensiy or drying emperaure), he greaer he HRY los. The highes percenage of HRY was obained by HA drying a 45 C, he lowes drying emperaure used in his sudy. The second highes percenage of HRY was 268 provided by VVIR drying a 734 W/m2. I is imporan o noice ha he laer can be operaed faser (more han 14 imes faser han he 45 C HA drying). Comparing beween VIR drying a 734 W/m2 and HA drying a 120 C, which ook he same drying ime of 40 min, HRY of paddy subjeced o he VIR drying was abou 2.6 imes greaer han ha of he HA drying. eeso e al. suggesed ha FIR heaing provides simulaneous moisure removal and moisure leveling [11]. Hence, moisure gradien and sress developmen wihin he paddy kernel decrease and HRY could be mainained. Whieness of dried paddy was in he range of 60-67%. Drying ime was an imporan facor affecing he whieness of paddy. In he same drying mehod, he shorer drying ime caused a higher value of whieness, excep he HA drying, of which he peak level of whieness was obained a he drying emperaure of 90 C. I should be noe ha an increase in infrared inensiy or drying emperaure which led o a decrease in drying ime consequenly resuled in a higher value of whieness. These resuls are in conras wih hose repored by Taechapairoj e al. for superheaed seam fluidized bed drying of paddy; higher drying emperaure led o lower whieness value [12]. Table 3 HRY and whieness percenages of dried paddy undergoing VVIR, VIR and HA drying Drying condiion HRY (%) Whieness (%) 734 W/m 2 38.31±1.63 b 61.83±9 de 853 W/m 2 30±1.48 c 62.52±0.54 cd 952 W/m 2 28.34±9 c 64.99±0.79 b 734 W/m 2 35.41±2.70 b 63.21±2 c 853 W/m 2 28.31±3.44 c 63.42±9 c 952 W/m 2 28±0.13 d 64.68±0.37 b 45 C 44.07±0.97 a 68±8 f 60 C 30±3.09 c 62±1 ef 90 C 17.79±9 e 67.08±0.18 a 120 C 13.57±0.78 f 65.23±0.56 b significanly differen (p 5). CONCLUSIONS In average, VVIR drying provided he highes maximum DR, followed by VIR drying and HA drying, respecively. VVIR and VIR drying also required shorer drying ime while
generaed lower paddy emper-aure han HA drying. HA drying a low emperaure of 45 C was he bes way o preserve HRY of paddy. However, i ook abou 14 imes longer han VVIR drying a 734 W/m 2, which offered he second highes percenage of HRY. Whieness of milled rice was higher when drying ime of paddy was shorer. ACKNOWLEDGEENT The financial assisance provided by he budge suppor from Faculy of Engineering, King ongku s Insiue of Technology Ladkrabang is graefully acknowledged. eeso, N., Nahakaranakule, A., adhiyanon, T. and Soponronnari, S. Influence of FIR radiaion on paddy moisure reducion and milling qualiy afer fluidized bed drying. Journal of Food Engineering 65: 293-301 (2004) Taechapairoj, C., Dhuchakallaya, I., Soponronnari, S., Wechacama, S. and Prachayawarakorn, S. Superheaed seam fluidized bed paddy drying. Journal of Food Engineering 58: 67-73 (2003) REFERENCES Bonazzi, C., du Peuy,.A. and Themelin, A. Influence of drying condiions on he processing qualiy of rough rice. Drying Technology 15: 1141-1157 (1997) Khir, R., Pan, Z., Salim, A., Harsough, B.R. and ohamed, S. oisure diffusiviy of rough rice under infrared radiaion drying. LWT Food Science and Technology 44: 1126-1132 (2011) eeso, N. Far-infrared heaing in paddy drying process, pp. 225-256, in A.P. Urwaye (Ed.) New Food Engineering Research Trends, Nova Science Publisher, Inc. (2008) Das, I., Das, S.K. and Bal, S. Research noe: Drying performance of a bach ype vibraion aided infrared dryer. Journal of Food Engineering 64: 129-133 (2004) Nindo, C.I., Kudo, Y. and Bekki, E. Tes model for sudying sun drying of rough rice using farinfrared radiaion. Drying Technology 13: 225-238 (1995) ujumdar, A.S. Research and developmen in drying: Recen rends and fuure prospecs. Drying Technology 22: 1-26 (2004) Jindal, V.K. and Siebenmorgen, T.J. Effec of oven drying emperaure and drying ime on rough rice moisure conen deerminaion. Ameri-can Sociey of Agriculural Engineers 30: 1185-1192 (1987) Assawarachan, R., Sripinyowanich, J., Theppadung porn K. and Noomhorm, A. Drying paddy by microwave vibro-fluidized bed drying using single mode applicaor. Journal of Food, Agriculure and Environmen 9: 50-54 (2011) Henderson, S.. A basic concep of equilibrium moisure. Trans. Am. Soc. Agric. Eng. 33: 29 (1952) Toyoda, K. Sudy in inermien drying of rough rice in a recirculaion dryer. Proceedings of he 6 h Inernaional Drying Symposium IDS 88, Versailles, France, pp. 171-178 (1988) 269