Drying Rough Rice in a Fluidized Bed Dryer

Transcription

1 J. Agric. Sci. Technol. (2008) Vol. 10: Drying Rough Rice in Fluidized Bed Dryer A. Krbssi 1, Z. Mehdizdeh 1 * ABSTRACT The objective of this study ws to exmine the effects of the fluidized-bed drying method on the finl qulity of two vrieties of Irnin rice, medium- nd long grin. The results were compred to tht of pddy drying using trditionl method. Rough rice ws treted in the fluidized bed drier t 140ºC for 2 minutes. Similr smples were dried for 8-10 hrs by the trditionl method. Dried smples were dehusked nd polished. Qulity fctors, including trde qulity (hed rice yield percent nd whiteness), cooking qulity (mylose content, geltiniztion temperture, gel consistency, rom nd flvor) nd nutritionl qulity (thimine nd lysine contents), were then mesured for ech smple. Finlly, the dt ws nlyzed. Results show tht pddy drying in fluidized bed dryer would reduce the qulity fctors except for rice whiteness for which conventionl drying is more cceptble. Therefore modifiction of fluidized-bed drying technique is recommended. Keywords: drying, Rice qulity, Rough rice, Sun drying. INTRODUCTION Rice is one of the mjor economic crops of the world nd the rice mrket involves both consuming nd producing countries. In order to retrd rice deteriortion fter hrvest, rough rice (pddy) should be dried down to level tht will enble sfe storge through reduction in respirtion nd prevention of mycotoxin production. This corresponds to moisture content of bout 13-14% w. b. which is considered dequte for sfe storge nd the milling process [2, 8]. In commercil drying of griculture products heted ir is used. Mechnicl systems, especilly those using hot ir for rpid drying of grins high in moisture content re becoming incresingly populr [18]. Two new efficient drying techniques re the fluidized bed drying nd solr drying systems. Reserches show tht rough rice drying cn ffect the qulity properties of rice which, in turn, ffects cceptnce of the commodity by the consumers t different stges of the mrketing chin [21]. Therefore, with incresing demnd for better nd higher qulity products nd for efficient opertions, the processing technique nd its control for minimizing product degrdtion is current chllenge for rice drying. The influence of therml shock hs been studied by Bonzzi et l. (1994) [2]. The results showed no loss of qulity due to therml grdients if pddy is exposed to temperture levels of 30ºC, 55ºC, 70ºC, 80ºC nd 90ºC. This study showed tht temperture lone cnnot explin the observed qulity degrdtion of rice during drying. Soponronnrit nd Prchyvrcorn (1994) hve studied fluidized bed dryer system nd their results showed tht the temperture of the dryer nd finl moisture content of pddy should be less thn 115ºC nd 24-25%, respectively [17]. Tweerttnpnish et l. (1999) investigted the drying of pddy with high moisture content using fluidized bed dryer sys- 1. Deprtment of Food Science nd Technology, College of Agriculture, Shirz University, Islmic Republic of Irn. * Corresponding uthor, e-mil: mehdizdeh_zhr@yhoo.com 233

2 Krbssi nd Mehdizdeh tem. Optimum ir temperture in their system ws 150ºC [20]. Wiset et l. (2001) studied the effects of two hot ir drying methods, fluidized bed drying t 90ºC for 11 minutes drying durtion (single stge), nd two-stge method of drying, tht is in first stge grin is dried down to 18% w. b. followed by store drying in mbient temperture. Results showed hed rice yield decresed in the first method, but good hed rice yield in the second one [21]. Pooms-d et l. (2001) showed tht tempering tretment provided better hed rice yield thn tretment without tempering using the fluidiztion technique [13]. Soponronnrit (1999) pplied three processes in series, for moist pddy: fluidized bed drying with n inlet ir temperture of 150ºC for 3 minutes, tempering in 30 minutes followed by cooling with mbient ir ventiltion for 20 minutes. The moisture content decresed from 33% to16.5% within bout 53 minutes. The qulity of pddy in terms of hed rice yield nd degree of whiteness ws cceptble in comprison to the trditionl method [16]. MATERIALS AND METHODS Rice Smples Smples of medium grin rough rice of the Kmphiroozi vriety nd long grin rough rice of the Szndegi vriety were used for ll tests. The smples were provided from the frms of Agriculturl Reserch Centers in Shirz nd Isfhn, with n initil moisture content of 20% d. b. Methods of Drying Two drying methods were dopted: 1. Drying in fluidized bed dryer system (Figure 1). The drying section of the experimentl dryer ws Pyrex column 70cm in height nd 8cm in dimeter. Drying durtion to 13% w. b. moisture content ws determined with intermittent smpling of the pddy nd mesuring the moisture with oven. Then, moisture control curve ws drwn. Therefore, drying process ws performed t temperture of 140ºC for 2 minutes the drying durtion, with n irflow rte of 500 lit min Trditionl method of sun drying [9]. About 4 kg of ech pddy smple with n initil moisture content of 20% d. b. for ech btch ws sun dried. The rough rice ws spred evenly on concrete floor mintining two centimeter depth of rough rice (tht is the optimum thickness for thin lyer rice drying). Periodic stirring of the rice ws performed every hlf n hour. Drying continued until moisture content of 13% w. b. ws Figure 1. Schemtic representtion of btch fluid-bed dryer. 234

3 Drying Rough Rice in Fluidized Bed Dryer estblished. This took 8 hours (drying durtion to 13% w. b. moisture content is lso determined similrly to tht method). The dried rough rice smple ws then kept in plstic bgs nd stored t 15ºC for lter tests [7]. In both cses, the drying process for ech vriety ws replicted. Dehusking nd Polishing Two hundred grms of rough rice from ech smple ws de-husked using rubber roller de-husker. (Lbortory Rubber Rolls Unit, SATAKE RICE MECHINE, nd Type- THU-Clss). The percentges of de-husked nd broken kernels were determined by the hnd-sorting of broken kernels. A kernel hving equl to or more thn 75% intct ws considered s whole kernel. According to the weight of whole kernels nd broken kernels, the percentge of hed rice yield ws clculted. De-husked smples were polished using n brsive type rice polisher (Rice Whitening nd Crcking Mchine, SATAKE Eng. Co. Ltd., Jpn) [12, 14, 15]. Smples were milled into flour nd mintined for subsequent qulity content experiments. Qulity Assessment In ddition to the hed rice yield percentge, the cooking qulity of rice, rom, flvor, whiteness, nd nutritionl vlues were lso evluted. Amylose content ws determined by the modified ssy method of Julino (1979) [11]. Gel consistency ws determined using technique proposed by Cgmpng et l. (1973) nd Cruz nd Khush in 2000 [4, 6]. The geltiniztion temperture of strch ws determined by the modified ssy method of Bhttchry (1979) [1]. The orgnoleptic chrcteristics of cooked rice (i.e. flvor, rom) nd pprent whiteness were ssyed by the tste pnel using sensory evlution method in triplicte. In respect to nutritionl vlue, lysine nd thimine were determined using biologicl ssy nd thiochorome fluorescence technique, respectively [3, 10]. The dt were rrnged s fctoril experiment in rndomized complete design with three replictions. The mens were compred by DMRT using the MSTATC softwre. RESULTS AND DISCUSSION Percentge of Hed Rice Yield Tble 1. Influence of vriety nd method of drying on hed rice yield percentge. Vriety Long Medium Trditionl c 58.9 b Different letters indicte significnt difference t 5% level of probbility. The results re shown in Tble 1 nd Figure 2. The experimentl dt indicted tht the hed rice yield is ffected by the drying system. Long nd medium grin btches dried in fluidized bed dryer from 21% d. b. initil moisture content down to 13% w. b. show lower mgnitude of hed rice yield nd higher percentge of broken kernels thn smples dried by the trditionl method. This result is similr to the findings of Soponronnrit et l. (1996) [19], Tweerttnpnish et l. (1999) [20], Wiset et l. (2001) [21], nd Chen et l. (1997) [5]. The results, however, didn't gree with those of Soponronnrit nd Prchywrtorn (1994) tht showed n increse in hed rice yield when pplying tempertures up to 150ºC [17]. 235

4 Krbssi nd Mehdizdeh Hed rice yield (%) Geltiniztion Temperture The geltiniztion temperture of strch ffects the velocity of wter bsorption nd the cooking time of rice. A high geltiniztion temperture represents higher wter bsorption nd longer cooking time. Results in Tble 2 nd Figure 3 show tht medium grin rice hs higher vlues of geltiniztion temperture thn long grin for ll tretments. Furthermore, drying t high temperture (fluidized bed dryer) resulted in decrese in geltiniztion temperture for long grin vrieties. In drying rough rice t high temperture, drying strts from the surfce of the kernel nd progresses inwrd. Drying too rpidly * c b Trditionl Long grin Medium grin probbility. Different letters indicte significnt difference t 5% level of Figure 2. Effects of drying method on hed rice yield for medium nd long grin rice. cuses cse hrdening whereby the surfce of the grin dries out, rpidly seling the moisture within the inner lyers. The internl pressure thus developed cuses crcks to develop. As result, penetrtion of moisture in the kernel is ccelerted nd geltiniztion time decreses. Amylose Content Results of experiments in Tble 3 nd Figure 4 stted tht both smples were in the medium rnge of mylose content (21-25%). However, the mylose content decresed when smples were dried in fluidized bed dryer Since, t high tempertures some of the mylose is decomposed. Tble 2. Influence of vriety nd method of drying on the geltiniztion temperture. Vriety Long Medium Trditionl 4.46 d 5.26 Different letters indicte significnt difference t 5% level of probbility. Tble 3. Influence of vriety nd method of drying on mylose content. Vriety Long Medium Trditionl cd d e Different letters indicte significnt difference t 5% level of probbility. 236

5 Drying Rough Rice in Fluidized Bed Dryer Geltiniztion temperture (score verge) * d Trditionl Long grin Medium grin probbility. Different letters indicte significnt difference t 5% level of Figure 3. Effects of drying method on the geltiniztion temperture for medium nd long grin rice. (Score verge: 1-2<70ºC, 4-5=70-74ºC, 5-6>74ºC). Amylose content (%) * cd d Trditionl Fliudized bed e Long grin Medium grin probbility. Different letters indicte significnt difference t 5% level of Figure 4. Effects of drying method on mylose content for medium nd long grin rice. Gel Consistency The results of this test re shown in Tble 4 nd Figure 5. Long grin nd medium grin rice lie in the rnge of medium nd hrd gel, respectively. Smples dried in fluidized bed dryer hd the lowest vlue of gel consistency, but those dried by the trditionl method showed no significnt differences. However, ll smples remined within their rnge. Gel consistency hs direct correltion with the mylose content of rice nd with decomposition nd chnge of mylose into smller components t high temperture; Tble 4. Influence of vriety nd method of drying on gel consistency, mm. Vriety Long Medium Trditionl c b d Different letters indicte significnt difference t 5% level of probbility. gel consistency of rice decreses nd results in more soft gel. 237

6 Krbssi nd Mehdizdeh Gel consistency (mm) These results show good greement with findings of Wiset et l. (2001) [21] who reported considerble loss of gel consistency in fluidized bed dryer t high temperture Thimine Content Results in Tble 5 nd Figure 6 show tht the thimine levels in smples dried in the Tble 5. Influence of vriety nd method of drying on thimine content, μg 100gr -1. Vriety Long Medium Trditionl c* b cd Different letters indicte significnt difference t 5% level of probbility. b Trditionl Fliudized bed d Long grin Medium grin probbility. Different letters indicte significnt difference t 5% level of Figure 5. Effects of drying method on gel consistency for medium nd long grin rice. Thimine content (μg /100gr) b * cd Trditionl Fliudized bed Long grin Medium grin probbility. Different letters indicte significnt difference t 5% level of Figure 6. Effects of drying method on thimin content for medium nd long grin rice. 238

7 Drying Rough Rice in Fluidized Bed Dryer fluidized bed dryer decresed, becuse Thimine is one of the B vitmins with very sensible to high temperture. In contrst to tht, the smples dried using other methods show no significnt differences. Lysine Content The results of the lysine determintion in smples subjected to fluidized bed dryer nd sun drying re shown in Tble 6 nd Figure 7. The results show tht the lysine levels in smples dried in the fluidized bed dryer decresed, but the smples dried by the other method show no significnt differences. Tble 6 lso shows tht, for the trditionl method of drying, lysine content does not differ for long nd medium grins, wheres for the fluidized-bed drier, the lysine content differs for the long nd medium grin smples. Qulity Chrcteristics of Cooked Rice Whiteness The whiteness of cooked smples from two different tretments of drying ssyed by the tste pnel group showed no significnt difference between smples. Smples from the trditionl method of drying were less glossy nd more opque thn smples dried with fluidized bed method. In other words, drying t high temperture resulted in more pprent whiteness of rice. These results hd good greement with the results of Tweerttnpnish et l. (1999) regrding incresing rte of whiteness Tble 6. Influence of vriety nd method of drying on lysine content, μg gr -1. Trditionl Long Vriety Medium 2960 b 1800 d Different letters indicte significnt difference t 5% level of probbility. Lysine content (μg /gr) b* Trditionl Fliudized bed d Long grin Medium grin probbility. Different letters indicte significnt difference t 5% level of Figure 7. Effects of drying method on lysine content for medium nd long grin. 239

8 Krbssi nd Mehdizdeh of smples dried t high temperture [20]. Flvor nd Arom Results of sensory evlution of cooked smples from two different tretments showed tht smples dried in fluidized-bed hd lower flvor, rom nd lower sensory scores thn smples dried in trditionl mnner s judged by the tste pnel. CONCLUSIONS The results of the study showed tht the following properties hve been ffected: Drying by fluidized bed from initil moisture content of 20% d. b. to 13% w. b. t temperture of 140ºC resulted in decresed hed rice yield, while drying with trditionl method resulted in the best hed rice yield. Gel consistency ws significntly decresed by the fluidized bed dryer method with high temperture. However, ll smples remined within their rnge. Amylose content decresed when smples were dried in fluidized bed dryer. The geltiniztion temperture of strch significntly decresed with the method of fluidized bed dryer in the long grin vriety. The fluidized-bed drying method resulted in more cceptble whiteness. Sensory scores (odor, flvor) of smples dried t high temperture were considerbly lower thn those of the other method. Thimine nd lysine contents of smples dried t high temperture in the fluidized bed dryer were decresed. ACKNOWLEDGEMENTS This reserch ws conducted t Shirz University for thesis of Mster of Science. The uthors re grteful to Dr. Jmlin, Professor of Food Science nd Technology nd Dr. Mowl, Professor of Chemicl Engineering both t Shirz University for their ssistnce during this reserch. They lso, would like to pprecite coopertion of Agriculturl Reserch Centers in Shirz nd Isfhn provinces. REFERENCES 1. Bhttchry, K. R Geltiniztion Temperture of Rice Strch nd its Determintion. In: Chemicl Aspects of Rice Grin Qulity, Proceedings of the Workshop, Interntionl Rice Reserch Institute: Mnil, Philippines, PP Bonzzi, C., Courteis, F., Geneste, C., Lhon, M. C. nd Bimbent, J Influence of Drying Conditions on the Processing Qulity of Rough Rice. Dry. Technol., 15(3; 4): Brinton, M. M. nd Litsky, W Industril Microbiology, Mc-Grw Hill Book Compny: New York, PP Cgmpng, G. B., Perez, C. M. nd Julino, B. O A Gel Consistency Test for Eting Qulity of Rice. J. Sci. Food Agri., 24: Chen, H., Siebenmorgen, T. J. nd Mrks, B. P Relting Drying Rte Content to Hed Rice Yield Reduction of Long Grin Rice. Trns. ASAE, 40(4): Cruz, N. D. nd Khush, G. S Rice Grin Qulity Evlution Procedure. In: Aromtic Rices, Mohn Primlni for Oxford nd IBH Publishing Co. Ltd.: New Delhi, PP Frounk, S. M. nd Islm, M. N Effect of Milling nd Prboiling on Brekge of Rice Grins. Agri.Mechniztion Asi, Afric nd Ltin Americ, 26(4): 33-38, Hll, C. W Hndling nd Storge of Fond Grins in Tropicl nd Subtropicl Ares. FAO Agriculturl Development, Pper No Imoud, P. B. nd Olufyo, A. A The Effects of Sun Drying on Milling Yield nd Qulity of Rice. Bioresource Technol., 74: Joslyn, M. A Vitmin Assy. In: Methods in Food Anlysis, 2 nd Ed., Acdemic Press: London, PP

9 Drying Rough Rice in Fluidized Bed Dryer 11. Julino, B. O Amylose Anlysis in Rice. In: Chemicl Aspects of Rice Grin Qulity. Proc. Workshop, Int. Rice Reserch Institute: Mnil, Philippines, PP Lu, R. nd Siebenmorgen, T. J Correltion of Hed Rice Yield to Selected Physicl nd Mechnicl Properties of Rice Kernels. Trns. ASAE, 38(3): Pooms-d, N., Soponronnrit, S., Teryothin, A. nd Prchywrkorn, S Hed Rice Yield fter Drying by Fluidiztion Technique nd Tempering. 2 nd Asin- Oceni Drying Conference Feringhi, B., Pinng, P., Mlysi, PP Siebenmorgen, T. J. Nehus, Z. T. nd Archor, T. R Milled Rice Brekge Due to Environmentl Conditions. Cerel Chem., 75(1): Siebenmorgen, T. J., Perdon, A. A., Chen, X. nd Muromoustkos, A Relting Rice Milling Qulity Chnges Adsorption to Individul Kernel Moisture Content Distribution. Cerel Chem., 75(1): Soponronnrit, S Fluidized Bed Pddy Drying. ScienceAsi, 25: خشككردن برنج در سيستم خشككن بستر سيال 17. Soponronnrit, S. nd Prchywrkorn, S Optimum Strtegy for Fluidized Bed Pddy Drying. Dry. Technol., 12(7): Soponronnrit, S., Prchywrkorn, S. nd Sripwtkul, O Development of Cross-Flow Fluidized Bed Pddy Dryer. Dry. Technol., 14(10): Soponronnrit, S., Prchywrkorn, S. nd Wngji, M Commercil Fluidized Bed Pddy Dryer. In: 10 th Interntionl Drying Symposium, Strumillo, C. nd Pkowski, Z. (Eds.), Krkow, Polnd, Vol. A, PP Tweerrttnpnish, A., Soponronnrit, S., Wetchkm, S., Kongseri, N. nd Wongpiychon, S Effects of Drying on Hed Rice Yield Using Fluidiztion Technique. Dry. Technol., 17(1; 2): Wiset, L., Srzednicki, G., Driscoll, R. H., Nimmutrin, C. nd Siwpornrk, P Effects of High Temperture Drying on Rice Qulity. Agriculturl Engineering Interntionl the CIGR: J. Sci. Res. Dev., Vol. ПI. و ا. كرباسي ز. مهدي زاده چكيده هدف از اجراي اين تحقيق بررسي تا ثير سيستم خشككن بستر سيال بر كيفيت نهايي دو واريته برنج ايراني دانهبلند و دانه متوسط بود. نتايج بهدست آمده با نتايج حاصل از روش سنتي مقايسه شد. فرايند خشككردن در روش بستر سيال در دماي 140ºC به مدت 2 دقيقه انجام شد. خشككردن نمونهها به روش سنتي 10-8 ساعت زمان طي كرد. پس از آن نمونهها آسياب و سفيد شدند. سپس فاكتورهاي كيفي آنها شامل كيفيت تجاري ) درصد راندمان تبديل برنج سالم و سفيدي برنج) كيفيت پخت ) ميزان آميلوز دماي ژلاتينهشدن نشاسته قوام ژل برنج و عطر و بو) وكيفيت تغذيهاي (ميزان تيامين و اسيد آمينه ليزين) آزمايش شدند. در نهايت نتايج بهدستآمده آناليز آماري شدند. نتايج نشان دادندكه دماي بالا باعث كاهش فاكتورهاي كيفي برنج ميشدند بجز ميزان سفيدي برنج كه نسبت به نمونه خشكشده سنتي مطلوبتر بود. بنابراين پيشنهاد ميشود در شرايط اعمالي سيستم خشككن بستر سيال تغييراتي صورت پذيرد. 241