Study of the optimisation of puffing characteristics of potato cubes by spouted bed drying enhanced with microwave

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1 Reserh Artile Reeived: 11 August 2009 Revised: 20 Novemer 2009 Aepted: 1 Deemer 2009 Pulished online in Wiley Intersiene: 23 Mrh 2010 ( DOI /jsf.3940 Study of the optimistion of puffing hrteristis of potto ues y spouted ed drying enhned with mirowve Wei-qing Yn, Min Zhng, Lue-lue Hung, Juming Tng, Arun S Mujumdr nd Jin-i Sun d Astrt BACKGROUND: In ommeril deep-ft frying of potto hips, the oil ontent of the finl produts rnges from 35 to 45 g 100 g 1 (wet sis). High-temperture frying my use the formtion of rylmide, mking the produts unhelthy to the onsumer. The im of this reserh ws to explore new method,spouted ed mirowve drying, to produe helthier puffed snk potto ues s possile lterntives to oil-fried potto hips. The influene of drying onditions of the spouted ed mirowve drying on puffing hrteristis of potto ues were studied nd ompred with the diret mirowve nd hot ir drying method. RESULTS: Tndem omintion drying of mirowve-enhned spouted ed drying (MWSB) ould hieve good expnsion rtio, rekingfore ndrehydrtion rtio.the puffing hrteristis of potto ues were signifintly ffeted (P < 0.05) y moisture ontent efore strting mirowve power in spouted ed mirowve drying, y mirowve (MW) power, nd y the originl size of potto ues. CONCLUSION: The optimum proessing prmeters were the moisture ontent t the strt of mirowve power (60%), the size of potto ues (10 12 mm), nd mirowve power (2 2.5 W g 1 ) 2010 Soiety of Chemil Industry Keywords: mirowve-enhned spouted ed drying; potto ues; expnsion rtio; reking fore; onversion point; puffing hrteristis 1300 INTRODUCTION Trditionl potto hips hve high oil ontent tht rnges from 35 to 45 g 100 g 1 (wet sis), whih gives the produt unique texture nd flvor to mke them ppel to the onsumer. 1 The retil sles of potto hips in the United Sttes re out $6 illion/yer. 2 However, during onventionl deep-ft frying proesses rylmide is formed in rohydrte- nd sprginerih foods through Millrd retions when the temperture exeeds 120 C. 3,4 Studies hve shown tht rylmide ould use dmge to the nervous system in oth humns nd nimls. 5 In reent yers, inresing puli onern over deep-oil-fried snk foods hs motivted the food industry nd reserh ommunities to explore new mens for the prodution of lower oil ontent or non-ft produts. Muh of the reserh hs een onentrted on pprohes to redue oil sorption in fried produts. 6 8 The initil solids ontent in the produt to e fried is ritil ftor tht influenes oil uptke during frying. 9 Drying of potto efore frying using mirowve, hot-ir tretment nd king n result in signifint redution in oil ontent of different produts. 10 Mirowve drying hs een studied s n lterntive method for improving the qulity of dehydrted produts. 11,12 Positive vpour pressure from internl mirowve heting produes puffed produts Yongswtdigl et l. 16 reported tht mirowve vuum dried (MWVD) rnerries hd softer texture ompred to hot-ir-dried rnerries. A mjor drwk of mirowve vuum drying is the non-uniform heting, used y uneven sptil distriution of the eletromgneti field inside the drying vity. Exessive lolised heting leds to poor-qulity produts. 11,17 Amirowve-enhnedspoutedednproduemoreuniform drying. In spouted ed dryers, uniform exposure of the produt to mirowve (MW) energy is hieved y pneumti gittion. 15,18,19 Fluidistion lso filittes het nd mss trnsfers due to onstntrenewedoundrylyerttheprtilesurfe.therefore, omined fluidised or spouted ed is onsidered s n effetive wy to solve the uneven prolem of mirowve drying. Nindo Correspondene to: Min Zhng, Shool of Food Siene nd Tehnology, Jingnn University, Wuxi , P. R. Chin. E-mil: min@jingnn.edu.n Stte Key Lortory of Food Siene nd Tehnology, Jingnn University, Wuxi , Jingsu, Chin Deprtment of Biologil Systems Engineering, Wshington Stte University, Pullmn, WA , USA Deprtment of Mehnil Engineering & Engineering Siene Progrm, Ntionl University of Singpore, 9 Engineering Drive 1, Singpore d Hitong Food Group Ltd. Co, Cixi , Zhejing, Chin J Si Food Agri 2010; 90: Soiety of Chemil Industry

2 Puffing hrteristis of potto using MWSB Tle 1. The oded vlues of the independent vriles used for response surfe design Codes Vrile Symol Conversion point (%) X Size of potto ues (mm) Mirowve power (W g 1 ) Figure 1. Shemti of the mirowve spouted dryer (dimension in mm). 1. Air ompressor (used for tomiztion nd lening); 2. lower; 3. eletri heting; 4. pressure detetor; 5. vlve; 6. nozzle; 7. peristlti pump (used for tomistion); MHz mgnetron; 9. oservtion window; 10. opertion door; 11. spouted ed; 12. ir detetor ( digitl disply detetor of ir veloity for deteting pressure, veloity nd flowing of inlet ir); 13. ontrol ox; 14. mirowve power regultor; 15. optil fire mesurement; 16. equipment support. et l. 20 used MWSB to evlute the retention of physil qulity nd ntioxidnts in slied sprgus. The results showed tht MWSB-dried sprgus prtiles hd good rehydrtion nd olour hrteristis. In ddition, the suitle MW power level (2 W g 1 ) nd heted ir temperture (60 C) resulted in the est retention of totl ntioxidnt tivity of sprgus. Mny reserhers onentrted on the nutritionl hrteristis of produts during mirowve-spouted drying. Few reported on texturl properties of puffed produts from mirowve-spouted ed drying. The ojetives of this study were to study the effets of MWSB drying on texturl properties of puffed potto ues in n effort to optimise drying onditions for omined MWSB proesses. MATERIALS AND METHODS Mterils nd equipment Fresh pottoes were purhsed from lol supermrket in Wuxi, Chin. The smples were wshed, peeled, slied to ues of different sizes (8, 10 nd 12 mm), lnhed in wter th (90 C, 5 min), nd ooled in old wter (out C) for 60 s. The surfe wter of the ues ws removed with dry pper towels efore eh drying test. The pilot-sle mirowve spouted ed dryer (Fig. 1) used in this reserh ws developed y the uthors. The system onsisted of 2450 MHz mirowve power soures, vity, hot-ir soure, spouted ed, nd ontrol system. Mirowve power ws provided y four mgnetrons, eh hving 1 kw mximum power pity. The totl mirowve power ould e regulted etween 0 nd 4 kw. The temperture of the ir for the spouted ed ould e ontrolled etween 30 nd 150 C through feed-k loop, nd ir veloity ws mintined with n djustle fn. A fire opti temperture sensor deteted the temperture in the drying vity. Drying methods Experiments were rried out y using one of the three different drying methods. 15,19 21 Method A ws single mirowve drying in spouted ed with mient ir temperture (MD). The mirowve output power ws set t 2.0 W g 1 (wet sis), nd the spouted ir temperture ws t 25 C (room temperture). Method B ws simultneous mirowve nd hot-ir spouted drying (or prllel drying). The mirowve output power ws set t 2.0 W g 1 (wet sis), nd the spouted ir temperture ws ontrolled t 60 ± 2 C. Method C ws omintion of mirowve drying nd spouted drying (or tndem drying). First, only hot ir spouted ed drying ws pplied (ir temperture t 60 ± 2 C) until the moisture ontent of the potto rehed 60% (wet sis), then the spouted ed ir temperture ws redued to 25 C (room temperture) efore strting mirowve power. Five hundred grms of smple were dried in eh test to finl moisture ontent under 5% (wet sis). Optimistion of MWSB puffing potto ues y response surfe nlysis Bsed on the results of preliminry testing, the drying proess ws rried out y Method C, nd five-level, entrl omposite experimentl design of three ftors ws used to optimise the MWSB drying proess C for puffed potto ues. 22 The three independent vriles were the moisture ontent fter the initil hot ir drying (onversion point, X 1 ), size of potto ues ( )ndmirowve power ( ). Five levels of eh of the three independent vriles were hosen for this study: 1.68, 1, 0, +1, The odedvlues of the three independent vriles re summrised in Tle 1. The expnsion rtio (ER) nd reking fore (BF) of the finl produts were mesured s the texture indies. All experiments were repeted three times nd the verges of the results were used for sttisti nlyses. Dependent vriles were represented mthemtilly y models using the regression eqution s follows: Y = X X X (1) Moisture ontent Moisture ontent ws determined y the oven method (AACC 44-16). At regulr time (10 min) intervls during the drying experiments, su-smples of 10 g were removed from the mirowve spouted ed dryer, nd dried in n ir oven for 2 3 h t 105 C until onstnt weight. Those smples were weighed on digitl lne, nd moisture ontents (wet sis) were lulted from the weights efore nd fter oven drying. The tests were performed in duplite. Expnsion rtio The volume of the potto ues ws mesured with n exlusive method using millet s the filling mteril. 23 The volume of potto ues ws lulted from: V m = V 1 V 0 (2) where V m isthevolumeofpottoues,v 1 is the totl volume of millet nd potto ue smples, nd V 0 is the volume of millet J Si Food Agri 2010; 90: Soiety of Chemil Industry

3 W-q Yn et l. Breking fore (g) Rehydrtion rtio Expnsion rtio Method A Method B Method C Drying method Figure 2. Breking fores, rehydrtion rtio nd expnsion rtio for puffed potto ues dried y three different methods. Method A: single stge mirowve drying; method B: AD+MD prellel; method C: AD nd MD tndem drying., Different letters indite signifint differene (P < 0.05) The expnsion rtio, β, ws lulted from: β = V V (3) where V is the finl volume of the puffed potto ues, nd V is the initil volume of potto ues. Rehydrtion rtio Dried potto ues were weighed nd then poured into wter. The smples were removed fter 2 min immersion t 50 C. After vuum filtrtion for 10 s, the smples were weighed. 24 The rehydrtion rtio, R,wsotinedfrom: R = M 2 M 1 M 1 (4) where M 1 is the initil weight of potto smple nd M 2 is the finl weight fter immersion nd vuum filtrtion. Texture The texture hrteristis of the potto ues were determined using TA-XT2 texture nlyser (Stle Miro Systems, Guildford, UK) fitted with spheril proe (P/0.25 s; Surrey, UK). The reking fore of the potto ues ws determined t room temperture in punture test. The proe speed ws set t 5.0 mm s 1 to trvel over distne of 5 mm. The prmeter mximum fore ws otined from the fore versus distne urves using the softwre Texture Expert (6.06) of the texture nlyser. All numeril results were expressed in grms. To mintin onsisteny, ll the tests were onduted on the dy the puffed potto ues were proessed. Three replites were performed for eh th of smples. Sttistil nlysis ANOVA ws onduted using Sttistil Anlysis System softwre (SAS Institute In., 1996). The lest signifine differene test ws used to determine differene etween mens t signifine level of P < RESULTS AND DISCUSSION Effets of drying methods on qulity ttriutes of dried potto ues The influene of three drying methods on the texture ttriutes of the dried potto ues is shown in Fig. 2 The tndem method (method C) produed puffed potto ues with the highest expnsion rtio, while methods A nd B resulted in low expnsion rtios (Fig. 2). These re lerly shown in the pperne nd the shpe of puffed potto ues (Fig. 3). The rehydrtion rtio of produts dried y method C ws lso higher thn the produts produed with the other two methods. The reking fore is n inditor of rispness s n importnt qulity ttriute of redy-to-et puffed snk foods. 6 The lower reking fore orresponded to higher rispness. Figure 2 shows tht the produt dried y method A is hrder thn the produts produed y the other two methods, while method C produed produt with the est rispness mong the three methods. It n e onluded from the ove experimentl results tht drying methods used in this studyhd signifinteffeton puffing hrteristis (expnsion rtio, rehydrtion rtio, rispness) of potto ues, nd method C (AD+MD tndem method) produed the est produts, expnsion rtio of 0.929, rehydrtion rtio of 2.549, reking fore of 1282 g. It is possile tht when using method C, the removl of surfe wter of the potto ues during the initil hot ir spouted drying nd onsequent ooling Soiety of Chemil Industry J Si Food Agri 2010; 90:

4 Puffing hrteristis of potto using MWSB Method A Method B Method C Figure 3. The piture of puffing potto ues dried with three different drying methods. Method A: single stge mirowve drying; method B: AD+MD prllel drying; method C: AD+MD tndem drying. Rehydrtion rtio Brekingfore (g) Expnsion rtio d Moisture ontent (%) Figure 4. Effet of moisture ontent fter hot-ir spouted ed drying (onversion points) on qulity ttriutes of puffed potto ues., Different letters indite signifint differene (P < 0.05). resulted in the formtion of reltively rigid nd seled surfe lyer. This lyer holds k the vpour pressure during mirowve heting nd results in puffed produt. Feng et l. 15 reorded up to 6 kp internl vpour pressure in mirowve spouted ed drying of pple dies of similr sizes ( mm) to those used in our study. In generl, pple tissues re more porous thn potto tissues. Therefore, we expeted similr or even high internl vpour pressure in potto ues in hot-ir spouted ed tndem drying in this study. On the other hnd, in method A, the mirowve hets the inner wter in produts to generte internl vpour pressure. The volume of potto ues inresed rpidly, ut sine no rigid shell ws formed prior to mirowve heting, the struture ollpsed s the wter ws removed. At the erly stge of drying, the reltively old produt surfe lso used prtil ondenstion s the internl vpour moves from the interior to the surfe, whih further redued produt qulity. With method B, externl wter nd inner wter evporte simultneously. As with method A, no dry shell ws formed prior to mirowve heting, nd shrinkge took ple in the finl dried produts. Therefore, we foused further optimistion studies only on method C. Effets of moisture ontent fter hot-ir spouted drying As shown ove, it is ritil to form desirle hrd shell in potto ues using hot-ir spouted ed efore pplying mirowve energy to produe puffed produts. The moisture ontent fter hot-ir spouted drying ws, therefore, onsidered s n importnt prmeter of the drying proess. For onveniene, we will refer to this moisture ontent s the onversion point. Experiments were rried out with four onversion points (70%, 60%, 50%, 40% moisture ontent) using 2.0 W g 1 (wet sis) mirowve drying power. The effets of different moisture onversion points on puffing hrteristis of potto ues re shown in Fig. 4. It n e seen tht moisture ontent t the onversion point hd signifint effet on the expnsion rtio of the puffed potto ues. The expnsion rtio of produts ws when the moisture ontent ws 60%. It ws the highest expnsion rtio mong the results of four moisture ontents. We oserved tht higher onversion 1303 J Si Food Agri 2010; 90: Soiety of Chemil Industry

5 W-q Yn et l. Rehydrtion rtio Breking fore (g) Expnsion rtio Potto ue size (mm) Figure 5. Effet of originl potto ue size on qulity ttriutes of puffed potto ues., Different letters indite signifint differene (P < 0.05). Rehydrtion rtio Breking fore (g) Expnsion rtio d Mirowve power (Wg 1 ) 1304 Figure 6. Effet of mirowve power on qulity ttriutes of puffed potto ues., Different letters indite signifint differene (P < 0.05) Soiety of Chemil Industry J Si Food Agri 2010; 90:

6 Puffing hrteristis of potto using MWSB point required longer mirowve drying time, nd longer drying time resulted in produt shrinkge fter puffing. The texture of the finl produts is stiff. On the other hnd, lower onversion point used potto ues to undergo signifint shrinkge during hotir spouted drying efore puffing with mirowve-spouted drying. Similr results were reported y Zhng et l. 14 nd Mudhr et l. 25 The onversion point lso hs n effet on the rispness of the puffed potto ues s shown in Fig. 4. The rispness ws the est t the onversion point, orresponding to 60% moisture ontent. A lower or higher onversion point used higher reking fore of puffedpottoues.songet l. 26 reportedsimilrresultsonpotto hips with vuum frying. There ws little differene in the rehydrtion rtio vlue mong different onversion points. This is euse similr porous struture in dried potto ues with MWSB. 21 Therefore, the 60% moisture ontent ws the optiml onversion point level for the following mirowve-spouted drying proessing. Effets of smple size on puffing hrteristis of potto ues During initil studies, itws oserved thtsome potto ues ould note puffed when ues of size 8 mm 8mm 8 mm were used. So series of sizes of potto ues ws investigted. The effets of different size on puffing hrteristis of potto ues re shown in Fig. 5. Inresing ue size improved the expnsion rtio nd size of mm hieved the est expnsion rtio. It is possile tht good lne etween n pproprite internl vpour pressure ws held k y desirle size of hrd shell so tht, fter drying, the produts retin the porous struture fter drying. Prtiles of too lrge size ontin more interior moisture nd require longer mirowve drying time, whih would upset the lne nd use shrinkge in puffing potto ues upon ooling. As for texture, when the size of the potto ues exeeded 10 mm, the reking fore of the ues deresed, whih mens tht the rispness of puffed produts ws improved. This is euse the interior struture of puffed potto ues is hollow nd the shell is very thin when the expnsion rtio ws lose to 1, whih leds to redued surfe reking fore of potto ues. The results were in greement with previous study on puffed potto hips with vuum frying. 6 Therefore, it ws pproprite to hoose mm s the size of potto ues for puff experiments. Effets of mirowve power on puffing hrteristis of potto ues Figure 6 presents the effets of mirowve power on puffed potto ues. It n e seen tht higher power level hieved higher expnsion rtio (P < 0.05) when ompred with 1.5, 3.0 W g 1 nd 2.0, 2.5 W g 1. It is ertin tht lower power output inresed the time of drying puffed potto ues nd redued the overll genertion of internl pressure, using more shrinkge of potto ues. However, ording to Fig. 6, power output t 2.0 W g 1 is the est for rispness of potto ues ompred to other power levels euse lower reking fore mens higher rispness. Greter mirowve intensity n result in thiker dry shell. Although the expnsion rtios inrese with mirowve intensity, the highest mirowve intensity ould not result in the smllest reking fore euse of reltively thik shell. Figure 6 lso illustrtes tht there is no signifint differene (P > 0.05) in rehydrtion rtios of smples dried y different mirowve power levels, whih ould e explin why dried produts with MWSB hve similr inner struture. Similr results hve een reported for dried sprgus with MWSB. 20 Tle 2. TheresultsofRSAofthevritionofexpnsionrtiond reking fore with onversion point (X 1 ), size of potto ues ( )nd mirowve power ( ) Coded vriles Run X 1 Expnsion rtio Breking fore (g) Tle 3. Regression nd nlysis of vrine for dependent vriles of MWSB drying potto ues Coeffiient Expnsion rtio Breking fore (g) X X X X X R P < 0.05, P < 0.01, P < 1. Optimistion of MWSB proedures y response surfe nlysis The vrile design nd experiment results re shown in Tles 1 nd 2. Regression oeffiients for ER nd BF re shown in Tle 3. The high R 2 vlues (0.914 nd 0.943) indite tht the independent vriles fitted well to regression eqution. Figure 7 shows the surfe plots of expnsion rtio (ER) nd reking fore (BF) of MWSB drying puffing potto ues s ffeted y size of potto ues ( ) nd mirowve power ( ) for fixed onversion point (X 1 ). As shown in Tle 3, the expnsion rtio of puffed potto ues ws signifintly (P < 0.05) ffeted y onversion point (X 1 )nd mirowve power ( ), nd size of potto ues ( )ffetedthe 1305 J Si Food Agri 2010; 90: Soiety of Chemil Industry

7 W-q Yn et l Expnsion rtio Breking fore (g) Figure 7. Surfe plots of expnsion rtio (ER) nd reking fore (BF, in grms) of MWSB drying puffing potto ues s ffeted y onversion point (X 1 ), size of potto ues ( ) nd mirowve power ( ). 0 Expnsion rtio Expnsion rtio 0 Expnsion rtio X 1 X 1 0 () Fixed levels: Breking fore (g) 0 () Fixed levels: Breking fore (g) 0 () Fixed levels: X 1 Breking fore (g) X 1 (d) Fixed levels: X 1 (e) Fixed levels: (f) Fixed levels: X 1 Figure 8. The ontour plots of expnsion rtio (ER) nd reking fore (BF, in grms) of MWSB drying puffing potto ues s ffeted y size of potto ues ( ) nd mirowve power ( ) ER insignifintly (P > 0.05). From Fig. 8, when ws fixed t 2 W g 1 ( ), ues size ws out 10 mm nd onversion point ws from 55 to 70%, the ER vlue ws ove 0.9%. When ws fixed t 10 mm ( ), or X 1 ws fixed t 60% (X 1 ), the ER vlues inresed s the mirowve power inresed. Evidently, high expnsion rtio of puffed potto ould e otined when the mirowve power exeeded 2.0 W g 1, the moisture ontent of onversion point ws out 50 70%, nd the size of potto ues ws 10 mm. AsshowninTle3,onversionpoint(X 1 ), size of potto ues ( ) nd mirowve power ( ) hd signifint effet (P < 0.05) on the reking fore. From Fig. 8d f, the reking fore of puffed potto ues ws less thn 1300 g when the moisture ontent of onversion point ws out 60%, mirowve power ws ove 2 W g 1, nd size of potto ues ws t mm. The onstrints were met in the region of moisture ontent of onversion point of out 60%, size of potto ues of mm, nd mirowve power t W g 1 (euse too high power would esily led to hrring in puffed potto ues). CONCLUSIONS Different drying methods hd signifint effets on texture ttriutes of puffed potto ues; tndem drying omintion of MWSB ould hieve good expnsion rtio, reking fore, nd rehydrtion rtio. The ftors whih ffeted the puffing Soiety of Chemil Industry J Si Food Agri 2010; 90:

8 Puffing hrteristis of potto using MWSB hrteristis were onversion point, size of potto ues, nd mirowve power. Results of response surfe nlysis showed tht expnsion rtio nd reking fore were signifintly (P < 0.05) ffeted y onversion point, size of potto ues, nd mirowve power, only the size of potto size hd nonsignifint effet (P > 0.05) on expnsion rtio. Using expnsion rtio nd reking fore s inditors of puffing hrteristis, the optimum onditions were moisture ontent of onversion point of out 60%, size of potto ues of mm, nd mirowve power t W g 1. ACKNOWLEDGEMENTS The uthors thnk Chin High-Teh (863) Pln (No 2007AA100406), Chin Ntionl Nturl Siene Foundtion (No ) nd Ningo Interntionl Projet (No. 2007C10076). REFERENCES 1 Mellem M, Mehnism nd redution of ft uptke in deep-ft fried foods. Trends Food Si Tehnol 14: (2003). 2 Gryo J nd Moreir R, Vuum frying of potto hips. J Food Eng 55: (2002). 3 Zeng XH, Cheng KW, Jing Y, Lin ZX, Shi JJ, Ou SY, et l, Inhiition of rylmide formtion y vitmins in model retions nd fried pottostrips. Food Chem 116:34 39 (2009). 4 BrdsethP,BlomH,SkredeG,MydlndLT,SkredeAndSlindeE, Lti id fermenttion redues rylmide formtion nd other Millrd retionsinfrenhfries. J Food Si 71:28 33 (2006). 5 Kuilmn M nd Wilms L, Sfety of the enzyme sprginse, mens of redutionofrylmideinfood. Toxiol Lett 172:S196 S197 (2007). 6 Song XJ, Zhng M nd Mujumdr AS, Optimiztion of vuum mirowve pre-drying nd vuum frying onditions to produe friedpottohips.drying Tehnol 25: (2007). 7 Pedreshi F nd Moyno P, Oil uptke nd texture development in friedpottoslies. J Food Eng 70: (2005). 8 Krokid MK, Oreopoulou V, Mroulis ZB nd Mrinos-Kouris D, Effets of pre-drying on qulity of Frenh fries. J Food Eng 49: (2001). 9 Pinthus EJ, Weinerg P nd Sguy IS, Criterion for oil uptke during deepftfrying. J Food Si 58: (1993). 10 Fn LP, Zhng M nd Mujumdr AS, Vuum frying of rrot hips. Drying Tehnol 23: (2005). 11 Zhng M, Tng JM, Mujumdr AS nd Wng S, Trends in mirowve relted drying of fruits nd vegetles. Trends Food Si Tehnol 17: (2006). 12 Wng J, Xi YS nd Yu Y, Mirowve drying hrteristis of potto nd the effet of different mirowve powers on the dried qulity ofpotto. Eur Food Res Tehnol 219: (2004). 13 Vdivml R nd Jys DS, Chnges in qulity of mirowve-treted griulturl produts review. Biosystems Eng 98:1 16 (2007). 14 Zhng J, Zhng M, Shn L nd Fng ZX, Mirowve vuum heting prmeters for proessing svory risp ighed rp (Hypophthlmihthys noilis) slies. J Food Eng 79: (2007). 15 Feng H, Tng J, Cvlieri RP nd Plum OA, Het nd mss trnsport in mirowve drying of porous mterils in spouted ed. AIChE J 47: (2001). 16 Yongswtdigl J nd Gunsekrn S, Mirowve vuum drying of rnerries: Prt 1, Energy use nd effiieny. J Food Proess Preserv 20: (1996). 17 Wng J nd Xi YS, Drying hrteristis nd drying qulity of rrot using two stge mirowve proess. J Food Eng 68: (2005). 18 Torring E, Esveld E, Sheewe I, Berg VB nd Brtels P, Osmoti dehydrtion s pre-tretment efore omined mirowve hotirdryingofmushrooms. J Food Eng 49: (2001). 19 Feng H nd Tng J, Mirowve finish drying of died pples in spouted ed. J Food Si 63: (1998). 20 Nindo C, Ting S, Wng SW, Tng J nd Powers JR, Evlution of drying tehnologies for retention of physil nd hemil qulity of green sprgus (Asprgus offiinlis L.). LWT Food Si Tehnol 36: (2003). 21 Feng H, Tng J nd Cvlieri RP, Comined mirowve nd spouted ed drying of died pples: Effet of drying onditions on drying kinetis nd produt temperture. Drying Tehnol 17: (1999). 22 Shyu SL nd Hwng LS, effets of proessing onditions on the qulity ofvuumfriedpplehips. Food Res Int 34: (2001). 23 Li YZ, Zhen SX nd Luo SC, Study on the proessing hrteristis of potto rispy hips y vuum mirowve [In Chinese]. Food Ferment Ind 29:40 43 (2003). 24 Vrnlis AI, Brennn JG, MDougll DB nd Gilmour SG, Optimistion of high temperture puffing of potto ues using response surfe methodology. J Food Eng 61: (2004). 25 Mudhr GS, Toledo RT nd Jen JJ, A response surfe methodology pproh to optimize potto dehydrtion proess. J Food Proess Preserv 14: (1990). 26 Song XJ, Zhng M nd Mujumdr AS, Effet of vuum mirowve pre-drying on qulity of vuum-fried potto hips. Drying Tehnol 25: (2007) J Si Food Agri 2010; 90: Soiety of Chemil Industry