Proceedings of the World Congress on Engineering and Computer Science 2009 Vol I WCECS 2009, October 20-22, 2009, San Francisco, USA

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1 Proceedngs of the World Congress on Engneerng and Computer Scence 9 Vol I WCECS 9, October -, 9, San Francsco, USA Texturng by Instant Controlled Pressure Drop DIC n the Producton of Cassava Flour: Impact on Dehydraton Knetcs, Product Physcal Propertes and Mcrobal Decontamnaton Puguh Setyopratomo, Akbarnngrum Fatmawat, and Karm Allaf Abstract Swell dryng s a new dryng process whch s coupled wth dehydraton tself, a stage of texturng by the nstant controlled pressure drop technology, called the Détente Instantanée Contrôlée (DIC), whch s nserted between pre and fnal dryng steps. Texturng step permts to modfy the materal texture, whch would then affect the dehydraton knetcs, the product physcal propertes, ncludng water and ol holdng capacty, and the mcrobal decontamnaton. The results of ths work showed that the cassava texturng by DIC mpled ncreasng the effectve mosture dffusvty, cassava flour capactes vs-à-vs ether the water holdng and the ol holdng. Texturng by DIC also reduced the bacteral content of cassava flour sgnfcantly. Index Terms cassava flour, effectve dffusvty, mcrobal decontamnaton, ol holdng capacty, water holdng capacty. I. INTRODUCTION In Indonesa, cassava s the fourth most mportance food crop after rce, maze and soybean. Whereas, most of the cassava product goes to starch extracton or s exported as pellet and chps. The average yeld per hectare of cassava s rather low at 1 tons, but the trend has been toward a constant ncrease n yelds. Cassava s grown on about 1.4 mllon hectares throughout the country, wth an average producton of 16.3 mllon tons/year [1]. On an estate of a tapoca plant n Lampung, a yeld of 5-3 tons/ha of cassava has been contnuously attaned [], as a result of a cassava ntensfcaton program started by the Government n Cassava flour processng began n 199 to dversfy cassava products. In the country most of cassava flour was Ths paper was submtted on July 5, 9, for revew. Puguh Setyopratomo s Head of the Indonesan Research Team of France-Indonesa Agro-ndustral Laboratory (FIALab), Chemcal Engneerng Department, Engneerng Faculty, Unversty of Surabaya, Raya Kalrungkut, Surabaya, Indonesa, 69 (Phone: ; fax: ; e-mal: puguh_sptm@yahoo.com). Akbarnngrun Fatmawat s Head of Boprocess Technology Laboratory, Chemcal Engneerng Department, Engneerng Faculty, Unversty of Surabaya, Raya Kalrungkut, Surabaya, Indonesa, 69 (emal: afatmawat@yahoo.com). Karm Allaf s Scentfc Drector of France-Indonesa Agro-ndustral Laboratory (FIALab); Head of Technologes for Agro-Industry of the Unversty of La Rochelle; Laboratory of Transfer Phenomena and Instantanety n Agro-ndustry and Buldng LEPTIAB. Pole of Scence and Technology; Avenue Mchel Crepeau, 174 La Rochelle Cedex 1 France (emal : kallaf@unv-lr.fr). consdered acceptable for household consumpton, whch was estmated at 4-7 kg/month per household. Snce cassava flour can substtute wheat flour by as much as 3 %, the entre local producton of cassava flour can be absorbed, especally by the food ndustres [3]. The Indonesan Government s attemptng to develop the potental of cassava flour as a food for domestc consumpton and as a raw materal for both household consumpton and the food ndustry to complement or substtute wheat flour. The Government has recommended that the agrcultural and ndustral sectors make specal efforts n promotng cassava by dversfyng cassava process products, mprovng ther qualty, and promotng ther use among the dfferent strata of the Indonesan populaton. Cassava flour s produced from fresh cassava roots through dehydraton (dryng) process. Bascally, the dehydraton process s the removal of water from the cassava roots to a certan level at whch mcrobal spolage s avoded. Up to now, sun dryng s the method mostly used to produce cassava flour n Indonesa. Snce very long tme exposure s needed for such method, sgnfcant deteroraton wll occur durng the dryng process, whch can result n very low qualty of the cassava flour product. In ths work, a new process of a texturng by nstantaneous control pressure drop, called the Déetente Instantanée Contrôlée (DIC), was ntroduced between pre and fnal hot ar dryng. The purpose of the texturng step s to modfy the materal texture to mprove the product qualty ncludng the product physcal propertes [4]. The DIC (Détente Instantanée Contrôlée) technology was ntally developed by ALLAF et al., (snce 1988) [5]-[8] n the Unversty of La Rochelle. It apply nstant pressure-drop to modfy the texture of the materal and ntensfy functonal behavour. DIC treatment usually starts by creatng a vacuum condton, followed by njectng steam to the materal keepng such a contact for several seconds, proceeds then the sudden pressure drop toward vacuum (about 5 kpa wth a rate hgher than.5 MPa/s). Ths treatment s also categorzed as a HTST (Hgh Temperature Short Tme) process. By suddenly droppng pressure, rapd autovaporsaton of the mosture from the materal wll occur, the materal wll swell, and lead to texture change whch results n hgher porosty [9]. It ncreases the materal porosty as well as the specfc surface area and reduces the dffuson resstance of mosture durng the fnal dehydraton step. Such a thermo-mechancal ISBN: WCECS 9

2 Proceedngs of the World Congress on Engneerng and Computer Scence 9 Vol I WCECS 9, October -, 9, San Francsco, USA treatment also nduces mcrobologcal decontamnaton [1]. Ths research was amed to apply the DIC technology n the producton of cassava flour. The varaton of the process varables.e. steam pressure/temperature and tme of treatment n DIC reactor wll be studed n accordance wth the knetcs of dehydraton, the physcal propertes whch nclude water and ol holdng capacty, and the mcrobal decontamnaton. II. MATERIALS AND METHODS A. Raw Materal Freshly harvested cassava roots (Manhot esculenta) were purchased locally and used n all experments. After washng and peelng, the cassava roots were cut nto peces of 16x16x mm 3. B. Dehydraton Method Raw and processed cassava peces were subjected to a stream of hot ar at 5 o C n a hot ar dryer (Ventcell Dryer). The cassava peces were dred untl the resdual water content of about -5 %wb. was reached before DIC treatment. The same hot ar dryer and condtons were used for ntal as well as for fnal dehydraton. C. The DIC Reactor The DIC reactor s shown schematcally n Fg. 1. The reactor conssted of four major components,.e. (a) the processng vessel (1.5x1-3 m 3 volume), where samples were placed and treated, (b) the vacuum system, whch conssted manly of a vacuum tank wth a volume 6-fold greater than the processng vessel, (c) the adequate vacuum pump, and (d) the pressure-droppng system, whch s a pneumatc valve, separated the processng vessel from the vacuum tank and could be operated after a hgh steam pressure treatment and f requred before the njecton of steam n order to establsh an ntal vacuum n the processng vessel. D. The Experment Procedure The general expermental protocol s detaled n Fg.. After preparng the raw materal, ntal partal dehydraton was carred out. Ths s requred pre-treatment before the DIC processng. Fgure 1. Schematc dagram of the DIC reactor: (a) treatment vessel wth heatng jacket; (b) vacuum tank wth coolng lqud jacket; (c) vacuum pump; (d) nstant pressure-drop valve. Fgure. Schematc dagram of global processng Fgure 3. DIC temperature and pressure hstory: P A and T A are the steam pressure and temperature respectvely n the processng vessel, P V the vacuum tank pressure, T P temperature of product: (a) sample at atmospherc pressure; (b) ntal vacuum; (c) saturated steam njecton to reach the selected pressure; (d) constant temperature correspondng to saturated steam pressure; (e) abrupt pressure drop towards vacuum; (f and g) releasng to the atmospherc pressure. The food sample was then treated n the processng vessel n whch a vacuum of 5 kpa was establshed by a bref connecton wth the vacuum tank (Fg. 3-b). The ntal vacuum treatment facltated the dffuson of steam nto the sample. Consequently, the tme necessary for the temperature of the sample to reach the steam temperature was reduced. Saturated steam was then ntroduced nto the vessel at a fxed pressure level (Fg. 3-c) and mantaned for a predetermned tme (Fg. 3-d). Ths step was followed by a sudden pressure drop (Fg. 3-e). The rapd pressure drop nsde the processng vessel nduced a rapd coolng of the sample whch passed n less than one second from C (dependng on the steam pressure condtons) to about 3 C. Treatment ended by a releasng to the atmospherc pressure (Fgure 3-f & g); as the atmospherc ar njecton then occurs under vacuum, the ar expanson decreased further the treated food temperature. ISBN: WCECS 9

3 Proceedngs of the World Congress on Engneerng and Computer Scence 9 Vol I WCECS 9, October -, 9, San Francsco, USA The equlbrum after the drop n pressure depended on operatng condtons: the hgher the steam pressure level, the hgher the equlbrum pressure. The steam generated by flash vaporzaton after the decompresson produced mcro-texturaton, whch was closely lnked to a complex process of mcro-alveolaton. Ths process depended on the dfference n temperature between the two thermodynamc equlbrum states, before and after decompresson. After treatment the sample was ar-dred at 5 C n convectve hot ar dryer to around 7% wb (7.5% db) mosture content. Afterward the dred cassava peces were grounded usng a commercal grnder (Phlp Grnder) to pass a mesh seve and stored at 5 C n sealed plastc contaners pror to further analyses. E. Fundamentals There are four transfer mechansms whch usually ntervene durng the dryng process [11]; they are: 1). Heat transfer from outsde towards the product surface; the energy can be generally brought by contact, convecton, or radaton. ).Heat transfer wthn the product; the energy s transmtted by conducton. 3). Water transfer wthn the product; t s carred out ether n lqud (by varous process ncludng capllarty and molecular dffusvty; the drvng force s the gradent of water content) and / or vapour phase (the drvng force s the gradent of the partal pressure of vapour). 4). Vapour transport from the surface towards outsde. Energy exchange to the product surface result n constant rate dryng perod and proceed n very short tme. Then, especally for bomaterals, durng almost overall dryng process the water transfer take place wthn the product that result n fallng rate of dryng. By assumng that external heat and mass transfers do not lmt the overall rate operaton thanks to adequate ar flow temperature and velocty, only nternal transfers are consdered as controllng the processes [1]. Mounr & Allaf [13] assumed that, when mass transfer s much slower than conducton heat transfer wthn the product, the dryng knetcs s controlled by mass transport of water wthn the granule; ths s the case of numerous bopolymers. The process s then descrbed by a frst stage of superfcal nteracton followed by a dffuson Fck-type s law wthn the materal; Allaf s formulaton [14] s generally used: ρ w ρ w ( ν w ν m ) = Deff grad (1) ρ ρ m where: ρ w : apparent densty of water n the materal (kg.m -3 ), ρ m : apparent densty of dry materal (kg.m -3 ), v w : absolute velocty of water flow wthn the porous medum (m.s -1 ). v m : absolute velocty of sold medum (m.s -1 ). D eff : effectve dffusvty of water wthn the sold medum (m².s -1 ). Mounr & Allaf [11] assumed neglectng effects of possble shrnkage, and wth the hypothess of constant effectve dffusvty durng dryng, Fck s second law becomes for 1-D: m ρ w ρ w = Deff t r The effectve dffusvty D eff s consdered as constant because of the constant temperature and homogeneous structure of the materal durng dryng. Dfferent mathematcal solutons have been proposed for ths equaton, dependng on the ntal and boundary condtons [15]; n our study, we can adopt the soluton gven by Crank, accordng to the geometry of the sold matrx [16]; by expressng the amount of water n the sold, equaton () becomes: MR = (3) e e = = 1 A exp( q t) where s the water content dry bass at t, e, the amount of at equlbrum (t ) and the value of at t =. For a slab geometry form, Eq. (3) becomes: 8 = MR π = n 1 ( n + 1) ( n 1) + π D exp 4L eff t Where D eff s the effectve dffusvty (m /s); L s the thckness of slab (m). For long dryng perod, Eq. (4) can be further smplfed to only the frst term of seres [17]-[18]. Thus Eq. (4) s wrtten n logarthmc form as follows: 8 D t ln MR = π ln π 4L (5) eff Dffusvtes are typcally determned by plottng expermental dryng data n term of ln MR versus dryng tme t n Eq. (5), because the plot gves a straght lne wth a slope as follows: π D Slope = (6) 4L eff F. Water and Ol Holdng Capacty Determnaton Method proposed by J.A. Larraur [19] was used wth slght modfcaton. Fve mlllters of dstlled water or commercal olve ol were added to, g of dry sample, ncubated at 4 o C for 1 h. After centrfugaton, the lqud phase was separated and the resdue was weghed. WHC and OHC were calculated as g water or ol absorbed per g of dry sample, respectvely. G. Determnaton of Mcrobal Content The mcrobal content of the cassava samples were analyzed usng total plate count method. A ten gram sample was aseptcally blended and serally dluted usng peptone salne water (.85% NaCl and.1% peptone) n test () (4) ISBN: WCECS 9

4 Proceedngs of the World Congress on Engneerng and Computer Scence 9 Vol I WCECS 9, October -, 9, San Francsco, USA tubes. As much as 1 ml of dluted samples n the test tubes was transferred nto plate count agar and ncubated for 48 hours at 35 o C. The colones formed were counted afterward. Table 1. Experment trals wth steam pressure P and thermal treatment tme t expressed n coded and real values. Tral No. Saturated steam pressure Coded levels Real values (MPa) Hgh temperature processng tme Coded levels Real values (s) 1 +α α α α α = 4 N, N s the number of ndependent varables. In the present case: N= and α = H. Expermental Desgn and Statstcal Analyss A two varable central composte rotatable desgn was used. Such desgn needs 13 experments ncludng 4 repetton runs at the centre pont. The experments were run n random n order to mnmze the effects of unexpected varablty n the observed responses due to extraneous factors. For each factor, the expermental range and the central pont are based on the results of other prelmnary trals. Table 1 lsts the ndependent varables, ther symbol, and the coded and real factor level. Regresson coeffcents and analyss of varance (ANOVA) are computed usng Mntab-11.1 (Mn Tab Inc., USA) software. The objectve s to observe the nfluence of the process varables.e. steam pressure/temperature and tme of treatment n DIC reactor on the dependent responses whch conssted of knetc of dehydraton (effectve mosture dffusvty) and cassava flour physcal propertes, ncludng water holdng capacty (WHC) and ol holdng capacty (OHC). Snce the processng pressure (ξ 1 ) and the treatment tme (ξ ) were set as the desgn varables, the responses were assumed to be affected by the two ndependent varables ξ. It was also assumed that the dependent varables (referred to as responses), η, whch were expermentally measured, defned the system, and was formulated as: η = (7) f ( ) ξ 1,ξ The obtaned expermental data were analyzed by RSM to ft to the followng second-order polynomal model: + β x + β x β1x1 = 1 = 1 η = β + (8) where β o, β, β and β 1 are regresson coeffcents and x are the coded varables lnearly related to ξ. The codng of ξ nto x s expressed by the followng equaton: * ( ξ ξ ) d x = / (9) where ξ = actual value n orgnal unts; ξ * mean of hgh and low levels of ξ ; and d = dfference between the low and hgh levels of ξ. III. RESULTS AND DISCUSSION A. Mosture Effectve Dffusvty ( D eff ) The observed profle of the mosture content change s presented on Fg. 4. It showed that the expermental data led on curvature profle, whch ndcated that fallng rate dryng mechansm had occurred durng the whole dryng perod. In such case, water dffuson mechansm would control the process. To nvestgate the mpact of DIC texturng on the dryng knetcs, the man parameter had been the water dffusvty wthn materal. Takng the prerequste assumpton, then the effectve dffusvty (D eff ) was calculated usng Eq. (5). For the DIC treated cassava, the surface plot of D eff s presented on Fg. 5 and the regresson coeffcents are showed on Table. Even though the obtaned regresson coeffcents were very low, the results showed that the DIC treatment ncreased the water effectve dffusvty. The reference D eff obtaned wth conventonal dryng (dryng wthout nsertng DIC treatment) had been 1.13 x 1-1 m /s, whereas the D eff values n all DIC treated cassava were somewhere hgher ( ) x 1-1 m /s. It ndcated that the change n cassava physcal propertes, such as capllary and molecular dffusvty, had occurred durng texturng by DIC treatment. The hgher D eff value due to the texture change s one among other advantages of DIC treatment applcaton, especally for bomateral products. B. The Water and the Ol Holdng Capacty The water holdng capacty (WHC) and the ol holdng capacty (OHC) are the physcal propertes that ndcate the capacty of a materal to hold water and ol, respectvely. Both physcal propertes were very mportant to be known for flour or powder food materal, as some dfferent food powders usually should be blended together to produce a certan fnal food product. Then approprate WHC or OHC of food raw materal becomes an mportant property. In ths work the effect of DIC treatment on WHC and OHC of the cassava flour was studed. Surface plots were presented n Fg. 6 for WHC and Fg. 7 for OHC. The ISBN: WCECS 9

5 Proceedngs of the World Congress on Engneerng and Computer Scence 9 Vol I WCECS 9, October -, 9, San Francsco, USA ncrease of the treatment tme up to around 3 s resulted n lower WHC, whereas lengthenng the treatment tme from 3 s resulted n hgher WHC. Increasng the steam pressure dd not affect the WHC sgnfcantly. At low steam pressure, whch s less than 4 x 1 5 Pa, ncreasng the treatment tme up to 3 s resulted n lower OHC, whereas lengthenng the treatment tme from 3 s resulted n hgher OHC. At hgh steam pressure, more than 4 x 1 5 Pa, lengthenng the treatment tme resulted n hgher OHC. Pre-Dryng Fnal Dryng Fgure 6. Surface plot of the water holdng capacty Pre-dryng Fnal dryng DIC Treatment at t = 11 mnutes Conventonal Dryng Fgure 7. Surface plot of the ol holdng capacty It was also found that texturng by DIC resulted n the ncrease of WHC from 1. g water/g dry cassava (dryng wthout DIC treatment) to.-8. g water/g dry cassava. Texturng by DIC also resulted n the ncrease of the OHC from.4 g ol/g dry cassava (dryng wthout DIC treatment) to.8-. g ol/g dry cassava. The ncrease of both WHC and OHC ndcated that the texturng by DIC mght change the mcro structure of cassava, such as the total pore volume and the specfc surface. Fgure 4. The profle of the mosture content change durng preand fnal-dryng. Table. The regresson coeffcents The The Responses coeffcents D eff WHC OHC β β β β β β R 17.67% % 1.81 % Fgure 5. Surface plot of the effectve dffusvty C. The Mcrobal Decontamnaton The observaton of the mcrobal content of treated cassava showed that no fung growth was detected n the fnal product, both for process wthout DIC treatment and for process wth DIC treatment. Ths showed that dryng at 5 o C for 4 5 hours has effectvely nhbted the fung growth on cassava. It would be one advantage compared to producng cassava flour by sun dryng, where fung growth was usually found due to the very low rate of dryng. The result of the bacteral content of treated cassava s ISBN: WCECS 9

6 Proceedngs of the World Congress on Engneerng and Computer Scence 9 Vol I WCECS 9, October -, 9, San Francsco, USA shown n Table 3. In ths case DIC treatment was conducted at 4x1 5 Pa steam pressure for 1.3 seconds. In process wthout DIC treatment the bacteral content decreased from 5, CFU/ml n the fresh cassava to 4,5 CFU/ml n the treated cassava samples after fnal dryng, whch meant that there was 6.7 % reducton of the bacteral content. Whereas n process wth DIC treatment, the bacteral content decreased from 65, CFU/ml n the fresh cassava to 86,5 CFU/ml n the treated cassava samples after fnal dryng whch meant that 85.7 % reducton of the bactera content had been acheved. The result showed that nsertng DIC treatment between the pre- and the fnal-dryng stage had ncreased the bacteral decontamnaton sgnfcantly. In ths work, the nvestgaton of the mcrobal decontamnaton was amed only to observe the ntal tendency of the role of DIC treatment n food sterlzaton process. Further work should be performed to nvestgate and to optmze the DIC process varables.e. the appled pressure and treatment tme to reach the optmum mcrobal decontamnaton by consderng the degree of nutrtonal damage due to exposure on hgh steam temperature for certan treatment tme. Table 3. The bacteral content the bacteral content (CFU/ml) sample wthout DIC treatment wth DIC treatment fresh cassava 5, 65, after fnal dryng 4,5 86,5 reducton 315,5 (6.7 %) IV. CONCLUSION 518,5 (85.7 %) The mpact of the texturng by Instantaneous Control Pressure Drop on the effectve mosture dffusvty, the water and the ol holdng capacty, and the mcrobal decontamnaton of cassava has been nvestgated. However, further observaton should be performed to obtan more comprehensve result. It s hghly recommended to conduct more specfc measurement related to the product physcochemcal characterstcs and qualtes such as electron mcroscope mage of ether product slce or powder to observe the mcro texture change, BET analyss to nvestgate the change n the total mcro pore volume, texture measurement, and nutrtonal content change analyss durng the process. REFERENCES [1] CBS (Central Bureau of Statstcs). Food balance sheet n Indonesa, Jakarta, Indonesa [] I. W. Rusastra, Study on aspects of natonal producton, consumpton, and marketng of cassava. Indones. Agr. Res. Dev. J., 7, 1988, pp [3] A. Dmyat & I. Manwan, Natonal coordnated research program : cassava and sweet potato, Central Research Insttute for Food Corp (CRIFC), Bogor, Indonesa, 199. [4] E. Debs-Louka, N. Louka, G Abraham, & K. Allaf, Décontamnaton des produts secs en morceaux ou en poudre par voe thermomécanque contrôlée, Actes des 1èmes Rencontres Scentfques et Technologques des Industres Almentares, AGORAL, Ed. Lavoser. 5-3, Montpeller, -3 Mars;. [5] K. Allaf & P. Vdal, (1989), "Feasblty study of a new process of dryng/swellng by nstantaneous decompresson toward vacuum of n peces vegetables n vew of a rapd re-hydraton" Gradent Actvty Plottng Unversty of Technology of Compegne UTC N CR/89/13, ndustral SILVA-LAON partner, June, [6] K. Allaf, N. Louka, J. M. Bouver, F. Parent, & M. Forget, Method for processng materals to change ther texture, apparatus therefore, and resultng materals, 1/5/1999, Document Type and Number: Unted States Patent French Patent No Internatonal extenson No. PCT/FR94/975, [7] M. Al-Haddad, S. Mounr, V. Sobolk, & K. Allaf, Fruts & vegetables dryng combnng hot ar, DIC technology and mcrowaves, Internatonal Journal of Food Engneerng IJFE, Vol 4, ss. 6, art. 9, 8. [8] M. Al-Haddad, S. Mounr, V. Sobolk, & K. Allaf, Double ntensfcaton of operaton of hot ar dryng of fruts and vegetables: mpact of swell dryng by DIC on the transfer phenomena, European Dryng Conference, Barrtz France, AFSIA 7, 4-5 May 7. [9] K. Allaf, Analyss of nstantanety n thermodynamc processes; Fundamental laws, 1st Franco- Lebanese Symposum on technologes and studes on Process Engneerng and Bochemstry. Lebanese Unversty, Berut, July/August,. [1] K. Allaf, N. Louka, A. Habba, Z. Maache, & S.A. Rezzoug, Dverse thermal, pressure and vacuum treatment for e.g. most foods, cosmetcs, chemcal and pharmaceutcal products, Publcaton No.: FR774913; Date of ssue: /8/1999; orgnal No. FR774913, [11] S. Mounr & K. Allaf, Study and modelng of dehydraton and rehydraton knetcs wthn porous medum, Proceedngs of AFSIA, Lyon (France), May, 9. [1] S. Mounr, Etude de nouveaux procédés de fabrcaton de poudres par nserton de la technologe de détentes nstantanée contrôlée DIC, dans les processus d atomsaton, de séchage/ texturaton et de pulvérsaton contrôlée sous vde de produts laters, PhD (Thèse de doctorat), Unversty of La Rochelle, 7. [13] S. Mounr & K. Allaf, Three-stage spray dryng: new process nvolvng nstant controlled pressure drop (DIC), Journal of Dryng Technology, Vol. 6, No. 4, 8, pp [14] K. Allaf, Transfer phenomena and ndustral applcatons, Teachng book publshed by the Lebanese Unversty, Faculty of Scence, 198. [15] A.S. Mujundar, Handbook of Industral Dryng, Thrd Edton, Edted by CRC Taylor & Francs Group Press, 6. [16] J. Crank, The mathematcs of dffuson, Oxford, England. Clarendon Press, [17] Z. Pakowsk & A.S. Mujumdar, Basc process calculatons and smulatons n dryng, n HANDBOOK OF INDUSTRIAL DRYING, Thrd Edton, Edted by CRC Taylor & Francs Group Press, 6. [18] M. A. Tutuncu, and T. P. Labuza, Effect of geometry on the effectve mosture transfer dffuson coeffcent, Journal of Food Engneerng, 3, 1996, pp [19] J.A. Larraur, P Rupe rez, B. Borroto, and F. Saura-Calxto, Mango peels as a new tropcal fbre: Preparaton and characterzaton, Lebensmttel-Wssenschaft und Technologe, 9, 1996, pp ACKNOWLEDGMENT The authors wsh to thank THE ABCAR-DIC PROCESS SAS, La Rochelle France for provdng a set of DIC equpment. ISBN: WCECS 9