Desorption Isotherm Model for a Malaysian Rough Rice Variety (MR219)

Transcription

1 Prtanika J. Trop. Agric. Sci. 36 (2): (203) TROPICAL AGRICULTURAL SCIENCE Journal hompag: Dsorption Isothrm Modl for a Malaysian Rough Ric Varity (MR29) M. Nordin Ibrahim, K. Tajaddodi Talab *, S. Spotar 2, Kharidah, M. 3 and Rosnita, A. T. Dpartmnt of Procss and Food Enginring, Faculty of Enginring, Unirsiti Putra Malaysia, Srdang, Slangor, Malaysia 2 Dpartmnt of Chmical Enginring, Unirsity of Nottingham, Malaysia Campus, Jalan Broga, Smnyih, Slangor, Malaysia 3 Dpartmnt of Food Scinc, Faculty of Food Scinc and Tchnology, Unirsiti Putra Malaysia, Srdang, Slangor, Malaysia ABSTRACT Moistur dsorption modl of long grain Malaysian rough ric arity (MR29) was xprimntally obtaind using th static graimtric mthod for diffrnt combinations of tmpratur (40, 45, 50, 55 C) and watr actiitis ( to 0.933). Fi most commonly usd modls with thr paramtrs namly modifid Chung Pfost, modifid GAB, modifid Halsy, modifid Hndrson and modifid Oswin and a four paramtrs modl (Zuritz t al., 978) wr dtrmind for thir ability to fit th xprimntal data using non linar rgrssion tchniqus. Comparisons btwn all modls wr mad on th basis of standard rror of stimat (SEE), rsidual sum squars (RSS) and rsidual plots. Basd on th rsults of this study, th Zuritz t al., modifid Chung Pfost and modifid GAB modls could b usful to prdict th dsorption EMC of MR29. Th modifid Halsy, modifid Hndrson and modifid Oswin prsntd a poor fitting to th xprimntal data. In addition, th modl by Zuritz t al. was found to b th most appropriat quation for rprsnting th dsorption isothrm modl for MR29 at th rang of tmpraturs from 40 C to 60 C. ARTICLE INFO Articl history: Rcid: 8 Dcmbr 20 Accptd: 9 Dcmbr 20 addrsss: nordin@ng.upm.du.my (M. Nordin Ibrahim), dr2ng@yahoo.com (K. Tajaddodi Talab), srgy.spotar@nottingham.du.my (S., Spotar), kharidah@putra.upm.du.my (Kharidah, M.), rosnita@ng.upm.du.my (Rosnita, A. T.) * Corrsponding author Kywords: Equilibrium moistur contnt, dsorption, static graimtric, fit ability, rough ric INTRODUCTION Rough ric is known as a hygroscopic matrial that can gain or los moistur n though its surrounding air conditions ISSN: Unirsiti Putra Malaysia Prss

2 M. Nordin Ibrahim, K. Tajaddodi Talab, S. Spotar, Kharidah, M. and Rosnita, A. T. undrgo changs. A product can gain or los its moistur whn it is subjctd to a continual supply of air at constant tmpratur, humidity and apour prssur (p), until th apour prssur of moistur in th product bcoms qual to p. In this stat, moistur contnt (MC) of a product is known as quilibrium moistur contnt (EMC) (Champagn, 2004). Thr is a rlationship btwn th MC of a product and its quilibrium rlati humidity (ERH) at a constant tmpratur which can b shown by an isothrm cur. It is ncssary to ha information on th adsorption or dsorption isothrms of a particular food. Ths isothrms can b applid in food procssing and nginring to impro product quality (Dlgado & Sun, 2002b). Th EMC affcts th rat of moistur transfr from krnls to th surrounding air which can affct ric milling quality (Fan t al., 2000., Kunz, 979). Chn (997) and Bonazzi, t al. (997) claimd that arity, tmpratur and rlati humidity wr th main factors that lad had ric yild (HRY) to dcras. Adsorption and dsorption ar important factors that can affct fissur formation in th ric krnl, and th subsqunt HRY during drying and storag. Th EMC is dlopd as a rsult of an intraction btwn th matrial and th nironmntal condition (Molna r, 2007): X * = X * ( p, T) [] MC of products can b changd bcaus of th condition ( p, T) dominating on th surfac of th products. Aftr an adquatly long tim with stabl limit conditions an intrnal moistur diffusion balanc occurrd until th EMC is rachd. Th sorption quilibrium is a condition whr th moistur adsorption and dsorption dos not occur in a product. Th quilibrium apour prssur (EVP) is th apour prssur at which th sorption quilibrium taks plac at a crtain ll of product MC ( X ) at a crtain tmpratur (T). EVP can b xprssd as follows: p * = p *(T) X [2] In drying rsarch, it is ncssary to ha nough information on EVP at a constant tmpratur. Thrfor, whn T is constant p * is constant, th quilibrium rlati apour contnt is applid in drying procss as a charactristic of th apour prssur (Molna r, 2007): p ψ = p * o [3] Gnrally, th sorption isothrm ( X * = X * ( p ) T ), sorption isobars ( X * = X * (T) p ), and sorption isostrs ( p = p (T) * x ) ar applid in drying procss. Thy ar drid from th sorption quilibrium function ( X * = X * ( p, T)). Th sorption isothrms ar most frquntly applid to dscrib th sorption bhaiour of a matrial. Sorption isothrms ar dtrmind from point to point (Molna r, 2007): X *( * ψ ) T, X ( * ψ 2 2 ) T X ( ψ n n ) T, [4] 90 Prtanika J. Trop. Agric. Sci. 36 (2): (203)

3 Dsorption Isothrm Modl for a Malaysian Rough Ric Varity (MR29) Each pair of alus for dtrmining a point is in gnral th rsult of a masurmnt. Th lmnts of this masurmnt ar as follows:. Prsntation of th pair of alus to b masurd on th condition that T is constant. 2. Masurmnt of th alu of p, and ψ should b don during or at th nd of th sorption masurmnt. 3. Th EMC ( X * ) of sampl should b dtrmind at th nd of th sorption masurmnt. Gal (98) riwd diffrnt mthods and finally classifid thm into thr basic tchniqus, namly, manomtric, graimtric and othr spcial mthods. Manwhil, Molna r (2007) statd that th graimtric tchniqu is th common mthod usd for EMC dtrmination. In this tchniqu, saturatd salt solutions or sulfuric acid dilutions at diffrnt concntrations ar usd to maintain constant rlati humidity in closd still moist air at crtain tmpratur (Gal, 98) and a thrmostat is usd to control th air tmpratur (Molna r, 2007). Champagn (2004) statd that diffrnt ric aritis quilibrat to slightly diffrnt moistur contnts in a gin nironmnt. Th sam ric arity also quilibrats to slightly diffrnt MC dpnding on whthr th grain is adsorbing or dsorbing moistur whil approaching th quilibrium stat. Chio t al. (200) riwd diffrnt ric hygroscopic quilibrium studis and finally concludd that ric typ and arity affct EMC/ERH rlationship significantly. Th rsarchrs addd that sinc nw aritis ar introducd by ric industry, it is ncssary to obtain suitabl EMC/ERH quation for ach to impro ric procssing and storag. Sinc th EMC modl is an important paramtr in computr drying simulation, slcting a propr modl can hlp to achi good rsults. It must b notd that all EMC/ ERH modls applid in this study ha bn rcommndd by prious rsarchrs for a limitd rang of tmpratur (0 C - 40 C). In addition, Zuritz t al. (978) conductd an quilibrium isothrm for a mdium grain. Thrfor, th main goal of this study was to obtain a dsorption quilibrium isothrm in th highr rang of tmpratur (40 C 60 C) for a slctd Malaysian long ric arity (MR 29) using th xisting modls. MATERIALS AND METHOD Long grain rough ric, MR29 with approximatly 8% moistur contnt (d.b.) was usd in this xprimntal study. Th graimtric mthod was chosn to find suitabl EMC quation. Sulphuric acid solutions wr usd to proid constant rlati humidity. Th following quation was applid to stimat ERH or watr actiity (Molna r, 2007): a log a w = ( a ) + log( ) T P Whr: T= absolut tmpratur (K) P 0 = apor prssur of watr (Pa) 0 [5] Prtanika J. Trop. Agric. Sci. 36 (2): 9-98 (203) 9

4 M. Nordin Ibrahim, K. Tajaddodi Talab, S. Spotar, Kharidah, M. and Rosnita, A. T. Th mpirical constant alus (a and a 2 ) which dpnd on th sulfuric acid wight prcntag ar prsntd by Molna r (2007). Watr actiity rangs from to was achid by diffrnt concntrations of sulphuric acid from 0% to 70% (w/w). About 20 g of rough ric sampls wr put insid a cloth nt and suspndd from jars cors abo 25 ml sulfuric acid solution. Th jars with rough ric sampls wr put in tmpratur controlld incubator st at 40, 45, 50, 55, 60 ºC. Th masurmnt of sampls masss commncd aftr 2 wks. Sampl masss wr chckd again ry 72 h. Dpnding on th rlati humidity and tmpratur, diffrnt tims wr rquird for sampls to rach an quilibrium condition. Th maximum tim for th sampls to rach quilibrium was 28 days. Moistur contnt of ach sampl was masurd in duplicats by drying 3-5 g sampls for 24 h in an on st at 30 C (Jindal & Sibnmorgn, 987). Th following quation was usd to calculat th EMC of th sampls (ASAE, 2007): Whr: MC ( d. b.) W W W d d [6] W = Sampl wight at quilibrium bfor on drying W d = Sampl wight at quilibrium aftr on drying Th xprimnts for ach tmpratur and watr actiity wr carrid out in triplicat. Fi thr-paramtr quations that had bn rcommndd by th ASAE standard D245.5 (ASAE, 2007) wr usd to dtrmin thir fit ability in this study. Thy can b xprssd as follows: Modifid Chung Pfost quation (Pfost t al., 976; ASAE, 2007; Basunia & Ab, 200; Choi t al., 200): M ln A B.ln[ B ( T C).ln RH] [7] Modifid Halsy quation (Iglsias & Chirif, 976; ASAE, 2007; Basunia & Ab, 200; Choi t al., 200): M [ xp( A B. T ) ] ln RH C [8] Modifid Hndrson quation (Thompson t al., 968, ASAE, 2007; Basunia & Ab, 200; Choi t al., 200): M [ ln( RH) ] A.( T C) B [9] and th modifid Oswin s quation (Oswin, 946; ASAE, 2007; Basunia & Ab, 200; Choi t al., 200): M ( A B. T ). RH RH C [0] Th dlopd and modifid GAB quation is as follows (Jayas & Mazza, C 993): A. B.( ). RH M T C ( B. RH)[ B. RH ( ). B. RH] T [] 92 Prtanika J. Trop. Agric. Sci. 36 (2): (203)

5 Dsorption Isothrm Modl for a Malaysian Rough Ric Varity (MR29) Whr, M RH T = Equilibrium moistur contnt (EMC, d.b., %) = Equilibrium rlati humidity (ERH, dcimal) = tmpratur ( C) A, B & C = paramtrs A four-paramtr quation by Zuritz t al. (978) was also usd for fitting th data. This particular quation was dlopd by Zuritz t al. (978) for mdium grain arity (CSM 5) at drying air tmpratur rang of 0 C - 40ºC and Rh of.2% %. It can b xprssd as follows: rror (SEE) was usd to masur th accuracy of th modl and th cofficint of dtrmination (R²) to show th ariability btwn th prdictd and masurd data. In a good mathmatical modl, th cofficint of dtrmination should b clos to (on) and sum of squar rrors should b clos to 0 (zro). Th suitability of th quations was aluatd and compard using rsidual sum of squar (RSS), standard rror of stimat (SEE) and cofficint of dtrmination (R²): R 2 Whr, St SEE = S t [3] M Whr, M RH T T c xp log (log( RH). T ) ( T A ). B T C. T = EMC (% d.b.) = ERH (dcimal) = Tmpratur (ºK) c D [2] = Critical tmpratur of watr=647. (ºK) A, B, C & D = Equation paramtrs Th paramtrs in th sorption quations wr stimatd using non-linar rgrssion analysis by applying th Lab Fit V softwar. Manwhil, th sum of squar S t = SEE N j= ( y y ) N N j ( y i jcal 2 df y 2 j xp) y N j= = Th rsidual sum squar (RSS) is dfind as: RSS = N j= ( y jcal y j 2 xp) N y i [4] df and N ar th dgr of frdom and th numbr of data points, rspctily, and y j xp and y ar xprimntal and jcal calculatd alus of y, rspctily. Th quation giing th smallst RSS and SEE and th highst R² alu ar considrd to b th bst fittd quation. Prtanika J. Trop. Agric. Sci. 36 (2): (203) 93

6 M. Nordin Ibrahim, K. Tajaddodi Talab, S. Spotar, Kharidah, M. and Rosnita, A. T. RESULTS AND DISCUSSION Tabl shows th dsorption isothrm alus for MR 29 at ERH of 93.3% to 5.07% and tmpratur of 40ºC 60ºC with quilibrium moistur contnt (M ) in dcimal and dry basis. Th xprimntal data wr usd to stimat paramtrs of isothrms quations of Zuritz, modifid Chung-Pfost, modifid GAB, modifid Oswin, modifid Halsy and modifid Hndrson. Tabl 2 shows th stimatd paramtrs of ths modls in which th EMC was takn as th dpndnt ariabl. Manwhil, th corrsponding corrlation cofficint btwn th xprimntal and prdictd data (R²), th standard rror of stimat (SEE) and rsidual sum of squar (RSS) which indicat th fitting ability of ach quation ar shown in Tabl 2. As illustratd, th corrlation cofficints ar ry high in most cass (R²> 0.97). Th Zuritz modl obtaind th highst R², th last SEE and th last RSS followd by modifid Chung- Pfost, modifid Gab and modifid Oswin at slctd tmpratur rang (40 C 60 C) and ERH (93.3% to 5.07%). According to Chn and Mory (989) and Aiara t al. (2004), statistical paramtrs lik R² or SEE may not b TABLE Dsorption isothrm alus for MR29 at diffrnt ERH (%) and tmpraturs. T= 40 º C T= 45 º C T= 50 º C T= 55 º C T= 60 º C ERH M ERH M ERH M ERH M ERH M TABLE 2 Th stimatd cofficints and th statistical paramtrs for slctd mathmatical sorption quations Equations paramtrs A B C D R² SEE RSS Zuritz Modifid Chung- Pfost Modifid GAB Modifid Oswin Modifid Halsy Modifid Hndrson Prtanika J. Trop. Agric. Sci. 36 (2): (203)

7 Dsorption Isothrm Modl for a Malaysian Rough Ric Varity (MR29) sufficint idnc for th goodnss of fit of a moistur sorption isothrm modl basd on xprimntal data. Thrfor, th natur of th rsidual plots should b considrd. Th rsidual plots of th Zuritz t al. modifid Chung-Pfost and modifid Gab modls wr random distributions or th rang of tmpratur and EMC tstd in this study. As shown in Fig. to Fig.3, th modifid Oswin, modifid Halsy and modifid Hndrson modls prsntd a pattrnd distribution for MR29 undr th tstd conditions in this study. Basd on th rsults shown in Tabl 2 and th rsidual plots, th Zuritz t al. modifid Chung- Pfost, and th modifid Gab modls could b usful for prdicting th EMC and its tmpratur dpndnc. From th thr modls, th Zuritz t al. s modl was th most appropriat modl to prdict moistur dsorption isothrms of MR29 at th tmpratur rangs from 40 C to 60 C. Th dsorption isothrms obtaind in this study ha a sigmoid shap (Fig.4). Undr fixd rlati humidity condition with incrasing air tmpratur, th EMC dcrass. In addition, at fixd air tmpratur, EMC dcrass with dcrasing rlati humidity. Masurd moistur contnt, % d.b Fig.: Rsiduals rsus prdictd EMC for th modifid Oswin s quation Masurd moistur contnt, % d.b Fig.2: Rsiduals rsus prdictd EMC for modifid Halsy quation Masurd moistur contnt, % d.b Fig.3: Rsiduals rsus prdictd EMC for modifid Hndrson quation Prtanika J. Trop. Agric. Sci. 36 (2): (203) 95

8 M. Nordin Ibrahim, K. Tajaddodi Talab, S. Spotar, Kharidah, M. and Rosnita, A. T. CONCLUSION Th dsorption isothrm obtaind in this study prsntd a sigmoid shap. Th rsults illustrat that th EMC of rough ric dcrass with an incras in tmpratur at constant ERH. Th corrlation cofficint (R²) obtaind for all th modls was in th rang of Among th moistur isothrm quations tstd in this study, th four-paramtr moistur isothrm quation of Zuritz t al. was idntifid as th most appropriat quation to rprsnt EMC of th Malaysian ric arity (MR29) at th tmpratur rangs from 40 C to 60 C. Thr paramtr quations of th modifid Chung-Pfost and th modifid Gab wr also found accptabl. Howr, th modifid Oswin, modifid Halsy and modifid Hndrson prsntd a poor fitting ability to th xprimntal data. NOTATIONS A, B, C, D = Cofficints EMC = Equilibrium moistur contnt ERH = Equilibrium rlati humidity EVP = Equilibrium apor prssur M = Equilibrium moistur contnt P = Partial prssur R² = Corrlation cofficint RSS = Rsidual sum squar SEE = Standard rror of stimat T = Tmpratur X = Moistur contnt of matrial ψ = Rlati quilibrium apor prssur Equilibrium moistur contnt (%, d.b.) C prdictd 40 C 45 C prdictd 45 C 50 prditd 50 C 55 C prdictd 55 C 60 C prdictd 60 C Equilibrium rlati humidity (%) Fig.4: Th xprimntal and Zuritz modl prdictd th dsorption isothrms for MR29 at 40, 45, 50, 55, and 60 C 96 Prtanika J. Trop. Agric. Sci. 36 (2): (203)

9 Dsorption Isothrm Modl for a Malaysian Rough Ric Varity (MR29) REFERENCES ASAE. (2007). Moistur rlationship of plant basd agricultural products. ASAE standard D Amrican Socity of Agricultural Enginrs: MI. Aiara, N. A., Ajibola, O. O., & Oni, S. A. (2004). Sorption quilibrium and thrmodynamic charactristics of soya ban. Biosystm Enginring, 87, Basunia, M. A., & Ab, T. (200). Moistur dsorption isothrms of mdium grain rough ric. Journal of Stord Products Rsarch, 37, Bonazzi, C., Puty, M., & Thmlin, A. (997). Influnc of drying conditions on th procss quality of rough ric. Drying Tchnology, 5, Champagn, E. T. (2004). Ric chmistry and tchnology (third dition). Minnsota: Amrican Association of Cral Chmists, Inc. Chn, C. C., & Mory, R. V. (987). Comparison of four EMC/ERH quations. Transactions of th ASAE, 32, Chn, H., Sibnmorgn, T. J., & Marks, B. P. (997). Rlating drying rat constant to had ric yild rduction of long-grain ric. Transactions of th ASAE. 40, Chio, B. M., Lanning, S. B., & Sibnmorgn, T. J. (200). A riw of hygroscopic quilibrium studis applid to ric. Transactions of th ASABE, 53, Dlgado, A. E., & Sun, D. W. (2002). Dsorption isothrms for cookd and curd bf and pork. Journal of Food Enginring, 5, Fan, J., Sibnmorgn, T. J., & Marks, B. P. (2000). Effcts of arity and harst moistur contnt on quilibrium moistur contnt of ric. Applid Enginring in Agricultur, 6, Gal, S. (98). Rcnt dlopmnts in tchniqus for obtaining complt sorption isothrm. In Rockland, L. B., & Stwart, G. F. (Eds.), Watr actiity: influnc on food quality. Nw York: Acadmic Prss, Inc. Iglsias, H. A., & Chirif, J. (976). A modl for dscribing th watr sorption bhaior of food. J. Food Sci., 4, Jayas, D. S., & Mazza, G. (993). Comparison of fi thr-paramtr quations for th dscription of adsorption data of oats. Transactions of th ASAE., 36, Jindal, V. K., & Sibnmorgn, T. J. (987). Effct of on drying tmpratur and drying tim on rough ric moistur contnt dtrmination. Transactions of th ASAE, 30, Kunz, O. R. (979). Fissuring of th ric grain aftr hatd air drying. Transactions of th ASAE., 22, Molnar, K. (2007). Exprimntal tchniqus drying. In Mujumdar, A. S. (Ed.), Handbook of Industrial Drying. Nw York: Marcl Dkkr, Inc. Oswin, C. R. (946). Th kintics of packag lif: III. Th isothrm. J. Soc. Chm., 65, Pfost, H. B., Maurr, S. G., Chung, D. S., & Millikn, G. A. (976). Summarizing and rporting quilibrium moistur data for grains. ASAE Papr No Amrican Socity of Agricultural Enginrs: Michigan. Thompson, T. L., Part, R. M., & Fostr, G. H. (968). Mathmatical simulation of corn drying a nw modl. Transactions of th ASAE,, Zuritz, R., Singh, P., Moini, S. M., & Hndrson, S. M. (978). Dsorption isothrms of rough ric from 0º C to 40º C. Transactions of th ASAE, 22, Prtanika J. Trop. Agric. Sci. 36 (2): (203) 97

10