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Revista Brasileira de Produtos Agroindustriais, Campina Grande, v.9, n.1, p.37-44, 2007 37ISSN 1517-8595ADSORPTION ISOTHERMS OF CHICORY INULIN POWDER: TEMPERATUREEFFECTRegina Isabel Nogueira 1 , Suely Pereira Freitas 2 , Kil Jin Park 3 , Estela Deyrmendjian 4ABSTRACTThe moisture sorption isotherms of chicory inulin powder at 25 to 45 o C were determined. Thechicory roots were submitted to hot water extraction, filtering and concentration by evaporationand spray drying. The encapsulating agents, hydrolyzed starch (7.5%) and modified starch(7.5%), were adding prior to atomization. BET, BET linear, GAB, Halsey, Langmuir, Oswin,Peleg and Chung models were tested to adjust the experimental data. BET, Halsey, Oswin andPeleg models presented the best adjust of experimental data. The moisture content of theformulated chicory inulin powder corresponding to the water activity considered as safe formicrobiological activity (65%) was inferior to 10g/100 g of dry solids in the temperature rangeanalyzed.Keywords: water activity, gravimetric method, mathematical model, encapsulating agent.ISOTERMAS DE ADSORÇÃO DE PÓ DE INULINA DE CHICÓRIA: EFEITODA TEMPERATURARESUMOAs isotermas de sorção de pó de inulina da Chicória foram determinadas de 25 a 45 o C. As raízesda Chicória foram submetidas à extração a água quente, filtração e concentração pelaevaporação e secagem por atomização. Os agentes encapsulantes, amido hidrolisado (7.5%) eamido modificado (7.5%), foram adicionados antes da atomização. Modelos de BET, BETlinear, GAB, Halsey, Langmuir, Oswin, Peleg and Chung foram testados para ajustar os dadosexperimentais. Modelos de BET, Halsey, Oswin and Peleg apresentaram o melhor ajuste dedados experimentais. O conteúdo de umidade do pó formulado de inulina de Chicóriacorrespondente à atividade de água considerada segura para a atividade microbiológica (65%) éinferior a 10g/100 g de sólido seco na temperatura analisada.Palavras-chave: atividade de água, método gravimétrico, modelo matemático, agenteencapsulante.1 Embrapa Agroindústria de Alimentos, Av. das Américas, 29501, Guaratiba, Rio de Janeiro – RJ, Brasil. E-mail:nogueira@ctaa.embrapa.br2 Escola de Química-UFRJ, Ilha do Fundão Cidade Universitária, Bloco E, sala 207, Rio de Janeiro-RJ, Brasil. E-mail:freitasp@eq.ufrj.br3 Agricultural Engineering School, Campinas State University, Campinas-SP, Brasil. E-mail: kil@agr.unicamp.br4Faculdade de Engenharia de Alimentos, Universidade Estadual de Campinas, Campinas-SP, Brasil. E-mail:edjian@gmail.comRevista Brasileira de Produtos Agroindustriais, Campina Grande, v.9, n.1, p.37-44, 2007

38 Adsorption isotherms of chicory inulin powder: temperature effect Nogueira et al.INTRODUCTIONThe Cichorium intybus L is a seasonalfood material, native of Europe, west andcentral Asia, north of Africa and South Americaand its tuberous roots store inulin (superiot to20%). Inulin is a reserve carbohydrate, whichconsists of a chain of fructose molecules with aterminal glucose molecule. The application ofinulin as a substitute for sugar or fat in foodsindustries has been increased recently due to itsuses to low caloric foods formulations. Theinulin also presents some functional properties.It acts on the organism in a similar way todietary fibers and have found applications in theproduction of functional foods and nutritionalcomposites and medicines (Figueira et al.,2004).The most stable form ofcommercialization of inulin is the powderedextract due to its better facility of manipulation.Conventionally, the chicory powder inulin isobtained by dehydration of the aqueous extractof chicory roots (Cichorium intybus L.) in aspray dryer (Nogueira, 2002).The relationship between moisturecontent and other constituents of foods affectthe hygroscopic properties of these materials.Moisture adsorption isotherms exhibitequilibrium relation between the moisturecontent of food and water activity at a giventemperature and pressure (Gustafson and Hall,1974). Knowledge of adsorption isotherms of afood product is essential to very importantapplications in food science and technology asprocessing, transport, storage and consumption.The deteriorative mechanism in food systems isvery dependent on water activity. In order toinhibit microbial growth and enhanced the shelflife of dry food, the water activity is oftenreduced (Labuza, 1986). The knowledge ofmoisture sorption characteristics for theseproducts would allow correctly specifying theconditions of storage and packaging.The moisture sorption curves aremathematically expressed as equilibriumisotherms equations. These equations predictthe effect of temperature and pressure in thequantity of adsorbed or desorbed water by agiven product. The just determination ofequilibrium moisture in dry products isimportant to optimization of dehydrationprocess (Erbas et al, 2004). Model ofexperimental sorption isotherms are of great usefor predicting thermodynamic tools fordetermining interactions between water and thefood matrix. Several empirical, semi-empiricaland theoretical models have been used fordescribing moisture sorption isotherms of foods(Labuza, 1985, Chirife & Iglesias, 1978;Valentini et al., 1997). Park and Nogueira(1992); Zhang et al. (1996); Kiranoudis et al.(1993); Lomauro, Baski & Labuza (1985),reported that the three-parameter BET and GABpolynomial models are the more appropriate fordescribing most food isotherms (fruits,vegetables, coffee, milk, condiments andothers) over a wide water activity range.Figueira et al, 2004 conclude that sorptioncurves of chicory roots at 60, 70 and 80 o C,fitted better to the GAB and Peleg models. Inthis case, the equilibrium moisture contentdecreased as temperature increased for constantvalue of water activity.No significant data is available in theliterature on water sorption isotherms offormulated inulin products. Considering thedevelopment a shelf stable inulin product, theobjective of the present study was to determine,at different temperatures, the adsorptionisotherms of formulated inulin powder and soas to adjust them different modelsrecommended in the literature.MATERIAL AND METHODSPreparation of inulin powderFormulated inulin powder was preparedaccording Nogueira (2000). The chicory rootswere submitted to following steps: hot waterextraction, filtering and concentration byevaporation and spray drying. Theencapsulating agents, hydrolyzed starch (7.5%)and modified starch (7.5%), were adding priorto atomization. The inlet and outlet dryingtemperature in spray dryer were 190ºC and95ºC, respectively.Chemical analysisProximate composition of inulin powderwas determined by standard methods indicatedin AOAC (2000).Sorption equilibrium measurementThe standard gravimetric technique (Bell& Labuza, 2000) was used for equilibriumstudies at different temperatures (25 o C, 35 o Cand 45 o C). It consisted of sorption measurementusing nine saturated salt solutions (LiCl,KCH 3 COO, KF, MgCl 2 , K 2 CO 3 , NaBr, KI,NaCl, KCl) for a range of relative humidityRevista Brasileira de Produtos Agroindustriais, Campina Grande, v.9, n.1, p.37-44, 2007

Adsorption isotherms of chicory inulin powder: temperature effect Nogueira et al. 39from de 0.1116 to 0.8434 according Greenspan(1977). These salts were recommended tomaintain the relative humidity inside thedesiccators (Bizou, Riou & Molton, 1987). Thedesiccators were immersed in an oven (OlidefCZ) adjusted to a fixed temperature to maintainthe salt solutions at a constant temperature.For the sorption experiments the samplesof inulin powder were weighted (1g 0.001g)in polystyrene dishes and placed into the sealeddesiccators for adsorption data acquisition. Theweight recording period was two days until aconstant weight determined in an analyticalbalance (Scientech). The difference betweentwo consecutives measurements was less than0.001 g. The dry solid of samples wasdetermined by drying at 105 o C in an ovenaccording to standard method (AOAC, 2000).Each experiment was carried out in triplicate.The equilibrium moisture in dry basis wasdetermined according to Eq. 1.Xemeq− ms=ms[Eq. 1]where:X e – equilibrium moisture content [gH 2 O/g drymass]m eq – weight of sample at equilibrium [g]m s – dry mass of sample [g]Data analysisLeast square regression analysis wasused to adjust the experimental data by BET,BET linear, GAB, Halsey, Langmuir, Oswin,Peleg Henderson and Chung mathematicalmodels (Table 1). The “STATISTICA”program was used to estimate the equilibriumparameters from experimental data of sorptionisotherms at constant temperature. The criteriato select the best fitted model was thecorrelation coefficient (r 2 ) and percent averagerelative deviation (ARD) as recommended byChen & Morey (1989). To practical purposes,ARD bellows 10% indicate the goodness ofadjust. The water content of the monolayer wasdetermined from the BET equation.Table 1. Mathematical models applied to the sorption isotherms of formulated inulin powderModel Mathematical expressionBET nn+1( Xm⋅ CBET⋅ aw) ⋅ ( 1−( n + 1) ⋅ aw+ n ⋅ aw)Xe=n+11−a ⋅ 1+( C −1)⋅ a − C ⋅ aBET linearX =( ) ( )wBET( 1−a )[ 1−( C −1)a ]wXmCBETGABXm ⋅CGAB⋅ KGAB⋅ awXe=( 1−KGAB⋅ aw) ⋅ (1 − K ⋅ aw+ CGAB⋅ KGAB⋅ aw)Halsey⎛ ⎞⎜ − Aa⎟w= exp⎜ BX ⎟e⎝ ⎠Langmuir XeCLAN+ aw=Xm 1 + CLAN+ awOswinD'⎛ aw⎞Xe= C ⋅⎜1 a⎟⎝ −w ⎠Peleg n1n2Xe= k1⋅ aw+ k2⋅ aw(n 1 1)ChungAln aw= − exp[ −BXe]R ⋅ TaBETwwwBETwRevista Brasileira de Produtos Agroindustriais, Campina Grande, v.9, n.1, p.37-44, 2007

40 Adsorption isotherms of chicory inulin powder: temperature effect Nogueira et al.RESULTS AND DISCUSSIONThe equilibrium moisture contents forpowder inulin are found in the range 0.0197 to0.8444 g/g in dry basis (Table 2). It can beobserved a significant effect of temperature inthe moisture equilibrium for aw between 0.5757and 0.8434. In general it can be observed thatX eq decrease as temperature increase (Table 3).The effect of temperature is more significant forwater activity superior to 0.60. The sorptionisotherms of formulated inulin powder can berepresented by Type III curve (non-sigmoidal),typical of many sorption isotherms of foodmaterial (Fig. 1). According Samaniego-Esguerra, Boag & Robertson (1990), food withhigh sugar content adsorbed low quantity ofwater at low relative humidity and very highquantity of water at high relative humidity. Italso can be observed in Fig 1 the interception ofexperimental curves as temperature varies. Thiscomportment is too typical of materials withhigh sugar content (Saravacos, Tsiourvas &Tsami (1986); Maroulis, Tsami & Marinos-Kouris, 1988). The same comportment wasobserved by Iglesias & Chirife (1978) fordifferent fruits with high sugar content. It canbe observed that the adsorption increases asrelative humidity increases promoting the sugardissolution. At higher temperatures theequilibrium moisture is lower, at a given wateractivity, indicating less hygroscopic capacity.The estimated parameters, the regressioncoefficients and average relative deviation forthe BET, BET linear, GAB, Halsey, Langmuir,Oswin, Peleg, Henderson and Chung modelsare presented in Table 3. According to criteriaadopted, it can be concluded that BET, Halsey,Oswin and Peleg models presented the bestfitted to experimental data with regressioncoefficients superior to 0.9816 and averagerelative deviation in the range of 2.54% a9.79%. The experimental and adjusted curves toBET models are presented in the Figure 1.Table 2 – Equilibrium moisture (Xe for.) data of chicory powder inulin obtained by sorption atdifferent relative humidity at 25ºC, 35ºC and 45ºC.25 o C 35 o C 45 o Ca w X e a w X e a w X e0.1130 0.0434 0.1125 0.0441 0.1116 0.04320.2251 0.0626 0.2459 0.0677 0.2146 0.05740.3278 0.0699 0.3205 0.0697 0.311 0.06530.4316 0.0910 0.4316 nd 0.4316 0.08990.5757 0.1261 0.5455 0.0902 0.5195 0.09770.6886 0.1581 0.6696 0.1551 0.6526 0.11860.7529 0.1830 0.7487 0.1800 0.7452 0.13580.8434 0.2508 0.8295 0.1854 0.8174 0.1616nd- no determined.Revista Brasileira de Produtos Agroindustriais, Campina Grande, v.9, n.1, p.37-44, 2007

Adsorption isotherms of chicory inulin powder: temperature effect Nogueira et al. 41e0.3000Equilibrium moisture (g/g)0.25000.20000.15000.10000.05000.00000 0.2 0.4 0.6 0.8 1.0Water activityE25P25E35P35E45P45Figure 1 – Sorption Isotherms fitted by BET model at 25ºC, 35ºC and 45ºC.E – experimental values P – predicted valuesMonolayer moisture content values (X m ),that is a important parameter in food storageand deterioration, are found 0.0522, 0.0528 and0.0505 g/g in dry basis at 25ºC, 35ºC and 45º,respectively (table 3). X m values indicates thatformulated inulin powder presented lowhygroscopic characteristics, similar to valueobtained to starchy products, between 0.0323and 0.1297, according to experimental datareported by Lomauro, Bakshi & Labuza (1985).Different to equilibrium moisture content, theeffect of temperature on the X m value can beconsidered neglected. Similar to data reportedby Schar & Rueg (1985), it can be consideredthat water molecules, surrounding the sample,presented the same kinetic energy astemperature change in the range evaluated. TheX m values obtained by the GAB model werehigher than those by the BET model. Thesimilar results were reported by the otherinvestigators (Sandoval & Bareiro, 2005).The X m values of foods change withcomposition and processing. Cadden (1988),reported that the processing of wheat flourcause a slight reduction in the X m values(0.0636 in the natural fiber to 0.0595 aftermilling). It was reported by Hebrard et al(2003) that proteins of wheat flour have aboutfive times higher hydration capacity than nativestarch.The BET constant (C BET ) was foundbetween 23.78 and 27.5. In the literature,reported value of C BET for wheat is 21.7(Timmerman et al 2001). This constant isrelated logarithmically to the differencebetween the chemical potential of the sorbatemolecules in the pure liquid state and in the firstsorption layer. So, these results are consideredas indicative of intermolecular attractive forcesbetween adsorption sites and water vapor.Revista Brasileira de Produtos Agroindustriais, Campina Grande, v.9, n.1, p.37-44, 2007

42 Adsorption isotherms of chicory inulin powder: temperature effect Nogueira et al.Table 3. Estimated parameters for all models selected of sorption isotherms for chicory inulin powderat at 25ºC, 35ºC and 45ºC.Model Parameters 25ºC 35ºC 45ºCX m 0,0522 0,0528 0,0505BETBET - linearGABHalseyLangmuirOswinPelegHendersonChungC BET 27,5005 23,7812 27,2331n 12,9135 8,7170 6,7035R 2 0,9977 0,9793 0,9950ARD (%) 0,0364 0,0779 0,0303X m 0,0436 0,0391 0,0354C BET 6,51E05 2,67E06 2,64E06R 2 0,9712 0,8901 0,9967ARD (%) 0,1139 0,1526 0,1781X m 0,0630 0,0727 0,0653C GAB 13,4816 10,3989 15,7780K GAB 0,4444 0,7820 0,0284R 2 0,9765 0,9719 0,9970ARD (%) 0,1494 0,1687 0,0284A 0,0203 0,0105 0,0053B 1,5523 1,8090 2,0261R 2 0,9979 0,9616 0,9906ARD (%) 0,0401 0,1144 0,0643X m 2,9072 0,6282 0,5153C LAN 0,0916 0,4666 0,4974R 2 0,9532 0,9468 0,1725ARD (%) 0,1551 0,1583 0,1037C 0,1070 0,1028 0,9340D 0,4987 0,4181 0,3650R 2 0,9985 0,9689 0,9973ERM (%) 0,0423 0,0940 0,0254K 1 0,1365 0,0630 0,1353K 2 0,2874 0,2044 0,1296n 1 0,5415 0,1492 0,5508n 2 4,9160 2,2365 5,8805R 2 0,9985 0,9781 0,9972ARD (%) 0,0291 0,0881 0,0308K HEND 0,0646 * *n’ 1,4897 * *R 2 0,9650 * *ARD (%) 0,1288 * *a 9,66E03 * *b 14,2362 * *R 2 0,7423 * *ARD (%) 0,2791 * *CONCLUSIONSThe moisture sorption isotherms ofchicory inulin powder at 25 to 45 o C werecharacteristic of the type III isotherm (nonsigmoidalcurve). Formulated chicory inulinpowder presented low hygroscopiccharacteristics in the temperature range of 25 to45 o C. BET, Halsey, Oswin and Peleg modelspresented the best adjust of experimental dataRevista Brasileira de Produtos Agroindustriais, Campina Grande, v.9, n.1, p.37-44, 2007

Adsorption isotherms of chicory inulin powder: temperature effect Nogueira et al. 43with regression coefficients superior to 0,98 andaverage relative deviation in the range of 2.54%to 9.79%. The moisture content of theformulated chicory inulin powdercorresponding to the water activity consideredas safe for microbiological activity (65%) wasinferior to 10g/100 g of dry solids in thetemperature range analyzed. If storage in thehigh relative humidity and temperature, typicalof tropical ambient air, the moisture content ofthe formulated chicory inulin powder wassuperior to 15 g/100g of dry solids.BIBLIOGRAPHY REFERENCEAssociation of Official Analytical Chemists.Official methods of analysis of A.O.A.C.international. 17 ed. Arlington, Virgínia,2000.Bell. L.N.; Labuza, T.P. Moistur sorptionisotherms: practical aspects of isothermsmeasurement and use. Apud In: Moreira,R.; Chenlo, F. Vasquez, M.J.; Cameán, P.Sorption isotherms of turnip top leave andstems in the temperature range from 298 to328 K. Journal of Food Engineering ,v.71, p.193-199, 2005.Bizot, H, Riou, N.; Molton, J.L. Guide pratiquepour la determination des isotherms et del’activité de l’eau. Sciences dês aliments:numéro hors série, 1987.Cadden, A. Moisture Sorption Characteristicsof Several Food Fibers. Journal of FoodScience, Chicago, v.53, n.4, p.1150-1155,1988.Chen, C.C.; Morey R.V. Comparison of fourEMC/ERH equations. Transaction of theASAE, v.32, p. 983-989, 1989.Chirife, J.; Iglesias, H. A. Equations for fittingwater sorption isotherms of foods: part 1 – areview. Journal of Food Technology,London, v. 13, p.159-174, 1978.Erbas, M.; Ertugay, M.F.; Certel, M. Moistureadsortion behaviour of semolina and farina.Journal of Food engineering, v.69, p. 191-198, 2005.Figueira, G.M.; Park, K.J.; Brod, F.P.R.;Honório, S.L. Evaluation of desorptionisotherms, drying rates and inulinconcentration of chicory roots (Chichoriumintybus, L) with and without enzymaticinactivation. Journal of Food Engineering,v.63, p. 273-280, 2004.Greenspan, L. Humidity fixed point of binarysaturated aqueous solutions. Journal ofReserch of National Bureau of Standards,v. 81, p. 89-96, 1977.Gustafson, R. J.; Hall, G. .Equilibrium moisturecontent of shelled corn from 50 to 155 o F.Transaction of the ASAE, v.17, n.1, p.120-124, 1974.Hebrard, A. Oulahna, D. Galet, L.; Cuq, B.Abecassis, J.; Fages, J. Hydration propertiesof durum wheat semolina: Influence ofparticle size and temperature. Powdertechnology, v. 130, p. 211-218, 2003.Kiranoudis, C. T.; Maroulis, Z. B.; Tssami, E.;Marinos-Kouris, D. Equilibrium moisturecontent of some vegetables. Journal ofFood Engineering, oxford, v.20, n.1, p. 55-74, 1993.Labuza, T. P. Sorption phenomena in foods.Food Technology, Chicago, v.22, n.3,p.263-272, 1968.Labuza, T.P.; Kaanane, A.; Chen, J.Y. effect oftemperature on the moisture sorptionisotherms and water activity shift of twodehydrated foods. Journal of Food Science,v. 50, n.2, p. 385, 1985.Lomauro C. J.; Bakshi, A.S.; Labuza, T.P.Moisture transfer properties of dry and semimoistfoods. Journal of Food Science,Chicago, v.50, n. 2 p.397-400, 1985.Marchetti, G. Inulina e fruttani. IndustrieAlimentari, Pinerolo, v.32, n.319, p.945-949, 1993.Maroulis, Z. B.; Tsami, E.; Marinos-Kouris, D.Aplicattion of the GAB Model to moisturesorption isotherms for dried foods. Journalof Food Engineering, Oxford, v.7, n.1,p.93, 1988.Nogueira, R. I. Processo de obtenção deinulina de chicória (Cichorium intybus)em pó, Campinas, 2002. 151p. Tese(Doutorado em Engenharia Agrícola)-Faculdade de Engenharia Agrícola,Universidade Estadual de Campinas,Campinas.Nogueira, R. I.; Park, K. J.; Deyrmendjian, E.Flow properties of chicory (Chicoriumintybus L) extract. In: INTERNATIONALCONGRESS ON ENGINEERING ANDFOOD, 8, 2000, Puebla. Proceedings….Lancaster: Technomic Publishing Co. Inc.,2001. p.425-429.Samaniego-Esguerra, C. M.; Boag, I.F.;Robertson, G.L. Comparison of RegressionMethods for fitting the GAB model to themoisture isotherms of some died fruits andvegetables. Journal of Food Engineering,Oxford, v.13, p. 115-133. 1990.Revista Brasileira de Produtos Agroindustriais, Campina Grande, v.9, n.1, p.37-44, 2007

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