Brandão, Teresa R. S.

Ramos, Inês Nunes

Silva, Cristina L. M.

English

Repositório Institucional da Universidade Católica Portuguesa

CIBIA IV – 5 to 8 October, Valparaíso - ChileMicrostructural changes during fruit drying -correlation between fundamental studies, with air drying and solar drying applications.Escola Superior de BiotecnologiaUniversidade Católica PortuguesaInês Nunes RamosTeresa S. BrandãoCristina L.M. SilvaCIBIA IV – 5 to 8 October, Valparaíso - ChileIntroductionSolar DryingSolar dryer.CIBIA IV – 5 to 8 October, Valparaíso - ChileDiversified productsBreakfast cerealsBakeryConfectioneryDairy productsIntroductionCIBIA IV – 5 to 8 October, Valparaíso - ChileIntegrated modelMass TransferIntroductionCIBIA IV – 5 to 8 October, Valparaíso - ChileIntegrated modelMass TransferIntroductionVariable DiffusivitySorption IsothermsXeCIBIA IV – 5 to 8 October, Valparaíso - ChileIntegrated modelMass TransferIntroductionVariable DiffusivitySorption IsothermsXeMeteorological dataHeat TransferCIBIA IV – 5 to 8 October, Valparaíso - ChileIntegrated modelMass TransferIntroductionVariable DiffusivitymicrostructureMacroscopic shrinkageSorption IsothermsXeMeteorological dataHeat TransferCIBIA IV – 5 to 8 October, Valparaíso - ChilePredict and simulate the drying behaviour:IntroductionCIBIA IV – 5 to 8 October, Valparaíso - ChilePredict and simulate the drying behaviour: Mechanistic models are more complex, but allow accurate predictions (Mulet, 1994). Empirical models are much simple, but appropriate to practical uses (e.g. dryers design). IntroductionCIBIA IV – 5 to 8 October, Valparaíso - ChilePredict and simulate the drying behaviour: Mechanistic models are more complex, but allow accurate predictions (Mulet, 1994). Empirical models are much simple, but appropriate to practical uses (e.g. dryers design). Balance of the advantages and disadvantages, depending on the final purpose.IntroductionCIBIA IV – 5 to 8 October, Valparaíso - ChilePhysical properties MicrostructureDrying mechanisms Quality changese.g. TextureIntroductionCIBIA IV – 5 to 8 October, Valparaíso - ChileMass TransferShort constant-rate periodLong falling-rate periodFick’s 2nd lawCIBIA IV – 5 to 8 October, Valparaíso - ChileFick’s 2nd lawWater concentration at the surface constant Sphere:)r tDπnexp(n1π6XeXoXeX2eff21222 Mass TransferCIBIA IV – 5 to 8 October, Valparaíso - Chile Consider uniform temperature inside the foodnon-isotropic characteristics of the mediumporosity Deff(effective diffusivity)variableMass TransferCIBIA IV – 5 to 8 October, Valparaíso - ChileEffective diffusivityDeff varies:- considerably with water content(Karathanos, Villalobos and Saravacos, 1990)- with temperatureArrhenius law: )T1T1(REaexpDDrefrefCIBIA IV – 5 to 8 October, Valparaíso - ChileEffective diffusivity Dependence on water content is usually neglected Proposed models:exponential, power-law, gamma functionExponetial are the most used modelsCIBIA IV – 5 to 8 October, Valparaíso - ChileDeff = exp (a + bX + cX2)(Vásquez, Chenlo, Moreira & Costoyas, 2000)Deff = exp (d + e/T + fX)(Mulet et al., 1989)Deff = Do exp (-DT/T) exp(-Dx/X)(Maroulis, Kiranoudis & Marinos-Kouris, 1995)Effective diffusivityCIBIA IV – 5 to 8 October, Valparaíso - ChileExperiments performed in a convective dryer.Pilot plant convective tray drier (Armfield UOP8).Effective diffusivityCIBIA IV – 5 to 8 October, Valparaíso - ChileEffective diffusivity00,40,81,21,60 1 2 3 4 5 6Water content (g H2O/g dm)Effective diffusivity (Deffx1010 m2/s)Data similar to Raghavan et al., 1995CIBIA IV – 5 to 8 October, Valparaíso - ChileEquilibrium valueSorption isothermsThe G.A.B. model is recently widely applied:)ak  Cak (1 )ak (1ak  CXXwwwwme RTexp CC 0 cH RTexp kk 0 kHTemperature dependentCIBIA IV – 5 to 8 October, Valparaíso - ChileHeat TransferSolar radiation originates a ‘greenhouse’ effectCIBIA IV – 5 to 8 October, Valparaíso - Chile01020304050607080900 0,5 1 1,5 2 2,5 3 3,5time(days)Temperature(ºC)Relative Humidity(%)Heat TransferAir conditions inside a solar drier :CIBIA IV – 5 to 8 October, Valparaíso - ChileHeat TransferGlobal energy balance :)Ta(T σ εA dtm) d(λ - Ta)-hA(TQ αdtT) Cp (m d 44s CIBIA IV – 5 to 8 October, Valparaíso - ChileHeat TransferGlobal energy balance :)Ta(T σ εA dtm) d(λ - Ta)-hA(TQ αdtT) Cp (m d 44s energy gainedCIBIA IV – 5 to 8 October, Valparaíso - ChileHeat TransferGlobal energy balance :)Ta(T σ εA dtm) d(λ - Ta)-hA(TQ αdtT) Cp (m d 44s energy gainedabsorved radiant energyCIBIA IV – 5 to 8 October, Valparaíso - ChileHeat TransferGlobal energy balance :)Ta(T σ εA dtm) d(λ - Ta)-hA(TQ αdtT) Cp (m d 44s energy gainedabsorved radiant energyconvective heat lossCIBIA IV – 5 to 8 October, Valparaíso - ChileHeat TransferGlobal energy balance :)Ta(T σ εA dtm) d(λ - Ta)-hA(TQ αdtT) Cp (m d 44s energy gainedabsorved radiant energyconvective heat loss evaporation heat lossCIBIA IV – 5 to 8 October, Valparaíso - ChileHeat TransferGlobal energy balance :)Ta(T σ εA dtm) d(λ - Ta)-hA(TQ αdtT) Cp (m d 44s energy gainedabsorved radiant energyconvective heat loss evaporation heat loss radiation heat lossCIBIA IV – 5 to 8 October, Valparaíso - ChileHeat Transfer)Ta(T σ εA dtm) d(λ - Ta)-hA(TQ αdtT) Cp (m d 44s obtained from meteorological dataGlobal energy balance :CIBIA IV – 5 to 8 October, Valparaíso - ChileHeat Transfer Lack of data on radiation properties of foodsCIBIA IV – 5 to 8 October, Valparaíso - ChileHeat Transfer Lack of data on radiation properties of foods Cp is strongly dependent on water content- compilation on Sweat (1986)- most of the research on freezing and refrigeration !!!CIBIA IV – 5 to 8 October, Valparaíso - Chile0,00,20,40,60,81,01,20 2 4 6 8 10 12 14 16 18 20time (days)X/X0Simulation under dynamic conditions on a pilot scaleand Data of solar dryerCIBIA IV – 5 to 8 October, Valparaíso - ChileShrinkageLoss of water shrinkagereduction in cellular dimensionsCommonly defined:VoVMacroscopic ShrinkageCIBIA IV – 5 to 8 October, Valparaíso - ChileMacroscopic ShrinkageMeasurement : direct with a calliper picnometry with organic solutions photography and image analysis:Grape shrinkage under dynamic conditions.CIBIA IV – 5 to 8 October, Valparaíso - ChileMacroscopic ShrinkageDependence of shrinkage on water contentcommon linear relationshipbXaVoV00,20,40,60,811,20 0,2 0,4 0,6 0,8 1X/XoShrinkageV/Vor/romodelCIBIA IV – 5 to 8 October, Valparaíso - ChileDecrease in water contentLoss of turgor pressureMainly from vacuolar compartmentLess from cytoplasm and cellular wallsRheological propertiesTextureMicroscopic ShrinkageCIBIA IV – 5 to 8 October, Valparaíso - ChileStero-microscope with video camera and air-drying tube.Microscopic ShrinkageCIBIA IV – 5 to 8 October, Valparaíso - ChileImages of grape cells shrinkage at 40°C as a function of time.Cellular geometric features quantified by image analysisMicroscopic Shrinkage0 min90 min 180 min 210 min20 min10 minCIBIA IV – 5 to 8 October, Valparaíso - Chile Parameters:Dimensional: area, perimeter,  major and minor axis length Feret diameterShape: πarea FD 2lengthaxisminorlengthaxismajorelongation 24perimeterarearoundness lengthaxismajorFDscompactnes Microscopic ShrinkageCIBIA IV – 5 to 8 October, Valparaíso - Chile0,60,70,80,91,01,10 50 100 150 200 250 300time (min)area / initial area   20°C30°C40°C50°C60°C30°Ca)-0 ,0 4-0,0 200,020,040,060,080 ,6 0,7 0,8 0 ,9 1 1 ,1pre d ic t e d  v a lue sb)Microscopic Shrinkage  t)T1T1( REaexpK exprrrefref0CIBIA IV – 5 to 8 October, Valparaíso - Chile00,20,40,60,811,20 100 200 300 400time (hr)radius/initial radiusmacroscopic shrinkagecellular shrinkageRelate Macroscopic and Microscopic ShrinkageCIBIA IV – 5 to 8 October, Valparaíso - ChileFinal Remarks Develop the mathematical basis and considerations for integrating heat and mass transfer phenomena.- include variable diffusivity- sorption isotherms- shrinkageCIBIA IV – 5 to 8 October, Valparaíso - ChileFinal Remarks Develop the mathematical basis and considerations for integrating heat and mass transfer phenomena.- include variable diffusivity- sorption isotherms- shrinkage Lack of data on thermal properties of foods.CIBIA IV – 5 to 8 October, Valparaíso - ChileFinal Remarks Developed the mathematical basis and considerations for integrating heat and mass transfer phenomena.- include variable diffusivity- sorption isotherms- shrinkage Lack of data on thermal properties of foods. Microstructure helps understanding drying mechanisms.CIBIA IV – 5 to 8 October, Valparaíso - ChileFinal Remarks Developed the mathematical basis and considerations for integrating heat and mass transfer phenomena.- include variable diffusivity- sorption isotherms- shrinkage Lack of data on thermal properties of foods. Microstructure helps understanding drying mechanisms. Correlating microstructure, texture measurements and sensory analysis is an attractive area.CIBIA IV – 5 to 8 October, Valparaíso - ChilePhD grant from Fundação para a   Ciência e a TecnologiaPraxis XXI BD/18543/98CYTED XI.13 “Relaciones Estructura -Propriedad en la Deshidratacion y Almacenaje de Alimentos Dehidratados”AcknowledgmentsCIBIA IV – 5 to 8 October, Valparaíso - ChileThank you

Microstructural changes during fruit drying: correlation between fundamental studies, with air drying and solar drying applications

https://repositorio.ucp.pt/bitstream/10400.14/6044/1/com-int_2003_ESB_239_Brand%c3%a3o_Teresa_62%20.pdf

Microstructural changes during fruit drying: correlation between fundamental studies, with air drying and solar drying applications

Abstract

Similar works

Full text

Available Versions

Repositório Institucional da Universidade Católica Portuguesa