Vacuum-cooling-technology-for-the-food-processing-

Vacuumcoolingtechnologyforthefoodprocessingindustry:areviewKarlMcDonald,Da-WenSun*FRCFTGroup,DepartmentofAgriculturalandFoodEngineering,UniversityCollegeDublin,NationalUniversityofIreland,EarlsfortTerrace,Dublin2,IrelandReceived28October1999;accepted31January2000AbstractVacuumcoolingisarapidevaporativecoolingtechnique,whichcanbeappliedtospeci®cfoodsandinparticularvegetables.Increasedcompetitivenesstogetherwithgreaterconcernsaboutproductsafetyandqualityhasencouragedsomefoodmanufac-turerstousevacuumcoolingtechnology.Theadvantagesofvacuumcoolingincludeshorterprocessingtimes,consequentenergysavings,improvedproductshelflife,qualityandsafety.However,thecoolingtechniquehasalimitedrangeofapplication.Tra-ditionally,productssuchaslettuceandmushroomshavebeencooledundervacuum.Recentresearchhashighlightedthepossibleapplicationsofvacuumcoolingforcoolingmeatandbakeryproducts,fruitsandvegetables.Thispapercomprehensivelyreviewsthecurrentstateofthetechnology.Itisconcludedthatwhilevacuumcoolingremainsahighlyspecialisedcoolingtechnique,withcontinuingresearchitsapplicationmaymakeitsuseinthefoodandvegetableprocessingindustriesmorecompetitiveandwide-spread.Ó2000ElsevierScienceLtd.Allrightsreserved.Keywords:Vacuumcooling;Rapidcooling;Chilling;Refrigeration;Foods;Vegetables;Meats;ReadymealsContents1.Introduction.............................................................................552.Applicationsofvacuumcooling...............................................................572.1.Fruitandvegetables....................................................................572.2.Meatandmeatproducts.................................................................582.3.Fishand®shproducts...................................................................592.4.Sauces,soupsandparticulatefoods.........................................................592.5.Bakeryproducts.......................................................................592.6.Readymeals..........................................................................603.Advantagesanddisadvantagesofvacuumcooling..................................................604.Factorsa€ectingvacuumcoolingrate...........................................................625.Conclusions.............................................................................63References..................................................................................631.IntroductionVacuumcoolingisabatchprocesswherebymoistproductscontainingfreewaterarecooledbyevapora-tionofmoistureundervacuum(Mellor,1980).Prod-uctstobecooledareloadedintoavacuumchamberandthesystemputintooperation(Anon,1994)asshowninFig.1.Thevacuumcoolingprocessisasfollows:Astheboilingpointchangesasafunctionofsaturationpres-sureasshowninFig.2,foraboilingtemperatureof0°C,thesaturationpressurewillbe6.09mbar.Asthepressureinthevacuumchamberisreduced,theenergyJournalofFoodEngineering45(2000)55±65*Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](D.-W.Sun).0260-8774/00/$-seefrontmatterÓ2000ElsevierScienceLtd.Allrightsreserved.PII:S0260-8774(00)00041-8requiredtoevaporatethewaterisfurnishedbytheproductitselfintheformoflatentheatofevaporation.Adrivingdi€erentialduetothevapourpressuredi€er-encebetweenwaterintheproductandthesurroundingcausesvapourtoescapeintothesurroundingatmo-spheresothatthesensibleheatoftheproductisreduced(Everington,1993).Priortothesaturationtemperaturehavingbeenreached,vacuumpumpsusedtoevacuateairfromthevacuumchamberwerenotachievingcoolingoftheproductbutweresolelyevacuatingairfromthechamber(Anon,1986).Thus,itisnecessarytoreducethepres-sureinthevacuumchambertothe¯ashpointasquicklyaspossibleforbothqualityandeconomicalreasons.Thepressureinthevacuumchamberisallowedtode-creaseuntiltheproducthasreacheditsdesiredtem-peratureorthetemperaturedropceasesatapointwherethereisnofreewateravailableforevaporation(Mellor,1980;Sun,1999a).Thepumpsusedtoevacuatevacuumchambersareoftwomaindesigns,withoneemployingmechanicalro-tarypumpsandtheotherusingsteamjetsandbaro-metriccondensers(Decker,1993;DiRisio,1994).Thewatervapourgivenofbyaproductinavacuumchamberduringevaporationmustberemovedtopre-ventsaturationoftheair,whichwouldpreventfurtherevaporationandecientcooling.Inmechanicalvacuumcooling,watervapourispassedoverrefrigeratedcoilswhereitcondensesonthecoldsurfaceandpassestodrain.Ifthewatervapourwerenotremoved,verylargepumpswouldberequiredtoremovethevapour,aseachkilogramofwaterexpandstoapproximately2000m3ofvapouratthelowpressuresusedinvacuumcooling(Barger,1961).Insteamjetvacuumcoolers,someofthewatervapourislique®edbyusingbarometriccondens-ersandexhaustingtotheatmosphere(Decker,1993;DiRisio,1994).Vacuumcoolingisahighlyproductspeci®cprocess.Ithasbeentraditionallyusedasaprecoolingtreatmentforproductssuchasleafyvegetables(Harvey,1963;Cheyney,Kasmire&Morris,1979;Shewfelt,1986;Anon,1981a;Turk&Celik,1993;Tambunan,Mori-shima&Kawagoe,1994;Varszegi,1994;Shewfelt&Phillips,1996;Sullivan,Davenport&Julian,