Lesson 14 Quality Factors in FoodWord下载.docx
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Lesson 14 Quality Factors in FoodWord下载.docx
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Acceptability,however,canbehighlysubjective.Qualityandpriceneednotgotogether,butfoodmanufacturersknowthattheygenerallycangetahigherpricefororcansellalagerquantityofproductswithsuperiorquality.Often“value”isthoughtofasacompositeofcostandquality.Moreexpensivefoodscanbeagoodvalueiftheirqualityisveryhigh.Thenutrientvalueofthedifferentgradesofcannedfruitsandvegetablesissimilarforallpracticalpurposes,yetthepricecanvaryasmuchasthreefolddependingonotherattributesofquality.Thisiswhyprocessorswillgotoextremestocontrolquality.
Whenweselectfoodsandwhenweeat,weuseallofourphysicalsenses,includingsight,touch,smell,taste,andevenhearing.Thesnapofapotatochip,thecrackleofabreakfastcereal,andcrunchofceleryaretexturalcharacteristics,butwealsohearthem.Foodqualitydetectablebyoursensescanbedividedintothreemaincategories:
appearancefactors,texturalfactors,andflavorfactors.
Appearancefactorsincludesuchthingsassize,shape,wholeness,differentformsofdamage,gloss,transparency,color,andconsistency.Forexample,applejuiceissoldbothascloudyandclearjuice.Eachhasadifferentappearanceandisoftenthoughtofasasomewhatdifferentproduct.
Texturalfactorsincludehandfeelandmouthfeeloffirmness,softness,juiciness,chewiness,grittiness.Thetextureofafoodisoftenamajordeterminantofhowlittleorwellwelikeafood.Forexample,manypeopledonotlikecookedliverbecauseofitstexture.Textureoffoodscanbemeasuredwithsophisticatedmechanicaltestingmachines.
Flavorfactorsincludebothsensationsperceivedbythetonguewhichincludesweet,salty,sour,andbitter,andaromasperceivedbythenose.Theformerareoftenreferredtoas“flavors”,andthelatter“aromas”,althoughthesetermsareoftenusedinterchangeably.Flavorandaromaareoftensubjective,difficulttomeasureaccurately,anddifficulttogetagroupofpeopletoagree.Apartoffoodsciencecalledsensoryscienceisdedicatedtofindingwaystousehumanstoaccuratelydescribetheflavorsandothersensorypropertiesoffoods.Therearehundredsofdescriptivetermsthathavebeeninventedtodescribeflavor,dependingonthetypeoffood.Expertteatastershavealanguagealloftheirown,whichhasbeenpasseddowntomembersoftheirguildfromgenerationtogeneration.Thisistrueofwinetastersaswell.
Sincewegenerallyexperiencethepropertiesoffoodintheorderof
(1)appearance
(2)texture,and(3)flavor,itislogicaltodiscussqualityfactorsinthisordernow.
1.AppearanceFactors
Inadditiontosize,shape,andwholeness,pattern(e.g.,thewayolivesarelaidoutinajarorsardinesinacan)canbeanimportantappearancefactor.Wholenessreferstodegreeofwholeandbrokenpieces:
thepriceofcannedpineapplegoesdownfromthewholerings,tochunks,tobits.Appearancealsoencompassesthepositiveandnegativeaspectsofproperlymoldedblue-veinedcheeses,andthedefectofmoldybread,aswellasthequalityattributeofgroundvanillabeanspecksinvanillaicecream,andthedefectofspecksandsedimentfromextraneousmatter.Althoughsomeicecreammanufacturershaveaddedgroundvanillabeanasamarkofhighestquality,othershaveconcludedthatasoftenasnotaless-sophisticatedconsumermisinterpretsthesespecksandrejectstheproduct.
SizeandShapeSizeandshapeareeasilymeasuredandareimportantfactorsinfederalandstategradestandards.Fruitsandvegetablescanbegradedforsizebytheopeningstheywillpassthrough.Sizealsocanbeapproximatedbyweightafterroughgrading,forexample,determiningtheweightofadozeneggs.
Shapemayhavemorethanvisualimportance,andthegradesofcertaintypesofpicklesincludethedegreeofcurvature.Suchcuriositiescanbecomequiteimportant,especiallyinthedesignofmachinestoreplacehandoperations.Whenanengineerattemptstodesignamachineforautomaticallyfillingpicklesintojarsathighspeeds,itmustberecognizedthatallpicklesarenotshapedthesame,andamachinethatwilldispenseroundobjectslikeolivesorcherriescanbetotallyinadequate.Mechanizedkitchen,restaurant,andvendingsystemsforrapidmassfeedinghavebecomecommonplace.Someofthemostdifficultengineeringproblemsencounteredinsuchfacilitieswereindesigningequipmentthatwoulddispenseodd-shapedfoodpiecesintomovingdishes.
ColorandGlossFoodcolornotonlyhelpstodeterminequality,itcantellusmanythings.Coloriscommonlyanindexofripenessorspoilage.Potatoesdarkenincolorastheyarefriedandwejudgetheendpointoffryingbycolor.Thebleachingofdriedtomatopowderonstoragecanbeindicativeoftoohighanoxygenlevelintheheadspaceofthepackage,whereasthedarkeningofdriedtomatocanreflecttoohighafinalmoisturelevelinthepowder.Thecolorofafoodfoamorbattervarieswithitsdensityandcanindicateachangeinmixingefficiency.Thesurfacecolorofchocolateisacluetoitsstoragehistory.Theseandmanyothertypesofcolorchangescanbeaccuratelymeasuredinthelaboratoryandintheplant—allinfluenceorreflectfoodquality.
Ifthefoodisatransparentliquidsuchaswine,beer,orgrapejuice,orifacoloredextractcanbeobtainedfromthefood,thenvarioustypesofcolorimetersorspectrophotometerscanbeusedforcolormeasurement.Withtheseinstruments,atubeoftheliquidisplacedinaslotandlightofselectedwavelengthispassedthroughthetube.Thislightwillbedifferentiallyabsorbeddependingonthecoloroftheliquidandtheintensityofthiscolor.Twoliquidsofexactlythesamecolorandintensitywilltransmitequalfractionsofthelightdirectedthroughthem.Ifoneoftheliquidsisajuiceandtheotheristhesamejuicesomewhatdilutedwithwater,thelattersamplewilltransmitagreaterfractionoftheincominglightandthiswillcauseaproportionatelygreaterresponseontheinstrument.Suchaninstrumentcanalsomeasuretheclarityorcloudinessofaliquiddependingontheamountoflighttheliquidletspass.Thereareseveralothermethodsformeasuringthecolorofliquids.
Ifthefoodisliquidorasolid,wecanmeasureitscolorbycomparingthereflectedcolortodefinedcoloredtilesorchips.Thequalitycontrolinspectorchangestilesuntiltheclosestcolormatchismadeandthendefinesthecolorofthefoodasbeingidenticaltothematchingtileorfallingbetweenthetwonearesttiles.Workingwithtomatoproducts,onewouldneedtohaveonlyafewgreenandreddiskstocovertheusualrangeoftomatocolor.Thegradestandardsfortomatoeshavebeenbasedonsuchamethod.
Colormeasurementcanbefurtherquantified.Lightreflectedfromacoloredobjectcanbedividedintothreecomponents,whichhavebeentermedvalue,hue,andchroma.Valuereferstothelightnessordarknessofthecolorortheamountofwhiteversusblack;
huetothepredominantwavelengthreflected,whichdetermineswhattheperceivedcoloris(red,green,yellow,blueetc),andchromareferstotheintensitystrengthofthecolor.Thecolorofanobjectcanbepreciselydefinedintermsofnumericalvaluesofthesethreecomponents.Anotherthree-dimensionalcoordinatescalefordescribingcolorutilizestheattributesoflightness-darkness,yellowness-blueness,andredness-greenness.Thesedimensionsofcolor,usedintri-stimuluscolorimetry,canbequantifiedbyinstrumentssuchastheHunterlabColorandColorDifferenceMeter.Foodsampleshavingthesamethreenumbershavethesamecolor.Thesenumbers,aswellasnumbersrepresentingvalue,hue,andchroma,varywithcolorinasystematicfashionthatcanbegraphedtoproduceachromaticitydiagram.Thecolorchemistandqualitycontrollercanrelatethesenumberstocolor,andthroughchangesinthenumberscanfollowgrossorminutechangesintheproductsthatmayoccurduringripening,processing,orstorage.Insimilarfashionaqualitycontrollercandefinethecolorofaproductandrelatethisinformationtodistantplantstobematchedatanyfuturedate.Thisisparticularlyusefulwherethefoodcolorissounstableastomaketheforwardingofastandardsampleunfeasible.
Aswithcolor,therearelight-measuringinstrumentsthatquantitativelydefinetheshine,orgloss,ofafoodsurface.Glossisimportanttotheattractivenessofgelatindesserts,butteredvegetables,andthelike.
ConsistencyAlthoughconsistencymaybeconsideredatexturalqualityattribute,inmanyinstanceswecanseeconsistencyandsoitalsoisanotherfactorinfoodappearance.Achocolatesyrupmaybethin-bodiedorthickandviscous;
atomatosaucecanbethickorthin.Consistencyofsuchfoodsismeasuredbytheirviscosity,higherviscosityproductsbeingofhigherconsistencyandlowerviscositybeinglowerconsistency.
Thesimplestmethodtodetermineconsistencyistomeasurethetimeittakesforthefoodtorunthroughasmallholeofaknowndiameter,oronecanmeasurethetimeittakesformoreviscousfoodstoflowdownaninclinedplaneusingtheBostwickConsistometer.Thisdevicemightbeusedforketchup,honey,orsugarsyrup.Thesedevicesarecalledviscometers.Thereareseveralothertypesofviscom
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