食品质地仪器测定

食品质地仪器测定第1页/共45页第2页/共45页第三节食品质地的仪器测定1.质构仪第3页/共45页第三节食品质地的仪器测定1.质构仪第4页/共45页第三节食品质地的仪器测定1.质构仪应用：面粉/面团、烘焙食品、面条、米饭、乳制品、休闲食品、水产畜牧及其加工制品、蔬菜、包装材料、凝胶测试等。

数据：硬度、酥脆性、胶着性、黏聚性、韧性、屈服点、纤维强度、弹性、延展性、回复性、弹性、黏着性、咀嚼度、凝胶强度等。

测试标准：AACC（美国谷物化学协会）、AOAC（美国与欧洲凝胶协会）、BS（英国国家标准）、ASTM（美国材料试验协会）等。第5页/共45页质构仪BackExtrusion反向挤出ForwardExtrusion正向挤出Bend弯曲（折断）Compression压缩Stressrelaxation应力松弛CreepA

B蠕变Penetration穿透（插入）Shear剪切StickinesstestA

B黏性Tension拉伸第6页/共45页质构仪-TPAtestTextureprofileanalysis(TPA，质地剖面分析)isanobjectivemethodofsensoryanalysispioneeredin1963bySzczesniak,whodefinedthetexturalparametersfirstusedinthismethodofanalysis.Laterin1978BourneadaptedtheInstrontoperformTPAbycompressingstandard-sizedsamplesoffoodtwice-二次压缩试验.SZCZESNIAK,A.S.(1963).Classificationoftexturalcharacteristics.J.FoodSci,28,385-389.BOURNE,M.C.(1978).TextureProfileAnalysis.FoodTechnol.,32(7),62-66,72.第7页/共45页TPAisbasedontherecognitionoftextureasamulti-parameterattribute.Forresearchpurposes,atextureprofileintermsofseveralparametersdeterminedonasmallhomogeneoussamplemaybedesirable.Thetestconsistsofcompressingabite-sizepieceoffoodtwotimesinareciprocatingmotionthatimitatestheactionofthejawandextractingfromtheresultingforce-timecurveanumberoftexturalparametersthatcorrelatewellwithsensoryevaluationofthoseparameters第8页/共45页Themechanicaltexturalcharacteristicsoffoodsthatgovern,toalargeextent,theselectionofarheologicalprocedure,andinstrumentcanbedividedintotheprimaryparametersofhardness,cohesiveness,springiness(elasticity),andadhesiveness,andintothesecondary(orderived)parametersoffracturability(brittleness),chewinessandgumminessSZCZESNIAK,A.S.(1966).TextureMeasurements.FoodTechnol.,20,50,55-58.第9页/共45页质构仪-TPAtestTPAtest第10页/共45页第三节食品质地的仪器测定1.质构仪-参数第11页/共45页Hardness(硬度)Hardnessisdefinedasthemaximumpeakforceduringthefirstcompressioncycle(firstbite)andhasoftenbeensubstitutedbythetermfirmness.第12页/共45页Brittleness,crunchiness,andcrumbliness,whichareasimilarconcept,canbemeasuredastheeasewithwhichthematerialfracturesunderanincreasingcompressionloadIngeneral,thesmallerthedeformationunderagivenload,thelowerthecohesivenessandthegreatertheabilitytofractureoftheproduct.Fracturability酥脆性，易碎性、脆性、脆度(originallycalledbrittleness)isdefinedastheforceatthefirstsignificantbreakintheTPAcurve.第13页/共45页第14页/共45页Adhesiveness黏着性，黏附性Adhesivenessisdefinedasthenegativeforceareaforthefirstbiteandrepresentstheworkrequiredtoovercometheattractiveforcesbetweenthesurfaceofafoodandthesurfaceofothermaterialswithwhichthefoodcomesintocontacti.e.thetotalforcenecessarytopullthecompressionplungerawayfromthesample.Formaterialswithahighadhesivenessandlowcohesiveness,whentested,partofthesampleislikelytoadheretotheprobeontheupwardstroke.第15页/共45页第16页/共45页Springiness（恢复性，弹性，回弹）Springiness(originallycalledelasticity)isrelatedtotheheightthatthefoodrecoversduringthetimethatelapsesbetweentheendofthefirstbiteandthestartofthesecondbite.第17页/共45页Cohesiveness凝聚性，黏聚性Cohesivenessisdefinedastheratioofthepositiveforceareaduringthesecondcompressiontothatduringthefirstcompression.第18页/共45页Cohesivenessmaybemeasuredastherateatwhichthematerialdisintegratesundermechanicalaction.Tensilestrengthisamanifestationofcohesiveness.Ifadhesivenessislowcomparedwithcohesivenessthentheprobeislikelytoremaincleanastheproducthastheabilitytoholdtogether.Cohesivenessisusuallytestedintermsofthesecondaryparameterschewinessandgumminess.第19页/共45页Gumminess胶黏性、胶着性Gumminessisdefinedastheproductofhardness×cohesiveness.Gumminessisacharacteristicofsemisolidfoodswithalowdegreeofhardnessandahighdegreeofcohesiveness.第20页/共45页Chewiness（咀嚼性）Chewinessisdefinedastheproductofgumminess×springiness(whichequalshardness×cohesiveness×springiness)andisthereforeinfluencedbythechangeofanyoneoftheseparameters.Chewiness,tendernessandtoughnessaremeasuredintermsoftheenergyrequiredtomasticateasolidfood.Theyarethechracteristicsmostdifficulttomeasureprecisely,becausemasticationinvolvescompressing,shearing,piercing,grinding,tearingandcutting,alongwithadequatelubricationbysalivaatbodytemperatures.第21页/共45页Itshouldbeunderstoodthatthesameproductcannotexhibitbothchewinessandgumminess,unlessasasoliditbecomesasemisolidduringsensorymastication.SuchatransitionispracticallyneveraccomplishedduringinstrumentalTPAevaluation.Thus,itisincorrecttoquantifyandreportchewinessandgumminessinTPAofsolidorsemisolidproducts.

Chewinessshouldbereportedforsolidsandgumminessforsemisolids.第22页/共45页Stringiness筋性Stringinessisthedistancetheproductisextendedduringdecompressionbeforeseparatingfromthecompressionprobe.第23页/共45页ItisnotaparameterfromtheoriginalTextureProfileAnalysisworkbutinsteadhasdevelopedfromlookingmorecloselyattheadhesivenessportionofthecurve.AlthoughthisparameterisnotbuiltintotheTPAmacroandresultsfiles，theflexibilityisavailabletoincludethisparameterifyousodesire.Theunitsofthisparameterwouldbeindistancee.g.mm.第24页/共45页InitialModulusInitialModulusisderivedasInitialStress/InitialStrain.Unitsareine.g.N/mm².TheInitialStressiscalculatedastheaverageforceofthepointsintherange0.5secondsto1.5secondsdividedbytheContactArea.InitialStrainisthestraincalculatedatthe1.5secondpointofthecurve.TheInitialStraincanonlybecalculatedifSTRAINisavailableandhencePRODUCTHEIGHTcanbederived.InitialModulusisnotaparameterfromtheoriginalTextureProfileAnalysisworkbutinsteadhasdevelopedfromlookingmorecloselyattheportionofthecurvebeforefracture.第25页/共45页第三节食品质地的仪器测定2.流变仪??流变仪可以进行各种压缩、拉伸、插入、剪断等测定，还可以完成几乎所有流变性质的力学测定。第26页/共45页第三节食品质地的仪器测定3.布拉班德粉质仪主要用于各种粉质的品质鉴定，如面粉、玉米粉、绿豆粉等。第27页/共45页第三节食品质地的仪器测定3.布拉班德粉质仪由调粉器和动力测定计组成。测定原理是把小麦粉和水用调粉器的搅拌臂揉成一定硬度的面团，并持续搅拌一段时间，并自动记录在揉面搅动过程中面团阻力的变化。1．搅拌槽2．测力计3．轴承4．连杆5．缓冲器6．指示盘7．记录仪8．恒温水槽9．循环管10．循环电机11．滴管第28页/共45页第三节食品质地的仪器测定3.布拉班德粉质仪数据分析粉质仪得出的面团阻力曲线叫粉质曲线。第29页/共45页第三节食品质地的仪器测定3.布拉班德粉质仪数据分析第30页/共45页第三节食品质地的仪器测定3.布拉班德粉质仪数据分析吸水率(waterabsorption)：小麦粉形成硬度为500B.U.的面团所需要的加水量。强筋粉吸水率大，弱筋粉吸水率小。面团形成时间(doughdevelopmenttime)：从揉面开始达到最高黏度的时间。面团稳定度Stab(stability)：阻力曲线中心线最初开始上升到500±20B.U.到下降到500±20B.U.所需要的时间，越长说明面团加工稳定性越好。第31页/共45页第三节食品质地的仪器测定3.布拉班德粉质仪数据分析面团衰落度(weakness)：曲线从开始下降开始12min后的下降值，衰落度值越小，说明面团筋力越强。综合评价值VV(valorimetervalue)：用面团形成时间和衰落度综合评价的指标。第32页/共45页第三节食品质地的仪器测定standarddeterminationmethod1AACC76-21.01和ICC国际标准No.162方法推荐标准方法1（STD1）进行测定4.淀粉粉力测定仪（RVA，rapidviscosityanalyser）第33页/共45页第三节食品质地的仪器测定4.淀粉粉力测定仪（RVA，rapidviscosityanalyser）测试结果：峰值黏度谷值黏度衰减值最终黏度回生值峰值时间糊化温度糊化特征曲线第34页/共45页第四节食品质地评价仪器的选择1.仪器测定和感官评价的特点第35页/共45页食品物性仪器测定的开展目的性要强感官评价科学分析方法要科学首先要明确要评价的感官性质及其内涵-进行分析型评价-确定重要的感官性质然后用仪器进行各种可能的评价建立感官与仪器评价之间的相关关系确定仪器评价方法和指标第36页/共45页替代感官评价时仪器测定的分析与选择以牛肉饼(hamburger)为例说明（1）感宫评价前首先使评审员理解和明确各项感官评价用语的定义(如表3-11所示)。往往一些评审员在许多情况下，搞不清“硬”和“弹性”的定义，或将这两者混同。因此，在感官评审前要认真进行必要的