Low Calorie Nonnutritive Sweeteners - Sweeteners: Nutritional Aspects, Applications, and Production Technology - page 100

theprocedureofimmersingthewirewithBLMintoaKClsolutionisrepeated.Thedetectionlimit
ofACS-Kis1μm,andthereproducibilityisontheorderof±4%to8%ina95%conidencelevel.
Therecoveryrangedbetween96%and106%andshowsnointerferencesfromthematrix(Nikolelis
etal.2001a).
EnzymeelectrodescoupledwithFIAhavealsobeenreported.Anammonia-sensitiveelectrode
l-aspartaseorcarboxypeptidaseAwithaspartateammonialyaseimmobilizedandathree-enzyme
system including aspartate, aminotransferase, glutamate oxidase, and ASP hydrolyzing enzyme
coupled with an H 2 O 2 probe have been reported. The major drawback of these biosensors is the
interferencesfroml-aspartate,whichisusuallypresentinsamples(Compagnoneetal.1997).
Potentiometryistheprocedureinwhichasinglemeasurementofelectrodepotentialisemployed
todeterminetheconcentrationofanionicspeciesinasolution.Apotentiometricmethodisdevel-
opedforthetitrationofASP.Itmakesuseofaselectivepolyvinylchloridemembraneelectrode.This
electrodeisbasedontheelectroactivespeciesofcetylpyridinium(CP + )and2,4,6-trinitrobenzene-
sulfonate(TNBS − ).TheelectrodeexhibitsarapidandNernstianresponsetoTNBS − from5.0×10 −5
Mto1.0×10 −2 Mat25°C±0.1°C.TheresponseisunaffectedbythechangeofpHovertherange
2to12.TheelectrodeissuccessfullyappliedtothedeterminationofASPinpuresolutionswitha
precisionandaccuracyof0.9%to1.3%withoutinterferencefromotherconstituents.Theselectivity
of ion-pair-based membrane electrodes depends on the selectivity of the ion-exchange process at
themembrane-testsolutioninterfaceandthemobilitiesoftherespectiveionsinthemembrane.The
CP-TNBSelectrodeishighlyselectivefortheTNBSanion.Theorganicandinorganicanionsdonot
interfereduetothedifferencesintheirmobilitiesandpermeabilitiesascomparedwiththeTNBS
anions.ItisfoundthattheperiodateionandpicricacidinterferewiththeCP-TNBSelectrode.Inthe
caseofsugars,highselectivityismainlyattributedtothedifferenceinpolarityandthelipophilic
natureoftheirmoleculesrelativetotheTNBSanionorCPcation.Thismethodhasahighdegree
ofaccuracy,ameanrecoveryof99.8%to101%,andexcellentprecisionbythesmallvaluesofthe
relativestandarddeviation(RSD).ItisfoundthatTNBSreactswiththeinvestigatedmoleculesin
theratio1:1.Theanalysisindicatesthehighaccuracyandprecisiondependingonlesscomplicated
instrumentationandtime-consumingpretreatmentsteps.Thecombinationofsensitivity,selectivity,
andsimplicityofion-selectiveelectrodepotentiometrymakesitanexcellentandversatileanalysis
technique(Buduwyetal.1996).AnestablishedpotentiometricassayfortheindicationofACS-Kis
performedbynonaqueoustitrationwith0.1Nperchloricacidinglacialaceticacid(JointFAO/WHO
2001).
Spectrophotometry is a detection technique widely used for the determination of sweeteners.
This technique is not commonly used in food samples because it is sensitive to interference due
tofoodadditives.SpectrophotometricproceduresfordeterminingASPinvolvedifferentchemical
reagentssuchasninhydrin,chloroanilicacid,diethyldithiocarbamate,andp-dimethylaminobenzal-
dehyde(Fatibello-Filhoetal.1999).
ThedeterminationofACS-KbyFTIRspectrahasbeenachievedusinganadvancedspectrom-
eterequippedwithamultibouncehorizontalattenuatedrelectanceaccessory.Theinstrumentcan
produce12relectionswithapenetrationdepth(infraredbeam)of2.0μm.Theaccessoryiscom-
posedofaZnSecrystalmountedinashallowtroughforsamplecontainmentwithanapertureangle
of45°andarefractiveindex(RI)of2.4at1000cm −1 .Singlebeamspectra(4000to400cm −1 )of
theACS-Kextractfromrealsamplesareobtainedandcorrectedagainstthebackgroundspectrum
ofpureMilli-Qwater.Allspectraarecollectedintriplicateandaveragedbeforesubjectingtomul-
tivariateanalysis(Shimetal.2008).
4.15.2 Determination of alitame
AnalysisofACS-K,alitame,ASP,caffeine,sorbicacid,theobromine,theophylline,andvanillin
intabletopsweeteners,candy,liquidbeverages,andotherfoodsusingaμ-BondapakC-18column