Abstract
The carbon stable isotope ratio (δ13C) is a valuable chemical parameter in the investigation of the geographic origin, quality, and authenticity of foods. The aim of this study is the evaluation of the feasibility of 13C-NMR (Nuclear Magnetic Resonance) spectroscopy to determine the carbon stable isotope ratio, at natural abundance, of small organic molecules, such as vanillin, without the use of IRMS (Isotope Ratio Mass Spectrometry). The determination of vanillin origin is an active task of research, and differentiating between its natural and artificial forms is important to guarantee the quality of food products. To reach our goal, nine vanillin samples were analyzed using both 13C quantitative NMR spectroscopy (under optimized experimental conditions) and IRMS, and the obtained δ13C values were compared using statistical analysis (linear regression, Bland–Altman plot, and ANOVA (analysis of variance)). The results of our study show that 13C-NMR spectroscopy can be used as a valuable alternative methodology to determine the bulk carbon isotope ratio and to identify the origin of vanillin. This makes it attractive for the analysis in the same experiment of site-specific and total isotope effects for testing authenticity, quality, and typicality of food samples. Moreover, the improvement of NMR spectroscopy makes it possible to avoid the influence of additives on carbon stable isotope ratio analysis and to clearly identify fraud and falsification in commercial samples.
Highlights
The carbon stable isotope ratio is considered a valuable chemical parameter for studying the geographic origin of food products as well as for checking food properties, such as typicality, quality, and authenticity, especially when conventional analytical methodologies provide ambiguous results [1,2,3,4,5]
Investigations of vanillin sources were usually focused on a combination of two techniques, namely, Isotope ratio mass spectrometry (IRMS) and NMR spectroscopy, to obtain site-specific enrichment of 13C by merging the δ13C values measured by IRMS with the molar fraction of 13C in the spectra
Starting from the results of our previous work on small molecules, such as carbonates and oxalic acid, nine commercially available vanillin samples were analyzed using our recent application of 13C-NMR spectroscopy
Summary
The carbon stable isotope ratio (expressed as δ13C) is considered a valuable chemical parameter for studying the geographic origin of food products as well as for checking food properties, such as typicality, quality, and authenticity, especially when conventional analytical methodologies provide ambiguous results [1,2,3,4,5]. Its determination gives the most important information concerning falsifications, adulterations, and fraud in food products [6] This method is the official method applied by the IOV (International Organization of Vines and Wine) [7] to quantify the sugar added into wine [8,9]. Isotope ratio mass spectrometry (IRMS) is the official methodology for the analysis of carbon stable isotope ratio due to its high accuracy (0.1‰) and sensitivity (up to 0.01‰) [10]. It requires expensive equipment and skilled technicians and measures the overall δ13C of a sample, a value that can be affected by the presence of a. Iinnfflaucetn, caed; iisnadtvhaentpagreesoenf ctheisotfecahncioqmuepilsexrelmataetdrixto, tahesmeleactrtiivxeinsflaumenpclee; ionf thpereppraersaetniocne otefcahcnoiqmupelsexinmaadtdriixti,oansetoleactniveeffsiacimenptleseopf aprraetpioanrastiyosntetmechbneifqoureesIRinMaSddaintaiolynstios aisnreefqfiuciireendt s[1e1p,a1r2a]t.iDonuseytsotetmhebienfcorreeaIsRinMgSinatnearleysstiisnisthreisqufiierledd, d[1i1ff,e1r2e].nDt auneatloyttihcealinmcreetahsoidngs hinatveerebset einn timhisplfieemlde,ndteifdferfeonrt aisnoatloyptiiccalamneatlhyosidss. hFaovre ebxeaemn ipmlep,leimnfernarteedd-fboarsiesdotosppieccatnroaslycosipsy. ,Fomr eidx-ainmfrpalree,din(fMraIrRed) -lbaasseerdspspeecctrtroossccooppyy,, nmoind--dinisfrpaerresdiv(eM(INR)DlIaRseSr),sapnedctrFoosucorpieyr, ntroann-sdfoisrpmer(sFivTe(INR)DhIRavSe),baenednFsouucrcieesrstfrualnlysfaoprpmli(eFdTi-nIRt)hhisavfieelbdeewnitshuclocewsscfouslltyaanpdpclioemd pinletxhitisyfi[1e,l1d3w–1i8th]. lTohwe caodsvtaanntadgceosmopf lsepxeictytro[1s,c1o3p–y18i]n.sTtrhuemaednvtaantitoangeasreofthsepiercvtreorsycocopmy minostnrupmreesnentacteioinn athree ptmaarmcsiiltnnahhetalslatbealetfeereaaelbaboktiurtrreflsreoreneeeiuaevstrndsanhtfrseita1toecestert3iterorovayCeδteydatreis1not-cnm,e3hNomapbcaCaeeencmnyeMle,oyvddcvtmcntsRwahhahoibtsle-soolhueemiibu.mddnceeaeRapapeyssipwrpurcoeoeobrreapcsdrfefeeodleiirlcqsittnimneonyiaeeuofatfonrdnoeilntobrriycteronge.fho,e1st3attTaonatCieih[nhnndnh1rs-seiedeo9fleNctitmas]lhucscofrMtbaewoaaeepgallmrnrseRlcilirbaueetcuteiphobshelsslptcnlooadoevpserouatrteeofiibanootbtroctetyrbpysotentossirhteccdttruoaaahoeyoctienssul,neifoecrudmasteeofmpsoδeunddbpeeu1ldpci3,yocrfCwofoowoniaotfmt.tshirrlryoetiIybeThtRptiooiayhnhmolsMpnfteveiirnhgstaetpeeSce.hitansqlsaeaTeitsatauelsishuahscglsdips[elurraea1ateeee1mltra9crai3rreanne]tδCtenplsiawg1asfamol-3ueliteCNtyfimnerlitaotesbdvhMskoopivneeosedfolatcc.RuesomalbeδRftuup1ats1tveet3ea3plhrshtcCCsasioeheeneeil-tfi.cuoonoeoNucTtcedfdtncrhsalMhooleyioetwywinsil,mfsoRocotaisefcnooat-riinrhabIcgspsgeRcdraapnayatoblMsnhenafnmoetocooilidoSdnssctrftsmoepthhiosdtiocalotigoines. very useful for investigating food falsifications and sophistication
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