外文翻译CHANGES IN ODOUR OF BARTLETT PEAR BRANDY INFLUENCED BY SUNLIGHT IRRADIATION.docx

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外文翻译CHANGES IN ODOUR OF BARTLETT PEAR BRANDY INFLUENCED BY SUNLIGHT IRRADIATION.docx

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外文翻译CHANGES IN ODOUR OF BARTLETT PEAR BRANDY INFLUENCED BY SUNLIGHT IRRADIATION.docx

外文翻译CHANGESINODOUROFBARTLETTPEARBRANDYINFLUENCEDBYSUNLIGHTIRRADIATION

CHANGESINODOUROFBARTLETTPEARBRANDYINFLUENCEDBYSUNLIGHTIRRADIATION

I.KraljCigi6,L.Zupan~i~-Kralj

UniversityofLjubljana,FacultyofChemistryandChemicalTechnology

A~ker~eva5,SI-1000Ljubljana,Slovenia

ABSTRACT

SensoryevaluationofBartlettpearbrandyrevealeddifferencesintasteandsmellbetweenthebrandyincolourlessandgreenbottles.Todeterminethedifferencesinchemicalcomposition,headspacesamplingwithsolid-phasemicroextractioncombinedwithgaschromatography-massspectrometrywasapplied.Themajoraromacomponentsinpearbrandystoredingreenbottleswereethyltrans-2-cis-4-decadienoate（68ppm）,ethyltrans-2-trans-4-decadienoate（21ppm）andmethyltrans-2-cis-4-decadienoate（27ppm）.Inpearbrandykeptincolourlessbottles,theconcentrationoftrans-2-cis-4-isomereswaslowerandtheconcentrationsofotherpossibleisomereswerehigher.Resultsshowapronounceddifferenceintheconcentrationratiosamongisomeresofethyl2,4-decadienoateandmethyl2,4-decadienoateinbothsamples.Sunlightirradiationwasfoundtobethereasonforthesechanges.Itwasconfirmedthattrans-2-cis-4-isomerepartlyconvertstotheotherthreeisomeresduringUVirradiation.

INTRODUCTION

Aromaisoneofthemostimportantqualitiesofdistilledbeverages,e.g.brandy.Itisdeterminedbythepresenceandthelevelofvolatilecompounds（complexmixtureofcarbonylcompounds,alcohols,carboxylicacidsandtheiresters）andallproductionstagescannoticeablycontributeandinfluencethefinalaromacompositionofbrandies.EarlierstudiesonBartlettpeararomahaveshownthatthecharacterimpactcompoundsaremethylandethylestersoftrans-2-cis-4-decadienoicacid[1].Thepleasantpear-likeodourhasbeenfoundtochangeduringfermentationasaresultofthetrans-2-cis-4-decadienoatesbeingpartlyisomerizedtotrans-2-trans-4-decadienoates,whichhaveanon-typicalsmell[2].Theodourcharacteristicsofsomevolatilecompoundsaresometimesaffectedbytheirgeometricisomerism[3].Headspace（HS）samplingwithsolid-phasemicroextraction（SPME）incombinationwithgaschromatography-massspectrometry（GC-MS）isthemainmethodforanalysingaromacompounds[1].TheaimofourworkwastodeterminethedifferencesinchemicalcompositionofthearomaofBartlettpearbrandystoredingreenandcolourlessbottlesandtodeterminewhydifferencesoccur.

EXPERIMENTAL

Standardsolutionsofethyltrans-2-cis-4-decadienoate（90+%,Aldrich）werepreparedinethanol（absolutep.a.,Merck）andwater（40:

60,v/v）.TheratioofethanolandwaterwaschosenaccordingtotheethanolcontentinBartlettpearbrandy.

UVirradiation

UVirradiationwasperformedwith50WHghigh-pressurelamp（Osram,Ultra-vitalux）.Thesampleswere

placedinvials1cmfromtheUVlamp.

HeadspaceGC-MSanalysis

Forheadspaceanalysissolid-phasemicroextractionwasused.Amanualholderforsolid-phasemicroextractionwa:

;,）btainedfromSupelco.SPMEstationaryphasewaspolydimethylsiloxanewithfilmthickness100gmfromSupelco.5mLaliquotofeachsamplewerethermostatedat40°Candtheextractionswereperformedfor15rain.TheanalytesweredesorbedfromtheSPMEfibreintheGCinjectorat220°CandseparatedonVOCOLfusedsilicacapillarycolumn（60m,0.25mm1D,1.50!

amfilmthickness,Supelco）andanalysedusingmass

spectrometerwithelectronimpactionization（HP5890IIgaschromatograph,5989Amassspectrometer,!

iwlett-Packard）.Temperaturesoftheionsource,quadrupolemassanalyzerandGC-MSinterfacewere200,100and250°Crespectively.Thetemperatureprogramwas:

70°Cfor4rain,andthenheatedupto210°Cat15°C/min.

RESULTSANDDISCUSSION

ChromatogramsobtainedbyGC-MSafterheadspacesamplingwithSPMEofthetwopearbrandysamplesarepresentedinFigure1（a,b）.Eightchromatographicpeakswereidentifiedas:

methylcis-2-trans-4-decadienoate

（1）,methyltrans-2-cis-4-decadienoate

（2）,methylcis-2-cis-4-decadienoate（3）,methyltrans-2-trans-4-decadienoate（4）,ethylcis-2-trans-4-decadienoate（5）,ethyltrans-2-cis-4-decadienoate（6）,ethylcis-2-cis-4-decadienoate（7）,andethyltrans-2-trans-4-decadienoate（8）.

Acomparisonofthetwochromatogramsrevealedthattheamountoftrans-2-cis-4-decadienoates（2and6）decreaseandtheamountofotherisomeresof2,4-decadienoates（peaks1,3,4,5,7and8）increasewhenbrandyisstoredincolourlessbottles（Figure1a,b）.

Figure1:

GC-MSchromatogramsafterSPMEsamplingshowingthecompositionofBartlettpearbrandystoredingreenbottle（a）andincolourlessbottle（b）.Peakidentitiesareasfollows:

methylcis-2-trans-4-decadienoate

（1）,methyltrans-2-cis-4-decadienoate

Thepeaksinthechromatogramscanbedividedintwogroups:

peaks1to4andpeaks5to8（Figure1）.Compoundsineachgrouphaveverysimilarmassspectraanditwasdeterminedthatthegroupwiththeshortestretentiontimesbelongtofourgeometricalisomeresofmethyl-2,4-decadienoate.Thesecondgroupofcompoundsareisomeresofethyl-2,4-decadienoate.Sincethemassspectraofgeometricalisomersaresimilar,itisimpossibletodistinguishamongdifferentisomeres.Howeverethyltrans-2-cis-4-decadienoatewasidentifiedbycomparingretentiontimesofpeak6withanauthenticstandard.Ethylcis-2-trans-4-decadienoateandethyltrans-2-trans-4-decadienoateweredeterminedbytheirvolatility.Cis-2-trans-4isomeresarethemostvolatileandtrans-2-trans-4isomerestheleastvolatileamongfourpossibleisomersandwecanconcludethatpeak5istheethylcis-2-trans-4-decadienoateandpeak8isethyltrans-2-trans-4-

decadienoate.Thefourthpeakinthesecondgroupcanonlyhetheethylcis-2-cis-4-decadienoate.Asimilarelutionorderwasproposedforisomeresofmethyl-2,4-decadienoate.

Wespeculatedthatchangesincompositionofisomereswerecausedbysunlightirradiation.Toconfirmthis,asolutionofethyltrans-2-cis-4-decadienoateinethanol-water（40:

60,v/v,concentration100ppm）wasexposedtoUVlight.TheresultsareshowninFigure2.Duringirradiationtheconcentrationofethyltrans-2-cis-4-decadienoatedecreasesandtheconcentrationsofethylcis-2-trans-4-decadienoate,ethylcis-2-cis-4-decadienoateandethyltrans-2-trans-4-decadienoateincrease.Thisexperimentconfirmsthatsunlightirradiationisresponsibleforthechangesinthecompositionoftheisomeresof2,4-decadienoateandconsequentlyinfluenceonpearbrandyaroma.

Figure2:

Changesinpeakareaforisomeresofethyl2,4-decadienoateduringUVirradiationofastandardsolutionofethyltrans-2-cis-4-decadienoateincolourlessvial.

ThearomaofBartlettpearbrandydidnotalterwhilebeingstoredingreenbottlesatthestandardroom

temperaturefor3months.Furthermore,theconcentrationratiosamongisomeresofethyl2,4-decadienoateingreenbottlesremainedconstantduringexposuretoUVirradiation.

Theestersinpearbrandywerequantifiedbycomparingpeakareaofastandardsolutionofethyltrans-2-cis-4-decadienoate.Duetoalackofstandardstheconcentrationsofallesterswereexpressedrelativelytothesamestandard.Quantitativedataforestersof2,4-decadienoicacidarepresentedinTable1.

Thesumofisomeresofethyl2,4-decadienoateandisomeresofmethyl2,4-decadienoateisequalinbothsamples,buttheconcentrationratiosamongisomeresaredifferentforbrandystoredingreenandcolourlessbottles.

Table1:

Quantitativedataforestersof2,4-decadienoicacidinBartlettpearbrandy

CONCLUSIONS

ThemaincompoundinthearomaofBartlettpearbrandyisethyltrans-2-cis-4-decadienoate（68ppm）anditisresponsibleforthepleasantodourandtaste.WhenexposedtoUVlightethyltrans-2-cis-4-decadienoateistransformedmostlytoitscis-2-trans-4-anditstrans-2-trans-4-isomere,whichproducealesspleasantodourandtaste.Thesameprocessmayalsotakeplaceduringstorageofbrandyincolourlessbottlesexposedtosunlight.Methyltrans-2-cis-4-decadienoateisalsotransformedbyUV.Itsconcentrationinbrandyis27ppm.TheexperimentaldatashowtheimportanceofstoringBartlettpearbrandyincolouredbottlestopreservethequalityofitsaroma.

REFERENCES

1.W.G.JenningsandR.Tressl,ProductionofvolatilecompoundsintheripeningBartlettpear,Chem.

Mikrobiol.Technol.Lebensm.3,52-55（1974）

2.L.Nyk~inenandI.Nyk~inen,Distilledbeverages.InVolatileCompoundsinFoodsandBeverages（Edited

byH.Maarse）,Chap.15.MarcelDekker,NewYork（1991）

3.H.Maarse,Introduction.InVolatileCompoundsinFoodsandBeverages（EditedbyH.Maarse）,Chap.1.

MarcelDekker,NewYork（1991）

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