1
ElisabethGuichard 1 ,CharfedinneAyed 2 andChristianSalles 1 1CentredesSciencesduGo^ utetdel’Alimentation,CNRS,INRAE,InstitutAgro,Université deBourgogneFranche-Comté,Dijon,France; 2DepartmentofFood,NutritionandDietetics, SchoolofBiosciences,UniversityofNottingham,SuttonBoningtonCampus, Loughborough,UnitedKingdom
1.1Introduction
Duringeating,foodissubjectedtomasticationandsalivationtoformabolus,whichis thenswallowedforfurtherdigestion.Aromaandtastecompoundsarereleasedfrom foodbolusduringthemasticatoryandpost-swallowingsteps.Aromacompounds aretransferredfromfoodtosaliva,thentotheairphaseintheoralcavityandtransportedtothenasalcavityviatherespiratory flowinordertoreachtheolfactoryreceptorsandbeperceived.Tastecompoundsaredeliveredtothereceptorslocatedonthe tongueinordertobeperceived.Thischapterwillpresentanoverviewofthedifferent aromaandtastecompounds,theirdynamicreleasefromthefoodmatrixintothesaliva andtheoronasalcavity,takingintoaccountthein-mouthphysiologicalprocess,and theinfl uenceon flavorperception.
1.2Aromaandtastecompounds
Inthispart,wewillgiveanoverviewofthephysicochemicalandsensorypropertiesof thearomaandtastecompoundsresponsibleforperception.
1.2.1Physicochemicalpropertiesofaromacompounds
Aromacompoundsarepresentinverylowamountinfood(<1%).Theyaresmallmoleculescharacterizedbylowmolecularweight(<400Da)andahighvaporpressure, whichallowthemtobeeasilyreleasedinthegasphase,inordertobeperceivedby theolfactoryreceptors.Infood,morethan15,000volatilecompoundshavebeenidenti fied,asreportedinthedatabaseonvolatilecompoundsinfood(http://www.vcfonline.nl/VcfHome.cfm).Notallthevolatilecompoundsareodorant.Around3500 compoundscanbeperceivedbythenose(odorthreshold)anddescribedwithvarious odorantnotesintheFlavorbase(http://www.lef fingwell.com/ flavbase.htm).Odor
Flavor. https://doi.org/10.1016/B978-0-323-89903-1.00006-2 Copyright © 2023ElsevierLtd.Allrightsreserved.
thresholdsandodorqualitiesdependonstructuralparameterssuchaschainlength, unsaturationdegree,doublebondsposition,functionalgroupsposition,molecular characteristics,andstereochemistryofmolecules.Odorthresholdsvaryinawide rangeandcanbelowerthan1ng/L.Itisstilldif ficulttopredictodorpropertiesby structuralparameters(Tromelin,2016).Forexample,2-methoxy-3,5dimethylpyrazine(earthysmelling)hasanodorthresholdinairof0.001ng/L,whereas asimilarcompound,3-methoxy-2,5-dimethylpyrazine(pea-likesmelling)hasanodor thresholdsof56ng/L(MolyneuxandSchieberle,2007).
Inarecentmeta-analysisof5642publicationsonfoodaromafrom1980to2013 and949otherdocuments,alistofthe226mainkeyfoododorantswasmadebased ontheirodoractivityvalue(OAV > 1)measuredinatotalof119publicationsdealing with227foodsamples(Dunkeletal.,2014).Themostfrequentlyoccurringkeyodorantsinfoodsaremethional(53.7%ofsamples,boiledpotatoesodor),2-and3-methyl butanal(50.7%,malty),butane-2,3-dione(41.9%,buttery),(E,E)-2,4-decadienal (41.4%,fried,fatty),andfuraneol(40.5%,caramel),followedbysotolon(seasoning), 1-octene-3-one(mushroom),aceticacid(vinegar),acetaldehyde(fruity,fresh),ethyl2and3-methylbutanoate(fruity),(E)-2-nonenal(cardboardlike),vanillin(vanillalike), 2-acetyl-1-pyrroline(roasted,popcorn),2-and3-methylbutanoicacid(sweaty),and butanoicacid(sweaty).
Aromacompoundsbelongtodifferentchemicalclasses,mainlyalcohols,acidsand esters,phenoliccompounds,carbonylcompounds,sulfurandnitrogenaliphaticcompounds,heterocyclicaromacompounds,terpenes,andnorisoprenoids.
1.2.1.1Alcohols
Alcoholsareimportant flavorcompounds,whicharewidelypresentinfoodsand mainlyinfruits.Unsaturatedalcoholshaveagreaterimpactonfood fl avorthansaturatedalcohols.Forexample,C6alcohols,suchas cis-3-hexenoland cis-6-hexenol (leafalcohol),areformedinplantsasaresultofenzymaticoxidationoflinoleicand linolenicacidbylipooxygenasesandhydroperoxidelyases(JelenandWasowocz, 2012)andareresponsibleforfreshlycutgrassaroma.Terpenealcoholssuchas linalool,nerol,geraniol,alpha-terpineolpresentfruityand floralnotes,whicharecharacteristic,forexample,ofMuscatgrapearomaandphenylethanol,withatypicalrose aroma.Alcoholsarealsoprecursorsforsynthesisofaldehydesandesters.
1.2.1.2Carbonylcompounds
Anotherimportantchemicalclassisthecarbonylcompounds,aldehydesandketones, whichareresponsibleforvarioustypicalodorantnotessuchastheapplelikeodorof acetaldehyde,almondodorofbenzaldehyde,vanillaodorofvanillin,raspberryaroma of4-hydroxyphenyl-2-butanone,alsocalledraspberryketone.Therearealsoimportant aromacompoundsindairyproducts(LeQuéréandMolimard,2002),withthe butteraromaofdiacetyl(2,3-butanedione)andacetoin(3-hydroxy-2-butanone), blue-cheesearomaof2-nonanoneand2-heptanone.
Retentionandreleaseofaromaandtastecompounds,influenceonperception5
1.2.1.3Estersandlactones
Estersandlactonespresentmainlyfruitynotessuchas,forexample,thebananaaroma ofisoamylacetate,applearomaofbutylacetate,peacharomaofgamma-decalactone, andcoconutaromaofgamma-nonalactone.Esterswithlowmolecularweightare mainlypresentinfruits, flowers,andfermentedbeverages;mostofthemareformed fromacidsandalcohols.Unsaturatedestershavelowerthresholdsthansaturatedones.
1.2.1.4Hydrocarbons
Amongthehydrocarbons,aliphatichydrocarbonsarenotorlittleodorantbutterpenes areimportantaromacompoundsinessentialoils,i.e.,limonene,whichisthemain compoundinorangejuice.Sesquiterpenehydrocarbonshavelowerimpactthanmonoterpenesduetotheirhigherdetectionthresholds.Otherterpenederivativespresentlow thresholdsandspeci ficodornotessuchasdamascenone(plum)orbeta-ionone(violet).
1.2.1.5Sulfurandnitrogencompounds
Sulfurandnitrogencompoundsarepresentinverylowamountandpossessverylow thresholds.Sulfurcompoundscontainthiols,thioesters,sul fides,polysulfides,dithiazins,oxathiazines,thiophenes,andthiazoles.Theyaremainlypresentinvegetablesas, forexample,dimethylsulfideresponsibleforcabbagearoma.Theyarealsoresponsibleforoff-flavorsuchasthe “rottenegg” aromaofhydrogensulfi de.Thiolsarepresentinfermentedfoods,drinks,cheese,andwine.Methanethiol,aproductof degradationofmethionine,hasacabbagelikeodorandisabundantinCamembert cheese.Thiolscanreactwithothervolatilecompoundsandformthioesters(Engel, 1999).
Ofallthealiphaticnitrogencontainingcompounds,amines,isothiocyanates,and aminophenolsarethemostimportantforaroma.Amineshaveastrongammonia likearoma.TheyareStreckerdegradationproductsandtheirodordependsonthepH. Isothiocyanateshavebothnitrogenandsulfurelements,andtheycontributetopungentnotesinvegetables(BurdockandFenaroli,2010).
1.2.1.6Heterocycliccompounds
Heterocyclicaromacompoundscontainsulfur,nitrogen,oroxygenatomsinaring, suchasthiophenes,pyrrolines,thiazoles,furanones,pyrenes,pyrazines,orpyridines. Theyareformedfromsimpleprecursorsathightemperature,mostlybyMaillardreaction.Heterocyclescontaininghydrogenarethemaincompoundsofcaramelaroma (Paravisinietal.,2015).Alkylpyrazinesdetectedincoffee,cocoa,peanuts,chipshave roasted,nutlikearomas(BaltesandBochmann,1987).
1.2.2Physicochemicalpropertiesoftastecompounds
Tastecompoundsbelongtodifferentchemicalclassessuchasorganicacids,carbohydrates,mineralsalts,aminoacids,peptides,proteins,nucleotides,andsomephenolic
orheteroatomiccompounds.Theypresentgreatdifferencesindetectionthresholds. Theyaredetectedbythetastebuds,locatedmainlyonthesurfaceofthetonguewithin tastepapillaeandareresponsibleforthe fivebasictastes:sweet,salty,sour,bitter,and umami.
1.2.2.1Mineralsalts
Sodiumchlorideismainlyresponsibleforsaltytasteinfood,butothersaltssuchas potassiumorcalciumchlorideareperceivedsaltytoalowerextend.However,they alsopresentbitternotes,aswasobservedforcalciumandmagnesiumsaltsingoat cheese(Engeletal.,2000).
1.2.2.2Organicacids
Acidperceptionisduetothepresenceofhydroniumionsfromorganicacids.Citric andmalicacidsaremainlyresponsibleforacidtasteinfruitsandvegetables,tartaric acidingrapes,aceticacidinvinegar,andlacticacidindairyproducts.Somealphaand betaacidsarealsoresponsibleforbitternotes(ChenandLin,2004).
1.2.2.3Aminoacids
Aminoacidsareinvolvedindifferenttasteperceptions.Sweettastehasbeenassociatedwithglycineincrabandwithmethionineinseaurchin(Sallesetal.,2012). L-aminoacids(L-leucine, L-isoleucine, L-valine, L-arginine, L-methionine, L-phenylalanine, L-tyrosine, L-tryptophan, L-histidine)presentabittertaste,butmorepolarones (L-glycine, L-alanine, L-serine, L-threonine, L-lysine, L-proline)presentasweettasteas D-aminoacids(Katoetal.,1989).Aminoacidswithalateralacidfunctionsuchas Lglutamicand L-asparticacidsareresponsibleforacidtaste.Theirsodiumsaltsare responsibleforumamitaste.Sodiumglutamatepresentinsomefoodsataconcentrationhigherthanitsdetectionthreshold(300mg/L)mainlycontributestoumamitaste. Biogenaminesobtainedbydecarboxylationofaminoacidsmayalsopresenta bittertaste.
1.2.2.4Nucleotides
Twotypesofribonucleotidespresentinfoodsareresponsibleforumamitaste,inosine monophosphateinanimalproductsandguanosinemonophosphateinvegetalproducts (Ninomiya,2002).Theyarealsousedasfoodadditivesandareknowntoactinsynergywithsodiumglutamate.
1.2.2.5Mono-anddisaccharides
Sweetnessperceptionismainlyduetothepresenceofmono-anddisaccharidesand mainlysucrose(composedofglucoseandfructose).Theotherdisaccharidesare perceivedlesssweetthansucrose.Lactose(derivedfromgalactoseandglucose)is themostabundantinmilkbutwithasweeteningpowerfourtimeslowerthansucrose. Maltose(twounitsofglucose)isproducedinmouthfromstarchbytheactionof 6FlavorReleaseinHumans
Retentionandreleaseofaromaandtastecompounds,influenceonperception7
amylaseduringmasticationandtrehalose(twounitsofglucosejoinedbyaonetoone alphabond)producedbytheactionofdifferentmicroorganismspresentinsaliva.They aretwotimeslesssweetthansucrose(Laffi tteetal.,2016).Themonosaccharides glucoseandfructosenaturallyoccurringinfruitsarealsoperceivedlesssweetthan sucrose.
1.2.2.6Terpenoids
Someterpenoidsareperceivedsweet.Rebaudiosideandstevioside,extractedfromthe leavesof Steviarebaudiana,areperceived300to450timessweeterthansucrose (Lindley,2012).Theycanbeusedasfoodadditivebuttheirsafetyisstillunderdebate. MogrosidesconstituteafamilyofterpenesextractedfromaChineseplantandpresent astronglicoriceafter-tastewithacoolingtastewhichlimitstheirpotentialuseas sweetener.
1.2.2.7Peptides
Thetasteofpeptidesdependsontheirstructureandtheirphysicochemicalproperties. Bitterpeptidescontainagreatnumberofbitteraminoacids.Theirdetectionthresholds varyasafunctionoftheirchainlengthandtheorderofaminoacids.Asanexample Pro-Gly-ArgandArg-Pro-Glyhavedetectionthresholdsinwaterof,respectively, 25mmol/Land0.8mmol/L(Laffi tteetal.,2016).Cyclicdipeptidesnameddicyclopiperazinesareperceivedmorebitterthantheirlinearhomologs.Incheese,bitterpeptidesareformedfromcaseindegradation.Othertastesarecoveredbysmall peptides.Asexamples,acidpeptidescontainglutamicorasparticacids,andarginyl dipeptideswerefoundassalttasteenhancingmolecules.
1.2.2.8Proteins
Ingeneral,moleculeswithahighmolecularweighthavenotaste.However,alimited numberofproteinselicitastrongsweettasteamongwhichthaumatin,constituentof theberriesofanAfricanplant(Masudaetal.,2011),hasreceivedapprovaltobeused assweetenerinfoodstuff,duetoitshighsweetnesspotency(1600timeshigherthan sucrose).Anothersmall(6.4kDa)sweetprotein,brazzein,isapproximately2000 timessweeterthansucrose(Poirieretal.,2012),withatastemoresimilartosucrose thanthaumatin.
1.2.2.9Othercompounds
Arti ficialsweet-testingmoleculeshavebeengeneratedthroughchemicalsynthesisas sucrosereplacertoanswertohealthproblemsassociatedtodiabetes.Theyareoften usedinmixture.Saccharinalsoknownaso-benzoicsul fimidewasthe firstartificial sweetenerdiscovered.Itcanbeusedassweeteneratlowconcentrationbutitelicits astrongbittertasteathighconcentration(Cohen,1986).Cyclamatehasasweettaste similartosucrosewithaweakmetallicandsaltyaftertaste(SchiffmanandGatlin, 1993).AcesulfameKisanintensesweeteneroftenusedinassociationtomaskthe
unpleasantaftertasteofothersweeteners(SchiffmanandGatlin,1993).Aspartameisa syntheticpeptide(Asp-Phe-O-Methyl)knowntosynergizewithothersweetenersand thusmainlyusedinmixturewithacesulfameKandsaccharin.Sucraloseisapproximately600timessweeterthansucroseanditsuseisapprovedinallmajorcountries.
1.3Influenceoffoodingredientsandfoodstructureon thereleaseof flavorcompoundsduringtheinmouthprocessinrelationwithperception
Flavorperceptionisadynamicprocess,whichbeginsasfoodisputinthemouth,then mixedwithsaliva,brokenwiththeteethinthecaseof fi rmfoods,formingaboluseasy toswallow.Afterswallowing,some flavorcompoundsremainontheoralmucosa, leadingtoaftertaste.Inordertounderstandtherelationshipsbetween flavorrelease and fl avorperception,thereisaneedtofollowthereleaseatthesedifferentsteps,in adynamicprocess.
1.3.1Retentionandreleaseofaromacompounds
Infoods,aromacompoundsaresolubilizedinthedifferentphasesaccordingtotheir hydrophobicpropertiesandaremoreorlessretainedbythemacromolecules,such asproteinsandpolyosides.Theirreleaseinthenasalcavitydependsbothonthe compositionofthefoodmatrixandonitsstructuralorganization.
Afoodmatrixiscomposedofmacromoleculesabletomodifythereleaseofaroma compoundsinthenasalcavityduetospeci ficinteraction,described firstinsimplesystems,theninrealfoods.
1.3.1.1Effectoffoodingredientsonaromaretentionand releaseinsimplemodelsystems
Mostoftheliteratureontheinteractionsbetweenaromacompoundsandfoodmatrix relatestosimplesystemscomposedoflipids,proteins,andcarbohydrates,aloneorin mixturebutotherconstituentssuchaspolyphenols,melanoidins,arti ficialsweeteners, alcohol,andsaltalsoaffectaromareleasefromwatersolution.
1.3.1.1.1Lipids
Insystemscontaininglipids,aromacompoundsarepartitionedbetweenthelipidand theaqueousphases,followingthephysicallawsofpartition.Thereleaseofaroma compoundsfrommodelsystemscontaininglipidsdependsonthenatureofboththe aromacompoundandthelipid.Mostofthearomacompoundsaremoresolublein oilthaninwater.Thesecompoundsareconsideredashydrophobic(log P > 1)and arethuslessreleasedinthevaporphasefromoilthanfromwater(lowerair/oilthan air/waterpartitioncoef ficient).Thereleaseofthemosthydrophobicaromacompounds alsodependsonthelevelandnatureofthelipid.Asanexample,ethylhexanoate(log 8FlavorReleaseinHumans
P ¼ 2.83)ismoresolubleinsunfl oweroilthaninoliveoil(Roudnitzkyetal.,2003). Thiswasexplainedbythehigheramountofunsaturatedfattyacidsinsunfloweroil (C18:2)whichleadstoahighersolubilityofaromacompounds(Guichard,2002). Aromacompoundsarealsomoresolubleinshortchainthaninlongchainsaturated triglycerides(Maier,1975).Asaromacompoundsareonlysolubleinliquidfat,a highamountofsolidfatreducedtheirsolubilityandthusincreasedtheirreleasein thevaporphase(Roudnitzkyetal.,2003).
1.3.1.1.2Proteins
Foodproteinsareknowntobindaromacompounds(Tromelinetal.,2006)bydifferent mechanismswhichdependbothonproteinstructureandnatureofaromacompound (Hengetal.,2004; Semenovaetal.,2002).Mostofthestudiesrelatedtoaromaproteininteractionshavebeendoneusingmilkproteinsamongwhich b-lactoglobulin hasbeenthesubjectofmanystudies(Hansen,1997; Lubbersetal.,1998; O’Neill, 1996)andonlyfewstudiesarerelatedtocaseins(Voilleyetal.,1991)evenifthey areamongthemostabundantmilkproteins. b-Lactoglobulinisabletobindaroma compoundsbyhydrophobicinteractions.Withinthesamechemicalclassofaroma compounds,thestrengthoftheinteractionincreasedwiththechainlength(Jouenne andCrouzet,2000; O’NeillandKinsella,1987; Sostmannetal.,1997).ThepH,temperature,andionicstrengthaffectedthestrengthofthebindingbymodifyingthestructureoftheprotein(JouenneandCrouzet,2000; Taveletal.,2010; Tromelinetal., 2006).Theseinteractionsreducedthereleaseofaromacompoundsintheairphase andthusaromaperception(Andriotetal.,2000).Theinteractionsbetweenmilkproteinsandaromacompoundsmainlyinvolvedhydrogenbondingorhydrophobiceffect (Tromelinetal.,2006).However,aldehydesandsulfurcompoundsinteractwithproteinsbyirreversiblebindingaswasdemonstratedbetweentrans-2-hexenalandwhey proteinswiththeformationof fluorescentcompounds(Meynieretal.,2004).
Proteinsofleguminousplantsareoneofthemostpromisingmaterialsforformulatingnewformsoffoodproducts.Theseproteinsareisolatedfromsoy,peas,and beansandusedasfunctionaladditives.NonspecificvanderWaalsbindingwasattributedforhydrocarbonswhereashydrogenbindinganddipoleforceshavebeensuggestedforesters,ketones,aldehydes,andalcohols(ZhouandCadwallader,2006), covalentbindingwasdemonstratedbetweenpeaproteinisolatesandoctanalordibutyledisul fide(WangandArnt field,2016).Theroleoftheproteinstructureinbinding andreleaseofaromawasinvestigatedinthecaseofhexylacetateandrevealedthatthe nativeleguminousmoleculespossessthehigherbindingaffinityforthiscompound (Semenovaetal.,2002).
1.3.1.1.3Carbohydrates
Carbohydratecompoundscanbeclassi fiedintothreecategoriesaccordingtotheirmolecularweight:simplesugarssuchasglucoseandsucrose(mono-anddisaccharides), oligosaccharides(2 10monosaccharides)suchasoligofructoseandpolysaccharides (>10monosaccharides)suchasstarch(DelarueandGiampaoli,2006).Theiraddition infoodsinfl uencedbothtaste,especiallysweetness,andtextureperception.Their Retentionandreleaseofaromaandtastecompounds,in
impactonaromareleasewasquitedifficulttopredict,sincetheyareabletoinduce bothretentionandreleaseeffects,dependingontheintrinsicpropertiesofthefoodmatrixsuchasthetypeofcarbohydrates,theirconcentration(Nawar,1971),andalsoon thepropertiesofaromacompoundssuchassterichindrance,polarity,andrelative volatility,asalreadyreviewed(Goubetetal.,1998).Amongthecarbohydrates,starch wasabletointeractwitharomacompounds,mainlybytheformationofinclusioncomplexeswithamylose(Biaisetal.,2006),whichalsomodifiedtherheologicalproperties ofstarch(Heinemannetal.,2005).Theadditionofpectininducedasmallretentionof aromacompounds,mainlyduetotheformationofamacromolecularnetwork(Rega etal.,2002),whichlimitedthediffusionofsmallmolecules.Inthecaseofcarrageenan,asmallretentionwasobservedforestersandasaltingouteffectforalcohols (Bylaiteetal.,2004).
1.3.1.1.4Othereffects
Otheringredientsfromthefoodmatrixinfluencedaromarelease.Anincreasedamount ofsaltinducedanincreaseintheair/waterpartitioningofmostofthearomacompounds,duetoasaltingouteffect,explainedbyareductionoftheavailablesolvent intheliquidphase.Thiseffectwasmoremarkedforhydrophobiccompounds,lesssolubleinwater(Lauverjatetal.,2009).Additionofethanoldecreasedthepartitioncoefficientofvariousclassesofvolatilecompoundsbyincreasingtheirsolubility (Voilleyetal.,1991).Othernonvolatilecompoundssuchaspolyphenols,melanoidins, arti ficialsweetenersalsoimpactedaromareleaseandperception.
1.3.1.2Effectoffoodingredientsonaromaretentionand releaseinrealfoods
Foodscannotonlyberepresentedbysimplesystemscontainingonemacromolecule. Theinteractionsbetweenaromacompoundsandmacromoleculeshavetotakeaccount ofthemultiphasicsystemscomprisingwater,lipids,andproteinsor/andcarbohydrates,inthepresenceofotheringredients.
Foodsystemscontaininglipidscanbeconsideredasoil-in-waterorwater-in-oil emulsions.Thevolatilityofaromacompoundsinemulsionsdependsontheamount offatbutalsoonthetypeoffat(Relkinetal.,2004).Anincreaseinfatcontent decreasedthereleaseofthemorehydrophobiccompounds;thiseffectwashigher thanthatofproteinsorpolyosides(Kopjaretal.,2010; Seuvreetal.,2000).Moreover, theeffectofproteinvariedaccordingtotheamountoflipidsinicecream(Ayedetal., 2018);anincreaseinproteincontentinducedadecreaseofaromareleasebutthiseffect wassignificantonlyatalowfatlevel.Anadditionofmonoglyceridesinemulsions inducedadecreaseinair/emulsionpartitioncoef ficientofthearomacompounds (Maoetal.,2014).Thepresenceofproteins(beta-lactoglobulinorsodiumcaseinate) asemulsifi ersattheoil/waterinterfaceincreasedtheresistancetotransferofhydrophobicaromacompoundsfromoiltowaterandthusinducedadecreaseintheirreleasein theairphase(Harveyetal.,1995; Rogachevaetal.,1999).Anadditionofpolyphenols inoliveoilemulsionsstabilizedbybeta-lactoglobulinmodifiedthestructureofthe interface,improvingthedispersiondegree(Genoveseetal.,2015a)andincreasing 10FlavorReleaseinHumans
Retentionandreleaseofaromaandtastecompounds,in
thereleaseofthemorevolatilecompounds(Genoveseetal.,2015b).Thiswas explainedbyinteractionbetweenpolyphenolsandwheyproteins,whichreduced thebindingbetweenaromaandproteinsbyacompetitioneffect.Theseresultsare ofgreatinterestintheformulationofhealthierfoodswithadditionofpolyphenols andprovidingagoodaromaperception.
Theadditionofsalt(NaCl)modifiedthestructureofthefoodmatrix.Asan example,beta-lactoglobulinwasmainlypresentinitsdimericforminthepresence ofNaClbecauseofamodificationofelectrostaticforces(Sakuraietal.,2001),leading toanincreaseinthebindingof2-octanone(JouenneandCrouzet,1997).Ahigher NaClcontentincreasedthestrengthofiota-carrageenangelsandtheself-diffusion ofethylbutanoate(Gostanetal.,2004),whichwasexplainedbythegreatersizeof theopenspacelocatedbetweenthegelchains,resultinginfewerobstaclestothe freediffusionofsolutes.Inmodelcheeses,theadditionofsaltmodifi edthetexture bydecreasingwateractivity,increasing firmness,andtherebyincreasingtherelease ofaromacompounds,thiseffectbeingsigni ficantatalowleveloffat(20%)and notatahigherfatlevel(40%)(Saint-Eveetal.,2009).
Hydroalcoholicsystems,suchaswine,havebeenextensivelystudied.Theyare complexmatrices,inwhichethanol,polyphenols,andpolysaccharidesareableto interactindividuallywitharomacompounds.Whenpresentinmixtures,tanninsgenerallyenhancedthereleaseofaromacompoundswhilefructoseinducedaretentioneffect,theseeffectsbeingmodulatedbyethanol(Villamoretal.,2013).Theeffectof increasinglevelsofpolysaccharidesinamodelwinecontainingtanninsdifferedaccordingtothetypeofpolysaccharide.Atlowconcentration,arabinogalactaninduced anincreaseinaromareleasewhateverthearomacompound(saltingouteffect), whereasatconcentrationhigherthan1g/Laretentionwasobservedforthemorehydrophobicaromacompounds,suggestingintermolecularbindingwhichwasnomore observedataconcentrationof5g/L,duetosaturationofthebindingsites(Mitropoulouetal.,2011).
1.3.1.3Effectoffoodstructureandtexture
Theeffectofmatrixstructureandtextureonthereleasepropertiesofaromacompoundshasbeenreviewedinmodelgels(Lubbers,2006)andindairyproducts (Gierczynskietal.,2011).Inmultiphasesystems,thecompositionandnatureofproteinsandlipidsinduceddifferentmicrostructures,whichexerteddifferenteffectsonthe retentionandreleasepropertiesofaromacompounds.Itwasthusdifficulttodissociate theeffectofcompositionfromtheeffectoftexture.Differentstudieshavetriedto demonstratetheeffectoftextureand/ormicrostructureatthesamefoodcomposition. Bymodifyingtheenergyofemulsification,emulsionswererealizedwithdifferent dropletsizes(Charlesetal.,2000).Withanincreaseinemulsiondropletsize,anincreaseinthereleaseofhydrophiliccompoundsandadecreaseofhydrophobiccompoundswereobserved.Thiswasexplainedbydifferencesinaromacompoundsmass transferinrelationtothemodificationofthesurfaceareaandthustheexchangesbetweentheoilandwaterphase.Inyogurtsrealizedwiththesameproteinconcentration, amechanicaltreatmentwasappliedtodecreasetheviscosity(Saint-Eveetal.,2006).
Itwasobservedthatthisinduceddecreaseinviscosityresultedinanincreaseinaroma releaseandthusintheintensityofaromaperception.Moreover,inthesamestudy,the natureofprotein-induceddifferencesinmicrostructureaffectingaromareleaseparameters,caseinateenrichedyogurtshadahigherviscositythanwhey-proteinenrichedyogurts,whichdecreasedthereleaseofaromacompoundsintheairphase.Inmodel cheeses,amodificationoftheproteinstructurebyacidificationwithchymosinwas showntoinduceanincreaseinviscosityandthusagreaterandfasterreleaseofall aromacompounds(Gierczynskietal.,2007).Similarobservationwasmadewith realcheesesvaryingin firmness(Repouxetal.,2012).Thereleaserateofethylpropanoateandnonan-2-oneduringthein-mouthbreakdownincreasedwiththe firmnessof thecheeses,duetoagreateramountofparticlesformedatthebeginningofthechewing processinthecaseof firmcheeses,whichledtoanincreaseintheexchangearea.After swallowing,thereleaseofthemosthydrophobiccompound,nonan-2-onedecreased moreslowlythanthatofethylpropanoateduetoitsgreatersolubilityinthelipid filmremaininginthemouth,leadingtoahigherin-mouthremanenceandthusalonger sensorypersistence(Guichardetal.,2017).
NaClalsomodifiedthestructureofthefoodmatrix;forexample,ahigherNaClcontent increasedthestrengthofiota-carrageenangelsandtheself-diffusionofethylbutanoate (Gostanetal.,2004),whichwasexplainedbythegreatersizeoftheopenspacelocated betweenthegelchains,resultinginfewerobstaclestothefreediffusionofsolutes.
Hydrocolloidmixturessuchastheoneusedforconfectionerygelscontaintypically apolysaccharide-proteinmixsuchaspectin,starch,orgelatin(Bureyetal.,2009). Phaseseparationofthesemixturesleadstoacontinuousphaserichinonehydrocolloid whichembedstheotherone.
Whilearomareleasefromonespeci fichydrocolloidmatrixisratherwellunderstood,thereisstilllimitedunderstandingofaromadistributionandreleasefrom morecomplexmixofhydrocolloidmatrices(Savaryetal.,2007; Tayloretal.,2001).
Tayloretal.(2001) haveinvestigatedthecorrelationbetweenaromareleaseand phaseseparatedgelsinvivo,andnosigni ficantdifferenceintimetomaximumintensityormaximumintensityofreleasewasobservedbetweenthegelswithdifferentmicrostructures.Morerecently, Suetal.(2021) observedthatgelatine-starchbiphasicgel withdiversemicrostructuresandtextureshasnosigni ficanteffectonaromarelease invivo.Nevertheless,theyobservedasignificantimpactonaromadistributionand releasewhensucrosewasaddedtothemixture.Themicrostructurewasaffected, anditsigni ficantlyaffectedthebehaviorofthemorehydrophobiccompounds.
Anothermicrostructuremodificationwasperformedby Chiuetal.(2015) who addedgasbubbletoasoftgel.Theseauthorsshowedthatincreasedaerationresulted inanincreaseoftotalaromareleaseof1-octen-3-ol.Airinclusionsleadtobiggersurfacearea,consequentlyacceleratingmasstransferofvolatilesatthefood-salivainterface. Suetal.(2021) showedthatthisphenomenonisdifferentfordifferentgroupsof aromacompounds.Airinclusionaffectsmorethebalanceofsomealdehydesinthe fi nalproduct.Nevertheless,thisairinclusionseemstobeanefficientstrategyto compensatethereductioninaromainsuchcomplexmixturewithoutcompromising onperceived flavor.
Volatilereleasecanberelatedtogelstrength; Franketal.(2015) showeda fl avor intensityincreaseinanagargelwhileitsstrengthattributesdecreased.Therefore,a loweroralprocessingwasrequiredinasoftgelreleasingmorevolatilesandincreasing perceived flavor. MaloneandAppelqvist(2003) showedthatgelledparticlesbasedon starchbreakdownwhenexposedtoamylasecontainedinsaliva,andthisaccelerates thereleaserateofvolatilecompounds,combinedwithfractureproperties.
1.3.2Retentionandreleaseoftastecompounds
Themobilitypropertiesofsmallmoleculesgoverntheirreleaseinthemouthduringthe in-mouthprocesswhenconsumingafood,whetherwithinthesamephaseorduringa transitionbetweenphases.Inthecaseofsodium,themainfactorsaffectingsodium migrationduringthefoodoralprocessingaretheconcentrationgradientofsodium andtheresistancetosodiummigration.Theresistancetosodiumdiffusionisgoverned bythetortuosityandsievingeffectsofthefoodmatrix,whereastheresistancetothe convectivetransportofsodiumisreflectedbythevelocityoftheserum flowduringthe foodmatrixcompression(KuoandLee,2014a,b).Thesetwophenomena,diffusion andconvection,areexacerbatedwithincreasedsurfacearea,asaresultofthematrix fragmentationduringthemastication.
Thereleaseofsaltfromlipoproteinmodelmatricesvaryingincompositionintoartificialsalivawasstudiedbymeasuringapparentdiffusioncoef ficientsofsodiumchloride(Flouryetal.,2009, 2010).Theauthorsreportedthatthevariationofthediffusion coef ficientaccordingtothecheesematrixcompositionwaslinkedtotheirstructural andtexturalproperties.Diffusioncoef ficientsdecreasedstronglywhenthedrymatter contentdecreased.Thiswasexplainedbythelowerproteinconcentrationinthematrix facilitatingthediffusionofthesolutes.Theauthorsalsoobservedthatthediffusion coef ficientincreasedwiththepHatrennetingandwiththeinitialsaltconcentration probablyduetochangesinthestructureandmicrostructureofthematrix.
Theinfluenceofmicrostructureonsodiumreleasewasconfirmedbyastudyon modelsolidlipoproteincolloidsvaryingincompositionandstructure(KuoandLee, 2017).Theauthorsshowedthatsodiumreleasecanbecontrolledviatheconvective transferordiffusivetransfermechanismsbycontrollingtheporosityandparticle sizeoffat,respectively.
1.3.2.1Effectoffoodstructureandtexture
Insemisolidandsolidproducts, flavorcompoundscanbeentrappedeitherinthelipophilicorthehydrophilicphase.Compoundscanbetrappedinahardhydrophilicphase (gel)andthatpreventstheirsolubilitytosaliva.Anincreaseintheirreleasecanbe observedwhenthematrixissoftening,melting,ordissolvingwhichhappensduring chewing(deRoos,2003).
Theimpactofairinclusioningelsonsaltinessandsweetnesswasdemonstratedby Gohetal.(2010).Theseauthorsshowedthatwithhighgelaerationthesaltyandsweet perceptionwasmaintainedwhiletastantconcentrationsweredecreased.Likewise, Chiuetal.(2015) observedsimilarpropertiesonsoftgelinsaltinessperception.Air Retentionandreleaseofaromaandtastecompounds,in
inclusionscreateagreatersurfacearea,consequentlyincreasingthemasstransferof tastanttosalivawhichresultsinhigherperception.
1.3.3Dynamicreleaseanddynamicperception
1.3.3.1Dynamicaromareleaseandperception
Inordertofollowthereleaseofaromacompoundsinthenasalcavityascloseas possibletotheolfactoryreceptors,differenttechnologieshavebeendevelopedusing atmosphericpressurechemicalionizationmassspectrometry(Tayloretal.,2000)or protontransferreactionmassspectrometry(Lindingeretal.,1998).Morerecently thecouplingwithatime-of-flightanalyser(PTR-ToF-MS)guaranteeshighmassresolutionuptothethirddecimal,allowingtoassignaformulatomostmasspeaks (Romanoetal.,2014).
Onlyfewpapersreportedsimultaneouslydynamicreleaseanddynamicperception. Therelationshipbetweenperceivedaromabysensoryscalingandtimeintensity wasstudiedingelatin-sucrosemodelgels(Baeketal.,1999).Byincreasinggelatin concentration,sensory fl avorperceptiondecreasedwithbothmethods;however,no signi ficantdifferenceswereobservedinthemaximumin-nosearomaconcentration, butonlyadecreaseintherateofaromarelease,suggestingthattherateofrelease correlatebetterwithsensoryperceptionthanthetotalamountofaromarelease.
Theeffectofcandytextureandeatingtechnique(meltingorchewing)wasstudied onthedynamicsofinvivoaromareleasefollowedbyPTR-MSandtemporaldominanceofsensations(TDS)usingatrainedpanel(Délérisetal.,2011).Relationships betweenthedynamicsofreleaseandperceptionhavebeenestablishedbetweendominancedurationandtimetoreachmaximalintensity.Similarapproacheswereconductedonfruityogurt(Mesurolleetal.,2013)andEspressocoffee(Barronetal.,2012), highlightingalsothedif ficultyto findclearrelationshipsbetweenthetwoanalyses. Infact,datafromPTR-MSmeasuretheamountofaromareleasedwhereasTDSmeasuresthedominantsensation.Moreover,eachsensoryattributecanbeissuedfrom severalaromacompoundsandeachiondetectedbyPTR-MSmaycomefromdifferent molecules.
Inbiscuits,nosignificantcorrelationwasfoundbetweenanetholeinvivorelease andperception,duetoahigheffectoftexturalpropertieson fl avorperceptionand oftheexistenceofaroma-sweetnessinteractions(Bursegetal.,2009).
1.3.3.2Dynamicreleaseoftastecompoundsandperception
Fewerstudieswerecarriedoutontastecompoundsreleasecomparedtothenumerous studiesreportingkineticsofvolatilecompoundrelease.Duringthein-mouthprocess, tastantsareprogressivelydissolvedinsaliva,whilefoodisbrokendownandtransformedintoabolusunderthecombinedactionofsalivaandchewing(Sallesetal., 2011).Thesephenomenacontrolthedeliveryoftastantstothereceptorslocatedon thetongue,whichisoneofthekeyfactorsdeterminingtheperceivedtasteoffoods. Thesamplingofsalivaatdifferenttimesofmasticationusingadsorbentsorbydirect 14FlavorReleaseinHumans
Retentionandreleaseofaromaandtastecompounds,influenceonperception15
spittingoutofsalivaintubesfollowedbyHPLCanalysisisthemorecommon approachthoughminiconductimetrysensorlocatedinthemouthhasbeenusedfor acontinuousandreal-timemeasureofthechangeinconductivity(Davidsonetal., 1998; Emorineetal.,2012).
Asforvolatilecompounds,thepatternsoftemporaltastecompoundsreleaseand temporaltasteperceptiondependonboththecompositionofthefoodmatrix(foodingredients)andtheoralphysiologycharacteristicsoftheconsumers(Lawrenceetal., 2012a,b; Sallesetal.,2011).
Thetastantsareretainedinfoodthroughphysicochemicalinteractionsandareprogressivelyreleasedinthemouthunderthecombinedactionofmasticationandsaliva. Importantdifferenceswereobservedaccordingtothenatureofthemacromolecules constitutingthefoodmatrix.Thenatureofthenonvolatilecompoundseemslesscriticalsince,foragivensubject,theshapeofthereleasecurveswerefoundsimilarfor mostofthe12compoundstested,theobserveddifferencesbeingdueonlytodifferencesinconcentration(Pionnieretal.,2004).However,asfor flavor,thedirectrelationshipsbetweentastecompoundreleasekineticsandtemporaltasteperceptionare complex.Inmodelcheesestheincreaseoffatcontentwasrelatedtoaglobaldecrease ofsodiumreleaseandanincreaseofsaltinessperception(Phanetal.,2008).However, theseeffectsvariedaccordingtothesaltconcentration(Lawrenceetal.,2012a).Atlow saltconcentration,noeffectoffatwasobservedforsodiumreleasewhilesaltiness perceptionwasmoreintensewhenthefatlevelwaslow.Atmediumsaltconcentration, noeffectwasobserved.Conversely,athighsaltconcentrationthesaltinessperception waslessintensewhenthefatcontentwaslowerwhilesodiumreleasewasthelowestat highfatcontent.
Thewatercontentoffoodalsoinfluencedthereleasedsaltconcentrationandsaltinessperception.Asanexample,incheeseproducts,ahighamountofwaterincreased sodiumreleaseduetoitssolvatingcapacitywhereasalowwatercontentassociatedto ahighsaltconcentrationincreasedsaltinessperception(Jacketal.,1995; P flaumetal., 2013).Thisphenomenonseemstobemainlyobservedatthebeginningofchewing (Phanetal.,2008).Moreover,inmodelcheeses,saltinessperceptionwasrather wellcorrelatedwithsaltreleasedinsalivaandsodiummobility(Boisardetal., 2014).Sucheffectsofwaterwerealsoreportedforbreads(Pflaumetal.,2013). Thestructureandtextureofbreadswerealsoreportedasimportantfactorsforsalt releaseandsaltinessperception(LeBleisetal.,2013; Panouilléetal.,2014; Pfl aum etal.,2013).
Themostrecentworksonthereleaseinthemouthoftastecompoundsandtheir perceptionarefocusedonsaltbecauseofthehealthrecommendationsconsidering thestructuralandmicrostructureaspectsofthefoodmatrix(KuoandLee,2017). Asexample,thestructureofsolidlipoproteincolloid(SLC)gelsobtainedbyheatinducedgelationofemulsionswasstudiedbyultrasmall-angleX-rayscatteringinordertobetterunderstandmechanismsinvolvedinsodiumrelease(Kuoetal.,2016). ThegyrationradiusofthefatglobuleofSLCgelswith3.5%NaClwasfoundnegativelycorrelatedwiththeCmax(themaximumconcentrationofreleasedsodium andtheAUCareaunderthecurveofsodiumreleasevs.timeplot).Anexplanation isthat,atthesametotalfatcontent,smallerfatglobulesimpliedagelnetworkwith
ahighernumberofdispersedfatparticles.Asfatinterferedwiththeproteinnetwork, thehighernumberofdispersedfatparticlescouldleadtoagreaterextentofbreakdown resultinginmoretotalsurfaceareaforthebrokengelsthusfavoringtheenhanced releaseofsodiumfromthegelwhencompressed.Thisphenomenonwasnotobserved atalowerNaClconcentration(1.5%),becauseoflowerforcesininterproteininteraction.Thus,strongerinteractionmadetheinitiationofbreakuponcompressionmore likelytooccurattheprotein-fatinterfacewhichdominatedthebreakdownproperties oftheSLCgelswith3.5%NaCl.Withthesamekindofsolidlipoproteincolloidfoods, thesaltinessperceptionwascorrelatedpositivelywithfracturablebutnotcrumblyattributes.Itwasthuspostulatedthatforthefat-containingSLCs,moderatebreakdown propertywouldfavorsodiumrelease.WhentheSLCbreaksdownrelativelyfast,the crumbledgelparticlesrequirelesschewingwork,andthus,mayleadtolowersodium releaseandsaltinessperception(KuoandLee,2017).Ithasbeenreportedthatoverall sodiummobilitydecreasedwithincreasingproteinandfatlevelsinlipoprotein matrices,influencingsaltinessperception(Boisardetal.,2014; OkadaandLee, 2017).Asanexample,increasingproteinorfatcontentcontributedtoamoreordered environment,contributingtoahigherboundsodiumfraction(OkadaandLee,2017).
1.4Influenceoforalphysiologyoninvivoreleaseand perception
Wheneatingfoods,notonlythefoodcompositionandstructureinfluencein-mouth fl avorrelease,butthefoodmatrixpropertiesandtheoveralloralprocessingareinteractive.Thisinteractionleadstodifferent fl avorreleaseprofilesrefl ectinginterindividualvariabilities.Variousoralparameterssuchasmastication,salivary fl owrate andcomposition,swallowing,oralvolumes,mouthcoating,mucousadhesion,and breathair fl owforvolatilecompoundsmayinfluencetheavailabilityof fl avorcompoundsforreceptorsdifferentlyaccordingtoindividualsandthusinfluence flavor perception.
1.4.1Influenceoforalphysiologyoninvivoaromacompound releaseandperception
Real-timeinvivomethodshavebeenusedextensivelytostudytheimpactofthe compositionand/ortextureofafoodproductonaromareleaseduringchewing (Bolandetal.,2006; Gierczynskietal.,2007; Mestresetal.,2005, 2006).Ageneral tendencyisthathigherhardnessinducedagreaterchewingactivityassociatedwith highersalivation,leadingtoagreaterexchangeareaandahigheramountofaroma released(Gierczynskietal.,2007).Anadditionofsaltinmodelcheesesinduceda greatersalivation,anincreaseinthenumberofswallowingeventsandchewingdurationwhichincreasedthetotalamountofreleaseofhydrophobicaromacompoundsin thenasalcavity(Boisardetal.,2013).
Retentionandreleaseofaromaandtastecompounds,influenceonperception17
Howeverdifferentbehaviorswereobservedbetweensubjectsexplainedby differentchewingstrategies(Yvenetal.,2012).Therelationshipsbetweenoralphysiology(respiration,salivation,mastication .)andaromareleasehavebeenstudied forsubjectsconsumingdifferentfoods(Gierczynskietal.,2008; Pionnieretal.,2004; Repouxetal.,2012).Subjectswithahighamountofaromareleasehadalsohigh valuesofrespiratoryrate,numberofchews,andmuscleactivity(Pionnieretal., 2004).Agreaterrespiratoryratecontributedtobringingmorevolatilestotheupper airways,andconsequentlymorevolatileswerepresentintheexpiredairofthesubjects.Ahighmuscleactivityinducedabetterdegradationofthebolus.Consequently, thefoodsurfaceincontactwiththevaporphaseincreasedandthusthetransferof aromacompoundsfromthematrixtothevaporphasewashigher.AstatisticalmultiblockPLSapproachwassuccessfullyusedtobetterunderstandtherelativeimpactsof differentphysiologicalparametersonaromarelease(Feronetal.,2014).Themain impactofmasticatorybehaviorwasobservedbutothersignifi canteffectscouldbe highlighted.Bolusrheologymainlyinfluencedaromareleasefrom firmercheeses. Thepersistenceofaromareleaseinthebreathwasmainlyexplainedbyhigherbolus spreadabilityandbolusmoistening,whichresultedinahigheramountofproduct remaininginthemouth.Thecompositionofstimulatedsalivainfluencedtheamount ofaromarelease,withalowerreleaseforsubjectswithahigheramountofsalivary proteins.
1.4.2Influenceoforalphysiologyoninvivotastecompound releaseandperception
Thecompositionofthefoodmatrixindirectlyinfluencestastecompoundreleaseby changesintheirtexturalpropertiesinducingchangesinthephysiologicalbehavior ofindividualsduringeating.Asalreadymentioned,hardfoodproductsgenerally requestedahigherchewingtime.Duringthecomplexfoodoralprocessing,thephysicochemicalpropertiesofthefoodaremodifi edandtheperceptionof flavorandtexture isaffected.Fragmentationincreasedthesurfaceexposedtosalivaandthusfacilitated thedissolutionoftastecompoundsinsalivaandinfluencedtasteperceptionwhilethe bolusisprogressivelybuiltfromfoodparticlesandsaliva.Themasticationpatternand salivacharacteristicsmayvaryconsiderablybetweenindividuals.Thesephysiological variationsareanimportantsourceofinter-individualvariabilityfortemporaltaste releaseandperception.Asanexample,inmodelcheeses,animportantreleaserate ofsodiumwascorrelatedwithahighsalivary flowrate,andimportantbiteforce andchewingworkwhilesalivary fl owrateandchewingefficiencyinfluencedthe speedofperception,notthesaltinessintensity(Phanetal.,2008).Moregenerally, ithasbeenreportedthatsodiumreleasewasratherrelatedtomechanicalchewingactivitywhilesaltinesstemporalperceptionwasratherrelatedtothesalivary flowrate (Lawrenceetal.,2012b).
Evenifmasticationandsalivarypropertiesarethemajortwooralparametersrelated totastecompoundreleaseinmouth,otherphysiologicalparameterswereshowntoinfluencetastereleaseandperception.Somecommonfoodmacromoleculessuchas
polysaccharideshavemucoadhesivepropertieswhichmayinfluencethedeliveryof activecomponents(Cooketal.,2017),andthuscontributetomodulatetheorganolepticpropertiesoffoodbyretainingtasteoraromamolecules.Asanexample, somepolysaccharides,commoninfoodcomposition,werefoundtoinfl uencesalt releaseintheoralcavityduringeating.Themucoadhesivepropertiesofcarboxymethylcellulosecanmodifyretention,release,andperceptionofsodiumovertime. Thisexplainstheretentionofsodiumionsinthemouthbeingprolongedduetothe mucoadhesivenatureofthepolysaccharide(Cooketal.,2018b).Therefore,the perceptionoftheretainedsodiumwasdiminishedduetotheanioneffect.Itwasreportedalsothat,moregenerally,theperceptionoftastantsandaromaovertimecan changedependingonthemucoadhesivepolysaccharideused(Cooketal.,2018a).
1.5Simulationoforalprocessingusingdifferentdevices
Sensoryperceptionof flavorreleaseduringeatingishighlydependentuponmouthparameters.Majorlimitationshavebeenreportedduringinvivo flavorreleasestudies, suchasmarkedintra-andinterindividualvariability.Toovercometheselimitations, someartificialdeviceshavebeendevelopedtomimicthehumanmasticationof foodsamples.Althoughtherearemanydevicesdedicatedtothesimulationofchewing,inthispartwewillfocusonthoseallowingthesimulationof flavorreleaseinoral conditions.
Oneofthesimplestartifi cialmouthswasdevelopedby vanRuthandRoozen (2000) andconsistedofajacketedreactorequippedwithaplungerthatperforms simultaneousverticalandrotationalmovementstosimulatecompressionandshearing simulatingchewingmovements.Thisarti ficialmouthwastestedonseveralmodeland realfoodstomimicthereleaseofkeyaromacompounds,showingagoodsimilarity withinvivodata.Thereactordevelopedby Rabeetal.(2002) allowedtocontrolsaliva andair flowsandwassuccessfullyusedforliquidmodelsystemsandbeverages(Rabe etal.,2004).TheRetronasalAromaSimulator(RobertsandAcree,1995)witharelativelyhighvolume(1L)allowedforaprecisecontrolofshearrateandwassuccessivelyusedtofollowaromareleasefromdifferentproducts(orangejuice,chocolate, icecream,andcookies)incomparisonwithinvivorelease(Deibleretal.,2001).
However,themodelsdescribedabovepoorlyrepresentedalimitednumberoforal functionswhicharefarfromanactualoralenvironment.
Theartificialmouthdevelopedby Sallesetal.(2007) reproducedmostofthefunctionsofthehumanmouth.Theactivecellcomprisesseveralmobilepartsthatcanaccuratelyreproduceshearandcompressionstrengthsandtonguefunctionsinreal-time, accordingtodatapreviouslycollectedinvivo.Themechanicalfunctionalitiesofthe systemwerevalidatedusingpeanuts,withafairdegreeofconsistencywiththehuman data.FlavorreleasecanbemonitoredonlineusingeitherAPCI-MSorchemicalsensors,orofflineusingHPLCfornonvolatilecompounds(Mielleetal.,2010).Thisdevicethushastheadvantageofallowinginvitrostudiesunderoralconditionson flavor releaseandbolusformationfromsolidmatrices.Flavoredlipoproteinmatricesvarying 18FlavorReleaseinHumans
Retentionandreleaseofaromaandtastecompounds,influenceonperception19
infatcontentwerechewedusingthisdevicewhereeachoralparameterwascontrolled anddecoupled.Eachcontrolledoralparameterhadsigni ficantlydifferentinfluenceson thereleaseofaromacompoundsaccordingtotheirphysicochemicalcharacteristics.In particular,itwasreportedthatbitingandshearingforcesinfluenceddifferentlythe releaseofaromacompoundsaccordingtotheircharacteristics.Thesalivary flow rateprimarilyinfluencedthemorehydrophobiccompounds.Moreover,signi ficantinteractionswerealsoobservedbetweenshearangle,salivary fl owrate,andfatcontent, accordingtothephysicochemicalpropertiesofthevolatilecompounds(Tarregaetal., 2019).
Therelationshipsbetweenthepropertiesofextrudedpea-basedsnackbolusesand themultiscalestructureofsaidfoodswereinvitrodeterminedusingthesamedevice, allowingcontrolofthe flowrateofarti ficialsalivary fluidandchewingtime(Kristiawanetal.,2021).Thestructureoftheextrudedpeasnackswascharacterizedbytheir densityandproteinsolubilityindithioerythritol,whichrefl ectedtheamountofprotein aggregatescross-linkedbydisul fidebonds.Thus,aphenomenologicalmodeloforal breakdownofextrudedpeasnackswasestablishedbylinkingtheevolutionofsalivary absorptioncapacityandthatofconsistencyofbolusinfunctionofthesnackdensity andthequantityofdisulfi debondsproteinaggregatescreatedduringtheextrusionprocess.Theuseoftheartificialchewerallowedcontrolofthemainmechanismspertainingtotheformationofextrudedpea flourboluses:fragmentationandsaliva absorption.Betweenthesetwomechanisms,salivaabsorptiongovernedtheevolution ofbolusshearviscosity,whichisanessentialpropertyforfoodswallowingandfor consumeracceptability.Thus,suchaninvitroapproach,extendedtoinvitro fl avor release,couldbeappliedtoalargerangeofsolidfoods,formodelingfoodoralprocessingphenomenaandusedforreverseengineeringtodesignfoodswithatargeted structure.
Thetongueplaysacrucialrolethroughoutfoodoralprocessing,inparticular,transportingfoodtothemolarorcheekteeth,compressingorsqueezingfoodagainstthe hardpalate,mixingfoodparticleswithsaliva,andtransportingbolustothepharynx. Itplaysamajorroleinfoodoralprocessingand flavorreleaseforsoftorsemisolid foods,whicharenotchewed.Verysimpleartificialtonguesweredesignedusing softpolymerssuchassiliconerubber(Ishiharaetal.,2014)orsonagel(Gaoetal., 2014).Theyweremainlyusedtosimulatetonguecompressionofgels,betweena softmaterialandahardplatetostudygelfracture(Kohyamaetal.,2019).
Theeffectsoftonguepressureandmasticationonthereleaseofvolatilecompounds inthemouthwereevaluatedusingamodelmouthwithanartifi cialtongue(Benjamin etal.,2012).Arangeoftongueintraoralpressureswasappliedforvariousperiods whilemonitoringthereleasedvolatilecompoundsonlineusingaprotontransferreactionmassspectrometer.Aclearpeakwasobservedaftereachcycle,followinga differentpatternaccordingtothephysicochemicalpropertiesofthevolatilecompoundsandthemechanicalparametersappliedtothearti ficialtongue.
Anotheroralfunctionthathasbeententativelysimulatedisswallowing.Tosimulatethedynamicconditionsofvolatilecompoundreleasefromliquidfoodsafterswallowing,amodelartifi cialthroatwasdesigned(Weeletal.,2004).However,thissimple modelsystemcannotfullysimulatetheeventsthatoccurinthehumanthroatasthe
invitrovolatilecompoundreleasepatternwasfoundmuchlowerthanthatobserved invivo.Later,apharyngealperistalsissimulatorwasdevelopedandenabledtodemonstratethatduringswallowing,thethicknessandthecomposition(rateofdilution)of boluscoatingsmaybehighlyinfluencedbothbytherheologicalpropertiesofthebolus andbythephysiologicalpropertiesofthepharyngealmucousmembrane(Mathieu etal.,2018).Thisisaveryinterestingmodeltostudythemechanicalinteractionsbetweenthefoodbolusandthelubricatedanddeformablepharyngealmucousmembranes.However,no flavorreleaseexperimentswereconductedwiththisdeviceyet.
1.6Conclusion
Inconclusion, flavormoleculesbelongtodifferentchemicalclassesandpossess varioussensoryproperties.Theyarepresentinthefoods,butinordertoreachthesensoryreceptorstheyhavetobereleasedinthesalivaduringtheeatingprocessandfor aromacompoundsintheairphasefromtheoraltothenasalcavity.In-mouth fl avor compoundreleaseand flavorperceptionareverycomplexphenomena,whichare notwellunderstoodyet.Thepropertiesofthefoodmatrixandoralphysiologicalcharacteristicsandtheirinteractionsarethemaindriversforinter-individualvariability. Thedevelopmentofmechanisticmodelsallowedabetterunderstandingoftherelease ofaromaandtastecompoundsduringtheeatingprocess.However,therelease behaviordoesnotalwaysexplainsensoryperception,duetootherphysiologicalmechanismsatthecentralandperipherallevels.Theseaspectswillbedescribedindetailin thefollowingchapters.
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