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Humulus lupulus L. as a Natural Source of Functional Biomolecules

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  • Centro Tecnológico de la Carne

Abstract and Figures

Hops (Humulus lupulus L.) are used traditionally in the brewing industry to confer bitterness, aroma, and flavor to beer. However, in recent years, it has been reported that female inflorescences contain a huge variety of bioactive compounds. Due to the growing interest of the consumers by natural ingredients, intense research has been carried out in the last years to find new sources of functional molecules. This review collects the works about the bioactive potential of hops with applications in the food, pharmaceutical, or cosmetic industries. Moreover, an overview of the main extraction technologies to recover biomolecules from hops is shown. Bioactivities of hop extracts such as antibacterial, antifungal, cardioprotective, antioxidant, anti-inflammatory, anticarcinogenic, and antiviral are also summarized. It can be concluded that hops present a high potential of bioactive ingredients with high quality that can be used as preservative agents in fresh foods, extending their shelf life, and they can be incorporated in cosmetic formulation for skincare as well.
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Appl.Sci.2020,10,5074;doi:10.3390/app10155074www.mdpi.com/journal/applsci
Review
HumuluslupulusL.asaNaturalSource
ofFunctionalBiomolecules
GonzaloAstray
1
,PatriciaGullón
2
,BeatrizGullón
3
,PauloE.S.Munekata
4
andJoséM.Lorenzo
4,5,
*
1
DepartmentofPhysicalChemistry,FacultyofScience,UniversityofVigo(CampusOurense),AsLagoas,
32004Ourense,Spain;gastray@uvigo.es
2
NutritionandBromatologyGroup,DepartmentofAnalyticalandFoodChemistry,FacultyofFoodScience
andTechnology,UniversityofVigo,OurenseCampus,32004Ourense,Spain;pgullon@uvigo.es
3
DepartmentofChemicalEngineering,FacultyofScience,UniversityofVigo(CampusOurense),AsLagoas,
32004Ourense,Spain;bgullon@uvigo.es
4
CentroTecnológicodelaCarnedeGalicia,RúaGalicia4,ParqueTecnológicodeGalicia,SanCibraodasViñas,
32900Ourense,Spain;paulosichetti@ceteca.net
5
ÁreadeTecnologíadelosAlimentos,FacultaddeCienciasdeOurense,UniversidaddeVigo,
32004Ourense,Spain
*Correspondence:jmlorenzo@ceteca.net
Received:30June2020;Accepted:21July2020;Published:23July2020
Abstract:Hops(HumuluslupulusL.)areusedtraditionallyinthebrewingindustrytoconfer
bitterness,aroma,andflavortobeer.However,inrecentyears,ithasbeenreportedthatfemale
inflorescencescontainahugevarietyofbioactivecompounds.Duetothegrowinginterestofthe
consumersbynaturalingredients,intenseresearchhasbeencarriedoutinthelastyearstofindnew
sourcesoffunctionalmolecules.Thisreviewcollectstheworksaboutthebioactivepotentialofhops
withapplicationsinthefood,pharmaceutical,orcosmeticindustries.Moreover,anoverviewofthe
mainextractiontechnologiestorecoverbiomoleculesfromhopsisshown.Bioactivitiesofhop
extractssuchasantibacterial,antifungal,cardioprotective,antioxidant,antiinflammatory,
anticarcinogenic,andantiviralarealsosummarized.Itcanbeconcludedthathopspresentahigh
potentialofbioactiveingredientswithhighqualitythatcanbeusedaspreservativeagentsinfresh
foods,extendingtheirshelflife,andtheycanbeincorporatedincosmeticformulationforskincare
aswell.
Keywords:hop;emergingextractiontechnologies;bioactivities;functionalmolecules
1.Introduction
Thecommonhopplant(HumuluslupulusL.)isahardyanddioeciousvinewhoseaerialpartis
herbaceousandannual,whiletherootstockisperennial,anditcancreateadventitiousrootsevery
year[1].ItisaspeciesofthegenusHumulusthatbelongstotheCannabaceaefamilywhosegenus
origincouldbeChina[2].ItcanbefoundprincipallyinEuropeanandinWesternAsiadeciduous
forestsandthickets,andinotherzoneareaswithatemperateclimate[3].Hopswerecultivatedin
Babylonaround200A.D.[4],andtheyhavebeeninongoinguseforcenturies(evenamillennium)
mainlyasabeeringredient[5].IntheEuropeanUnion,themainproducerisGermany,registering
for2018aproductionof41,792tonsforatotalof57,239tonsfromthememberstates[6].Thehop
conesarethemostutilizedportionofthisplant[2];nevertheless,therearepartssuchastheyoung
shootsorasparagusthatcanbeeatenindifferentMediterraneancountries[7].
Inthelastdecades,thebiologicalbenefitsofplants,traditionallyusedinfolkand/ortraditional
medicine,havebeenexploredbythescientificworld[5,8].Inthissense,besidestheiruseinthe
Appl.Sci.2020,10,50742of18
brewingindustry,traditionallyhopconeshavebeenappliedwithmedicalpurposesforthecontrol
ofthespasms,anxiety,fever,inflammation,activationofthegastricfunction,andthetreatmentof
sleepingdisorders,amongothers[2,9].Indeed,hopspresentnumerousbenefitsforhumanhealth
duetotheirantibacterial,antifungal,cardioprotective,antioxidant,antiinflammatory,
anticarcinogenic,andantiviralbioactivities[2,5,9–13].
Thefemaleinflorescences(calledhopconesorsimplyhops)aswellasotherpartsoftheplant
(leaves,stems,andrhizomes)arerichindifferentbiologicallyactivemoleculesaspolyphenolic
compoundsandacylphloroglucides,whichareresponsibleforthedifferenthealthpromotingeffects
andbioactivities[3,9].Thelupulinglands,whichpresentayellowgreencolor,arelocatedonthehop
umbel(intheinnerandouterbracteoles)andcontainbitterresinsandaromasubstances[1].The
secondarymetabolitesofthefemaleinflorescences(presentedinthelupulinglands)canbedivided
intothreegroups:(1)thehopresins,(2)thehopoil,and(3)thehoppolyphenols[14].Thelevelsof
thearomaticessentialoilandthebitterhopαandβacidsdependonseveralfactorssuchasthe
varietyorripeningstageandevenonclimatologicalconditions[15].Themainuseofhops
worldwide,around97%,isusedforbrewingpurposes[16]toaddbitterness,aroma,andtastetothe
beer.
Takingtheaboveintoaccount,andthecurrenttrendofsearchingnaturalcompoundswithnovel
biologicalproperties,thewealthofthehopinbioactivecompoundsmakesitanexcellentsourceto
extractbiologicallyactivemoleculeswithmultipleapplicationsinthealimentary,pharmaceutical,
andnutraceuticalindustries[12,15,17–20].Thishaspromotedintenseresearchinthefieldofbioactive
compoundsfromhopsthatallowsontheonehandachievinghighyieldsandontheotherhand
keepingthebioactivitiesoftheextractedcompounds.Forthis,theselectionofadequateextraction
technologyaswellastheappropriatesolventisfundamental.
Inthiscontext,manypublicationsrelatedtotheisolationoftheactivecompoundshavebeen
developedoverthepastdecades[5].Severalisolationtechnologiesarewellestablishedusing
conventional(organic)solvents[5,21];nevertheless,theirresiduallevelsmustbecontrolled[21],
becausetheycanremaininthefinalproductandhavedetrimentalhealtheffects[5].Accordingto
Marriott[21],EUlegislationandorganiccertificationbodiesestablishtheallowedextractionsolvents,
theirmaximumresiduelevels,andfurtherrestrictions,respectively.Toovercometheshortcomings
oftheconventionalsolvents[22],ecofriendlysolventssuchasnaturaldeepeutecticonesrepresenta
saferalternative,andtheirusehasincreasedinthelastdecades[23].Moreover,theuseofemerging
technologiessuchas(1)ultrasoundassistedextraction(UAE),(2)microwaveassistedextraction
(MAE),(3)pressurizedliquidextraction(PLE),and/or(4)supercriticalfluidextraction(SFE)has
increasedinthelastdecade[24–28].Theseapproachesopennewalternativesinthedesignofthe
extractionprocessofmoreefficientofbiocompoundsfromnaturalbiomasswithintheframeworkof
GreenChemistry[23].
Inlightoftheaboveandencouragedbythegrowinginterestinhopsduetotheirsignificant
potentialasasourceofbioactivecompounds,thisreviewcollectsthestudiesabouttheuseofhops
asanaturalsourceofthesebiocompounds.Aspectsrelatedtothedifferentcurrentextraction
methodsappliedintherecoveryofphytochemicalsfromhopaswellastheevaluationoftheir
differentbioactivitiesarereviewed.Moreover,theapplicationsofthesecompoundsindifferentfields
suchaspharmaceutical,nutraceutical,andcosmeticarealsosummarized.
2.MainComponents
Thehopconeshavedifferentcomponents,suchas(1)resins,(2)essentialoils,(3)proteins,and
(4)polyphenols,amongothers[16,29,30].Theclassificationofhopconecompoundsisshownin
Figure1.Someofthesephytochemicalsarebrieflydescribednext.
Appl.Sci.2020,10,50743of18
Figure1.Abriefclassificationofhopsconecompoundsbasedonthereviewedliterature[16,29,31–
36].
2.1.HopResin
Theresinsarehopplantsecondarymetabolitesthatcanbesolubilizedincoldmethanoland
diethylether[14,16].Thetotalresinscanbedividedintotwokinds:softandhardresins[1,14,16,37],
andtheyarecharacterizedbytheirsolubilityandinsolubilityinhexane,respectively[14,16].
AccordingtoAlmagueretal.[16],thesoftresincontentinwholehopconesishighcomparedtothe
hardresin;infact,softresinsrangewithin10–25%,whilethehardresinscomprisebetween3%and
5%ofthetotalweightofdriedhops.Thesoftresinsareformedbytwodifferentbitteracids:α‐acids
(between3%and17%)andβ‐acids(between2%and7%)[1].Thereisathirdgroup,uncharacterized
components,thattogetherwithβ‐acidsformtheβ‐fraction[16,38].Theαacidshavefivecomponents:
humulone,cohumulone,adhumulone,prehumulone,andposthumulone[1,15].Thefirstthreeare
themajority,andtheprehumuloneandposthumulonearetheminority[15].Inthesameway,β‐acid
hasanotherfivehomologs(lupulones)[1,15].Dependingonthehopvariety,cultivationconditions,
andclimate,thecontentofthesesubstanceshomologsmayvarygreatly[5].Moreover,thehopresins
couldsufferfromdifferentchangesinthestoragewiththeoxidationstartoftheα‐acidsandβ‐acids;
duetothisprocess,theseacidswoulddecreaseduringthestorage[16].Itiscommonlyacceptedthat
hardresinscanfromtheoxidationofthesoftresins(althoughitisnotyetwelldefined)[16].During
thetraditionalbrewingprocess,rawhopsareaddedtotheboilingwort,andα‐acidsareisomerized
toiso‐α‐acids[15],whicharethemaincompoundsresponsibleforthebittertasteofbeer[15,39].
2.2.HopOil
Essentialoilsaresecondarymetabolitesexudedinthelupulinglands[14,16],andtheyarecalled
essentialsbecausetheyprovidethehopswiththeirdistinctivesmellandtransfertheiraromaand
flavortobeer[16].Essentialoilsaccountfor0.5–3%ofthedriedhops,withover400different
compoundsidentifiedinthehopoilfraction[16].Theircomponentswouldbedividedintothree
hugegroups:(1)hydrocarbons,(2)oxygenated,and(3)sulfur[5,16].Accordingtothebibliography
compiledbyAlmagueretal.[16],differentfamiliesofmoleculessuchasaliphatic,monoterpenes,
andsesquiterpenesarepresentinthefirstgroup,thesecondgroupcontainsalcohols,aldehydes,
acids,andesters,amongothers,andfinally,thesulfurgroupisconstitutedbythioestersandcyclic
terpenoidsulfides,amongothers.
Appl.Sci.2020,10,50744of18
Thehydrocarbonfractionisthemostabundant(between50%and80%oftotaloil)andthemost
abundantcompoundsfromthisfractionaremonoterpenesα‐andβpineneandmyrcene,among
others[12].Accordingtotheauthors[12],theoxygenatedfractionrepresents30%ofthetotaloil,
beingacomplexmixtureofdifferentcompoundssuchasaldehydesorketones,amongothers.The
maincompoundsstudiedfromthisfractionarelinaloolorgeraniol,amongothers[12].Thesulfur
fractionispresentinsmallquantitiesintheessentialoilofhops(upto1%).Thesecompoundshave
potentaromasandlowodorthresholds,sotheyplayakeyroleintheoverallflavorofbeer[12,16].
2.3.HopPolyphenols
Polyphenolsareawidegroupofbiologicallyactivesecondarymetabolites[14,16]whosecontent
andprofiledependonthehopvarietyaswellasthedifferentclimaticconditionsofcultivation[3,16].
Theconebractpresentsthegreatestcontentofpolyphenolsinthehopplant,andtheircontentinthe
conecanfluctuatebetween4%and14%(drymatter)[40].Thehoppolyphenolscanbegroupedinto
(1)flavonols,(2)flavan3ols,(3)phenoliccarboxylicacids,and(4)otherpolyphenoliccompounds
[16,36].Themostabundantflavonols,accordingtoitscontent,arequercetinandkaempferol,and
amongthedominantflavan3ols,(+)catechin,()epicatechin,and(+)gallocatechinstandout,as
wellastheirpolymersproanthocyanidinsandcondensedtannins[12,16].Ferulicacidisthemost
representativecompoundofthegroupofphenoliccarboxylicacids[12,16].Otherphenolic
compoundsthatareuniquetohopinflorescencesaremultifidolglucosides(phloroglucinol
derivativeswithprenylsidechains)andprenylflavonoids(xanthohumol,isoxanthohumol,
desmethylxanthohumol,and6‐ and8prenylnaringenin)[5,12].Numerouseffortshavebeen
developedtoproducehopextractswithhighpolyphenoliccontentduetotheirpossibleuseasnatural
additives(antioxidantand/orantimicrobial)inindustrialapplications[5].
3.ExtractionTechniques
Theextractionefficiencyoftheplethoraofphytochemicalsthatcanbeobtainedfromhopsis
highlydependentontheextractiontechnologyapplied.Thesemethodsmustbefast,versatile,easy
touse,environmentallyfriendly,costeffective,andbeabletobothextractwithhighyieldsandkeep
thequalityofthetargetcompounds[28].Theextractiontechniquesusedfortherecoveryofbioactive
compoundsrangefrom(1)theconventionalmethodstoinnovativetechnologiessuchas(2)
ultrasoundassistedextraction,(3)microwaveassistedextraction,(4)pressurizedliquidextraction,
and(5)supercriticalfluidextraction,includingtheuseofgreensolventsasdeepeutecticsolvents
(DES).
3.1.ConventionalMethods
Solid–liquidextraction(SLE)andsteamdistillationhavebeenappliedforextractingbioactive
compoundsfromhops.Forthispurpose,severalorganicsolventssuchasethanol,methanol,
methylenechloride,ethylacetate,acetone,hexane,andtheirmixtureswithwaterhavebeenused.
Theextractionefficiencyisgreatlyaffectedbythetypeandpolarityofthesolvent,theexperimental
conditionsoftimeandtemperature,andtheextractionnumberofcycles[41].Severalphytochemicals
havebeenextractedfromhopsusingconventionalmethods.Forinstance,hydrodistillationwas
appliedtoextractessentialoilsfromtheconepowder,obtainingayieldof6.3mL/kgofdrycones
[10].Usinggaschromatographycoupledtomassspectrometry(GCMS/MS),theauthorsidentified
thepresenceof16compounds,ofwhichmyrcene,transcaryophyllene,andα‐humulenewerethe
threemaincomponentsofhopsessentialoil[10].Inanotherstudy,Jeliazkovaetal.[42]evaluatedthe
yieldandcompoundprofileofessentialoilextractedfromwholehopconesviasteamdistillation
usingasequentialelution.Theresultsindicatedthat83.2%oftheoilwasextractedduringthefirst
hour,incomparisonwithcontrolperformedduring4hnoninterrupteddistillation[42].
Furthermore,theprofileofelutedcompoundswasalsosignificantlydifferent,observingthat
monoterpeneswereelutedbeforesesquiterpenes.
Appl.Sci.2020,10,50745of18
Theeffectoffourorganicsolventswithdifferentpolarities(ethylenechloride,acetone,ethyl
acetate,andmethanol)ontherecoveryofflavonoidsfromspenthopswasstudiedbyBartmańskaet
al.[43].Accordingtotheirresults,theincreaseofpolarityoftheextractantimprovedtheefficacyof
extraction,obtainingthehighestyieldwithmethanol(92.95g/kg).Theauthorsfoundthatthemost
abundantextractcompoundwasxanthohumol,andtheyindicatedthatthehighestefficiencyand
selectivitytorecoverthiscompoundfromspenthopswasethylacetate(3.51g/kg)andthesolvent,
whichledtothelowestextractionyieldbeingmethylenechloride(1.33g/kg)[43].Inhydroalcoholic
extractsobtainedbymacerationfromhopcones,twomaingroupsofcompoundswereidentifiedby
reversephaseHPLCUV:prenylatedchalconesandacylphloroglucinolderivatives[10].
Prencipeetal.[44]indicatedthatthedynamicmacerationofhopswithMeOH–HCOOH(99:1,
v/v)ledtothebestresultintermsofhopcomponentsrecovery,specificallyprenylflavonoidsand
bitteracids,incomparisonwithothermethodsincludingheatrefluxextraction,microwave,or
ultrasound.
Althoughtheapplicationoforganicsolventsiswidespreadinindustrialextractionprocesses,
theiremploymentpresentssomeinconveniencesrelatedtohealthriskandenvironmentalpollution,
limitingtheiruseintherecoveryofbioactivecompounds[27].Duetothis,anewmethodofsolvents
generationknownasdeepeutecticsolvents(DESs)hasbeenappliedinthelastdecadeasapromising
greenalternativesubstitutionforconventionalorganicsolventsintherecoveryofbiomolecules[27].
Inthisline,Lakkaetal.[23]testedtheabilityofaeutecticmixturecomposedofglycerolandLalanine
toextractpolyphenolsfromhops.Inthisstudy,theauthorsappliedaresponsesurfacemethodology
(RSM)basedonaBox–Behnkendesignfortheoptimizationofprocessparameters(DES
concentrationinaqueousmixtures(CDES:55–85%w/w),liquidtosolidratio(LSR:20–60mL/g),and
speedofstirring(SS:200–800rpm)).Undertheoptimizedextractionconditions(CDES=85%(w/w),
LSR=59mL/gandSS=688rpm),atheoreticallyoptimalyieldoftotalpolyphenolsof118.97mggallic
acidequivalents(GAE)/gdmwasobtained[23].
3.2.EmergingExtractionTechnologies
Theefficientrecoveryofvaluablecompoundsfromdifferentbioresourceslargelydependson
thetechnologyusedfortheirextraction.Conventionalextractionmethodspresentvarious
disadvantagesassociatedwiththehighconsumptionofsolvents,prolongedextractiontimes,and
degradationofthermosensitivebiomolecules.Toavoidoperationalhazardsandthepresenceof
harmfulsolventtracesintheextractmaterial,novelalternativeextractiontechniqueshavebeen
exploredtomeetthedemandofgreenerprocessestoextractandfractionatethedifferenthop
valuablecomponents(eventovalorizethehopexhaustedsolid)[15].
3.2.1.UltrasoundAssistedExtraction(UAE)
Ultrasoundhasbeenidentifiedforitspotentialuseinthephytopharmaceuticalextraction
industry[45].TheUAEsystemisanuncomplicated,economical,andefficientalternativetothe
extractionmethodsusedtraditionallythatcanimproveextractionyield,extractionrates,orthe
recoveryofheatsensitivecompounds[46].Thiskindoftechniqueuseshighfrequencywavesthat
promotetheformationofbubblesinthemedium,leadingtotheformationofthecavitation
phenomenon[47].Theimplosionofthesebubblesdisruptsthecellularstructureandfacilitatesthe
diffusionofthesolventintothecellularplanttissue,whichincreasesmasstransferandconsequently
improvestheextraction[47].TheefficiencyoftheUAEisinfluencedbyvariousoperatingparameters
suchasthetypeandconcentrationofthesolvent,sonicationtime,temperature,LSR,ultrasonic
power,andfrequency,whichmustbeoptimizedtoreachhighextractionyields[48].Togivean
example,Almeidaetal.[49]appliedaCentralCompositeRotationalDesign(CCRD)tooptimizethe
recoveryofphytochemicalswithantioxidantcapacityfromBrazilianhops.Theauthorsevaluatedthe
effectofthreeextractionparameters:temperature(33–67°C),EtOHconcentration(43–77%),andLSR
(17–33mL/g)onthetotalphenoliccontent(TPC).Accordingtotheresultsofregressionanalysis,the
LSRwastheparameterthatshowedagreaterinfluenceonTPCoftheextracts,whilethetemperature
andtheconcentrationofethanolhadalessereffect.Underoptimizedextractionconditions(52°C,
Appl.Sci.2020,10,50746of18
49%ethylicalcoholandLSRof34mL/g),aTPCof33.93mgGAE/gforBrazilianhopswasobtained.
Moreover,theauthorscomparedBrazilianhopextractswiththoseobtainedwiththesamevarietyof
hopsgrownintheUSA.TheresultsshowedthattheBrazilianhopsshowedahighercontentof
phenolsandflavonoidsandbetterantioxidantpotentialanalyzedbytheABTS(2,2’azinodi(3
ethylbenzothiazoline6suslfonicacid)andDPPH(α,α‐Diphenylpicrylhydrazyl)testscomparedto
theUSAhops.
Inanotherstudy,theUAEhasbeenappliedwithsuccessfortheextractionofdiversetypesof
biocompoundsfromhops.Forexample,Muzykiewiczetal.[3]usedthistechniquewithdifferent
extractants(methyl,ethyl,andisopropylalcohol)underthreedifferentconcentrationstoassessthe
totalphenoliccontentandtheantioxidantactivity.Thisresearchwascarriedoutusingfreshhop
leavesfromdifferentharvestedyears(2017and2018).Processparameterswerefixedat40kHz
duringdifferenttimes(15,30,and60min)atroomtemperatureandunderdifferentsolvent
concentrations(40%,70%and96–99.5%(v/v)).Theauthorsreportedthattheextracts(fromyoung
hopleavesharvestedatthestartingvegetation)presentedahighantioxidantactivity,andthis
antioxidantpotentialwasinfluencedbydifferentfactors(includingthesolventtypeorextraction
time)andconcludedthatthemosteffectiveprocesswasusingundilutedmethanolduringonehour
ofultrasoundassistedextraction.Theantioxidantscontentdependsontheharvestingtimeandcan
bealsoinfluencedbyclimaticconditions,amongotherenvironmentalelements[3].
3.2.2.MicrowaveAssistedExtraction(MAE)
Inthelastdecade,theuseofmicrowaveassistedextraction(MAE)torecoveractivemolecules
fromseveralnaturalsources,includinghops,hasalsobeenaddressed.Thisextractiontechniqueis
basedontheapplicationofmicrowaveenergy,whichisconvertedintoheatmainlythroughtwo
mechanisms,whichareionicconductionanddipolerotation[48].Thisprocessincreasesthepressure
andtemperatureinsidethecellmatrix,whichcausestheruptureofthecellstructure,improvingthe
releaseofthedesiredcompounds.MAEhasbeenrecognizedasapromisinggreentechniqueover
conventionalextractionmethodssinceitpresentsvariousadvantages,including(1)shorterextraction
time,(2)minorenergyinput,(3)decreasedsolventconsumption,(4)easeofoperation,and(5)a
minimumdegradationofbioactivecompounds[28,48].
Tyśkiewiczetal.[50]exploredtheuseofmicrowaveassistedhydrodistillation(MAHD)to
extractessentialoilsfromhopsscCO2(sc:supercritical)extract,andtheresultswerecomparedwith
thoseobtainedusingconventionalhydrodistillation(HD).Underoptimizedconditions(335W
microwavepoweratLSRof8:3),MAHDyielded3.77%ofessentialoilsinanextractiontimeof30
min,whilewithconventionalHD,only1.90%wasreachedusingalongertime(276min).Theresults
ofquantitativeanalysesofmyrceneandαhumuleneoftheobtainedoilbyMAHDwere77.36%
and9.47%,respectively.
3.2.3.PressurizedMethods
Anotherinterestingtechniqueisthepressurizedliquidextraction(PLE),whichisalsonamed
acceleratedsolventextraction(ASE)orpressurizedhotwaterextraction(PHWE)whenwaterisused
[51];also,pressurizedsolventextraction(PSE)presentsimportantbenefitscomparedtoconventional
extractions[52].
Formatoetal.[53]studiedtheefficiencyofcyclicallypressurizedsolid–liquidextractionusinga
NaviglioExtractorfortherecoveryofacidiccompoundsfromhopsflowersincomparisonwith
supercriticalfluidextraction(SFE).Theresultsshowedthatthecyclicallypressurizedsolid–liquid
extractionwasmoreeffectivefortheextractionofαacidsandiso‐α‐acids,whileSFEexhibiteda
greaterpotentialfortheisolationofβacids.Theauthorsconcludedthatbothtechnologiescanbe
usedtoobtainhighyieldsofhopsextracts,confirmingthepossibilityofadjustingtheexperimental
parametersofbothmethodstomakeitselectiveforspecifickindsofcompounds.
GilRamírez[51]assessedthesuitabilityofPHWEfortheselectiveextractionofisoxanthohumol
(IX)againstxanthohumol(XN)fromhops.Waterextractionwasperformedusing1500psiat150°C
andanextractiontimeof30min(5minpercyclefor6cycles).Ethanolextractionat150°Cduring30
Appl.Sci.2020,10,50747of18
min(5minpercyclefor6cycles)wascarriedoutforcomparativepurposes.Besides,sequential
extractionswereperformedusingasolventinincreasingpolarityorder(hexane,ethanol,andwater).
Basedontheresults,PHWEshowedhighselectivitytowardisoxanthohumolagainstxanthohumol
(2.34mg/gand0.11mg/g,respectively,witharatioIX/XNof21)incomparisonwithPLEusingEtOH
asasolvent,afterusinghexane(5.15mg/gand2.57mg/g,respectively,withaIX/XNratioof2)[51].
PSEhasbeenproposedtoextractαacidsandβacidsfromhopsandhopproducts[52].The
authorsstudiedthesamplepreparationmethodinfluenceandtheparametersthataffectthe
extractionefficiencytofindanalternativemethodtotheEBC7.7extractionmethod(usedforbitter
acidsdeterminationinhopproducts)tosavetimeandfacilitatethelaboriousextraction.Themost
importantparameterswereoptimized(1)temperature,(2)extractionsolventtype,(3)processof
samplepreparation,and(4)numberofcycles.ThePSEmethodsavedsolvent,itwaslessarduous
andtimeconsuming,andaccordingtothestatisticalevaluationcarriedoutbytheauthors,the
developedPSEprocesscanbeconsideredcomparabletotheEBC7.7extractionmethod.
3.2.4.SupercriticalFluidExtraction(SFE)
Anotheremergingtechnologythathasbeenadvantageouslypositionedforthegreenextraction
ofheatsensitivebiocompoundsissupercriticalfluidextraction(SFE).CO2iswidelyusedforSFEdue
toitbeinglowtoxic,nonflammable,inexpensive(comparedtoorganicsolvents),andrecyclable.
AccordingtoHrnčičetal.[5],newopportunitiesusingunconventionalsupercriticalsolventshave
beenappearedsuchasSF6ornoblegases(ortheirmixtures),althoughsupercriticalCO2remainsas
themoreusedsolventfortheseoperations.However,CO2isintrinsicallynonpolar;thus,toimprove
theextractionofpolarcompoundssuchasphenoliccompounds,itrequirestheadditionofpolar
cosolvents(modifiers)suchasethanolormethanol[28].Formatoetal.[53]evaluatedtheextractive
efficiencyofSFECO2,withorwithoutacosolvent,toextracttheacidiccompoundscontainedinhops
flowers.TheresultsrevealedthattheuseofsupercriticalCO2withcosolventimprovedthe
performanceofαacids(28.3%)comparedtopureCO2(21.5%).Incontrast,thehighestyieldinβacids
(46.2%)wasfoundintheextractsobtainedwithsupercriticalCO2versus37.5%forSFECO2with
ethanol.
SFEhasbeenappliedsuccessfullyfortheselectiveisolationofbitteracidsfromtwohopcultivars
(HallertauMagnumandHerkules)[54].Theauthorsidentified,byHPLCanalysis,thepresenceof
twomaingroupsofmolecules:αacids(55.2w/wand46.9w/wintheHerkulesandHallertau
Magnumhops,respectively)andβacids(18.3w/wand22.9w/w,respectively)[54].Cohumulone
accounted38.7%ofαacidsinHerkuleshopsand24.9%inHallertauMagnumhops,andthe
colupulonewasthemajorcomponentofβ‐acids,reaching57.2%and44.2%inHerkulesandHallertau
Magnum,respectively[54].
Tovalorizethespenthops,Jackowskietal.[55]proposedtheiruseasarawmaterialforthe
recoveryofxanthohumol.Under80°Cand850bar,ayieldof1.23%ofxanthohumolwasobtained.
Somestudiesabouttheextractiontechnologiesofdifferentphytochemicalsfromhopsare
presentedinTable1.
Appl.Sci.2020,10,50748of18
Table1.Extractiontechnologiesforobtainingactivemoleculesfromhops.
MatrixTargetCompoundMethodExtractionConditionsOutcomesReference
Hops
Essentialoil
(desmethylxanthohumol,
xanthohumol,cohumulone,
lupulone,colupulone,and
lupulone)
Maceration
Extractionwithethanol:H2O(9:1)with3
cyclesof2handafullnightinstirringin
thedark
Fractionationoftheactivefractionwas
carriedoutusingaliquid/liquidextraction
withmethylenechlorideinproportion
CH2Cl2/H2O(5:5)
Essentialoilyield:6.3
mL/kgofdrycones
Identificationof16
compounds,thethree
majorcompoundsbeing
myrcene,trans
caryophyllene,andα‐
humulene
[10]
Wholehop
cones
Essentialoil(monoterpenesand
sequiterpenes)
Steam
distillationSequentialelutionat8distillationtime
Essentialoilyield:83.2%
(thefirsthour),9.6%(the
secondhour),and7.2%
(secondhalfofthe
distillation)
Chemicalprofile:
Monoterpenesarethefirst
tobeelutedand
sequiterpeneswerelater
eluted
[42]
SpenthopsFlavonoids(xanthohumol)SLE
Extractionwithmethylenechloride,
acetone,ethylacetate,andmethanolfor24
honarotaryshakerandLSR4:1(mL/g)
Yield:92.95g/kg
(methanol);38.57g/kg
(ethylacetate);29.82g/kg
(acetone);26.01g/kg
(methylenechloride)
Xanthohumol:3.51g/kg
(ethylacetate);2.97g/kg
(acetone),2.94g/kg
(methanol);1.33g/kg
(methylenechloride)
[43]
HopsPrenylflavonoidsandbitteracids
(prenylphloroglucinols)
Dynamic
maceration
ExtractionwithMeOH–HCOOH(99:1,
v/v),atroomtemperaturefor30minunder
magneticstirringusinganLSRof20mL/g
17.5mg/gbitteracidsand
1.4mg/g
prenylflavonoids
[44]
HopsPolyphenolsSLE
ExtractionwithDESbasedonglyceroland
Lalaninefor150min,at50°Cinanoil
bath.Optimalconditionsofextraction:
CDES=85%(w/w),LSR=59mL/g,andSS=
688rpm
Yield:118.97mgGAE/of
drymass[23]
HopleavesPolyphenolsUAE
Extractionwithmethyl,ethyl,and
isopropylalcoholatdifferent
concentrations(40%,70%,and96–99.5%
(v/v))usingafrequencyof40kHzfor15,
30,and60minatroomtemperature
TPC:0.51–6.60mgGA/g
rawmaterial(collectedin
2017)and0.02–6.22GA/g
rawmaterial(collectedin
2018)
[3]
HopextractsEssentialoils(β‐myrceneandα‐
humulene)MAHD335Wmicrowavepowerfor30minusing
anLSRof8:3(usingwaterassolvent)
Yield:3.77%;β‐myrcene:
77.36%;α‐humulene:
9.47%
[50]
HopflowersAcidiccompounds(αacids,isoα
acids,βacids)
PLEwitha
Naviglio
Extractor
Sampleweight:21g;solvent:ethylalcohol;
staticphase:2min;dynamicphase:5
cycleswith12secofstoppiston;total
cycles:360(24h)
αacids:50.2%;isoαacids:
9.3%;βacids:16.3%[53]
Hops
(pellets)
Isoxanthohumoland
xanthohumolPHWE/PLE
PHWE:1500psiat150°Candextraction
timeof30min(5minbycycle‐6cycles)
PLE:EtOHasasolvent,afterusinghexane
at150°Cfor20mineachextraction
PHWE:2.34mg/gof
isoxanthohumoland0.11
mg/gofxanthohumol
PLE:5.15mg/gof
isoxanthohumoland2.57
mg/gofxanthohumol
[51]
Hopandhop
productsα‐andβ‐acidsPSE
PSEoptimalconditions:numberofcycles3
(5mineach),staticmode,80°C,15MPa,
solvent:methanoldiethylether(1:1),inert
matrix:seasand(50to70μm),solvent
rinsing:20sec,nitrogenblowdown:2min,
amountofsample:1.5gofgroundhop
conesorpelletsor0.3gofhopextract
Yieldsbetween96.8%and
102.7%[52]
HopflowersAcidiccompounds(αacids,β
acids)SFE
SFECO2(SFEI)andSFECO2withethanol
(SFEII):350barat35°C,astaticperiodof
10min,andadynamicphaseof260min
SFEI:21.5%αacids;46.2%
βacids
SFEII:28.3%αacids;
37.5%βacids
[53]
Hoppellets
(Herkules
and
Hallertau
Magnum)
Acidiccompounds(α‐acids
(cohumulone),β‐acids
(colupulone))
SFESFECO2wascarriedoutatapressureof
29MPa,50°Cduring4h
H.lupulus‘Herkules’:
55.2%ofα‐acids(38.7%of
cohumulone);18.3%ofβ‐
acids(57.2%colupulone)
H.lupulus‘Hallertau
Magnum’:46.9%ofα‐acids
(24.9%ofcohumulone);
22.9%ofβ‐acids(44.2%
colupulone)
[54]
SpenthopsXanthohumolSFESFECO2wascarriedoutatapressureof
850barat80°C
1.23%ofyieldof
xanthohumol [55]
DES:deepeutecticsolvents;LSR:liquidtosolidratio;SFE:supercriticalfluidextraction;SLE:solid–
liquidextraction;UAE:ultrasoundassistedextraction;MAHD:microwaveassisted
hydrodistillation;PSE:pressurizedsolventextraction;GAE:gallicacidequivalents;IX:
isoxanthohumol;XN:xanthohumol;PLE:pressurizedliquidextraction;PHWE:pressurizedhotwater
extraction;SS:speedofstirring;CDES:concentration.
Appl.Sci.2020,10,50749of18
4.BiologicalActivitiesofHopCompounds
Asmentionedpreviously,hopcontainsseveralbioactivemoleculesthatexhibitmultiple
therapeuticproperties,suchas(1)antioxidant,(2)antimicrobial,(3)antifungal,(4)antiviral,(5)anti
inflammatory,and(6)anticancer,interalia[5,12,53].
4.1.AntioxidantActivity
Severalofthecompoundsidentifiedinhopsandhopproductshavebeeninvestigatedfortheir
antioxidantproperties.Theantioxidantpotentialofhopextractsdependsonvariousfactors
includingthetypeofassayusedtodeterminetheantioxidantactivity,theextractionsolvent,aswell
asthecultivarofhop[43,49,56].Forexample,KobusCisowskaetal.[56]evaluatedtheantioxidant
potentialofhopconeextractsfromthreedifferentcultivars(Magnum,Lubelski,andMarynka)
measuredbyDPPHandABTSmethods.Theaqueousextractsofthethreecultivarspresentedthe
highestDPPHvalues;however,theethanolicextractsexhibitedahighervalueofantioxidantactivity
bytheABTSassay.
AlonsoEstebanetal.[2]testedtheantioxidantcapacityofmethanolicextractfromhopseeds
throughdifferentinvitroassays,namelytheDPPH,reducingpower,β‐carotenebleachinginhibition,
andthiobarbituricacidreactivesubstances(TBARS)formationinhibition.Thisextracthadagreater
inhibitoryeffectonthegenerationofTBARSfromtheexvivodecompositionofcertainlipid
peroxidationproducts(withanEC50valueof128μg/mL),butitexhibitedtheworstbehaviorforthe
β‐carotenebleachinginhibitioncapacity(withanEC50valueof1330μg/mL).Thelatterindicatesthat
thehopextractislessactivetoneutralizethelinoleichydroperoxylradicalsformedinvitrofromthe
oxidationoflinoleicacid.Theauthorsattributedtheantioxidantpotentialmainlytothepresenceof
(+)catechinand()epicatechininhopseedextract.
Inapreviousstudy,Abrametal.[57]foundthatethanolicextractsofhopconespresentedupto
ca.5foldmoreDPPHactivitycomparedtothatobtainedintheleafextracts.Onthecontrary,thebest
activitymeasuredbytheferricreducingantioxidantpower(FRAP)trialwasfoundintheleaf
extracts.Inanotherstudy,Gerhauseretal.reportedthatthexanthohumolpresentinthehopsshowed
anantioxidantactivitythatwas8.9and2.9timeshigherthanthereferencecompound6hydroxy
2,5,7,8tetramethylchroman2carboxylicacid(TROLOX)inscavenginghydroxylandperoxyl
radicals,respectively[58].
InastudycarriedoutbyLiuetal.[59],thehydroxylradicalscavengingactivityofdifferenthops
fractions(hopbitteracids,isomerizedhopbitteracids,andothers)wasevaluated.Theresults
indicatedthatallthecompoundsshowedantioxidantpotentialatdifferentlevels,ofwhichtheα
acidswerethosethatexhibitedalowerEC50.Humulone,lupulone,andsometerpenes(linalool,β‐
pineneandγ‐terpinene,βfarnesene)fromhopessentialoilshavealsobeenreportedfortheir
antioxidantpotential[12].
4.2.AntimicrobialActivity
Hopshavetraditionallybeenusedinbeerasanaturalpreservativebecauseoftheirhighcontent
ofbitteracidsandpolyphenols,whichinhibitthegrowthofabroadspectrumofmicroorganisms.
Pilnaetal.[54]studiedtheantimicrobialpotentialofextractsoftwohopvarieties.Allextractsshowed
antimicrobialactivityagainstallpathogenicbacteriatestedatminimuminhibitoryconcentrations
(MICs)intherangeof8–512μg/mL.Grampositivestrains(MICs8–64μg/mL)weremoresensitive
thanGramnegativestrains(MICs≥32μg/mL)andyeast(MIC=512μg/mL).Theauthorsidentified
α‐andβ‐acidsasthemainsubstancesinvolvedintheinhibitoryeffectsofhopextracts.Humulinic
acid(derivedfromiso‐α‐acids)hasalsobeenreportedfortheirantimicrobialactivityagainst
Lactobacillusbrevis[60].
Today,thereisaglobalconcerntofindnewactiveagentstocombatmicrobialresistanceto
antibiotics[61].Inthissense,methicillinresistantStaphylococcusaureus(MRSA)strainscause
differentpathologiesthataredifficulttotreatduetotheirvirulence,resistancetoalmostalluseful
antibiotics,aswellastheformationofpersistentbiofilms[61].Plantderivednaturalcompounds,
Appl.Sci.2020,10,507410of18
characterizedbythepresenceofawidespectrumofactivebiomolecules,havebeenstudiedas
potentialantimicrobialagentsthatareusefultotreatseveraldiseasescausedbymultidrugresistant
microorganisms.AccordingtoBartmánskaetal.[43],sevenflavonoids,amongthemtwonatural
(α,β‐dihydroxanthohumoland8prenylnaringenin)flavonoidsidentifiedinspenthopsextracts,
showedremarkableantimicrobialactivityagainstmethicillinsensitive(MSSA)andresistant
Staphylococcusaureus(MRSA)strains.Lupulone,xanthohumol,anddesmethylxanthohumolalso
exhibitedstrongantimicrobialactivityagainstMRSAaswellastheabilitytoinhibitbiofilmformation
[61].SimilarfindingswerealsofoundbyBogdanovaetal.[62],whoreportedthathumulone,
lupulone,andxanthohumolhadstrongantimicrobialandantibiofilmactivityagainstMRSAstrains.
Inthisresearch,theauthorsindicatedthatlupuloneexhibitedthestrongesteffect,whichwas
followedbyxanthohumol.Ethanolicextractsofhopsalsoexhibitedanantimycobacterialeffecton
rifampinsensitiveandresistantstrainsofMycobacteriumtuberculosis[63].
Someauthorshavealsodemonstratedtheantifungalactivityofhopextracts.Bocquetetal.[10]
testedcrudeextractsofdifferentpartsofhop(leaves,stems,rhizomes,andfemalecones)andthe
essentialoilofhopsagainstZymoseptoriatritici.Allextractsandessentialoilshowedantifungal
activity,althoughonlyfemaleconesandtheessentialoilexhibitedavisibleactivity,observinga
reductionof85%and100%inthegrowthofZ.triticiat1.25g/L,respectively.Theauthorsattributed
theantifungalactivityofhopconeextractstothepresenceofdesmethylxanthohumolandco
humuloneandconcludedthatthecombinationofhopsessentialoilwithsyntheticfungicidescould
beanappropriatestrategytoreducethedoseofconventionalfungicidesincropprotection.Similarly,
AlonsoEstebanetal.[2]alsoreportedtheantifungalactivityofhopseedextract.Theresults
indicatedthatthisextracthadaremarkableantifungaleffect,whichwasevenbetterthanthepositive
control,againstfungiofthegenusPenicillium.
4.3.EffectsonSpecificDiseases
4.3.1.AntiInflammatoryActivity
Inflammationisabiologicalresponseoftheorganismtoinjuryorinfection[12].However,
accordingtotheauthors,anexcessiveinflammatoryreactionisassociatedwithcertaindiseasessuch
ascancerorischemicheartdisease,amongothers.Bitteracidsandpolyphenoliccompoundsfrom
hopshavebeenidentifiedaspromisingmoleculestoinhibitinflammatoryprocesses.Bothmolecules
actonthenuclearfactorkappaB(NFkB)thatisinvolvedintheexpressionofproinflammatory
genessuchastumornecrosisfactoralpha(TNF‐α),induciblenitricoxidesynthase(iNOS),kinases,
cyclooxygenases1and2(COX1andCOX2),andanamountinterleukins[12,64].Severalinvitro
andinvivostudiesevidencedthattheantiinflammatoryeffectsofhopsareprimarilyattributedto
humulone,xanthohumol,and8prenylnaringenin[12,64].Forinstance,Leeetal.[65]reportedthat
thetopicalapplicationofhumuloneinhibited12Otetradecanoylphorbol13acetate(TPA)induced
COX2expressionthroughtheregulationofnuclearfactorkB.Humulonealsoreducestheexpression
ofvariouskinasesrelatedtotheinflammatoryresponse[66].Xanthohumoland8prenylnaringenin
alsoshowedastrongantiinflammatoryeffectviatheinactivationofNFkcinmicroglialcelllines
[67].Ithasalsobeenstudiedthattheisoxanthohumolreducedinflammatoryfactorsincludingtumor
necrosisfactoralpha(TNF‐α)andnuclearfactorkappaBinhumanaorticsmoothmusclecellsand
humanumbilicalveinendothelialcells[68].Inbothanimalmodelsandhumaninterventiontrials,
isohumuloneshavebeeneffectiveinthetreatmentofinflammatoryarthritis[69].
4.3.2.CancerRelatedActivities
Cancer,animportantcausesofdeathinthe21stcentury,supposesforthehealthsystemsan
importanteconomicimpact,duetothehighcostofitstreatment[12].Forthisreason,itisnecessary
todevelopnewsubstanceswithanticancerpotentialthatcanprevent,stop,orreversethedisease
progression,whichisthereasonwhythesesubstanceshavebeenthefocusofalargenumberof
scientificstudies[12].Inthiscontext,ithasbeenreportedthatsomeofthebioactivecompounds
presentinhopshaveanticancerproperties.Forinstance,xanthohumolhasbeenidentifiedasanew
Appl.Sci.2020,10,507411of18
agentforthetreatmentofdifferenttypesofcancer[12,64].Yongetal.[11]demonstratedthat
xanthohumolhadanapoptoticeffectonthehumanalveolaradenocarcinomacelllineinadose‐and
timedependentmanner.Recently,Roehreretal.[13]evaluatedtheantiproliferativeeffectof
xanthohumol,xanthohumolC,andcrudehopextractonhumanbreastcancercells.Accordingtothe
authors,after2daysofincubation,xanthohumolCpresentedthestrongestgrowthinhibitionwith
anIC50of4.18μM,incomparisonwithcrudehopextract(8.84μM)andxanthohumol(12.25μM).
Lupulone,aβ‐acidpresentinhopextracts,displayedanticanceractivityonprostatecancercellsvia
theinductionofcaspase8dependentcelldeath[70].
4.3.3.OtherBiologicalActivities
Otherbioactivitiesattributedtohopcomponentsincludeneuroprotective,antidiabetic,and
cardioprotectiveeffects.Xanthohumolpromotedneuronalrecoveryinratswithintracerebral
hemorrhage[71],anditalsoshowedaprotectiveeffectonthebraindamageinducedbyaging[72].
Thiscompoundalsohastheabilitytoinhibitadipogenesissoitcanbeusedinthepreventionof
obesity.Inastudyinmicefedwithahighfatdiet,thesupplementationwith2%or5%hopextract
reducedtheincreaseinbodyandadiposetissueweightandimprovedtheglucoseintolerance[73].
Adietrichinxanthohumoland8prenylnaringeninimprovesmetabolicdisordersrelatedtotype2
diabetesbymodulationoftheglucoseandlipidpathways[74].
Table2summarizesseveralbiologicalactivitiesofdifferentbiocompoundsextractedfromhop
andthemainresultsfound.
Table2.Biologicalactivitiesofcompoundsextractedfromhops.
ResponsibleCompound MethodologyOutcomesReference
AntioxidantActivity
PhenolicAcidsandflavonolsDPPHandABTS
DPPHrangedfrom3.50mmolTrolox/gdwfor
Marynkavarietyethanolextractto4.75mmolTrolox/g
dwforMagnumvarietywaterextract.ABTSvaried
from1.32mmolTrolox/gdwforMagnumvariety
waterextractto2.43mmolTrolox/gdwforMarynka
varietyethanolextract
[56]
(+)catechinand()epicatechin
DPPH,reductionpower,
β
carotenebleachinginhibition
capacity,TBARS
EC50values:DPPH:505μg/mL;Reductionpower:530
μg/mL;β‐Carotenebleachinginhibitioncapacity:1330
μg/mL;TBARS:128μg/mL
[2]
PhenoliccompoundsDPPHandFRAPDPPHEC50:0.070mg/mL;FRAP:reductionof0.117
mL/μgofferricionsin25min[57]
XanthohumolORAC
TheantioxidantactivitydeterminedbytheORAC
assaywashigherthanthereferencecompound
TROLOX
[58]
QuercetinandisoquercetinDPPHandABTSDPPHEC50:3.91μL/mL;ABTSEC50:21.29μL/mL[49]
Bitteracids,isomerizedhop
bitteracids,hopoil,and
hexahydro‐β‐acids
Hydroxylradicalscavenging
activity
EC50:α‐acid:0.21mg/mL;β‐acid:0.96mg/mL;
Dihydroiso‐α‐acid:1.36mg/mL;tetrahydroiso‐α‐acid
1.77mg/mL;hexahydroiso‐α‐acid1.40mg/mL;
hexahydro‐β‐acid0.50mg/mL;oil0.18mg/mL
[59]
AntimicrobialActivity
α‐andβ‐acidsMicrodilutionmethod
Grampositivebacteria:MICs8–64μg/mL;Gram
negativebacteria:MICs≥32μg/mL;yeast:MIC=512
μg/mL
[54]
Flavonoidsamongthemtwo
natural(α,β‐
dihydroxanthohumoland8
prenylnaringenin)
MicrodilutionmethodGrowthinhibitionofMSSAandMRSAatMIC80values
of5–50μg/mL[43]
HumulinicacidMicrodilutionmethodInhibitionofLactobacillusbrevisatMIC<10μM[60]
Lupulone,xanthohumol,and
desmethylxanthohumolMicrodilutionmethod
AntimicrobialeffectagainstMSSAandMRSAwith
MICsvaluesof0.6–1.2μg/mLforlupulone,9.8–19.5
μg/mLforxanthohumoland19.5–39μg/mLfor
desmethylxanthohumol
Xanthohumoltotallyinhibitedthebiofilmformationat
theMICvalue.Desmethylxanthohumolandlupulone
inhibitedthebiofilmformationatsubinhibitory
concentrations
[61]
Humulone,lupulone,and
xanthohumolMicrodilutionmethod
MICsvalues:7.5–30μg/mLforhumulone,0.5–4μg/mL
forlupulone,2–4μg/mLforxanthohumol
MBCsvalues:30–125μg/mLforhumulone,1–15μg/mL
forlupulone,2–7.5μg/mLforxanthohumol
[62]
Appl.Sci.2020,10,507412of18
90%reductioninbiofilmformationusing2–7.5μg/mLof
lupulone,15–30μg/mLofxanthohumoland30–250
μg/mLofhumulone
Desmethylxanthohumolandco
humuloneSpottingmethod
AntifungalactivityagainstZymoseptoriatritici.
IC50values:0.36g/Lforessentialoiland0.73g/Lforcone
extracts
[10]
(+)catechinand()epicatechinMicrodilutionmethod
MIC:0.15mg/mLforPenicilliumochrochloron,0.075
mg/mLforPenicilliumfuniculosum,0.15mg/mLfor
Penicilliumverrucosumvar.cyclopium
MBC:0.30mg/mLforPenicilliumochrochloron,0.15
mg/mLforPenicilliumfuniculosum,0.30mg/mLfor
Penicilliumverrucosumvar.cyclopium
[2]
AntiInflammatoryActivity
Humulone
Mouseskinstimulatedwiththe
tumorpromoter12O
tetradecanoylphorbol13
acetate(TPA)
Humuloneat10μmolinhibitedTPAinducedCOX2
expressionthroughtheregulationofnuclearfactorkB[65]
Isoxanthohumol
Humanumbilicalvein
endothelialcells(HUVEC)and
humanaorticsmoothmuscle
cells(HASMC)
Isoxanthohumolatadoseof10μmolreducedin
HASMCtheTNF‐αby26%andnuclearfactorkappaB
by24%;inHUVEC,thedecreasewas40%forTNF‐α
and42%fornuclearfactorkappaB
[68]
AnticancerActivity
XanthohumolSulforhodamineBassayInducedcelldeathinhumanalveolaradenocarcinoma
cellline[11]
Xanthohumol,xanthohumolC,
andcrudehopextract
CellTiter96AqueousNon
RadioactiveCellProliferation
AssayfromPromega
Antiproliferativeeffectsonbreastcancercells[13]
LupuloneMTTAssay
Anticancerpotentialon2prostatecancercelllines(PC3
andDU145cells).IC50was5μMforbothcelllinesafter3
daysoftreatment
[70]
HopextractMTTAssayAntiproliferativeeffectsonhumanhepatoma
carcinomaatdosesof0.6–1mg/mL[75]
OtherBioactivities
Xanthohumol
Intracerebralhemorrhage
modelwasinducedby
intrastriatalinjectionof
bacterialcollagenase
Reducedthehemorrhagicinjuryandpromotethe
neuronalrecovery[71]
Xanthohumol
Senescenceacceleratedprone
malemice
(SAMP8)
Preventstheexpressionofbraindamageinducedby
aging[72]
Hopextract
MaleC57BL/6Jmice(4weeks
old)feda
highfatdiet
Inhibitedtheincreasingbodyandadiposetissueweight,
adiposecelldiameter,andliverlipids,andimproved
glucosetoleranceinducedbyahighfatdiet
[73]
Xanthohumolor8
prenylnaringenin
Type2diabetesmellitus
(T2DM)micemodel
Improvesmetabolicdysfunctionsassociatedwith
diabetes:bodyweightgain;decreasedglycemia,
triglyceride,cholesterolandalkalinephosphataselevels;
andimprovedinsulinsensitivity
[74]
ORAC:oxygenradicalabsorbancecapacity;TBARS:thiobarbituricacidreactivesubstances;MIC:
minimuminhibitoryconcentration;MBC:minimumbactericidalconcentration;MSSA:methicillin
sensitivestrainsStaphylococcus;MRSA:methicillinresistantstrainsStaphylococcus;TPA:12O
tetradecanoylphorbol13acetate;MTT:3(4,5dimethylthiazol2yl)2,5diphenyltetrazolium
bromide.
5.CurrentApplicationsofFunctionalMoleculesfromHop
Takingintoaccountthepropertiesofthehopextracts,inthelastyears,theyhavebeenusedas
preservativeagentsindifferentfoodproducts.Inthecaseoffreshmeatandmeatproducts,plant
extractspreventtheiroxidativeandmicrobialdeterioration,extendingtheirshelflifeandsafetyas
wellasconferringfunctionalproperties[76–78].Forexample,Krameretal.[18]studiedthe
antimicrobialeffectinvitroofseveralhopextractsagainstL.monocytogenes,Staphylococcusaureus,
Salmonellaenterica,andEscherichiacoliinamodelmeatmarinadeandonmarinatedporktenderloins.
TheresultsobtainedbytheseauthorsdemonstratedthattheGrampositivebacteriawerehighly
inhibitedbyhopextractsduetoitscontentinβ‐acid,butinthecaseofextractscontainingα‐acid,the
inhibitionwaslower;incontrast,Gramnegativebacteriaexhibitedahighresistanceagainstall
evaluatedhopextracts.
Inanotherwork,VillalobosDelgadoetal.[79]evaluatedtheeffectoftheincorporationofhop
infusionorpowderinrawandcookedlambpatties,overtheoxidativestabilityoflipids,proteins,
Appl.Sci.2020,10,507413of18
and/orcolorundertwoscenarios:refrigeratedorfrozenconditions,aswellasintheirsensory
acceptability.Theseauthorsconcludedthattheuseofhoppowdershowedhigherantioxidant
activitythanhopinfusioninlambpatties.Moreover,thelipidandproteinoxidationofcookedpatties
underrefrigeratedconditionswasreduced.However,thesensorialacceptancebytheconsumers
decreasedduetochangesinflavorwhenhoppowderwasadded.
Hopextractsfindalsoapplicationasnaturalingredientstoextendtheshelflifeofbreaddueto
theirantifungalproperties.Forinstance,Nionellietal.[19]formulatedwheatbreadwithhopextracts
andassessedtheireffectsonitsshelflife,aswellasonitsrheologicalandsensoryfeatures.They
reportedthatthehopextractexhibitedantifungalpropertiesagainstAspergillusparasiticus,Penicillium
carneum,Penicilliumpolonicum,Penicilliumpaneum,Penicilliumchermesinum,Aspergillusniger,and
Penicilliumroqueforti.Moreover,theseauthorsisolatedlacticacidbacteriafromhopsandselected
threeforsourdoughfermentationforbreadmakingwithhopextracts.Theauthorsconcludedthat
theadditionofhopextractsincreasedtheantioxidantactivityandtheconcentrationofphenols.
Moreover,theuseofhopsourdoughwithorwithouttheincorporationofhopextracttoelaborate
breaddelayedthegrowthoffungiuntil14days,extendingitsshelflife.Therheologicalandsensory
propertieswerenotaffected.
Incosmetics,hopsareusedinbathlotions,amongothers[80].Vogtetal.[17]usedsupercritical
CO2extractsofhopconestoformulateshowergels,andtheresultsobtainedshowedthattheir
additionenhancedtheirskinconditioningpropertiesduetotheircontentinbioactiveingredients.
Moreover,theformulationscontainingtheextractofhopconespresentcompoundstotreatoiland
dandruffinhair.Theuseofhopextractinhaircosmeticsissupportedbyitsantifungaland
antiseborrheicpropertiesthatdecreaseitsbrittleness,nourishit,giveitshine,increaseitsstrength,
andpreventitsloss[17].
6.Conclusions
Traditionally,hopshavebeenusedinbrewing,butrecentstudieshaverevealedtheirwealthin
bioactivemoleculeswithahugerangeoftherapeuticproperties.Thishasencouragedintense
researchinthedevelopmentofasustainableprocessthatusesecofriendlysolventscombinedwith
intensificationtechnologiesthatguaranteehighyieldsandextractswithhighqualityfromhops.In
fact,inthisreview,severalworksbasedonthesetechnologiesdemonstratetheirsuitabilitytorecover
extractsthatarebiologicallyactive.Amyriadofpropertiesrelatedtothehopextractshavebeen
evaluated,amongthemantibacterial,antifungal,cardioprotective,antioxidant,antiinflammatory,
anticarcinogenic,andantiviral.Therefore,hopsareshapingupasanexcellentandalternativesource
ofbioactivecompoundswithpotentialgreatacceptabilitybytheconsumersthatincreasingly
demandnaturalingredientswithhealthyproperties.Moreover,theextractsfromhopsfind
applicationsinthealimentary,cosmetic,nutraceutical,andpharmaceuticalsector,openingnew
alternativesintheformulationofdifferentcommoditiesbeyondtheirconventionaluses.However,
duetothehugevarietyofbiomoleculespresentinthehopextracts,itisnecessarytoinvestigatetheir
interactionwithothercomponentsofthematrixwheretheyareincorporated,aswellastheir
bioavailabilitywhenareingestedaspartofafoodorusedatatopical