Valorization Challenges to Almond Residues

27 Pages·2017·3.75 MB·English

molecules
Review
Valorization Challenges to Almond Residues:
Phytochemical Composition and
Functional Application
IvaPrgomet1,*,BertaGonçalves1,RaúlDomínguez-Perles1,NúriaPascual-Seva2 ID and
AnaI.R.N.A.Barros1
1 CentrefortheResearchandTechnologyofAgro-EnvironmentalandBiologicalSciences,CITAB,
UniversityofTrás-os-MonteseAltoDouro,UTAD,QuintadePrados,5000-801VilaReal,Portugal;
[email protected](B.G.);[email protected](R.D.-P.);[email protected](A.I.R.N.A.B.)
2 DepartmentofPlantProduction,UniversitatPolitècnicadeValència,46022València,Spain;
[email protected]
* Correspondence:[email protected];Tel.:[phone]
Received:30August2017;Accepted:16October2017;Published:20October2017
Abstract: Almondischaracterizedbyitshighnutritionalvalue;althoughinformationreportedsofar
mainlyconcernsediblekernel. Eventhoughthenutritionalandcommercialrelevanceofthealmond
isrestrictedtoalmondmeat;todate;increasingattentionhasbeenpaidtootherpartsofthisfruit(skin;
shell;andhull);consideredby-productsthatarescarcelycharacterizedandexploitedregardingtheir
propertiesasvaluablesourcesofbioactivecompounds(mainlyrepresentedbyphenolicacidsand
flavonoids). Thislackofpropervalorizationproceduresentailsthecontinuationoftheapplication
oftraditionalprocedurestoalmondresiduesthatnowadaysaremainlyaddressedtolivestockfeed
and energy production. In this sense; data available on the physicochemical and phytochemical
compositionofalmondmeatanditsrelatedresiduessuggestpromisingapplications;andallowone
to envisage new uses as functional ingredients towards value-added foods and feeds; as well as
asourceofbioactivephytochemicalstobeincludedincosmeticformulations. Thisobjectivehas
promptedinvestigatorsworkinginthefieldtoevaluatetheirfunctionalpropertiesandbiological
activity. Thisapproachhasprovidedinterestinginformationconcerningthecapacityofpolyphenolic
extracts of almond by-products to prevent degenerative diseases linked to oxidative stress and
inflammation in human tissues and cells; in the frame of diverse pathophysiological situations.
Hence;thisreviewdealswithgatheringdataavailableinthescientificliteratureonthephytochemical
compositionandbioactivityofalmondby-productsaswellasontheirbioactivitysoastopromote
theirfunctionalapplication.
Keywords: Prunus dulcis; by-products; phenolic compounds; biological activity;
functionalapplication
1. Introduction
Thealmondtree(Prunusdulcis(Mill.)D.A.Webb,PrunusamygdalusBatchorAmygdaluscommunisL.)
isoneofthemostpopularnuttreesgrownworldwideunderaridconditionsduetoitsresistanceand
capacityagainstwatershortageandirrigationdeficit. ThealmondtreebelongstothefamilyRosaceae
andisplacedunderthegenusPrunus,togetherwithpeach,plum,apricot,cherry,andnectarine—agroup
offruitscollectivelyknownas“stonefruits”,i.e.,fruitswithastonyendocarp. Nowadays,thebiggest
almondproduceristheUSA,accountingfor80.0%oftheworldproduction,whichreached1.11×108kg
(onthekernelbasis)inthe2015/2016season,beingthemostproducednutintheworld[1].Alongwiththe
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Molecules2017,22,1774 2of27
kernel,around0.8–1.7Mtonnesofalmondshellsarediscardedannually[2],whiletheamountofalmond
hullsisestimatedtoexceed6Mtonnes[3].
The edible part of almonds, the kernel, is a seed with two large cotyledons [4]. During fruit
development,kernelisprotectedbytheshellandthehull,whilstduringfruitripening,thehullstarts
tosplit,andoncedried,thekerneleasilyseparatesfromtheshell. Intermsofyield,averagekernel
weightisthemostimportantparameter,asthisinvolvesthemostvaluablenutritionalcomposition.
Generally,kernelweightincreasescontinuouslyuntilmaturity,althoughdifferentgrowingconditions
andseveralenvironmentalstressorssuchaswaterandtemperaturecancauseabnormalfilling[4],
making productions less appreciable by the market. In the last several years, market demand for
the consumption of almonds as edible nuts and as an ingredient in manufactured food products
hassignificantlyincreasedduetothephysico-chemical,nutritional,andsensorialfeaturesofthese
fruits[5]. Indeed, almondkernelsareconsumedrawworldwide, cookedordry-roasted, slicedor
whole,blanched(withouttheskin)orunblanched(withtheskin). Itisextensivelyusedinbakeryand
confectioneryproducts,andinfoodpreparationingeneral[6,7].
Asmentionedbefore,thegrowinginterestinalmondsisbasedontheirpropertiesasareliablesource
ofnutrients,suchaslipids,proteins,minerals,anddietaryfiber,whereinlipidsprovidearound50.0%
ofthekernelweight(49.9goftotallipids/100g,accordingtoUSDepartmentofAgriculture(USDA)
database),andmostunsaturatedfattyacids(oleic,about70.0%andlinoleic,about20.0%).Theprotein
contentrangesfrom16.0to22.0%ofkernelweightamongstdifferentvarieties(21.2gofprotein/100g,
accordingtoUSDAdatabase).Theaminoacidsaremainlyboundtothealmondproteinamandin,whilst
thecontentoffreeaminoacidsisnegligible. Ontheotherhand,thecontentofdietaryfiberofalmond
kernels ranges from 10.8 to 13.5% (12.5 g of total dietary fiber/100 g, according to USDA database),
beingconstitutedbypectin,cellulose,andxyloglucans,asthemostimportantcomponents.Regarding
vitamins,almondsarerichinlipid-soluble(Etype,withitsmajorhomologueα-tocopherolandminor
onesγ-tocopherol,β-tocopherol,andα-tocotrienol)andinsmallamountsofwater-soluble(Btype,B1,B2,
B3,B5,B6,B7,B9)vitamins.Themostabundantmineralsinalmondkernelsarecalcium,iron,magnesium,
sodium,zinc,manganese,andselenium,andtheyareanespeciallyvaluabledietarysourceofpotassium
andphosphorus(733and481mg/100g,respectively,accordingtoUSDAdatabase)[8].Amarowiczet
al.(2005)reportedhighconcentrationsofphenoliccompoundsinalmondseeds,includingbenzoicand
cinnamicacidderivates(vanillic,caffeic,p-coumaric,andferulicacids),flavonols(quercetin,kaempferol,
andisorhamnetin),anthocyanidins(delfinidinandcyanidin),andprocyanidins(B2andB3)[9].
Althoughalmondconsumptionwastraditionallyperceivedasunhealthyduetoitshighfatcontent,
recentstudieshaveevidencedthebeneficialeffectsenclosedtothefrequentconsumptionofnutsdue
tothecapacityoftheirbioactivenutrientsandnon-nutrientstolowertheplasmalevelsoflow-density
lipoprotein cholesterol (LDL-C) and the incidence and severity of cardiovascular disorders [10–14].
Indeed, resultsobtainedsofarsuggestthatthepresenceofdifferentmechanismsareresponsiblefor
beneficialeffectssignificantlycorrelatedwiththechemicalandphytochemicalcompositionofalmonds.
The bioactivity of the almond bioactives is closely linked to the bioavailability of these molecules.
Grassbyetal.(2017)recentlyreportedtheimportanceofthecell-wallbarriermechanismintheregulation
oflipidbioaccessibilityfromdifferentsizesofalmondparticles,andhighlightedthecrucialroleplayed
bythefoodmatrixinthebioaccessibilityofnutrients[15].Berrymanetal.(2011)tentativelyidentified
nutrientscontributingtoLDL-Cdecreasesinplasmathathavebeenassociatedwithalmondsconsumption.
Therefore,amongthemostrelevantcontributors,theyhighlightfattyacids,phytosterols,dietaryfibers,
proteins,aminoacidarginin,andmicronutrients,suchasα-tocopherol[14].
Foodqualityisanessentialcharacteristicthatinvolvesphysico-chemicalandcompositionalissues.
Inthissense,theInternationalOrganizationforStandardization(ISO)definesqualityas“thetotality
offeaturesandcharacteristicsofaproductorservicethatbearonitsabilitytosatisfystatedorimplied
needs” [16]. Product quality is determined by distinct characteristics or properties such as sensorial
properties(appearance,texture,aroma,andtaste),nutritivevalues,chemicalconstituents,mechanical
properties,functionalproperties,andtypeandpercentageofpresentdefects[17].Almondkernelqualityis
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Molecules 2017, 22, 1774 3 of 26
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Figure 1. Parts of almond fruit.
Figure1.Partsofalmondfruit.
Considering the physico-chemical properties of the diverse solid wastes from almond
Consideringthephysico-chemicalpropertiesofthediversesolidwastesfromalmondprocessing,
processing, the heaviest material is represented by the green hull, with an average of 52.0% of the
theheaviestmaterialisrepresentedbythegreenhull,withanaverageof52.0%ofthetotalfreshweight,
total fresh weight, whilst the shell and kernel (including skin) account for around 33.0% and 15.0%
whilst the shell and kernel (including skin) account for around 33.0% and 15.0% of the total fresh
of the total fresh weight, respectively [25]. During the industrial process of removing skin (in the
weight,respectively[25]. Duringtheindustrialprocessofremovingskin(intheblanchingprocess),
blanching process), two further by-products, in addition to the shell and the hull, are produced:
twofurtherby-products,inadditiontotheshellandthehull,areproduced: blanchedskin(4.0–8.0%
blanched skin (4.0–8.0% of the total shelled almond fresh weight) and blanch water. Thus, 70.0–85.0%
ofthetotalshelledalmondfreshweight)andblanchwater. Thus,70.0–85.0%ofthewholealmond
of the whole almond fruits constitute residues of this agro-food activity at the end of processing
(Figure 2). Currently, almond by-products (mainly hulls and shells) are mostly used as cattle feed,
Molecules2017,22,1774 4of27
fruits constitute residues of this agro-food activity at the end of processing (Figure 2). Currently,
almondby-products(mainlyhullsandshells)aremostlyusedascattlefeed,andbedding. Hullingand
Molecules 2017, 22, 1774 4 of 26
shellingareexpensiveoperations,whilstthereturnsobtainedfromthemdonotcovertheprocessing
investamnde nbtesd,dwinhgi.c Hhujelloinpga ardndiz sehtehlleinsgu asrtea ienxapbeinlsitivyea onpdercaotimonpse, twithivilestn tehses roeftuthrniss oinbdtauinsetrdi afrloamct tihveitmy [26].
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these materials suggest possible alternative applications and have prompted researchers to envisage
shouldbeconsidered,suchastherecoveryofvaluablebio-basedcompoundsandtheiruseasnatural
different solutions that should be considered, such as the recovery of valuable bio-based compounds
foodpreservationadditivesanddietary/nutraceuticalsupplements.
and their use as natural food preservation additives and dietary/nutraceutical supplements.

Figure 2. Process of obtaining almond by-products in the almond industry.
Figure2.Processofobtainingalmondby-productsinthealmondindustry.
2.1. Almond Skin
2.1. AlmondSkin
Almond skin (seed coat) can be removed and discarded after blanching. The proximate
Acolmmopnodsitsikoinn o(fs eaelmdocnodat s)kciann inbceluredmeso tvoetadl adniedtadriys cfiabredre (d47a.f5t earnbdl a45n.c1h gin/1g0.0T gh oef pbrloanxcimheadte acnodm npatousriatilo nof
skin, respectively), soluble dietary fiber (2.7 and 3.8 g/100 g blanched and natural skin, respectively),
almondskinincludestotaldietaryfiber(47.5and45.1g/100gofblanchedandnaturalskin,respectively),
lipids (22.2 and 24.2 g/100 g of blanched and natural skin, respectively), and proteins (12.8 and 10.3
soluble dietary fiber (2.7 and 3.8 g/100 g blanched and natural skin, respectively), lipids (22.2 and
g/100 g of blanched and natural skin, respectively) [27]. In addition to the basic chemical composition,
24.2g/100gofblanchedandnaturalskin,respectively),andproteins(12.8and10.3g/100gofblanched
although skin represents only about 4.0% of the total almond weight [23] and has been associated
andnaturalskin,respectively)[27].Inadditiontothebasicchemicalcomposition,althoughskinrepresents
with a very low economic value, a number of recent studies have reported that it contains about 60.0–
only about 4.0% of the total almond weight [23] and has been associated with a very low economic
80.0% of total phenolic compounds existing in the nut. It is important to state that phenolic
value,coamnpuomunbdesr porfesreencet nint satlumdoiensd hsakvine arreep orertsepdontshibalte ittoc oan staiginnisfiacabnotu etx6te0n.0t– f8o0r. 0t%he ohfigtoht araldpihcaeln olic
compsocuanvdensgeixnigs taicntgiviintyt chaepnaucitt.yI dteismiomnpstorrattaendt fotor ssutacthe mthaatterpiahles n[2o8li–c3c2o],m anpdo uponsdssibplyr efsoern thtein baenlmefoicniadl skin
areresepffoecntssi baslesotcoiaatesdig wniitfhic aalnmtoenxdte cnotnfsourmthpetiohnig. hradicalscavengingactivitycapacitydemonstratedfor
suchmaterials[28–32],andpossiblyforthebeneficialeffectsassociatedwithalmondconsumption.
2.2. Almond Shell
2.2. AlmondShell
Almond endocarp is known as shell, composed of compact arrangements of lignocellulosic
sclereid cells. It is primarily composed of cellulose (ranging from 29.8 to 50.7%), hemicellulose (from
Almondendocarpisknownasshell,composedofcompactarrangementsoflignocellulosicsclereid
19.3 to 29.0%), and lignin (from 20.4 to 50.7%) [33]. The hardness of a shell is associated with the total
cells.Itisprimarilycomposedofcellulose(rangingfrom29.8to50.7%),hemicellulose(from19.3to29.0%),
amount of lignin formed during the nut development [4], morphology, fiber content, and the outer
andlignin(from20.4to50.7%)[33].Thehardnessofashellisassociatedwiththetotalamountoflignin
shell adherence [33].
formedduringthenutdevelopment[4],morphology,fibercontent,andtheoutershelladherence[33].
2.3. Almond Hull
2.3. AlmondHull
The almond hull is the thin mesocarp or green shell cover, which forms 35.0–62.0% of total
Tahlmeoanlmd ofrnedshh wuleliigshtth [e34th]. iIntsm theiscokcnaersps oarndg rweeenigshht edllifcfeorv seirg,nwifhiciacnhtlfyo rammso3n5g. 0v–a6ri2e.t0ie%s; oifn tsootmalea lomf ond
freshweight[34]. Itsthicknessandweightdiffersi gnificantlyamongvarieties;insomeofthem,itis
Molecules2017,22,1774 5of27
thinanddryandprovidesasmallportionofthewholefruit,whileothervarietieshavethickandfleshy
hulls,providingalargeproportionofthefruitweight[4]. Thehullcharacteristicsconditionthefruit
removalfromthetree. Inaddition,thefeaturesofhullshaveadirectinfluenceondryingafterharvest
aswellastheefficiencyofhullremoval[4]. Thenutritionalcompositionofalmondhullsdepends
notonlyonthealmondvarietytoagreatextent,butalsoonenvironmentalfactorsandagronomical
managementthatcontributestronglytothefinalphysico-chemicalandphytochemicalpropertiesof
almondkernelanditsby-products. Hence,thesugarcontentinalmondhullsreportedlyrangesfrom
18.0to30.0%,proteincontentvariesfrom2.1to8.8%,andcrudefiberrangesfrom10.0to24.9%. Acid
detergentfibervariesfrom20.6to35.2%,neutraldetergentfiberfrom10.0to15.0%,cellulosefrom20.6
to35.2%,andcrudeligninrangesfrom7.5to15.6%. Dependingontheharvestmethod,ashescanvary
from7.0to8.3%,butcanbeevenhigherthan9.0%. Inthesecasestheyareclassifiedas“almondhulls
anddirt”[35].
3. PhytochemicalCompositionofAlmondBy-ProductsandTheirRadicalScavengingPower
Plants are rich sources of natural antioxidants including tocopherols, vitamin C, carotenoids,
andphenoliccompounds[36]. Thesecompoundshavebeenpromotedasrelevantmoleculesagainst
oxidativestressbecauseoftheirradicalscavengingactivity.
Althoughfreeradicalsandotherreactiveoxygenspeciesarecontinuouslyformedinthehuman
body,animbalancebetweenoxidants(freeradicals)andantioxidants,infavorofoxidants,hasbeen
relatedtooxidativestress,whichisimplicatedinthepathophysiologyofseveralhumandiseases.
Resortingtotheirfunctionalfeatures,naturalantioxidantshavebeenpromotedasmoleculesthat
increasetheshelflifeofproductsinthefoodindustry,preferablyusedinsteadofsyntheticantioxidants
(such as BHAand BHT). In this view, the presence of thebioactive compounds in almond andits
by-products(Figure3)andtheirbiologicalactivitiesinalmondhulls[3,37–41],almondskin[28–32],
almondshells[7,42],andblanchwater[23,32,43]havebeenstudied,andisthemainaspectdiscussed
furtherinthismanuscript.
Molecules2017,22,1774 6of27
Molecules 2017, 22, 1774 6 of 26

Figure 3. Bioactive compounds in almond by-products.
Figure3.Bioactivecompoundsinalmondby-products.
MMooleleccuuleless 22001177, ,2222, ,11777744 77 ooff 2267
Molecules 2017, 22, 1774 7 of 26
33..11.. PPhheennoolilcic CCoommppoouunnddss
3.1. Phenolic Compounds
PPhheennoolilcic ccoommppoouunnddss aarree tthhee mmaajjoorr ggrroouupp ooff pphhyyttoocchheemmiiccaallss iinn aallmmoonnddss.. TThheessee ccllaasssseess ooff
Phenolic compounds are the major group of phytochemicals in almonds. These classes of
ccoommppoouunnddss araer efefaetautruerde dbyb iyncilnucdliundgi nagt leaatslte oanste aornoemaartoicm raintigc, wrinitgh, owneit hor omnoereo rhymdororexyhl ygdrorouxpysl
compounds are featured by including at least one aromatic ring, with one or more hydroxyl groups
agtrtaocuhpesda, tatancdh eadre, acnladssairfeiecdla asss ififleadvoansoflidav (oFnigouidre( F4i)g aunred 4n)oann-dflanvoonn-floaidv ocnoomidpocuomndpso (uFnigdusr(eF i5g)u. rTeh5e) .
attached, and are classified as flavonoid (Figure 4) and non-flavonoid compounds (Figure 5). The
fTlahveonfloaivdos ncolaisdss (Fcilgaussre( 4F)i gisu croem4p)oissedc oomf fplaovsoendeso (f4afl)a, vfloanveasno(n4eas) ,(4flba),v falanvoonneosls( 4(4bc)),, ffllaavvaonnoollss (4(d4c),) ,
flavonoids class (Figure 4) is composed of flavones (4a), flavanones (4b), flavonols (4c), flavanols (4d),
aflnatvhaoncyoalsn(i4nds )(,4aen),t hcohcaylcaonniness ((44fe)),, acnhdal caounroesne(4s f()4,ga)n, danadu rtohnee nso(4ng-f)l,aavnodnothidesn (opnh-eflnaovloicn oaicdidss()p mheaninollyic
anthocyanins (4e), chalcones (4f), and aurones (4g), and the non-flavonoids (phenolic acids) mainly
ianccildusd)em baeinnzlyoiicn acnludd ceinbnenamzoiicc aacniddsc (in5an aamndic 5abc,i rdess(p5eactainvdely5b) ,[4re4s,4p5e]c. tively)[44,45].
include benzoic and cinnamic acids (5a and 5b, respectively) [44,45].

Figure 4. Structures of flavonoids class.
Figure4.Structuresofflavonoidsclass.
Figure 4. Structures of flavonoids class.
Figure 5. Non-flavonoids: benzoic (5a) and cinnamic (5b) acids.
Figure 5. Non-flavonoids: benzoic (5a) and cinnamic (5b) acids.
Figure5.Non-flavonoids:benzoic(5a)andcinnamic(5b)acids.
3.1.1. Flavonoids
3.1.1. Flavonoids
3.1.1. Flavonoids
Flavonoids are water-soluble pigments, sharing a common structure of two aromatic rings
Flavonoids are water-soluble pigments, sharing a common structure of two aromatic rings
boundF ltaovgoenthoeidr sbya rtehrweea ctearr-bsoonlu abtloempsi gfomrmenintsg, asnh aorxinyggeanactoemd hmeotenrosctryuccletu [4re6]o. Tfhtwis otyapreo omf apthicenrionlgics
bound together by three carbon atoms forming an oxygenated heterocycle [46]. This type of phenolic
cboomupnodutnodges thiesr bsyyntthhreeseizceadrb otnhraotuomghs fothrem ipngheannyolpxryogpeannaoteidd hpeatethrowcyaycl,e [w46h]e.rTe hipshteynpyeloalfapnhineen oliisc
compounds is synthesized through the phenylpropanoid pathway, where phenylalanine is
tcroamnspfoorumndeds itsos 4y-nctohuemsizaerdoythl-rCoouAgh, wthheipchh etnhyenlp eronptearnso tihdep falathvwonaoy,idw bhieorseypnhthenesyilsa lpaantihnweiasyt.r aBniosfloogrmiceadl
transformed to 4-coumaroyl-CoA, which then enters the flavonoid biosynthesis pathway. Biological
ftuon4c-tcioonusm oafr folayvl-oCnooAid,sw ihn ipchlatnhtes nareen rteerlasttehde tflo adveofnenoside abgioasinysntt hUeVsi srapdaitahtiwona ya.nBdio ploatghicoaglefnu inncfteioctniosno,f
functions of flavonoids in plants are related to defense against UV radiation and pathogen infection,
pfloalvleonn ofeirdtsiliitny, pnloadntuslaatrioenr e[l4a7t]e, dsytmobdieofteicn sneitraoggaeinns ftixUaVtiorna,d ainatdi ofnloraanld pipgamtheongtaetnioinn,f aeccttiinong ,aplsool laesn
pollen fertility, nodulation [47], symbiotic nitrogen fixation, and floral pigmentation, acting also as
Molecules2017,22,1774 8of27
fertility,nodulation[47],symbioticnitrogenfixation,andfloralpigmentation,actingalsoaschemical
messengers,cellcycleinhibitors,andphysiologicalregulators[48]. Inplants,flavonoidscanoccurina
formofaglyconesorglycosides,moreoftenfoundasthelatterone[49].
The composition of flavonoids in plants is influenced by several factors such as variety,
geographical origin, agronomical practices, ripeness stage, processing, storage, environmental
conditions,exposuretopestsanddiseases,environmentalconditions,andUVradiation[23].
3.1.2. PhenolicAcids
Phenolic acids are secondary metabolites characterized by hydroxylated aromatic ring(s).
Hydroxybenzoic and hydroxycinnamic acids are produced via shikimic acid through the general
phenylpropanoid pathway. However, despite the long term during which the chemical features
andbiologicalfunctionsofphenolicacidshavebeenstudied,todate,thedataarestillscarce,with
gaps of information regarding their capacity to modulate biological processes in plants. Anyway,
the biological functions of phenolic acids have been related to protein synthesis, photosynthesis,
andnutrientuptake[50]. Inplants,phenolicacidscanbefoundindifferentforms,suchasaglycones,
glycosides,esters,andboundcomplexes[49].
3.2. PhenolicCompositionofAlmondSkin
Intheindustry,almondskinisobtainedbyblanchingorroasting. Upontheseprocesses,theentire
almondissubjectedtohightemperatures(around100◦Cforblanchingandupto200◦Cforroasting)
toobtainskinlessalmondkernels. Eventhoughthealmondskinrepresentsjustaround4.0%ofthe
totalalmondweight,60.0–80.0%ofthealmondphenoliccompoundsaredistributedwithinthealmond
skin[23,51]. However,thermalprocessesinthefoodindustrymayaffectthestabilityofpolyphenols
and promote the degradation and loss of bioactive compounds [52]. For instance, albeit subjected
tolowertemperaturescomparedtoindustrialroasting, almondskinpolyphenolsareeasilylostby
hotwaterblanchinganddemonstratealowerphenoliccontent[53]. Furthermore,resultsfromone
studysuggestedthatthemajorityofthephenoliccompoundsinthekernelitselfdoesnotconsistof
flavonoids[23]. Elevenoutof19phenoliccompoundsidentifiedinalmondkernels,skin,andblanch
water(Table1)werefoundonlyintheskin,whilst95.0%oftheindividualflavonoidsidentifiedwere
also present in the skin [23]. This situation also points out the role of flavonoids as phytoalexins,
secondarymetabolitesthatplantssynthesizeforself-defense,protectingtheskinfromdifferentstresses.
Molecules2017,22,1774 9of27
Molecules 2017, 22, 1774 9 of 26
Table1.Phenoliccompoundspresentinalmondby-products.
Table 1. Phenolic compounds present in almond by-products.
Almond Almond
PhenolicClass Compound Radicals Content References
Phenolic class Compound Radicals Fruit ConFtreunitt Parts References
Phenolicacids Parts
Phenolic acids
CCiinnnnaammiicc aacciiddss RR11 R2R2 RR33 R4R 4
CCaaffffeeiicc aacciidd HH OOHH OOHH H H Hull TraceHs ull [2T4ra] ces [24]
Skin TraceSs kin [2T4ra] ces [24]
SSiinnaappiicc aacciidd CCHH3O3O OOHH CCHH33OO H H HSkuinll 99..9512 aaH ull [[22944.9]] 2a [24]
Skin 9.51a [24]
Hull 2.71 a [24]
FFeerruulliicc aacciidd HH OOHH CCHH33OO H H Skin 2.19 aH ull [224.7] 1a [24]
Hull 42.52 Sc kin [524.1] 9a [24]
3.12–10H.6 ua ll [3402].5 2c [54]
1.76–3.77 a [53]
Chlorogenic acid H OH OH C7H11O5 3.12–10.6a [30]
Skin + [55]
Chlorogenicacid H OH OH C7H11O5 9571.26 b 1.[7362–]3 .77a [53]
Skin + [55]
62.21 e 9[55761] .26b [32]
Crytochlorogenic acid H OH OH C7H11O5 Hull 7.9 c [6524.]2 1e [56]
CNryeotocchhlolorrooggeennicic aaccidid HH OOHH OOHH C7CH71H1O115 O5 Hull 3.04 cH ull [547].9 c [54]
Hull 1.34 a [24]
Neochlorogenicacid H OH OH C7H11O5 4.55 aH ull [234.]0 4c [54]
0.725 Ha ull [310.3] 4a [24]
trans-p-coumaric acid H OH H H Skin 1.06 a [543.5] 5a [24]
trans-p-coumaricacid H OH H H + [05.57]2 5a [30]
367.71 b [312.0] 6a [53]
Skin
31.87 e [56]+ [55]
Phenolic acids 36 7.71b [32]
31.87e [56]
Benzoic acids R1 R2 R3
+ [28]
17.5 d [23]
5.33–6.88 a [30]
p-hydroxybenzoic acid H OH H Skin 3.08–7.18 a [53]
+ [57]
+ [55]
6401.20 b [32]
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Table1.Cont.
Almond
PhenolicClass Compound Radicals Content References
FruitParts
Phenolicacids
Benzoicacids R1 R2 R3
Molecules 2017, 22, 1774 +10 of 26 [28]
17.5d [23]
127.17 e 5.[3536–]6 .88a [30]
p-hydroxybenzoicacid H OH H + Skin 3.[0288–]7 .18a [53]
+ [57]
18.2 d [23]
+ [55]
7.65–14.5 a 6[43001] .20b [32]
Vanillic acid H OH CH3O Skin 11.1–19.2 a 1[5237]. 17e [56]
+ [55]
+ [28]
5805.23 b [32]
18.2d [23]
425.15 e 7.[6556–]1 4.5a [30]
Vanillicacid H OH CH3O Hull + Skin 11[3.17–]1 9.2a [53]
+ [6]+ [55]
+ 5[82085] .23b [32]
17.6 d [42235]. 15e [56]
+ [6] + [37]
Protocatechuic acid H OH OH 14.5–32H.0u al l [30]+ [6]
Skin 6.69–17.2 a [53]
+ [28]
+ [5177]. 6d [23]
Protocatechuicacid H OH OH + [55]+ [6]
1541.67 b 14[3.52–]3 2.0a [30]
285.12S ek in 6.[6596–]1 7.2a [53]
Flavonoids + [57]
Flavanols R3 R5 R7 R3’ R4’ R5’ + [55]
1541.67b [32]
Hull + [37]
285.12e [56]
+ [28]
35.7 d [23]
36.40–90.10 a [30]
Catechin OH OH OH H OH OH 20.1–38.3 a [53]
Skin
+ [57]
+ [55]
15,569.00 b [32]
183.67 e [56]
33.9 d [23]
14.8–36.6 a [30]
7.17–26.5 a [53]
Epicatechin OH OH OH H OH OH Skin + [57]
+ [55]
10,955.6 b [32]
52.4 e [56]
Flavonoids