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Industrial
Crops
and
Products
j o u r n al hom ep a g e :w w w . e l s e v i e r . c o m / l o c a t e / i n d c r o p
Evaluation
of
antioxidant
activity
of
dilute
acid
hydrolysate
of
wheat
straw
during
xylose
production
Ozlem
Akpinar
a,∗,
Serdal
Sabanci
a,
Okan
Levent
a,
Abdulvahit
Sayaslan
baGaziosmanpasaUniversity,DepartmentofFoodEngineering,Taslıciftlik60100,Tokat,Turkey
bKaramanogluMehmetBeyUniversity,Karaman,Turkey
a
r
t
i
c
l
e
i
n
f
o
Articlehistory:
Received12November2011
Receivedinrevisedform1February2012
Accepted24February2012 Keywords: Xylose Xylitol Antioxidant Phenolic
a
b
s
t
r
a
c
t
Wheatstraw,alignocellulosicwastematerial,canbeusedasarawmaterialfortheproductionof high-valueproductssuchasxyloseforxylitolproductionorphenoliccompoundsthathaveantioxidantactivity. Thereisagrowinginterestintheuseoflignocellulosicwastesforconversionintovariouschemicals becauseoftheirlowcostandthefactthattheyarerenewableandabundant.Theobjectiveofthisstudy wastodeterminetheeffectsofH2SO4concentration,temperatureandreactiontimeontheproduction
ofsugars(xylose)andphenoliccompounds.Responsesurfacemethodology(RSM)wasusedtooptimize thehydrolysisprocesstoobtainhighxyloseyieldandphenoliccompounds.Theoptimumreaction tem-perature,reactiontimeandacidconcentrationwere120◦C,45minand4.7%respectively.Underthese
conditions,xyloseandphenolicofthehydrolysatewasfoundtobe0.16g/g-wheatstrawand0.014g-gallic acid/g-wheatstraw,respectively.
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
Mildacidtreatmentsoflignocellulosicmaterialsinthe
pres-ence of mineral acid (which acts as a catalyst) are currently
usedforconvertingthehemicellulosicfractionoflignocellulose
into monosaccharides. The main component of the
hemicellu-losicfractionisxylan,aheteropolysaccharidewithhomopolymeric
backbone of xylose units, which can be a source for
produc-tionofchemicals,includingfood-relatedproducts,suchasxylose
orxylitol(Saha,2003).Acidhydrolysis processnot onlybreaks
down the hemicellulose to monosaccharides, but also cleaves
the-1-4 alkyl-aryl linkages in ligninand lignin-hemicellulose
linkages to form soluble phenolic compounds (Garrote et al.,
2004; Nabarlatz et al.,2007).Lignin is eithercovalently linked
topolysaccharidesviasugar residues,orphenolic acidsesterify
topolysaccharides.Althoughmostoftheligninisacid-insoluble
(klason lignin), a part of it can be solubilized in acidic media
(acid-soluble lignin).While hot watercanextract thefree
phe-nolicacids,acidhydrolysiscanreleasesimpleesterifiedphenolic
acids. These phenolics, considered as the byproducts of acid
hydrolysisoflignocellulosicmaterials,havepotentialapplication
asfoodadditiveswithantioxidantactivity(Moureet al.,2008).
Theacid-solubleligninfractionssuchasp-hydroxybenzoicacid,
∗ Correspondingauthor.Tel.:+903562521613x2894;fax:+903562521729.
E-mailaddresses:ozlem.akpinar@gop.edu.tr,akpinar99@yahoo.com
(O.Akpinar).
ferulicacid,vanillicacid,syringicacid,coumaricacid,
syringalde-hyde,p-hydroxybenzaldehydeandvanillinarewellknown.Among
them, ferulic acid has received enormous attention due to its
potential application in food (preservative agent, gel-forming
properties, flavor precursor), health (antioxidant, antimicrobial,
anti-inflammatory)andcosmetic(photoprotectingagent)
indus-tries(Barberousseetal.,2009).
Hemicellulosehydrolysisofdifferentlignocellulosicmaterials
usingdiluteacidhasbeenstudiedbymanyresearchers(Rahman
etal.,2007;Robertoetal.,2003;Canettierietal.,2007).Theresults
showedthattheyield ofsugarand sugardehydration products
suchasfurfuralandsolublephenoliccompoundsisdependenton
thetypeofmaterialandtheoperationalconditions(measuredby
theseverityfactor)(Rahmanetal.,2007).Thepresenceofphenolic
compoundsandsugardegradationproductswithxyloseis
unde-sirablebecausetheyeitherdecreasethepurityofxyloseorinhibit
itsmicrobialmetabolism.Toovercomethisproblem,itisnecessary
torunthehydrolysisreactionatlesssevereconditionstokeepthe
degradationproductsatlowconcentration.
Wheatstrawisoneofthemostwidelydistributedandabundant
lignocellulosicwastefoundinTurkey(Bascetinceliketal.,2006).
Utilizationofwheatstrawforindustrialpurposesasarenewable
materialfortheproductionofvalue-addedproductsisreceiving
interestduetoitshugeamountofpolymers(celluloseand
hemicel-lulose),lowcost,wideavailabilityandreductionofenvironmental
pollution.
Theaimofthepresentinvestigationwastoevaluatetheeffectof
operationalconditions(temperature,timeandacidconcentration)
0926-6690/$–seefrontmatter © 2012 Elsevier B.V. All rights reserved.
ontheproductionofsugars(xylose,glucose,arabinoseandsugar
dehydrationproducts)and phenoliccompounds,anddetermine
theantioxidantactivityofacidhydrolysateofwheatstraw.
2. Materialsandmethods
2.1. Materials
Wheat straw was collected from local farmers in Turkey,
air-dried and milled to obtain particles of 1–5mm length
and 1mm thickness. Aminex HPX 87H column (dimension:
300mm×7.8mm;averageparticlesize:9m)andcationH
car-tridgewerepurchasedfromBio-RadLaboratories,CA,USA.Allthe
chemicalswere of analytical grade obtainedeither fromSigma
ChemicalCompany,MO,USAorMerckKGaA,Germany.
2.2. Acidhydrolysis
Hydrolysisexperimentswereperformedina100-ml
stainless-steelpressure batchreactor.Thereactorwasloadedwith2gof
wheatstrawand20mlofsulfuricacidsolution.Thereactionswere
carriedoutintherangeof100–140◦Cunderdifferentsulfuricacid
concentrations (2–6% H2SO4)and residence times (15–45min).
Afterthereactionwascomplete,thesolidmaterialwasseparated
byfiltrationandthefiltratewasanalyzedforxylose,glucose,acetic
acidandfurfural.
Hydrolysate samples were analyzed using HPLC system
equippedwitharefractiveindexdetector(PerkinElmerSeries200),
andcolumnoven(PerkinElmerSeries200)onAminexHPX87H
(300mm×7.8mm), which was preceded by its complimentary
cationHcartridgeonAminexHPX87H(300mm×7.8mm),which
wasprecededbyitscomplimentarycationHcartridge.Sugarsand
aceticacidwereelutedwith5mmol/lH2SO4fromthecolumnat
45◦Cwithaflowrateof0.5ml/min(Canettierietal.,2007).A
com-pleteanalysiswascarriedoutin70min.Theirconcentrationwas
quantifiedusingtheaveragepeakareaswhencomparedwiththe
mixtureofstandard (xylose, glucose,arabinose, acetic acidand
furfural)andexpressedasg/lsugar.
2.3. Ferulicacid
Thedeterminationofferulicacidwascarriedoutfollowingthe
methoddevelopedbySaulnieretal.(1995).Atotalof0.1mlofthe
solutionfromtheacidhydrolysateofwheatstrawwasmixedwith
abufferofpH10(0.1Msodiumtetraborate–0.1Mglycinebuffer
atpH10).Theamountoffreeandesterifiedferulicacidwere
cal-culatedfromtheabsorptions(A)at375and345nmusingmolar
absorptioncoefficients(ε345=19,662,ε375=7630for freeferulic
acid;andε345=23,064,ε=31,430foresterifiedferulicacid).The
concentrationsforbothfree[FA]fandesterified[FA]eferulicacid
werecalculatedusingthefollowingequations:
[FA]e= [(A375×ε345)−(A345×ε375)] [(ε 375×ε345)−(ε345×ε375)] [FA]f= [A345−(ε345×[FA]e)] [ε345]
2.4. Determinationoftotalphenoliccontent
The phenolic content was measured by the Folin–Ciocalteu
method (Singleton and Rossi, 1965) with slight modifications
andexpressedasgramsof gallicacidequivalents.Thesamples,
0.1ml and 2.3ml of distilled water were mixed with0.1ml of
Folin–Ciocalteureagentandincubatedfor8min,followedbythe
additionof1mlof70g/lsodiumcarbonatesolutionwith2mlof
water.Themixturewasallowedtostandfor2hatroom
tempera-turebeforereadingtheabsorbanceat750nm.
2.5. Antioxidantactivity
2.5.1. Ferric-reducingantioxidantpower(FRAP)
Solutionsof300mMacetatebuffer(pH3.6),10mmol/lTPTZand
20mmol/lFeCl3·6H2Owereprepared,andfreshworkingsolutions
wereusedbymixingstocksolutionsinaratioof10:1:1to
pre-paretheFRAPreagent.TheFRAPreagent(2900l)wasmixedwith
100lofthesampleorstandard,andthemixtureswerekeptat
roomtemperatureunderdarkfor30min.Theabsorbanceofferrous
tripyridyltriazinecomplexwasmeasuredat593nmwitha
spec-trophotometer.Astandardcalibrationcurvewaspreparedusing
Troloxataconcentrationrangebetween10and50M(Benzieand
Strain,1996).
2.5.2. Troloxequivalentantioxidantcapacity(TEAC)
Solutions of2,2-azinobis(3-ethyl-benzothiazoline-6-sulfonic
acid) (ABTS) (7mM)and potassium persulfate(2.45mM) were
mixed and allowed tostand for 12–16h togenerate the ABTS
2,2-azinobis(3-ethyl-benzothiazoline-6-sulfonate)radicalcation
(ABTS•+). The ABTS•+ stock solution was diluted with 20mM
sodiumacetatebuffer(pH4.5)toobtain0.7absorbancereading
at734nm.Theantioxidantcapacitywasmeasuredbymixing2ml
of thesample with0.2ml of radical solution and by following
thedeclineintheabsorbancefor10minwithappropriatesolvent
blanksforeachaddition.Theradicalscavengingcapacitywas
com-paredwiththatofTroloxandtheresultswereexpressedasTEAC
values(mmolTrolox)(Reetal.,1999).
2.6. Experimentaldesignandresponsesurfacemethodology
(RSM)
A23 rotatablecentralcompositedesign(CCD)wasusedtofit
asecond-ordermodel.Thedesignconsistedof20setsof
experi-ments.Thequadraticmodelwasselectedforpredictingtheoptimal
pointandexpressedas:
Y = b0+b1X1+b2X2+b3X3+b11X12+b22X22+b33X32+b12X1X2
+b13X1X3+b23X2X3 (1)
whereYrepresentstheresponse variables(xyloseand phenolic
yield);b0istheinterceptioncoefficient;b1,b2,andb3arethelinear
terms;b11,b22,andb33arethequadraticterms;andX1,X2,andX3
representthevariablesstudied.
TheDesignExpertv.7(Stat-EaseInc.,Minneapolis)wasusedfor
regressionandthegraphicalanalysesofthedataobtained.Fischer’s
testwasusedforthedeterminationofthetypeofmodelequation,
whilethestudent’st-testwasperformedforthedeterminationof
statisticalsignificanceofregressioncoefficients.
3. Resultsanddiscussion
3.1. Sugarandbyproducts
Inthepreviousstudy,glucan(37%)wasreportedasamajor
com-ponentofwheatstrawfollowedbyxylan(23%)andlignin(klason
lignin:20%andacid-solublelignin:2%).Therestofitscomponents
werearabinan(2%),acetylgroups(1%),uronicacid(3%),protein
(3%),ash(6%)andextractives(3%)(Akpinaretal.,2010a).
Theconcentrationsofxyloseandotherdegradationproducts
showeddependence onthe experimentaloperating conditions,
which werealsoexplainedbytheseverityfactor (R0)(Fig.1A).
Severityfactorcombinestheexperimentaleffectsoftemperature,
reaction time and acid concentration to make the comparison
oftheresultseasy (Kabelet al.,2007).Thehighestxyloseyield
was0.169g/g-wheat straw, achievedat 140◦C for 15min with
0.000 0.005 0.010 0.015 0.020 0.025 2.08 1.99 1.62 1.62 1.39 1.21 1.13 1.08 1.07 1.05 1.03 1.01 0.88 0.86 0.27 0.23 0.19 0.38 -0.02 -0.08 (LogRo) Severity factor
Total phenolic (g gallic acid/g wheat straw) FRAP (mmol trolox/g wheat straw) TEAC (mmol trolox/g wheat straw)
Esterified ferulic acid (g ferulic acid/g wheat straw) Free ferulic acid (g ferulic acid/g wheat straw)
B
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 2.08 1.99 1.62 1.62 1.39 1.21 1.13 1.08 1.07 1.05 1.05 1.03 1.01 0.88 0.44 0.38 0.27 0.23 -0.02 -0.08Severity factor (LogRo)
g/g wheat straw
Xylose Glucose Arabinose Acetic acid Furfural
A
Fig.1.(A)Formationofxylose,glucose,arabinose,aceticacidandfurfuralunderselectedhydrolysisconditions;(B)phenolic,freeandesterifiedferulicacidcontent,and
antioxidantactivityofacidhydrolysateunderselectedhydrolysisconditions.Severityfactor:R0=[10−pH×t×exp(T−100)/14.75]ofthepretreatmentscalculatedfrompH
ofhydrolysate.
agriculturalwastes,othersugars,mainlyglucose,werereleased,
whichwereproducedeitherfromcellulosicfractionorfromsome
heteropolymers of hemicellulosic fraction. The level of glucose
in the fermentation media is important due to its the advers
effectonxylosebioconversiontootherchemicalssuchasxylitol
(Robertoetal.,2003).Inaddition,duringtheproductionofxylose,
anotherreactiontakesplace,whichisthedehydrationofxylose
tofurfural. Furfural formation not only decreases
monosaccha-rideyieldbutalsocausesproblemsassociatedwiththeinhibition
offermentationofthesugarsto,e.g.,ethanolorxylitol(Karimia
etal.,2006).Whentheoperatingtemperatureandreactiontime
were 153.3◦C and 30min respectively and the acid
concentra-tion was maintained at 4% (LogR0=1.99), glucose (0.063
g/g-wheat straw) and furfural (0.037g/g-wheat straw) yields were
maximum.
In all the experiments, arabinose yield remained between
0.01and0.02g/g-wheatstrawandaceticacidyieldwasbetween
0.002 and 0.014g/g-wheat straw. Low concentration of acetic
acid in the hydrolysate is particularly important for xylose
bioconversionbecausethisacidisoneofthepotentialinhibitors
ofthemicrobialmetabolism(Robertoetal.,2003).
3.2. Antioxidantactivityandphenoliccontent
TheFolin–Ciocalteutest,usedasameasureoftotalphenolics
valueinthehydrolysate,indicatestheamountreleasedfromthe
extractivesandligninfractionduringmildacidtreatment.TheABTS
scavengingtestwasselectedbecauseitisoneofthewidelyused
andsimpletechniques,andhasbeenproposedasoneofthe
meth-odsconsideredforstandardizationofantioxidantactivityinfood
andnutraceuticals(Prioretal.,2005).Astheantioxidantcapacity
of a lignin fractionis related to itsreducing ability, the
ferric-reducing powerwasselectedto measurethereducing capacity
(Castroetal.,2008).Theamountsoffreeandesterifiedferulicacid
werealsoevaluatedintheacidhydrolysateofwheatstrawbecause
theyhavepowerfulantioxidanteffect.Itwasreportedthat
esteri-fiedferulicacidshowshigherantioxidantcharacteristicsthanfree
0.0000 0.0050 0.0100 0.0150 0.0200 0.0250 4% 4% 4% 7.3% 4% 0.7% 4% 4% 4% 55 min 30 min 5 min 30 min 30 min 30 min 30 min 30 min 30 min 120 oC 120 oC 120 oC 120 oC 120 oC 120 oC 153.3 oC 120 oC 86.7 oC
Total phenolic (g gallic acid/g wheat straw) FRAP (mmol trolox/g wheat straw) TEAC (mmol trolox/g wheat straw)
Esterified ferulic acid (g ferulic acid/g wheat straw) Free ferulic acid (g ferulic acid/g wheat straw)
Fig.2.Theeffectoftemperature,timeandacidconcentrationofpenolic,freeandesterifiedferulicacidcontent,andantioxidantactivityofacidhydrolysate.
Table1
Experimentalrangeandlevelsofindependentprocessvariables.
Independentvariable Symbol Rangeandlevels
−˛ −1 0 +1 +˛
Temperature(◦C) X1 86.7 100 120 140 153.3
Reactiontime(min) X2 5 15 30 45 55
Acidconcentration(%) X3 0.7 2 4 6 7.3
Table2
Experimentaldesignandresultsobtainedbyhydrolysisofwheatstrawandseverityfactorofthepretreatments.
Runs LogR0 Variables Responses
X1 X2 X3 Y1(g-xylose/g-wheatstraw) Y2(g-gallicacid/g-wheatstraw)
1 −0.08 100 15 2 0.005 0.0084 2 −0.02 86.7 30 4 0.021 0.0071 3 0.19 100 45 2 0.033 0.0093 4 0.23 120 5 4 0.156 0.0104 5 0.27 120 30 0.7 0.080 0.0113 6 0.38 100 15 6 0.045 0.0121 7 0.86 120 30 4 0.168 0.0138 8 0.88 100 45 6 0.120 0.0110 9 1.01 120 30 4 0.128 0.0134 10 1.03 120 30 4 0.153 0.0145 11 1.05 120 30 4 0.164 0.0128 12 1.07 120 30 4 0.128 0.0146 13 1.08 120 30 4 0.143 0.0130 14 1.13 140 15 2 0.169 0.0143 15 1.21 120 55 4 0.155 0.0125 16 1.39 120 30 7.3 0.134 0.0141 17 1.62 140 45 2 0.124 0.0167 18 1.62 140 15 6 0.142 0.0175 19 1.99 153.3 30 4 0.119 0.0227 20 2.08 140 45 6 0.089 0.0199
Y1,xyloseyield(g-xylose/g-wheatstraw);Y2,totalphenolic(g-gallicacid/g-wheatstraw);R0:severityfactors(R0=[10−pH×t×exp(T−100)/14.75]).
Table3
Analysisofvarianceforxyloseyieldandtotalphenolicscontent.
Source Sumofsquares Degressoffreedom Meansquare F-value P-value
Y1 Y2 Y1 Y2 Y1 Y2 Y1 Y2 Y1 Y2 Model 0.046 0.00025 7 5 0.0066 0.00005 23.03 27.36 <0.0001 <0.0001 Residual 0.0034 0.000014 12 14 0.00029 0.000001 Lackoffit 0.0019 0.000012 7 9 0.00028 0.0000013 0.91 2.62 0.5597 0.1913 Pureerror 0.0015 0.0000028 5 5 0.00030 0.00000057 Total 0.05 0.00026 19 19 R2 0.93 0.95
Fig.3. (A)EffectofH2SO4concentrationandreactiontemperatureonxyloseyieldwhentimewassetat30minasthecenterpoint.(B)Effectofreactiontemperatureand
timeonxyloseyieldwhenacidconcentrationwassetat4%asthecenterpoint.(C)EffectofH2SO4concentrationandreactiontemperatureonphenoliccontentwhentime
wassetat30minasthecenterpoint.(D)Effectofreactiontemperatureandtimeonphenoliccontentwhenacidconcentrationwassetat4%asthecenterpoint.
reduced the oxidation of low-density lipoproteins (Li et al.,
2008).
Themostactiveradicalscavengerofwheatstrawhydrolysate
wasgeneratedat153.3◦Cfor30minwith4%acidconcentration.
TheredoxpotentialofFe3+saltsusedintheFRAPassaywas
com-parablewiththatoftheTEACvalue,andcorrelationwithphenolic
contentwasobserved(Fig.1B).Esterifiedferulicacidwashighestat
140◦Cfor15minand2%acidconcentration(LogR0=1.13),andits
amountwashigherthanfreeferulicacid.Whentheseverityofthe
operationconditionswasincreased,theamountoffreeferulicacid
startedtoincreaseandthevaluebecamehigherthantheesterified
one.
Theyieldinphenoliccompound,includingantioxidantactivity
andfreeandesterifiedferulicacid,wasnotaffectedsignificantly
bythesulfuricacidconcentrationandthereactiontimeusedinthe
acidhydrolysisstage,butwasstronglyaffectedbythe
tempera-ture.Thehighestphenoliccontentwas0.0227g-gallicacid/g-wheat
straw,achievedat153.3◦Cfor30minwith4%acidconcentration
(LogR0=1.99)(Fig.2).
3.3. Statisticalmodeling
Theexperimental range and levelsof independent variables
investigatedaregiveninTable1.Thedesignofthisresearch,
includ-ingthedependentvariables orresponses,xyloseyield(Y1)and
phenoliccontent(Y2),isgivenin Table2.Thequadraticmodels
withcodedvariablesareshowninEqs.(2)and(3),which
repre-sentthexyloseyield(Y1)andphenoliccontent(Y2)asafunctionof
temperature(X1),time(X2)andacidconcentration(X3).
Y1 =0.15+0.035X1+0.00026X2+0.012X3−0.03X12 −0.023X2 3−0.025X1X2−0.024X1X3 (2) Y2 =0.013+0.0039X1+0.00060X2+0.0013X3+0.00057X12 −0.00064X2 2 (3)
Regression analysiswasperformedtofit theresponse
func-tionandexperimentaldata.Thesecond-ordermodelsforxylose
andphenolicyieldwereevaluatedbyANOVA,whichareshown
inTable3.Forbothresponses,theregressionwasstatistically
sig-nificantat95%confidencelevel.Themodelforbothresponsesdid
notshowlackoffit.Thedeterminationcoefficient(R2)forthefirst
(Y1)andthesecondresponse(Y2)was0.93and0.95respectively,
explainingthe93and95%ofvariabilityintheresponses.
Fig.3showstheresponsesurfacestoestimatethexyloseand
phenolicyieldovertheindependentvariablesoftemperature(X1),
time(X2)andacidconcentration(X3).Whenthereactiontimewas
setat30minascenterpoint,asshown inFig.3AandC,it was
interpretedthatthemaximumxyloseyield(0.16g/g-wheatstraw)
wasobtainedwitha3.8%acidconcentrationand129◦Creaction
temperature.Themaximumphenolic contentwas0.019g-gallic
acid/g-wheatstrawat6%acidconcentrationwith140◦Creaction
temperature.Fig.3BandDshowstheeffectoftemperatureand
timeonxyloseyieldandthephenoliccontentofthehydrolysate
whenthereactiontimewassetacidconcentrationwas4%asthe
center point.Themaximumxyloseyield(0.18g/g-wheatstraw)
wasobtainedat140◦Cand15minreactiontime,andthe
maxi-mumphenoliccontent(0.018g-gallicacid/g-wheatstraw)ofthe
hydrolysatewasobtainedat140◦Cand45minreactiontime.
Whentheoverallxyloseyieldandphenoliccontentoftheacid
hydrolysateofwheatstrawwerecomparedwiththoseobtained
from previousstudies carried out for theproduction of xylose
(Robertoet al.,2003; Akpinaret al.,2010b)and phenolic
com-pounds(Moureetal.,2008)fromlignocellulosicmaterialswithacid
hydrolysis,itwasfoundthatthexyloseyieldandthephenolic
100.00 115.00 130.00 145.00 160.00 0.00 15.00 30.00 45.00 60.00 A: Temperature B: Time Y1: 0.12 Y1: 0.12 Y1: 0.16946 Y2: 0.012 Y2: 0.0227
Fig.4.Overlayingplotsofxyloseyieldandphenoliccontentoftheacidhydrolysate
ofwheatstraw.
thehydrolysisconditionsofwheatstrawresultedwithincreasein
phenolicyieldsanddecreaseinxyloseyield.
Basedonthetwomodels,a graphicaloptimizationthat
con-sisted of overlaying thecontour plots of both the modelswas
conducted.Theoptimalworkingconditionsbasedonhighlevel
xylose yield and phenolic content were chosen using the
fol-lowingcriteria:xyloseyield>0.12g/g-wheatstrawandphenolic
content>0.012g-gallicacid/g-wheatstraw.Intheoverlayingplot
(Fig.4),theregionswitha shadedareadonotfit the
optimiza-tioncriteria,whilethenon-shadedareameetstheoptimization
criteria. As an optimum point, 4.7% acid concentration, 120◦C
and45minwereselected.Underthiscondition,theseverity
fac-torofthe treatment,calculated as LogR0,wasfoundto be1.2.
Undertheseconditions,thexyloseyieldandphenoliccontentwere
predictedas0.15g/g-wheatstrawand0.014g-gallicacid/g-wheat
straw,respectively.Toconfirmtheseresults,hydrolysisrunswere
conductedundertheseoptimizedconditions,thexyloseand
phe-nolicyieldofwheatstrawwereobtainedas0.16g/g-wheatstraw
and0.014g-gallicacid/g-wheatstraw,respectively.
4. Conclusion
Higherseveritiesofconditionsresultedinimprovedyieldsof
phenolic contentof the acidhyrolysate of wheat straw, but in
decreased xylose yield. The optimum reaction conditions were
foundas 4.7%acid concentration,120◦C and 45minfor wheat
straw.Underselectedhydrolysisconditions,wheatstrawproved
tobeapromisingsourceofhighyieldxylose,whichcouldbeused
fortheproductionofdifferentchemicals,mainlyxylitoland
phe-noliccompoundswhichexhibitedhighantioxidantactivities.The
resultsshowedthatwheatstrawhadthepotentialapplicationsarea
forthepolysaccharide-basedantioxidantsinfood,pharmacyand
cosmetics.
Acknowledgment
ThisworkwaspartiallysupportedbyTheScientificand
Tech-nologicalResearchCouncilofTurkey.
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