Extraction and fractionation of phenolic acids and
glycoalkaloids frompotato peels using acidied water/ethanol-based
solventsAlma Fernanda Snchez Maldonadoa, Elizabeth Mudgea, Michael
G. Gnzlea, Andreas Schiebera,b,aDepartment of Agricultural, Food
and Nutritional Science, University of Alberta, 4-10
Agriculture/Forestry Centre, Edmonton, Canada, AB T6G 2P5bInstitute
of Nutritional and Food Sciences, Chair of Food Technology and Food
Biotechnology, University of Bonn, Rmerstrasse 164, D-53117 Bonn,
Germanyabstract arti cle i nfoArticle history:Received 3 February
2014Received in revised form 3 June 2014Accepted 4 June
2014Available online 20 June 2014Keywords:Potato peelsPhenolic
acidsGlycoalkaloidsWater/ethanol-based extractionSolid-phase
extractionUFLCMSPotato processing generates potato peels as
byproducts. Methanolic extracts fromthe peels result in mixtures
ofphenolic acids and glycoalkaloids. Phenolic acids have potential
for food applications owing to their antioxidantand antibacterial
properties. However, when extracted from potatoes, their separation
from toxic glycoalkaloidsis needed prior to their applications in
foods. Moreover, glycoalkaloids may be used as feedstock for
synthesis ofpharmaceuticals. This study aimed to develop a method
for the extraction and fractionation of phenolic acids
andglycoalkaloids from potato peels using food grade
water/ethanol-based solvents. Samples were analyzed byultrafast
liquid chromatography (UFLC) and/or ultrafast liquid
chromatographymass spectrometry (UFLCMS). A methanol-based solvent
for extraction was used as a control to be compared with two
aqueous ethanolicsolvents acidied with acetic acid. The recovery of
the predominant compounds from potato peels was compa-rable for all
three solvents. Extraction yielded per 100 g of potato peel fresh
weight 17.0 mg -chaconine, 7.1mg -solanine, 0.1 mg solanidine, 4.8
mg caffeic acid, 13.3 mg neochlorogenic acid, and 77.6 mg
chlorogenicacid. More than 90% of these compounds were recovered
after two consecutive extractions. The crude extractwas
fractionated by solid-phase extraction at pH 7 and eluted with
aqueous ethanol. Quantitative recovery ofthe phenolic acids and
glycoalkaloids was achieved in their corresponding fractions.
Hydrolysis followed bysolid-phase fractionation of the crude
extract allowed recovery of 139 mol caffeic acid/100 g potato peel
freshweight. Partial degradation of caffeic acid and glycoalkaloids
occurred during the process. Degradation of caffeicacid can be
likely mitigated by the addition of antioxidants and metal
chelators. The method developed in thisstudy allows the sustainable
recovery of secondary plant metabolites from potato peels and their
fractionationusing food grade water/ethanolic solvents for
application of phenolic extracts free of toxic glycoalkaloids
forfood preservation, and of glycoalkaloid extracts for synthesis
of pharmaceuticals. 2014 Elsevier Ltd. All rights reserved.1.
IntroductionPotatoes (Solanum tuberosum L.) are among the most
important staplecrops consumed by humans (Mattila & Hellstrom,
2007). The productionof value-added potato products has increasedto
satisfy the demand of con-sumers for conveniencefoods, whereas
freshpotatoconsumptionis contin-uouslydecreasing.
Processingleadstotheproductionof signicantamounts of waste(FAO,
2008; Schieber &Aranda Saldaa, 2009).
Processedpotatoproductsaccountonlyfor50to60%ofthe rawmaterial.
Thebyproducts include cull potatoes andprocessing waste
(Charmley,Nelson, & Zvomuya, 2006). Peels constitute the main
fraction of the pro-cessing waste. While considered waste, potato
peels also contain valuablecomponents (Mder, Rawel, & Kroh,
2009). Phenolic compounds andglycoalkaloids are particularly
interesting because they are suitable forapplication in the food
and pharmaceutical industries after extraction andpurication (Mder
et al., 2009; Schieber & Aranda Saldaa, 2009).Phenolic acids
are the main phenolic compounds in potatoes (Mderet al., 2009;
Schieber & Aranda Saldaa, 2009; Singh & Saldaa, 2011).They
have shown antioxidant and antibacterial activities (Rodriguezde
Soltillo, Hadley & Wolf-Hall, 1998; Snchez-Maldonado, Schieber,
&Gnzle, 2011; Svensson, Sekwati-Monang, LopesLutz, Schieber,
&Gaenzle, 2010). Therefore, these compounds hold promise for
applica-tionaspreservativesinfoods, feeds, andpackingmaterials.
Plantextracts containing phenolic acids were suitable as food
preservatives(Corrales, Han, & Tauscher, 2009; Ejechi &
Akpomedaye, 2005; Elegir,Kindl, Sadocco, & Orlandi, 2008).
However, chlorogenic acid constitutes90%of the phenolic compounds
inpotato peels (Imet al., 2008; Schieber& Aranda Saldaa, 2009).
Chlorogenic acid exists in the form of threemain isomers, which
include chlorogenic acid (5-O-caffeoylquinic acid),neochlorogenic
acid (3-O-caffeoylquinic acid) and cryptochlorogenicacid
(4-O-caffeoylquinic acid) (Lee & Finn, 2007; Nandutu, Clifford,
&Howell, 2007; Shui, Leong, & Wong, 2005). Chlorogenic acid
isomersdo not have strong antibacterial activity but can be
hydrolyzed to quinicFood Research International 65 (2014) 2734
Corresponding author at: Institute of Nutritional and Food
Sciences, Chair of FoodTechnology and Food Biotechnology,
University of Bonn, Rmerstrasse 164, D-53117Bonn, Germany. Tel.:
+49 228 73 4452; fax: +49 228 73 4429.E-mail address:
[email protected] (A.
Schieber).http://dx.doi.org/10.1016/j.foodres.2014.06.0180963-9969/
2014 Elsevier Ltd. All rights reserved.Contents lists available at
ScienceDirectFood Research Internationalj our nal homepage:www. el
sevi er . com/ l ocat e/ f oodr esandcaffeicacids(Fig. 1).
Caffeicacidshowsantimicrobialactivityagainst gram positive and gram
negative bacteria at concentrationsranging from 0.1 to 1 g/L
(Rodriguez de Soltillo et al., 1998; Snchez-Maldonado et al.,
2011). Quinic acid, the second product of chlorogenicacid
hydrolysis, is a starting material for the synthesis of drugs such
asOseltamivirforinuenzatreatment(Yeung, Hong&Corey, 2006;Satoh,
Akiba, Yokoshima, & Fukuyama, 2007).Glycoalkaloids are plant
steroids that contain nitrogen and a
sugarmoietyattachedtothe3-OHposition(Fig. 2).
-Chaconineand-solanine are the main glycoalkaloids found in
potatoes (Friedman,2004). They are suitable for utilization in
pharmaceutical industry. Theaglycone solanidine is an intermediate
for the synthesis of hormonessuch as progesterone and cortisone
derivatives (Nikolic & Stankovic,2003). Additionally,
glycoalkaloidsandtheiraglyconeshavebeenshown to possess
anti-allergic, antipyretic, anti-inammatory, hyper-glycemic, and
antibiotic properties (Friedman, 2006).
Furthermore,potatoglycoalkaloidshaveantifungalactivities(Fewell&Roddick,1993,
1997). However, they are toxic for humans and should be
absentinpotatoproducts or potatoextracts usedfor
foodapplications(Rodriguez-Saona, Wrolstad, & Pereira, 1999).
For fresh potatoes, amaximum of 200 mg of glycoalkaloids per
kilogram is acceptable forhuman consumption (Fewell & Roddick,
1993; Friedman, 2006).Conventional methods for the extraction of
phenolic compounds fromplant material use organic solvents such as
methanol, acetone, ethanolandethyl acetate (Dai &Murpher, 2010;
Svensson et al., 2010).Glycoalkaloids from potatoes are
traditionally extracted with chloroform/methanol mixtures (Bushway
& Ponnampalam, 1981; Friedman,Roitman, & Kozukue, 2003).
These methods are detrimental for the envi-ronment. Water and
ethanol are alternatives for the recovery of
phenoliccompoundsfrompotatopeels,
facilitatingfoodapplications(Kannat,Chander, Radhakrishna,
&Sharma, 2005;Onyeneho&Hettiarachchy,1993; Singh &
Rajini, 2004). Water/acetic acid mixtures have been
usedtoextractglycoalkaloids(Friedmanetal., 2003;Machado, Toledo,
&Garca 2007; Sotelo & Serrano, 2000). However, to our
knowledge thereis no method for the simultaneous recovery and
subsequent separation ofphenolic acids and glycoalkaloids to obtain
food grade phenolic extractsfree of toxic glycoalkaloids and the
corresponding glycoalkaloids fractionfor pharmaceutical purposes.
In addition, recovery of these compoundsfrom potato peels using
food grade solvents would be an advantage forthe food industry
since it reduces the organic waste that causes disposalproblems
(Kim & Kim, 2010) and minimizes the environmental impact
oftoxic solvents. Therefore, this study aimed to develop a
sustainable methodfor the simultaneous extraction of these
compounds from potato peelsusing food grade acidied water/ethanol
based solvents. Furthermore, ex-periments aimed to achieve
separation of polyphenols and glycoalkaloidsfrom potato peels to
allow applications of both fractions in the food andpharmaceutical
industries, respectively.2. Materials and methods2.1. External
standardsChlorogenic acid (5-O-caffeoylquinic acid) and caffeic
acid werepurchased from Sigma (St. Louis, MO, USA). -Chaconine,
-solanineand solanidine were obtained from Extrasynthese (Genay,
France).2.2. Extraction of potato peelsPotatoes from the
cultivarRusset purchased in a local grocerystore in Edmonton,
Alberta, Canada were used for this study. Aftermanual peeling, 30 g
of fresh peels was simultaneously crushed andmixed with 75 mL of
extraction solvent in a domestic blender. Peelsand solvent were
left in the dark for 30 min, stirred for an additional30 min,
sonicated for 20 min, and centrifuged at 4696 g. The supernatantwas
recovered andltered. Extraction was performed three times perbatch
and samples from each extraction were collected. Three
differentsolvents were used for extraction; acetic acid was used to
equal the pHto that of the control solvent (3.2). Solvent A
contained 25% water, 70%methanol,
and5%aceticacid;solventBcontained24%water, 67%ethanol, and 9%
acetic acid; and solvent C contained 46% water, 51%ethanol and 3%
acetic acid. The organic solvent was evaporated undervacuum at 40 C
using a Rotavapor RE21 (Bchi, Flawil, Switzerland).The dry potato
peel extract was resuspended in 15 mL of water. A40 mg/L standard
solution of chlorogenic acid was extracted underthe same conditions
as the potato peels in order to evaluate stabilityof chlorogenic
acid during the process.2.3.
Fractionationofphenolicacidsandglycoalkaloidsbysolid-phaseextractionPhenolic
acids were fractionated fromthe glycoalkaloids using a SepPak Vac 6
cc C18 cartridge. Solvents and water were adjusted to pH 7.Prior to
use, the column was conditioned by elution with 5 mL of etha-nol
followed by 5 mL of water. Two milliliters of the extract
previouslyresuspended in water was passed through the column and
washedwith 5 mL of water (pH 7). Subsequently, 20 mL of the
correspondingsolvent was added,phenolic acids were elutedwith
water/ethanol(80:20, v/v) andglycoalkaloids were
elutedwithwater/ethanol(20:80, v/v). To determine the volume of
solvent required for completeelution, the fractions were collected
successively in 2 mL tubes, and theconcentration of phenolic acids
and glycoalkaloids was determinedsubsequently.2.4. Alkaline
hydrolysis of chlorogenic acidThree mL of the extract obtained from
solvent C, previously dis-solved in 15 mL of water, was centrifuged
and the supernatant wasmixed with 750 L of NaOHsolution (10 M) and
ushed under nitrogenfor 2 min. The vial was hermetically closed and
the solution was stirredfor4 hoursat roomtemperature. Subsequently,
thesolutionwasadjusted to pH 4 with HCl and used for fractionation
as described inSection 2.3. To evaluate whether alkaline hydrolysis
results in the lossof caffeic acid, a 40 mmol/mL standard solution
of chlorogenic acidwassubjectedto
alkalinehydrolysisunderthesameconditionsaspreviously mentioned.2.5.
Quantication of phenolic acids and
glycoalkaloidsTheseparationandquanticationofphenoliccompoundsfrompotato
peels were performed using an ultrafast liquid
chromatography(UFLC)systemconsistingof aLC20ADXRpump,
SIL-20ACXRFig. 1. Products of alkaline hydrolysis of chlorogenic
acid.28 A.F. Snchez Maldonado et al. / Food Research International
65 (2014) 2734Prominence autosampler, a Prominence columnovenand a
ProminenceSPD-M20 diode array detector (Shimadzu, Kyoto, Japan).
Separationswere performed on a Kinetex PFP column (100 3.0 mm, 2.6
m).The injection volume was 5 L and theow rate was 0.9 mL/min.
Thetemperature of the oven was 25 C. The mobile phase consisted of
(A)0.1%(v/v)formicacidinwaterand(B)0.1%(v/v)formicacidinwater/acetonitrile
(10:90), according to the method of Cruz, Novak,and Strnad
(2008).The gradient program was as follows: 020%B(01.5 min),
20%B(1.54.5 min), 2090%B(4.57.5 min), 90%B(7.58 min) and 900% B
(814 min). Phenolic acids were detected at280 and 320 nm.
Quantication of chlorogenic and caffeic acids wasperformed using
external standards dissolved in a mixture
ofmethanol/water/formicacid(80:20:0.1).
Neochlorogenicacidandchlorogenicacidwerequantiedbasedonthestandardcurveofchlorogenic
acid. Calibration curves, with a correlation coefcient of0.99,
wereestablishedusingconcentrationrangesfrom0.005to0.15 and from
0.01 to 0.32 g/L for caffeic acid and chlorogenic acid,
re-spectively. Fresh standard solutions were prepared on the same
day ofthe analysis for each run.Phenolic compounds in the extracts
were characterized by ultrafastliquidchromatographymass
spectrometry(UFLCMS) under thesame LC conditions mentioned above.
The UFLC system was coupledto an Applied Biosystems MDS SCIEX 4000
Q TRAP LC/MS/MS System(AB Sciex, Concord, Ontario, Canada) equipped
with an ESI Turbo Vsource operating in negative mode with the
pneumatically assistedelectrospray probe using high-purity nitrogen
gas (99.995%) as thenebulizing(GS1)andheatinggas(GS2).
Thevaluesforoptimumspray voltage, source temperature, GS1, GS2, and
curtain gases were4kV, 600C, and50, 30, and25psi, respectively.
Identicationof phenolic compounds was performed using enhanced mass
spectrom-etry (EMS) with information dependent acquisition (IDA) of
enhancedproduct ion scans (EPI). Q1 and Q3 were operated at low and
unitmass resolution. The spectra were obtainedover a range
fromm/z50 to 1300 in 2 s. LITll time was 20 ms. The IDA threshold
was100cps. EPI spectrawerecollectedfromtheeight most intensepeaks
abovethis parameter. TheEPI scanratewas 1000
amu/s.Collision-induceddissociation(CID)
spectrawereacquiredusingnitrogen as the collision gas under two
different collision energies.The collision energy (CE) was 20 eV
and collision energy spread(CES) was 0 eV. Declustering potential
(DP), entrance potential (EP),andcollisionexitpotential(CXP)were
70V, 10Vand 7V,respectively.The analysis of glycoalkaloids was
performed using the same UFLCMS system described above, performed
in positive MS mode. Quanti-cation was done by MS using the
multiple reaction monitoring mode(MRM). AKinetexC18100A(1003.0mm,
2.6m)columnwasused as the stationary phase. The injection volume
was 5 L and theow rate was 0.6 mL/min. The temperature of the oven
was 25 C.The mobile phase consisted of (A) 0.5% (v/v) formic acid
in water/acetonitrile (95:5) and (B) 0.5% (v/v) formic acid in
water/acetonitrile(5:95). The gradient was as follows: 20% B (012.5
min), 2090% B(12.513.5 min), 90% B (13.514.5 min), 9020% B (14.516
min) and20% B (1620 min). An IDA, MRMEPI, was used to prole and
quantifythe glycoalkaloids. Q1 and Q3 were operated at low and unit
massresolution. The spectra were obtained over a scan range from
m/z 50to 1000 in 2 s. LITll time was set at 20 ms. The IDA
threshold was setat 100 cps, above which enhance product ion
spectra were collectedfromthe eight most intense peaks. For the
MRMthe values for optimumspray voltage, source temperature, GS1,
GS2, and curtain gases were+4.5 kV, 600 C, 60, 45, and 15 psi,
respectively. The MRM scan ratewas 1000 amu/s. Optimization of DP,
EP, CE and CXP was done
speci-callyforeachtransitionandthevaluesusedwereintherangeof5570 V,
814 V, 60100 eV and 1040 V, respectively. The two mostabundant
transitions for each compound were selected (Q1 Q3),for
quantication and conrmation. For -chaconine, -solanine
andsolanidine the transitions for quantication were (Q1 852 Q3
706),(Q1 868 Q3 398) and (Q1 398 Q3 98), respectively. For the
EPI,thescanratewas4000 amu/sandthevaluesforoptimumsprayvoltage,
source temperature, GS1, GS2, and curtain gases were +5 kV,600 C,
50, 30, and 10 psi, respectively. Standard solutions dissolved
inmethanol/water/formic acid (80:20:0.1) were used for the
calibrationcurves that gave a correlation coefcient of 0.99. The
concentrationranges were 100 to 10000 ppb for -chaconine, and 50 to
5000 ppbfor both -solanine and solanidine.The limits of detection
(LODs) and quantitation (LOQs) of phenolicacids and glycoalkaloids
were determinedaccording to the InternationalConference on
Harmonization (ICH) (Chandran &Singh, 2007; Nandutuet al.,
2007) as LOD = 3/S and LOQ = 10/S, where is the standarddeviationof
responseandSistheslopeof thecalibrationcurve.TheLODandLOQof
chlorogenic acidwere determinedas 0.36and 1.20 ng/L, respectively.
The LOD and LOQ for caffeic acid were0.16 ng/L and 0.55 ng/L,
respectively. The LODs for -chaconine, -solanine and solanidine
were 3.22, 5.42 and 0.01 g/L,
respectively.TherespectiveLOQswere10.7, 18.07and0.033 g/L,
inthesameFig. 2. Product of hydrolysis of -chaconine and
-solanine.29 A.F. Snchez Maldonado et al. / Food Research
International 65 (2014) 2734order. Data are reported as means
standard deviations of triplicateindependent experiments.2.6.
Quantication of quinic acidAfter alkaline hydrolysis, quinic acid
was quantied according to themethod for organic acids published by
Teixeira, McNeil, and Gnzle(2012), using anAgilent 1200 series
HPLCunit comprising of a degasser,binary pump, autosampler,
thermostated column compartment,and diode array detector (Agilent
Technologies, Palo Alto, CA, USA).Separation was performed using an
Aminex HPX-87 column (Bio-Rad,Mississauga, ON, Canada) at 70 C.
Quinic acid was detected at 210 nm.Isocratic elution with aow rate
of 0.4 mL/min during 60 min wasused. The solvent consisted of 5 mM
H2SO4. No peaks were detected,indicating that the amount of quinic
acid in the samples was belowthe detectionand quanticationlimits of
the method. For the standards,only concentrations above 1 mmol/L
were detected.2.7. Statistical analysisDataarereportedasmeans
standarddeviationsoftriplicateindependent experiments. SigmaPlot
software (Systat Software, Inc., SanJose, CA, USA) was used to
perform all statistical analyses. To determinestatistically
signicant differences between the three extraction methods,data
were subjected to two-way analysis of variance (ANOVA). For therest
of the experiments, the recovery of eachcompoundwas
statisticallyanalyzed by one-way ANOVA followed by the HolmSidak
method formultiple pairwise comparisons when required. For all
analyses statisti-cal signicance was based on P b 0.05.3.
Results3.1. Extraction of potato peels using three different
solventsThreesolventsweretestedfortheextractionofphenolicacidsand
glycoalkaloids from fresh potato peels to compare their
recoveryusing acidied aqueous methanol and ethanol-based mixtures.
Therewas no signicant difference between the phenolic compounds
andglycoalkaloids extracted from potato peels with any of the
solvents(Fig. 3). To evaluate possible hydrolysis of chlorogenic
acid into caffeicacid during the extraction, a standard solution of
chlorogenic acid wasextracted using the same conditions as for
potato peels (Fig. 3(1)). Nohydrolysis into caffeic acid was
observed and the extraction efciencywas higher than 99%.3.2. MS
identication of phenolic compounds and glycoalkaloids in
theextractsUFLCMSanalysis of constituents showedfour
mainphenoliccompounds and three alkaloids in the potato peel
extract (Table 1).Chlorogenic and caffeic acids and the three
alkaloids were identiedusing standards. Mass spectra of the three
rst peaks inthe phenolics ex-tract matched those of caffeic acid,
chlorogenic acid and neochlorogenicacid. Their maximumabsorption
wavelength was 324, 326 and 322 nm,respectively, which is typical
for hydroxycinnamates (Nandutu et al.,2007). Chlorogenic acid and
neochlorogenic acid were distinguished bythe order of elution under
reversed-phase HPLC conditions and peakintensity as previously
reported by Clifford et al. (2003), Matsui et al.(2007) and Nandutu
et al. (2007). The fourth compound with a massspectrumshowing m/z
529 as parent ion and base peak, anda maximumwavelength of 322 nm,
might correspond to a caffeoylferuloylquinic acid(Nandutu et al.,
2007). However, no fragmentation was observed tosupport the
identity of this compound. The glycoalkaloids were identi-ed as
-chaconine, -solanine and solanidine.3.3. Recovery of phenolic
acids and glycoalkaloids from potato peelsThe amount of
neochlorogenic, chlorogenic and caffeic acids recov-ered from
potato peels was 13.3, 77.6, and 4.8 mg/100 g of potato peelfresh
weight, respectively. The recovery of -chaconine, -solanineand
solanidine was 17.0, 7.1 and 0.1 mg/100 g of potato peel
freshweight, respectively. The recovery was calculated as average
of theyield obtained with three different solvents.3.4. Consecutive
extractions of bioactive metabolites from potato peelsTo determine
howmany extraction steps are needed for the quanti-tativerecoveryof
secondarymetabolitesfrompotatopeels, threeconsecutive extractions
were performed with the same batch of freshpotato peels. Samples
from each extraction were collected and investi-gatedbyUFLCMS(Fig.
4). After the secondextraction, 97%ofchlorogenic acid, 94% of
neochlorogenic acid and 89% of caffeic acidwere recovered. The
recovery of -chaconine and -solanine after thesecond extraction was
higher than 99%. In addition, 95% of solanidinewas recovered after
the second extraction.3.5.
Fractionationofphenolicacidsandglycoalkaloidsbysolid-phaseextractionTo
accomplish fractionation of phenolic acids and glycoalkaloidsfrom
the potato peels extract, solid-phase extraction with a Sep PakVac
6 cc C18 cartridge was used. The extract obtained using solvent CA
B CWFleepotatopg001/gm020406080100SolventA B C0510152025S S+
EL/gmdicacinegorolhC010203040501 3 2Fig. 3. Recovery of phenolic
acids and glycoalkaloids. (1) Amount of chlorogenic acid ( ) in a
standard solution (S) and recovery after extraction from that
standard solution (S + E),using solvent C. (2) Phenolic acids
recovered frompotato peels using 3 different solvents (A, B or C):
chlorogenic acid ( ), neochlorogenic acid ( ), caffeic acid ( ).
(3) Glycoalkaloidsrecovered frompotato peels using 3 different
solvents (A, B or C): -chaconine ( ), -solanine ( ), solanidine (
). Data are means standarddeviations (n =3). Signicant
differenceswere determined by two-way ANOVA (P b 0.05). For (2) and
(3) the yields of compounds were compared as a function of the
solvents used. There were no signicant differences.30 A.F. Snchez
Maldonado et al. / Food Research International 65 (2014) 2734was
employed for this purpose (Fig. 5). Statistical analysis showed
thatthe solid-phase extractionachieved quantitative recovery of
chlorogenicacid. However, there was a signicant difference between
the amountsof neochlorogenic acid and caffeic acid before and after
fractionation.Theamount of neochlorogenic aciddecreased,
whilecaffeic acidincreased.For completeelution, phenolic compounds
andglycoalkaloidsrequired 10 and 8 mL of solvent, respectively
(Fig. 6). The fractionationallowedcompleterecoveryof
glycoalkaloidsandnohydrolysistosolanidine was observed. The
concentration of glycoalkaloids inthe frac-tion containing phenolic
acids was below the detection limit of 3.2, 5.4and 0.01 g/L of
-chaconine, solanine and solanidine, respectively.Vice versa, the
concentrations of phenolic acids in the glycoalkaloidsfraction were
below their respective detection limits.3.6. Alkaline hydrolysis of
the potato peel extract followed by fractionationof phenolic acids
and glycoalkaloidsThe extract obtained from solvent C was
subsequently subjected
toalkalinehydrolysisandfractionatedbysolid-phaseextraction.
Thecrude extract, the hydrolyzed extract and the recovered
fractions wereanalyzed by UFLCMS (Fig. 7). The initial crude
extract contained 226,37 and 29 mol/100 g of potato peel FWof
chlorogenic, neochlorogenicand caffeic acids, respectively. After
alkaline hydrolysis, no chlorogenicacid isomers were detected and
the extract contained 179 mol caffeicacid/100 g potato peel FW.
After fractionation, 139 mol caffeic acidand 100 g potato peel FW
were recovered. To evaluate the efciencyof the hydrolysis and the
recovery after fractionation, the amounts inmol/100 g potato peel
FW of chlorogenic acid, neochlorogenic acidand caffeic acid present
in the initial extract were summarized andcomparedto the yieldof
caffeic acidafter hydrolysis andafter hydrolysisand fractionation.
There was a signicant difference between the sumofthe three initial
compounds and the yield of caffeic acids after hydrolysis.However,
no signicant difference was observed between caffeic
acidafterhydrolysisandafterhydrolysisandfractionation.
Toevaluatewhether alkaline hydrolysis results inthe loss of caffeic
acid, a chlorogenicacid standard was subjected to alkaline
hydrolysis (Fig. 7(1)). Afterhydrolysis, 44% of the molar
concentration of chlorogenic acid wasrecovered as caffeic acid,
indicating high losses of caffeic acid
duringhydrolysis.Followingalkalinehydrolysis, theamount of
-chaconineand-solanine signicantly decreased to about 50% of their
initial quantity(Fig. 7). Moreover,
nosolanidinewasdetectedinthehydrolyzedextract, indicating not only
hydrolysis but also degradation of thesealkaloids. However, the
recovery of glycoalkaloids did not change signif-icantly between
after hydrolysis and after hydrolysis and fractionation.3.7. Purity
of extractsTo obtain an approximation of the purity of the extracts
regardingthe amount of the phenolic compounds before and after
hydrolysis,the percentages of the compounds were calculated related
to the totalpeak area of the chromatograms at 280 nm and 210 nm.
These wave-lengths were used because a wide range of compounds
shows absor-bance there. Before alkaline hydrolysis, the summarized
amounts ofneochlorogenic acid, chlorogenic acid and caffeic acid
accounted for75% and 69% of the material absorbing at 280 nm in the
crude extractand phenolic acids fraction, respectively. In the
hydrolyzed phenolicacids fraction, caffeic acid accounted for 80%
of the UV absorbance at280. At 210 nm and before alkaline
hydrolysis, neochlorogenic acid,Table 1Main compounds recovered
from potato peels.Compound Retention time m/z (% Intensity)Phenolic
compoundsNeochlorogenic acid (3-O-caffeoylquinic acid) 2.3 353(59),
191(100), 179(53), 173(4), 135(55)(Clifford, Johnson, Knight, &
Kuhnert, 2003; Nandutu et al., 2007)Chlorogenic acid
(5-O-caffeoylquinic acid) 2.6 353(41), 191(100), 179(10), 173(18),
135(9)Caffeic acid 2.8 179(2), 135(100)Unknown compound 3.2 529
(100)Glycoalkaloids-Solanine 12.4 868(100), 722(50),
398(37)-Chaconine 12.8 852(100), 706(32), 398(28)Solanidine 15.6
398(100), 382(23), 98(8)Standards of all compounds, except
neochlorogenic acid, were analyzed under the same conditions and
their MS spectrum matched that of the
samples.WFleepotatopfog001/gm02040608010012005101520253011st2nd3rd1st2nd3rd2AB
C A B C A B C A B C A B C A B CSolvent Fig. 4. Recovery of phenolic
acids and glycoalkaloids from potato peels in 3
consecutiveextractions withdifferent solvents. (1) Phenolic acids:
chlorogenic acid( ), neochlorogenicacid ( ), caffeic acid ( ). (2)
Glycoalkaloids: -chaconine ( ), -solanine ( ), solanidine( ). Data
are means standard deviations (n = 3). Signicant differences were
deter-mined by two-way ANOVA (P b 0.05). The yields of the
compounds were compared as afunction of the solvent used for each
extraction (rst, second and third). There were nosignicant
differences.WFsleepotatopfog001/gm020406080100051015201 2**Fig. 5.
Recovery of phenolic acids and glycoalkaloids before and after
separation bysolidphaseextraction.
(1)Phenolicacids;incrudeextract:chlorogenicacid( ),neochlorogenic
acid ( ), caffeic acid ( ); recovered in water/ethanol (80:20)
fraction:chlorogenic acid ( ), neochlorogenic acid ( ), caffeic
acid ( ). (2) Glycoalkaloids; incrude extract: -chaconine ( ),
-solanine ( ), solanidine ( ); recovered in water/ethanol (20:80)
fraction: ( ) -chaconine, -( ) solanine, ( ) solanidine. Data
aremeans standard deviations (n = 3). Signicant differences were
determined by one-wayANOVAfollowedbyHolmSidakmethodfor
multiplepairwisecomparisons(Pb 0.05). Comparisons between
extraction and separation were performed for eachcompound.
*Indicates signicant difference in the recovery after fractionation
comparedto the crude extract.31 A.F. Snchez Maldonado et al. / Food
Research International 65 (2014) 2734chlorogenic acid and caffeic
acid together accounted for 74% and 59% inthe crude extract and the
phenolics fraction. After alkaline hydrolysis,caffeic acid in the
phenolic acids fraction was equivalent to 72% of thetotal material
absorbing at 210 nm.4. DiscussionThis study comparedthe recovery of
phenolic acids andglycoalkaloidsfrom fresh potato peels comparing a
water/methanol-based solvent andtwo water/ethanol-based solvents.
Additionally, fractionation of phenolicacids and glycoalkaloids was
achieved with solid-phase extraction andwater/ethanol-based
solvents. The recovery of phenolic acids withoutmodication or after
alkaline hydrolysis of chlorogenic acid isomersinto caffeic acid
was
determined.Thethreesolventsystemsresultedincomparablerecoveriesofbioactive
compounds. Among the solvents evaluatedinthis study, solventC with
the highest proportion of water is the most
environmentallybenignandleast costlyalternative. Therecoveryof
chlorogenic,neochlorogenic and caffeic acids reported in this study
is two- to three-fold higher compared to literature data. Rodriguez
de Soltillo, Hadley,and Holm (2006) found 24 to 30 mg/100 g of
chlorogenic acid and 1.4to 2.7 mg/100 g of caffeic acid fromfresh
potato peels and also reportedthe presence of protocatechuic and
gallic acids. Mattila and Hellstrom(2007)detectedmainly
chlorogenicacid(15to26 mg/100g)andcaffeic acid (4.1 to 4.4 mg/100
g) from fresh potato peels. Because theprole and quantity of
phenolic compounds vary with the plant source,variety, season,
climate, and several other factors, these differences like-ly
represent different levels of phenolic compounds in the
rawmaterialused. The recovery of glycoalkaloids obtained in this
study (Fig. 3) iswell in agreement with previous studies, which
achieved between 0.9to 37 mg/100 g of -chaconine and from 0.4 to 17
mg/100 g of -solanine in fresh potato peels (Friedman et al.,
2003).Consecutive extractions of potato peels revealed that 97%, 94
and89% of chlorogenic acid, neochlorogenic acid, and caffeic acid,
respec-tively, were recovered after the second extraction,
indicating that theextraction is more efcient for chlorogenic acid
than for caffeic acid.Higher amounts of caffeic acid in the third
extraction are not likely toberesultant of thehydrolysis of
boundphenolic components tohydroxycinnamates as reported by Nara,
Miyoshi, Honma, and Koga(2006), since no hydrolysis was
observedwhen a chlorogenic
acidstandardwasextractedunderthesameconditionsasthesamples(Fig.
3(1)). Therefore, the higher efciency for extraction of
chlorogenicacid is attributable to the higher capability of the
solvents to dissolvethis compound, which is more polar than caffeic
acid. Between 95 and99% of all glycoalkaloids were extracted after
the second extraction.This indicates that in general, two
consecutive extractions are sufcientfor recovery of more than 90%
of the secondary metabolites frompotatopeels.Alternative procedures
for the extraction of bioactive compoundsfrom plants include
subcritical water extraction, which eliminates theneed for organic
solvents. Subcritical water was used to extract phenoliccompounds
from bitter melon (Budrat & Shotipruk, 2009), rosemaryplants
(Ibaez et al., 2003) and oregano (Rodriguez-Meizoso et al.,2006).
This process employs high pressure and high temperature
andthusaccelerateschemicalreactionsincludingthereleaseofboundphenolic
compounds and the degradation of caffeic and chlorogenicacid. Singh
and Saldaa (2011) compared the recovery and prole
ofphenolicacidsextractedfrompotatopeelsusingsubcritical
waterextraction to the recovery achieved with methanol extraction.
The totalamount of phenolic acids obtained from subcritical water
extractionwas approximately twofold higher compared to the methanol
extractsand ethanol extracts. However, the recovery of chlorogenic
and caffeicacids withsubcritical water was only50%and75%,
respectively,compared to methanol extraction; subcritical water
extractedhydroxybenzoic acids which were not recovered with
methanol. Simi-larly, catechin was extracted from bitter melons
with subcritical waterbut not with solvent extraction (Budrat &
Shotipruk, 2009). Our studyadditionally demonstrates that the use
of acidied ethanolic solventsavoids side reactions and the
resulting extract is relatively pure andstable. As shown by purity
analysis, the methods utilized in this studygenerate relatively
pure mixtures, consisting mainly of chlorogenic andcaffeic acids. A
major advantage of the method developed in this studycompared to
subcritical water extraction is the low cost, since sophisti-cated
equipment is not required. The use of acidied ethanolic
solventsFraction of the of solvent1 2 3 4 5
6WFsleepotatopg001/gm010203040501 2 3 4 50246810 1 2Fig. 6.
Recovery of phenolic acids in several fractions of the solvents
during solid phaseextraction. Fractions were collected successively
in 2 mL tubes. Axis X: Fractions are 1(02 mL), 2 (24 mL), 3 (46
mL), 3 (68 mL) and 4 (810 mL). (1) Phenolic acids elutedwith
water/ethanol (80:20); chlorogenic acid ( ), neochlorogenic acid (
), caffeicacid( ).(2) Glycoalkaloids
elutedwithwater/ethanol(20:80);-chaconine ( ),-solanine ( ),
solanidine ( ). Data are means standard deviations (n = 3). E E+H
E+H+FWFleepotatopgK/lom050100150200250 E E+H E+H+F010203040S
S+HLm/lomm0102030401 2 3ABBB BAab bABFig. 7. Recovery of phenolic
acids and glycoalkaloids after hydrolysis and fractionation. (1)
Chlorogenic acid ( ) standard solution before (S) and after
hydrolysis (S +H). Panels (2) and(3) showcompounds recovered in
crude extract (E), hydrolyzed crude extract (E +H) and hydrolyzed
crude extract after fractionation (E +H+F). (1) Phenolic acids:
chlorogenic acid( ), neochlorogenic acid ( ), caffeic acid ( ). (2)
Glycoalkaloids: -chaconine ( ), -solanine ( ), -solanidine ( ).
Data are means standard deviations (n =3). Signicant dif-ferences
were determined by one-way ANOVA followed by HolmSidak method for
multiple pairwise comparisons (P b 0.05). For panel (2) since
hydrolysis of chlorogenic andneochlorogenic acids releases caffeic
acid, thesummarizedamounts of chlorogenic, neochlorogenic
andcaffeic acids were compared to the amount of caffeic
acidrecoveredafter extractionand alkaline hydrolysis, and after
extraction, alkaline hydrolysis and fractionation. For panel (3)
the yield of each compound was compared between extraction,
extraction and alkaline hydro-lysis andextraction, alkaline
hydrolysis andfractionation(capital letters were usedtocompare
amounts of -chaconine andnon-capital letters tocompare -solanine).
Different superscripts inthe same panel indicate signicant
difference. Solanidine was not quantied after hydrolysis, since its
concentration was below the lowest concentration of the calibration
curve.32 A.F. Snchez Maldonado et al. / Food Research International
65 (2014) 2734was also shown to allowhigh yields of phenolic
compounds fromonionwaste (Khiari, Makris, & Kefalas,
2009).Solid-phase extraction of the crude extract containing
phenolic com-pounds andglycoalkaloids allowed separation
andcomplete recovery ofall target compounds. Fractionation was
carried out at pH7, which mayaccount for the slight increase in
caffeic acid after fractionation; esterhydrolysis occurs faster
under alkaline conditions (Kim, Tsao, Yang, &Cui, 2006).
Glycoalkaloids were stable during fractionation. Previousattempts
to separate glycoalkaloids and phenolic acids from potatopeel
extract by alkaline precipitation resulted in degradation of 30%
ofphenoliccompoundsand90%of glycoalkaloids(Rodriguez-Saonaet al.,
1999). In addition, the amount of solvent required for elution
ofboth fractions is relatively small and comparable with other
protocolscarriedout withacetonitrile (Abreu, Relva, Matthew, Gomes,
&Morais, 2007; Machado et al., 2007). Therefore, solid-phase
extractionperformed in this study is a signicant improvement in the
recoveryof phenolic compounds and glycoalkaloids as separate
fractions.Alkaline treatment of the crude extract achieved
virtually quantita-tive hydrolysis of chlorogenic and
neochlorogenic acids. However, theyield of caffeic acid was only
57%. Degradation of caffeic acid was alsoobservedduring alkaline
hydrolysis of a standardinthe same conditionsas performed for the
extract. Although alkaline hydrolysis is a commonmethod for the
determination of bound phenolic acids (Kimet al., 2006;Mattila
& Kumpulainen, 2002), degradation of more than 50% of
caffeicacid during hydrolysis of chlorogenic acid has been reported
(Krygier,Sosulsky, &Hogge, 1982; Maillard&Berset, 1995;
Nardini et al.,2002). Under alkaline conditions, o-dihydroxy
benzenes are oxidizedto their corresponding quinones when oxygen is
present. The degrada-tion of caffeic acid during alkaline
hydrolysis can be mitigated by theaddition of antioxidants such as
ascorbic acid, or by chelating metalions with EDTA (Nardini et al.,
2002). Enzymatic hydrolysis with bacte-rial esterases is also an
alternative to increase caffeic acid recovery.Lactobacilli have the
strain-specic capacity to hydrolyze
chlorogenicacid(RodriguezdeSoltilloetal.,
1998;Snchez-Maldonadoetal.,2011) and hydroxycinnamoyl esterases of
lactic acid bacteria wererecently characterized(Esteban-Torres,
Reveron,Mancheno, De lasRivas, & Munoz, 2013).Glycoalkaloids
and solanidine were also degraded during alkalinehydrolysis.
However, all glycoalkaloidspresent
inthehydrolyzedextractwererecoveredusingsolid-phaseextraction,
indicatingnodegradation at pH 7. Rodriguez-Saona et al. (1999)
reported minimumprecipitationof glycoalkaloids ina potato peel
extract at pH7but increasedprecipitationabovepH8.
Quantitativerecoveryofglycoalkaloids thus requires solid-phase
extraction prior to alkalinehydrolysis of chlorogenic acid
isomers.Caffeic acid, a product of chlorogenic acid hydrolysis,
hasdemonstrated substantial antimicrobial activity
(Snchez-Maldonadoet al., 2011), and both chlorogenic and caffeic
acids have been
highlycorrelatedtotheantioxidantactivityofpotatopeelextracts(Naraet
al., 2006). Therefore, due to their purity and stability, the
phenolicacidfractionsobtainedinthisstudybeforeorafterhydrolysiscansuccessfully
be applied as food preservatives. In addition, solid
phasefractionation provided a high recovery of glycoalkaloids from
potatopeels, allowing their utilization as raw materials in the
pharmaceuticalindustry.In conclusion, this study demonstrates that
acidied ethanol-basedsolvents recover phenolic acids and
glycoalkaloids from potato peelsand are thus suitable alternatives
to the use of environmentally harmfulsolvents. Simultaneous
fractionation and hydrolysis of esteried
pheno-licacidswerealsoachieved. However, useof
antioxidantsduringalkaline hydrolysis or enzymatic hydrolysis
should be considered toallow quantitative recovery of caffeic and
quinic acids, and hydrolysisof phenolic acids after fractionation
may avoid degradation ofglycoalkaloids. Solid-phase extractionof
phenolic acids andglycoalkaloidsis a suitable method that will
allowthe use of phenolic acids extracts asfood preservatives
without any toxicological concerns, while recoveredglycoalkaloids
can be utilized for pharmaceutical purposes. Thus,
thisstudyprovides
avaluablecontributiontosustainableproductionthrough utilization of
by-products as a source of biologically
activecompounds.AcknowledgmentsWe would like to thank the Alberta
Agriculture Funding Consortium,Alberta Innovates-BioSolutions,
fornancial support. Alma FernandaSnchez-Maldonado acknowledges
support from the Mexican NationalCouncil for Science and Technology
and Secretara de Education Pblica(Mxico). Michael G. Gnzle
acknowledges support from the CanadaResearch Chairs
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