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Cinc. ecnol. Aliment., Campinas, 28(4): 949-952, out.-dez. 2008 949

Cincia e ecnologia de Alimentos ISSN 0101-2061

Recebido para publicao em 6/8/2007Aceito para publicao em 20/3/2008 (002735)1 Laboratrio de Qumica de Alimentos LQA, Instituto Biomdico, Universidade Federal do Estado do Rio de Janeiro UNIRIO, Rua Frei Caneca, 94, 4 andar,

CEP 20211-040, Cidade Nova - RJ, Brazil, E-mail: carreb@uol.com.br*A quem a correspondncia deve ser enviada

Volatile prole o heated soybean oil treated with quercetin and chlorogenic acid

Perfl de compostos volteis do leo de soja aquecido e tratado com quercetina e cido clorognico

Adriana Leo de MIRANDA1, Mariana Carvalho RIBEIRO1,

Ricardo Felipe Alves MOREIRA1

, Carlos Alberto Bastos de MARIA1

*

1 Introduction

Rened edible oils containing substantial amounts opolyunsaturated atty acids undergo oxidative rancidityand produce o-avors. Autoxidation is a major route o oil

rancidity and its progression occurs via a ree radical chainmechanism (SHERWIN, 1976). Te addition o primary anti-oxidants (e.g. polyphenolic compounds) retards the autoxida-tion process by acting as chelators o transition metals and/oras hydrogen donors and produces relatively stable ree radicalsand non-radical products (HAMILON et al., 1997). Syntheticphenolic compounds (e.g. BHQ) are the most commonlyantioxidants used in lipids. However, there is a tendency o

consumer groups to decrease the amount o synthetic addi-tives in oods. As a consequence, naturally occurring phenoliccompounds (e.g. avonoids and phenolic acids) have drawn

attention because they have been ingested or centuries and areassumed to be relatively sae or human consumption. Indeed,the daily dietary intake o these natural components is approxi-mately 1 g via the ingestion o vegetables (LIU, 2004). Quer-cetin (avonol) and chlorogenic acid (5-CQA) (cinnamate)are typical phenolic compounds widely distributed in plantsincluding many oods and beverages. In recent years, thesebiophenolic compounds have proved to provide protective

Resumo

As alteraes no perl de compostos volteis, aps o aquecimento de leo de soja renado sem a adio de antioxidantes e tratado previamentecom quercetina e cido clorognico (5-ACQ), oram investigadas atravs da CG/DIC, CG/EM e CG/SNIFFING. A temperatura de aquecimentodo leo oi de 20 C no primeiro minuto e aumentada at 160 C taxa de 10 C min 1. A temperatura nal oi mantida por 10 minutos.Um total de 19 compostos volteis oi identicado nas amostras aquecidas sem a adio de antioxidantes. As carbonilas de cadeia mdiapredominaram na rao voltil. Cerca de 15 e 11 compostos volteis oram detectados no leo aquecido com adio prvia de quercetina e5-ACQ, respectivamente. As amostras tratadas com quercetina mostraram uma menor proporo de carbonilas com esqueletos de carbonoC

6

-C9

. A composio estimada de compostos volteis mostrou que amostras tratadas com quercetina tiveram valores signicativamente(p < 0,05) menores para 1-pentanol, 2,4-heptadienal e 2,4-decadienal em comparao com as amostras sem antioxidantes adicionados ecom as tratadas com 5-ACQ. A anlise por meio de CG/SNIFFING revelou um nmero menor de odores em amostras tratadas com 5-ACQem comparao quelas sem tratamento algum. Nenhum odor oi percebido nas amostras aquecidas com adio prvia de quercetina.Estes resultados indicam uma maior eetividade da quercetina no retardamento do processo oxidativo em amostras de leo de soja sujeitasa aquecimento a 160 C 10 C min1 por 10 minutos . Aparentemente, os compostos enlicos naturais usados neste trabalho mostraramboa estabilidade oxidativa, j que nenhum composto voltil novo oi detectado nas amostras aquecidas e tratadas com eles.Palavras-chave: cido clorognico; CG/EM; compostos volteis; leo de soja; quercetina.

Abstract

Changes in the prole o volatile compounds aer the heating o rened soybean oil without adding antioxidants, and treated with quercetinand chlorogenic acid (5-CQA) were investigated by GC/FID, GC/MS, and GC/SNIFFING. Te heating temperature o the oil sample was20 C or the rst minute, and then it was increased up to 160 C at the rate o 10 C min1. Te nal temperature was kept or 10 minutes.19 volatiles were identied in the heated samples without antioxidants. Medium-chain carbonyls predominated in the volatile raction,mainly 2-heptenal, 2,4-heptadienal and 2,4-decadienal. Around 11 to 15 volatile compounds were detected in the heated samples treatedwith 5-CQA and quercetin, respectively. 5-CQA was not very ecient in delaying the ormation o oxidative volatile compounds. Tesamples quercetin presented lower proportion o carbonyls with C

6-C

9.. Te GC peak area data were used as an approach to estimate the

relative content o each volatile compound and indicate that the samples treated with quercetin (p < 0.05) had signicantly lower values or,1-pentanol, 2,4-heptadienal, and 2,4-decadienal compared with those without antioxidants and treated with 5-CQA. GC/SNIFFING analysisrevealed a smaller odor perception in the samples treated with 5-CQA compared to those without antioxidants. No odor was perceived in

the heated samples treated with quercetin. Tese results indicate greater eectiveness o quercetin in delaying the ormation o oxidativevolatile compounds in soybean oils subjected to mild heating conditions. Apparently, biopolyphenols used in the present work showed goodoxidative stability since no new volatile compound was detected in the heated samples treated with them.Keywords: soybean oil; GC/MS; oxidative volatiles; quercetin; chlorogenic acid.

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Volatiles o heated soya oil with antioxidants

eects against oxidative stress in animal and in vitro models(ZHANG et al., 2006; MORALES et al., 2006). Reactive oxygenspecies appear to be major contributors in the pathogenesiso degenerative diseases such as arteriosclerosis, cancer, andchronic inammation.

In a previous work, some studies were perormed aim-ing at elucidating the eectiveness o 5-CQA and quercetin

in stabilizing reined soybean oil subjected to acceler-ated oxidation (MAGDA et al., 1997; MAGDA et al., 1998;DE MARIA et al., 2000). Chemical analysis o the oxidized oilsamples included the determinations o the peroxide values(PV), the conjugated dienes at 233 nm (MAGDA et al., 1997;MAGDA et al., 1998), and the induction time obtained using anoxidative stability index instrument (DE MARIA et al., 2000).It was observed that primary antioxidative action o quercetinwas greater than that o 5-CQA. In act, results rom anotherinvestigation have shown that quercetin is eective in delayingrancidity in canola oil (WANASUNDARA; SHAHIDI, 1994).

Nevertheless, the eect o natural phenolic antioxidants on

the volatile prole o soybean oil submitted to orced oxidationhas not been thoroughly studied yet. Tese biophenols couldmodiy the volatile raction not only by aecting the oxidativeormation o volatile compounds, but also by providing vola-tiles through their thermal degradation. Te present work aimis to study changes in the volatile prole o rened soybeanoils treated with quercetin and 5-CQA and submitted to mildheating conditions.

2 Materials and methods

2.1 Materials

Reagents: Quercetin and 5-CQA were rom Sigma (St. Louis,MO, USA). enax A was rom Supelco (Belleonte, PA, USA).Absolute ethanol was rom Merck (Darmstadt, Germany). Allother chemicals were rom Aldrich (Sheboygan, WI, USA).

Samples: Tree resh rened soybean oil samples were ob-tained rom Cargill Agrcola S.A. (Brazil). Te good quality othe samples was conrmed by the atty acid composition andPV analysis (MAGDA et al., 1997).

2.2 Methods

Sample preparation: Due to the low solubility o the phenolic

compounds in soybean oil, it was necessary to dissolve them inabsolute ethanol. Quercetin or 5-CQA (40 mg) was dissolved in1 mL o ethanol in a magnetic stirrer, added to the oil (120 mL),and mixed until dissolution. Te sample without antioxidantscontained the same amount o ethanol as the one that was usedto dissolve the additives. Samples without adding antioxidantsand with quercetin or 5-CQA were placed in a 10 cm diameterat eon-coated pan (with deep o 4 cm) with ared sides andsubjected to accelerated oxidation, as ollows: the oil sample tem-perature was 20 C or the rst minute and then it was increasedto up 160 C at the rate o ~10 C min1. Te nal temperaturewas kept or 10 minutes. Te skillet was heated in a hot plateconnected to an electronic thermometer used to regulate the

temperature o the sample. Each heated sample was cooled atroom temperature or 30 minutes and immediately submittedto the enrichment o the headspace raction.

Isolation o the headspace volatile raction: 100 mL oilsample was placed in a 500 mL Pyrex heavy-walled lter-ing ask with a side hose-connection (Brand, Wertheim,Germany), o.d. 10 mm, and heated at 60 C under stirring.

Puried nitrogen (0.9-1.0 L min1) was passed through thissystem or 2 hours, and the entrained volatiles were adsorbedon a enax trap. Tis adsorvent was previously conditioned ina oven at 225 C or 3 hours under a N

2ow o 0.9-1.0 L min1.

Desorption o the compounds was done with 200 mL o ac-etone. Tis volume was settled by monitoring 10 mL aliquotso acetone until no more volatiles could be detected usingGC/FID. Te eluate was then concentrated to 200 L in arotatory evaporator at 20 C.

GC/FID: A Carlo Erba 4300 GC equipped with a30 m x 0.25 mm i.d. x 0.25 m SupelcowaxM 10 used-silicapolar capillary column (Supelco, Milord, USA) was used. Te

injector and FID temperatures were 230 and 240 C, respectively.Helium was used as the carrier gas at 0.83 mL min1 rate. Teoven temperature ranged rom 50 to 230 C at 3 C min1. Tesplit ratio was 1:20. Linear retention indices (LRI) were esti-mated using the modied Kvatz method (VAN DEN DOOL;KRAZ, 1963). All oil samples were analyzed in two replicates.Te GC peak area data were used as an approach to estimate therelative content o each volatile compound. Te mean, standarddeviation, and one-way analysis o variance (p < 0.05) wereperormed using a statistical graphics system (SSC, 1986).

GC/MS: A Shimadzu GC-17A/QP5050 quadrupole massspectrometry with National Institute o Standards and echnology(NIS) 12.lib and 62.lib data system was used. Te instrument wasoperated in the electron ionization mode at 70 eV, taking scansrom 20 to 300 m/z in a 1 s cycle. Te column and chromato-graphic conditions were the same as described or the GC/FIDanalysis. entative identication o the volatiles was based on thecomparison o the mass spectra o unknown compounds againstNIS library data. Wherever possible, the results were conrmedby comparison with authentic substances. Only the compoundsidentied using at least reerence standards and mass spectra datawere considered to be denitively identied.

CG/SNIFFING: Te same above-mentioned chromato-graphic conditions were used, splitting the efuent o the capil-lary column (1:10) between FID, and the artisanal sning port.

Odor port evaluation was carried out reely by two testers.

3 Results and discussion

3.1 PV analysis

he PV o the resh oil was 0.7 0.02 meq.L1 whichproved the good quality o the product (MAGDA et al., 1997).On the other hand, there were dierences in PV o in theheated oil samples containing quercetin (12 0.4 meq.L1)and 5-CQA (13 0.5 meq.L1) to those without antioxidants(17 0.7 meq.L1). Tereore, the addition o either quercetin or5-CQA was capable o delaying oil peroxide ormation.

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Miranda et al.

3.2 Volatile profle

Changes in the volatile prole aer the heating o renedsoybean oil without antioxidants and treated with quercetinand 5-CQA were investigated. Te estimated composition o volatiles in the headspace raction is shown in able 1. Norecovery methodor GC standardization were applied, and thus,the data presented are estimated values. A total o 19 volatilecompounds were identied in the heated soybean oil withoutantioxidants. Among them, 63% were denitively identied by

comparing the retention time and mass spectral data with thoseo authentic standards. Te chie oxidative volatile compoundswere aldehydes, especially 2-heptenal, 2,4-heptadienal, and 2,4-decadienal. Te detection o 2-heptenal and 2,4-decadienal inthe soybean oil samples is in accordance with reports rom otherauthors (KAO et al., 1998; SEENSON et al., 2002). On the otherhand, this is the rst time, to our knowledge, that 2,4-heptadie-nal was detected in heated soybean oil. As previously reported,

2,4-heptadienal was detected during the autoxidation o methyllinolenate at room temperature (ULLRICH; GROSCH, 1987).

In another study, tri cis,cis 9,15-linoleoylglycerol was submittedto accelerated oxidation orming allylic radicals that reactedwith O

2orming monohydroperoxides at the C

8-C

11positions

(NEFF; SELKE, 1993). Tese monohydroperoxides could un-dergo additional reactions to produce oxidative volatiles. Tus,the occurrence o 2,4-heptadienal and 2,4-decadienal in heated

soybean oil may be attributed to the thermal decomposition o8, 9, 10 and 11 hydroperoxides o linoleic and linolenic esters.

A total o 15 and 11 oxidative volatile compounds weredetected in heated soybean oil treated with 5-CQA and quer-cetin, respectively (able 1). In general, 5-CQA was not veryecient in delaying oxidative volatile ormation. Te addition

o quercetin, on the other hand, increased the oxidative stabilityo the heated oil samples. Te estimated concentration o thevolatiles by means o relative GC peak areas showed that soy-bean oil samples treated with quercetin had signicantly lowervalues or 1-pentanol, 2,4-heptadienal, and 2,4-decadienal incomparison with those without antioxidants and treated with5-CQA. Furthermore, samples treated with quercetin exhibited

a lower proportion o aldehydes with C6-C9 skeletons. A previ-ous study reported that 14, 15, 16, and 17 monohydroperoxideswere expected precursors o medium-chain carbonyls (NEFF;SELKE, 1993). Tese monohydroperoxides are derived rom theoxidation o allylic radicals at the C

15-16position. Ten, it is pos-

sible that quercetin reduces the ormation o oxidative volatilesby acting as an inhibitor o the oxidation o allylic radicals or bydelaying the thermal decomposition o the monohydroperoxidespreviously ormed. Tese ndings are in accordance with previ-ous data rom our laboratory (DE MARIA et al., 2000), whichshowed that the antioxidative potency o quercetin was signi-cantly greater than that o 5-CQA. Te structural characteristicsimparting the highest antioxidant activity in the quercetin was

ound to be the ollowing (DE BEER et al., 2002): a) the ortho3,4-dihydroxy moiety in the B-ring; b) the 2,3-double bond incombination with the 4-keto group; and c) the 3- and 5-hydroxylgroups in the C- and A-ring. Tese characteristics avor theelectron delocalisation in the C-ring promoting maximumscavenging potential. In contrast to quercetin, 5-CQA containsonly a 3,4-dihydroxy group in the aromatic ring (caeic acidmoiety) (Figure 1).

3.3 Odor perception

Aroma concentrates obtained rom the headspace o heatedsoybean oil samples by adsorptive column chromatography,

Table 1. Volatile composition o heated soybean oil samples without antioxidants and treated 5-CQA and quercetin.

Compounds SamplesPercentual area (Mean SD)

Odor perception LRI

Oil Oil + 5-CQA Oil + QUE Oil Oil + 5-CQA Oil + QUE

Heptanala 0.30 0.06 0.29 0.02 nd slightly green slightly green nd 1164

2-hexenala 0.80 0.20 0.77 0.15 nd nd nd nd 1204

Octanala

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