Meat Science 90 (2012) 60–65

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Meat Science

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Total antioxidant capacities of raw and cooked meats

Arda Serpen a,⁎, Vural Gökmen a,b, Vincenzo Fogliano c

a Food Research Center, Hacettepe University, 06800 Beytepe, Ankara, Turkeyb Department of Food Engineering, Hacettepe University, 06800 Beytepe, Ankara, Turkeyc University of Naples “Federico II”, Department of Food Science, I-80055 Portici, Naples, Italy

⁎ Corresponding author. Tel.: +90 312 297 7120; faxE-mail address: aserpen@hacettepe.edu.tr (A. Serpen

0309-1740/$ – see front matter © 2011 Elsevier Ltd. Aldoi:10.1016/j.meatsci.2011.05.027

a b s t r a c t

a r t i c l e i n f o

Article history:Received 15 February 2011Received in revised form 28 May 2011Accepted 31 May 2011

Keywords:MeatAntioxidant activityQuencher procedureHeatingDenaturation

This study investigated the total antioxidant capacity (TAC) of meats (beef, chicken, pork and fish) and itschanges on thermal treatment. The QUENCHER procedure, which is performed directly on the solid materialwithout extraction, was selected and proved to be particularly suitable for meat samples. The ABTS•+

scavenging capacity of rawmeats ranged between 25.9±1.0 and 51.7±1.2 mmol Trolox Eq./kg. Raw chickenhad the highest TAC followed by pork, beef and fish. Upon heating at 180 °C, TAC of meats increased to anapparent maximum at 5 min followed by sudden decreases until 15 min, while the final stage of heating wascharacterized by slight increases. The modifications of TAC during cooking can be explained consideringfactors such as denaturation and exposure of reactive protein sites, degradation of endogenous antioxidantsand the formation of Maillard reaction products having antioxidant properties.

: +90 312 299 2123.).

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© 2011 Elsevier Ltd. All rights reserved.

1. Introduction

The primary importance of meat in human nutrition is related toits high quality proteins that provide essential amino acids upondigestion. However, besides the high protein contents, meat alsoprovides valuable amounts of many essential micronutrients such assome unsaturated fatty acids, vitamins and minerals (Tornberg,2005).

Meat as a food has a complex physical structure and chemicalcomposition that is very susceptible to oxidation (Wood et al., 2008).The oxidative stability of meats depends upon the balance and theinteraction between endogenous anti- and pro-oxidant substancesand the composition of substrates prone to oxidation includingpolyunsaturated fatty acids (PUFA), cholesterol, proteins and pig-ments (Bertelsen et al., 2000; Decker & Xu, 1998). Endogenousantioxidant systems are composed of non-enzymatic hydrophilic andlipophilic compounds such as vitamin E, vitamin C, carotenoids,ubiquinols, polyphenols, cellular thiols, and enzymes like superoxidedismutase, catalase and glutathione peroxidase. Together, enzymaticand non-enzymatic antioxidant systems operate to counteract theaction of pro-oxidants in muscle tissues (Chan & Decker, 1994;Decker, Livisay, & Zhou, 2000) both in living animals and also afterslaughter.

The composition of endogenous antioxidants and pro-oxidantcompounds can differ among meat of different species, amonganimals of a single species (Descalzo & Sancho, 2008; Pradhan,

Rhee, & Hernandez, 2000) andmuscle type. Also the diet of the animalby means of pasture or grain plays a significant role in modifying theconcentration of antioxidants, pro-oxidants and fatty acids in themeat. (Hernandez, Park, & Rhee, 2002; Hernandez, Zomeno, Arino, &Blasco, 2004). Depending on the consumers' preferences meatundergoes a wide range of cooking procedures and thermaltreatments. Compositional and structural changes during cookingcould significantly affect the TAC of meats (Palka & Daun, 1999;Tornberg, 2005). Therefore, a reliable estimation of the TAC value ofmeat can be useful to describe the capacity of muscle to resistoxidation processes and to determine modifications in TAC valuesduring thermal processing.

Due to its complex structure, various extraction methodologiesinvolving different solvents (water, aqueous buffers, alcohols,chloroform, etc.) have been applied to assess the TAC of meats(Descalzo et al., 2007; Sacchetti, Di Mattia, Pittia, & Martino, 2008).Unfortunately, extraction-based methodologies can only measure theantioxidant capacities of the soluble and extractable hydrophilic or/and lipophilic fractions of meat. On the other hand, independent of thecooking process, meat contains a significant insoluble fraction.Moreover, various factors like the type and the pH of the extractionsolvents, molecular interactions, aggregation phenomena, denatur-ation and oxidation can affect the extraction capacities and lead to anunderestimation in TAC values of meat.

A robust extraction-independent procedure to measure the TAC ofsolid foods, based on the interaction occurring at the interfacebetween the solid matrix and a liquid colored radical probe has beendeveloped (Serpen, Capuano, Fogliano, & Gökmen, 2007). Themethod, so called QUENCHER has been applied to various foodmatrices including cereals, bakery products and nuts and seeds (Açar,

61A. Serpen et al. / Meat Science 90 (2012) 60–65

Gökmen, Pellegrini, & Fogliano, 2009; Gökmen, Serpen, & Fogliano,2009; Serpen, Gökmen, Pellegrini, & Fogliano, 2008). The QUENCHERprocedure in principle can be used for all foodmatrices and adapted tovarious assays commonly used to measure antioxidant activity(Amigo-Benavent, del Castillo, & Fogliano, 2010).

In this work, the QUENCHER procedure was used to measure theTAC of four types of meat (beef, chicken, pork and fish) and toevaluate changes in TAC by thermal treatment.

2. Materials and methods

2.1. Chemicals

All chemicals and solvents used were analytical grade. Water,potassium persulfate (di-potassium peroxdisulfate), acetic acid(glacial), sodium acetate and ferric chloride were purchased fromMerck (Darmstadt, Germany). Cellulose (powder from spruce) and2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) werepurchased from Fluka Chemie AG (Buchs, Switzerland) and ethanolfrom Carlo Erba (Italy). 2,4,6-tris-2,4,6-tripyridyl-2-triazine (TPTZ),1,1 diphenyl-2-picryl-hydrazyl (DPPH) and 6-hydroxy-2,5,7,8-tetra-methylchroman-2 carboxylic acid (Trolox) were purchased fromSigma-Aldrich (Steinheim, Germany).

2.2. Thermal treatments of meat samples

Fresh samples from chicken breast, pork tenderloin, beef fillet andsea bream (Sparus aurata) fillets were purchased from a local market.Proximate composition of the meats determined by AOAC (1996)official procedure is reported in Table 1. Minced meat samples wereshaped into cylinders, having a diameter of 5 cm and thickness of1 cm, by spreading them into aluminum caps. Using this procedure,any variation in the rate of heat transfer during cooking, whichwould further affect the rate of antioxidant/pro-oxidant degradation/formation, was limited.

Meat samples were put into a preheated and air-ventilated oven(REX, Italy) at 180 °C and cooked for 5, 10, 15 and 20 min. Aftercooking, samples were immediately cooled in an ice bath and storedat −20 °C before freeze drying.

Freeze dried meat samples were ground to powder form using amortar andwere consecutively passed through a sieve (Endecotts TestSieve, London, U.K.) having 50 mesh size (297 μm). All raw andcooked meat powders were stored at −20 °C prior to analysis and allanalyses were performed within 3 days.

2.3. Preparation of meat samples for QUENCHER procedure

Freeze dried meat samples prepared as described above could bedirectly used for the QUENCHER procedure. Due to the highantioxidant activity (the values of absorbance were below the linearresponse range of the radical discoloration/color formation) apreliminary dilution was necessary. Dilution was performed bymixing the freeze dried meat samples with cellulose at a ratiobetween 1:1 to 1:10 (w:w) in a tube depending on the TAC values,following by rigorously shaking or squeezing in a mortar to achievebetter homogeneity. Preliminary tests showed that a 1:5 (w:w) solid-state dilution with cellulose was suitable for both ABTS and DPPH

Table 1Proximate composition of the raw meat samples.

Meat Water Protein Lipid Ash

Chicken (breast) 73.3±0.47 23.1±0.37 2.4±0.21 1.2±0.09Pork (tenderloin) 73.2±0.21 22.1±0.39 3.6±0.33 1.1±0.11Beef (tenderloin) 73.1±0.28 20.0±0.33 5.9±0.52 1.0±0.12Fish (Sea bream, fillet) 67.4±1.12 19.7±0.25 10.6±0.51 1.4±0.06

assays, but not for the FRAP assay where no dilution was necessary.After dilution with cellulose 10 mg per sample was used, an amountensuring good reproducibility for high antioxidant materials.

Cellulose was found to be inert towards the various colored probes(Serpen et al., 2007): mixing cellulose powder (10.0 mg) with eachradical probe solution no discoloration (i.e. decrease in absorbance)was observed over the 180 min of the assay.

2.4. Preparation of ABTS•+, DPPH• and FRAP radical solutions

2.4.1. ABTS•+ solutionABTS solution was prepared by adding 5 mL of deionized water to

38.41 mg of ABTS. Potassium persulfate solution was prepared bymixing 5 mL of deionized water with 6.615 mg potassium persulfate.A total of 10 mL of stock solution of ABTS•+ was prepared by reacting5 mL of each solution described above which resulted in finalconcentrations of 7 mmol/L ABTS and 2.45 mmol/L potassiumpersulfate. The stock solution of ABTS•+ was allowed to stand in thedark at room temperature for 12–16 h before use (Re et al., 1999). Theworking solution of ABTS•+ having absorbance of 0.75–0.80 at734 nm was prepared daily by diluting the 10 mL of stock ABTS•+

solution with approximately 800 mL of a water/ethanol (50:50, v/v)mixture.

2.4.2. DPPH• solutionStock solution of DPPH•was prepared daily by dissolving 40 mg of

DPPH• in 100 mL of ethanol. Then the ethanolic solution of DPPH•wasfurther diluted with 100 mL of deionized water to obtain a DPPH•stock solution in ethanol/water mixture (50:50, v/v). The workingsolution of DPPH• having an absorbance value of 0.75–0.80 at 525 nmwas prepared by diluting 200 mL of stock DPPH• solution withapproximately 800 mL of water/ethanol (50:50, v/v) mixture (Brand-Williams, Cuvelier, & Berset, 1995).

2.4.3. FRAP solutionFRAP solution was prepared by diluting an aqueous solution of

10 mM TPTZ and 20 mM ferric chloride in 300 mM sodium acetatebuffer (pH 3.6) at a ratio of 1:1:10 (v:v:v) as described by Benzie andStrain (1996).

2.5. Measurement of Trolox Equivalent TAC of meats by directQUENCHER method

Ten (±1.0) mg of powdered meat sample (diluted at a ratio of 1:5(w:w)with cellulose for the ABTS and DPPH assays) was weighed intoa centrifuge tube. The reaction was started by adding 10 mL ofABTS•+, DPPH• or FRAP working solution. The tube was shakenrigorously for 1 min and placed on an orbital shaker in the dark. Themixture was shaken at 300–400 rpm at room temperature on theorbital shaker until centrifugation to facilitate the surface reactionbetween the solid meat particles and the ABTS•+, DPPH• or FRAPsolution.

15, 30, 60, 120 and 180 min after introduction of the radicalsolution to the solid meat samples, centrifugation was performed at9200 g for 2 min. The clear supernatant (2 mL) was transferred into acuvette and the absorbance measured at 734 nm (for ABTS assay),525 nm (for DPPH assay) or 593 nm (for FRAP assay) at roomtemperature. Measurements at five different times (15, 30, 60, 120,180 min) were needed to estimate the time required to reach theplateau (i.e. the end point of the reaction).

The inhibition percentage of the ABTS•+ or DPPH• radicals wascalculated using the following equation (Eq. (1)):

Inhibitionsample %ð Þ = Absblank–Abssample

� �= Absblank × 100 ð1Þ

Fig. 1. Calibration curve for (a) ABTS, (b) DPPH and (c) FRAP assay probes as a functionof standard trolox concentration.

62 A. Serpen et al. / Meat Science 90 (2012) 60–65

where, Absblank is the initial absorbance of the ABTS•+ or DPPH•radical solution without sample and Abssample is the absorbance of theABTS•+ or DPPH• radical solution having sample after t min (15, 30,60, 120, 180 min) of incubation.

Trolox was used as a standard reference to convert the inhibitioncapability of each sample to the trolox equivalent antioxidant capacity(TEAC). First, standard trolox solutions in methanol were prepared ata concentration range between 0 and 600 μg/mL. A 0.1 mL of eachtrolox solution was added to 9.9 ml of ABTS•+ or DPPH• radicalsolution (0–24 μM trolox in radical solution). After 30 min ofincubation at room temperature, (enough time to reach a stablevalue) 2 mL of the radical solution was transferred into a cuvette andthe absorbance measured at 734 nm (for ABTS assay) or 525 nm (forDPPH assay).

Standard calibration curves were constructed by plotting percent-age inhibition (Eq. (2)) against concentration of trolox at 734 nm and525 nm for the ABTS and DPPH assays, respectively (Fig. 1a and b).

Inhibitiontrolox %ð Þ = Absblank–Abstroloxð Þ= Absblank × 100 ð2Þ

where, Absblank is the absorbance of the ABTS•+ or DPPH• radicalsolution without trolox (only methanol) and Abstrolox is theabsorbance of the ABTS•+ or DPPH• radical solution with troloxafter 30 min of incubation.

The ratio between % inhibition of the sample and the slope of thetrolox calibration curve was defined as the TEAC, which was used toindicate the scavenging free radical capability of the samples on a drybasis by the following equation (Eq. (3)).

TEACmmol Trolox Eq:kg meat d:w:

� �=

% inhibitionsample

s × m� 10 ð3Þ

where, s represents the slope of trolox calibration curve for ABTS(sABTS=4.0895) and for DPPH (sDPPH=3.0069) and m is the sampleamount in mg dry basis, 10 is the conversion factor to obtain TEACvalues in mmol Trolox Eq./kg of meat (d.w).

Since color formation is monitored in the FRAP assay, no inhibitionpercentagewas calculated as in the DPPH or ABTS assays. A calibrationcurve was constructed at room temperature by plotting concentrationof trolox (0–20 μM in radical solution) against the absorbance at593 nm (Fig. 1c). TEAP values of the samples were calculated by(Eq. (4))

TEAPmmol Trolox Eq:kg meat d:w:

� �=

Abs593nm−ns × m

� 10 ð4Þ

where, Abs593nm represents the absorbance of the FRAP solution withthe sample at 593 nm after t min (15, 30 60, 120, 180 min) ofincubation. n and s represent the intercept (0.04) and the slope(0.0444) of the trolox calibration curve of the FRAP assay, respectivelyand m indicates the sample amount in mg (dry basis), 10 is theconversion factor to obtain TEAC values inmmol Trolox Eq./kg of meat(d.w).

2.6. Statistical analysis

The analytical data are reported as mean±standard deviation oftriplicate independent measurements and were subjected to ANOVA,the significance of mean differences was determined by Duncans'posthoc test and t test using SPSS version 14.0 (2005).

3. Results and discussion

Most natural antioxidant or neo-formed antioxidants uponprocessing are multifunctional, and in complex heterogeneous foodssuch as meat and meat products, their activity cannot be evaluated bya single method (Perez-Jiménez & Saura-Calixto, 2005). Two or more

radical scavenging capacity assays are required to investigateheterogeneous samples since each assay involves different chemicalmechanism(s) and may reflect different aspect(s) of their antioxidantproperties. Here three common radical probes were used, namelyABTS, DPPH and Fe+3 (FRAP) to assess in-vitro antioxidant activity/power of meat in the QUENCHER procedure. Scavenging of DPPHradical allows evaluation of the hydrogen-donating potency ofantioxidative compounds (Brand-Williams et al., 1995) while theABTS radical determines the single electron-transfer capabilities of

these (Re et al., 1999). Fe+3 probe in FRAP assay reflects the reductiveantioxidant power (Benzie & Strain, 1996).

To determine the appropriate end point for the evaluation of theTAC of meat, the reaction with the different probes was followed fordifferent times. In Fig. 2 representative time-antioxidant capacitycurves obtained with the three radical solutions (ABTS, DPPH, FRAP)for the pork samples cooked at 180 °C for 15 min are reported. Similartime-antioxidant capacity curves were obtained for all raw or cookedmeat samples studied. As shown in Fig. 2, the reaction between theprobes and themeat samples is completed within 60 min for the ABTSand FRAP assays and within 120 min for the DPPH assay. Therefore,60 min for the ABTS and FRAP assays and 120 min for the DPPH assaywere considered satisfactory end-points to determine the TAC of meatby the direct QUENCHER procedure.

TAC of the samples determined by the ABTS•+ and DPPH• radicalprobes are presented in Fig. 3 and expressed in mmoles of Trolox perkg of dryweight. The total ABTS•+ scavenging capacity of the rawmeatsamples was in the range 25.9±1.0 mmol Trolox Eq./kg d.w. to 51.7±1.2 mmol Trolox Eq./kg (d.w). Comparing the ABTS•+ results of theraw meat samples, the TAC of chicken was significantly higher thanthat of pork, beef and fish (pb0.05), while no significant differenceswere observedwhen the DPPH• probewas used. Considering per freshweight values (the average content of water in meat is 70%), the TACfor raw meats is around 10 mmol Trolox per kg.

Different components are responsible of this TAC. It has beendemonstrated that proteins and peptides have an important antiox-idant action in meats due to their ability to scavenge free radicals andchelate prooxidative metals (Diaz & Decker, 2004; Elias, Kellerby, &Decker, 2008; Elias, McClements, & Decker, 2007). Chan and Decker(1994) reported that chicken meat is rich in histidine-containingdipeptides such as carnosine and anserine, which have highantioxidant activities. The presence of these antioxidant peptides inchicken could account for its higher ABTS•+ scavenging activity.

Sacchetti et al. (2008) investigated the ABTS•+ scavengingantioxidant capacities of hydrophilic and lipophilic extracts of chickenmeat by classical extraction dependent procedures. They reported theaverage ABTS•+ scavenging antioxidant capacities of chicken meat(breast) as 10.3 mmol Trolox Eq./kg (d.w.) and 5.3 mmol Trolox Eq./kg (d.w.) for the hydrophilic and lipophilic extracts, respectively. Thisled to a total of 15.6 mmol Trolox Eq./kg (d.w.) which is almost 70%lower than the value obtained in present study (51.7 mmol Trolox Eq./kg d.w.). This result, which was previously found comparingQUENCHER with conventional extraction based procedures on othermatrixes, is likely due to the fact that the QUENCHER procedure

includes the contribution of compounds which are not solubilizedwith the traditional extraction procedure.

The total DPPH• scavenging capacity of the raw meat samples inthis were between 19.1±1.8 mmol Trolox Eq./kg (d.w.) and 31±0.9 mmol Trolox Eq./kg (d.w.). The DPPH• scavenging capacity ofchicken, pork and beef was similar (pN0.05) while that of fish wassignificantly lower (pb0.05).

Interestingly, the TAC value measured with the two total radicalscavenging antioxidant capacity assays was significantly different forchicken and fish meats but not for raw pork and beef (pb0.05) whichcould be ascribed to the different affinities of the radicals to scavengethe various antioxidant groups present in different samples. Dean,Yamamoto, and Niki (1991) demonstrated that hydrophobic radicalshave less ability to attackmacromolecules such as proteins in solution.Therefore, it could be one of the reasons that DPPH•, a relativelyhydrophobic radical, would have less interaction with polar macro-molecular antioxidant compounds than more hydrophilic probes likeABTS. In addition, DPPH• is likely more selective than ABTS•+ in thereaction with H-donors (Roginsky & Lissi, 2005) and this couldexplain the low TAC values obtained by the DPPH compared with theABTS assay.

On the other hand, the TAC values of fish samples were the lowestin both assays. Beside a lower content of blood in the fish sample theloss of endogenous antioxidant compounds that may inhibit unsat-urated lipid oxidation could be one of the reasons for the low totalradical scavenging antioxidant capacity of fish compared with beef,pork and chicken.

FRAP of raw meat samples is presented in Fig. 4 expressed asmmoles of Trolox Eq. per kg of meat (d.w.). Among the raw meatsamples, the highest FRAP value was in beef (4.9±0.2 mmol TroloxEq./kg d.w.) whereas the lowest level of 3.0±0.1 mmol Trolox Eq./kg(d.w.) was that of the fish sample. The differences in FRAP valuesbetween the raw beef and chicken were not statistically significant(pN0.05). Similarly, there were no significant differences between theFRAP values of raw fish and pork. In general, reductive antioxidantpower of the raw samples was lower as compared to the ABTS•+ andDPPH• scavenging capacities. The FRAP method is based on thereduction of the Fe+3–TPTZ complex to the ferrous form at low pH.The low values of FRAP could be due to the poor ability of meatantioxidants to reduce ferric ion to its ferrous form.

The influence of thermal treatment on the TAC of themeat sampleswas measured using the ABTS•+ and DPPH• radical probes; Figs. 4 and

0

10

20

30

40

50

60

0 30 60 90 120 150 180Ant

ioxi

dant

Cap

acity

/Pow

er,m

mol

Tro

lox

Eq.

/kg

reaction time, min

ABTS DPPH FRAP

Fig. 2. Representative time antioxidant capacity/power curve of pork cooked for 15 minat 180 °C using ABTS, DPPH and Fe+3 (FRAP) as antioxidant assay probes.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

Chicken Pork Beef Fish

TAC

, mm

ol T

rolo

x E

q./k

g.

ABTS

DPPH

Fig. 3. TAC of raw meats determined using ABTS and DPPH as antioxidant probes.

63A. Serpen et al. / Meat Science 90 (2012) 60–65

5, respectively. The TAC of most meat samples increased on heating atthe beginning of the cooking period peaking after 5–10 min usingboth assays. The maximum TAC values were clearly visible in all themeat samples but not the fish. On increasing the heating time, TAClevels started to decrease, although at the longest heating time afurther increase of TAC is seen, particularly using the ABTS probe.

The behavior on heating of proteins, which are the maincomponent of meat, helps explain this result. Thermal treatmentscan alter the secondary and tertiary structure of proteins, resulting inmodifications of their physical properties (Sante-Lhoutellier, Aubry, &Gatellier, 2007; Tironi, Tomas, & Anon, 2002). Unfolding of theproteins (i.e. denaturation) can increase their ability to scavengeradicals by increasing the solvent exposure of antioxidant amino acidsthat would normally be located in the core of the native proteinstructure (Elias et al., 2007). Therefore, it is possible that mild heattreatments could increase the antioxidant activity of some proteinsdue to changes in their quaternary and tertiary structures.

On the other hand, it is well known that more severe thermaltreatments can cause thermoxidation of different components of

muscle foods resulting in consumption of antioxidant substances anda decrease of TAC.

The trend of TAC in the first minutes of heating (Figs. 5 and 6) canbe explained because in the initial period, the consumption ofantioxidant substances is less marked compared to the exposure of“hidden” antioxidant amino acids due to protein denaturation.Moreover some antioxidant compounds (for example GSH) can bereleased as a consequence of cell membrane destruction, thus beingmore reactive towards the radical probes.

Prolongation of the heating process reduced the TAC of meats inboth radical scavenging assays (Figs. 5 and 6). This can be due to theaccumulation of oxidized proteins and the loss in functionality ofactive meat peptides. Moreover, degradation of endogenous antiox-idative factors such as vitamin E, vitamin C, carotenoids, ubiquinols,polyphenols, and cellular thiols could be promoted by heating. In thisstage, the prooxidant–antioxidant balance was dominated by theprooxidant properties.

In the last stage of the heating process, the TAC of some meatsamples showed a marked increase in both assays. This could be dueto reactions between reducing sugars and free amino acids or freeamino groups in proteins, the Maillard reaction. There have beenseveral reports on the antioxidative properties of MRPs (Bailey & Um,1992; Borrelli, Visconti, Mennella, Anese, & Fogliano, 2002; Serpen etal., 2007). Since theMaillard reaction is favored at lowwater activity asignificant increase in the MRPs concentration could be achieved onlyat the end of the cooking time. The highest increases in TAC levels inthe final cooking period were observed in chicken, beef and fishsamples by the ABTS assay while the net increase was only observedin pork samples by the DPPH assay. Low reactivity of the hydrophobicDPPH radicals against hydrophilic MRPs could explain the differencesbetween the two assays.

The effects of heating on the FRAP values of meats are reported inFig. 7. The FRAP assay gave different results showing a sharp increase ofactivity for all samples, particularly beef. All the samples producedMRPsupon thermal treatment, but with different properties depending ontheir composition of proteins and carbonyl groups.The rapid increase ofFRAP values in beef in the last heating stage might be due to theaccumulation of MRPs with higher reducing properties than those offish, chicken and pork.

In order to detect a possible release of free iron from myoglobin tothe matrix that would account for the increase in FRAP value duringheating, the FRAPmeasurementswere performedwithout adding ferriciron to the reaction mixture, this resulted in no color development

0.0

1.0

2.0

3.0

4.0

5.0

6.0

Chicken Pork Beef Fish

FR

AP,

mm

ol T

rolo

x E

q./k

g.

Fig. 4. FRAP of raw meats.

Fig. 5. Effects of time at 180 °C on TAC values of meats measured using ABTS as theantioxidant probe.

Fig. 6. Effects of time at 180 °C on TAC values of meats measured using DPPH as theantioxidant probe.

64 A. Serpen et al. / Meat Science 90 (2012) 60–65

Fig. 7. Effects of time at 180 °C on FRAP values of the meats.

65A. Serpen et al. / Meat Science 90 (2012) 60–65

indicating that there was no detectable free ferrous iron formed fromthe reduction of iron released from the heme group. Also there were nodetectable agents in the heated meat samples that could react directlywith TPTZ to form the blue chromogen. These results agree withprevious reports regarding the relatively high stability of the hemegroup to thermal treatments and the binding of released iron toproteins(Berisha, Yasushi, & Fujimoto, 2003; Kristensen & Andersen, 1997). As aresult it is concluded that the increase of FRAP values with heating ismainly related to the development ofMRPs and does not reflect the lossof endogenous antioxidative factors during the cooking of meat.

4. Conclusions

Traditional extraction-basedmethodologies for TAC evaluation areonly partially useful as they take into account only the soluble andextractable hydrophilic or/and lipophilic fractions of meat. TheQUENCHER procedure which measures the antioxidant capacity ofboth soluble and insoluble parts together, gives a reliable measure ofthe TAC value for raw and processed meat. The QUENCHER approachrevealed that the effect of cooking on TAC is dependent on meat typeand severity of heating. The balance between phenomena occurringduring cooking such as i) denaturation and exposure of reactive sitesof proteins; ii) thermoxidation and degradation of endogenousantioxidants; iii) formation of antioxidant MRPs might be responsiblefor the overall trend of TAC observed for different cookedmeats. Usingthe direct QUENCHER procedure it will be possible to build a databaseand compare results for the TAC of meat samples, particularly aftervery different cooking procedures.

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