GRASAS Y ACEITES, 61 (4) ,OCTUBRE-DICIEMBRE, 4 0 9 - 4 1 5 , 2 0 1 0 ,

ISSN: 0 0 1 7 - 3 4 9 5DOI: 10.3989/gya. 110309

Antioxidative effects of stabilized and unstabilized defatted rice bran methanolicextracts on the stability of rice bran oil under accelerated conditions

By Abdalbasit Adam Mariod,^ '^ Hadiza Altine Adamu.^^lVlaznah Ismail^"' and Norsharina Ismailab

""Laboratory of Molecular Biomedicine, Institute of Bioscience, University of Putra Malaysia, 43400 UPMSerdang, Selangor. Malaysia.

''Department of Nutrition and Dietetic, Faculty of Medicine and Health Sciences, University of PutraMalaysia, 43400 UPM Serdang, Selangor. Malaysia.

''Department of Food Science & Technology, Sudan University of Science & Technology, P. O Box 71,Khartoum North, Sudan.

(Corresponding author: maznah@medic.upm.edu.my or myhome.e@gmail.com)

RESUMEN

Efecto antioxidante de extractos metanllcos de sal-vado de arroz desengrasado estabilizado y no-estabili-zado en la estabilidad de aceite de salvado de arroz bajocondiciones aceleradas.

La presente investigacin evala ia actividad antioxidan-te mediante el radical sinttico 1,1-difenil-2-picrilhidrazil y elensayo -caroteno-acido linoleico de extractos metaniicosde salvado de arroz desengrasado procedente de salvadode arroz estabilizado y no-estabilizado. El efecto de los ex-tractos (0.1 y 0.25% w/w) sobre la estabilidad oxidativa delaceite refinado de salvado de arroz fue determinado y com-parado con el del BHA (antioxidante sinttico). El estudio fuellevado a cabo durante un periodo de 168 hr a 70G y la pro-gresin de la oxidacin fue medida mediante ei valor deperxidos, valor de p-anisidine y substancias reactivas delcido tiobarbitrico (TBARS). El porcentaje relativo del a-to-coferol y y-orizanol residual en el aceite de germen de arrozconteniendo extracto metanlico de germen de arroz desen-grasado estabilizado y no estabilizado durante el almacena-miento a 70C fueron estudiados.

PALABRAS CLA VE: Aceite de germen de arroz - Activi-dad antioxidante - Estabilidad - Germen de arroz desengra-sado y estabilizado

SUMMARY

Antioxidative effects of stabilized and unstabilizeddefatted rice bran methanolic extracts on the stability ofrice bran oil under accelerated conditions.

The present research assessed the antioxidant activityagainst the synthetic 1, 1-diphenyl-2-picrylhydrazyl radical,and |i-carotene-linoleic acid assay of the methanolic extractsof defatted rice bran from stabilized and unstabilized rice bran.The effects of the extracts (0.1 and 0.25% w/w) on the oxidativestability of refined-bleached rice bran oil were determined andcompared with those of BHA (synthetic antioxidant). The studywas carried out over a 168 hr period at 70C and the progressionof oxidation was measured by peroxide value, p-anisidine value,and thiobarbituric acid-reactive substances (TBARS). Therelative % of residual a-tocopherol and y-oryzanol of the rice branoil containing methanolic extracts of stabilized and unstabilizeddefatted rice bran during storage at 70C were studied.

KEY- WORDS: Antioxidant activity - Rice bran oil - Stability- Stabilized defatted rice bran.

1. INTRODUCTION

Many studies have focused on rice bran asa source of natural antioxidants e.g. rice bran(Chotimarkorn et al, 2008) and defatted ricebran (Devi and Arumughan, 2007), which is thepredominant byproduct of rice bran oil and a goodsource of insoluble dietary fiber, protein, phyticacid, inositol and vitamin B (Hargrove, 1994). Theantioxidant potential of defatted rice bran was alsodetennined (Shin etal, 1992; Devi etal, 2007), butit still remains a relatively unexplored source material,which demands further investigation especially withregards to its phytochemical composition related topossible health benefits as antioxidants. According toliterature reports, several authors have demonstratedthe antioxidative effects of rice bran extracts such asfree radical scavenging, chelating ability and reducingpower in vitro systems (Iqbal et al, 2005; Nam et al,2006). However, stabilized and unstabilized defattedrice bran extracts have not been investigated as asource of natural antioxidant substitutes for syntheticantioxidants in bulk oil during storage. Moreover, thechanges in the antioxidative components of crudedefatted rice bran extracts have not been exploredduring autoxidation. The objectives of this researchwere to investigate the phenolic compounds ofstabilized and unstabilized defatted rice bran extractsand to evaluate their antioxidant activity (AOA) usingdifferent in vitro methods. The different extractswere dissolved in a small amount of methanol andapplied to rice bran oil at levels of 0.25 and 0.5% toexamine their antioxidative activity; the developmentof the peroxide, anisidine, conjugated deine (CD), andTBRAS values during the oxidation of rice bran oilwere also evaluated at 70C for 168 hour.

2. MATERIALS AND METHOD

2.1. Materials

All solvents used were of analytical grade.Methanol, ethyl acetate, hexane, chloroform, butylated

409

ABDALBASIT ADAM MARIOD, HADIZA ALTINE ADAMU, MAZNAH ISMAIL AND NORSHARINA ISMAIL

hydroxyanisole (BHA), -carotene, linoleic acid andFolin-Ciocalteau reagent as well as polyoxyethylenesorbitan monopalmitate (Tween 40) were obtained fromMerck (Merck, Damnstadt, Gemriany). (-^)-a-tocopherol(Sigma-Aldrich Co., St. Louis, MO, USA),

Rice bran samples were obtained from alocal milling factory in Tanjung Karang, Selangor,Malaysia. Samples were collected directly from themilling system and immediately placed in squareplastic (polypropylene) containers that were half-filled and transported to the Molecular BiomedicineLaboratory of the Institute of Bioscince, IBS, UPMSerdang in a cool box. To stabilize the rice bransamples, they were heated for 2 min at 2450MHz,using a national microwave/convection oven (modelNN-C2003S, Matsushita Electric Industrial Co.,Japan). The heating was carried out one by one untilall samples had been heated. The stabilized sampleswere left to cool at room temperature before sealingthe lids with cellophane tape. Samples of stabilizedrice bran (SRB) and unstabilized rice bran (USRB)were stored at 4C in a cold room until furtheranalyses.

Rice bran oil

The refined edible rice bran oil which wasproduced by Green Love Distribution Sdn Bhd,Kuala Lumpur, Malaysia was obtained from thelocal store Serdang, Malaysia; the oil was free ofany synthetic antioxidant.

2.2. Methods

Extraction of phenolic compounds

Twenty grams of the dried defatted (stabilizedSRB and unstabilized USRB) rice bran wereextracted successively with 80% methanol (3x200ml)by sonication (Hwasin Technology, Seoul, Korea) toobtain methanolic extract at room temperature for 1hour. The extracts were filtrated through Whatmanno. 1 filter paper and the solvent was removed. Theresidual of defatted rice bran was further extractedtwice with 80% methanol and the extracts werecombined. Then the solvents were removed using arotary evaporator (Buchi, Flawil, Switzerland) at 40Cand subjected to a nitrogen gas flow until dry (Deviand Arumughan, 2007). The yield of each extract wasmeasured before storing at -80C for further analysis.The total phenolic (TPC) in the methanolic extractsof defatted rice bran was determined with the Folin-Ciocalteu reagent following the method of Kaur et al(2008) using gallic acid as standard. The TPC of thesample was expressed as gallic acid in terms of mggallic acid equivalents (GAE)/100 g dried samples.

The antioxidant activity

The antioxidant activity of phenolic extracts fromdefatted (stabilized SRB and unstabilized USRB)rice bran was measured using the stable radical

1,1-diphenyl-2-picrylhydrazyl (DPPH) according toGordon et a/.(2001) and using -carotene-^inoleicacid assay according to the method of Amarowiczet al (2003). All determinations were performed intriplicate. The collected different methanolic rice branextracts were applied to 100 g commercial ediblerice bran oil obtained from a local market (free of anyantioxidant) at levels of 0.1% and 0.25% to examinetheir antioxidative activity. BHA at a level of 0.02% was used as a standard. A control sample wasprepared using the same amount of methanol usedto dissolve the antioxidant and the extracts (Moure etal, 2001). The commercial rice bran oil with addedantioxidants was heated at 70C for 168 hours.Samples (5 g) were removed periodically every 24,48, 72, 96, 120, 144 and 168 hours for analysis.Peroxide value (PV) and p-anisidine value (AV), andthiobarbituric acid-reactive substances (TBARS) weredetermined by the (AOCS, 1993) methods.

TBARS test. Each sample (200 mg) wasweighed into a 25-mL volumetric flask. It was thenmade up to the mark with 1-butanol (ACS grade)and mixed thoroughly. A 5-mL portion of thissolution was transferred into a dry test tube, and a5-mL quantity of fresh TBA reagent (200 mg TBA in100 mL 1-butanol) was added to it. The tube wasplaced in a 95C water bath for 120 min. The tubewas cooled, and the absorbance of the solution wasread at 532 nm. The TBARS value was calculatedas follows:

TBARS value = {A'0.4^5)/m (Chirinos et al,2009).

where A = absorbance at 532 nm and m = massof the sample

Identification of phenolic compounds

Phenolic compounds were identified and quantifiedby comparing their retention time and UV-Vis spectraldata to known previously injected standards (Chirinoset al, 2009). The changes in gamma-oryzanol anda-tocopherol content in rice bran oil treated withrice bran methanolic extract during storage weremeasured according to the method of Rogers etal (1993) The content of gamma-oryzanol anda-tocopherol were quantified using the HPLC systemconsisting of a Hewlett-Packard (Germany) ModelG1311A HPLC connected to an ALS Auto-injectorSeries 1100 (Hewlett Packard, Germany) basedon the peak area of the standard curve of standardgamma-oryzanol and a-tocopherol.

Statistical analyses

Statistical analyses were conducted using SPSS(Statistical Program for Social Sciences, SPSSCorporation, Chicago, IL) version 12.0 for Windows.The analysis of variance (ANOVA) and Pearson'scorrelation coefficients were perfonmed to comparethe data. All determinations were done at least intriplicate and all were averaged. The confidence limitsused in this study were based on 95% (P < 0.05).

410 GRASAS Y ACEITES, 61 (4), OCTUBRE-DICIEMBRE, 409-415, 2010, ISSN: 0017-3495, DOI: 10.3989/gya.110309

ANTIOXIDATIVE EFFEOTS OF STABILIZED AND UNSTABILIZED DEFATTED RIOE BRAN METHANOLIO EXTRAOTS ON THE STABILITY...

3. RESULTS AND DISCUSSION

3.1. Phenolic compound analysis

Previous research has been interested in theidentification of phenolic compounds from variousnatural sources (Moure, 2000; Mariod et al, 2009a;Mariod et al, 2009b). Rice bran was one of the mostpotential sources of plant phytochemicals. However,the content and stability of phenolic compounds instabilized and unstabilized defatted rice bran extractshave not previously been investigated. The contentof the total phenolic compounds of methanolicextracts from stabilized defatted rice bran (SRB) andunstabilized defatted rice bran (USRB) expressedas gallic acid equivalents are shown in Table 1. Theresults in this table reveal that the SRB exhibiteda higher phenolic content of 519.6 mg/100g GAEfollowed by the USRB extract (480.1 mg/100g).These results were higher than the previous resultsof Devi and Arumughan (2007), who reported 5.3%of total phenolics in defatted rice bran, and Chathaei al (2006) who reported that the TPC of differentrice bran extracts ranged from 250-397 mg/100gwith 80% methanol as the most efficient solventsystem in extracting the phenolic antioxidants fromrice bran as compared with other solvents. Gerardand Roberts (2004) reported that the total phenolicand flavonoid content of apple juice increased withincreasing microwave heating. In contrast, Abdul-Hamid et al. (2007) reported that total phenolicspresent in stabilized rice bran showed decreasingconcentrations in different milling fractions.

3.2. Antioxidant activity assessment

The antioxidant activity of SRB and USRBextracts was evaluated through the DPPH methodand the results are presented in terms of ICjo (Table1). The IC50 values of the scavenging activities on

DPPH radical were found to be 0.69 mg/ml, 0.79 mg/ml, and 0.17 mg/ml for SRB, USRB and ascorbicacid (standard), respectively. The DPPH radical-scavenging activity was found to be in the order ofascorbic acid > SRB >USRB. The stabilized defattedrice bran extract showed the most potent activity.This radical-scavenging activity of extracts could berelated to the nature of phenolic compounds or mightbe related to compounds other than phenolics.

Table 1 shows the individual phenolic acidsfound in the methanolic extract of SRB andUSRB respectively, monitored at 280 nm. Gallic,chlorogenic, syringic, vanillin, and ferulic acids werethe predominant phenolics showing the levels of0.003, 0.008, 0.004, 0.006 and 0.005 mg/100 g DW,in USRB, respectively. While in SRB fewer levels of0.002, 0.003 and 0.003 mg/100 g in SRB for syringic,vanillin, and ferulic acids were found.

3.3. Lipid oxidation compound assessment

Increasing primary and secondary lipidperoxidation products of rice bran oil treated withphenolic extract from SRB and USRB during 168hr storage were measured by peroxide, p-anisidineand thiobarbituric acid reactive substance (TBARS)values. The changes in peroxide value (PV) of thetreated oils as a function of time are shown in Table 2.Rice bran oil treated with SRB, and USRB exhibitedlower PV (

ABDALBASIT ADAM MARIOD, HADIZA ALTINE ADAMU, MAZNAH ISMAIL AND NORSHARINA ISMAIL

Table 2Peroxide, anisidine values and thiobarbituric acid reactive substances of defatted stabilized

and unstabilized rice bran methanolic extract at 100, 250mg/100 g and BHA at 200 ppm in rice branoil at hour 0 and 168 of storage at 70c*

Time[hr]06

1224487296

120144168

06

1224487296

120144168

06

1224487296

120

144168

Control3.50.17.90.39.40.412.70.516.40.620.01.123.52.327.22.131.13.034.43.3

0.50.10.80.21.80.42.90.53.70.64.60.84.90.85.31.15.91.26.51.3

0.90.42.90.75.1 0.96.80.98.71.111.20.313.80.215.30.416.40.520.40.4

BHA3.20.13.40.13.70.14.50.14.90.25.20.27.00.28.50.311.30.514.60.5

0.40.10.50.10.60.10.80.21.20.31.50.31.80.32.20.42.80.53.00.5

Peroxide value (PV)SRB 1003.20.14.50.25.90.26.90.27.50.38.40.310.40.414.80.517.80.622.52.4

Anisidine value (AV)0.40.10.60.11.20.31.40.31.60.32.1 0.42.60.52.90.53.50.63.80.6

SRB 2503.20.13.80.14.70.25.50.25.90.27.20.38.80.312.50.415.30.618.60.7

0.40.10.60.10.80.21.1 0.31.40.31.80.32.20.42.60.43.30.63.50.6

Thiobarbituric acid reactive substances (TBARSj0.20.10.50.10.80.31.1 0.41.30.42.20.63.40.84.70.25.20.36.70.3

0.50.11.20.41.50.41.60.42.1 0.63.1 0.35.1 0.96.60.27.00.37.70.4

0.40.10.80.31.1 0.41.20.41.60.42.20.64.20.35.60.26.70.38.50.4

USRB 1003.30.15.40.27.40.38.80.310.90.412.40.515.20.518.41.322.22.126.62.3

0.40.10.90.21.80.42.20.42.60.42.90.53.20.53.60.64.60.85.11.0

I0.60.21.80.41.90.52.20.62.60.73.80.86.20.47.60.28.30.39.60.3

USRB 2503.30.14.80.26.70.37.80.38.90.310.00.413.80.516.90.619.80.725.12.6

0.40.10.70.21.50.41.80.42.20.42.60.42.80.53.30.53.80.64.30.7

0.50.11.60.51.70.52.00.62.30.63.40.35.20.36.60.27.80.28.40.4

Results are mean values of three determinations SD. Means in a row sharing the same superscript are not significantly (P> 0.05)different from one another. PV: (meqO2/kg oil), AV: (), TBARS: (as pmol malonaldehyde equivalents/g sample)

12.7, 23.5, and 34.4 (meq/kg oil). These data alsoindicate that the antioxidant activity of most of thenatural antioxidants added as well as BHA decreasedwith the length of storage time. The antioxidant activityof SRB and USRB are concentration dependent. Themain purpose of using antioxidants in lipids is to delaya significant accumulation of free radicals and thusto improve oxidative stability. Natural antioxidants

extracted from defatted rice bran possessed goodantioxidant activity and extended the storage time anddecreased the formation of peroxides in rice bran oilless effectively than BHA.

The formation of p-anisidine values during thestorage of rice bran oil containing 0.1%, and 0.25%(w/w) of stabilized and unstabilized defatted ricebran extracts are shown in Table 2. Before storing

412 GRASAS Y ACEITES, 61 (4), OCTUBRE-DICIEMBRE, 409-415, 2010, ISSN: 0017-3495, DOI: 10.3989/gya. 110309

ANTIOXIDATIVE EFFECTS OF STABILIZED AND UNSTABILIZED DEFATTED RICE BRAN METHANOLIC EXTRACTS ON THE STABILITY..

Table 3Decrease in a-tocopherol, and y-oryzanol contents of rice bran oil in various concentrationsof antioxidants obtained from stabilized and unstabilized defatted rice bran during storage

at70cfor 168 hours*

Antioxidant Concentration(mg/100goil) Storage time (hrs)a-Tocopherol(mg/100 g oil)

y-Oryzanol(pg/IOOgoil)

Control

USRB 100

USRB 250

SRB 100

SRB 250

BHA 20

024487296120144168024487296120144168

0244872961201441680

24487296120144168

024487296120144168

024487296120144168

13.20.812.10.311.70.211.60.311.60.511.40.210.90.310.50.316.80.216.60.316.41.115.80.415.20.214.60.314.20.113.80.517.90.216.70.116.40.115.80.215.40.115.10.214.60.113.50.215.60.215.40.215.20.114.50.213.90.113.60.313.40.212.80.316.90.316.50.216.20.215.90.315.80.115.70.215.50.114.80.213.20.213.10.212.90.212.80.212.70.212.70.212.50.212.30.2

2.0 0.11.30.31.60.31.50.21.6 0.21.50.31.40.31.20.12.6 0.42.5 0.32.3 0.22.3 0.12.20.12.20.12.0 0.11.80.22.7 0.32.4 0.32.3 0.22.3 0.22.3 0.22.3 0.32.3 0.22.3 0.22.7 0.32.2 0.12.10.12.10.12.10.12.0 0.12.0 0.12.0 0.12.7 0.32.4 0.22.2 0.22.10.11.80.11.60.11.30.11.10.12.0 0.21.80.11.70.11.60.11.60.11.50.11.50.11.40.1

Results are mean values of three determinations SD. SRB:(Stabilized rice bran), USRB: (Unstabilized rice bran), BHA: (butylatedhydroxyanisole).

GRASAS V ACEITES, 61 (4), OCTUBRE-DICIEMBRE, 409-415, 2010, ISSN: 0017-3495, DOI: 10.3989/gya.110309 413

ABDALBASIT ADAM MARIOD, HADIZA ALTINE ADAMU, MAZNAH ISMAIL AND NORSHARINA ISMAIL

Figure 1.Effect of stabilized and unstabilized defatted rice bran methanolic extracts (SRB, USRB and BHA) on

oxidation of -carotene/linoleic acid at 50c.

at 70C, the initial p-anisidine value of rice bran oilwas 0.5. The P-anisidine values of rice bran oilwithout SRB, and USRB extracts were significantlyhigher (p > 0.05) than those of rice bran oilcontaining such extracts and BHA during storage.The P-anisidine value of rice bran oil withoutSRB and USRB extracts was rapidly increased (p> 0.05) to 4.9 after 96 hr storage and it was alsosignificantly different to the rice bran oil with SRBand USRB extracts after 48 hr storage (p > 0.05).From the results presented in Table 2, it can beconcluded that the anisidine value of rice branoil without defatted rice bran extracts after 24 hrstorage was significantly different (p > 0.05) to ricebran oil containing 0.1% (w/w) of USRB and SRBextracts and 0.02 % of BHA after 72, 120 and 168hr storage at 70C, respectively.

The effects of the different extracts and syntheticantioxidants on the TBARS values of rice bran oilafter accelerated oxidation at 70C are shown inTable 2. TBARS formation of the control increasedwith an increase in storage time. However, thevalues for the samples treated with the defatted ricebran extracts and BHA were significantly (P < 0.05)lower than those of the control. Among the phenolicextracts used, SRB and USRB extracts at 250 mgshowed better antioxidant activity than at 100 mgmethanolic extract. The different extracts loweredthe content of TBARS significantly (P < 0.05) after168 hr of storage. TBARS measure the formation ofsecondary oxidation products, which may contributeto the off-flavor of oxidized oil (Wanasundara andShahidi, 1994). These results indicate that the SRBand USRB extracts exhibited antioxidant activitynot only in -carotene linoleic acid (Fig. 1) but alsoduring rice bran oil peroxidation (Table 2).

3.4. Endogenous antioxidant content

Tocopherols and oryzanols are the mainantioxidants present in rice bran. The antioxidantactivity of oryzanols is almost 10 times higher thanthat of tocopherols. The changes of gamma-oryzanoland a-tocopherol content in rice bran oil treated withrice bran methanolic extract during storage weremeasured according to method of Rogers et al,(1993), and the results are shown in Table 3. After 168hrs of storage, the residual of a-tocopherol contentwas reduced by 17.9 and 20.1% of initial rice bran oilcontaining 100 and 250 mg USRB, respectively, 17.9and 12.9% initial rice bran oil containing 100 and 250mg SRB extracts, respectively.

Gamma-oryzanol contents in rice bran oil weredecreased during the storage of defatted rice branoil. The initial y-oryzanol contents of rice bran oilcontaining 100 and 250 mg USRB extracts were2.6, and 2.7 |jg/100g oil, respectively. After 168 hrsof storage, the y-oryzanol contents of rice bran oiladded with 100 and 250 mg USRB extracts were1.8 and 2.3 ^ig/100g oil, respectively. The initialy-oryzanol contents of rice bran oil containing100 and 250 mg SRB extracts were 2.7, and 2.7^Jg/100g oil, respectively. After 168 hrs of storage,the y-oryzanol contents of rice bran oil added with100 and 250 mg SRB of rice bran extracts was 2.0and 1.1 |jg/100g oil, respectively. These resultswere in good agreement with Nystrom et al., (2007)who reported that, y-oryzanol was more heat stablethan a-tocopherol at high temperatures. Severalstudies found that the y-oryzanol obtained from ricebran extracts had a strong stabilizing effect duringstorage and frying (Kochhar, 2000; Chotimarkornand Silalai, 2008).

414 GRASAS Y ACEITES, 61 (4), OCTUBRE-DICIEMBRE, 409-415, 2010, ISSN: 0017-3495, DOI: 10.3989/gya.110309

ANTIOXIDATIVE EFFECTS OF STABILIZED AND UNSTABILIZED DEFATTED RICE BRAN METHANOLIC EXTRACTS ON THE STABILITY...

4. CONCLUSIONS

From the present work, it could be concludedthat stabilization of rice bran has a significant effecton its methanolic extract antioxidant properties andthat antioxidant potential differs among the stabilizedand unstabilized samples up to a significant extent.Peroxide, TBARS and p-anisidine values werereliable methods that can be used to determinethe lipid peroxidation in rice bran oil, containingvarious concentrations of stabilized and unstabilizeddefatted rice bran extracts. These extracts whenadded in rice bran oil can reduce the changes ofa- tocopherol, and y-oryzanol contents due to lipidperoxidation during oil storage. Therefore, theseextracts can provide potential sources of naturalantioxidants suggesting their use in the inhibition oflipid oxidation in nutraceuticals and functional foods.

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Recibido: 3/11/09Aceptado: 15/3/10

GRASAS Y ACEITES, 61 (4), OCTUBRE-DICIEMBRE, 409-415, 2010, ISSN: 0017-3495, DOI: 10.3989/gya. 110309 415

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