Food Chemistry 123 (2010) 1019–1026

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Food Chemistry

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Antioxidant efficacy of potato peels and sugar beet pulp extracts in vegetableoils protection

Adel Abdelrazek Abdelazim Mohdaly a,b,*, Mohamed Atef Sarhan b, Awad Mahmoud b,Mohamed Fawzy Ramadan c, Iryna Smetanska a

a Methods of Food Biotechnology, Institute of Food Technology and Food Chemistry, TU Berlin University, Germanyb Food Science and Technology, Faculty of Agriculture, Fayoum University, Egyptc Agricultural Biochemistry Department, Faculty of Agriculture, Zagazig University, Zagazig 44511, Egypt

a r t i c l e i n f o a b s t r a c t

Article history:Received 17 December 2009Received in revised form 23 March 2010Accepted 11 May 2010

Keywords:Accelerated storageAntioxidant activityOxidative stabilityPotato peelsSoybean oilSugar beet pulpSunflower oil

0308-8146/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.foodchem.2010.05.054

* Corresponding author. Address: Methods of FoodInstitute of Food Technology and Food Chemistry, TKoenigin-Luise-Str. 22, D-14195 Berlin, Germany. Tel.30 832 7663.

E-mail address: adola2010@yahoo.com (A.A.A. Mo

The antioxidant properties of potato peels and sugar beet pulp, in comparison with synthetic antioxidant,were investigated. The bioactive materials were extracted with methanol and examined for their antiox-idant activity under accelerated oxidation conditions, using sunflower and soybean oils as oxidation sub-strates at different concentrations for 72 h at 70 �C. Inverse relationships were noted between peroxidevalues and oxidative stabilities and also between secondary oxidation products, measured by p-anisidinevalue and stabilities at termination of the storage. Absorptivity at 232 nm and 270 nm increased gradu-ally with the increase in time, due to the formation of conjugated dienes and polyenes. The order of oxi-dative stability was as follow: TBHQ > potato peels > BHT = sugar beet pulp > BHA. The predominantphenolic compounds identified by thin-layer chromatography in potato peels and sugar beet pulp werechlorogenic and gallic acids. The results of different antioxidant parameters demonstrated that potatopeels and sugar beet pulp are potent sources of natural antioxidants that might be explored to preventoxidation of vegetable oils.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

Food lipids undergo a variety of chemical reactions such asaccelerated oxidation, thermolysis, and polymerisation under heatexposure (Jinyoung, Yoosung, & Eunok, 2008). Oxidation of oilsmodifies their organoleptic properties and affecting the shelf lifeof the product. It results in the loss of nutritional value of food aswell as changes in colour, texture, sensory and other physiologicalproperties (Iqbal & Bhanger, 2007). Due to these changes, consum-ers do not accept oxidised products and industries suffer fromeconomic losses. The oil industry has to pay special attention inthis context, as oils, fats and fatty foods suffer stability problems(Valenzuela, Sanhueza, & Nieto, 2003). The oils with higher con-tents of unsaturated fatty acids, especially polyunsaturated fattyacids, are more susceptible to oxidation. It is, therefore, importantto evaluate the oxidative stability (OS) of oils as affected by pro-cessing and storage conditions.

The oxidative stability of oils and fats with added antioxidants,can be determined during storage under normal ambient

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hdaly).

conditions and packing. However, in general, oxidation can take along time to occur, e.g., a few days to a few months, which isimpractical for routine analysis. For this reason, accelerated oxida-tion tests or ageing tests are conducted. Tests like Schaal oven test,Sylvester test and Swift test are used for accelerated oxidation testat elevated temperature. Normally Schaal oven test is used fordetermination of oxidation of oils (Mahuya, Runu, & Utpal, 2008).

In order to overcome the stability problems of oils and fats, syn-thetic antioxidants, such as butylated hydroxyanisole (BHA), butyl-ated hydroxytoluene (BHT), tert-butyl hydroquinone (TBHQ) havebeen used as food additives. However, recent reports reveal thatthese compounds may be implicated in many health risks, includ-ing cancer and carcinogenesis (Prior, 2004). Therefore, the mostpowerful synthetic antioxidant (TBHQ) is not allowed for foodapplication in Japan, Canada and Europe. Similarly, BHA has alsobeen removed from the generally recognised as safe (GRAS) listof compounds (Goli, Barzegar, & Sahari, 2005). Due to these safetyconcerns, there is an increasing trend among food scientists to re-place these synthetic antioxidants with natural ones, which, ingeneral, are supposed to be safer (Yanishlieva & Marinova, 2001).Phenols are one of the most important groups of natural antioxi-dants (Artajo, Romero, Morello, & Motilva, 2006). They occur onlyin material of plant origin and are known to protect easily-oxidiz-able constituents of food from oxidation. Polyphenols possess idealstructural chemistry for free radical scavenging activity, and they

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have been shown to be more effective antioxidants in vitro thantocopherols and ascorbate. Antioxidant properties of polyphenolsarise from their high reactivity as hydrogen or electron donors,and from the ability of the polyphenol derived radical to stabiliseand delocalise the unpaired electron (chain-breaking function),and from their ability to chelate transition metal ions (terminationof the Fenton reaction) (Rice-Evans, Miller, & Paganga, 1997).

Processing of fruits, vegetables, and oilseeds results in largeamounts of waste materials such as peels, seeds and stones. Dis-posal of these materials usually represents a problem that is fur-ther aggravated by legal restrictions. Thus, new aspectsconcerning the use of these wastes as by-products for further pro-duction of food additives or supplements with high nutritional va-lue have gained increasing interest because these bioactives arehigh-value products and their recovery may be economicallyattractive (Vasso & Constantina, 2007).

Beet pulp is a sugar-depleted and highly fibrous material that isproduced after sugar is extracted from sugarbeet (Beta vulgaris L.).Pulp is a valuable cattle feed and supplies carbohydrates, proteins,and minerals. The pulp content of sugarbeet ranges from 4% to 6%(Mosen asadi, 2007, Chapter 3). Most of the liquid and solid wastesfrom potato (Solanum tuberosum L.) arise from peeling, trimming,slicing, cleaning, and rinsing operations which creates a pollutionproblem. Mohdaly, Sarhan, Smetanska, and Mahmoud (2010) re-ported that methanolic extract of potato peels and sugar beet pulpexhibited the highest extraction ability for phenolic compounds,and also showed the strongest antioxidant capacity in the three as-says used, 2,2-azinobis (3-ethylbenzthiazoline sulphonate) (ABTS)radical scavenging activity, 1,1-diphenyl-2-picrylhydrazyl (DPPH)radical scavenging capacity, and b-carotene/linoleic acid test sys-tem. The antioxidant properties of potato peels and sugar beet pulpextracts in lipophilic system under accelerated oxidation conditionhave not yet been studied. Therefore, the objectives of this studywere to evaluate the antioxidant effectiveness of potato peelsand sugar beet pulp extracts during oxidation of sunflower andsoybean oils by measuring both primary (hydroperoxides) and sec-ondary oxidation products and to compare its antioxidant activitywith commercially antioxidants. The study also attempted to iden-tify the antioxidant compounds present in the extracts using chro-matographic and spectroscopic techniques.

2. Materials and methods

2.1. Materials and reagents

Potato peels (Solanum tuberosum cv Diamond) obtained from lo-cal potato chip manufacturing industry (6 October, Egypt) inNovember 2007 and stored at �20 �C until use, whereas the sugarmanufacturing industry (Fayoum, Egypt) supplied sugar beet pulp(B. vulgaris cv Gloriato) carry out this study. BHA, BHT, and chloro-genic acid were purchased from Sigma, whilst p-Anisidine (4-Ami-no-anisol; 4-Methoxy-anilin), TBHQ, and caffeic acid were fromFluka (Buchs, Switzerland). Sunflower oil was produced by Brökel-mann–Oelmühle GmbH (Hamm, Germany) was obtained from Aldisupermarket (Berlin, Germany), whilst soybean oil which obtainedfrom Edeka aktivmarkt (Berlin, Germany) was produced by KunellaFeinkost GmbH (Cottbus, Germany) and the oils were free of anysynthetic antioxidant.

2.2. Sample preparation

Potato peels and sugar beet pulp were washed, dried in a hot airat 40 �C then ground into a fine powder in a mill. Ground materials(10 g) were extracted with (100 ml) of methanol overnight in ashaker at room temperature followed by filtration through What-

man No.1 filter paper. The residues were re-extracted under thesame conditions. The combined filtrates were evaporated in a ro-tary evaporator below 40 �C. The extracts obtained after evapora-tion of methanol were stored at �20 �C for further use.

2.3. Analysis of potato peels and sugar beet pulp

The major chemical constituent, moisture, ash, crude fat, crudefibre, and crude protein were determined in triplicate; according tothe methods describe in the AOAC (1990) whilst carbohydrateswere calculated by subtraction of difference.

2.4. Storage studies

2.4.1. Selection of oilsThe selection of test oils was based on the presence of varying

polyunsaturated fatty acids (PUFA) composition. Thus, sunfloweroil (SFO) which includes high level of linoleic acid (18:2n � 6)and soybean oil (SBO) which is rich in a-linolenic acid(18:3n � 3) in addition to linoleic acid were used in this investiga-tion. Schaal oven test (Fennema, 1976) was conducted to evaluatethe effect of antioxidants against oxidation during the acceleratedoxidative storage of oils.

2.4.2. Sample preparation for oxidative stability determinationThe extracts of potato peels and sugar beet pulp were applied to

commercial edible sunflower and soybean oils obtained from localmarket (free of any antioxidant) at different concentrations (5, 10,50, 100 and 200 ppm, based on extract weight), in a series of trans-parent glass bottles having a volume of 20 ml each, to examinetheir antioxidative activity. TBHQ, BHA and BHT at a level of200 ppm were also applied for comparison. The bottles were com-pletely filled with oil and sealed. A control sample was prepared byusing the same amount of methanol used to dissolve the antioxi-dant and the extracts (Moure et al., 2000). The antioxidant-en-riched oil samples were evaporated in a vacuum evaporatorbelow 40 �C to evaporate the solvent and subjected to acceleratedoxidation in the dark in an oven at 70 �C for 72 h. Aliquot (20 g)were removed periodically every 4, 8, 24, 32, 36, 48, 56, and 72 hfor analysis. Immediately after storage period, oil samples werewithdrawn for triplicate analyses. The oils were sampled for eachmeasurement from separate bottles.

2.4.3. Analytical procedures2.4.3.1. Peroxide value (PV). Peroxide value of samples was mea-sured according to Kirk and Sawyer (1991). The method is basedon iodometric titration, which measures the iodine produced frompotassium iodide by the peroxides present in the oil. In a stopperconical flask (250 ml) vegetable oils sample (4 ± 0.5 g) was takenalong with chloroform (10 ml), glacial acetic acid (15 ml) and freshsaturated aqueous potassium iodide solution (1 ml). The flask wasstoppered and shaken vigorously for 1 min and then kept in thedark for further 5 min (IUPAC, 1987). In the next step, double dis-tilled water (10 ml) was mixed thoroughly with the solution andtitrated against 0.002 N sodium thiosulphate solution until the yel-low colour almost disappeared. Then about 0.5 ml of soluble starchindicator (1%) solution was added. Titration was continued untilthe blue colour just disappeared. One blank reagent (without sam-ple) was prepared.

Peroxidevalue ðmeq kg�1Þ ¼ ðV � V0Þ � N � 103W

;

where V is the titre value (ml) of sodium thiosulphate solution forsample, V0 the titre value (ml) of sodium thiosulphate solution forblank, N the normality of sodium thiosulphate solution and W theweight of sample in gram.

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2.4.3.2. p-Anisidine value (AV). The p-anisidine value (AV) wasdetermined according to Cd 18-90 method (AOCS, 1995). Themethod is based on the spectrophotometric determination of prod-ucts formed in the reaction between aldehydic compounds in theoil and p-anisidine. Oil samples (0.5–2.0 g) were dissolved in25 ml iso-octane and absorbance of this fat solution was measuredat 350 nm using a spectrophotometer (Hitachi U-3000, Tokyo, Ja-pan). Five millilitres of the above mixture was mixed with 1 ml0.25% p-anisidine in glacial acetic acid (w/v) and after 10 minstanding, absorbance was read at 350 nm using a spectrophotom-eter. The p-anisidine value (AV) was calculated according to theequation:

AV ¼ 25� ð1:2As� AbÞ=m

where As is the absorbance of the fat solution after reaction withthe p-anisidine reagent; Ab is the absorbance of the fat solutionand m is the mass of oil sample (g).

2.4.3.3. Conjugated dienes (CD) and conjugated trienes (CT). Specificextinctions at 232 nm and 270 nm (i.e., conjugated dienes and con-jugated trienes) were determined using a spectrophotometer. Oilsamples were diluted with iso-octane to bring the absorbance

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Fig. 1. Relative increase in peroxide value (PV) of treated sunflower oil samples: (A)sunflower oil samples: (C) with potato peels, (D) with sugar beet pulp under accelerateddeviation.

within limits following the standard method of IUPAC method II.D. 23 (IUPAC, 1979).

2.4.4. Thin-layer chromatography and UV scan of methanolic extractsAn aliquot of extracts (10 ll) was spotted on a precoated silica

gel plate (F254, 0.25 mm, Merck, Darmstadt, Germany). The plateswere developed in the ascending direction for 17 cm with chloro-form: methanol (1:1, v/v) then sprayed with 10�4 M DPPH in meth-anol. UV spectrum (200–400 nm) of diluted extracts in methanol(1%) was recorded by spectrophotometry (Shimadzu UV-260 visi-ble recording spectrophotometer; Kyoto, Japan).

2.5. Statistical analysis

Statistical analyses were conducted using SPSS (Statistical Pro-gramme for Social Sciences, SPSS Corporation, Chicago, IL, USA)version 16.0 for Windows. All analyses were performed in tripli-cate and data reported as means ± standard deviation (SD). Datawere subjected to analysis of variance (ANOVA). The confidencelimits used in this study were based on 95% (P < 0.05).

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with potato peels, (B) with sugar beet pulp and p-anisidine value (AV) of treatedstorage. Error bars show the variations of three determinations in terms of standard

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3. Results and discussions

3.1. Composition of the raw materials

Composition analysis of potato peels extract showed 6.55%moisture, 8.46% of crude fat, 13.9% of crude protein, 8.48% of ashes,13.0% of crude fibre, and 56.2% of carbohydrates by difference,whilst sugar beet pulp contained moisture, crude fat, crude pro-tein, ash, crude fibre, and carbohydrates being 6.90%, 6.92%,10.8%, 6.64%, 17.8%, and 57.8%, respectively. This indicates thatthese by-products could be used as a source of carbohydrate, fatand protein.

3.2. Stability of oils as affected by addition of potato peels and sugarbeet pulp extracts

3.2.1. GeneralOil stability is usually determined under accelerated oxidation

conditions (60 �C or more) because ambient conditions demandan excessively long period. To evaluate the antioxidant efficaciesof the extracts in soybean and sunflower oils, PV, AV and UVabsorptivity were determined as indices of lipid oxidation. The oxi-dative stability studies were carried out at 70 �C in an oven. This

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Fig. 2. Absorptivity at 232 nm of treated sunflower oil samples: (A) with potato peels, (B(C) with potato peels, (D) with sugar beet pulp during oven test. Error bars show the va

temperature was ideal, because at higher temperatures the perox-ides will decompose very fast (Duh & Yen, 1997; Mariod, Ibrahim,Ismail, & Norsharina, 2010).

3.2.2. Effect of different extracts on sunflower oil oxidationPeroxide value (PV) is a measure of the concentration of perox-

ides and hydroperoxides formed in the initial stages of lipid oxida-tion. Peroxide value is one of the most widely-used tests for themeasurement of oxidative rancidity in oils and fats. A continuousincrease in PV with the increase in storage period was observedfor all the samples (Fig. 1A and B). Initially rate in PV was veryslow, but it started to increase after 32 h of storage and went onincreasing further with the increase in storage period. Peroxide va-lue was in the range of 1.34 ± 0.21–15.8 ± 0.26 meq kg�1 for potatopeel extracts (PPE), whilst it was 1.34 ± 0.21–16.9 ± 0.24 meq kg�1

for sugar beet pulp ones (SBP). Sunflower oil samples without anti-oxidant (control) reached a maximum PV of 25.8 ± 0.24 meq kg�1

after 72 h of storage. A significant difference (P < 0.05) in PV wasobserved between the control and sunflower oil samples contain-ing extracts and synthetic antioxidants, which slowed the rate ofperoxide formation. The PV of sunflower oil containing 200 ppmof potato peels, sugar beet pulp, TBHQ, BHT, and BHA werefound to be 11.9 ± 0.19, 13.8 ± 0.26, 11.0 ± 0.26, 13.4 ± 0.26 and

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) with sugar beet pulp and Absorptivity at 270 nm of treated sunflower oil samples:riations of three determinations in terms of standard deviation.

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13.9 ± 0.24 meq kg�1 after 72 h of storage, respectively. This datasuggests the superiority of antioxidant activity of potato peelsand sugar beet pulp extracts over synthetic antioxidants. However,among these treatments, TBHQ remained the most effective andgave the lowest PV (Ying et al., 2010).

Antioxidants are mainly used in lipids to delay the accumula-tion of primary oxidation products and thus to improve the oxida-tive stability. The primary products of lipid peroxidation arehydroperoxides, which are generally referred to as peroxides.Therefore the results of PV estimation give a clear indication of li-pid autoxidation. For further confirmation of these results, otheroxidation parameters, such as conjugated dienes, conjugated tri-enes and p-anisidine values were also measured. The p-anisidinevalue (AV), which measures the secondary oxidation products pro-duced during the oxidative degradation of oil, was determined byreacting p-anisidine with the oil in iso-octane and the resultantcolour was measured at 350 nm. Fig. 1C and D depicts the p-ansi-dine values for sunflower oil samples stabilized with methanolicextracts, TBHQ, BHT, BHA, and control. The p-anisidine value ofcontrol reached a maximum of 14.2 ± 0.14 from an initial valueof 0.98 ± 0.13 after 72 h of storage. The values for potato peels, su-gar beet pulp, BHA, BHT and TBHQ at 200 ppm were 9.10 ± 0.24,9.40 ± 0.31, 9.42 ± 0.14, 9.36 ± 0.14, and 8.84 ± 0.14, respectively.A significant difference was noted between the values for control

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Fig. 3. Relative increase in peroxide value (PV) of treated soybean oil samples: (A) with posamples: (C) with potato peels, (D) with sugar beet pulp under accelerated storage. Erro

and experimental samples. The results demonstrated that potatopeel extracts followed by sugar beet pulp extracts had higher anti-oxidant activity than BHA and BHT but lower than TBHQ.

Fig. 2 shows the relative increase in conjugated dienes (CD) andtrienes (CT) contents of sunflower oil under accelerated storage asfunction of storage time. The assessment of CD and CT is a goodparameter for the measurement of oxidative deterioration of oils,hence indicates the effectiveness of antioxidants in oils (Shahidi& Wanasundara, 1997). Initially, rate of formation of CD was high-er, and went on decreasing with the increase in storage time,whilst the reverse behaviour was observed for CT content, i.e., ini-tially rate was lower, and went on increasing with the storage time.Formation of high contents of CD may be related to the presence ofhigher contents of polyunsaturated fatty acids (Liu & White, 1992)in sunflower oil. Conjugated trienes may be produced by dehydra-tion of conjugated diene hydroperoxides (Fishwick & Swoboda,1977). Highest contents were observed for control, indicatinggreater intensity of oxidation, followed by BHA = BHT, SBP, PPEand TBHQ. The increase in CD and CT contents is proportional tothe uptake of oxygen. The greater the levels of CD and CT the lowerthe oxidative stability of the oils will be (Chatha, Anwar, Manzoor,& Bajwa, 2006). Iqbal and Bhanger (2007) described the antioxi-dant activity of garlic extracts in sunflower oil, assessed underaccelerated conditions, using CD and CT as indicators of oxidative

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tato peels, (B) with sugar beet pulp and p-anisidine value (AV) of treated soybean oilr bars show the variations of three determinations in terms of standard deviation.

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degradation. Siddiq, Anwar, Manzoor, and Fatima (2005) alsoinvestigated the antioxidant efficacy of methanolic extract ofMoringa oleifera leaves, indicating antioxidant potential of stabil-ization of sunflower oil under accelerated ageing by measuring ofCD and CT contents.

3.2.3. Effect of different extracts on soybean oil oxidationFig. 3A and B show the PV developments during the storage of

soybean oil at 70 �C for 72 h with various concentrations of potatopeels and sugar beet pulp extracts. Additional treatments includedTBHQ, BHA, and BHT at 200 ppm and a control without additives.Highest PV was observed for control followed by BHA, sugar beetpulp, BHT, potato peels, and TBHQ at 200 ppm after 72 h of storage.A significant difference (P < 0.05) in PV was observed between thecontrol and soybean oil containing extracts, BHT, BHA, and TBHQ.These results indicated that potato peels and sugar beet pulp ex-tracts inhibited soybean oil oxidation. Further, the antioxidant ef-fect of potato peels at 100 and 200 ppm and sugar beet pulp at200 ppm were better than BHT and BHA at 200 ppm. During incu-bation, TBHQ maintained significantly the lowest PV.

The effect of potato peels and sugar beet pulp extracts on soy-bean oil oxidation (measured by p-anisidine value) is shown inFig. 3C and D. In control sample formation of carbonyls was higherthan in samples with added extracts (P < 0.05). When compared

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Fig. 4. Absorptivity at 232 nm of treated soybean oil samples: (A) with potato peels, (B)with potato peels, (D) with sugar beet pulp during oven test. Error bars show the variat

with the control, potato peels and sugar beet pulp extracts at200 ppm were found to be even more effective in retarding the for-mation of carbonyl components than BHT and BHA, which pre-dicted their high antioxidant potential. However, at all the stagesof storage periods, these extracts were less effective than TBHQ.Utilisation of p-anisidine measurement to assess the potential ofnatural antioxidants in vegetable oils under accelerated storageconditions is generally accepted (Chatha et al., 2006).

Absorption at 232 nm and 270 nm, due to the formation of pri-mary and secondary compounds of oxidation (Fig. 4), showed apattern in good agreement with that of the PV and AV. CD andCT contents continued to increase with the increase in storagetime. Control exhibited the highest content of CD followed byBHA, BHT, SBP, PPE and TBHQ. On the other hand, CT levels fol-lowed the pattern control > BHA > BHT = SBP > PPE > TBHQ, respec-tively. CD and CT of all stabilized samples are lower than thecontrol sample; thus indicating that the extracts under investiga-tion had good antioxidant activity (Liu & White, 1992).

3.3. Identification of phenolic compounds using TLC and UV spectra

To know what is/are the responsible active ingredient(s) in po-tato peels and sugar beet pulp, TLC and absorptivity spectra be-tween 200 nm and 400 nm were screened. Phenolic compounds

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with sugar beet pulp and Absorptivity at 270 nm of treated soybean oil samples: (C)ions of three determinations in terms of standard deviation.

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exhibit two major absorption bands in the ultraviolet/visible re-gion: a first band in the range between 320 nm and 380 nm anda second band in 250–285 nm range (Matthäus, 2002). As can beseen from Fig. 5, extracts of potato peels and sugar beet pulpshowed maximum absorption in the range between 220 nm and380 nm. This absorbance was more accentuated for potato peelsextract than sugar beet pulp. These results are in agreement withthe peroxide and p-anisidine values, which showed that potatopeels extract had a higher antioxidant activity than sugar beetpulp. Absorption maxima of extracts at 220 nm may be due tothe presence of flavone/flavonol derivatives (Chang, Yen, Huang,& Duh, 2002).

Fig. 5. UV absorbance scanning between 200 nm and 400 nm of m

Fig. 6. Thin layer chromatography profile of the samples and standard. Lanes: 1, sugarcumaric acid; 6, caffeic acid; 7, Qurecetin; 8, gallic acid; 9, chlorogenic acid; and 10, Sin

Some authors have reported that the total phenolic content didnot correspond well with the antioxidant activity of the extracts.Thus, individual phenolic compounds may provide a better indica-tion of the antioxidant activity of the extracts in vegetable oils (Bin& Clifford, 2008). Fig. 6 shows a representative TLC profile of thesamples and standard. It shows that the methanolic extract of po-tato peels contains chlorogenic, gallic, p-cumaric, and caffeic acids,whilst in sugar beet pulp chlorogenic and gallic acids were identi-fied. The results confirmed our previous contributions (Mohdalyet al., 2010), wherein methanolic extract of potato peels showedthe highest total phenols (2.91 mg gallic equivalent/g dry weight)followed by sugar beet pulp (1.79 mg gallic equivalent/g dry

ethanolic extracts of potato peels (1) and sugar beet pulp (2).

beet pulp extract; 2, potato peels extract; 3, Ferulic acid; 4, p-cumaric acid; 5, o-abic acid.

1026 A.A.A. Mohdaly et al. / Food Chemistry 123 (2010) 1019–1026

weight). p-Cumaric, and caffeic acids may play an important role inthe antioxidant activity of potato peels extract.

In present research, phenolic acids are proven, using TLC analy-sis, to be present in potato peels and sugar beet pulp and the anti-oxidant activity of these compounds is mainly due to their redoxproperties, which can play an important role in adsorbing and neu-tralising free radicals, quenching singlet and triplet oxygen, ordecomposing peroxides (Osawa, 1994). This finding may indicatethat these compounds contribute to the antioxidant activity of po-tato peels and sugar beet pulp extracts.

4. Conclusion

From the present study, it can be concluded that potato peelsand sugar beet pulp can stabilize both sunflower and soybean oilsvery effectively at all concentrations. They inhibit thermal deterio-ration of oil by improving its hydrolytic stability, inhibiting doublebond conjugation and reducing the losses of polyunsaturated fattyacids. Potato peel extract at concentration of 100 ppm and200 ppm and sugar beet pulp extract at 200 ppm have stabilizationefficiency comparable to commonly-employed synthetic antioxi-dants BHT and BHA at their legal limit, but less effective than thesynthetic antioxidant TBHQ. This is in accordance with results ofAruoma, Halliwell, Aeschbach, and Loliger (1992) who reportedthat in soybean oil carnosic acid was more active than BHT andBHA, but less active than TBHQ. Potato peel extract has a strongantioxidative effect during initial and final steps of oxidation inthe dark, in an oven at 70 �C for 72 h, followed by sugar beet pulp.Therefore, potato peels and sugar beet pulp can be recommendedas potent sources of antioxidants for the stabilization of food sys-tems, especially unsaturated vegetable oils. The phenolic com-pounds appear to be responsible for the antioxidant activity ofpotato peels and sugar beet pulp, although further studies are re-quired to reveal whether they contain other antioxidative constit-uents. In addition, in vivo evidence and isolation of antioxidantcomponents in potato peels and sugar beet pulp merit furtherinvestigation.

Acknowledgements

Financial support for this study was provided by Egyptian Min-istry of Higher Education and Berlin University of Technology(Germany).

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