antioxidative effects of ethanol extracts from rhus verniciflua stoke on yukwa (oil popped rice...

2474 JOURNAL OF FOOD SCIENCE—Vol. 67, Nr. 7, 2002 © 2002 Institute of Food Technologists

Food Chemistry and Toxicology

JFS: Food Chemistry and Toxicology

Antioxidative Effects of Ethanol Extracts fromRhus verniciflua Stoke on Yukwa (Oil PoppedRice Snack) Base During StorageY.S. PARK, Y.S. KIM, AND D.H. SHIN

ABSTRACT: This study was designed to evaluate the antioxidative effectiveness of ethanol extracts of Rhus vernicifluaStoke (RVE) in frying oil of Yukwa base (rice snack). RVE showed a strong antioxidant activity, but commercialantioxidants — BHA and dl-d-tocopherol — did not demonstrate a significant ifmprovement over the controltreatment (Yukwa bases prepared without any antioxidants and extracted oil from these). In particular, inductionperiod, peroxide value, and acid value of RVE treatment exhibited a higher oxidative stability than that of the othertreatments. In addition, the decrease in linoleic acid (C18:2)/palmitic acid (C16:0) ratio was much less than the othertreatments. Texture properties (hardness and crispiness) of Yukwa base were not significantly different. Resultsshowed strong antioxidant properties of RVE on Yukwa base during storage.

Keywords: Rhus verniciflua Stoke, antioxidant activity, storage stability, Yukwa, peroxide value

Introduction

YUKWA IS A KOREAN TRADITIONAL RICE SNACK MADE FROM

glutinous rice popped in frying oil, and used traditionally as aholiday food. Currently, its consumption is increasing. Its distin-guished texture and unique flavor is generated during the fryingprocess. The oil absorbed during the frying process producessecondary products such as hydroperoxide, dimer, and polymers(Frankel 1984), which can cause development of undesirable fla-vors and tastes in Yukwa. Lipid oxidation is a major deteriorativereaction in frying oils and fried foods, and often results in signifi-cant loss of quality (Alexander 1978). Also, lipid oxidation canlead to changes in functional, sensory, and nutritive values andeven the safety of fried food (Pearson and others 1983; Wu andothers 1986). Generally, these changes reduce consumer accep-tance of oxidized products. Antioxidants are usually added tofats, oils, and foods containing fat to inhibit the development ofoff-flavors arising from the oxidation of unsaturated fatty acid.However, the commercial use of synthetic antioxidants is strictlycontrolled, and increasing consumer awareness of food additivesand safety has prompted increased interest in the use of naturalantioxidants as alternatives to synthetic compounds. According-ly, many studies on the antioxidant activity of medicinal and edi-ble plants and their application to food preservation have beenconducted (Choi and others 1992; Gadow and others 1997; Piettaand others 1998; Kähkönen and others 1999; Masuda and others1999).

Traditionally, the Rhus verniciflua Stoke (RVS) has been usedas a lacquer which is a natural varnish and paint derived fromthe lacquer tree and used for preservation, as an antiseptic, andas an agent for medical purposes. East and South Asian peoplehave historically eaten it with chicken to improve their health.The major components of RVS sap consist of 55% to 70% urushiol,4% to 8% rubber substances, 2% to 3% nitrogen-containing sub-stances, 10% to 40% laccase and moisture, and 1% to 2% fla-vonoids ( Jung 1998). As a new source for natural antioxidant,crude ethanol extract from RVS was found to have inhibitory ef-fects against oxidation of cholesterol and CT-26-induced tumor

growth, as well as scavenging ability against reactive oxidants inchemical reaction assay (Lee and others 1999). Lee and others(2000) reported that RVS ethanolic extract is an effective microbi-al inhibitor.

Up to now the roles of natural antioxidants as fat stabilizerSand health protecting agents have always been studied sepa-rately. In most cases, these studies do not take into considerationthat when an antioxidant reacts with food peroxyl radicals, it cannot maintain the initial health protecting properties. In complexfood systems, where different ingredients are mixed together,possible interactions between fats and natural antioxidants areexpected, but very little data is available on the consequences ofthese reactions on food stability and health protecting proper-ties. Food processing and storage can make these interactionseven more complicated, being responsible for opposite effectson the stability of the product. Furthermore, heat treatments canenhance the rate of lipid oxidation and cause thermal degrada-tion of natural antioxidants (Maria and others 1999).

In our laboratory, we have tried to discover natural antioxi-dants from plants. Those screened with antioxidant activity wereisolated and identified. Free phenolic acid fraction (200 ppm) ofchloroform extracts from 75% ethanol extract of Rhus vernicifluaStoke (RVE) was reported to have strong antioxidant activity andthe major active components were found to be gallic acid, butin,and butein (Kim and others 1999). Therefore, we obtained ex-tracts from RVS by using 75% ethanol. It was applied to oil beforethe frying process. From this study, we observed advantageousresults with RVE treatment of frying oil that has a Yukwa base.

Materials and Methods

Preparation of RVE and chemical reagentsThe dried bark of RVS (about 800 g) was purchased from a lo-

cal medicinal store in Jeonju, Korea. After crushing the bark us-ing a cutting mill (Cutting mill VR-70, Victory Industries Co.,Kyeonggi, Korea), it was extracted with 75% ethanol in a waterbath at 80 0C for 3 h. The extracts of RVS were filtered by using fil-

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Antioxidant effects of Rhus verniciflua stoke. . .

ter paper (Whatman No. 40) and concentrated by a rotary vacu-um evaporator (Eyela N-N series, Tokyo Rikakikai Co. Ltd., To-kyo, Japan) at 45 0C. The residues of RVS were extracted oncemore by the same procedure. We obtained 120 g of RVE from thebark of RVS. Soybean oil without antioxidant and preservativeadditives was used in the frying process of Yukwa base. 3-Tert-butyl-4-hydroxy anisole (BHA) and dl-�-tocopherol (SigmaChemical Co., St. Louis, Mo., U.S.A) were used to compare the an-tioxidant activity of RVE treatment.

Preparation of Yukwa baseThe manufacturing methods of Yukwa differ according to the

region. Yukwa is usually manufactured by the following process:1st, glutinous rice is soaked in water overnight (about 12 h), di-gested, molded, dried at 40 °C (12% moisture content), and thenfried in soybean oil. Fried Yukwa base is then coated with rice syr-up and popped rice. We obtained Yukwa base prior to frying pro-cess from Lee Sun Ja Korea Traditional Cookie in Jeonju, Korea. Be-fore frying, the RVE (400 ppm, 1000 ppm), BHA (200 ppm) and

dl-�-tocopherol (200 ppm) were added into the oil, respectively.The concentration of RVE 1000 ppm corresponds to 200 ppm chlo-roform fraction of 75% ethanol extract of RVS (Kim 1999). After Yuk-wa base was fried at 80 0C for 1 min, it was fried again at 160 0C for2 min to obtain desirable expansion rate, hardness, crispiness,and stickiness. Fried Yukwa base was placed in bamboo basket for30 to 60 min to remove the excessively absorbed surplus oil andthen stored without packing in an incubator at 40 0C for 60 d.

Extraction of oil from stored Yukwa baseAt intervals of 10 d, the fried Yukwa base was removed from the

incubator to extract the absorbed oil. After the Yukwa base wascrushed, n-hexane was added and stirred for 30 min without lightat room temperature to prevent oxidative rancidity caused by ex-posure to light. The oil extracted with n-hexane from Yukwa base(about 300 g) of each treatment was immediately filtered (What-

Table 1—Hardness and crispiness value1 changes of Yukwa base prepared during storage at 40 oC for 60 d

Storage time (d)Treatment 0 10 20 30 40 50 60

HardnessControl2 590.0Aa 562.6Aa 568.1Aba 571.6Aa 601.9Aa 599.5Aa 585.8Aa

BHA 200 ppm 565.4Aa 568.4Aa 567.5ABa 539.3Aa 563.5Aa 544.5Ba 578.3Aa

dl-�-Tocopherol 200 ppm 595.1Aa 577.1Aa 543.1ABa 523.3Aa 566.3Aa 588.2ABa 558.5Aa

RVE3 400 ppm 624.4Aa 601.4Aa 597.2Aa 587.9Aa 575.6Aa 586.2ABa 582.2Aa

RVE 1000 ppm 592.3Aa 564.5Aab 525.7Bb 578.8Aab 586.3Aab 569.3ABab 541.7Aab

CrispinessControl 54.8Aa 57.2Aa 56.8Aa 55.6Aa 59.6Aa 60.0Aa 56.8Ba

BHA 200 ppm 59.2Aa 55.4Aa 57.4Aa 59.2Aa 59.6Aa 57.2Aa 59.2ABa

dl-�-Tocopherol 200 ppm 56.8Aa 59.4Aa 60.6Aa 61.4Aa 58.4Aa 63.0Aa 56.2Ba

RVE 400 ppm 56.0Aa 57.4Aa 58.0Aa 56.2Aa 65.2Aa 60.8Aa 57.8ABa

RVE 1000 ppm 56.4Aab 52.6Ab 54.0Aab 61.6Aab 57.2Aab 59.6Aab 63.4Aa

A-B Within each column of the table, means followed by the same letter are not significantly different from each other at P < 0.05.a-b Within each row of the table, means followed by the same letter are not significantly different from each other at P < 0.05.1 These values are average of 10 determinations.2 The control is Yukwa base prepared without any antioxidants.3 The RVEs are the extracts of Rhus verniciflua Stoke extracted with 75% ethanol in water bath at 80 oC for 3 h.

Figure 1—The induction period (IP) changes of extractedoil from Yukwa base prepared with and without antioxi-dants during storage at 40 oC for 60 d. The control is theextracted oil with n-hexane from Yukwa base preparedwithout antioxidants and the RVEs are the 75% ethanol ex-tracts of Rhus verniciflua Stoke.

Figure 2—The peroxide value (POV) changes of extractedoil from Yukwa base prepared with and without antioxi-dants during storage at 40 oC for 60 d. The control is theextracted oil with n-hexane from Yukwa base preparedwithout antioxidants and the RVEs are the 75% ethanolextracts of Rhus verniciflua Stoke.

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man No. 40), then concentrated in a rotary vacuum evaporator.The extracted oil samples (about 45 g/treatment) were stored in afreezer (-60 0C) under a blanket of nitrogen until it was assayed.

Chemical assays of extracted oil from Yukwa baseThe accelerated oxidative test was performed by induction

period (IP) of oil sample using a Metrohm Rancimat Model 679(Metrohm AG, CH-9101 Herisau, Switzerland). The oil sample(2.5 g) was heated at 120 ± 0.1 0C and the rate of air flowingthrough the samples was adjusted to 20 L/h. The volatile compo-nents produced from the heated oil were trapped in 70 mL of dis-

tilled water (Frega and others 1999). The peroxide value (POV )and acid value (AV) (Paguot and others 1987) were also mea-sured to compare the oxidative stability of the extracted oil.

Texture analysis of Yukwa baseTexture properties of Yukwa base were evaluated with TA-XT2i

Texture Analyser (Stable Micro Systems, Surrey GU7 1YL, En-gland). Samples of Yukwa base were punctured by P/3 probe to80% deformation. Hardness was measured with max force (g),and crispiness was calculated with peak number after puncturetest. The parameter setting and operation of the instrumentwere accomplished through a personal computer with TextureExpert software version 1.0. The force and probe calibration pro-cedures for the system were set before the actual test. The pre-test, test, and post-test speeds were set to 2.0, 0.3, and 2.0 mm/srespectively. Each test was repeated 10 times to minimize any ex-perimental error.

Color analysisUsing the Color and Color Difference Meter (Model TC-3600,

Tokyo Denshoku Co., Ltd., Tokyo, Japan), the color of the Yukwabase was determined. A standard white color plate with reflec-tance values of X=79.9, Y=81.3, Z=90.8 was used as a reference.The sample was filled in the round cell and after measurement ofHunter X, Y, Z color scales, it was converted into CIE L*a*b* valuewith the following equation; L* = 116 (Y/Yo)1/3 – 16, a* = 500 [(X/Xo)1/3 – (Y/Yo)1/3], b* = 200 [(Y/Yo)1/3 – (Z/Zo)1/3]. CIE L (light-ness), +a (red) to –a (green), and +b (yellow) to –b (blue) werethen determined for each sample.

The change of free fatty acid compositionThe extracted oil samples (200 mg) were weighted and methy-

lated using 0.5 N BF3-MeOH at 95 �C for 5 min to produce methylesters (AOAC 1995). Fatty acid compositions of the methylated oilsamples were determined by capillary gas chromatography (GC)analysis with Shimadzu GC 17A (Shimadzu Co., Kyoto, Japan)equipped with a flame-ionization detector. Supelcowax™-10capillary column (30 m � 0.25 mm i.d., 0.25 �m film thickness;

Table 2—CIE L*a*b* value changes of Yukwa base powder prepared with and without antioxidants during storage at40 oC for 60 d


L*

Control1 86.0CDb 83.6Cd 85.3BCc 85.8Cb 85.3BCc 85.8Bb 86.5Ca

BHA 200 ppm 87.7Ba 86.3Ac 85.5Bd 86.8Bbc 85.4BCd 87.0Ab 86.5Cc

dl-d-Tocopherol 200 ppm 88.4Aa 86.2Ae 86.5Ade 87.8Ab 85.5Bf 87.3Abc 87.0BCcd

RVE2 400 ppm 86.4Cb 85.3Bc 86.4Ab 85.7Cc 86.4Ab 87.3Aa 87.7Aa

RVE 1000 ppm 85.7Dbc 85.2Bcd 84.8Cd 84.8Dd 84.8Cd 85.7Bb 87.1Ba

a*

Control 6.7Ac 7.6Aa 7.5Aa 7.1Ab 6.7Ac 7.6Aa 6.9Ac

BHA 200 ppm 4.2Cc 4.5Cc 5.3Cab 4.5Cc 5.5Ba 5.3Cab 5.0Cb

dl-�-Tocopherol 200 ppm 3.7Dd 4.5Cc 4.7Dbc 4.5Ec 5.3Ba 4.9Db 4.5Dc

RVE 400 ppm 3.9CDc 4.2Dc 4.2Ec 5.0Da 4.9Cab 4.9Dab 4.7Db

RVE 1000 ppm 5.7Bc 5.7Bc 6.4Bc 6.4Bb 7.0Aa 5.9Bc 5.5Bc

b*

Control 21.6Ad 23.7Aa 23.0Abc 23.4Aab 22.7Bc 23.8Aa 22.7Ac

BHA 200 ppm 18.7Cd 20.7Dc 21.5Cb 21.8Bab 22.0Ca 21.7Cab 20.7Cc

dl-d-Tocopherol 200 ppm 17.9De 20.9Dc 20.3Dc 19.7Cd 21.0Db 21.6Ca 20.4Cc

RVE 400 ppm 19.4Bd 21.1Cbc 19.9Ed 21.7Ba 21.1Dc 21.7Cab 21.6Babc

RVE 1000 ppm 22.2Ad 23.0Bbc 22.6Bbcd 23.3Ab 24.2Aa 22.5Bcd 22.9Abc

A-E Within each column of the table, means followed by the same letter are not significantly different from each other at P < 0.05.a-f Within each row of the table, means followed by the same letter are not significantly different from each other at P < 0.05.1 The control is Yukwa base prepared without any antioxidants.2 The RVEs are the extracts of Rhus verniciflua Stoke extracted with 75% ethanol in water bath at 80 oC for 3 h.

Figure 3—The acid value (AV) changes of extracted oil fromYukwa base prepared with and without antioxidants dur-ing storage at 40 oC for 60 d. The control is the extractedoil with n-hexane from Yukwa base prepared without anti-oxidants and the RVEs are the 75% ethanol extracts of Rhusverniciflua Stoke.

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Supelco Inc., Bellefonte, Pa., U.S.A.) was employed. Columntemperature was programmed from 200 oC to 250 oC at 2.5 oC/min and held at 250 oC for 10 min. The injector and detector tem-perature was 260 oC. Helium was used as a carrier gas with a flowrate of 0.586 mL/min. The split ratio was 1:100. Peaks were iden-tified by comparing the relative retention times of each peakwith the Oil Reference Standard AOCS No. 5 (Sigma ChemicalCo., St. Louis, Mo., U.S.A.) and OmegawaxTM Test Mix No. 4-8476(Supelco Inc., Bellefonte, Pa., U.S.A.). Percentage of each fattyacid was calculated as the ratio of the peak area to the total chro-matographic area.

Sensory evaluationTrained panelists formed from graduate students who were fa-

miliar with Yukwa evaluated all the stored samples every 10 d for60 d. They were instructed in the purpose of the test, how to evalu-ate and what to judge before the test. Judgements were quanti-fied by measuring the mark on the line using a 9-point hedonicscale (Moskowitz 1983). For the color and rancid odor, 1-point indi-cated extremely light yellow and fresh flavor, while 9-point washeavy yellow and extremely distasteful flavor. All samples werecoded and presented in a randomized arrangement.

Statistical design and analysisData was analyzed using the Statistic Analysis System (SAS

Institute, Inc. 1996) package software for the analysis of variance(ANOVA). Duncan’s multiple range tests were used to obtaincomparisons among sample means at a significance level of P <0.05. All experiments were made in triplicate except for hardnessand crispiness measured by the Texture Analyser and color andrancid odor by sensory evaluation.

Results and Discussion

IP changes of extracted oil from Yukwa baseIn Fig. 1, the curve of IP obtained in the Rancimat method for

Yukwa base stored for up to 60 d are presented. In the earlystage, the IPs of control, BHA, and dl-�-tocopherol treatmentwere measured 2.50, 2.75, and 2.56 h, respectively and were sig-nificantly lower than those of RVE 400, 1000 ppm (3.17 h, 3.75 h)(P < 0.05). This tendency continued as the storage period in-creased over the time. The IPs of control and dl-�-tocopherolsamples were less stable than that of the BHA sample to 40 d (P <0.05). Moreover, after 50 d of storage the IP of the 3 samples werenot measured as it was below 0.5 h, indicating its detection limit.For the RVE 1000 ppm treatment, IP was observed higher thanthat of RVE 400 ppm treatment. From the results of Rancimatmethod, the amount of added RVE determined the oxidative sta-

bility and IP of oil. As shown in Figure 1 the IPs of control, BHA,and dl-d-tocopherol treatment decreased drastically for compar-ison the RVE treatments. These results were quite unexpectedbecause BHA and dl-�-tocopherol are generally considered asstrong antioxidants. Antioxidant activity of RVE treatment con-tinued until 60 d, suggesting that its activity is strong. Therefore,IP measurement is possible to determine the stability of extract-ed oil from Yukwa base.

POV changes of extracted oil from Yukwa baseHydroperoxides initiate autoxidation of oil rancidity by ab-

sorbing oxygen and subsequently produce carbonyl compoundbyproducts. Therefore, POV is used to express oxidation level ofthe oil. As shown in Figure 2, POV gradually increased for alltreatments during storage time. The initial POV of each samplewas not significantly different (P < 0.05). The POV in RVE treat-ments 400 ppm and 1000 ppm were 124.84 meq/kg and 66.31meq/kg respectively after 60 d of storage. On the contrary, BHA(267.48 meq/kg), control (301.93 meq/kg), and dl-�-tocopheroltreatments (350.10 meq/kg) were higher than the RVE treat-ment. Jung and others (1990) found that optimum concentrationof �-, �-, and �-tocopherol to increase oxidative stability was 100,250, and 500 ppm, respectively. The tocopherols had significantpro-oxidant effect (P < 0.05) at higher concentration above this.In our study, POV of dl-�-tocopherol treatment was considerablyhigher than that of the other treatment. It is suggested that theactivity of tocopherol dropped drastically and degraded the oxi-dative stability of tocopherol during deep-fat frying. (Gordonand others 1995; Holownia and others 2001).

AV changes of extracted oil from Yukwa baseA tendency of AV for extracted oil was similar to POV. Up to 30

d, AV of each treatment was not significantly different (P < 0.05).AVs of control, BHA, dl-�-tocopherol, RVE 400, and 1000 ppmtreatments were 0.36, 0.35, 0.37, 0.37, and 0.37 mg/g on 30 d re-spectively. However, AV of each treatment after 40 d was signifi-cantly different (P < 0.05) (Figure 3). AV of control treatment was2-fold (1.88 mg/g) and the result of dl-�-tocopherol treatmentwas 3-fold (2.34 mg/g) compared to that of RVE 1000 ppm treat-ment (0.88 mg/g) on 60 d. These results indicate that RVE treat-ment showed strong antioxidant property.

Hardness and crispiness changes by Texture AnalyzerTable 1 shows the result of hardness and crispiness by Tex-

ture Analyzer. The change of hardness and crispiness was notconsiderably different within a fixed period of storage (P < 0.05).From the result, the measurement of shelf-life for Yukwa base de-pended on quality degradation by chemical variations.

Table 3—Rancid odor changes1 by sensory evaluation of Yukwa base prepared with and without antioxidants duringstorage at 40 oC for 40 d


Control2 3.3ABd 4.3Adc 4.7Ac 6.5Ab 7.1Aab 7.6ABab 8.2Aa

BHA 200 ppm 4.0Ad 4.0Ad 4.4Ad 5.1Bdc 5.7Bbc 6.6BCab 7.5Aa

dl-d-Tocopherol 200 ppm 2.3Be 4.6Ad 5.6Adc 6.7Abc 7.4Aab 8.0Aab 8.2Aa

RVE3 400 ppm 3.3ABc 4.0Ac 4.3Abc 4.7Babc 5.6Bab 5.9Ca 6.1Ba

RVE 1000 ppm 3.3ABc 3.8Ac 4.1Abc 4.7Babc 5.4Bab 5.6Ca 5.7Ba

A-C Within each column of the table, means followed by the same letter are not significantly different from each other at P < 0.05a-e Within each row of the table, means followed by the same letter are not significantly different from each other at P < 0.051 These values are average of 10 determinations.2 The control is Yukwa base prepared without any antioxidants3 The RVEs are the extracts of Rhus verniciflua Stoke extracted with 75% ethanol in water bath at 80 oC for 3 h.

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Cooked-rice texture was thought to be due to amylose con-tent. However, Radhika and others (1993, 1994) suggested thatrice texture was determined by the content of externally locatedlong-B chains of the high molecular weight branched compo-nent, amylopectin, of rice starch. It is, therefore, concluded thatrice starch contains branched molecules of amylopectin varyingfrom big to small sizes (Ramesh and others 1999). In previouswork, Shin and others (1990) reported that hardness and chang-es of number of peaks on Yukwa base observed by Instron Uni-versal Testing Machine did not change during storage at 30 oC.On this basis, the inconsistent result of texture in our study infersthat texture is due to the weight and size of Yukwa base, differ-ence of expansion rate, and deep frying time during frying pro-cess.

CIE L*a*b* value change by color and color differencemeter

The color change of Yukwa base during storage at 40 oC wasshown in Table 2. Results showed that the CIE a* value (red) andCIE b* value (yellow) increased slightly with increasing storagetime. In general, a minor change was observed for the CIE L* a* b*

value, implying that it is not a major contributing factor to thecolor of Yukwa base. Although Lim and others (1993) reportedthat L*, a*, b* values of soybean oil decreased according to frying

time, the color changes in our study were not responsible for theshelf-life of Yukwa base.

Sensory evaluationColor score of each treatment by a trained panelist was 7.1

(control), 6.8 (BHA), 6.5 (dl-�-tocopherol), 6.7 (RVE 400 ppm),and 6.8 (RVE 1000 ppm) on 60 d, but these scores were not statis-tically different (P < 0.05). Rancid odor scores by sensory evalua-tion gradually increased. The score for each sample was not sig-nificant up to 20 d and as it reached 60 d the score of RVEtreatment (400, 1000 ppm) was lower than that of the other treat-ments and were not significantly different from control, BHA,and dl-�-tocopherol (Table 3). Sensory evaluation was employedto assess the effect of an antioxidant on the rancid odor and colorof stored Yukwa base. Although somewhat subjective, sensoryevaluation remains the ultimate measure of rancidity, as no com-bination of chemical or physical tests is currently available in as-sessing the composite sensory attributes of a food (Robards andothers 1988).

Free fatty acid compositionOxidation of oil can easily occur in the presence of oxygen.

Consequently the oil becomes rancid due to the reaction of oxy-gen with unsaturated fatty acids to form oxidative products. The

Table 4—Fatty acid composition changes of extracted oil from Yukwa base prepared with and without antioxidantsduring storage at 40 oC,

Fatty acid composition (wt%)1

Treatment Storage time (d) 14:0 16:0 18:0 18:1 18:2 18:3 18:2/16:0

Control2 0 0.07 10.79 4.65 22.64 52.11 6.31 4.83Aa

10 0.08 11.27 4.34 22.21 52.39 6.25 4.65Aab

20 0.09 11.37 4.33 22.23 52.29 6.25 4.60ABabc

30 0.08 11.38 4.59 22.50 51.64 6.19 4.54ABbcd

40 0.09 11.78 4.70 22.74 51.01 6.01 4.33Cd

50 0.09 11.66 4.74 23.02 50.92 5.94 4.37ABcd

60 0.09 12.31 5.03 23.78 49.62 5.56 4.03Ce

BHA 200 ppm 0 0.09 11.35 4.35 22.04 52.38 6.37 4.62Aab

10 0.07 11.20 4.27 22.04 52.60 6.32 4.70Aa

20 0.07 11.16 4.33 22.23 52.39 6.32 4.69Aa

30 0.08 11.35 4.40 22.40 51.78 6.12 4.56Abab

40 0.08 11.38 4.60 22.69 51.58 6.08 4.53Ab

50 0.08 11.43 4.65 22.89 51.33 5.99 4.49ABb

60 0.09 12.39 5.00 23.68 49.53 5.58 4.00Dc

dl-�-Tocopherol 200 ppm 0 0.07 10.96 3.97 21.71 53.43 6.37 4.88Aa

10 0.07 11.09 4.29 22.14 52.62 6.15 4.74Aa

20 0.08 11.31 4.50 22.46 51.94 6.05 4.60ABb

30 0.11 11.57 4.52 22.54 51.58 6.00 4.46Bc

40 0.09 11.58 4.62 22.87 51.30 5.85 4.43Bc

50 0.09 11.92 4.84 23.50 50.37 5.57 4.23Bd

60 0.10 12.84 5.18 24.49 48.72 5.19 3.80Ee

RVE3 400 ppm 0 0.09 11.41 4.29 22.23 52.36 5.77 4.59Ab

10 0.08 10.97 4.11 22.26 52.92 5.81 4.83Aa

20 0.08 11.42 4.40 22.41 52.01 5.77 4.55Bbc

30 0.08 11.54 4.41 22.42 51.87 5.79 4.50ABbcd

40 0.09 11.49 4.79 22.88 50.98 5.49 4.44Bd

50 0.09 11.54 4.62 22.97 51.26 5.54 4.44Acd

60 0.10 11.99 4.67 23.16 50.75 5.43 4.23Be

RVE 1000 ppm 0 0.08 11.22 4.25 22.34 52.46 5.78 4.68Aab

10 0.08 11.13 4.23 22.12 52.55 5.92 4.72Aa

20 0.08 11.31 4.38 22.38 52.23 5.78 4.62ABab

30 0.08 11.26 4.43 22.49 51.97 5.79 4.62Aab

40 0.09 11.39 4.49 22.57 51.80 5.71 4.55Ab

50 0.09 11.36 4.57 22.70 51.61 5.66 4.55Ab

60 0.09 11.67 4.67 23.06 51.04 5.49 4.37Ac

A-E Within same storage time of each column of the table, means followed by the same letters are not significantly different from each other at P < 0.05.a-f Within each column of the table, means followed by the same letters are not significantly different from each other at P < 0.05.1The wt% of each fatty acid in the oil sample was calculated as the percentage of the sum of total wt (g/100 g oil) of fatty acids in the extracted oil sample.2 The control is the extracted oil with n-hexane from Yukwa base prepared without any antioxidants.3 The RVEs are the extracts of Rhus verniciflua Stoke extracted with 75% ethanol in water bath at 80 oC for 3 h.

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change of fatty acid composition was carried out to study correla-tion between fatty acid amount and physicochemical propertiessuch as POV, AV, and IP. Soybean oil consists of myristic acid(0.1%), palmitic acid (10.6%), stearic acid (4.0%), oleic acid(23.3%), linoleic acid (53.7%), linolenic acid (7.6%) (Weiss 1983).Linoleic acid and palmitic acid are usually used as indicators ofthe extent of fat deterioration because linoleic acid is more sus-ceptible to oxidation, whereas palmitic acid is more stable towardoxidation. Therefore, the ratio of C18:2/C16:0 was also used to indi-cate the degree of oxidative deterioration of frying oil in thisstudy. According to storage time, the content of palmitic acid(C16:0), stearic acid (C18:0), and oleic acid (C18:1), slightly increased,while the content of linoleic acid (C18:2) and linolenic acid (C18:3)decreased (Table 4). The difference of C18:2/C16:0 ratio of RVEtreatments 400 ppm and 1000 ppm were 0.36 and 0.31 respec-tively, while the difference of ratio for control, BHA, and dl-�-to-copherol treatments were 0.8, 0.62, and 1.08 during storage time,respectively. That is, it shows the RVE treatment is more stablethan other treatments to oxidation. The content of polyunsatu-rated fatty acid in fresh soybean oil was around 60%. In thisstudy, the decrease in linoleic acid and linolenic acid contents forall oils was significant (P < 0.05).

Table 5 shows the correlation between IP, POV, AV, and C18:2/C16:0

ratio. The measurement of POV in extracted oil is one of the best in-dicators of frying oil quality. IP, AV, and C18:2/C16:0 ratio had high cor-relation (0.83-0.91) with POV, but AV and C18:2/C16:0 had low correla-tion (0.62-0.69) with IP. From these results, it can be concluded thatthe composition of fatty acid depends on the oxidative degradationof fried oil. Further investigation on the storage stability of friedfood is needed, but IP, AV, and C18:2/C16:0 ratio showed good correla-tion with POV. These 4 simple and rapid methods can, therefore, beemployed to monitor the quality of fried food during storage.

Conclusions

THE ANTIOXIDANT ACTIVITY OF ETHANOL EXTRACTS OF RHUS

verniciflua Stoke for Yukwa base was investigated using sev-eral assay methods. The assay results indicated that RVE couldbe a good antioxidant source. Antioxidant activity of compoundsaccording to Rancimat method, POV, and AV decreased in the or-der as follows, RVE 1000 ppm > RVE 400 ppm > BHA (200 ppm) >control > dl-�-tocopherol (200 ppm) treatment. When comparingthe ratio of C18:2/C16:0 during storage, dl-�-tocopherol 200 ppmtreatment again showed the greatest decrease, followed by con-trol, BHA 200 ppm, RVE 400, and 1000 ppm treatments. From theresults of this study, it can be concluded that RVE is a strongsource of antioxidant. Therefore RVE can be used to enhance theoxidative stability in oil-containing food. However further studyfor the mechanism and interaction between food and RVE, and

research on biological activities of RVE should be followed to cer-tify the safety of the extracts.

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MS 20010211 Submitted 5/1/01, Accepted 1/10/02, Received 1/14/02

This research was funded by the MAF-SGRP(Ministry of Agriculture and Forestry - SpecialGrants Research Program) in Korea.

Authors Park, Kim, and Shin are with the Faculty of Biotechnology (FoodScience and Technology Major), Chonbuk National University, Dukjin-Dong, Jeonju, Jeonbuk 561-756, Republic of Korea. Direct inquiries to au-thor Shin (E-mail:[email protected]).

Table 5—Correlation between analytical values of IP, POV,AV, and C18:2/C16:0 by Pearson correlation analysis

IP1 POV AV C18:2/C16:0

IP NA 0.83 0.64 0.69POV 0.83 NA 0.93 0.89AV 0.64 0.93 NA 0.90C18:2/C16:0 0.69 0.89 0.90 NA1 IP = Induction Period, POV = Peroxide Value, AV = Acid Value, C18:2/C16:0 =Linoleic acid/Palmitic acid.

jfsv67n7p2474-2479ms20010211-MO.p65 9/19/2002, 11:10 AM2479

antioxidative effects of ethanol extracts from rhus verniciflua stoke on yukwa (oil popped rice...

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