J Sci Food Agric 1997, 75, 19È26

Effects of Seed Roasting Temperature and Timeon the Quality Characteristics of Sesame

indicum) Oil(Sesamum

Hiromi Yoshida* and Sachiko Takagi

Department of Nutritional Science, Kobe-Gakuin University, Arise, Ikawadani-cho, Nishi-ku, Kobe651-21, Japan

(Received 20 September 1996 ; accepted 25 February 1997)

Abstract : The quality characteristics and composition of sesame oils prepared atdi†erent roasting temperatures (160È250¡C) from sesame seeds using a domesticelectric oven were evaluated as compared to an unroasted oil sample : only minorincreases (P\ 0É05) in characteristics, such as peroxide value, carbonyl value,anisidine value and thiobarbituric acid reactive substances, of sesame oilsoccurred in relation to increasing roasting temperature and time between 160and 200¡C, but colour units of oils increased markedly over a 220¡C roastingtemperature. SigniÐcant decreases (P\ 0É05) were observed in the amounts oftriacylglycerols and phospholipids in the oils prepared using a 250¡C roastingtemperature. The amounts of c-tocopherol and sesamin still remained over 80and 90%, respectively, of the original levels after roasting at 250¡C. In the oilprepared using a 250¡C roasting temperature, sesamol was detected at 3370 mgper kg oil, but sesamolin was almost depleted after 25 min of roasting. Burningand bitter tastes were found in the oils prepared at roasting temperatures over220¡C. The results suggested that a high-quality product would be obtained byroasting for 25 min at 160 or 180¡C, 15 min at 200¡C and 5 min at 220¡C whencompared with the other samples.

J Sci Food Agric 75, 19È26 (1997)No. of Figures : 2. No. of Tables : 5. No. of References : 29

Key words : antioxidants, chemical analyses, composition, fatty acid distribu-tions, lipid class, oxidative stability, roasting temperature, quality, sensory evalu-ation, sesame oil

INTRODUCTION

Sesame (Sesamum indicum L) is one of the worldÏs mostimportant oil seed crops. Not only is it a source ofedible oil, but the seed itself provides a nutritious foodfor humans. Therefore, sesame seed is used extensivelyin baked goods and confectionery products. Oils fromroasted and unroasted sesame seeds are widely used inthe eastern Asian countries, especially in Japan andChina. One excellent characteristic of sesame oil is itsresistance to oxidative deterioration. Although attemptshave been made to demonstrate the stability of theroasted seed oil without a chemical reÐning process

* To whom correspondence should be addressed.

(Kumazawa and Sugiura 1958 ; Okada and Koyama1969), the stability of the oil has not previously beenchemically investigated in detail. The roasted-seed oilhas a special Ñavour and is more prevalent in the FarEast. Sesame oil has a mild, pleasant taste and is anatural salad oil requiring little or no winterising. Itsremarkable stability may be due to the presence of theendogenous antioxidants, sesamol and sesaminol,together with tocopherols. Sesame oil prepared fromroasted sesame seeds has a distinctive Ñavour andlonger shelf-life (Manley et al 1974 ; Kikugawa et al1983) and is used as a cooking oil and in shorteningsand margarines. The conventional method for the prep-aration of sesame oil involves cleaning, roasting, grind-ing, cooking and pressing but not reÐning (Fukuda and

191997 SCI. J Sci Food Agric 0022-5142/97/$17.50. Printed in Great Britain(

20 H Y oshida, S T akagi

Namiki 1988). The roasting process is the key step formaking sesame oil, since the colour, composition andquality of sesame oil are all inÑuenced by the conditionsof the roasting process. The overall Ñavour of roastedsesame signiÐcantly depends on the roasting conditions,and changes in the relative concentrations of volatileshave been observed to depend on roasting time andtemperature (Asai et al 1994). A higher roasting tem-perature has usually been used to obtain a strongÑavour, but it results in a sesame oil of poorer quality(Yen et al 1986). Therefore, in order to make goodquality sesame oil, the optimum roasting conditionshould be established. Hitherto, few data concerning thee†ect of the domestic roasting process on the composi-tion and quality characteristics of sesame oil have beenreported. When the roasting time was Ðxed at 30 minusing a domestic electric oven (Yoshida 1994), theoptimum roasting temperature was around 180¡C forpreparation of sesame oil with better quality andÑavour. However, little has been mentioned on howseed roasting temperature and time a†ect the sesame oilquality.

The purpose of the present study was to elucidate therelationship between roasting temperature and time forpreparation of oil with good quality from sesame seedswhen roasted in a domestic electric oven.

EXPERIMENTAL

Materials

Sesame seedsThe sample of sesame seeds (Sesamum indicum L) in thisstudy was a white species which were all grown in thesummer of 1995 (Tokushima, Japan). The seed cultivars(Takii Seed Co, Kyoto, Japan) were selected for uni-formity based on seed weight (2É5È2É8 mg) and dividedinto several groups for storage in stainless-steel con-tainers at 4¡C until required.

Antioxidative componentsSesamol (reagent grade) was purchased from AldrichChemical Co. (Milwaukee, WI, USA). Sesamin andsesamolin were puriÐed from sesame oil according tothe method of Soliman et al (1985). The purity of eachcompound was about 980 g kg~1 as determined byhigh-performance liquid chromatography (HPLC).Vitamin E homologues (a, b, c and d) were purchasedfrom Eisai Co. (Tokyo, Japan). All the tocopherols wereof the D-form (RRR-) and the purity of each tocopherolwas greater than 985 g kg~1 by HPLC.

ReagentsAll chemicals were of analytical grade (Nacalai tesque,Kyoto, Japan) and were used without further puriÐ-cation. Thin-layer chromatography (TLC) precoated

Silica-Gel G 60 plates (10] 20 or 20 ] 20 cm, 0É25 mmlayer thickness) were purchased from Merck(Darmstadt, Germany). The phospholipid and glyco-lipid standards were obtained from Serdary ResearchLab (London, Ontario, Canada). Methyl pentadeca-noate (Merck, Darmstadt, Germany) was used as inter-nal standard. in methanol (140 g kg~1 ; Wako PureBF3Chemical Ind, Osaka, Japan) was used to prepare thefatty acid methyl esters.

Methods

Roasting of sesame seedsWhole sesame seeds were placed as a single layer in aPyrex petri dish (8É0 cm diameter) and then roasted at160, 180, 200, 220 and 250¡C for 5, 10, 15, 20 and25 min, respectively, in an electric oven (Model R-5550,Sharp, Osaka, Japan) after covering the dish. Fivedishes were treated once at each of the di†erent roastingtemperatures and times to obtain sufficient samplematerial for analysis and testing. After roasting, theseeds were allowed to cool to ambient temperaturebefore lipid extraction. The weight loss of a sampleexposed to electric oven roasting was calculated bydividing the weight of moisture loss after each roastingtime by the weight of the sample before roasting. Theother roasting conditions were as described previously(Yoshida 1994).

L ipid extractionThe roasted sesame seeds (1000 seeds) were crushed bymeans of a commercial blender with 50 ml ofchloroform/methanol (1 : 1, v/v) at 0¡C, and the lipidswere further extracted by vigorous shaking of triplicatesamples, essentially as described by Yoshida (1994). Thesolvents contained butylated hydroxytoluene (100 mglitre~1), added to inhibit the oxidative degradation oflipids and antioxidants during experimental procedures.The combined extracts, dried in a rotary vacuum appar-atus at 35¡C, were dissolved in chloroform/methanol(2 : 1, v/v). The solution was washed with water asdescribed by Folch et al (1957) and dried over anhy-drous The lipid extracts were Ðltered throughNa2SO4 .lipid-free Ðlter paper and the solvent was removed invacuo at temperatures below 35¡C. The extracted lipidswere weighed to determine the lipid content of the seedsand then kept in chloroform/methanol (2 : 1, v/v) solu-tions in a 25-ml brown glass volumetric Ñask undernitrogen in the dark at [25¡C until required for furtheranalysis. Lipids were also extracted from raw seeds bythe same procedure as a control.

Analysis of antioxidant componentsSimultaneous determination of sesamol, sesamolin,sesamin and tocopherol homologues in the oils wascarried out using a Shimadzu LC-6A HPLC (Coors and

Seed roasting and sesame oil quality 21

Montag 1985) equipped with a Shim-pack CLC-SIL(M) column (5 km, 25É0 cm] 4É6 mm id, Shimadzu).The mobile phase was a mixture of n-hexane/ethylacetate (90 : 10, v/v) at a Ñow rate 1É0 ml min~1. Fiftymilligrams of total lipids was placed in a 5-ml brownvolumetric Ñask and dissolved with the mobile phasefor HPLC. An aliquot (8 kl) was injected with a fullyloaded 20-kl loop. Antioxidant components were moni-tored with a Ñuorimetric detector (Shimadzu RF-535)set at an excitation wavelength of 296 nm and emissionwavelength of 320 nm. The amount of each compoundwas calculated by comparison to the peak areas of thestandard.

Analysis of lipidsOfficial methods (AOCS 1990) were used for determi-nation of peroxide (method Cd 8-53) and 2-thiobarbituric acid reactive substances (TBARS, methodCd 19-90). The TBARS was expressed as milligrams ofmalonaldehyde equivalent per kilogram of oil. The car-bonyl and p-anisidine values of the roasted seed oilswere measured according to standard methods (JOCS(1981) and IUPAC (1987), respectively). As an index ofcolour development, the absorbance at 450 and 670 nmof a 50 g litre~1 solution of lipid in chloroform wasdetermined with a Shimadzu spectrophotometerUV-2500 PC. The colour unit was calculated as 77É4

to 31É2 (Stillman 1953). This value is equal toA450 A670the red value as determined by Lovibond TintometerModel E.

L ipid class analysisThe crude lipid extracts were applied to the TLC platesas 7-cm bands (ca 20 mg per plate) with a micro-syringe(Hamilton Co, Reno, NV, USA). The triacylglycerolfraction was separated from total lipids by TLC devel-oped in n-hexane/diethyl-ether/acetic-acid (70 : 40 : 1,v/v/v). On the other hand, the phospholipid fractionwas isolated from total lipids by multiple-developmentTLC; neutral lipids were removed by developing withthe Ðrst solvents described above, and glycolipids werefurther removed by developing with the second solventsof acetone/acetic-acid/water (100 : 2 : 1, v/v/v). Bandscorresponding to triacylglycerols and phospholipidswere scraped separately into test-tubes(10É5 cm] 16 mm) with TeÑon-coated screw caps.Methyl pentadecanoate (15 : 0) was added as internalstandard to the total lipids and to each fraction at ca100 g kg~1 level (w/w esters). The fatty acids were con-verted to methyl esters by heating in BF3-methanol(Morrison and Smith 1964) and were analysed by gaschromatography (GC) as described previously (Yoshidaet al 1995).

Sensory evaluationA trained panel of 15 people, experienced in analytical-descriptive sensory testing (Powers 1989), evaluated the

oils for overall odour and Ñavour intensity and individ-ual odour and Ñavour characteristics. Ratings weremade according to a nine point hedonic scale : 9, likeextremely ; 8, like very much ; 7, like moderately ; 6, likeslightly ; 5, neither like nor dislike ; 4, dislike slightly ; 3,dislike moderately ; 2, dislike very much ; 1, dislikeextremely. Tasting was conducted according to theexperimental design detailed under statistical methods.

Statistical analysis of experimental dataEach reported value is the mean of three determi-nations, and the data were subjected to one-wayanalysis of variance with a randomised complete blockdesign to partition the e†ects of di†erent parameters(Steel and Torrie 1980). SigniÐcant di†erences amongtreatment means were separated by using DuncanÏsmultiple range test (1955), at a level of P\ 0É05.

RESULTS AND DISCUSSION

Proximate analyses using AOAC (1980) proceduresshowed composition (as is) of the seeds before roastingto be as follows : moisture 72 g kg~1, protein210 g kg~1, fat 523 g kg~1. When roasted for 5, 10, 15,20 and 25 min at di†erent temperatures in an electricoven, the higher the roasting temperature and thelonger the roasting time, the greater the rate of theweight loss of (1000) sesame seeds (Fig 1). After 25 minof roasting, the loss attained 58É3, 67É8, 76É3, 88É4 and121É8 g kg~1 of the original weight, at 160, 180, 200,220 and 250¡C, respectively. These losses may reÑecttotal volatile substances, but it was considered to bemostly moisture. As shown in Fig 2, the sesame oils pre-pared by roasting at di†erent temperatures had a

Fig 1. Relationship between roasting time and weight loss ofsesame seeds at di†erent temperatures roasted in an electricoven : 160¡C; 180¡C; 200¡C; 220¡C;(L) (…) (|) (>) ())250¡C. All data points represent the means of measurementsfrom three replicates ; the standard errors are within the size of

the symbols.

22 H Y oshida, S T akagi

Fig 2. Changes in the sensory evaluation of the oils prepared from sesame seeds roasted at di†erent temperatures in an electricoven : (A) 180¡C; (B) 200¡C; (C) 220¡C; (D) 250¡C. Each value represents the average of three replicates and vertical bars represent

standard error of the replicates.

Ñavour score signiÐcantly (P\ 0É05) higher than thoseof other oil samples as follows : for 25 min at 160 or180¡C, 15 min at 200¡C and 5 min at 220¡C. TheÑavour score at 160¡C was omitted from Fig 2because the scores were very similar to the changingpatterns at 180¡C. However, the burning and bittertastes were found in the oils prepared at roasting tem-perature over 220¡C. When the roasting temperaturewas increased to above 220¡C, the typical dark-brownish colour was apparent at 15 min and thesample had a characteristic burnt smell, and poorquality oils resulted (Table 1). Therefore, the optimumroasting temperature should be not more than 200¡Cwhen roasted using a domestic electric oven.

The characteristics and qualities of sesame oilsroasted at di†erent temperatures in the range of 5È25 min are shown in Table 1. There were only minorsigniÐcant increases (P\ 0É05) in parameters such asperoxide, carbonyl, anisidine and TBARS values, in thesesame oils prepared below 200¡C. Thereafter, thesevalues increased with higher roasting temperature, espe-cially anisidine and TBARS values as indicators for sec-ondary oxidation products. The results imply thatanisidine and TBARS values would be more availablethan peroxide value or carbonyl value when evaluatingby chemical means the quality of sesame oils after roast-ing. However, the colour formation in sesame oil wasdependent on the extent of roasting (Shyu 1986).According to the results shown in Table 1, the colourunit (red value) of oils increased markedly with roasting

temperature up to 220¡C. The colour formation insesame oil could be attributed to both non-enzymicbrowning and phospholipid degradation during roast-ing, since phospholipids were reported to cause brown-ing during roasting (Husain et al 1986). The browningsubstances are generally very polar due to active rad-icals (Kawakishi et al 1983). The increase in browningsubstances may be attributed to the increase to totallipids (Table 2). Such increases were expected becauselipid extraction was carried out after roasting treat-ments. Table 2 clearly shows that the phospholipidcontent decreased from ca 48 mg in 1000 unroastedseeds to 1É7 mg in 1000 seeds prepared using a 250¡Croasting temperature.

Table 3 shows the changes in the antioxidants of theoils prepared from sesame seeds roasted at di†erenttemperatures. The variation in vitamin E contents andlignan levels of sesame seeds may be due to genetic dif-ferences or to the geographical origin of the seeds(Kamal-Eldin and Appelqvist 1994). However, themajor tocopherol homologue in sesame oil was c-tocopherol, with d-tocopherol as a very small com-ponent, but no a- and b-tocopherols were detectable.Although c-tocopherol has a lower vitamin E valuein biological systems (Burton and Traber 1990) thana-tocopherol, it is a more potent antioxidant in oils.c-Tocopherol was still retained at more than 80% afterroasting for 25 min at all temperatures. On the otherhand, sesamin decreased only by 2È6% in that time.Furthermore, the higher the roasting temperature and

Seed roasting and sesame oil quality 23

TABLE 1Characteristics and qualities of the oils prepared from sesame seeds roasted at di†erent temperatures in an electric ovena,b

Roasting temperature Roasting time Peroxide Carbonyl Anisidine T BARS Colour(¡C) (min) value value value value units

160 Unroasted 1É42a 1É82a NDc 0É08a NDc10 4É13c 2É00a 0É62a 0É08a NDc20 4É80c,d 2É10a 1É85b 0É15b 0É05a25 5É38d 2É13a 1É88b 0É17b,c 0É12b

180 10 2É69b 2É01a 1É40b 0É09a 0É04a20 4É29c 2É26a 2É69b 0É21c 1É03c25 5É28d 2É58a,b 3É57b,c 0É27c 2É15c

200 10 3É24b 2É46a,b 2É24b 0É18b,c 1É78c15 4É86c,d 2É73a,b 3É30b,c 0É31c,d 3É92d25 5É95d 3É46b 6É23c,d 0É54d 12É68e

220 5 1É73a 2É38a 2É09b 0É28c 4É58d15 2É15a,b 3É05b 7É11d 0É43c,d 35É12f25 5É92d 3É61b 8É67d 0É71e 58É08g

250 5 1É86a 2É81a 3É43b,c 0É34c,d 10É73e15 3É04b 3É90b 9É12d,e 0É62d,e 64É43g25 7É07e 4É61c 15É66e 0É74e 141É31h

a Each value is an average of three determinations, and the TBARS are expressed as mg malonaldehyde equivalent per kg oil.b Values in the same column with di†erent following letters are signiÐcantly di†erent from those for unroasted seeds (P\ 0É05).c ND \ 0É01.

TABLE 2Lipid contents in the oils prepared from sesame seeds roasted at di†erent temperature in an

electric ovena,b

Roasting temperature Roasting time T otal lipids T riacylglycerols Phospholipids(¡C) (min)

160 Unroasted 1420É8a 1364É7a 47É6a10 1434É2a 1359É6a 47É2a20 1442É3a,b 1343É7a 45É8a,b25 1463É5a,b 1322É8a,b 42É3b,c

180 10 1434É7a 1341É4a 46É9a20 1457É2a,b 1323É1a,b 43É7b,c25 1489É5a,b 1304É8a,b 39É2c,d

200 10 1434É8a 1332É5a,b 42É8b,c15 1474É5a,b 1324É3a,b 38É6c,d25 1495É6a,b 1290É7b 34É5d

220 5 1459É0a,b 1320É4a,b 35É3d15 1484É2a,b 1309É5a,b 23É0e,f25 1508É2b 1200É5c 13É0g

250 5 1462É8a,b 1268É2b,c 19É8f15 1537É5b 1236É2b,c 4É3h25 1645É3c 1130É3d 1É7i

a Each value is an average of three determinations and expressed as mg lipid per 1000 seeds.b Values in the same column with di†erent following letters are signiÐcantly di†erent from thosefor unroasted seeds (P\ 0É05).

24 H Y oshida, S T akagi

TABLE 3Antioxidant contents in the oils prepared from sesame seeds roasted at di†erent temperatures in an electric ovena,b

Roasting temperature Roasting time(¡C) (min)

T ocopherol L ignan

c d Sesamol Sesamolin Sesamin

160 Unroasted 392É6a 17É3a 5É1a 4830É2a 7396É8a10 374É0a,b 12É3b,c 5É7a 4791É3a,b 7359É7a20 358É1b,c 8É5c 8É3a 4687É2a,b 7277É6a,b25 344É8c 6É7d 8É7a 4587É9a,b 7246É3a,b

180 10 372É0a,b 12É0b,c 7É7a 4791É4a,b 7354É5a20 356É0b,c 8É2c 26É0c 4582É9b 7255É9a,b25 340É3c 5É8d 67É2d 4396É3b 7176É5a,b

200 10 372É0a,b 11É8b,c 12É5b 4772É0a,b 7350É8a15 368É3b,c 9É8c 35É6c 4602É3a,b 7312É9a,b25 332É9c,d 5É6d 122É0e 4118É0c 7165É2a,b

220 5 381É0a,b 12É6b,c 10É4b 4626É0a,b 7374É1a15 365É9b,c 9É4c 153É2e 3857É6c 7305É2a,b25 330É5c,d 5É5d 352É4g 2742É7f 7045É2a,b

250 5 375É2a 12É4b,c 56É8d 4578É3b 7373É5a15 363É5b,c 8É7c 315É9g 642É5g 7253É8a,b25 324É8d 5É2d 3370É5i 25É7i 6968É7b

a Each value is an average of three determinations and expressed as mg per kg oil.b Values in the same column with di†erent following letters are signiÐcantly di†erent from those for unroasted seeds (P\ 0É05).

the longer the roasting time, the greater the rate ofdecrease of sesamolin (P\ 0É05), which was almostdepleted after 25 min of roasting at 250¡C. Conversely,sesamol, as a potent phenolic antioxidant, increased 13-,24-, 70- and 570-fold at 180, 200, 220 and 250¡C, respec-tively, after 25 min roasting ; it was detected as a verysmall component (5É1 mg kg~1 oil) in the unroastedseed oil. When roasted above 220¡C, sesamol was con-siderably (P\ 0É05) liberated from sesamolin with thelonger roasting. As compared to other vegetable oils,the high stability of sesame oil could be attributed toendogenous antioxidants together with tocopherols(Fukuda et al 1986).

Table 4 represents the fatty acid composition(expressed in terms of the esters by weight) of tri-acylglycerols in the oils prepared from sesame seedsbefore and after roasting at di†erent temperatures.However, the fatty acid compositions of total lipidswere omitted from Table 4 because triacylglycerolsoccupied above 98% in the sesame oils (Table 2) andtheir fatty acid compositions were considered to beessentially the same as the fatty acid proÐles of totallipids. However, phospholipids were minor componentsof the seeds (Table 2) and their fatty acid distributionswere not reÑected by those of total lipids or tri-acylglycerols. A small but signiÐcant di†erence(P\ 0É05) occurred in fatty acid compositions betweentriacylglycerols and phospholipids (Table 5) of thesesame oil before roasting. In the phospholipid fractions

the proportions of palmitic was higher, and those ofoleic acid was lower, compared with triacylglycerols.There was almost no change in fatty acid compositionof triacylglycerols of the sesame oil when prepared byroasting below 200¡C. But the higher the roasting tem-perature and the longer the roasting time, the greaterwas the percentage of palmitic and oleic acids, and theless was that of linoleic acid. These trends became morepronounced in phospholipid fractions than in tri-acylglycerol fractions. Particularly, the fatty acid con-tents of linoleic acid were drastically reduced inphospholipids when roasted at 250¡C. However, totalfatty acid contents in triacylglycerols of sesame oils pre-pared by roasting at 220 and 250¡C were still retainedat high levels : 92É1 and 84É3% at 15 min, 82É7 and72É5% at 25 min, respectively. On the other hand, sig-niÐcant di†erences (P\ 0É05) occurred in fatty acid dis-tributions of phospholipids in the oils after 15 minroasting at 220¡C. Furthermore, the retention of totalfatty acid contents in phospholipids of sesame oils pre-pared by roasting at 250¡C decreased substantially(P\ 0É05) : 41É2, 9É0 and 3É6% at 5, 15 and 25 min,respectively. The higher the roasting temperature andthe longer the roasting time, the more pronounced thesetrends became (P\ 0É05) and poor quality oils resulted.The di†erences may be attributed to the degradation ofphospholipids depending on the formation of browningsubstances by roasting. Hafez et al (1983) observed thatan increase in roasting time was accompanied by

Seed roasting and sesame oil quality 25

TABLE 4Fatty acid composition of triacylglycerols in the oils prepared from sesame seeds roasted at di†erent temperatures in an electric

ovena,b

Roasting temperature Roasting time T otal fatty 14 : 0 16 : 0 16 : 1 18 : 0 18 : 1 18 : 2 18 : 3 20 : 0(¡C) (min) acid (%)

160 Unroasted 100a 0É2a 8É3a 0É3a 3É9a 35É6a 51É0a 0É4a 0É3a10 98É63a 0É5a 8É4a 0É3a 3É9a 35É4a 50É7a 0É4a 0É4a20 96É78a 0É3a 8É5a 0É4a 4É0a 35É8a 50É2a 0É3a 0É5a25 94É07b 0É4a 8É7a 0É4a 4É2a 36É6a 48É8b 0É3a 0É6b

180 10 97É54a 0É3a 8É5a 0É5a 4É3a 35É4a 50É2a 0É3a 0É5a20 94É82a 0É5a 8É8a 0É4a 4É5a 36É9a 48É0b 0É3a 0É6b25 90É56b 0É6b 9É0b 0É4a 4É6a 37É2a 47É1b 0É3a 0É8b

200 10 96É75a 0É5a 8É4a 0É4a 4É4a 35É8a 49É7a 0É3a 0É5a15 93É26a 0É7b 8É4a 0É4a 4É5a 36É7a 48É5b 0É3a 0É5a25 89É45b 0É7b 8É5a 0É4a 4É5a 37É5a 47É5b 0É3a 0É6b

220 5 95É32a 0É5a 8É5a 0É3a 5É0b 36É2a 48É6b 0É3a 0É6b15 92É08b,c 0É7b 8É5a 0É4a 5É2b 37É5a 46É6b,c 0É3a 0É8b25 82É74c,d 1É2c 9É1b 0É3a 5É2b 37É8a 45É4c 0É2a 0É8b

250 5 91É62b 0É8b 8É6a 0É2a 5É2b 36É6a 47É6b,c 0É3a 0É7b15 84É27b,c 1É2c 8É7a 0É2a 5É4b 37É7b 45É8c 0É2a 0É8b25 72É45d 1É6c 9É8b 0É2a 5É5b 38É0b 43É8c 0É2a 0É9b

a Each value is an average of three determinations. The content of total fatty acids in each sample was calculated relative to theunroasted sample (100%). The content of each individual fatty acid is given as a percentage of the corresponding total.b Values in the same column with di†erent following letters are signiÐcantly di†erent from those for unroasted seeds (P\ 0É05).

TABLE 5Fatty acid distribution of phospholipids in the oils prepared from sesame seeds roasted at di†erent temperatures in an electric

ovena,b

Roasting temperature Roasting time T otal fatty 14 : 0 16 : 0 16 : 1 18 : 0 18 : 1 18 : 2 18 : 3 20 : 0(¡C) (min) acid (%)

160 Unroasted 100a 0É9a 15É3a 0É8a 4É8a 31É5a 46É5a 0É7a 0É3a10 98É21a 0É8a 15É3a 0É8a 5É0a 31É6a 45É5a 0É7a 0É3a20 94É25a,b 1É0a 15É7a 0É7a 5É1a 32É3a 44É3a 0É6a 0É3a25 88É43b,c 1É0a 16É0a 0É7a 5É2a 32É8a 43É3b 0É6a 0É4a

180 10 98É03a 0É9a 15É9a 0É7a 5É2a 31É5a 44É9a 0É6a 0É3a20 91É65b,c 0É9a 16É0a 0É6a 5É3a 32É4a 43É8b 0É5a 0É5a25 82É25c,d 1É2a 16É5a 0É6a 5É4a 32É6a 42É7b 0É5a 0É5a

200 10 89É92b,c 1É0a 15É8a 0É5b 5É4a 31É7a 44É8a 0É4b 0É4a20 81É03c,d 1É5b 16É7a 0É4b 5É4a 32É5a 42É6b 0É4b 0É5a25 72É85d 3É5c 17É3a 0É3b 5É6a 33É9a 42É5b 0É4b 0É6a

220 5 74É63d 1É2a 17É6a 0É4b 5É5a 32É3a 42É1b 0É4b 0É5a15 48É36e,f 2É3b 18É0b 0É4b 5É6a 34É5a 38É2c 0É4b 0É6b25 27É31g 2É5b 18É5b 0É3b 5É7a 35É2a 37É0c 0É3b 0É7b

250 5 41É16f 1É7b 18É5b 0É4b 5É5a 34É8a 38É2c 0É3b 0É6a15 9É03h 2É8b 19É0b 0É3b 5É6a 36É0b 35É3d 0É3b 0É7b25 3É57i 3É5c 19É5b 0É3b 5É9a 37É5b 32É2e 0É3b 0É8b

a Each value is an average of three determinations. The content of fatty acids in each sample was calculated relative to theunroasted sample (100%). The content of each individual fatty acid is given as a percentage of the corresponding total.b Values in the same column with di†erent following letters are signiÐcantly di†erent from those for unroasted seeds (P\ 0É05).

26 H Y oshida, S T akagi

increasing browning substances in soybeans. In theMaillard reaction, phospholipids are particularly reac-tive, as they contain both polyunsaturated fatty acidsand amines (Pokorny 1981). The amino group of phos-pholipids could contribute to the formation of brown-ing substances.

CONCLUSIONS

When sesame seeds were roasted at di†erent tem-peratures in a domestic electric oven, the longer theroasting time the higher was the weight loss of the seedsat the end of roasting. However, no signiÐcant di†er-ences (P[ 0É05) were observed in the quality character-istics of sesame oil below 200¡C. Therefore, theformation of browning substances was considerablyaccelerated over 220¡C at roasting temperature. Thequality of roasted sesame seed oils signiÐcantly(P\ 0É05) depended on the roasting time and tem-perature. These results indicated that a high-qualityproduct would be obtained by roasting for 25 min at160 or 180¡C, 15 min at 200¡C and 5 min at 220¡Cunder the experimental conditions in this study. Adomestic electric oven is available as a quick and simplemethod for preparing sesame oil of good quality whencompared with other roasting means.

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