This article was downloaded by: [113.161.64.163]On: 02 August 2015, At: 20:44Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: 5 Howick Place, London, SW1P 1WG

Agricultural and Biological ChemistryPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/tbbb19

Studies on Cause of Color Reversion of Edible Soybean Oil and its PreventionMamoru Komodaa, Noriji Ōnukia & Ichiro Haradaa

a Sugiyama Chemical Research Institute, Mitaka-shiPublished online: 09 Sep 2014.

To cite this article: Mamoru Komoda, Noriji Ōnuki & Ichiro Harada (1967) Studies on Cause of Color Reversion of Edible Soybean Oil and its Prevention, Agricultural and Biological Chemistry, 31:4, 461-469

To link to this article: http://dx.doi.org/10.1080/00021369.1967.10858833

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinionsand views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly orindirectly in connection with, in relation to or arising out of the use of the Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

[Agr. BioI. Chern., Vol. 31, No.4, p. 461~469, 1967]

Studies on Cause of Color Reversion of Edible Soybean Oil

and its Prevention

Part II. Tocored as a Precursor of Color Reversion of

Soybean Oil

By Mamoru KOMODA, Noriji ONUKI and Ichiro HARADA

Sugiyama Chemical Research Institute, Mitaka-shi

Received November 16, 1966

Tocored as a precursor of color reversion of soybean oil has been isolated and identi­fied. We have found that the moisture of raw soybeans is closely related to the tocoredcontent in crude oil and the yield of tocored is maximum when the moisture of soybeans

is 15~ 18%. It seemed that tocored in crude oil were completely removed by the refiningprocesses, but 30% of it remained in the colorless form in refined and deodorized oil and

turned into tocored during storage or on heating the oil to a higher temperature. Tocopherolsare relatively stable in refined oil and are not oxidized to tocored under a milder condition,such as the oxidation with air. Neither tocopherol nor tocored but "tocored in colorless

form" is reall y the precursor of color reversion in soybean oil.

INTRODUCTION

Hitherto, the coloring of refined and de­odorized soybean oil (later this is called soybe­an salad oil) by oxidation has been presumedto be due to tocored in soybean oil. Severalinvestigators have attempted to prove this, butsome of them have shown only an indirectevidence and tocored has never been identifiedin soybean oil.

It has previously been reportedll that to­copherol content in crude oil decreased whenthe soybeans were moistened and that thesoybean salad oil obtained from them showedextremely distinct color reversion.

This report treats the isolation and identifica­tion of tocored from soybean oil, the relationbetween quantity of tocored in extractedsoybean oil and the moisture level of rawsoybeans and also the influence of tocoredupon color reversion of soybean salad oil.

This researh has been financed by a grant made bythe United States Department of Agriculture underP.1. 480.

MATERIALS AND EXPERIMENTAL METHOD

Soybeans and soybean oil. Raw soybeans usedin this experiment were the 1965 crop Illinois soybe­ans. From these, soybeans with various moisture con­

tents were prepared and extracted with n-hexane bythe same process described already. II

Tocopherols. dl-a-Tocopherol (2,5, 7, 8-tetrameth­yl-2-(4',8', 12'-trimethyItridecyl )-6-chromanol) (DaiichiPure Chemical Co., Ltd.) EiY;;, (292 mp. max. in ethyl

alcohol)=73.20, EiY;;, (256~272 mp. min.)= 13.40 andd-r-tocopherol (2, 7, 8-trimethy-2-(4', 8', 12'-trimethy1­

tridecyl)-6-chromanol) (Distillation Products Inc.) E iJ:;,(298 mp. max.)=94.68, EiJ:;, (258~260 mp. min.)=5.48were used without further purification, for the extinc­

tion coefficients of these compounds were found to bein good agreement with those reported by Baxter et

al.21 for their highly purified products.Tocored. [2,7, 8-trimethyl-2-(4', 8', 12'-trimethyl-

tridecyl-2- )-chroman-5, 6-quinone]. Tocored was syn­thesized as follows: 100 ml of concentrated nitric acid

I) M. Nakamura, S. Tomita and M. Komoda,Yukagaku., 9, 319 (1960); S. Tomita, M. Komoda. S.Enomoto, N. Onuki, ibid., 13, 530 (1964).

2) J. G. Baxter, C. D. Robson, J. D. Tayler andR. W. Leaman, ]. Am. Chem. Soc., 65, 918 (1943).

Dow

nloa

ded

by [

113.

161.

64.1

63]

at 2

0:44

02

Aug

ust 2

015

462 Mamoru KOMODA, Noriji ONUKI and !chiro HARADA

was added to 1 g of dl-a-tocopherol in 400 ml of ethylalcohol, and the solution was then heated in a waterbath at 80°C for five minutes. The solution, whichturned to bright red color, was poured into 2.5 I ofice water and the reaction products were extractedwith ethyl ether. The combined etherial extracts

dried with sodium sulfate were concentrated and thenchromatographed on a Florisil column.

The chromatogram was developed with u mixtureof ethyl ether and petroleum ether (1: 2) and theband containing the red reaction product was ex­tracted with ethyl alcohol. The solvent was removedunder vacuum and the residue, a clear red oil,was used in the following experiments. Absorptionspectrum maxima were at 260~265 and 460~465mp

in ethyl alcohol and extinction coefficient E iJ";" max­

ima were 153.0 and 20.1, respectively. A.max (CS2)

2900, 1727, 1677, 1649, 1630, 1586, 1388, 1375 (do­ublet), 1320, 1275, 1162, IllS, 1003, 1070, 1035,940,900, 735, 700 (em-I).

Tocopherylquinone. [3-hydroxy-3, 7, 11, 15-tetra­methy Ihexadecyl)-trimethyl-p-benzoquinone] To 1 gof dl-a-tocopherol in 100 ml of ethyl ether was added50 ml of 50,% (v/v) aqueous methanol containing 5 gof ferric chloride. The mixture was stirred at 20°Cfor fifteen minutes and the lower methanol layer wasdiscarded. After this process had been repeated twicemore, the ethereal layer was washed with water,from which a red-brown oil was obtained by thedistillation of dried extracts. This oil in petroleumether was chromatographed on a Florisil column.

Orange colored oil was obtained upon a elutionwith d mixture of ethyl ether and petroleum ether(I : 2) from a yellow-orange band which moved rapid­ly down in the column. Absorption spectrum maximaare 255, 270 and 335 mp in ethyl alcohol and the

corresponding extinction coefficient EiJ";" are 338.4,

341.1 and 9.0, respectively.

A.max (film) 3450, 2900, 1640, 1460, 1375, 1305, 1275,1255,1212,1143,1101,1060,1010,930,915, 870,830,715 (em-I).

Accelerated test of color reversion. This testwas carried out according to the procedure previouslyreported. ' )

Estimation of tocored in soybean oil. Accurate­Iy 20 g of the oil was weighed into a 150~ 200 mlseparate funnel, into which 100 ml of petroleum etherwas added. This solution was subjected to the chroma­tographic analysis, using Florisil as adsorbent and thecolumn was washed several times with 5 ml of petro-

leum ether. After development of the chromatogramfirst with 200 ml of petroleum ether and then with100 ml of 20% (v/v) ethyl ether in petroleum ether,a tocored fraction was eluted with 200 ml of 50%(v/v) ethyl ether in petroleum ether.

Tocored fraction was evaporated under vacuum atd temperature not exceeding 40°C and the residuedissolved in a minimum quantity of benzene wassubjected to the thin layer chromatography. Afterdevelopment the tocored spot was loosened with athin spatula. The loosened material was transferedinto a small glass filter and extracted with 5 ml ofabsolute ethanol. A similar area of silica gel wetwith the solvent was also taken for a blank test.

The tocored content of the alcoholic extract wasdetermined by optical density at 465 mp in a 1cm cell.Standard graph was obtained by using pure tocored.

Thin layer chromatography. Ordinary silica gelG thin layer chromatogaphic method was employed,and the plates were activated at 110°C for two hoursbefore use. Ethyl acetate-benzene (15: 85) was usedas the developing solvent.

The benzene solution of the sample was appliedwith a micro syringe on 0.5 mm thin layer, 2 cmfrom the lowest edge and the solvent was allowed torun a distant of 15 cm.

Molecular distillation. Five-inch centrifugal mole­cular still, CMS-5 (Consolidated ElectrodynamicsCorporation, Rochester Division) was used in thisexperiment.

RESULTS

1) Isolation of Unsaponifiable Matter as a Pre­cursor of Color Reversion of Soybean Oil byMolecular Distillation.

The extracted crude oils from (A) ordinarysoybeans (moisture 13.5%) and (B) moisture­controlled soybeans (moisture 18.3%) weredegummed, refined and deodorized by theusual process. The color reversion curves ofdeodorized oils are shown in Fig. 1.

The degummed oils described above werefractionated by molecular distillation into 7fractions. The conditions of molecular distil­lation and properties of each fraction areshown in Table 1.

The mixture of the fractions 4, 5 and 6with least tocopherol was deodorized and thereversion of color was determined as shown

Dow

nloa

ded

by [

113.

161.

64.1

63]

at 2

0:44

02

Aug

ust 2

015

Studies on Cause of Color Reversion of Edible Soybean Oil and its Prevention Part II. 463

TABLE I. CONDITIONS OF MOLECULAR DISTILLATION AND PROPERTIES OF EACH FRACTION

Temp. Press. Yield Properties of each Fraction~

/ ,Fraction Acid Iodine Total Color

Value Value Tocopherol (Lovibond)(0C) (p.) (%) (Wijs) (mg/g of oil) (5 1/4")

(A) Soybean Oil from Ordinary Soybeans (Moisture 13.5%)(Degummed Oil) 0.35 131. 4 1.22 R-2.8, Y-30(1")

A-I -230 3.5~6.5 3.77 21.91 R-3.5, Y-40A-2 -240 2.5 5.60 0.39 131. 2 2.14 R-5.5, Y-40A-3 -245 2.5 19.92 0.09 129.3 0.56 R-3.0, Y-35A-4 250~255 2.5 31.66 0.07 132.4 0.22 R-2.0, Y-30A-5 255~257 2. 3~2.5 19.76 0.08 135.2 0.11 R-1.0, Y-30A-6 ~262 2.5 10.33 0.09 136.8 0.05 R-0.8, Y-30

Residue 7.47

(B) Soybean Oil from Moisture-Controlled Soybeans (Moisture 18.3%)(Degummed Oil) 0.46 129.1 0.35 R-4.7, Y-40(1")

B-1 ~230 5.8~7.8 2.45 7.07 R-IO.0, Y-30B-2 ~240 3.8~4.8 4.94 0.88 125.3 1.19 R-5.5, Y-50B-3 ~245 3.1~3.3 9.95 0.17 126.5 0.37 R-2.5, Y-35B-4 250~255 3.0 22.81 0.09 128.2 0.12 R-1.5, Y-30B-5 255~257 4.5 33.75 0.11 132.0 0.09 R-l.2, Y-20B-6 -260 4.5~5.5 15.03 0.13 135. I 0.04 R-l.9, Y-20

Residue 9.15

l.°l_o--~::~.;'----<i.!l---<!._-@·C. :==<!!>"",d~-'@·>----<!·!l--@·--@·D.~ .

in Fig. 1.Fig. 1 indicates that soybean salad oil from

moistened soybeans which showed a distinctcolor reversion came to show only a slightcolor reversion when the unsaponifiable mat­ters in the oil had been removed by means ofmolecular distillation.

Chromatographic purification and identificationof tocored in unsaponifiable matters of fractionA-I and B-1.

Thirty grams of Florisil was packed into a15 mm internal diameter chromatographicabsorption tube to a height of 300 mm. Twen­ty grams of each first fraction of A-I and B-1were dissolved in the minimum quantity ofpetroleum ether (b. p. 30_60°C), and thesterol precipitate was removed by filteration.The sterol was washed several times withpetroleum ether. The petroleum ether extractwas concentrated and analysed by chromato­graphy.

A-I gave a reddish oragne, a yellow and apale yellow bands and B-1 gave a reddishpurple, a purple and a yellow bands. Eachof the reddish orange band (A-I) and the

A

10 12

Soybean Salad

Heating at 100°C (hrg)

Color Reversion Curves of

6.0

5.0-••"-..,..;

on 4.0-"-'"u'"'0 3.0"..'0~0

.D'- B>0

...l

FIG. 1.

Oil

A: Soybean oil from moistened soybeans (moisture18.3%)

B: Unsaponifiable matters in the oil A were re­moved by molecular distillation.

C: Soybean oil from ordinary soybeans (moisture13.4%)

D: Unsaponifiable matters in the oil C were re­moved by molecular distillation.

Dow

nloa

ded

by [

113.

161.

64.1

63]

at 2

0:44

02

Aug

ust 2

015

464 Mamoru KOMODA, Noriji ONUKI and !chiro HARADA

AND B-1 BY FLORISIL CHROMATOGRAPHY

Fraction

TABLE II. FRACTIONATION OF A-I

Eluant (ml) Yield (g) Remaks

B-I-2 2096 (vjv) E in PB-I-3 5096 (vjv) E in PB-I-4 3596 (vjv) B in EB-I-5 BP: petroleum ether E: ethyl ether B:

A-I-IA-I-2A-I-3A-I-4A-I-5B-I-I

P2096 (vjv) E in P5096 (vjv) E in P3596 (vjv) B in EBP

(200)(200)(200)(250)(200)(250)

(200)(200)(300)(200)

benzene

17.281.67

0.380.170.01

16.16

2.520.580.270.01

yellow, oilpale yellow, oil, sterol

yellow, oilorange, filmorange, oilreddish orange, oil

red, oil, sterolorange, filmred, viscus oilred, viscus oil

10

A

110

140

150

B~8 130 20o u~~

'-tl ,A

15120

Solvent: Absolute Ethanol A: Compound I; B:Tocored

Wave Length (mp)

FIG. 3. Ultraviolet Absorption Spectra of CompoundI and Tocored,

at RF 0.48, and it was confirmed that thecompound in this red spot was identical withthe authentic tocored. In the case of A-I-4, 5a red spot was not clear.

Red spots on the chromatogram (B-I-4) wereloosened from 3 plates (20 X 20 cm) and extract­ed with ethyl ether. The ether solution wasdried over anhydrous sodium sulfate and thesolvent was removed by passing a stream ofnitrogen gas. A red viscus oil (compound I)

-

-

-

- Oy

- .', R ..... R 'R 'R eR• •• • • •'., • •....- -. P ". P'., • •• •••

- Oy ."" y :.... y• •• • • •'.' • •'.,

- I,I

IAy "'y Iy If- I •

',,'

0.2

0.6

1.0

0.4

0.8

oA-I-4 A-I-5 B-I-4 B-I-5 Tocorerl

FIG. 2. Silica Gel Thin Layer Chromatograms offractions A-I-4, 5 B-I-4, 5 and Tocored.

Developing Solvent; Ethyl Acetate in Benzene(15: 85) Intensity of Spots; • Strong, 0 Medium,() _Weak, Color of Spots; R, Red; P, Pink; Y,Yellow.

reddish purple band (B-1) was eluted with 3596(vjv) benzene in ethyl ether and the orangefilm or oil (A-lA, 5) and the red viscus oil(B-I-4,5) were obtained from A and B re­spectiveIy.

As shown in the data of thin layer chromato­graphy on silica gel A-I-4,5; B-I-4,5 andauthentic tocored (Fig. 2) all gave a red spot

Dow

nloa

ded

by [

113.

161.

64.1

63]

at 2

0:44

02

Aug

ust 2

015

Studies on Cause of Color Reversion of Edible Soybean Oil and its Prevention Part II. 465

1\r" ~(B)\ff\

-

-, I , I , I , I , I , I I I

\ry ~ ./

'0 (Y 'IAl vf-

f-

r, I , , , , , , I I

4,000 3,000 2,000 1,800 1,600 1,400 1,200 1,000 800

Wave Number (em-')

FIG. 4. Infrared Absorption Spectra of CompoundI and Tocored (in CS2)

A: Compound I; B: Tocored

was obtained. Ultraviolet absorption spectraof I and authentic tocored in absolute ethanolwas measured as shown in Fig. 3. Ultravioletspectra of I showed the absorption peaks at270 and 460 mp, which were very similar tothose of tocored reported by Frampton31 andShone/I and also to those of the authentictocored.

As shown in Fig. 4, infrared absorption

spectra of I were perfectly identical with thoseof the authentic tocored.

Both the tocored isolated above and theauthentic tocored yield phenazine 31 whichshows the same strong yellow-green fluor­escence in ultraviolet ray and identical absorp­tion spectra. Amax (ethyl alcohol) 270, 370 mp.

In the thin layer chromatography of eachfraction of a column chromatograph, a traceof tocored is found in A-1-4 and A-I-5 fromthe control oil, while tocored is detected inall fractions from the moistened soybeans.Fractions B-1 and B-2 give an orange oil ondistillation of the solvent but the oil turns toheavy red during storage in diffused light.Tocopherylquinone was not detected. Theoxidation derivatives of this show absorptionat 270 and 335 mil characteristic to a- and (3­unsaturated ketones. Absorption at 335 mpwas not observed in each fraction. But thereis some doubt that the tocopherylquinonemay be oversighted owing to the unclearnessof the absorption at 335 mp characteristic toa- and (3-unsaturated ketones, to the thin colorof tocopherylquinone, and also to the difficulty

TABLE III. TOTAL TOCOPHEROL AND TOCORED CONTENT IN DEGUMMED SOYBEAN

OILS OBTAINED BY EXTRACTION OR EXPRESSION

Moisture of Process Color (Lovibond) Total Tocopherol TocoredSoybeans(9o) (5 1/4") (mg/g of oil) (pg/g of oil)

6.9 Expression R-2.4, Y-30 1. 34 nil

9.3 Expression R-2.6, Y-30 1.09 trace12.0 Extraction R-2.8, Y-30 1.43 12.5

12.0 Expression R-2.6, Y-30 1.43 trace

14.5 Extraction R-3.3, Y-30 1.15 43.5

14.5 Expression R-3.3, Y-30 0.61 102.2

17.8 Extraction R-4.2, Y-30 0.72 83.7

17.8 Expression R-3.4, Y-30 0.35 97. I

19.7 Extraction R-3.6, Y-30 0.59 45.0

Expressed soybean oilFour hundred g of raw soybeans or moisture-controlled soybeans was crushed into 4

pieces or so by an iron mortar, and the pieces Were devided into 6 parts. Each part of thecrushed beans was put into a cylinder with 'I 107 mm internal diameter, and a stainlessdiscs with 105 mm diameter were placed between each part. The crude oil was obtained byexpelling at the maximum pressure of 382.0 kg/cm 2 at the room temperature.

3) V. L. Frampton, W. A. Skinner, P. S. Baily,]. Am. Chern. Soc. 76, 282 (1954).

4) G. Shone, Chern & Ind, 23, 335 (1963).

Dow

nloa

ded

by [

113.

161.

64.1

63]

at 2

0:44

02

Aug

ust 2

015

466 Mamoru KOMODA, Noriji ONUKI and Ichiro HARADA

of its separation from tocored by thin layerchromatography.

2) Relation between Moisture of Soybeans andQuantity of Tocored in Crude Oils.

The crude oil from soybeans with less moist­ure is light in color and it becomes darker asthe moisture of the raw soybeans increases. lI

From the experiment described in previoussection, we have found that the moisture ofsoybeans is closely related to the tocoredcontent in crude oil. There is some doubtthat the formation of tocored may be attribut­ed to the oxidation of tocopherol in soybeanoil during the distillation of miscella.

The following experiment was carried outin order to clarify this point. Analytical re­sults of the oil obtained from soybeans withvarious moisture contents by extraction orexpression are shown in Table III.

As shown in Table III, tocopherol contentsin crude soybean oil obtained by the expres­sion process was less in quantity than extract­ed crude oil from the soybeans with the samemoisture level. The tocored was obtained inmaximum yield when the moisture of soybeanswas 15-1896.

The above experimental results showed thatthe tocored is derived from tocopherol in rawmoistened soybeans, and is not produced bythe oxidation during the distillation process ofmiscella.

3) Decrease in the Quantity of Tocored inSoybean Oil during Refining Processes and itsRestoration through Color Reversion of SoybeanSalad Oil.

Two kinds of crude soybean oil with dif­ferent quantity of tocored were refined, bleach­ed and deodorized. The color and tocoredcontent of the oils at each stage were determin­edas shown in Table IV. The tocored con-

TABLE IV. TOCORED CONTENT IN OILS AT EACHSTAGE OF REFINING PROCESSES AND ALSO

IN COLOR REVERTED OILS

Color (Lovibond) TocoredSoybean Oil (5 1/4") (pg/g of

oil) (%)Crude oil (a) R-3.5, Y-40(l") 23.3 (100)

(b) R-5.0, Y-40(l") 169.2 (100)Deacidified oil (a) R-8. 2, Y-50 nil ( 0)

(b) R-lO.8, Y-50 99.8 ( 59)Bleached oil (a) R-l. 3, Y-30 nil ( 0)

(b) R-l .5, Y-30 2.0 ( I)Deodorized oil (a) R-0.8, Y- 5 nil ( 0)

(b) R-O. 8, Y- 5 nil ( 0)Color reverted oil (a) R-2.0, Y-15 5.5 ( 24)

(b) R-3.3, Y-30 46.5 ( 27)

(a) Soybean oil from ordinary soybeans, (b) Soybeanoil to which synthetic tocored was added.

tents in color reverted oils heated for ten hoursat 100°C were also determined.

Tocored in crude oil was decreased by about40% by alkali refining. About 601'6 drop oftocored occurred in the bleaching of refinedoil using 1.5% of active clay. We could notobserve any trace of tocored in deodorizedoils. Yet, 30% of tocored was determined incolor reverted oil. It seems that the greaterportion of tocored is decomposed or removedduring the refining processes but some portionis transformed into a colorless compound,which is retransformed into tocored during thecolor reversion test.

4) Discoloration of Tocored by Steam Deodori­zation.

From the experiment in 3), we have foundthat tocored in soybean oil is discolored bydeodorization. The reason for this is not clearwhether the tocored is bleached by heatingor distilled out of soybean oil by steam de­odorization.

This part of experiment was undertaken inorder to make this reason clear.

TABLE V. COLOR CHANGE OF SOYBEAN OILS DUE TO TOCORED

Color Reverted Color

Deodorized oilHeated oil

~'----:::--.,..----"L. ____Before Heating After HeatingR-Il.O, Y-30 R-0.6, Y-6R-ll.O, Y-30 R-4.8, Y-5

~---_----"L. ____Max. Absorbancy at 465 mp

R-4.8, Y-30 0.134R-4.8, Y-30 0.145

Dow

nloa

ded

by [

113.

161.

64.1

63]

at 2

0:44

02

Aug

ust 2

015

Studies on Cause of Color Reversion of Edible Soybean Oil and its Prevention Part II. 467

Tocored was added (0.02596) to moleculardistilled soybean oil. Half of it was deodoriz­ed at 250-260°C by the usual manner, andthe rest was heated at the same temperaturefor twenty minutes in the atomosphere ofnitrogen. The results of accelerated color re­version tests are shown in Table V.

The properties of oils shown in Table V toindicate that tocored is not removed by steamdeodorization. The mechanisms of transforma­tion of tocored to a colorless substance andthe properties of this substance will be madeclear by further studies.

5) Effects of Tocopherol and Tocored on ColorReversion of Purified Soybean Oil.

One kg of soybean oil from which theunsaponifiables were removed by the moleculardistillation was dissolved in 4 liters of petrole­um ether and was percolated through a columnof active carbon (8 X 16 cm).

The effuluent from the column was con­centrated in vacuum and redistilled by meansof the molecular distillation as in the preceed-

ing experiment. Fractions with least unsa­ponifiable matters were used in this experi­ment. The content of the unsaponifiablematters was reduced from 0.759"6 to 0.16%;the color was reduced (Lovibond red scalewas decreased from 1.3 to 0.6); the tocopherolcontent was reduced from 0.63 to 0.04 mg/gof oil; and iodine value increased from 131to 136.

a-, r-Tocopherol, tocored and tocopheryl­quinone were added to the molecular distilledsoybean oil and the oil was deodorized andthen the color reversion test were carriedat 100°C. After heating for ten hours, thesecolor reverted oils, except the control, weredeodorized and the reversion of color wastested again. The results are shown in Fig.5 and 6.

As indicated in Fig. 5 and 6, two kinds ofoils (No.5, 6) which contain tocored show acharacteristic color reversion, while othersshow only a slight color reversion. By com­paring Fig. 5 and 6, it is clear that the peakred values of the color reversion decreaseconsiderably by the treatment of deodorization.

3.0 No.6

1086

--------.--... No.5

4

p---o---o...~No.6

2

:0--::::~~=~~=~=3 No.4No.2,...?::::-. • • • No.3

o

2.0

'"-'"u"'il 1.0..."0

"o.0.~

>oo-l

'"-..,."-- 1.5

­••

Heating at 100°C (hrs)

FIG. 6. Color Reversion Curves of Redeodorized

Soybean Oils

The color reverted oils shown in Fig. 5 were de­odoized and were subjected to the color reversion

•test agalll.

__• __... No.5

No.4No.2

• • • No.3- x No.1x x

Lt'>-

."~o.0.~

>oo-l

"-'"u'"." 2.0"...

­••:::~ 2.5

1.0~1 I I I

o I 2 4 6 8 10

Heating at 100°C (hrs)

FIG. 5. Color Reversion Curves of Soybean Oils

No. I ControlNo. 2 r-Tocopherol 0.1 %No.3 a-Tocopherol 0.1%No. 4 r-Tocopherol 0.1 % + Tocopherylquinone

0.02%No.5 r-Tocopherol 0.196+a-Tocopherol 0.196+

Tocored 0.02%No. 6 r-Tocopherol 0.1 % + Tocored 0.02%

Dow

nloa

ded

by [

113.

161.

64.1

63]

at 2

0:44

02

Aug

ust 2

015

468 Mamoru KOMODA, Noriji ONUKI and !chiro HARADA

5) P. D. Boyer, J. Am. Chern. Soc., 73,733 (1951).

TABLE VI. CHANGES IN THE QUANTITY OF Toco­PHEROL BEFORE AND AFTER THE COLOR

REVERSION TEST. (mg/g of oil)

Color Reversion Test

Changes in quantity of tocopherol and tocoredduring the color reversion test.

Tables VI and VII summarise the resultsof total tocopherol and tocored contents in 6kinds of soybean oil determined by spectro­photometry before and after the color reversiontests. Tocored was determined by opticaldensity at 465 mp, which corresponded to themaximum absorption of purified tocored.

Tocopherol decreases by a few percent bythe deodorizing process but this gives no dif­ference on the color reversion tests. Tocoredor tocopherylquinone does not affect the decre-

TABLE VII. CHANGES IN THE QUANTITY OFTOCORED BEFORE AND AFTER THE COLOR

REVERSION TEST. (A'65mp X 1000)

Color Reversion Test-./ ~

Sample No. 1-st Test 2-nd Test• •• - / -Before After Before After

1. Control 0 02. r-Tocopherol 0.1 % 0 16 0 183. 0:-Tocopherol 0.1 % 0 0 0 04. r-Tocopherol 0.1% 0 24 0 23

Tocopherylquinone 0.02%5. r-Tocopherol 0.1% 12 65 1 42

Tocored 0.02%6. r-Tocopherol 0.1 %

0:-Tocopherol 0.1 % 0 48 10 41Tocored 0.02%

ase of tocopherol during the color reversiontest.

The optical density at 465 mp of the oilcontaining tocored is zero or very low afterthe deodorizing process. It increases gradual­ly during the color reversion test, the rate ofreforming of tocored being from 15 to 34%.

The color reversion curves of the oil con­taining tocored show the peaks characteristicto the soybean salad oil, while the curves ofthe oil containing tocopherol or tocopheryl­quinone show a very slow upward slope ona long heating.

DISCUSSION

A trace of tocored is detected in crudesoybean oil from soybeans with 14% moisture,but a large quantity of it is found in crudesoybean oil from soybeans with high moisturelevel (1896). From the fact that the quantityof tocopherol decreases in the later case, tocor­ed is clearly derived from tocopherol.

From the fact that the miseella from soybe­ans with high moisture is pale, we supposedthat tocopherol is not oxidized to the form oftocored in soybeans but exist in the form ofthe pale intermediate (for instance, tocopher­oxide51

) and turns into tocored on contact withair during distillation of the solvent. But itis made clear that tocored is already contain­ed in soybeans from the fact that a largeamount of it is found in the crude oil obtain­ed from moistened soybeans by the expressionprocess carried out at the room temperature.The quantity of tocored is maximum whenthe moisture of soybeans is 15,...,18%.

It seems that tocored can be totaly removedby the ordinary refining and deodorizing pro­cesses, but about 30% of it is detected in thecolor reverted soybean salad oil. Therefore,it can be concluded that some part of tocoredremains in the colorless form in the deodoriz­ed oil and it turns into tocored again givingred color to the oil. This transformation oftocored into colorless compound takes placealso in a bleaching process.

~---"-'--~lost Test 2-nd Test

1.02 1.02 0.83 0.84

1.99 1.91 1.74 1.75

... ""-~ ~ / --- ,Before After Before After0.04 0.040.97 0.96 0.81 0.891.01 0.941. 10 1.06 0 .90 0 .90

Sample No.

1. Control

2. r-Tocopherol 0.1 %3. 0:-Tocopherol 0.1 %4. r-Tocophero1 0.1%

Tocophery1quinone 0.02%5. r-Tocopherol 0.1%

Tocored 0.02%6. r-Tocopherol 0.1 %

0:-Tocopherol 0.1 %Tocored 0.02%

Dow

nloa

ded

by [

113.

161.

64.1

63]

at 2

0:44

02

Aug

ust 2

015

Studies on Cause of Colot Reversion of Edible Soybean Oil and its Prevention Part II. 469

Tocored recovered from the color revertedsoybean salad oil cannot be distinguished bymeans of the spectro absorption from thatsynthesized from tocopherol by nitric acidoxidation. But the compound separated fromthe color reverted soybean salad oil by thinlayer chromatography is far paler than tocor­ed and the ultraviolet absorption maximumis some-what shifted to shorter wave length.

According to Baxter, 61 16.796 of tocopherolin crude soybean oil is removed by neutrali­zation, 6% by bleaching, 5% by deodorizationand about 70% remains in the salad oil. Inour experiments in laboratory scale, about

6) J. G. Baxter, H. W. Rawlings and N. H. Kuhrt,J. Am. Oil Chern. Soc., 25, 24 (1948).

8096 of tocopherol remains in the soybeansalad oil from the soybeans with ordinarymoisture and the loss of tocopherol increasesas the level of moisture of soybeans rises.

A few percent of tocopherol is lost by de­odorization but no changes in quantity canbe observed after color reversion test. Fromthis it can be derived that tocopherol hasnothing to do with the color reversion ofsoybean salad oil.

In our experiment, any trace metals or otheringredients that may affect the oxidation oftocopherol are removed by molecular distilla­tion. Tocopherol in soybean salad oil on themarket is supposed to be oxidised becausethe oil may contain various trace compounds.

Dow

nloa

ded

by [

113.

161.

64.1

63]

at 2

0:44

02

Aug

ust 2

015