journal of the american oil chemists' society volume 70 issue 6 1993 [doi 10.1007_bf02545322] jia...

8/11/2019 Journal of the American Oil Chemists' Society Volume 70 Issue 6 1993 [Doi 10.1007_bf02545322] Jia Mingyu; Andr

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575

The Ef fect of dd ed Solvents on So y Oi l Lute in dso rpt ion

by SU ic ic c id

J i a M i n g y u a n d A n d r e w P r o c t o r

Department of Food Science and Technology, The Ohio State University, Columbus, Ohio 43210-1096

I t h a s b e e n r e p o r t e d t h a t a d d i t i o n o f is o p r o p a n o l t o a s o y

o i l m i s c e l l a i n h i b i t s t h e b i n d i n g o f s o y l u t e i n t o a d d e d

s i li c ic a c id b y c o m p e t i t i v e a d s o r p t i o n . I t w a s s u g g e s t e d

t h a t t h e c o m p e t i t i o n w a s b a s e d o n t h e p o l a r it y o f t h e

m i s c e l la c o n s t i t u e n t s . T h i s i n v e s t i g a t io n s t u d i e d t h e e f f e c t s

o f a h o m o l o g o u s s e r ie s o f l o w e r a lc o h o l s t o c o m p e t i t i v e l y

i n h i b i t l u t e in b i n d i n g t o s i li c i c a c id f r o m a s o y o i l h e x a n e

m i s c e l l a . L u t e i n b i n d i n g i n h i b i ti o n b y m o l e c u l e s o f c a r b o n

c h a i n s w i t h t h e s a m e l e n g t h s , b u t w i t h d i f fe r e n t f u n c t i o n a l

g r o u p s, w a s a l s o e x a m i n e d . M i n o r d i ff e r e n ce s w e r e f o u n d

b e t w e e n m e m b e r s o f a h o m o l o g o u s s e r i e s o f a l c o h o l s . A

s i m i l a r r e s u l t w a s f o u n d w i t h s h o r t - c h a l n f a t t y a c i d s . T h e

a b i li t y o f v a r i o u s f u n c t i o n a l g r o u p s t o d i s p l a c e l u t e i n f r o m

s i li c ic a c id w a s d e p e n d e n t o n t h e m o l e c u l e s a b i l it y t o f o r m

h y d r o g e n b o n d s , r a t h e r t h a n o n p o l a r i ty .

KEY WORDS: Adsorption, lutein, miscel las , s i l ic ic acid, solvents ,

soy oi l .

Oil is extracted from soy flakes with hexane, which is then

evaporated to produce the crude oil. Crude soy oil contains

a number of substances, such as pigments, phospholipids

and free fat ty acids, which must be removed to produce a

bland, light-colored oil that is acceptable to consumers. The

commercial removal of pigments is achieved by an adsorp-

tion process at 100C on bleaching clays under reduced

pressures (1). Soy oil pigment is almost exclusively the

carotenoid lutein (2}. Hassler and Hagberg (3) showed that

the adsorption of soy oil pigment on bleaching clay occurs

according to a Freundlich isothern~

Adsorption of phospholipids (4) and lutein (5) onto silicic

acid from soy oil/hexane misceUas also conforms to a

Freundlich isotherm. An advantage of this bleaching tech-

nique, relative to conventional methods, is that it is con-

ducted at ambient temperatures, and the binding of these

oil components is modified by the addition of a polar sol-

vent to the miscell~ One percent isopropanol in the misceUa

promotes adsorption of phospholipid, which presumably oc-

curred by removal of triglyceride from adsorption site~ This

then facilitates phospholipid binding (4). Free fa tty acid ad-

sorption to amorphous cristobalite silica was also promoted

by isopropanol in a similar system (5). In contrast, iso-

propanol inhibited adsorption of lutein to silicic acid

(5).

This

inhibition was explained in terms of competition between

misceUa constituents for silanol sites. Polarity was sug-

gested to be a basis for competition because of the is~

propanol effect. However, reducing triglyceride concentra-

tion promoted lutein adsorption, suggesting that concen-

tration and/or molelcular weight of competing species may

also be factors tha t determine adsorption.

The objective of this investigation is to study the effect

of alcohol molecular weight on lutein binding from a soy

oil miscella and the adsorption isotherm. The effect on the

*To whomcorrespondenceshouldbe addressedat Departmentof Food

Science, Universityof Arkansas, 272 Young Avenue, FayetteviUe,

AR 72703.

lutein isotherm of C3 and C4 compounds with different

functional groups was also examined.

MA TE R IA LS A N D ME TH OD S

O i l a n d s o l v e n t s Commercially extracted alkali-refined

soy oil was stored at 4C and used throughout the in-

vestigations. Soy oil miscellas were prepared by diluting

soy oil with hexane

Water an d the following alcohols were added to modify

miscella polarit y (0.1 M concentration} prior to lutein ad-

sorption: methanol, ethanol, n-propanol, isopropanol, n-

butanol, isobutanol, 2-octanol, 1-nonanol and 1-decanol.

The following aldehydes, ketones, acids and esters were

also used: propanal, acetone, 2-butanone, acetic acid, pro-

pionic acid, n-bu tyric acid, isobutyric acid, octanoic acid,

methyl acetate and ethyl acetate.

A d s o r b e n t s The adsorbent u sed was silicic acid (Bio-

Sil A., 100-200 mesh, Bio-Rad Laboratories, Richmond,

CA). Silicic acid was heated in a dry ing oven to remove

moisture and was stored in a desiccator until used. The

term silica is used as a syn onym for silicic acid.

L u t e i n m e a s u r e m e n t Pigment concentration in the

miscellas was measured as lutein by reading optical ab-

sorbance at 445 nm, according to the method of Proctor

and Snyder (5).

L u t e i n i s o t h e r m s

Lutein isotherms were determined by

preparing 100-mL volumes of 2.5, 5, 10, 20, 30 and 40%

(vol/vol) concentra tions of soy oil miscellas in hexa ne The

lutein conten t of each miscella was measured before 0.5

g of silica was added. The misceUas were agitated with

a magne tic stirr er in a closed vessel at 22C for 15 min.

The concentration of residual lutein remaining unadsorbed

was then found, and the amount of lutein adsorbed was

calculated by difference Isotherms were plotted as the

amount of lutein adsorbed, per gram of silica, v s the

residual concentration of lutein. Duplicate determinat ions

were made. This was the control experiment.

M i s c e l l a p o l a r i ty Isotherms were prepared as described

above but with 0.1 M concentration of additional solvent

present in the miscella.

RESULTS AN D DISCUSSION

Figure l a shows the effect of adding water and low molecu-

lar weight alcohols (C1-C3), to the misceUa on pigment

binding. Lutein adsorption followed a Freundlich

isotherm, and added solvent reduced lutein adsorption

relative to the control in each case There is little difference

in the isotherms obtained with ethanol, n-propanol and

isopropanol, which were more effective than water in in-

hibit ing lutein binding. Me thano l was slightly less effec-

tive in reducing lutein adsorption. The differences in the

results obtained with different solvent systems were best

seen at high residual lutein levels.

Water was the l east effective solvent, but it did signifi-

cantly reduce lutein adsorption relative to the control.

Water can hydrogen bond to the silica or to other water

molecules. In th is lipid sys tem it is probab ly more thermo-

Cop yr ight 1993 by the Am er ican Oi l Che mists Soc iety JAOCS, Vol . 70, no. 6 (June 1993)


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576

J. MINGYU AND A.

P R O C T O R

O

9

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2 . 5 0

~

2.00

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b

I I

6 1 2 1 8


F I G . 1 . L u t e i n i s o t h e r m s w e r e o b t a i n e d b y i n c u b a t i n g 0 . 5 g o f s i l ic i c

a c i d w i t h 1 0 0 m L o f 2 . 5, 5 , 1 0 , 2 0 , 3 0 a n d 4 0 ( v o l /v o l ) a l k a l i - r e f in e d

s o y o i l / h e x a n e m i s c e l l a f o r 1 5 m i n a t 2 2 C i n t h e p r e s e n c e o f 0 . 1 M

c o n c e n t r a t i o n o f ( a ) w a t e r { ~ ,~ , m e t h a n o l ( O ) , e t h a n o l ( ) , n - p r o p a n o l

( A ) o r is o p r o p a n o l ( A ) . A c o n t r o l { + ) w a s p r e p a r e d w i t h o u t a d d e d s o l -

v e n t ; ( b ) n - b u t a n o l ( D ) , i s o b u t a n o l ( . ) , 2 - o c t a n o l ( Y) , 1 - n o n a n o l { ~ )

a n d 1 - d e c a n o l ([ 7) . A c o n t r o l ( + ) w a s p r e p a r e d w i t h o u t a d d e d s o l v e n t .

d y n a m i ca l l y s ta b l e fo r w a ter mo l ecu l e s to a s s o c i a te to -

g e th e r . T h e e f f e c t o f ad d e d w a t e r i n t h i s s y s t e m m a y b e

d u e to th e s t ren g th o f w a ter / w a ter h y d ro g en b o n d i n g a n d

w a ter s l i p o p h o b i c n a tu re . T o en a b l e w a ter mo l ecu l e s to

bind to s il ica , w ater hydrogen bondin g has to b e disrupted,

a n d i n d i v i d u a l mo l ecu l e s mi g ra te to th e a d s o rp t i o n s u r -

fa ce . T h i s i s p ro b a b l y n o t a s en erg e t i ca l l y fa v o ra b l e a s

d i s ru p t i o n o f a l co h o l h y d ro g en b o n d i n g . F u r th ermo re , a n

a lkane s tructure wou ld increase so lubi l i ty in a l ip id sys tem

a n d p erm i t b i n d i n g to a n a d s o rb e n t . T h ere fo re, co mp et i -

t i v e a d s o rp t i o n w o u l d b e ex p ec t ed to b e i mp ro v ed b y a d -

2 . 5 0

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0

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c - o . 5 o

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i i I i ~ I I J i I I I I I i I I

6 2


F I G . 2 . L u t e i n i s o t h e r m s w e r e o b t a i n e d b y i n c u b a t i n g 0 . 5 g o f s i li c i c

a c i d w i t h 1 0 0 m L o f 2 .5 , 5, 10 , 2 0 , 3 0 a n d 4 0 ( v o l /v o l ) a l k a l i - r e f in e d

s o y o i l / h e x a n e m i s c e l l a f o r 1 5 r ai n a t 2 2 C i n t h e p r e s e n c e o f 0 . 1 M

c o n c e n t r a t i o n o f a c e t i c a c i d ( A ); p r o p i o n i c a c i d ( A ) , n - b u t y r i c a c i d

( [7 ), i s o b u t y r i c a c i d ( B ) a n d o c t a n o i c a c i d ( O ) . A c o n t r o l ( + ) w a s

p r e p a r e d w i t h o u t a d d e d s o l v e n t .

18

d i t i o n o f a n a l k y l g ro u p . M eth a n o l i s s l i g h t l y l e s s e f f ec -

t i v e th a n e th a n o l a t r ed u c i n g l u te i n b i n d i n g , b u t th e e f -

f ec t o f e th a n o l i s s i mi l a r to th a t o f p ro p a n o l i s o mers .

T h ere fore , th e m eth y l g ro u p s b o u n d to th e h y d ro x y l car -

b o n o f i s o p ro p a n o l d o n o t s t er i ca l l y h i n d er a d s o rp t i o n

re l a t i v e to th e p r i ma ry a l co h o l .

B u ta n o l i s o mers , o c ta n o l a n d n o n a n o l a l s o p ro d u ced

s i mi l a r i s o th erms to th o s e o b ta i n ed w i th p ro p a n o l (F i g .

l b ) . T h es e d a ta i n d i ca te th a t w i th l o w er a lco h o l s th ere a re

s ev era l s ma l l d i f f eren ces i n a d s o rp t i o n o n th e b a s i s o f

i s o mer i s m o r mo l ecu l a r w e i g h t . M o l ecu la r s h a p e a n d s i ze

a re rep o r ted to b e i mp o r ta n t fa c to rs p rev en t i n g h y d ro g en

b o n d i n g t o s i l i ca d u e to s t er i c h i n d era n ce (6 ) . I n s tu d i e s

of long-cha in species , H au a nd New ar (7 ) reported tha t the

n u mb er o f mo l e s a d s o rb ed to s i l i ca d ecrea s e s a s ch a i n -

l e n g t h i n c r e a se s . T h e r e s u l ts o f s t u d y i n g t h e c o m p e t i t i v e

a d s o rp t i o n o f l u te i n s u g g es t th a t w i th a l co h o l s (C 0-C 10 )

(F i g. l a a n d l b ) th ere i s n o l a rg e ch a n g e i n th e i s o th erm ,

a s a l co h o l l en g th i s i n crea s ed b u t s ma l l d i f f eren ces a re

s een .

T h es e i s o th erm s tu d i e s g i v e i n d i rec t ev id en ce th a t l o w er

a l co h o l s b i n d la rg e l y i n d ep en d en t l y o f ch a i n l en g th . T h i s

s tud y i s com pl icated by the presence o f triglycer ide , wh ich

is the major species bound overa l l (5 ) .

F i g u re 2 s h o w s th e e f f ec t o n l u te i n a d s o rp t i o n o f a d d i n g

m e m b e r s o f a h o m o l o g o u s s e r i e s o f f a t t y a c id s t o t h e s o y

o i l mi s ce l l a s . A l th o u g h l u te i n a d s o rp t i o n i s r ed u ced re la -

t i v e to th e co n tro l , th ere i s l i t t l e d i f f eren ce b e tw een i s o -

therm s. Therefore, t he a bi l i ty o f free fa tt y ac id s to com-

p e te w i th l u te i n fo r b i n d i n g s i t e s i s i n d ep en d en t o f

ch a i n l en g th . T h e d a ta co n fo rm to W u a n d M ea d s (8 ) f in d -

i n g s th a t fa t ty a c i d a d s o rp t i o n to s i l ica i s in d ep en d en t

o f c h a in l e n g th . T h i s s h o w s t h e i m p o r t a n c e o f e x t r a c t in g

free fa t ty a c i d s f ro m s o y o i l b e fo re p i g m en t a d s o rp t i o n .

JAOCS, Vo l . 70 , no . 6 ( June 1993)


3/4

EFFECT OF SOLVENTS ON LUTEIN ADSORPTION

577

2 . 5 0

0

~ 2 0 0

( ~ 1 . 5 0

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Res idua l lu te in (pM)

F I G . 3 . L u t e i n i s o t h e r m s w e r e o b t a i n e d b y i n c u b a t i n g 0 . 5 g o f s il i c ic

a c i d w i t h 1 0 0 m L o f 2 .5 , 5 , 10 , 2 0 , 3 0 a n d 4 0 ( v o l /v o l ) a l k a l i - re f i n e d

s o y o i l /h e x a n e m i s c e l l a f o r 1 5 m i n a t 2 2 C i n t h e p r e s e n c e o f 0 .1 M

c o n c e n t r a t i o n o f n - p r o p a n o l (A ), i s o p r o p a n o l ( A ) , p r o p i o n i c a c i d ( I ) ,

a c e t o n e (C :]), p r o p a n a l ( ) a n d m e t h y l a c e t a t e ( O ). A c o n t r o l ( + ) w a s

p r e p a r e d w i t h o u t a d d e d s o l v e n t .

2 , 5 0

0

~ 2 . 0 0

( D 1 . 5 0

6

E

O

~ D 1 . 0 0

. O

0 )

0

e- 0 50

_

0 00

0

6 1 2 1 8

Res idua l lu te in (pM)

F I G . 4 . L u t e i n i s o t h e r m s w e r e o b t a i n e d b y i n c u b a t i n g 0 . 5 g o f s i l ic i c

a c i d w i t h 1 0 0 m L o f 2 .5 , 5 , 1 0 , 2 0 , 3 0 a n d 4 0 ( v o l/ v o l) a lk a l i - r e fi n e d

s o y o i l / h e x a n e m i s c e l l a f o r 1 5 m i n a t 2 2 C i n t h e p r e s e n c e o f 0 . 1 M

c o n c e n t r a t i o n o f n - b u t a n o l , ( [: ]) , i s o b u t a n o l ( I ) , n - b u t y r i c a c i d ( A } ,

i s o b u t y r i c a c i d ( A }, 2 - b u t a n o n e ( } a n d e t h y l a c e t a t e ( O ). A c o n t r o l

( Jr ) w a s p r e p a r e d w i t h o u t a d d e d s o l v e n t .

The effect of an added Ca alcohol, aldehyde, ketone,

acid and ester on lutein binding is illustrated in Figure

3. Freundlich isotherm s were observed in the presence of

each solvent, but there were differences in the solvent's

ability to inhibit lutein binding. The alcohols were the

mos t effective in inhibitin g lutein binding, which is prob-

ably because they are best able to form hydrogen bonds

with silanol groups. Hau and Newar (7) repor ted tha t the

greater the tendency for hydrogen bonding, the stronger

the adsorption. This study supports that premise, with

the alcohols being mos t effective. A silanol hydroxyl is

capable of forming two hydrogen bonds with a single

alcohol hydroxyl group, or can hydro gen bond t o two dif-

ferent alcohols (9).

Propionic acid was the most effective of the nonalcohol

solvents, despite the fact th at it has a lower polari ty than

the aldehydes and ketones used. This is most likely due

to its ability to hydrogen bond. Each molecule is capable

of forming two hydrogen bonds to a silanol group (9).

Organic acids are not boun d to silica to the s ame degree

as alcohols, but the acid binding strength is greater (7).

At low miscella residual c oncen trat ions (


4/4

578

J . M I N G Y U A N D A . P R O C T O R

C K N OW L E D G M E N T S

S a l a r i e s a n d r e s e a r c h s u p p o r t p r o v i d e d b y s t a t e a n d f e d e r a l f u n d s

a p p r o p r i a te d t o t h e O h i o A g r i c u l t u r a l R e s e ar c h a n d D e v e l o p m e n t

C e n t e r , T h e O h i o S t a t e U n i v e r s i t y , w e r e g r e a t l y a p p r e c i a t e d . T h i s

i s J o u r n a l A r t i c l e n u m b e r 6 4 -9 3. T h a n k s i s e x p r e s s e d t o D r . J o h n

L o w b r i d g e f o r h i s u s e f u l c o m m e n t s o n t h e d a t a .

R E F E R E N C E S

1. Brekke, O.L. , in Handbook of Soybean Processing and Utiliza-

tion e d i t e d b y D . R . E r i e k s o n , E . H . P r y d e , O . L . B r e k k e , T . L .

M o u n t s a n d R . A . F a lb , A m e r i c a n S o y b e a n A s s o c i a t io r ~ S t . L o u is ,

a n d A m e r i c a n O i l C h e m i s t s ' S o c i e t y , C h a m p a i g n , 1 98 0, p p .

7 1 - 8 8 .

2. Vogel, P.V. , Fette Seifen Anstrichm. 79.97 (1977).

3 . H a s s l e r , J . W . , a n d R . A . H a g b e r g ,

Oil and Soap

16:188 (1946).

4 . B r o w n , H . G . , a n d H . E . S n y d e r , J . Am. Oil Chem. Soa 62:753

1985).

5 . P roc tor , A . , an d H .E . Snyder ,

Ibid

64:1163 1987).

6 . I le r , R .K. , in The Chemistry o f Silica C h a p t e r 6 , J o h n W i l e y

Sons Co . , New York , 1979 .

7 . Hau , L .-B ., and W ~ . Nawar , J . Am. Oil Chem. Soa 62:1596 (1985).

8 . W u , G . S . , a n d J . F . M e a d , Lipids 12:965 (1977).

9 . M a r s h a l l , K . , a n d C . H . R o c h e s t e r , J .

Chem. Soc. Faraday Trans.

I 71:1754 (1975).

10 . McC le l lan , A.L . , Tables of Exper imental Dipole Moments W.H.

F r e e m a n a n d C o . , S a n F r a n c i s c o a n d L o n d o n , 1 9 6 3 .

[ R e c e i v e d N o v e m b e r 5 , 1 9 92 ; a c c e p t e d A p r i l 8 , 1 99 3 ]

J A OC S , V o l . 70 , no . 6 J une 1993 )

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