Solubilization of Water and Water-Soluble Compounds in

Chapter 3 Solubilization of Water and Water-Soluble Compounds in Triglycerides

Downloaded by UNIV OF LIVERPOOL on December 9, 2015 | http://pubs.acs.org Publication Date: December 26, 1991 | doi: 10.1021/bk-1991-0448.ch003

Magda El-Nokaly, George Hiler, Sr., and Joseph McGrady Food and Beverage Technology Division, Miami Valley Laboratories, The Procter and Gamble Company, P.O. Box 398707, Cincinnati, O H 45239-8707

A water-in-oil (W/O) microemulsion was chosen as the delivery system for water soluble nutrients, and flavors in foods. An ingestible, co-surfactant free system, with no off-taste or change in performance is described. Commercially available food surfactants are evaluated based on their structures and performance in solubilizing water in the high triglyceride concentration range (above 90%). The conditions needed to form such a microemulsion with minimum surfactant amounts are discussed. Microemulsions were considered in an effort to develop the capability to deliver water-soluble nutrients, flavors, and flavor enhancers to foods through a lipid based system. This paper describes our successful attempt to formulate a good tasting and performing water-in-oil microemulsion, containing a minimum amount of surfactant using commercially available surfactants. A generally accepted definition of a microemulsion is: "A clear, thermodynamically stable homogeneous dispersion of two immiscible liquids containing appropriate amounts of surfactants and co-surfactant". Friberg points out a great number of systems are not thermodynamically stable and a change of the definition requiring spontaneous formation would be more suitable (1). The term "microemulsion" has been used to describe different types of solutions (2): A substance which is otherwise insoluble in the bulk phase, may form a molecular solution upon addition of a third solvent component. Such systems of enhanced solubility by mixing solvents are often termed "detergentless microemulsions" (Figure la). Addition of a proper surfactant (SAA) with or without a co-surfactant (COS), will form a clear solution of the insoluble substance. It can be a co-solubilization in which the surfactant and co-surfactant form a liquid which can dissolve both oil or water as a molecular solution (Figure 1b). Another possibility is the formation of large and well defined surfactant aggregates, with or without co-surfactants. 0097-^156/91/044a-0026$06.00/0 © 1991 American Chemical Society In Microemulsions and Emulsions in Foods; El-Nokaly, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.

EL-NOKALY ET AL.

Solubilization of Water in Triglycerides

27


3.

Figure 1: Schematic Illustrations of the Structure of (a) Detergentless Microemulsion (Molecular Solution); (b) Co-Solubilization (Molecular Solution); and (c) Microemulsion (Water-in-Oil).

In Microemulsions and Emulsions in Foods; El-Nokaly, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.

28

MICROEMULSIONS AND EMULSIONS IN FOODS

The c o r e o f such a g g r e g a t e s d i s s o l v e s the i n s o l u b l e i n the b u l k s u b s t a n c e s ( F i g u r e 1 c ) . Such systems have been d i s c u s s e d i n o t h e r C h a p t e r s o f t h i s book and i n the l i t e r a t u r e ( 3 - 5 ) . There a r e v e r y few a v a i l a b l e examples of i n g e s t i b l e w a t e r - i n - o i l o r o i l - i n - w a t e r m i c r o e m u l s i o n systems f o r food a p p l i c a t i o n s , even though much has been a c c o m p l i s h e d i n r e c e n t y e a r s i n the g e n e r a l f i e l d o f m i c r o e m u l s i o n s .


E a r l i e r Work on Food M i c r o e m u l s i o n s A p p l i c a t i o n s Examples o f O i l - i n - W a t e r A p p l i c a t i o n s . R e p o r t s on m i l k f o r t i f i e d w i t h v i t a m i n A s o l u b i l i z e d i n a m i c r o e m u l s i o n have been r e c e n t l y published (6). D i s s o l v i n g e s s e n t i a l o i l s i n water w i t h and w i t h o u t an a l c o h o l c o - s u r f a c t a n t f o r a r o m a t i z a t i o n o f beverage o r p h a r m a c e u t i c a l f o r m u l a t i o n s , have been r e p o r t e d ( 7 - 9 ) . F i g u r e 2 shows the m i c r o e m u l s i o n s i n g l e phase r e g i o n o f a peppermint o i l / T w e e n 20/water system s t u d i e d by Treptow ( 9 ) . F r i b e r g s o l u b i l i z e d up t o 15 wt% t r i c a p r y l i n i n an i s o t r o p i c aqueous s o l u t i o n o f m o n o c a p r y l i n and a h y d r o t r o p e such as sodium x y l e n e s u l f o n a t e (10) Treptow d i s s o l v e d l e s s than 10% soybean o i l i n water w i t h a 30/70 s u r f a c t a n t m i x t u r e o f Tween 20 and G1045 r e s p e c t i v e l y ( I C I , I n c . ) . T h i s m i x t u r e had an HLB o f 13.1 ( 9 ) . Examples o f W a t e r - i n - O i l A p p l i c a t i o n s . The l i t e r a t u r e a v a i l a b l e on w a t e r - i n - o i l , the o i l b e i n g t r i g l y c e r i d e s , m i c r o e m u l s i o n i s r e v i e w e d i n T a b l e I . With the e x c e p t i o n o f the work done by L a r s s o n (12) and Treptow ( 9 ) , an a l c o h o l o r a c i d c o - s u r f a c t a n t was needed t o form the m i c r o e m u l s i o n . Such c o - s u r f a c t a n t s a r e u s u a l l y not a c c e p t a b l e f o r t a s t e , s a f e t y , o r performance reasons in ingestible o i l formulations. Examples o f n o n - i n g e s t i b l e w a t e r - i n - t r i g l y c e r i d e s a r e more numerous. They have g a i n e d c o n s i d e r a b l e a t t e n t i o n r e c e n t l y due t o the a p p l i c a b i l i t y of these o i l s i n a number o f new ways, such as e n g i n e f u e l s , l u b r i c a t i n g o i l s , and c a r r i e r l i q u i d s (14,15). The s p a r c i t y o f work a v a i l a b l e on water s o l u b i l i z a t i o n i n t r i g l y c e r i d e f o r food a p p l i c a t i o n s i s o b v i o u s l y due t o d i f f i c u l t i e s i n h e r e n t i n the s t r u c t u r e o f o i l , i n f i n d i n g a p p r o p r i a t e c o - s u r f a c t a n t s , and the need t o use minimum amounts o f food approved s u r f a c t a n t s ( e m u l s i f i e r s ) not to a d v e r s e l y a f f e c t the o i l p r o p e r t i e s . The paragraphs below d e s c r i b e our e f f o r t s t o b e t t e r u n d e r s t a n d what i s needed t o be taken i n t o c o n s i d e r a t i o n t o form e d i b l e w a t e r - i n - t r i g l y c e r i d e microemulsions. C h a r a c t e r i s t i c s of Microemulsions M i c r o e m u l s i o n s o f the aggregate type ( F i g u r e l c ) possess s p e c i a l c h a r a c t e r i s t i c s o f r e l a t i v e l y l a r g e i n t e r f a c i a l a r e a , u l t r a low i n t e r f a c i a l t e n s i o n , and l a r g e s o l u b i l i t y c a p a c i t y as compared to many o t h e r c o l l o i d a l systems.


3.

EL-NOKALY ET AL.

29



Peppermint Oil

Tween 20 Figure 2: Phase Diagram: Peppermint Oil/Water/Tween 20 at 25 Microemulsion Phase Region. (Reprinted from ref. 9.)

#

C Showing the Single

TABLE I . EARLIER WORK EXAMPLES OF WATER-IN-TRIGLYCERIDES

References

Oil

Surfactant

Soybean o i l

P0E S o r b i t o l oleate

Tricaprylin

Alkyl aryl p o l y g l y c o l ether

Pentanol

10

Trioctanoin

Sodium octanoate (soap)

Octanoic acid

11

Soybean o i l

Monoglyceride

l,2,3-[Tris (2 ethylhexanoyloxy)] propane

Tetraethylene g l y c o l dodecyl ether (R E0 )

Hexadecane

13

Canola o i l

Monoglyceride Acetic acid ester of monoglyceride

Tert-butanol Isopropanol 1-Hexanol

14

Triglyceride

None*

Ethanol 1-Butanol

15

Soybean o i l

0-Alkyl-3 D-glucose

Ethanol

16

*Detergentless

1 2

Co-Surfactant

9

12

4

microemulsion


30



The c o n d i t i o n s n e c e s s a r y f o r m i c r o e m u l s i o n f o r m a t i o n a r e : • L a r g e a d s o r p t i o n o f SAA o r SAA/COS m i x t u r e a t t h e W/0 i n t e r f a c e a c h i e v e d by c h o o s i n g a SAA m i x t u r e w i t h p r o p e r HLB. • H i g h f l u i d i t y o f t h e i n t e r f a c e . The i n t e r f a c i a l f l u i d i t y can be enhanced by u s i n g a p r o p e r c o - s u r f a c t a n t o r an optimum temperature. • Optimum c u r v a t u r e . The importance o f o i l p e n e t r a t i o n i n t h e SAA/COS i n t e r f a c e and t h e a p p r o p r i a t e SAA/COS s t r u c t u r e s ( 1 7 ) . Importance o f B u l k O i l P r o p e r t i e s . Why i s i t d i f f i c u l t t o form a t r i g l y c e r i d e microemulsion? T r i g l y c e r i d e s a r e s e m i - p o l a r compared t o h y d r o c a r b o n s . A s u r f a c t a n t o f h i g h e r HLB i s thus needed t o f a v o r t h e w a t e r - i n - o i l system, w i t h lower s o l u b i l i t y i n b u l k and i n c r e a s e d a d s o r p t i o n a t the i n t e r f a c e . I n t h e case o f t r i g l y c e r i d e , t h e r a t i o o f SAA/W i s l a r g e . The e m u l s i f i e r e f f i c i e n c y i s d e c r e a s e d i f i t i s l o s t to t h e b u l k and i s u n a v a i l a b l e t o t h e i n t e r f a c e . Treptow found a maximum normal ( L ) and r e v e r s e ( L ) m i c e l l a r r e g i o n s ( 3 ) , were formed w i t h a s u r f a c t a n t HLB o f 13.1 and 9.2 r e s p e c t i v e l y ( 9 ) . E d i b l e t r i g l y c e r i d e s such as soybean, r a p e s e e d , o r s u n f l o w e r o i l s c o n t a i n l o n g a l k y l c h a i n s m a i n l y C , C , C , and C . The o i l may be t o o b u l k y t o p e n e t r a t e t h e i n t e r f a c i a l f i l m t o a s s i s t t h e f o r m a t i o n o f the optimum c u r v a t u r e ( F i g u r e 3 ) . Reports o f o i l being s o l u b i l i z e d i n the aggregates p a l i s a d e l a y e r may be due t o t h e s h o r t n e s s o f t h e a l k y l c h a i n s i n t h e t r i g l y c e r i d e s used ( 1 3 ) . x

2

1 6

1 8

2 0

2 2

/ v w O Surfactant \ A / 0 Co-Surfactant • Oil F i g u r e 3: Optimum C u r v a t u r e , Ro=Radius o f Spontaneous Curvatures.



3.

EL-NOKALY ET AL.


R o l e of a C o - S u r f a c t a n t . A c o - s u r f a c t a n t i s u s u a l l y a medium c h a i n f a t t y a l c o h o l , a c i d , o r amines (18,19). I t i s usually chosen to be w i d e l y d i f f e r e n t i n h y d r o c a r b o n m o i e t y s i z e compared to the s u r f a c t a n t . The r o l e o f the c o - s u r f a c t a n t t o g e t h e r w i t h the s u r f a c t a n t i s to lower the i n t e r f a c i a l t e n s i o n down to a v e r y s m a l l even t r a n s i e n t n e g a t i v e v a l u e a t w h i c h the i n t e r f a c e would expand to form f i n e d i s p e r s e d d r o p l e t s , and s u b s e q u e n t l y adsorb more SAA and SAA/COS u n t i l t h e i r b u l k c o n d i t i o n i s d e p l e t e d enough to make i n t e r f a c i a l t e n s i o n p o s i t i v e a g a i n . T h i s p r o c e s s known as "spontaneous e m u l s i f i c a t i o n " , forms the m i c r o e m u l s i o n . Thus, based on a b i l i t y o f the c o - s u r f a c t a n t t o a f f e c t the s o l v e n t p r o p e r t i e s of o i l and/or water and to p e n e t r a t e the s u r f a c t a n t i n t e r f a c i a l monolayer, i t can: Decrease f u r t h e r the i n t e r f a c i a l t e n s i o n . I n c r e a s e the f l u i d i t y of i n t e r f a c e s • D e s t r o y l i q u i d c r y s t a l l i n e and/or g e l s t r u c t u r e s w h i c h prevent the f o r m a t i o n o f m i c r o e m u l s i o n s • A d j u s t HLB v a l u e and spontaneous c u r v a t u r e o f the i n t e r f a c e by changing s u r f a c t a n t p a r t i t i o n i n g c h a r a c t e r i s t i c s Decrease the s e n s i t i v i t y to c o m p o s i t i o n f l u c t u a t i o n s and b r i n g s f o r m u l a t i o n to i t s optimum s t a t e The presence o f a c o - s u r f a c t a n t i n t r i g l y c e r i d e i n c r e a s e s the m i c r o e m u l s i o n s a r e a (10, 11, 13-16). N a t u r e and C o n c e n t r a t i o n of S u r f a c t a n t . The c o n d i t i o n s s u r r o u n d i n g our a p p l i c a t i o n a r e : C o - s u r f a c t a n t s a r e not easy to f i n d i n foods and t h e i r a d d i t i o n i s not a t h e o r e t i c a l requirement. The o i l s t r u c t u r e and p r o p e r t i e s a r e c o n s t a n t . The f o r m u l a t e d w a t e r - i n - t r i g l y c e r i d e m i c r o e m u l s i o n a r e to be s h e l f s t a b l e a t room temperature. The temperature c o u l d not be v a r i e d to f a v o r m i c r o e m u l s i o n f o r m a t i o n . Thus, the n a t u r e and c o n c e n t r a t i o n o f the s u r f a c t a n t become o f utmost importance to o b t a i n a maximum s o l u b i l i z a t i o n i n a g i v e n W/0 microemulsion. The n a t u r a l r a d i u s and f l u i d i t y of the i n t e r f a c e s h o u l d be a d j u s t e d to o p t i m a l v a l u e s a t which the bending s t r e s s and the a t t r a c t i v e f o r c e of the i n t e r f a c e s a r e b o t h m i n i m i z e d . The c o n c e p t s t o be c o n s i d e r e d when d e s i g n i n g COS-free W/0 m i c r o e m u l s i o n s were r e p o r t e d to be ( 2 0 ) : • Near e q u a l p a r t i t i o n i n g of s u r f a c t a n t between the l i q u i d phases. Maximal l i n e a r e x t e n s i o n o f h y d r o p h o b i c o r h y d r o p h i l i c end o f the m o l e c u l e o r both. Forming a f l u i d i n t e r f a c i a l f i l m u s i n g d o u b l e o r branched c h a i n s u r f a c t a n t a t a temperature above the t h e r m o t r o p i c phase t r a n s i t i o n temperature by weakening s u r f a c t a n t l a t e r a l interaction. I t i s n e c e s s a r y but not a s u f f i c i e n t c o n d i t i o n t h a t the s u r f a c t a n t h y d r o c a r b o n volume ( v ) , e f f e c t i v e c h a i n l e n g t h ( L ) , and head group ( a ) s h o u l d s a t i s f y the r e l a t i o n v / a L > 1 (W/0) ( 2 1 ) . Thus, a s u r f a c t a n t w i t h a l a t e r a l l y b u l k y h y d r o c a r b o n p a r t on a r e l a t i v e l y s m a l l head group, such as some o f the d o u b l e c h a i n s u r f a c t a n t , f a v o r s the f o r m a t i o n o f W/0 aggregates. c

c


c

c


32

A number of d o u b l e - t a i l e d i o n i c s u r f a c t a n t s such as A e r o s o l OT a r e known to form c o - s u r f a c t a n t - f r e e m i c r o e m u l s i o n s . Abe e t . a l . ( 2 0 ) , have shown t h a t a spectrum o f e t h o x y l a t e d double branched t a i l a l k a n e s u l f o n a t e s have the a b i l i t y to m i c r o e m u l s i f y h y d r o c a r b o n and e l e c t r o l y t e w i t h o u t added COS. The o p t i m a l s t r u c t u r e s were o b t a i n e d through p a r a l l e l o p t i m i z a t i o n o f : • Hydrophobe b r a n c h i n g S u r f a c t a n t m o l e c u l a r weight i n c l u d i n g b o t h hydrophobe and hydrophile • S u r f a c t a n t head group


Food E m u l s i f i e r s o r

Surfactants

S u r f a c t a n t s i n food a r e u s u a l l y c a l l e d e m u l s i f i e r s whether t h e i r i n t e n d e d use i s e m u l s i f i c a t i o n o r not. An A c c e p t a b l e D a i l y I n t a k e (ADI) v a l u e has been a l l o c a t e d to most food e m u l s i f i e r s by h e a l t h a u t h o r i t i e s i n many c o u n t r i e s (FDA, FAO, EEC) ( T a b l e I I ) . C h e m i c a l l y , most food s u r f a c t a n t s a r e e s t e r s o f f a t t y a c i d s w i t h n a t u r a l l y o c c u r r i n g a l c o h o l s and a c i d s . The p r i m a r y raw m a t e r i a l s f o r food s u r f a c t a n t s p r o d u c t i o n a r e f a t s and o i l s which can be u t i l i z e d d i r e c t l y or a f t e r h a v i n g been hydrogenated, f r a c t i o n a t e d , o r s p l i t to f a t t y a c i d s and g l y c e r o l ( 2 2 ) . They have to impart no t a s t e or s m e l l on foods. They a r e m o s t l y n o n i o n i c s u r f a c t a n t s w i t h few e x c e p t i o n s such as s u c c i n i c , c i t r i c , and d i a c e t y l t a r t a r i c a c i d s e s t e r s of m o n o g l y c e r i d e s and soaps. Amphoteric l e c i t h i n i s the o n l y food approved s u r f a c t a n t c o n t a i n i n g a p o s i t i v e charge.

MATERIALS AND Crisco O i l :

METHODS Soybean o i l

Surfactants: Many food s u r f a c t a n t s were t e s t e d some are r e p o r t e d i n T a b l e I I I a and b. The f o l l o w i n g a r e the ones found most efficient: P o l y g l y c e r o l o l e a t e (AM #506, G r i n d s t e d ) based on e s t e r i f i c a t i o n w i t h o l e i c a c i d (min. 9 2 % ) . • P o l y g l y c e r o l l i n o l e a t e (AM #507, G r i n d s t e d ) based on e s t e r i f i c a t i o n with sunflower o i l f a t t y a c i d s . The average c o m p o s i t i o n , o f the p o l y g l y c e r o l m o i e t y i n these e s t e r s a r e 18 d i - , 18 t r i - , 31 t e t r a - , 13 p e n t a - , 10 hexa-, 2% h e p t a and the r e m a i n i n g 8% i s g l y c e r o l and h i g h e r g l y c e r o l . The FA c o m p o s i t i o n i s 36 mono-, and 63 d i - . • M o n o g l y c e r i d e (AM #505, G r i n d s t e d ) i s Dimodan LS w i t h no saturated f a t t y acid chains. • A t l a s G1186, P o l y o x y e t h y l e n e s o r b i t o l o l e a t e , ( I C I ) . Preparation of Surfactants. P o l y g l y c e r o l l i n o l e a t e (AM #507), was not c o m p l e t e l y s o l u b l e i n C r i s c o o i l as s u c h , u n l e s s water was added to form the m i c r o e m u l s i o n .


3.

EL-NOKALY ET AL.


The C r i s c o o i l / w a t e r / A M #507 phase diagram i n F i g u r e 4, was c o n s t r u c t e d u s i n g t h e s u r f a c t a n t samples:


• •

Sample - 1, AM #507 as p r o v i d e d by G r i n d s t e d . Sample - 2, AM #507 p u r i f i e d as f o l l o w s t o remove polyglycerol. 70 grams o f p o l y g l y c e r o l l i n o l e a t e and 350 grams o f e t h y l a c e t a t e were p l a c e d i n a l a r g e s e p a r a t o r y f u n n e l . 1500 m i l l i l i t e r s o f h o t (75°C) water was then added and t h e m i x t u r e shaken w e l l . I t was l e f t s t a n d i n g o v e r n i g h t . The e t h y l a c e t a t e l a y e r was s e p a r a t e d and d r i e d o v e r magnesium s u l f a t e . The e t h y l a c e t a t e was e v a p o r a t e d i n a r o t a r y e v a p o r a t o r f o l l o w e d by e i g h t hours on a vacuum pump, 65.427 grams were recovered.

P r e p a r a t i o n o f Phase Diagram. A Zymark Pye R o b o t i c system, F i g u r e 5, d e s c r i b e d e l s e w h e r e (23) was used t o p r e p a r e samples t o c o n s t r u c t phase diagrams o f t h e v a r i o u s s u r f a c t a n t / C r i s c o o i l / w a t e r systems t e s t e d . I n some c a s e s , t h e whole phase diagram was c o n s t r u c t e d , but g e n e r a l l y o n l y t h e r e g i o n below 12 wt% s u r f a c t a n t was screened. The samples were l e f t t o e q u i l i b r a t e i n 75 and 100°F s t o r a g e rooms.

Crisco Oil

F i g u r e 4: Linoleate

Phase Diagram: C r i s c o O i l / W a t e r / P o l y g l y c e r o l AM#507 (Sample 1) AM#507 E x t r a c t e d w i t h E t h y l A c e t a t e (Sample 2) (The lower p a r t o f t h e c u r v e ( ) was n o t done)


33



F i g u r e 5:

Zymark Pye R o b o t i c System


3.

EL-NOKALY ET AL.


RESULTS AND DISCUSSION Effect of Surfactant

Structures


S u r f a c t a n t s chosen from the d i f f e r e n t c l a s s e s p r e v i o u s l y l i s t e d i n T a b l e I I , were t e s t e d f o r w a t e r - i n - o i l m i c r o e m u l s i o n f o r m a t i o n a t 12:1, SAA/W by w e i g h t . P a r t i a l Glycerides. ( T a b l e I I I A) V a r y i n g the g l y c e r i d e s f a t t y a c i d c o m p o s i t i o n , as seen i n T a b l e I I I A, showed Dimodan LS ( 1 2 ) and AM #505 (Dimodan LS w i t h no s a t u r a t e d f a t t y a c i d c h a i n s ) , t o g i v e the l o w e s t s u r f a c t a n t t o water r a t i o 10:1 wt/wt. Dimodan LS i s a l s o the h i g h e s t i n u n s a t u r a t i o n compared t o o t h e r g l y c e r i d e s t e s t e d , - 80% i n C18:2. N e v e r t h e l e s s , t o d i s s o l v e 0.1% w a t e r , a minimum amount o f 4% s u r f a c t a n t was needed. Dimodan LS c o u l d not be chosen because o f the r e l a t i v e h i g h SAA/W r a t i o needed t o form a m i c r o e m u l s i o n and an o b j e c t i o n a b l e c o a t i n g o f the mouth and a f t e r t a s t e . Removing i t s s a t u r a t e d f a t t y a c i d components as i n AM#505 improved the m o u t h f e e l , b u t not the SAA/W r a t i o . Fatty Acid Esters of Polyols. Surfactants containing varied h y d r o p h i l i c groups such a s s o r b i t o l , s o r b i t a n , o r p o l y g l y c e r o l e s t e r s w i t h d i f f e r e n t g l y c e r o l u n i t s were t e s t e d t o s t u d y t h e i r e f f e c t on SAA/W r a t i o . T a b l e I I I B shows the e f f e c t o f v a r y i n g the number o f g l y c e r o l u n i t s i n commercial p o l y g l y c e r o l e s t e r s . The o l e a t e and l i n o l e a t e groups were p r e f e r r e d f o r t e s t i n g because o f t h e i r u n s a t u r a t i o n and i t s known e f f e c t i n i n c r e a s i n g f l u i d i t y o f interfacial film. Some l a u r a t e s were t e s t e d u n s u c c e s s f u l l y . The optimum number o f g l y c e r o l u n i t s t o have i n the m o l e c u l e f o r a m i c r o e m u l s i o n a t SAA/W below 12:1, was f o u r as seen i n T a b l e I I I B f o r P o l y a l d o 4-2-0 and AM#507. A n o t h e r requirement seems t o be the presence o f l a r g e amounts o f d i - f a t t y a c i d c h a i n s mixed w i t h mono. AM#507 c o n t a i n s 6 3 % d i l i n o l e a t e and 36% mono. The s o r b i t a n and s o r b i t o l e s t e r s o f o l e a t e and l i n o l e a t e d i d not g i v e m i c r o e m u l s i o n s a t SAA/W r a t i o below 12:1. Crisco 0il/Vater/AM#507 Phase Diagrams E x t r a c t i o n o f the p o l y g l y c e r o l l i n o l e a t e (AM#507) w i t h e t h y l a c e t a t e removed the f r e e u n r e a c t e d p o l y g l y c e r o l . The m i c r o e m u l s i o n r e g i o n formed by the sample-1, a s p r o v i d e d by G r i n d s t e d , was s m a l l e r than t h a t o f the p u r i f i e d sample-2, as seen i n F i g u r e 4. Except f o r the upper o i l c o r n e r , above 90%, where they behaved s i m i l a r l y . T h i s b e i n g the a r e a o f i n t e r e s t f o r our s t u d y , we d i d not f i n d i t n e c e s s a r y t o work f u r t h e r w i t h p u r i f i e d samples.


36


TABLE II A CHEMICAL CLASSFICATION OF FOOD EMULSIFIERS AND LEGAL STATUS (US FDA 21 CFR*)

General C l a s s


P a r t i a l Glycerides

API Values** mg/kg body vt/day

Example

Mono- and d i g l y c e r i d e s

Not l i m i t e d

L a c t i c acid esters of monoglycerides

Not l i m i t e d

A c e t i c a c i d e s t e r s of monoglycerides

Not l i m i t e d

C i t r i c acid esters of monoglycerides

Not l i m i t e d

Diacetyl t a r t a r i c acid esters of monoglycerides

50

Succinic acid esters of monoglycerides

F a t t y A c i d E s t e r s of Polyols

Ethoxylated E m u l s i f i e r s

Phosphatides, Phosphorylated P a r t i a l Glycerides

Propylene g l y c o l e s t e r s o f f a t t y acids Polyglycerol esters of f a t t y acids Sucrose e s t e r s of f a t t y a c i d s Sorbitan esters

25 25 10 25

Ethoxylated p a r t i a l g l y c e r i d e s Polysorbates

25

Lecithin

Not l i m i t e d

F r a c t i o n e d phosphatides Phosphorylated

Miscellaneous

3% by wt. of shortening; 5% by wt. of flour

monoglyceride

Sodium s t e a r o y l - l a c t y l a t e Caldium s t e a r o y l - l a c t y l a t e S a l t s o f f a t t y a c i d s (Na,K) Sodium dodecyl s u l f a t e

20 20 Not l i m i t e d

*CFR Code o f F e d e r a l R e g u l a t i o n s **Acceptable D a i l y Intake (ADI) f o r man


3.

EL-NOKALY ET AL.

37


TABLE III SURFACTANTS FORMING V/O MICROEMULSION IN CRISCO OIL AT S/W = 12 OR LESS

A.

GLYCERIDES


Surfactants

Dimodan AM #505 Dimodan AM #489

Trade Name

LS (G) (G) 0 (G) (G)

AM #490 (G) Monooleate (P) Aldo MD ( L ) Aldo MLD ( L )

Composition

Sunflower ( 8 0 % C18:2; 20% C18:l) No s a t u r a t e d FA Soybean o i l ( 5 1 % C18:2; 23% C18:l) Rapeseed o i l ( 4 0 % d i - ) (21% C18:2; 62% C18:l) Sunflower O i l ( 3 9 % d i - ) Monooleate Mono- and d i o l e a t e Monolaurate

S/V wt/wt

10:1* 10:1* None None None None None None

B. P0LYGLYCER0L ESTERS OF FATTY ACIDS

Surfactant

Trade Name

Composition

S/V wt/wt

C a p r o l 3G0 (C) P o l y a l d o 4-2-0 ( L ) C a p r o l 6G20 (C) P o l y a l d o 2010 ( L ) AM #506 (G)

T r i g l y c e r o l monoleate , Tetraglycerol dioleate Hexaglycerol dioleate Decaglycerol dioleate Polyglycerol oleate**

None 10:0.71 None None None

Experimental ( L ) P o l y a l d o 4-2-L ( L ) 93-919 ( L ) AM #507 (G) T r i o d a n 20 (G) Homodan PT (G)

Tetraglyceryl laurate Tetraglyceryl dilaurate P o l y g l y c e r o l monolaurate Polyglycerol mono-dilinoleate** Polyglycerol esters Polyglycerol ester of d i m e r i z e d soybean o i l

None None None 9:1 14:1 None

*Microemulsion formed * * P o l y g l y c e r o l : mainly t e t r a G = Grindsted L = Lonza/Glyco C = Capitol City P = P f l a t z & Baur



38


Comparison of Microemulsion Region i n Phase Diagram: Crisco O i l / V a t e r / E m u l s i f i e r for Different Emulsifiers. The s u r f a c t a n t s ( e m u l s i f i e r s ) used t o form the phase diagram i n F i g u r e 6 a r e t h e p o l y g l y c e r o l l i n o l e a t e (AM#507), o l e a t e (AM#506), m o n o g l y c e r i d e (AM#505), and p o l y o x y e t h y l e n e s o r b i t o l o l e a t e ( A t l a s G1186). The s u r f a c t a n t s behave d i f f e r e n t l y i n the upper o i l and l o w e r s u r f a c t a n t c o r n e r s . P o l y g l y c e r o l o l e a t e forms the s m a l l e r m i c r o e m u l s i o n r e g i o n throughout the whole range. I n the lower 50% towards the s u r f a c t a n t c o r n e r , the POE s o r b i t o l o l e a t e and m o n o g l y c e r i d e form the l a r g e r m i c r o e m u l s i o n a r e a . The m o n o g l y c e r i d e shows t h e t y p i c a l knee, i n d i c a t i n g the presence o f l i q u i d c r y s t a l s . I n the upper o i l c o r n e r , above 90%, t h e p o l y g l y c e r o l l i n o l e a t e s o l u b i l i z e s more water a t l o w e r s u r f a c t a n t c o n c e n t r a t i o n as seen i n F i g u r e 7. T a b l e I V shows the r a t i o o f s u r f a c t a n t t o water f o r t h e d i f f e r e n t food e m u l s i f i e r s used. F o r e v e r y m o l e c u l e o f p o l y g l y c e r o l l i n o l e a t e (AM#507) f o u r m o l e c u l e s o f water a r e solubilized. The r e s t o f the phase diagram C r i s c o oil/water/AM#507, was scanned f o r a one phase o i l - i n - w a t e r m i c r o e m u l s i o n o r l i q u i d c r y s t a l l i n e r e g i o n s . None were found i n s t e a d m i x t u r e o f two and t h r e e phases o f o i l , w a t e r , and l i q u i d c r y s t a l s . Structure of Crisco 0il/Water/AM#507 Microemulsion. The s u r f a c t a n t p o l y g l y c e r o l l i n o l e a t e (AM# 507) s t r u c t u r e and c o m p o s i t i o n were d e s i g n e d t o g i v e optimum c o n d i t i o n s f o r a COS-free W/0 m i c r o e m u l s i o n and they d i d . The c o n c e p t s e a r l i e r d e s c r i b e d ( 2 0 ) , w h i c h s h o u l d g i v e spontaneous c u r v a t u r e , i n c r e a s e the i n t e r f a c e f l u i d i t y , and d e c r e a s e f u r t h e r t h e i n t e r f a c i a l t e n s i o n were f o l l o w e d a s p r a c t i c a l l y p o s s i b l e . The p o l y g l y c e r o l l i n o l e a t e i s a l o n g c h a i n s u r f a c t a n t a f f o r d i n g a maximal l i n e a r e x t e n s i o n o f t h e h y d r o p h o b i c and h y d r o p h i l i c end o f the m o l e c u l e . I t may even be worth m e n t i o n i n g t h a t the l e n g t h o f the extended h y d r o p h o b i c and h y d r o p h i l i c groups, as measured from the c a r b o x y group, i s almost e q u a l , 19.148A and 19.75A, f o r the m o n o l i n o l e a t e and t h e t e t r a g l y c e r o l r e s p e c t i v e l y ( F i g u r e 8 ) . The s u r f a c t a n t i s a m i x t u r e o f 6 3 % branched d i l i n o l e a t e , the r e s t s t r a i g h t m o n o l i n o l e a t e w i t h some o l e a t e . B r a n c h i n g s h o u l d be a n o t h e r f a c t o r i n increasing the i n t e r f a c i a l f l u i d i t y . F i g u r e 8 shows the s p e c i a l k i n k i n the l i n o l e a t e m o l e c u l e w h i c h makes i t s a l i g n m e n t d i f f i c u l t , thus l e a d i n g t o an i n c r e a s e i n t h e interfacial fluidity. The presence o f u n s a t u r a t i o n was found t o be i m p o r t a n t . The t e t r a g l y c e r o l o l e a t e d i d no g i v e as good a SAA/W r a t i o as t h e l i n o l e a t e . Those a t t r i b u t e s were chosen t o l o w e r t h e t h e r m o t r o p i c phase t r a n s i t i o n temperature by weakening s u r f a c t a n t l a t e r a l i n t e r a c t i o n . The monooleate and l i n o l e a t e c o u l d a c t as c o - s u r f a c t a n t s i n c e they a r e d i f f e r e n t i n hydrocarbon moiety s i z e compared t o the d i l i n o l e a t e . The h y d r o p h i l e group s i z e g i v i n g the l o w e s t SAA/W r a t i o was t h e t e t r a g l y c e r o l ( T a b l e I I I B ) . A t t e m p t s were made a t s t u d y i n g the s t r u c t u r e o f t h e m i c r o e m u l s i o n formed by the p o l y g l y c e r o l l i n o l e a t e (AM #507), water and C r i s c o o i l . The r e s u l t s were i n c o n c l u s i v e a s t o t h e


3.

EL-NOKALY ET AL.



Soybean Oil

Emulsifier F i g u r e 6: Complete Phase Diagram o f C r i s c o Oil/Water/Emulsifier Emulsifiers AM#507 P o l y g l y c e r o l L i n o l e a t e (sample 1) AM#506 P o l y g l y c e r o l O l e a t e AM#505 M o n o g l y c e r i d e A t l a s G1186 P o l y o x y e t h y l e n e S o b i t o l Oleate

Crisco Oil

10 Emulsifier

F i g u r e 7: The Upper O i l Corner (Above 90%) o f t h e Phase Diagram C r i s c o Oil/Water/Emulsifier E m u l s i f i e r s • • • • AM#507 P o l y g l y c e r o l L i n o l e a t e (sample 1) -••AM#506 Polyglycerol Oleate IHIUUIUUIIM AM#505 Monoglyceride


39

40


TABLE I V RATIO OF SURFACTANT TO WATER FOR DIFFERENT FOOD EMULSIFERS


Emulsifier

SAA/W moles/moles

AM #505

-1.83

AM #506

Solubilization of Water and Water-Soluble Compounds in

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