Flavor Encapsulation with Alginates - ACS Symposium Series (ACS...
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Chapter 13
Flavor
Encapsulation with Alginates Alan H. King
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Kelco Division of Merck and Company, Inc., 75 Terminal Avenue, Clark, NJ 07066 Alginates, unique hydrocolloids extracted from selected species of brown seaweed (kelp), interact with calcium ions to produce thermally stable gels. Using this interaction, flavor oils may be encapsulated or entrapped in the algin gel matrix. Encapsulation is accomplished at ambient temperatures. Products may be used "as is" (wet) or subsequently dried. This technique offers the potential for novel flavor effects, flavor protection, and new food products. Because o f t h e i r a b i l i t y t o r e a c t w i t h c a l c i u m i o n s a t ambient temperatures t o form t h e r m a l l y s t a b l e g e l s o r f i b e r s , a l g i n a t e s c a n p r o v i d e a u s e f u l e n c a p s u l a t i n g o r e n t r a p p i n g system f o r o i l s o l u b l e f l a v o r compounds. A l g i n i s t h e s t r u c t u r a l p o l y s a c c h a r i d e o f t h e brown seaweeds. One o f t h e most abundant and u s e f u l s p e c i e s o f t h e s e marine p l a n t s i s Macrocystis p y r i f e r a , also c a l l e d giant kelp. T h i s p l a n t grows i n water as deep as 100 f t . , and under optimum c o n d i t i o n s can grow one i n c h / h o u r 1 Giant kelp i s harvested with mechanical harvesters which c u t o n l y t h e t o p p o r t i o n o f t h e p l a n t , about t h r e e f e e t below the w a t e r s s u r f a c e . A l g i n i s then e x t r a c t e d from t h e k e l p p l a n t through an i o n exchange p r o c e s s and c o n v e r t e d t o various salt forms. The most common s a l t i s sodium a l g i n a t e , s o l d as a water s o l u b l e powder. D u r i n g m a n u f a c t u r i n g , p r o p e r t i e s such as v i s c o s i t y , c l a r i t y and c a l c i u m c o n t e n t a r e c o n t r o l l e d t o a c h i e v e p r o p r i e t a r y products of s p e c i f i e d f u n c t i o n a l i t y . Alginates a r e composed of two monomeric sugar acids; D-Mannuronic a c i d and L - G u l u r o n i c acid. These two monomers a r e connected by 1 — > 4 g l y c o s i d i c l i n k a g e s . Commercially a v a i l a b l e polymers range from m o l e c u l a r w e i g h t s (M.W.s) o f 12,000 - 180,000 D a l t o n s (_1 ). The p r o p o r t i o n s o f t h e two monomers vary from one s p e c i e s t o a n o t h e r , b u t i n a l l s p e c i e s s t u d i e d t h e r e a r e homogeneous blocks o f each type of residue, polymannuronic (M-blocks),
c
0097-6156/88/0370-0122$06.00/0 1988 American Chemical Society
In Flavor Encapsulation; Risch, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
Downloaded by NORTH CAROLINA STATE UNIV on May 9, 2015 | http://pubs.acs.org Publication Date: May 31, 1988 | doi: 10.1021/bk-1988-0370.ch013
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p o l y g u l u r o n i c ( G - b l o c k s ) , or c o n t i n u o u s l y a l t e r n a t i n g r e s i d u e s (MG-blocks). A s i n g l e a l g i n molecule will contain a l l three segments. For example, the g i a n t k e l p , M a c r o c y s t i s pyrifera, c o n t a i n s c a . 40% M-blocks, c a . 18% G - b l o c k s , and c a . 42% M/G-blocks, w h i l e a l g i n from L a m i n a r i a hyperborea c o n t a i n s 13% M-blocks, c a . 60% G - b l o c k s , and c a . 27% M/G-blocks (2). The geometries of these segments are c o n s i d e r a b l y d i f f e r e n t . The M-blocks have an "extended r i b b o n " - t y p e c o n f o r m a t i o n , w h i l e the G-blocks are much more b u c k l e d . When two G-block r e g i o n s a l i g n s i d e by s i d e , diamond shaped h o l e s are formed, having dimensions i d e a l l y s u i t e d f o r the c o o p e r a t i v e b i n d i n g of c a l c i u m i o n s . The c a l c i u m i o n s are bound between two a l g i n c h a i n s l i k e eggs i n an egg box. T h e r e f o r e , the c a l c i u m r e a c t i v i t y of a l g i n s i s the r e s u l t of c a l c i u m induced d i m e r i c a s s o c i a t i o n of the G-block r e g i o n s ( 3 - 4 ) . Depending on the amount of c a l c i u m added t o a 0.5% h i g h M.W. ( h i g h v i s c o s i t y ) a l g i n a t e s o l , and the method of a d d i t i o n , h i g h v i s c o s i t y " s o l u t i o n s " , f r e e s t a n d i n g g e l s , or i n s o l u b l e , f i b r o u s p r e c i p i t a t e s may be produced. Because of the i o n i c n a t u r e of the c a l c i u m / a l g i n r e a c t i o n , g e l s so formed p o s s e s s t h e r m a l s t a b i l i t y and do not melt upon h e a t i n g . A l t h o u g h the g e l s are not r e v e r s i b l e by h e a t i n g , they can be r e v e r s e d or weakened through i o n exchange w i t h c h e l a t i n g agents (séquestrants) or extended treatment w i t h Na, K, Mg or ammonium s a l t s . Diffusion setting i s one of s e v e r a l methods used t o form alginate gels. T h i s method r e q u i r e s h y d r a t i o n of the a l g i n a t e s e p a r a t e l y from the c a l c i u m s o u r c e . When the a l g i n a t e s o l c o n t a c t s a c a l c i u m s a l t s o l u t i o n (such as 3-5% c a l c i u m c h l o r i d e , a c e t a t e , or l a c t a t e ) , a g e l forms i n s t a n t l y at the i n t e r f a c e . Calcium ions c o n t i n u e t o d i f f u s e i n t o the a l g i n a t e , c a u s i n g the g e l t o s t r e n g t h e n w i t h time. T h i s r e a c t i o n can be e a s i l y demonstrated by s i m p l y p o u r i n g a 2% sodium a l g i n a t e s o l i n t o a 5% c a l c i u m c h l o r i d e solution. A g e l forms i n s t a n t l y , and can be removed from the c a l c i u m c h l o r i d e and handled as a s o l i d . Many e x t r u d e d , reformed food products p r e s e n t l y use this g e l a t i o n method t o b i n d food p a r t i c l e s i n t o s p e c i f i c shapes. Often the g e l a t i o n r e a c t i o n not o n l y performs a b i n d i n g f u n c t i o n but a l s o a c t s as a p r o c e s s i n g a i d . A l g i n i s hydrated by m i x i n g i t w i t h the comminuted f o o d , the m i x t u r e i s extruded i n a s p e c i f i c shape and sprayed w i t h , or dipped i n , the c a l c i u m s o l u t i o n t o produce the instant surface g e l . The food p r o d u c t s are u s u a l l y b a t t e r e d , breaded, and f r i e d p r i o r t o packaging and f r e e z i n g . The a p p l i c a t i o n of an a l g i n f i l m , by f i r s t c o a t i n g a food product such as o y s t e r s or f i s h f i l l e t s w i t h an a l g i n s o l , f o l l o w e d by a c a l c i u m s o l u t i o n s p r a y , forms an e f f e c t i v e c o a t i n g t o minimize f r e e z e r burn d u r i n g prolonged s t o r a g e . A p p l i c a t i o n of t h i s c o a t i n g t o foods n o r m a l l y f r i e d ( o n i o n r i n g s , f o r example) p r o v i d e s an e f f e c t i v e f a t b a r r i e r , and the g e l does not m e l t . I t i s important t o r e a l i z e t h a t an a l g i n / c a l c i u m g e l or f i l m i s permeable t o water s o l u b l e m o l e c u l e s w i t h m o l e c u l a r weights of l e s s than 5,000 D a l t o n s . M o l e c u l e s of h i g h e r m o l e c u l a r weight may a l s o s l o w l y d i f f u s e through the g e l , but those w i t h m o l e c u l a r w e i g h t s of 10,000 and h i g h e r w i l l not d i f f u s e (5). For example, sugar and s o l u b l e c o l o r s w i l l d i f f u s e out of a g e l p l a c e d i n w a t e r , and water i t s e l f can be l o s t from a l g i n g e l s i n dry environments. Lipid
In Flavor Encapsulation; Risch, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
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m a t e r i a l s w i l l be h e l d i n the g e l m a t r i x even though they are of low molecular size, however. Consequently, a l t h o u g h water soluble f l a v o r compounds w i l l not be h e l d by a l g i n g e l s , o i l s o l u b l e compounds can be e n c a p s u l a t e d or t r a p p e d i n a l g i n / c a l c i u m m a t r i c e s . An interesting example of e n c a p s u l a t i o n and diffusion i s the p r o d u c t i o n of e t h a n o l by y e a s t c e l l s (Saccharomyces c e r e v i s i a e ) e n c a p s u l a t e d i n an a l g i n a t e g e l . The c e l l s are i m m o b i l i z e d i n the a l g i n g e l , sugar d i f f u s e s i n t o the g e l where the y e a s t c o n v e r t s i t to a l c o h o l , which then d i f f u s e s out of the g e l . A l c o h o l can thus be produced c o n t i n u o u s l y by p a s s i n g a g l u c o s e s o l u t i o n through a column of the encapsulated cells {5). In a similar f a s h i o n , the a l g i n / c a l c i u m g e l has been used t o i m m o b i l i z e v a r i o u s enzymes. Even v i a b l e , i n s u l i n p r o d u c i n g c e l l s ( i s l e t s ) , have been e n c a p s u l a t e d . Injection of these e n c a p s u l a t e d cells into rats with induced d i a b e t e s c o r r e c t e d the d i a b e t i c s t a t e f o r two t o t h r e e weeks ( 6 ) . In o r d e r t o e n c a p s u l a t e or e n t r a p o i l s o l u b l e f l a v o r s w i t h a l g i n a t e s , i t i s f i r s t n e c e s s a r y t o form an e m u l s i o n , u s i n g s t a n d a r d emulsion technology. Once the e m u l s i o n i s formed, the a l g i n a t e s o l / e m u l s i o n i s added d r o p w i s e , or atomized, i n t o a c a l c i u m c h l o r i d e s o l u t i o n ( 5 % or h i g h e r ) . G e l beads w i l l form i n s t a n t l y , w i t h the o i l s o l u b l e m a t e r i a l t r a p p e d i n s i d e the beads. The diameter of the beads can be varied from 200 - 5000 m i c r o n s , depending on f o r m u l a t i o n and m e c h a n i c a l equipment used. The g e l beads may be kept i n the h y d r a t e d g e l s t a t e or d e h y d r a t e d , depending on needs. The use of h i g h c a l c i u m c h l o r i d e c o n c e n t r a t i o n s (__> 20%) h e l p s t o dehydrate the beads, but the b i t t e r c h l o r i d e f l a v o r may persist. Rinsing off excess CaCl2 helps or calcium lactate may be s u b s t i t u t e d ( s o l u b i l i t y l i m i t s the c o n c e n t r a t i o n t o < 5%, however). E n c a p s u l a t i o n of heat s e n s i t i v e m a t e r i a l s i n t h i s manner h e l p s reduce heat d e g r a d a t i o n . A second method f o r e n t r a p p i n g o i l s o l u b l e f l a v o r s i n v o l v e s r e v e r s i n g the above p r o c e d u r e . By the a d d i t i o n of a c a l c i u m s a l t s o l u t i o n t o an e f f i c i e n t l y mixed a l g i n a t e f l a v o r o i l e m u l s i o n , i n s o l u b l e c a l c i u m a l g i n a t e f i b e r s a r e formed which a l s o e n t r a p f l a v o r o i l s , a l t h o u g h not q u i t e as e f f i c i e n t l y as the p r e v i o u s method. These h i g h l y r e a c t e d c a l c i u m a l g i n a t e f i b e r s a r e v e r y s t a b l e t o h e a t , a c i d , and f u r t h e r m i x i n g , r e t a i n i n g t h e i r i n t e g r i t y and s e r v i n g as u s e f u l t e x t u r i z i n g i n g r e d i e n t s under c o n d i t i o n s f r e e of s i g n i f i c a n t i o n exchange. T h i s f i b r o u s - l i k e m a t e r i a l may a l s o have a t e x t u r e v e r y s i m i l a r t o f r u i t p u l p , and s e r v e a t e x t u r e f u n c t i o n as w e l l as t h a t of a f l a v o r c a r r i e r , e s p e c i a l l y f o r f r u i t , v e g e t a b l e , or meat p r o d u c t s . By the proper a d d i t i o n of v a r i o u s i n g r e d i e n t s p r i o r t o the r e a c t i o n w i t h c a l c i u m ( e . g . , o t h e r gums, s t a r c h , f a t s , p r o t e i n s , f r u i t or v e g e t a b l e f i b e r , d e x t r i n s , e t c . ) , the t e x t u r e of the f i n a l f i b e r s can be m o d i f i e d w i t h i n broad l i m i t s (7). U s i n g t h i s method, e x t r e m e l y h i g h v i s c o s i t y develops as the c a l c i u m s a l t i s i n t r o d u c e d t o the a l g i n a t e e m u l s i o n ; c o n s e q u e n t l y e f f i c i e n t m i x i n g , such as t h a t o b t a i n e d w i t h a Hobart mixer i s r e q u i r e d . The a l g i n a t e f i b e r s i z e may be c o n t r o l l e d by the type of m i x i n g used d u r i n g the c a l c i u m / a l g i n a t e r e a c t i o n p e r i o d and the few minutes immediately f o l l o w i n g c a l c i u m s a l t a d d i t i o n . The h i g h e r the shear r a t e , the s m a l l e r the f i b e r s w i l l be. T h i s method has p o t e n t i a l f o r f l a v o r entrapment i n such p r o d u c t s as f r u i t - or v e g e t a b l e - l i k e p u l p f o r beverages, hard candy, bakery f i l l i n g s , and i c e cream t o p p i n g s .
In Flavor Encapsulation; Risch, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
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Although a l g i n a t e e n c a p s u l a t i o n o r entrapment o f o i l s o l u b l e f l a v o r s i s q u i t e d i f f e r e n t from t r a d i t i o n a l e n c a p s u l a t i o n methods, i t c o u l d s e r v e a s a v a l u a b l e t o o l f o r l i q u i d systems where a p r o t e c t i v e e f f e c t , delayed r e l e a s e , or combination t e x t u r e / f l a v o r e f f e c t i s needed.
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Literature Cited 1. Diemair, W.; Weichel, H.H. Deut. Lebensm-Rundschan 1958, 54, 51. 2. Penman, A . ; Sanderson, G.R. Carbohyd. Res. 1972, 25, 273-82. 3. ANON. Structured Foods with the Algin/Calcium Reaction, Technical Bulletin #F-83; KELCO, Div. of Merck & Co., Inc.; San Diego, 1984. 4. Rees, D.A. In Advances in Carbohydrate Chem & Biochem; Wolfrom, M.L. and Tipson, R.S., Eds.; Academic: NY, 1969, 24, 267-332. 5. Kierstan, M.; Bucke, C.; Biotechnol. Bioeng., 1977, l 9 , 387-97. 6. Lim, F . ; Sun, A.M. Science 1980, 210, 908-10. 7. King, A.H. In Food Hydrocolloids; Glicksman, M., Ed.; CRC Press: Boca Raton, 1983, Vol. II, Chapter 6. RECEIVED December 29, 1987
In Flavor Encapsulation; Risch, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
