Emulsifiers: Milk Proteins - American Chemical Society

10 Emulsifiers: Milk Proteins C. V. MORR

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 12, 2016 | http://pubs.acs.org Publication Date: March 6, 1981 | doi: 10.1021/bk-1981-0147.ch010

Department of Food Science, Clemson University, Clemson, SC 29631

Emulsions, such as those in food products, may be defined as macroscopic dispersions of two immiscible liquids, one of which forms the continuous, dispersion phase and the other, the discontinuous, dispersed phase, commonly termed globules. An emulsion of two immiscible liquids, one polar and one nonpolar, will rapidly separate into two distinct phases upon standing unless a third phase, an adsorbed surfactant, is present in the interface to stabilize it. Surfactants, e.g., chemical emulsifiers and proteins, stabilize emulsions by protecting against close contact and the association of individual globules. The DLVO theory (1) ascribes emulsion stability to a balance of attractive van der Waals forces and electrostatic repulsive forces, derived from oppositely charged ions in a double layer surrounding the globules (Figure 1). The emulsion remains stable so long as the magnitude of the repulsive forces exceeds that of the attractive forces between the globules. There are a number of factors that influence the stability of emulsions: 1) i n t e r f a c i a l t e n s i o n between the two phases; 2) chara c t e r i s t i c s of the adsorbed f i l m i n the i n t e r f a c e ; 3) magnitude of the e l e c t r i c a l charge on the g l o b u l e s ; 4) s i z e and surface/volume r a t i o of the g l o b u l e s ; 5) weight/volume r a t i o of dispersed and d i s p e r s i o n phases; and 6) v i s c o s i t y of the d i s p e r s i o n phase. Four c l a s s e s of emulsion s t a b i l i z i n g agents can be d i s t i n g u i s h e d : 1) i n o r g a n i c e l e c t r o l y t e s ; 2) surface a c t i v e agents o r s u r f a c t a n t s ; 3) f i n e l y d i v i d e d i n s o l u b l e s o l i d s ; and 4) macromolecular e m u l s i f y i n g agents, such as p r o t e i n s , gums and starches ( 2 ) . The immense i n t e r f a c i a l area s e p a r a t i n g dispersed globules from the d i s p e r s i o n phase i s of c r i t i c a l importance i n determining t h e i r s t a b i l i t y . For example, i t i s estimated that a t y p i c a l emuls i o n has approximately 7 X 10^ cm^ i n t e r f a c i a l area per l i t e r ( 3 ) . Thus, those f a c t o r s c o n t r o l l i n g the p r o p e r t i e s of the i n t e r f a c i a l membrane are extremely important i n determining the s t a b i l i t y of the emulsion. Chemical and e l e c t r o n m i c r o s c o p i c techniques have been used to v e r i f y the presence of an adsorbed l a y e r surrounding emulsion globules. P r o t e i n s are examples of h y d r o c o l l o i d s that e x h i b i t 0097-6156/81/0147-0201$05.00/0 © 1981 American Chemical Society

Cherry; Protein Functionality in Foods ACS Symposium Series; American Chemical Society: Washington, DC, 1981.


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unique s u r f a c t a n t p r o p e r t i e s due to t h e i r l a r g e molecular weights and t h e i r m u l t i p l i c i t y of hydrophobic and h y d r o p h i l i c r e s i d u e s , each of which e x h i b i t a spectrum of a f f i n i t i e s f o r the p o l a r and non-polar phases i n the emulsion system. The polymer s t r u c t u r e of p r o t e i n molecules adsorbed i n the i n t e r f a c i a l l a y e r provide m u l t i p l e attachment s i t e s (4) and are b e l i e v e d t o adsorb i n a manner that exposes amino a c i d segments t o the aqueous phase (1). Each p r o t e i n system e x e r t s i t s own unique i n f l u e n c e on emulsion s t a b i l i t y , s i n c e each possesses a c h a r a c t e r i s t i c complement of amino a c i d s , arranged i n a s p e c i f i c sequence that c o n t r o l s i t s a b i l i t y to adsorb i n the i n t e r f a c e . For these reasons, p r o t e i n s provide a v a r i e t y o f responses t o compositional f a c t o r s , e.g., pH, i o n i c composition, chemical e m u l s i f i e r s , and processing treatments. P r o t e i n s c o n t r i b u t e t o emulsion s t a b i l i t y under those compositional and processing c o n d i t i o n s that favor t h e i r own s t a b i l i t y , but a l s o produce emulsion i n s t a b i l i t y under adverse compositional and proc e s s i n g c o n d i t i o n s which reduce t h e i r s t a b i l i t y . U n d e r proper cond i t i o n s p r o t e i n s provide an i n d i s p e n s a b l e s t a b i l i z i n g f u n c t i o n i n emulsions which are subsequently subjected t o a v a r i e t y of food processing treatments such as freeze-thaw, d e h y d r a t i o n - r e h y d r a t i o n , u l t r a - h i g h temperature (UHT) s t e r i l i z a t i o n , and o t h e r s . M i l k P r o t e i n s as E m u l s i f i e r s i n M i l k Systems P r o p e r t i e s o f m i l k f a t g l o b u l e s . M i l k f a t g l o b u l e s (MFG) range i n s i z e from 0.1 t o 10 ym diameter, w i t h an average of 2 t o 4 ym and are surrounded by a p r o t e c t i v e membrane (MFGM), which c o n s i s t s of p h o s p h o l i p i d s , l i p o p r o t e i n s , caseins and immunoglobulins 05,6). Several models have been proposed f o r the s t r u c t u r e of MFGM i n f r e s h l y drawn m i l k (_5,6., 7). King's model (7) d e p i c t s a h i g h l y ordered s t r u c t u r e w i t h successive l a y e r s o f high m e l t i n g t r i g l y c e r i d e s , phospholipids and adsorbed p r o t e i n s . Harper and H a l l (5) present a somewhat more s i m p l i f i e d model w i t h an intermediate p h o s p h o l i p i d l a y e r that provides p o l a r regions f o r attachment o f strongly-bound, i n s o l u b l e p r o t e i n s surrounded by an outer l a y e r o f loosely-bound, s o l u b l e p r o t e i n s (Figure 2). The loosely-bound p r o t e i n l a y e r i s r e a d i l y removed by t r e a t i n g w i t h detergents and by processing treatments that provide s u f f i c i e n t shear f o r c e s , such as mixing and churning. The most t i g h t l y bound p r o t e i n s i n the MFGM are h i g h l y a s s o c i a t e d , hydrophobic l i p o p r o t e i n s whose o r i g i n i s membrane m a t e r i a l derived from s e c r e t o r y processes i n the mammary system (5). The p r o t e i n s and phospholipids i n the MFGM c o n t r i b u t e s u b s t a n t i a l l y t o the s t a b i l i t y of the n a t u r a l MFG by c o n t r o l l i n g the degree of c l u s t e r i n g o f the globules v i a an a g g l u t i n a t i o n mechanism s i m i l a r t o that o f b a c t e r i a l c e l l s , but does not c o n t r i b u t e s i g n i f i c a n t l y t o emulsion s t a b i l i t y i n homogenized m i l k products. Casein m i c e l l e s , adsorbed from the aqueous phase, cont r i b u t e most t o the s t a b i l i t y o f d e r i v e d MFG i n homogenized m i l k products (8), but phospholipids a l s o c o n t r i b u t e t o t h e i r s t a b i l i t y . Homogenization i s an i n d i s p e n s a b l e processing treatment f o r



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Emulsifiers: Milk Proteins

Figure 1.

INSOLUBLE

DLVO Theory for explaining emulsion stability

PROTEIN . APOLAR GROUP JL (HYDROPHOBIC) POLAR GROUP A (NYDROPHYUO

SOLUBLE PROTEINUPK> COMPLEX

"PHOSPHOLIPID

Figure 2. AVI Publishing Company, Inc.

Diagram of milk fat globule membrane (5)



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m i l k products that r e q u i r e high emulsion s t a b i l i t y , e.g., f l u i d homogenized m i l k , evaporated m i l k , i c e cream and others. The s m a l l s i z e of the MFG i n these products (0.1 to 1.0 urn) i s important i n that i t r e s u l t s i n a l a r g e surface/volume r a t i o and enhanced p r o t e i n a d s o r p t i o n , which p r o t e c t s against a s s o c i a t i o n of the MFG and f u r t h e r minimizes t h e i r tendency to cream by i n c r e a s i n g t h e i r buoyant d e n s i t y . The u n i f o r m i t y of s i z e a l s o minimizes t h e i r tend ency f o r v a r y i n g r a t e s of r i s e , as p r e d i c t e d by Stokes' Law ( 3 ) . The MFG-casein m i c e l l e complex that forms during homogenizat i o n i s s t a b i l i z e d by van der Waals and hydrophobic bonding (6,10). Various workers have confirmed the a s s o c i a t i o n of c a s e i n m i c e l l e s and t h e i r subunits at f r e s h l y formed MFG during homogenization (8). Berger (11) proposed that c a s e i n m i c e l l e s are d i s r u p t e d during high pressure treatments such as during homogenization. This i n t e r p r e t a t i o n i s l o g i c a l i n view of the previous f i n d i n g s of Schmidt and Buchheim (12) that c a s e i n m i c e l l e s are e f f e c t i v e l y d i s r u p t e d under high pressure treatments. M i l k p r o t e i n system. The nomenclature and physico-chemical p r o p e r t i e s of the major m i l k p r o t e i n s and t h e i r subunits have been provided by Whitney et a l . (13) and Brunner (14). The conformation and r e l a t e d p r o p e r t i e s of the i n d i v i d u a l p r o t e i n s and t h e i r subu n i t s and aggregates have been reviewed by Morr (15) with s p e c i a l reference to t h e i r f u n c t i o n a l p r o p e r t i e s i n food systems, and drawing h e a v i l y upon previous c o n s i d e r a t i o n s by Bloomfield and Mead (16) and S l a t t e r l y (17). The c a s e i n s , which represent about 80 % of the t o t a l p r o t e i n s i n m i l k , and are p r e c i p i t a t e d from m i l k by a d j u s t i n g the pH to t h e i r i s o e l e c t r i c p o i n t s (4.5-5.0),are composed of three major components, o t - , 3- and κ-caseins, each of which has been f u r t h e r f r a c t i o n a t e d i n t o a number of s u b f r a c t i o n s (13). The caseins are present i n m i l k as an e q u i l i b r i u m between s o l u b l e , s u b m i c e l l a r complexes and the l a r g e r , s p h e r i c a l aggregates, termed m i c e l l e s . This e q u i l i b r i u m i s dependent upon pH, i o n i c a c t i v i t i e s (mainly Ca and PO4 i o n s ) , temperature and other f a c t o r s (18). The caseins are a s s o c i a t e d w i t h a f a i r l y constant p r o p o r t i o n of i n o r g a n i c c o l l o i d a l phosphate which c o n t r i b u t e s s u b s t a n t i a l l y to t h e i r s t r u c t u r a l arrangement and i n t e g r i t y . Casein m i c e l l e s i n m i l k range i n s i z e from about 100 to 250 nm diameter, e x h i b i t sedimenta t i o n constants of 8 to 22 X 1 0 S, molecular weights of 2 to 18 X ΙΟ** Daltons, and are composed of from 450 to 10,000 casein subu n i t s (15,17). A number of models have been proposed f o r these complex s t r u c t u r e s (15) and even though they remain the subject of i n t e n s i v e research by m i l k p r o t e i n chemists (19), the model pre sented i n Figure 3 accomodates most of the present knowledge of the m i c e l l a r system. Even though c a s e i n m i c e l l e s are remarkably s t a b l e i n m i l k under normal c o n d i t i o n s , they are q u i t e s u s c e p t i b l e to minor a l t e r a t i o n s i n pH, i o n i c composition and to treatment w i t h the enzyme rennin which cleaves the glycomacropeptide (GMP) p o r t i o n of the κs

2



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c a s e i n component of the m i c e l l e (18). Of s p e c i a l i n t e r e s t to the present c o n s i d e r a t i o n i s the observation that c a s e i n m i c e l l e s are e f f e c t i v e l y d i s r u p t e d by a p p l i c a t i o n of high pressures (12) and i t may be p o s t u l a t e d that such d i s r u p t i o n s probably i n v o l v e the rup ture of hydrophobic bonding that i s so important i n s t a b i l i z i n g the m i c e l l a r s t r u c t u r e . Whey p r o t e i n s , e.g., α-lactalbumin, β-lactoblobulin, bovine serum albumin and the immunoglobulins, remain s o l u b l e when m i l k i s t r e a t e d w i t h a c i d o r r e n n i n t o p r e c i p i t a t e the c a s e i n s . The whey p r o t e i n s , other than the e u g l o b u l i n component of the immunoglobu l i n s , do not p l a y a s i g n i f i c a n t r o l e i n s t a b i l i z i n g the MFG i n m i l k . E u g l o b u l i n i s reported t o p l a y an important f u n c t i o n i n the c l u s t e r i n g of MFG due to an a g g l u t i n a t i o n r e a c t i o n s i m i l a r t o that f o r b a c t e r i a l c e l l s . The whey p r o t e i n s exert a pronounced i n f l u e n c e on the physico-chemical p r o p e r t i e s of the c a s e i n m i c e l l e s (18)by t h e i r strong tendency to i n t e r a c t w i t h the κ-casein subunits i n the m i c e l l e through d i s u l f i d e interchange r e a c t i o n s when subjected to processing c o n d i t i o n s that promote p r o t e i n denaturation. I t may be presumed that such p r o t e i n - p r o t e i n i n t e r a c t i o n s probably a l t e r the a b i l i t y of the c a s e i n m i c e l l e s to be d i s r u p t e d by high pressure treatments and might thereby i n h i b i t t h e i r a b i l i t y to s t a b i l i z e MFG i n c e r t a i n m i l k products subjected t o high heat p r o c e s s i n g . Attempts to i s o l a t e and c h a r a c t e r i z e MFGM p r o t e i n s have not been completely s u c c e s s f u l due to t h e i r strong tendency to a s s o c i ate i n most p r o t e i n d i s s o c i a t i n g b u f f e r s . Thus, t h e i r r o l e i n s t a b i l i z i n g m i l k emulsions i s not e n t i r e l y understood (6,14), even though i t i s assumed that they are an i n t e g r a l part of the MFGM system. M i l k P r o t e i n s as E m u l s i f i e r s i n Food Systems M i l k p r o t e i n products. As i n d i c a t e d i n Table 1, the food i n d u s t r y i s p l a c i n g major emphasis on the production and u t i l i z a t i o n of m i l k p r o t e i n products i n a wide v a r i e t y of formulated food products (20,21,22). Although nonfat dry m i l k (NFDM) and whey powder are major m i l k p r o t e i n i n g r e d i e n t s i n formulated foods, c a s e i n and whey p r o t e i n concentrates, which c o n t a i n t h e i r p r o t e i n s i n a more h i g h l y concentrated and f u n c t i o n a l form, are e s s e n t i a l f o r c e r t a i n food product a p p l i c a t i o n s , such as those products that r e q u i r e the p r o t e i n s as an e m u l s i f i e r agent. A d d i t i o n a l d e t a i l s on the processing methods and c o n d i t i o n s used t o produce the v a r i o u s m i l k p r o t e i n products a r e a v a i l a b l e (23). NFDM, which r e t a i n s c a s e i n m i c e l l e s s i m i l a r to those i n f r e s h m i l k , i s produced by p a s t e u r i z a t i o n of skimmilk, vacuum concentra t i o n and spray d r y i n g under processing c o n d i t i o n s that r e s u l t i n e i t h e r "low heat" or "high heat" product. Low heat NFDM i s r e q u i r e d f o r most a p p l i c a t i o n s that depend upon a h i g h l y s o l u b l e p r o t e i n , as the case f o r most e m u l s i f i c a t i o n a p p l i c a t i o n s , s i n c e i t i s manufactured under m i l d temperature c o n d i t i o n s t o minimize whey p r o t e i n denaturation and complexation w i t h c a s e i n m i c e l l e s .



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Table 1. U.S. P r o d u c t i o n / U t i l i z a t i o n of M i l k P r o t e i n Products i n Human Foods - 1978 Amount, m i l l i o n //

Product Non-Fat Dry M i l k Casein & Caseinate

928.8 75-90

IN

a

P r o t e i n Content, %, dry b a s i s 36 95

Concentrated Whey S o l i d s

118.2

13

Dry Whey

534.7

13

P a r t l y Delactosed Whey

32.2

20

P a r t l y Demineralized Whey

28.6

13+

Whey P r o t e i n Concentrate Whey S o l i d s i n wet blends

FOODS

8.9

50

34.4

13

S t a t i s t i c a l data provided by:American Dry M i l k I n s t i t u t e , Chicago, I L ; Whey Products I n s t i t u t e , Chicago, I L ; and New Zealand M i l k Products, I n c . , Rosemont, I L .


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CASEIN MICELLE

» Figure 3.

100 - 250 nm

1

Proposed model for casein micelles and submicelles

SKIMMILK

I

PASTEURIZE RENNET"

ADJUST pH TO 4.5-5 HCI/H2S0 OR LACTIC FERMENTATION 4

FILTRATION/CENTRIFUGATION

FILTRATION/CENTRIFUGATION

WASH

I

I

WASH

DRY

1

1 RENNET CASEIN

NEUTRALIZE NoOH/ CcK0H) / Κ0Η 2

I

CASEINATE DRY Figure 4.

Production scheme for casein and caseinate



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Casein i s o l a t e s , produced as caseins and c a s e i n a t e s , are ob tained by two procedures: rennet treatment and a c i d p r e c i p i t a t i o n (Figure 4). Rennet c a s e i n i s produced by t r e a t i n g skimmilk w i t h the enzyme rennin to cleave the GMP component of the κ-casein subunit and thereby render the e n t i r e c a s e i n m i c e l l e system u n s t a b l e . The product represents an e n z y m a t i c a l l y modified p r o t e i n product, which otherwise c l o s e l y resembles the n a t i v e c a s e i n m i c e l l e system i n m i l k . I t contains the o r i g i n a l Ca content of the n a t i v e m i c e l l e s , but i s i n s o l u b l e and n o n f u n c t i o n a l as an e m u l s i f i e r unless the Ca i o n content i s diminished. A c i d c a s e i n i s produced by t r e a t i n g skimmilk w i t h h y d r o c h l o r i c or s u l f u r i c a c i d s , or by fermentation w i t h a l a c t i c a c i d c u l t u r e to lower the pH to i s o e l e c t r i c point c o n d i t i o n s to p r e c i p i t a t e the c a s e i n s . Casein m i c e l l e s are comp l e t e l y d i s s i p a t e d under the l a t t e r treatment and the c a s e i n subu n i t s undergo a high degree of p r o t e i n - p r o t e i n i n t e r a c t i o n to form p r e c i p i t a t e d p a r t i c l e s that are e a s i l y recovered by f i l t r a t i o n or c e n t r i f u g a t i o n . Sodium and potassium c a s e i n a t e s , and calcium caseinates are produced by n e u t r a l i z a t i o n w i t h the appropriate a l k a l i to pH's of 8-10 to s o l u b i l i z e the c a s e i n p r e c i p i t a t e , and then spray dryed. Both sodium and potassium caseinates are t o t a l l y s o l u b l e i n water and form v i s c o u s s o l u t i o n s that e x h i b i t e x c e l l e n t f u n c t i o n a l i t y i n a wide v a r i e t y of food products which r e q u i r e e m u l s i f i c a t i o n . On the other hand, calcium caseinate i s v i r t u a l l y i n s o l u b l e and performs r a t h e r poorly i n most e m u l s i f i e r a p p l i c a t i o n s (21) . P a r t l y delactosed whey i s produced by concentrating cheese whey or c a s e i n whey s u f f i c i e n t l y to exceed the s o l u b i l i t y l i m i t of l a c t o s e , followed by c o o l i n g , seeding w i t h l a c t o s e c r y s t a l s and removal of the c r y s t a l l i n e l a c t o s e . The r e s u l t i n g l i q u o r f r a c t i o n i s recovered and dryed. P a r t l y demineralized whey i s produced by s u b j e c t i n g whey to e l e c t r o d i a l y s i s or i o n exchange processing treatments to prederent i a l l y remove p o l y v a l e n t i o n s , vacuum concentrated and spray dryed. Whey p r o t e i n concentrates (WPC) are produced by a v a r i e t y of processing treatments to remove both l a c t o s e and minerals (20) as i n d i c a t e d i n F i g u r e 5. Even though i t would be h i g h l y d e s i r e a b l e to remove most of the l a c t o s e and minerals i n these processes, i t i s not p r a c t i c a l from an economic standpoint and thus most of these products only range i n p r o t e i n content from 35 to 50 %.The major o b j e c t i v e of most of these processes i s to produce a WPC w i t h minimal p r o t e i n denaturation i n order to o b t a i n a product w i t h maximum p r o t e i n s o l u b i l i t y and f u n c t i o n a l i t y . However, from a p r a c t i c a l c o n s i d e r a t i o n t h i s o b j e c t i v e i s not r e a d i l y o b t a i n a b l e , and thus most WPC products commercially a v a i l a b l e e x h i b i t v a r i a b l e whey p r o t e i n denaturation and f u n c t i o n a l i t y (20). Lactalbumin i s an i n s o l u b l e whey p r o t e i n product produced by heating whey to high temperatures ( > 90 C) to denature and render the p r o t e i n s i n s o l u b l e when adjusted to i s o e l e c t r i c c o n d i t i o n s by the a d d i t i o n of a c i d . These p r o t e i n s o f f e r l i t t l e f u n c t i o n a l i t y in emulsification applications.


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209


C o - p r e c i p i t a t e i s an i n s o l u b l e m i l k p r o t e i n product that i s produced by heating skimmilk t o high temperatures ( > 90 C) t o denature the whey p r o t e i n s and complex them w i t h the c a s e i n m i c e l l e s . The heated system i s subsequently adjusted t o i s o e l e c t r i c p o i n t c o n d i t i o n s of pH 4.5-5 to p r e c i p i t a t e the complexed whey p r o t e i n - c a s e i n m i c e l l e s , c e n t r i f u g e d or f i l t e r e d t o recover the p r e c i p i t a t e , washed and dryed. The r e s u l t i n g product, which i s v i r t u a l l y i n s o l u b l e , e x h i b i t s only minor f u n c t i o n a l i t y i n most typical emulsification applications. E m u l s i f i c a t i o n p r o p e r t i e s . Caseins and caseinates a r e common l y s e l e c t e d f o r food product a p p l i c a t i o n s that r e q u i r e s u r f a c t a n t p r o p e r t i e s , e.g., e m u l s i f i c a t i o n and foam s t a b i l i z a t i o n , s i n c e they c o n t a i n high p r o t e i n contents o f > 90 %, are h i g h l y s o l u b l e , and are r e s i s t a n t to heat-induced denaturation i n products to be subjected t o high temperature processing c o n d i t i o n s (15). C o n s i d e r a t i o n of the conformational s t a t e s of the major c a s e i n subunits (Figure 6) r e v e a l s that they c o n s i s t of a non uniform d i s t r i b u t i o n of p o l a r and hydrophobic residues along t h e i r polypeptide chains (16,17) l e a d i n g t o an amphophilic molecule (17). These amphophilic c a s e i n subunits e x h i b i t s i m i l a r primary s t r u c t ures among the d i f f e r e n t c a s e i n s , e.g., a - , 3-, and κ-, that account f o r t h e i r e x c e l l e n t s u r f a c t a n t p r o p e r t i e s (15). These c a s e i n subunits are h i g h l y s u s c e p t i b l e t o i n t e r a c t i o n s v i a l hydro phobic and i o n i c bonding, and thus e x i s t i n the form of h i g h l y a s s o c i a t e d aggregates that r e q u i r e h i g h l y a l k a l i n e pH c o n d i t i o n s , removal of Ca i o n s , and the use of strong p r o t e i n d i s s o c i a t i n g against Such as urea and others to o b t a i n complete monomerization (24). I t should t h e r e f o r e be assumed that caseins and caseinates e x i s t and f u n c t i o n i n most food a p p l i c a t i o n s i n t h e i r h i g h l y a s s o c i a t e d form which possess the a b i l i t y t o r e l e a s e subunits as needed t o s t a b i l i z e emulsion globules as they are formed i n homogenization processing (15). I f i t i s assumed that those * f a c t o r s that favor d i s s o c i a t i o n of c a s e i n complexes favor i t s f u n c t i o n a l i t y as an e m u l s i f i e r , i t may be p o s s i b l e t o p r e d i c t what compositional and processing c o n d i t i o n s would optimize f u n c t i o n a l i t y . However, such adjustments i n processing c o n d i t i o n s would a l s o a f f e c t the i n t r i n s i c .properties o f the emulsion system. Thus, i t becomes o b l i g a t o r y , i n most i n s t a n c e s , to i n v e s t i g a t e and determine experimentally the s p e c i f i c c o n d i t i o n s that should be s e l e c t e d to optimize the f u n c t i o n a l i t y of caseins i n food emulsion systems. s

E m u l s i f i c a t i o n p r o p e r t i e s i n model food systems. Pearson et a l . (25) i n v e s t i g a t e d the e m u l s i f i c a t i o n p r o p e r t i e s of caseinate and NFDM i n model emulsion systems produced by blending soybean o i l i n t o an aqueous b u f f e r system as a f u n c t i o n of pH and i o n i c strength (Figures 7 and 8). They found that caseinate e x h i b i t e d good e m u l s i f i c a t i o n p r o p e r t i e s under a l l pH and i o n i c s t r e n g t h c o n d i t i o n s s t u d i e d , but was p a r t i c u l a r l y e f f e c t i v e a t pH 10.4.


210

PROTEIN

CONCENTRATION: VACUUM EVAPORATION REVERSE OSMOSIS

FUNCTIONALITY

IN

FOODS

t>

DEMINERALIZATION: ELECTRODIALYSIS TRANSPORT DEPLETION ION EXCHANGE

CONCENTRATED WHEY I

ψ

PARTIALLY

LACTOSE


CRYSTALLIZATION

DEMINERALIZED WHEY

PARTIALLY DELACTOSEDI WHEY I

{ FRACTIONATION: ULTRAFILTRATION CENTRIFUGAL G E L FILTRATION POLYPHOSPHATE COMPLEX CMC COMPLEX

DEMINERALIZATION: ELECTRODIALYSIS TRANSPORT DEPLETION ION EXCHANGE

P A R T I A L L Y DELACTOSED/ DEMINERALIZED WHEY

WHEY PROTEIN CONCENTRATE

Food Technology

Figure 5.

Processflowchartfor preparing whey protein concentrate (20)

10 20 H.Arg-Pro- Lys- Hit - Pro - lit - Lye-His- G l n - G l y - L t u - P r o - G l n ^ l u - V » l - L t u - - A « n - G l u - A » n - L t u Absent in variant A , 30 40 L^-Arg-Prie-Pbe-Val--Ale|-f*o-Pne-Pro-Gln-Val-P^ 50 00 S ^ - L y « - A « p - l t e - G r y - S ^ - G l u - S ^ - T h r - G l u - A i p - G I n jÂlâVMtt-Glu-Aip-lla - L y s - G l u - M t t P Ρ ThrP (variant D) 70 80 Glu-Ala-Glu-Sar-lle - Sar-Ser-Sar-Glu-Glu-lla - V a l - P r o - A i n - S e r - V a l - G l u - G I n - L y s - H l t 90 100 lie - Gln-Lys-Glu-Asp-Val-Pro-Sar-Glu-Arg-Tyr-Lau-Gly -Tyr-Leu-Glu-Gln-Lau-Leu-Arfl110 120 Lau-Lys-Lyi-Tyr-Lys-Val-Pro-Gln-Lau-Glu-lle - V a » - P r o - A » n - S e r - A l a - G l u - G l u - A r g - L j t u P 130 140 His - Sar - Mat- Lys- Gln-Gly-lla - His - A l a - G i n - Gin- Lys-Glu-Pro -Mat-lia - Gly-Val-Asn-GIn ISO 100 Glu-Leu-Ala -Tyr-ΡΝβ -Tyr-Pro-Glu-Leu-Phe-Arg - G l n - P h e - T y r - G l n - L e u - A t p - A l a - T y r - P r o 170

180

Sar- Gly-Ala - T r p - T y r - T y r - V a l - P r o - Ltu-Gly-Thr-Gln-Tyr-Thr-Asp-Ala-Pro-Sar-Pha-Sar190

199

Asp-Ik - Pro- As η - P r o - I la-Gly-Sar - G lu-Asn-Sar-JGÎ3-Lys -Thr -Thr-Mat-Pro- Lau-Trp.OH Gly (variante)

American Chemical Society

Figure 6.

Primary structure of bovine casein a -CN-B (15) 8


10.

MORR

211


pH βΗ βΗ βΗ

6.43,μ Ό.Ο5 δ.ΒΟ.μ Ό.Ο5 10.40.μ Ό.05 ê.90, WATER SOLUTION —μ Ό

^ 40f


•sof

?

I Of

0.1 a s - 0.4 OA 0.6

0.7

0J

OJ

PROTEIN NITROGEN CONCENTRATION

Food Technology

PROTEIN NITROGEN CONCENTRATION

Food Technology

Figure 7. Emulsification properties of potassium caseinate (25)

Figure 8. Emulsification properties of ΝFDM (25)



212

PROTEIN

FUNCTIONALITY IN FOODS

The e m u l s i f i c a t i o n p r o p e r t i e s o f NFDM were s l i g h t l y b e t t e r than f o r caseinate a t a l l p r o t e i n l e v e l s . However, NFDM e x h i b i t e d lowest e m u l s i f i c a t i o n p r o p e r t i e s a t pH 10.4 and highest e m u l s i f i c a t i o n a t pH 5.6, which was d i r e c t l y opposite the r e s u l t s w i t h caseinate. Thus, the molecular s t a t e of c a s e i n s , whether i n the. m i c e l l a r o r s o l u b l e complex form i s important i n determining t h e i r f u n c t i o n a l i t y as an e m u l s i f i e r . Subharwal and V a k a l e r i s (26,27) i n v e s t i g a t e d the emulsion s t a b i l i z i n g a b i l i t y of caseinate i n model emulsion systems c o n t a i n ing added chemical e m u l s i f i e r s to provide a range of HLB values (Figures 9 and 10). The e m u l s i f i c a t i o n p r o p e r t i e s of caseinate were c o n c e n t r a t i o n dependent, e x h i b i t i n g maximum e m u l s i f i c a t i o n at 0.2 t o 0.4 % caseinate i n the absence of chemical e m u l s i f i e r s , but e x h i b i t e d e m u l s i f i c a t i o n impairment a t 0.5 % caseinate i n the presence of HLB 11 e m u l s i f i e r s . A d d i t i o n of Ca and HLB 3-5 emulsif i e r s improved emulsion s t a b i l i t y , whereas, a d d i t i o n of c i t r a t e reduced emulsion s t a b i l i t y . These f i n d i n g s a r e c o n s i s t e n t w i t h the concept that Ca and c i t r a t e ions i n f l u e n c e emulsion s t a b i l i t y by a l t e r i n g the r e l a t i v e extent of caseinate d i s s o c i a t i o n and i n a d d i t i o n they undoubtedly i n f l u e n c e emulsion s t a b i l i t y by t h e i r e f f e c t s on the charge and other inherent p r o p e r t i e s of the emulsion g l o b u l e s , per se. Whey p r o t e i n concentrates (WPC), which a r e r e l a t i v e l y new forms of m i l k p r o t e i n products a v a i l a b l e f o r e m u l s i f i c a t i o n uses, have a l s o been s t u d i e d (4,28,29). WPC products prepared by g e l f i l t r a t i o n , u l t r a f i l t r a t i o n , metaphosphate p r e c i p i t a t i o n and carboxymethyl c e l l u l o s e p r e c i p i t a t i o n a l l e x h i b i t e d i n f e r i o r emulsi f i c a t i o n p r o p e r t i e s compared t o c a s e i n a t e , both i n model systems and i n a simulated whipped topping f o r m u l a t i o n (28). However, a d d i t i o n a l work i s proceeding on t h i s t o p i c and i t i s expected that WPC w i l l be found to be capable of p r o v i d i n g reasonable f u n c t i o n a l i t y i n the e m u l s i f i c a t i o n area, e s p e c i a l l y i f proper processing c o n d i t i o n s a r e followed t o minimize p r o t e i n denaturat i o n during t h e i r production. Such adverse e f f e c t s on the f u n c t i o n a l i t y of WPC a r e undoubtedly due t o t h e i r i r r e v e r s i b l e i n t e r a c t i o n during heating processes which impair t h e i r a b i l i t y to d i s s o c i a t e and u n f o l d a t the emulsion i n t e r f a c e i n order t o f u n c t i o n as an e m u l s i f i e r (22). Conclusions The f o l l o w i n g f a c t o r s appear t o c o n t r o l the e m u l s i f i c a t i o n p r o p e r t i e s of m i l k p r o t e i n s i n food product a p p l i c a t i o n s : 1) the physico-chemical s t a t e of the p r o t e i n s as i n f l u e n c e d by pH, Ca and other p o l y v a l e n t i o n s , denaturation, aggregation, enzyme m o d i f i c a t i o n , and c o n d i t i o n s used t o produce the emulsion; 2) compo s i t i o n and processing c o n d i t i o n s w i t h respect t o l i p i d - p r o t e i n r a t i o , chemical e m u l s i f i e r s , p h y s i c a l s t a t e of the f a t phase, i o n i c a c t i v i t i e s , pH, and v i s c o s i t y of the d i s p e r s i o n phase s u r rounding the f a t g l o b u l e s ; and 3) the sequence and process f o r i n c o r p o r a t i n g the r e s p e c t i v e components of the emulsion and f o r forming the emulsion.



MORR

213


02

OA

0.6

08

1.0

20

1.5

25

SODIUM CASEINATE (%)

Journal of Dairy Science

Figure 9. Emulsification properties of sodium caseinate in the absence of chemical emulsifiers (26)

40

J

02

OA

06

1

//

1

//

08 LO 15 S O D I U M C A S E I N A T E (%)

'

2.0

// J

2J5

Journal of Dairy Science

Figure 10. Emulsification properties of sodium caseinate in the presence of HLB 11 emulsifiers (26)



214

PROTEIN

FUNCTIONALITY

IN FOODS

I t i s e s s e n t i a l t o consider the physico-chemical p r o p e r t i e s of each WPC and c a s e i n product i n order t o e f f e c t i v e l y evaluate t h e i r e m u l s i f i c a t i o n p r o p e r t i e s . Otherwise, r e s u l t s merely i n d i c a t e the previous p r o c e s s i n g c o n d i t i o n s r a t h e r than the inherent f u n c t i o n a l p r o p e r t i e s f o r these v a r i o u s products. Those p r o c e s s i n g treatments that promote p r o t e i n d e n a t u r a t i o n , p r o t e i n - p r o t e i n i n t e r a c t i o n v i a d i s u l f i d e interchange, enzymatic m o d i f i c a t i o n and other b a s i c a l t e r a t i o n s i n the physico-chemical p r o p e r t i e s of the p r o t e i n s w i l l o f t e n r e s u l t i n p r o t e i n products w i t h u n s a t i s f a c t o r y e m u l s i f i c a t i o n p r o p e r t i e s , s i n c e they would l a c k the a b i l i t y t o u n f o l d a t the emulsion i n t e r f a c e and thus would be unable t o f u n c t i o n . I t i s recommended that those f a c t o r s normally considered f o r production of p r o t e i n products t o be used i n foam formation and foam s t a b i l i z a t i o n be considered a l s o , s i n c e both phenomena possess s i m i l a r physico-chemical and f u n c t i o n a l i t y requirements (30,31).

Literature Cited 1. Friberg, S., "Food Emulsions", Marcel Dekker, Inc., New York, N.Y. 1976. 2. Cante, C.J.; Franzen, R.W.; Saleeb, F.Z. J. Am Oil Chem. Soc., 1979, 56, 71A. 3. Jenness, R.; Patton, S."Principles of Dairy Chemistry", Wiley and Sons, New York, N.Y., 1959. 4. Tornberg, E.; Hermannson, A.M. J. Food Sci., 1977, 42, 468. 5. Harper, W.J. In "Dairy Technology and Engineering" W.J. Harper and C.W. Hall, Eds. AVI Pub. Co., Inc., Westport, Conn., 1976. 6. Brunner, J.R. In "Fundamentals of Dairy Chemistry", B.H. Webb and A.H. Johnson, Eds. AVI Pub. Co., Inc., Westport, Conn., 1965. 7. King, N. "The Milk Fat Globule Membrane", Comm. Agr. Bur., Farnham Royal, Bucks, England, 1955. 8. Graf, E.; Bauer, H. In "Food Emulsions", S. Friberg, Ed., Marcel Dekker, Inc., New York, N.Y., 1976. 9. Ogden, L.V.; Walstra, P.; Morris, H.A. J. Dairy Sci., 1976, 59, 1727. 10. Fox, K.K.; Holsinger, V.; Caha, J.; Pallansch, M.J. J. Dairy Sci., 1960, 43, 1396. 11. Berger, Κ.G. In "Food Emulsions", S. Friberg, Ed. Marcel Dekker, Inc., New York, N.Y., 1976. 12. Schmidt, D.G.; Buchheim, W. Milchwissenschaft, 1970, 25, 596. 13. Whitney, R. McL.; Brunner, J.R.; Ebner, K.E.; Farrell, H.M., Jr.; Josephson, R.V.; Morr, C.V.; Swaisgood, H.E. J. Dairy Sci., 1976, 59, 795. 14. Brunner, J.R. In "Food Proteins", J.R. Whitaker and S.R. Tannenbaum, Eds. AVI Pub. Co., Inc., Westport, Conn., 1977. 15. Morr, C.V. In "Functionality and Protein Structure", A. Pour-El, Ed. American Chemical Society, Washington, D.C., 1979.


10. MORR 16. 17. 18. 19. 20. 21. 22.


23. 24. 25. 26. 27. 28. 29. 30. 31.


215

Bloomfield, V.A.; Mead, R.J., Jr. J. Dairy Sci., 1975, 58, 592. Slatterly, C.W. J. Dairy Sci., 1976, 59, 1547. Morr, C.V. J. Dairy Sci., 1976, 58, 977. Payens, T.A.J. J. Dairy Res., 1979, 46, 291. Morr, C.V. Food Technol., 1976, 30, 18. Morr, C.V. J. Dairy Res., 1979, 46, 369. Morr, C.V. New Zealand J. Dairy Sci. and Technol., 1979, 14, 185. Fox, K.K. In "Byproducts from Milk", B.H. Webb and E.O. Whittier, Eds. AVI Pub. Co., Inc., Westport, Conn., 1970. von Hippel, P.H.; Waugh, D.F. J. Am. Chem. Soc., 1955, 77, 4311. Pearson, A.M.; Spooner, M.E.; Hegarty, G.R.; Bratzler, L.J. Food Technol., 1965, 19, 1841. Subharwal, K.; Vakaleris, D.G. J. Dairy Sci., 1972, 55, 277. Subharwal, K.; Vakaleris, D.G. J. Dairy Sci., 1972, 55, 283. Morr, C.V.; Swenson, P.E.; Richter, R.L. J. Food Sci., 1973, 32, 324. Wit, J.N. de; Boer, R. de Zuivelzicht, 1976, 68, 442. Cooney, C.M. Dissertations Abstracts International, 1975, B36, 1123. Richert, S.H.; Morr, C.V.; Cooney, C.M. J. Food Sci., 1974, 39, 142.

RECEIVED

September 5, 1980.


Emulsifiers: Milk Proteins - American Chemical Society

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