SURFACTANTS: BASICS AND VERSATILITY IN FOOD INDUSTRIES

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If we discuss about an ice cream, partially frozen foam that is 40–50% air (by volume). The first step in formulating ice cream is to create an emulsion. The homogenization step forces the hot ingredients (milk fats, milk solids-no-fat, sweeteners, corn-syrup solids, stabilizers/ emulsifiers, other dry solids) through small stirring under moderate pressure. Diameter of fat droplet decreases to 0.4 to 2.0 μm approximately, allowing a large surface area for adsorption of proteins (which in responsible for stabilization of emulsion), and the uniformity of drop sizes result in greater stability of fat droplets during ageing process and made more uniform final food product. The adsorption of emulsifiers (such as Lecithins, Tweens, MDG) decreases the interfacial tension between fat globules and the surrounding liquid phase, even more than does just mere adsorption of proteins (to about 2.2 dyne/cm). The stabilizers (such as guar, carboxymethyl cellulose, xanthan, etc.) are used to produce smoothness in body and texture, reduce the ice content and lactose crystal growth during storage,  provide the product uniformity and resist against easy melting20.The second stage in ice cream production is foaming and emulsion destabilization. This is analogous to the foaming step in whipped cream21,22.Air is incorporated by whipping or by air injection. The added shear causes controlled partial coalescence (enhanced by the adsorbed surfactants), causing air to be trapped in clumped fat globules, and also ice formation. When whipping and freezing occur simultaneously, good fat destabilization is achieved and a complex internal structure is achieved20.

Surfactants are a key component in the manufacture of edible coatings. A finish coat or polish may be added to chocolate- and sugar-panned confectionery products to produce an aesthetically pleasing gloss. These are commonly alcohol-based shellac and corn zein coatings, but may also include water-based whey proteins23.Surfactants are added to create a dispersion of the coating particles, which then allows for proper wetting and adhesion over the candy surface. The problem with chocolate blend coating is happened when the fat crystalizes and the cocoa butter separates. MDG, LACTEM, polysorbates are added as crystal modifiers/emulifiers to stabilize the coating. The latter may also be used to increase the palatability of the confection by forming an emulsion between the fat and mouth saliva, which minimizes the waxy mouthfeel24.

As monoglycerides, MDGs increase the fermentation stability of dough, bread and fermented bakery goods. The general dosage is 0.2% of the flour weight. Other major uses of MDGs are sponge cakes and cakes margarines, ice creams and chewing gums19. Diacetyltartaric acid esters, DATEM, are commonly used as dough conditioners for all baked products, particularly yeast-leavened products, white bread and in flour mixes for quality foods. Their approximate dosage is between 0.2% and 0.5% of the flour weight. They are also used in dairy products and approved for use in special infant formulae based on crystalline amino acids16. Sodium stearoyl-2-lactylate (SSL) and calcium stearoyl-2-lactylate (CSL), commonly applied anionic surfactants in breadmaking processes to improve dough gas retention and stability to yield a finer structure in the final product. SSL is used in yeast-leavened products usually in a dosage of about 0.4%. They are also used in breakfast cereals, cookies, crackers, cereal and potato based snacks and quick cook rices16,25.

In the USA sucrose esters are used in breads but oppsitely the use of sucrose esters is not permitted in breads at Europe. As sucrose esters have excellent ability to stabilize emulsions these are utilized to dressing sauces, mayonnaise-like products, and ice creams. The use of sucrose ester in infant foods is very vital. During the production of infant formulas (given instead of milk) the proteins which are already in the product are usually enough to ensure colloid stability of the emulsion. However, in the case of hypoallergenic products containing hydrolyzed proteins, peptides or free amino acids, the use of emulsifiers is necessary to stabilize the emulsion. That is the reason why sucrose esters are used in special baby formula products made for allergic infants19,25. Polyglycerol esters of fatty acids are applied in the formulation of low fat margarines, spreads, butter creams and breakfast cereals. Special types of polyglycerol esters are used as crystallization inhibitors in the oil and fat industry to prevent the formation of turbidity of sunflower oils during storage. Sorbitan esters of fatty acids (Span series) and their ethoxylated derivatives Polysorbates (Tween series) are excellent emulsifiers, aerating agents and lubricants in cakes, toppings, cookies and crackers. Polysorbate 60 is used as dough strengthener co-emulsifier in bakery products. The usual dosage is 0.2% of flour weight. Polysorbate 80 is often used in dairy products, ice creams, and whipped cream and non-dairy cream alternatives26. Surfactant mixtures are usually much more effective than using a single surfactant alone. Therefore, surfactants are usually used in combinations. For example a common bread surfactant combination contains mono- and diglycerides of fatty acids. A fluid cake shortening (semisolid fats used in food preparation, especially for baked goods) can contain a combination of Polysorbate 60, glyceryl monostearate and propylene glycol monostearate. Other popular example in food was shown in beer manufacturing26. The quality of beer is mainly judged by the foam creation of the dispensed beer. Desirable visual qualities include stability, lacing (adhesion), whiteness, creaminess and strength.Foam stability is the perceived best indicator of a good beer. Foam stabilization comes from amphipathic polypeptides from malt and bitter compounds, particularly iso-α-acids, and from the absence of lipophilic materials. Unlike champagne, where foam film lifetimes are short (hydrodynamic control), beer foam has a slower drainage rate due to the effect of disjoining pressure of two interfaces in close proximity. A beer that has smaller bubbles of uniform size tends to have more stable foam. Several reviews have been written on this aspect of beer (and champagne) foams27,28.

4. Conclusions
Surfactants are amphiphilic compounds containing both hydrophobic (nonpolar) and hydrophilic (polar) moieties that confer ability to accumulate between fluid phases such as oil/water or air/water, reducing the surface and interfacial tensions and forming emulsions and micelles. The surface activity properties make surfactants one of the most important and versatile class of chemical products, used on a variety of applications in household, food, paint, paper, and agriculture industries. Surfactant molecules, which are an important part of the food emulsions, play a key role in determining the microstructure of the product and in affecting its structural and textural stability in the food. Naturally occurring surfactants like lecithins, MDGs, various saturated, unsaturated and trans fatty acids and functionalized proteins as well as synthetic surfactants Tweens, SSL, CSL and sucrose esters etc. are often used in the preparation of food products such as mayonnaise, salad creams, dressings, deserts, coffee, icecreams etc. Also the biocompatible, biodegradable, and/or nontoxic emulsion-based formulations of surfactants like ACETAM, LACTEM, CITREM as well as DATEMhave great potential for food applications and which are discussed.

5. Acknowledgement
Financial assistance from University Grants commission(UGC), New Delhi Project no. F.41-1327/2012(SR) is gratefully acknowledged

6. References
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2. Myers, D., Surfactant Science and Technology, VCH, New York, 1988.
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12. Holmberg, K., Jonsson, B., Kronberg, B. and Lindman, B., “Surfactant and Polymer in Aqueous Solution”, Wiley & Sons, 2002.
13. Remington, A.R.G., The science and practice of pharmacy, 19th edition, Easton, PA, Mack publishing, 1995, 1 : 250–251.
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15. Zhang, W., Dai, X., Zhao, Y., Lu, X. and Gao, P., Langmuir, 2009, 25(4) : 2363-2368.
16. Hasenhuettl, G.L., Synthesis and Commercial Preparation of Food Emulsifiers, In “Food Emulsifiers and Their Applications”, (eds.) Hasenhuettl, G.L. and Hartel, R.W., Chapter-2, Springer Science, New York, 2008.
17. Kralova, I. and Sjoblom, J., “Surfactants used in Food Chemistry”, J. Dis. Sci. Tech., 2009, 30 :1363.
18. Web source; ec.europa.eu/food/food/fAEF/additives
19. Whitehurst, R.J., (ed) Emulsifiers in food technology, Oxford: Blackwell Publishing Ltd., 2004.
20. Goff, H. D., Int. Dairy J., 1997, 7 : 363.
21. Leser, M. E. and Michel, M., Curr. Opin. Colloid Interface Sci., 1999, 4 : 239.
22. Stainsby, G. and Dickinson, E., Actual. Chem., 1988, 3 : 35.
23. Trezza, T. A. and Krochta, J. M.,  J. Food Sci., 2000, 65 : 658.
24. Dziezak, J. D., Food Technol., 1988, 172.
25. Csáki, K. F., Med Hypotheses, 2011, article in press
26. Polysorbates, Evaluation report of food additives, Food safety commission, June 2007.
27. Evans, D. E., J. Am. Soc. Brewing Chem., 2002, 60 : 47.
28. Bamforth, C. W., J. Sci. Food Agric., 2000, 80 : 1371.

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