Surfactants in the food industry

Many food formulations contain mixtures of surfactants (emulsifiers) and hydrocolloids. Interaction between the surfactant and polymer molecule plays a major role in the overall interaction between the particles or droplets, as well as the bulk rheology of the whole system. Such interactions are complex and require fundamental studies of their colloidal properties. As discussed later, many food products contain proteins that are used as emulsifiers. Interaction between proteins and hydrocolloids is also very important in determining the interfacial properties and bulk rheology of the system. In addition, the proteins can also interact with the emulsifiers present in the system and this interaction requires particular attention. 

Applied Surfactants Pritwiples and Applications. Tharwat F. Tadros Copyright 2005 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 3-527-30629-3 

The structures of many food emulsions are complex and, often, several phases may exist. Such structures may exist under non-equilibrium conditions and the state of the system may depend largely on the preparation process employed, its prehistory and the conditions to which it is subjected. Unsurprisingly, therefore, fundamental studies on such systems are not easy, and in many cases one is content with some qualitative observations. However, due to the great demand of producing consistent food products and the introduction of new recipes, a great deal of fundamental understanding of the physical chemistry of such complex systems is required. 

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The high molar mass species reside mostly in the aqueous phase with a number of peptide groups residing in the oil/water interface [293]. Although these latter surfactants are less effective at reducing interfacial tension, they can form a viscoelastic membrane-like film around oil droplets or air bubbles. These tend to be used in the preparation of, for example, O/W emulsions. These trends are by no means exclusive, mixtures are the norm and competitive adsorption is prevalent. Caseinate, one of the most commonly used surfactants in the food industry, is itself a mixture of interacting proteins of varying surface activity [814],... 

The use of surfactants in the food industry has been known for centuries. Naturally occurring surfactants such as lecithin from egg yolk or soybean and various proteins from milk are used for the preparation of many food products, such as mayonnaise, salad creams, dressing, and desserts. Polar lipids such as monoglycerides have been introduced as emulsifiers for food products. More recently, synthetic surfactants such as sorbitan esters (Spans) and their ethoxylates (Tweens), sucrose esters, have been used in food emulsions. It should be mentioned that the structures of many food emulsions is complex, and in... 

Transitional phase inversion is a very effective process, but it is not used in the food industry due to the properties of the oils commonly used in foods, finding a surfactant system that exhibits this behaviour has not yet succeeded. The process is applied widely, however, in the cosmetic and coating industries. 

In the food industry the term emulsifier traditionally refers to a small molecular surfactant. An emulsifier does not necessarily confer long term stability - it simply has the capacity to adsorb rapidly at the fresh interface created during emulsification, thereby protecting newly formed oil-water droplets against immediate re-coalescence. 

Polysorbates are also commonly used as (O/W) emulsifiers in the food industry (salad dressing, ice cream), and in cosmetics, pharmaceuticals, detergents, and in a myriad of other industrial applications. Current Western Europe consumption of sorbitol for surfactants manufacture can be estimated at around 15,000 tons per year. 

With a few exceptions, most of the detailed research has been performed on relatively few proteins. Of these, the caseins (a , B and k) and whey proteins P-lactalbumin and B-lactoglobulin) predominate. This is principally because these proteins are readily available in pure and mixed forms in relatively large amounts they are all quite strongly surfactant and are already widely used in the food industry, in the form of caseinates and whey protein concentrates or isolates. Other emulsifying proteins are less amenable to detailed study by being less readily available in pure form (e.g., the proteins and lipoproteins of egg yolk). Many other available proteins are less surface active than the milk proteins, for example, soya isolates (49), possibly because they exist as disulfide-linked oligomeric units rather than as individual molecules (50). Even more complexity is encountered on the phos-phorylated lipoproteins of egg yolk, which exist in the form of granules (51), which themselves can be the surface-active units (e.g., in mayonnaise) (52). 

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