Alpha-cyclodextrin opens up a new emulsifying and texturizing technology

From ice-cream to mayonnaise, emulsifiers are used widely in the food industry to stabilize foods containing an oil and a water phase. At the same time, hydrocolloids are often added to achieve the desired food texture. However, in view of the current debate on clean labeling, as well as cholesterol and allergen contents, the use of these two types of food additive is often fraught with difficulties. Alpha-cyclodextrin, on the other hand, is able to both stabilize and texturize oil-in-water emulsions and thus makes it possible to achieve two effects with a single ingredient. The ring-shaped dextrin is non-animal derived, non-allergenic and obtained from renewable raw materials.

Ice-cream, salad dressings, whipping cream or mayonnaise: when it comes to food, oil-in-water emulsions are all around us. To stabilize these emulsions, emulsifiers are widely used in the food industry. By the same token, hydrocolloids are often added to influence the texture and viscosity of the end product. For food producers, this means having to constantly choose the right combination of emulsifier and texturizer to ensure a stable food matrix and the desired mouth-feel.

Classical emulsifiers and their drawbacks

Common emulsifiers include mono- and diglycerides (derivatives of fatty acids), lecithins which are also contained in egg yolk, as well as proteins and some low molecular weight emulsifiers. Animal-derived emulsifiers, however, have certain properties and characteristics that pose challenges to food manufacturers. These classical emulsifiers are usually quite sensitive to heat and acidic conditions, they can be allergenic and provide an undesired source of cholesterol. Liquid egg-based products also have the drawback of being difficult to handle and of losing viscosity during storage. Further, due to their animal origin, egg and protein-based emulsifiers raise concerns regarding possible contamination and food safety risks. There is thus great interest in finding a feasible alternative to animal-based emulsifiers for stabilizing oil-in-water emulsions.

Alpha-cyclodextrin

A possible solution to this problem is using alpha-cyclodextrin as a stabilizer. Cyclodextrins are naturally occurring cyclic oligosaccharides. The molecules are composed of several α-D-glucose units linked alpha-(1,4)-glycosidically to form a ring [Figure 1]. Depending on the number of glucose units and consequently on the ring size, a distinction is made between alpha-, beta- and gamma-cyclodextrin: alpha-cyclodextrin consists of six glucose units, beta-cyclodextrin of seven, and gamma-cyclodextrin of eight.

The glucose units are configured in such a way that a hydrophobic cavity results. This cavity is able to accommodate a lipophilic molecule as "guest," provided that its size and shape are compatible. The cohesion between the two molecules is relatively weak (van der Waals forces), so that, under suitable conditions, the guest molecule may subsequently be released. Van der Waals forces do not chemically alter either partner of such an inclusion compound. The ring-shaped molecules are stable in alkaline solutions, but are hydrolyzed in acidic solutions (at pH < 2.5). In general, cyclodextrins are well-defined, chemically pure substances with consistent technical properties.

Renewable and non-animal derived source

An important factor considered by food producers in choosing an ingredient is often its source. Consumers tend to favour naturally manufactured products or products with ingredients from renewable sources. Pandemics like BSE and avian influenza have reinforced a trend toward avoiding animal-based raw materials, and are fueling increased consumer demand for food ingredients from a safe origin. Alpha-cyclodextrin is fully in line with this trend, being a natural conversion product of starch. For industrial use, it is manufactured from vegetable raw materials such as corn or potato starch by enzymatic degradation.

Stabilizing emulsions by molecular encapsulation

With its hydrophobic interior and hydrophilic exterior, the doughnut-shaped alpha-cyclodextrin is able to attract and encapsulate selected molecules, like triglycerides. This leads to the build-up of a surfactant like structure which has emulsion stabilizing properties.

Figure 2 illustrates a triglyceride encapsulated by an alpha-cyclodextrin as a model hydrophobic ingredient. One of the fatty-acid tails of the triglyceride is encapsulated in the hydrophobic cavity of the alpha-cyclodextrin – the other two fatty-acid tails are not. This generates a surfactant-like complex comprising an alpha-cyclodextrin and a triglyceride molecule: the two non-encapsulated fatty-acid tails form the lipophilic portion of the surfactant, while the hydrophilic exterior of the cyclodextrin represents the hydrophilic portion of the surfactant.

Figure 3 shows how this surfactant-like structure works in oil-in-water emulsions: the triglyceride / cyclodextrin complex ‘sits’ on the oil droplet surface and stabilizes the oil droplet like a surfactant. In this way, stabilized oil-in-water micelles are generated, with the two free triglyceride tails extending into the oil droplet and the hydrophilic cyclodextrin exterior mediating contact with the surrounding aqueous phase.

Figure 4 illustrates the stabilities of a range of oil-in-water emulsion compositions with a gradual increase in alpha-cyclodextrin content. The conditions below the line yield unstable emulsions that sooner or later separate into two phases, while conditions above the line yield stable emulsions that do not separate. The higher the oil content of the oil-in-water emulsion, the lower the amount of alpha-cyclodextrin needed to achieve a stable emulsion. The higher the water content at the other side, the more alpha-cyclodextrin is needed for a stable system.

More than stabilizing

Alpha-cyclodextrin, however, can do more than just stabilize emulsions. Depending on the oil-to-water ratio and the amount of alpha-cyclodextrin used, the viscosity, and therefore the organoleptic properties, of the emulsion are altered. From ketchup-like to icing-like, all viscosities are possible [see Figure 5].

Furthermore, stable emulsions are feasible even at elevated temperatures – a critical aspect important for processing operations performed at higher temperatures.

Alpha-cyclodextrin can be used for a variety of emulsion applications in the food industry: wherever it is necessary to stabilize an oil-in-water emulsion, to modulate its viscosity or to achieve a stable emulsion at elevated temperature. Applications include sauces, dressings, mayonnaise-like applications, beaten foods, whipped desserts or margarines, to name just a few.

Figure 6 illustrates a viscosity comparison of commercial product samples with oil-in-water emulsions stabilized with alpha-cyclodextrin. As can be seen, the viscosity can be reproduced with alpha-cyclodextrin as an emulsion stabilizer.

Alpha-cyclodextrin as emulsifiers

In general, the use of alpha-cyclodextrin as an emulsifier for oil-in-water emulsions offers multiple advantages. The most important factor is, of course, its dual effect, namely the stabilization of emulsions by molecular encapsulation while at the same time providing a texturizing effect. Thus, two important characteristics are mediated by just one ingredient.

Apart from that, the product is suitable for hot and cold processing and offers easy handling and good storage stability. From the point of view of consumer health and safety issues, alpha-cyclodextrin also offers considerable other benefits. It is cholesterol-free and non-allergenic. What’s more, the ingredient is purely vegetarian-grade and completely based on natural, renewable raw materials such as corn starch. This makes alpha-cyclodextrin an ideal solution for stable oil-in-water emulsions in food manufacturing.

The author

Dr. Philipp Osterloh

Business Development Food Solutions

WACKER BIOSOLUTIONS

www.wacker.com