As an emulsifier, soy lecithin is used in food applications as an aerating agent, viscosity modifier, dispersant and lubricant. Typically, an emulsion is a suspension of small droplets of one liquid in another liquid with which it is incapable of mixing.
Oil-in-water (O/W) and water-in-oil (W/O) are the two primary types of emulsions. Lecithin’s molecular structure makes it an effective emulsifier for the interaction of water and oil. Phospholipids, the major component of lecithin, are partly hydrophilic (attracted to water) and partly hydrophobic (repelled from water).
It is lecithin’s ability to simultaneously interact with both oil and water that makes it such an effective and stable emulsifier. When introduced into a system, an emulsifier such as lecithin acts to help maintain a stable emulsion between two unmixable liquids. The emulsifier decreases the surface tension between the two liquids and allows them to mix and form a stable, heterogeneous dispersion.
The classification of emulsifiers is often expressed as the relation between hydrophilic and lipophilic groups = HLB-System (hydrophilic-lipophilic balance). Numbers of a scale from one to 20 are allotted to the emulsifiers.
Lipophilic emulsifiers have a lower HLB-Number, whereas emulsifiers of a hydrophilic character have a higher number. The turning point between lipophilic and hydrophilic emulsifiers lies at number 10 of the scale.
This HLB-System can very well be applied to non-ionic synthetic emulsifiers. By means of the HLB-Value, conclusions can be drawn regarding the behaviour as an emulsifier.
It is a general rule that when preparing an emulsion, the phase, in which an emulsifier has better dispersing properties, becomes the outer phase. Therefore, a lipophilic emulsifier with an HLB-Value of six is likely to facilitate the preparation of a w/o emulsion and vice versa, ie: a hydrophilic emulsifier will support the creation of an O/W emulsion.
In practical applications, often a mixture and/or combinations of different emulsifiers are used. Experience has shown that by this procedure, very stable emulsions can be prepared. The HLB-Value helps in the calculation of the optimum mix for a certain types of emulsifiers.
As the HLB-System is traditionally a good aid for characterising emulsifiers, the effort has been made to also apply this system to lecithins. The HLB-Value (the determination of the HLB-value was only possible by comparing water-dispersibility of the lecithins with reference standards of synthetic nonionics) when applied to lecithins, however, it provides only little information about their functionality as emulsifiers, ie: whether a certain lecithin quality is suitable as a W/O or as O/W emulsifier.
It appears as if other mechanisms play a more important role for the preparation of a stable emulsion besides the hydrophilic and lipophilic balance, eg: tendency of lecithins in an aqueous dispersion to form extended lamellar structures and networks.
For lecithins, the HLB-Value can just only be used as an indicator for water dispersibility, ie: the higher the number, the better the water dispersibility of a certain lecithin.
Versatile Natural Ingredient
Lecithin is nature’s principal emulsifying agent. It greatly speeds up the dispersion of the fatty and aqueous components in many types of food production, for example, in the manufacture of bread, biscuits, sweet pastries, convenience foods, ice cream, chocolate and margarine.
The following examples show the manifold application possibilities.
Due to its specific properties, soy lecithin is widely used in margarine applications. In frying margarines, it is used for its anti-spattering characteristics. Lecithin also promotes browning due to its interaction with proteins. It improves the aroma, avoids sediment sticking to the pan, keeping particles dispersed, and limits foam formation.
Spattering during frying is caused by the explosion of water droplets. During frying, water comes free. When frying in oil, water droplets will not be emulsified and will coalescence and become bigger. The bigger droplets will sink to the bottom of the frying pan and come in contact with the hot pan bottom.
This will heat up the water droplet in such a degree that it explodes, producing fat spattering. The lecithin in a frying margarine will emulsify the water droplets, avoiding coalescence, keeping the droplets small, facilitating fast evaporation before reaching the hot pan bottom and avoiding explosion of water droplets.
In margarine for baking applications, lecithin improves the elasticity of the margarine and its baking properties.
Lecithin improves the anti-sticking and release characteristics of the food product out of a pan and mould. It forms an interaction barrier between the food product and the metal surface.
Lecithin is used in different formulations like:
- Pure low viscous lecithin compounds: oil/lecithin mixtures
- Pump and aerosol sprays: oil, lecithin, propellant
Next to these formulations, it can also be an emulsion of water and oil.
Improved heat-resistant lecithin provides a reduction in the darkening process during heating. The release agents can directly be applied on the cooking surfaces or used in the food grinders, extruders, cutters.
Lecithin can also be incorporated in the food formula to encourage mould release. Different lecithin is used for iron release of waffles and wafers, and also provides improvements in break-resistance, even browning and uniform surface.
Continuous Cooking/Freezing Belt Release
Oily and aqueous formulas with lecithin are developed for better release and non-sticking of the food from the belt. This layer will also control the formation of the final shape and dimensions of the end product, when food products are extruded from the dough mass on the belt, eg: biscuits.
The lecithin systems are also used for a better cleaning and rinsing of the belt. Examples of applications are: fried, baked, pre-cooked or marinated products, like meat products, breaded products, pizza, biscuits, snack and dehydrated or frozen products like fruits and vegetables (potatoes, and fries).
Food Release/Separation Agent
Cheese and meat products have varying moisture levels and are stored under different conditions of temperature and humidity. These conditions provoke sticking of slices of cheese or meat to each other or to the cutting knives, wires, grinders and extruders.
Low viscous lecithin can be used as a non-sticking aid and forms a barrier between the sliced and shredded products.
Additionally, lecithin interacts with the wheat starch, delaying retrogradation of the amylose, and improves water binding which results in a longer shelf life.
In deep frozen doughs, lecithin improves the freezing and thawing stability. The growth of large ice crystals is inhibited. This reduces mechanical damage of the dough gluten network and protects yeast cells.
The quality of biscuits, wafers and other pastry products is improved by adding lecithin as it assures: a better homogenisation of the different ingredients; a better emulsification of the fat; improved water binding.
This results in better cohesion and a more uniform browning of the product. It will also reduce breakage. Wafers can be more easily removed from the waffle irons. The nutritional quality of the biscuit and wafer is also improved due to the reduction of fat and oil. Because of the emulsifying properties, fat is more evenly distributed which results in a more efficient use of the fat or oil.
Chocolate & Confectionery
Lecithin is a traditional additive in chocolate production. Chocolate is a dispersion of sugar, milk powder and cacao particles in a fat phase, the cacao butter. The chocolate production process requires significant energy as the chocolate mass is kneaded during the conching process over a period of several hours. This processing is necessary for the homogenisation of the different ingredients and the aroma development.
The conching process is highly energy consuming due to the high viscosity of the chocolate mass and the increase in viscosity during the conching process.
Chocolate mass viscosity is a complex processing variable and is influenced by several parameters: particle size distribution (the finer it is, the more particle surface to coat, the less available ‘free’ cacao butter there is, the higher the viscosity), and the relative proportion of cacao butter in comparison to the solid particles (the more ‘free’ cacao butter there is, the lower the viscosity).
In order to reduce the viscosity during processing, chocolate producers add lecithin as it improves the dispersability of the particles in the cacao butter, and therefore, reduces viscosity and increases the yield value of the chocolate significantly.
Lecithin disperses solids in a much more efficient way in comparison to a chocolate without lecithin due to its amphiphilic characteristics. A dosage of 0.35 percent lecithin results in a comparable viscosity reduction realised with a dosage of eight percent of cacao butter.
This viscosity reduction results in significant cost savings for the chocolate producer by allowing savings on energy and cacao butter, the most expensive ingredient in chocolate. The optimal dosage varies between 0.4 to 0.6 percent in chocolate. The addition of lecithin also impacts the crystallisation of the chocolate and improves the gloss of the chocolate.
Windell Oskay, California, US
Caramel and toffees demand a very homogeneous texture for good mouthfeel because of the slow melting process in the mouth. Lecithin will improve the distribution of the emulsified fats and particles. This will also increase the shelf life of the products as lecithin reduces the probability of fat bleeding. In the recrystallisation of sugar, lecithin acts as a mild anti-oxidant.