Soy lecithin is one of the most important emulsifiers for the pharmaceutical, paint, food, and feed industries. The world uses hundreds of thousands of tons of soy lecithin every year. The production of soy lecithin is a well-established but customer-specific process that provides just the right mix of the products from the manufacture of lecithin to produce the emulsifier the customer needs.
What is an Emulsifier?
On a very basic level, an emulsifier reduces the interfacial tension of droplets of oil in water or droplets of water in oil. Many of the products in which soy lecithins are used, however, are mixtures of much more than just oil and water.
(A definition may be helpful here. “Native lecithin,” the product made during the first pass of the production process, is composed of choline and cephalin among other chemical products, so the product is called “lecithins,” not “lecithin” in this stage.)
Uses of Lecithin as an Emulsifier
Pharmaceuticals suspend their active ingredients in oil and water mixtures with stabilizers (which may also be lecithins), preservatives, and chemicals that enhance absorption of the drug by the desired site in the body. In paints, soy lecithin may be added to reduce viscosity or as a dispersant. Soy lecithin is also used in applications that need to “make water wetter.” Soy lecithins may emulsify mixtures of water, fats, protein, and carbohydrate in foods, and they assist in the extrusion of dry food for pets and livestock. Soy lecithin can be tailor-made for the customer’s end-product, taking into consideration ingredients, pH, globule size, and volume of the dispersed phase.
In food, soy lecithin is most important for making oil and water mix. It almost makes products creamier and more spreadable.
All forms of soy lecithin are emulsifiers, but not all forms of emulsifiers are equally efficient for every application. A molecule of soy lecithin has hydrophobic (oil-loving) and hydrophilic (water-loving) groups. Native lecithin has only a weak ability to emulsify oil in water or water in oil. However, a mixture of soy lecithins heavy on choline has a stronger ability to emulsify a smaller amount of oil in a larger amount of water. A soy lecithin mixture in which cephalin predominates has a stronger ability to emulsify a smaller amount of water in a larger amount of oil.
The type of emulsion manufacturers can obtain with soy lecithin does not depend solely on the ratio of water to oil. Especially when manufacturers are working with native or “mixed” lecithins, the purity of the water is another important consideration. In hard water, calcium and magnesium ions flocculate with the cephalin component of soy lecithin, forming small clumps in the end-product.
This can, of course, be a desired and intentional result.
The main way soy lecithin is modified for specific applications is by modifying the cephalin content of the mixture of soy lecithins. Choline is more soluble than cephalin in ethanol, so dissolving the mixture of lecithins in 90 percent alcohol can create a product that is over 90 percent cephalin-free. Or lecithin can be treated with the enzyme phospholipase when it is in the “sludge” stage of production. The enzyme makes the lecithins more hydrophilic and less sensitive to calcium impurities in the ingredients.
In addition to some other methods that produce undesirable colors in soy lecithin, the native product can be treated with hydrogen peroxides and acids, especially lactic acid, to create hydroxylated soy lecithin that is easy to mix in cold water. However, many countries limit or prohibit the use of hydroxylated lecithins in food. The US FDA permits the use of hydroxylated soy lecithin made with a limited number of mild acids or bases.
How Can Manufacturers Recognize High-Quality Soy Lecithin?
Soy lecithin is naturally reddish-brown. It can be bleached to a light brown with hydrogen peroxide. This does not affect its permitted use in foodstuffs, although it has to be listed on the label and the product cannot be branded as “organic.”
Soy lecithin contains a high percentage of unrefined soybean oil. The soybean oil can be removed as needed for taste and color, but separation adds to the cost of lecithin.
Soy lecithin for food use is heated to 50 to 70 degrees Celsius. Despite this step, soy lecithin manufacturers continuously monitor for bacteria contamination.
Technically speaking, it is possible to make lecithin from egg yolks, rapeseed, sunflower seed, corn germ, cottonseed, and flaxseed. Soy lecithin has the advantage of continuous, worldwide availability and superior color, taste, and emulsification properties.