Soybean-based Surfactants and Their Applications

The soybean is a legume that contains no cholesterol and is low in saturated fat. Soybeans have been consumed as a major source of protein by people in Asia for centuries, while their consumption in the West only spans several decades. The soybean is the only vegetable food that contains all eight essential amino acids. It is also a good source of fibre, iron, calcium, zinc, and vitamins. In 2009, the world soybean production was 210.9 million metric tons, about 53% of the world oilseed production [American Soybean Association, 2010]. Soybeans are made up of about 40% protein and 20% oil and are therefore considered to be a major source of proteins and oils. They are also an important source of three natural surfactants: soy lecithin, soy protein, and soy saponin. However, the use of saponin has some limitations [Oleszek & Hamed, 2010]. In this chapter, we are focusing on soy lecithin and soy protein. A surfactant is a surface-active substance. The molecular structure of a surfactant is characterised by the presence of hydrophilic heads and lipophilic tails. This structural property enables surfactant molecules to adsorb at surfaces or interfaces. Surfactants are generally classified according to the type and charge of the hydrophilic groups, namely, anionic, cationic, nonionic, and amphoteric surfactants. Surfactants are involved in many aspects of our lives, including detergents, cosmetics, foods, and drinks. Not only natural surfactants but also a wide range of synthetic surfactants are used in various applications. The world surfactant market was valued at about $14.3 billion [Karsa & Houston, 2006] with a market volume of about 18 million tons [Cirelli et al., 2008] in 2003, and it reached $23 billion in 2007 [Acmite Market Intelligence, 2008]. However, the market has recently been experiencing stricter regulations and has been hit by the current financial crisis. Surfactants can be produced both from oleochemical and petrochemical feedstocks. The use of natural renewable materials (e.g., seed oils and animal fats) to produce surfactants coupled with the development of new production methods may provide a solution to these challenges. Furthermore, it has been demonstrated by life cycle analysis that the use of renewable resources for surfactant production is more cost-effective and eco-friendly than petrochemical resources. The substitution of the use of seed oils for surfactant production would lead to a significant reduction in surfactant-associated CO2 emissions [Patel, 2004]. Therefore, it is expected that the production of seed oil-based surfactants will continuously increase and that surfactants with novel and improved properties will be developed.