Safety of Soy Refining Techniques

Soy has become increasingly popular the past few decades, mainly because of the growth in the health food industry. Soy is used in a wide range of food products, including meat and dairy substitutes. Soy also produces an edible oil and is a potential biofuel crop. Close to one-third of all oil-producing plants grown are soy crops. Soy refining involves complex techniques that prepare soy oil, but also raise safety concerns regarding nutrition quality.

Soy Refining

• Soil oil is rich in polyunsaturated fats, making it a desirable health product. Hexane is used to extract oil from soybeans. This crude oil then undergoes several processes to yield a final product of refined soy oil, including degumming, neutralization, bleaching and deodorization. Each stage is beneficial for the refined product, but also introduces potential health concerns.

Degumming

• Crude soy oil contains gums such as phospholipids and other compounds that require removal before the deodorization stage, as they cause the oil to darken when heated. Extracted phospholipids are sold as lecithin. Traditional water degumming does not remove all impurities, especially oxidative metals. Thus, other solvents such as phosphoric acid and acetic anhydride are applied, which have undesirable effects such as contaminating oil with inorganic phosphates, degrading recovered phospholipids, and corroding stainless steel equipment.

Neutralization

• Degummed oil undergoes neutralization with a caustic alkaline solution followed by acid treatment. This is necessary to remove macromolecules, as caustic treatment eliminates fiber while acid treatment precipitates protein. There are concerns that neutralization impairs the nutritional quality of oils, particularly the vitamin, mineral and protein content, and also adds potential carcinogenic compounds such as nitrosamines. For other oils such as palm oil, a physical refining process is used, which disregards the neutralization stage.

Bleaching and Deodorization

• Bleaching removes toxic substances from oil such as polycyclic aromatic hydrocarbons, but also removes nutrients such as carotenoids. Subsequent to bleaching, the oil is susceptible to oxidation, and some useful fatty acids are oxidized. The deodorization step combats this by removing oxidized fatty acids as well as any pesticides or mycotoxins possibly present. Deodorization also, however, eliminates beneficial components including sterols and tocopherols from the oil.

Supercritical Carbon Dioxide

• Supercritical carbon dioxide could be applied to soy refining as a replacement for degumming, neutralization and bleaching. The technique already is used extensively in the food industry as a means of extracting undesirable compounds, eliminating microbial presence and limiting enzyme activity. Thus it could be possible to produce stable, high-quality refined soy oil without the safety concerns associated with current techniques.