Hexanal Synthesis in Isolated Soy Proteins

Soybeans are the second largest food crop in the U.S. with about 3 billion bushels produced in 2001. In 2000, only about 2 percent of the available protein from soybeans was used in human foods largely because of the characteristic flavor. We have discovered that reducing agents such as sodium erythrobate and sodium nitrite (which are commonly added to food products as antioxidants) caused heads pace hexanal from aqueous slurries of commercial isolated soy proteins (ISP) to increase by as much as 16-fold compared to the controls (no additive). When linoleic acid was also added, headspace hexanallevels were further increased by as much as 24-fold. Headspace hexanal from laboratory prepared ISP increased by as much as 38-fold compared to the control. When carbon-13 labeled linoleic acid was added to aqueous mixtures of laboratory ISP along with reducing agents, 96 percent of the resulting hexanal contained the carbon-13 isotope. CommerciallSP samples had about 40 percent of the isotopically labeled carbon incorporated into hexanal. These large increases in hexanal are almost completely prevented by heating the aqueous ISP to ~ 100°C prior to adding the reducing agent and linoleic acid. This research will isolate and identify the hexanal-synthesizing enzyme(s) from ISP that are activated by reducing agents (e.g., sodium erythrobate). The enzymes' physical and chemical properties will be determined. The effect that commerciallSP processing conditions have on the survival of the enzyme's activity will also be examined. A basic understanding of the mechanism, and reactants, involved in the synthesis of hexanal after ISP is rehydrated is necessary for the development of commercially practical solutions to the longstanding flavor problem associated with soy protein products.