An improved method to determine SH and –S–S– group content in soymilk protein

Ellmanʹs method is a simple, rapid and direct method to determine the SH and –S–S– group content in proteins. However, this method has difficulties in directly determining SH and –S–S– group content in soymilk because of the high turbidity and low SH group content of soymilk. In this experiment, low-turbidity protein solutions were prepared by separating the proteins from soymilk by acetone precipitation, the proteins were then dissolved in Tris–glycine buffer (pH=8.0) containing or not containing 8 mol/L of urea. The content of SH and –S–S– groups in the separated protein was determined by a spectrophotometric method. Tests of soy protein isolates proved that the contents of SH and –S–S– groups were not significantly affected by the acetone treatment. be concluded that acetone treatment is an effective method to determine the SH and –S–S– groups content of proteins in high turbidity solutions such as milk, soymilk, etc.