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

Ellman's 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. It can 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. (C) 2004 Elsevier Ltd. All rights reserved.