Determination of the soybean protein content in soybean liquid milks by reversed-phase HPLC

A reversed-phase high performance liquid chromatography method, previously optimized, was applied to determine the soybean protein content in commercial soybean liquid milks. Quantitation of soybean proteins was first performed by using soybean protein isolate as external standard. Although this standard seemed suitable for the quantitation of soybean proteins in some soybean liquid milks, for those soybean milks directly prepared from whole soybeans, a best estimation of the soybean protein content was obtained by using soybean flour as external standard.