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 commerci al soybean liquid milks. Quantitation of soybean proteins was first perform ed by using soybean protein isolate as external standard. Although this sta ndard seemed suitable for the quantitation of soybean proteins in some soyb ean liquid milks, for those soybean milks directly prepared from whole soyb eans, a best estimation of the soybean protein content was obtained by usin g soybean flour as external standard.