Determination by perfusion reversed-phase high-performance liquid chromatography of the soybean protein content of commercial soybean products prepared directly from whole soybeans

The use of soybean flour as external standard for the determination of soybean proteins in soybean products directly prepared from whole soybeans is investigated. For that purpose a perfusion reversed-phase high-performance liquid chromatography method consisting of a linear binary gradient acetonitrile–water (both with 0.1% trifluoroacetic acid) in 3 min at a flow-rate of 3 ml/min, and a temperature of 60°C is used. Samples dissolved in water are directly injected in the chromatographic system. The method is validated by evaluating detection limits, precision, and accuracy and applied to the quantitation of soybean proteins in soybean products directly prepared from whole soybeans.