Simultaneous detection of glycinin and β-conglycinin in processed soybean products by high-performance liquid chromatography-tandem mass spectrometry with stable isotope-labeled standard peptides.

Glycinin and β-conglycinin are the two main allergic proteins in soybean. Due to their complex structures and lack of protein standards, it is difficult to achieve quantitative determination of these proteins in soybeans. In this study, an HPLC-MS/MS method was developed for the simultaneous determination of five subunits of glycinin (G1, G2, G3, G4, and G5) and three subunits of β-conglycinin (α, α', and β) in processed soybean products based on 8 specific peptides and their stable isotope-labeled peptides. Here, each specific peptide was derived from one of the above 8 subunits. When soy protein was extracted and digested with trypsin, 8 specific peptides, and corresponding stable isotope-labeled peptides were analyzed by HPLC-MS/MS. The linear range for the specific peptides was between 3.2 and 1000 ng/mL (R > 0.9955). The recoveries of added peptides ranged from 83.4% to 117.8%, and the intra-day precisions (% CV) were below 17.4%. The limit of quantification of each subunit of glycinin and β-conglycinin in processed soybean products (in terms of protein amount) was between 15.1 and 156.1 g/g. This method was successfully applied to the analysis of 8 subunits of glycinin and β-conglycinin in 68 different processed soybean products, which provides technical support for processed product quality evaluation and monitoring soybean processing technology.