Absolute quantification of the α, α', and β subunits of β-conglycinin from soybeans by liquid chromatography/tandem mass spectrometry using stable isotope-labelled peptides

Abstract

β-Conglycinin, a major protein in soybeans, shows improvement effect of lipid metabolism. Moreover, this protein influences the processing properties of soybeans. β-Conglycinin is a hetero-trimer constituted by α, α', and β subunits. In this work, a method for the selective quantification of these subunits was developed by means of protein absolute quantification (AQUA) technology using liquid chromatography/tandem mass spectrometry with the stable isotope-labelled internal standard peptides LQSGDALR[¹³C₆,¹⁵N₄], NILEASYDTK[¹³C₆,¹⁵N₂], and NPIYSNNFGK[¹³C₆,¹⁵N₂]. This method exhibited linear relationships (r² > 0.99) in the concentration range of 1.2-300 fmol/μL for LQSGDALR[¹³C₆,¹⁵N₄] and NILEASYDTK[¹³C₆,¹⁵N₂], and of 4.7-300 fmol/μL for NPIYSNNFGK[¹³C₆,¹⁵N₂]. As a result, the content of these subunits in β-conglycinin-rich and both α and α' subunit-deficient soybean cultivars was successfully determined. This quantitative assay is promising for the evaluation of the food functionality and processing properties of soybeans.

Keywords: Absolute quantification; Glycine max (L.) Merr.; Liquid chromatography/tandem mass spectrometry; Soybean; Stable isotope-labelled peptide; β-Conglycinin α, α′, and β subunits.