Analytical assay for β-conglycinin in soybeans using cryogenic milling and the absolute quantification (AQUA) method

Abstract

β-Conglycinin, a major protein in soybeans (Glycine max (L.) Merr.), improves human lipid metabolism and influences the processing properties of soybeans. Recently, an analytical method based on the absolute quantification (AQUA) strategy for β-conglycinin was developed by us. In this study, the performance of an assay combining trichloroacetic acid (TCA)/acetone protein extraction and the AQUA method with cryogenic milling in dry ice was evaluated, which is used for measuring pesticide residues in foods to prepare homogeneous comminuted samples. The homogeneity of soybean powder obtained by cryogenic milling and the linearity and precision of the analytical assay were satisfactory; however, its recovery was not high. Guanidinium-mediated denaturation and trypsin digestion of β-conglycinin in the AQUA method, following the TCA/acetone extraction, were suggested to have a substantially higher negative effect on recovery than the TCA/acetone method. Overall, as this assay is based on AQUA strategy using stable isotope-labelled peptides as internal standards, and its performance except for recovery was satisfactory, it is thought to be available for the analysis of β-conglycinin in cases where a high trueness of measurement is not needed (e.g. comparative semi-quantification of β-conglycinin).