Soybean β-conglycinin constituent subunits: Isolation, solubility and amino acid composition

A protocol to purify soybean β-conglycinin constituent subunits (α, α′, β) from soybean (Glycine max Linn. Merr.) was investigated. The combination of anion exchange chromatograph and Immobilized Metal Ion Affinity Chromatography (IMAC), under 6 M urea was used. The subunits were evaluated by SDS–PAGE, Differential Scanning Calorimetry (DSC) and Size Exclusion Chromatography (SEC). The subunits α, α′ and β exhibited isoelectric precipitation at pH 4.0–5.0, 4.0–5.0 and 4.0–6.0, respectively. β subunit exhibited constant solubility around 56% at pH ⩾ 6. Total Essential Amino Acid (TEAA) and Essential Amino Acid Index (EAAI) revealed that both TEAA and EAAI of α′ subunits were lower than α and β subunits. This new fractionation method has practical significance for the researchers to prepare enough suitable amounts of samples to study the structure–physicochemical function relationships of β-conglycinin constituent subunits, and to supply enough diet for animal experiments to study the physiological function of single β-conglycinin constituent subunit.