Physicochemical Properties of β and α′α Subunits Isolated from Soybean β-Conglycinin

Soy protein has shown great potential for use in biobased adhesives. beta-Conglycinin is a major component of soy protein; it accounts for 30% of the total storage protein in soybean seeds beta-Conglycinin was isolated and purified, and its subunits' (beta,alpha',alpha) physicochemical and adhesive properties were characterized. Crude beta-conglycinin was isolated from soy flour and then purified by the ammonium sulfate precipitation method. The alpha'alpha and beta subunits were isolated from the purified beta-conglycinin by anion exchange chromatography. Yields of a'a subunits and beta subunits from 140 g of soy flour were 1.86 g (1.3%) and 0.95 g (0.67%), respectively. The minimum solubility for alpha'alpha subunits, beta subunits, and beta-conglycinin occurred in pH ranges of 4.1-5.4, 3.5-7.0, and 4.8-5.3, respectively. Transmission electron microscopy showed that the beta subunits existed as spherical hydrophobic clusters, whereas a'a subunits existed as uniformly discrete particles at pH 5.0. Differential scanning calorimetry showed that beta subunits had higher thermal stability than alpha'alpha subunits. The pH had a lesser effect on adhesion strength of the beta subunits than on that of the a'a. subunits. The adhesives made from beta subunits also showed greater water resistance than those from a'a subunits and beta-conglycinin. Soy protein rich in beta subunits is likely a good candidate for developing water-resistant adhesives.