ENZYMATIC PHOSPHORYLATION OF SOY PROTEIN ISOLATE FOR IMPROVED FUNCTIONAL-PROPERTIES

A commercial soy protein isolate (SPI) was phosphorylated using the catalytic subunit of a commercially available protein kinase from bovine cardiac muscle. On the basis of scintillation counting and autoradiography, incorporation of P-32(i) into SPI increased with increased incubation time and reached a level of 13-mu-mol of phosphorus incorporated/g of protein after a 4-h incubation at 37-degrees-C. SDS-PAGE and autoradiography of timed protein kinase assays showed P-32(i) initially incorporated into glycinin acidic polypeptides and then into glycinin basic polypeptides. Very little P-32(i) was associated with the beta, alpha/alpha' subunits of beta-conglycinin. Compared with nonphosphorylated SPI, the phosphorylated protein showed significantly improved solubility and emulsifying activity over a pH range of 3-6. Emulsion stability and foam expansion were also significantly improved with phosphorylation, but foam stability was lower using the phosphorylated protein.