Biochemical characterization and enzymatic hydrolysis of different commercial soybean protein isolates

Thirteen commercial soybean protein isolates (SPIs) were characterized and submitted to the same conditions of hydrolysis with pancreatin to the same degree of hydrolysis (DH). The 13 SPIs differed with respect to their phytate contents (7.41-15.62 mg/g of protein), presence of trypsin inhibitor (5.17-94.72 UTI/mg of protein), protein dispersibility index (PDI) (11.7-88.7%), and relative compositions of the 7S subunits and 11S polypeptides present in the soluble fraction: alpha' (0-100%); alpha (0-26%); beta (0-44%); acid polypeptide (50-100%); basic polypeptide (0-50%). The reaction time necessary for the hydrolysis to attain a DH of 21.5% varied from 48 to 252 min and was longer for isolates with complete 7S and 11S globulin fractions and higher PDI values. The 10% TCA soluble nitrogen index of the hydrolysates varied from 61.5 to 100%. The total free amino acids varied between 7.5 and 31.0%, with basic and hydrophobic amino acids being present in greater amounts. Electrophoresis indicated differences in the molecular weight profiles of the hydrolysates. The 13 SPIs analyzed were shown to be different, resulting in different products when submitted to the same conditions of hydrolysis.