Studies on the Emulsifying Properties of Soybean Proteins

Part III. Effect of partial hydrolysis by dilute hydrochloric acid

Abstract

The emulsifying capacity(EC)and emulsion stability(ES)of isolated soybean proteins which were partially hydrolyzed by holding them in 0.05-0.10N HCI at 95°C for various durations were compared with the EC and ES of unhydrolyzed soybean protein isolate. The EC and ES of unhydrolyzed proteins decreased to a minimum level in the isoelectric region(around pH4.5)regardless of protein concentration, while those of the partially hydrolyzed proteins showed no decrease in that region and exhibited a remarkably high level throughout the pH range. The effect of partial hydrolysis was especially marked on the ES, e.g., the ES of 34mgN% unhydrolyzed proteins at pH4.5 increased by hydrolysis from a level below 10% to a level of around 80%, and the effect of hydrolysis on the ES was clearly observed even in the condition of high NaCl concentration(0.5M). The partial hydrolysis by dilute hydrochloric acid had high specificity and liberated aspartic acid selectively in the initial stage. The maximum effect of hydrolysis on EC and ES was obtained in the range in which 5-20% of aspartic acid was liberated with no other amino acids being liberated yet. This condition corresponded to 5-40 hours of hydrolyzing time.