The objective of the investigation was to understand the biochemical activities of
hydrolysate of soybean milk protein (SMP). Hydrolysis was carried out by different
concentrations of papain (0.008 g·L−1, 0.016 g·L−1, 0.032 g·L−1 and 0.064 g·L−1).
The antioxidant capacity was measured by the ferric-reducing ability of plasma (FRAP)
and 2,2-Diphenyl-1-picrylhydrazyl (DPPH) assays. The anti-angiotensin activity of
hydrolysate was measured by the recombinant angiotensin converting enzyme and substrate
Abz-FRK(Dnp)-P. The contributions of the Kunitz trypsin inhibitor (KTI) and Bowman–Birk
inhibitor (BBI) on antigenicity, and the in vitro digestion of papain-hydrolyzed SMP
were studied. Rabbit polyclonal anti-KTI and anti-BBI antibodies together with peroxidase-labelled
goat anti-Rb IgG secondary antibody were used to identify the antigenicity of KTI
and BBI in unhydrolyzed and papain-hydrolyzed SMP. The antioxidant capacity and anti-angiotensin
activity of SMP were increased after the papain hydrolysis of SMP. The KTI- and BBI-specific
antigenicity were reduced in SMP by increasing the concentration of papain. However,
there was interaction between papain-hydrolyzed SMP and trypsin in native gel, while
interaction with chymotrypsin was absent. The interaction between trypsin and SMP
was reduced due to the hydrolysis of papain in a concentration-dependent manner. According
to the in vitro gastrointestinal digestion simulation protocol (Infogest), the digestibility
of SMP was not statistically increased.
