Effect of protein oxidation on the in vitro digestibility of soy protein isolate.

Soy protein isolate (SPI) was modified by 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH) oxidation pretreatment, and the in vitro digestibility of oxidised SPI was investigated. Results indicated that oxidation induced amino acid modification. The amount of most amino acids decreased, accompanied by decreasing digestive proteolysis susceptibility. Peptide size distribution implied that oxidation generated protein aggregates that could not be degraded by pepsin, but could be digested by pancreatin. Oxidation induced a maximum of 16.6% and 14.6% loss, respectively, for free essential and free total amino acid in the digests of oxidised SPI. Antioxidant activities evaluation of oxygen radical absorbance capacity (ORAC) value and DPPH scavenging activity showed that oxidation deteriorated the antioxidant activities of the digests from oxidised SPI.