Abstract
Zein and a soy protein isolate (SPI), the peptide derived from SPI (SPI-P), and an amino acid mixture corresponding to these proteins (zein-AA and SPI-AA) were examined for their antioxidative ability in a powder model system and sorption isotherms.
The relationship between their antioxidative ability and the state of water molecules was investigated.
The antioxidative ability of zein was apparent at high water activity (Aw), while that of zein-AA was shown in the range from low to moderate Aw.
The major amino acids of zein, e. g. proline, glutamine, leucine and alanine, were individually examined for their antioxidative ability. Only proline showed this ability. In the absence of an amino acid from the amino acid mixture corresponding to zein, the sample without proline showed no antioxidative ability.
The antioxidative ability of SPI was demonstrated in the range of high Aw. On the other hand, the ability of SPI-AA was shown in the range from low to moderate Aw, while an intermediate pattern between these was obtained for SPI-P.
The sorption isotherms for these samples rose in the high range of Aw. Under the same conditions, the proteins and the peptide showed antioxidative ability, but the amino acid mixture did not.
