Deamidation-induced fragmentation of maize zein, and its linked reduction in fatty acid-binding capacity as well as antioxidative effect

Zein lost its antioxidative effect in proportion to the degree of deamidation. Changes in molecular weight distribution of the protein fraction by deamidation were examined by means of gel filtration with Sephacry S-200 and SDS-electrophoresis in 12% polyacrylamide gel. The deamidation reaction (mild acid-hydrolysis by 0.05N HCl in 70% ethanol) was accompanied by fragmentation of zein subunits. Concomitantly, the surface hydrophobicity as well as fatty acid-binding capacity decreased with progressed deamidation. There was a close correlation (r = 0.98) between the antioxidative effect and the fatty acid-binding capacity, but not the surface hydrophobicity. A large part of the antioxidative effect of zein is directly or indirectly attributable to its capacity of burying unsaturated lipid in the inter- or intra-molecular hydrophobic spaces in which the amide groups are intimately involved.