When stored at high relative water activity (Aw 0.9), zein has a prominent antioxidant activity against the peroxidation of methyl linoleate, while its papain hydrolysate does not. Using a lipid-soluble radical initiator, AMVN [2,2′-Azobis(2,4-dimethyl-vaIeronitrile)], to alter the induction period of peroxidation of methyl linoleate, we found a turning point just at 24 hr where the rate of oxygen absorption declined. The formation of a solid, tightly aggregated outer shield was observed by scanning electron microscopy. A rather amount of embedded substrate oil (methyl linoleate-methyl stearate, 7: 3) was obtained when aggregations formed, and there was little change in the level of embedded oil for at least 16 days. On the other hand, a hydrolysate of zein had scarcely any embedding effect. The ratio of methyl linoleate to methyl stearate showed that embedded oil (hexane unextractable) was more protective to oxidation than hexane-extractable oil. These findings indicate that the substrate oil must have been embedded in the shield formed by zein protein at Aw 0.9 to avoid outer oxygen attack.
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)
- Agricultural and Biological Sciences(all)