Powdered milk was oxidized in the state of powder by heating at 80℃. The ascorbate (Asc) level determined specifically by our method and the total SH groups in the milk decreased gradually. TBA-reactive substances and malondialdehyde showed to increase to a small degree when the heating was continued for more than 2 days. On the other hand, tocopherols (α, γ and δ) did not decrease even after 4 days when browning of the milk proceeded. Similar results were obtained when milk was oxidized in aqueous suspension. The preferential disappearence of hydrophilic anti-oxidants (SH groups and Asc) was reproduced when milk suspension was oxidized with water-soluble radical initiator. These results suggest that Asc and SH groups are sensitive indices of oxidative damage of powdered milk, while tocopherol decreased simultaneously with a reduction of water-soluble anti-oxidants by a hydrophobic initiator.
