and its levels in milk can increase when samples are exposed to high temperatures, light, or oxygen, as well as to the presence of some heavy metals, such as iron or copper. Dehydroascorbic acid still exhibits vitamin C activity, since it can be reconverted into ascorbic acid in the hu- man body (Combs, 1998). However, this compound is unstable and most of it is lost as diketogulonic acid, which has no vitamin C activity (Combs, 1998).