Non-susceptible milk

Non-susceptible milk does not oxidize even in the presence of iron or copper. 

Non-susceptible milks that do not become oxidized even in the presence of added Cu or Fe. 

It has been proposed that spontaneous milks have a high content (10 times normal) of xanthine oxidase (XO). Although addition of exogenous XO to non-susceptible milk induces oxidative rancidity, no correlation has been found between the level of indigenous XO and susceptibility to oxidative rancidity. The Cu-ascorbate system appears to be the principal pro-oxidant in susceptible milk. A balance between the principal antioxidant in milk, a-tocopherol (Chapter 6), and XO may determine the oxidative stability of milk. The level of superoxide dismutase (SOD) in milk might also be a factor but there is no correlation between the level of SOD and the propensity to oxidative rancidity. 

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