Oxygen in milk

Aurand, L.W., Boone, N.H., Giddings, G.G. 1977. Superoxide and singlet oxygen in milk lipid peroxidation. J. Dairy Sci. 60, 363-369. 

Xanthine oxidase, mol wt ca 275,000, present in milk, Hver, and intestinal mucosa (131), is required in the cataboHsm of nucleotides. The free bases guanine and hypoxanthine from the nucleotides are converted to uric acid and xanthine in the intermediate. Xanthine oxidase cataly2es oxidation of hypoxanthine to xanthine and xanthine to uric acid. In these processes and in the oxidations cataly2ed by aldehyde oxidase, molecular oxygen is reduced to H2O2 (133). Xanthine oxidase is also involved in iron metaboHsm. Release of iron from ferritin requires reduction of Fe " to Fe " and reduced xanthine oxidase participates in this conversion (133). 

Xanthine dehydrogenase from chicken liver reacts readily with NAD as acceptor (77) while that from Micrococcus lactilyticus is inactive towards this, reacting instead with ferredoxin (18). Both enzymes react only slowly with oxygen. It seems reasonable to assume, however, that for each member of this group of enzymes, reducing substrates all react via molybdenum, as in milk xanthine oxidase. Presumably, different... 

A glass jug of milk on a gas ring appears to "sweat" The jug is not leaking What is happening is that hydrogen from the gas supply and oxygen in the air burn together, to form steam. This condenses as tiny droplets of water on the cold surface of the ]ug - a microcosm of how the oceans were formed. 

Folate is sensitive to light and may be subject to photodecomposition. Heat treatment influences folate levels in milk. Pasteurization and the storage of pasteurized milks have relatively little effect on the stability of folate but UHT treatments can cause substantial losses. The concentration of oxygen in UHT milk (from the headspace above the milk or by diffusion... 

The often conflicting reports in the literature indicate that more research is needed to clarify the role of interacting enzyme systems that control the generation and survival of active forms of oxygen and their involvement in the initiation and propagation of lipid oxidation in milk. 

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McKellar, R.L., Dishburger, H.J., Rice, J.R., Craig, L F., Pennington, J.J. (1976) Residues of chlorpyrifos, its oxygen analogue, and 3,5,6-trichloro-2-pyridinol in milk and cream from cows fed chlorpyrifos. J. Agric. Food Chem. 24, 283-286. 

Effect of Oxygen Content and Packaging the Oxidation of Fat in Milk Powder... 

Oxygen scavengers can be used to reduce the 02 content in packaged milk powder but this approach may not be cost-effective (Zimmerman et al., 1974). Another approach to reducing the 02 content in the package involves using H2 in the presence of a palladium or platinum catalyst. Although the use of several antioxidants is permitted in the manufacture of edible oils, fats and butter, their use in milk powder is prohibited. 

Successive, univalent reduction of oxygen may yield reactive oxygen species. This reduction can be effected photochemically, chemically or enzymatically (Korycka- Dahl and Richardson, 1980). A number of enzymes, including Xanthine oxidoreductase in milk, are capable of producing large amounts of superoxide via the univalent reduction of oxygen (Fridovich, 1976). 

The superoxide radical (O ) is another reactive oxygen species. Although the superoxide radical may not react readily with unsaturated fatty acids, it is capable of oxidizing phenolic compounds such as tocopherols, thiols and ascorbic acid (Korycka-Dahl and Richardson, 1980). This, in turn, may lead to earlier oxidation of lipids. However, the significance of superoxide as a pro-oxidant in milk is unclear. Superoxide rapidly dismu-tates in water, yielding hydrogen peroxide which, itself, may be involved in oxidative reactions (Korycka-Dahl and Richardson, 1980) ... 

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