Oxidation of milk

Photo-oxidation of milk constituents was discused in detail by Walstra and Jenness (1984). 

The distribution of trace elements among the compounds and physical phases in milk has not been elucidated completely. Molybdenum appears to be found exclusively in xanthine oxidase and Co in vitamin B12. Iron is an essential component of xanthine oxidase, lactoperoxi-dase, and catalase. About half of the total Fe and 10% of the Cu are in the fat globule membrane. Copper has been studied extensively in relation to oxidation of milk lipids. The trace metal present in highest con-... 

King, R. L. 1962. Oxidation of milk fat globule membrane material. I. Thiobarbituric acid reaction as a measure of oxidized flavor in milk and model systems. J. Dairy Sci. 45, 1165-1171. 

Interactions with Membrane Components. In aqueous systems milk fat globule membrane lipids and the non-lipid membrane solids were found to accelerate the oxidation of milk fat at 50°C, but exhibited antioxidant effects at 95°C (Chen, Z. Y. Nawar, W. W., University of Massachusetts at Amherst, unpublished data). 

Christy, G. E., Amantea, G. F., and Irwin, R. E. T. (1981). Evaluation of effectiveness of polyethylene over-wraps in preventing light-induced oxidation of milk in pouches. Can. Inst. Food Sci. Technol. J. 14,135-138. 

To minimize and control oxidation of milk-fat in milk powder, Van Mil and Jans (1991) suggests ... 

Off-flavor due to spontaneous oxidation of milk fat is a troublesome issue because the process and its prevention are not well understood and it tends to occur in otherwise well-managed, high-yielding dairy herds... 

Spontaneous oxidation of milk fat, which has been known for over 60 years (Corbett and Tracy, 1943), is influenced by heredity, stage of lactation and feeding practices (Shipe, 1964). Some cows consistently produce spontaneous milk, others occasionally, and others not at all (Parks et al, 1963). Differences between milk from the different quarters of the same cow may occur. 

Clearly, more research is required to clarify the somewhat confused picture regarding the role of enzymes in the oxidation of milk lipids. However, the key factor affecting the susceptibility of milk to oxidation appears to be its relative content and distribution of pro-oxidants and antioxidants. Bruhn and Franke (1971) reported that spontaneous oxidation is directly proportional to the copper content and inversely proportional to the a-tocopherol content of milk. Charmley et al. (1991) showed that intramuscular injection of cows with a-tocopherol may overcome a spontaneous oxidized flavor problem caused by low levels of a-tocopherol in milk. In general, milk from pasture-fed cows is less susceptible to oxidation due to a higher content of tocopherols than milk from cows given dry feed (Bruhn and Franke 1971 Urbach, 1989, 1990). 

Schwartz and Parks (1974) noted that awareness of the role of metal ions in the oxidation of milk fat has existed since 1905. ft has long been recognized that Cu and Fe are the principal metals involved. Both these metals are normal constituents of milk but may also be present as contaminants concentrations of Cu and Fe in U.S. milk have been reported to be highest in winter and lowest in summer (Murty et al., 1972). Copper is present at a level of 20-400 pg/l and Fe at a level of 100-900 pg/l (Horvat et al., 1965 Koops, 1969 Murty et al., 1972 Johnson, 1974 Jarrett, 1979). However, as noted above, Cu is the principal catalytic metal in lipid oxidation. 

Chen, Z.Y., Nawar, W.W. 1991a. Role of milk fat globule in the auto-oxidation of milk fat.. / Food Sci. 56, 398-401, 426. 

Day, E.A., Lillard, D.A., Montgomery, M.W. 1963. Auto-oxidation of milk lipids. III. Effect of flavor of the additive interactions of carbonyl compounds at sub-threshold concentrations.. / Dairy Sci. 46, 291-294. 

Hill, R.D., van Leeuwen, V., Wilkinson, R.A. 1977. Some factors influencing the auto-oxidation of milks rich in linoleic acid. N.Z. J. Dairy Sci. Technol. 12, 69-77. 

Schaffer, P.S., Greenbank, G.R., Holm, G.E. 1946. The rate of auto-oxidation of milk fat in atmospheres of different oxygen concentration. J. Dairy Sci. 29, 145-150. 

Oxidation of milk fat is one of the most important factors limiting the keeping qnality of dairy prodncts. Lipid oxidation yields hydroperoxides that decompose to a broad group of carbonyl componnds, which can contribnte to off-flavors in dairy prodncts. The oxidative stability of fat depends on its composition. Compared with many edible fats, milk fat is relatively resistant to oxidation because of its low PEFA content, and high proportion of satnrated FA, and the presence of natural antioxidants, principally a-tocopherol and P-carotene. Milk fat from the summer contains... 

Oxidation of milk lipids is an important cause of flavor deterioration of dairy products that is often referred to as oxidative rancidity, to distinguish it from hydrolytic rancidity resulting from lipolysis. Milk products have complex compositions, physico-chemical properties, and contain natural prooxidants... 

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