Whole milk powder peroxide value

Several methods have been introduced which express the degree of oxidation deterioration in terms of hydroperoxides per unit weight of fat. The modified Stamm method (Hamm et at 1965), the most sensitive of the peroxide determinations, is based on the reaction of oxidized fat and 1,5-diphenyl-carbohydrazide to yield a red color. The Lea method (American Oil Chemists Society 1971) depends on the liberation of iodine from potassium iodide, wherein the amount of iodine liberated by the hydroperoxides is used as the measure of the extent of oxidative deterioration. The colorimetric ferric thiocyanate procedure adapted to dairy products by Loftus Hills and Thiel (1946), with modifications by various workers (Pont 1955 Stine et at 1954), involves conversion of the ferrous ion to the ferric state in the presence of ammonium thiocyanate, presumably by the hydroperoxides present, to yield the red pigment ferric thiocyanate. Newstead and Headifen (1981), who reexamined this method, recommend that the extraction of the fat from whole milk powder be carried out in complete darkness to avoid elevated peroxide values. Hamm and Hammond (1967) have shown that the results of these three methods can be interrelated by the use of the proper correction factors. However, those methods based on the direct or indirect determination of hydroperoxides which do not consider previous dismutations of these primary reaction products are not necessarily indicative of the extent of the reaction, nor do they correlate well with the degree of off-flavors in the product (Kliman et at. 1962). 

Pyenson, H. and Tracy, P. H. 1946. A spectrophotometric study of the changes in peroxide value of spray-dried whole milk powder during storage. J. Dairy Sci. 29, 1-12. 

Figure 3.13 Headspace analysis of volatiles of whole milk powder stored in air at 40 C (peroxide value 1.01). 1 = pentanone 2 = pentanal 3 = methyl butyrate (internal standard) 4 = hexanal 5 = heptanone 6 = heptanal 7 = octanal 8 = octanoic 9 = nonanal. Chromatographic conditions were as in Fig. 3.12. Reproduced from Ulberth, F. and Roubicek, D., Monitoring of oxidative deterioration of milk powder by headspace gas chromatography. International Dairy Journal, 5, 523-31, 1995.

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