Whole milk powder 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. 

In an attempt to standardize the analysis of OS, a round-robin test on whole milk powder and skim-milk powder was organised by Appelqvist (1996). Analyses of OS were carried out in 17 laboratories and the differences in the level found led Appelqvist (1996) to conclude that it is still premature to establish true values for the level of OS in certain foods. The results of a second round-robin study on egg and milk powders showed that several OS in the samples were not determined or were below the determin-... 

For example, the cohesion of dairy powders has been studied with an unconfined yield test by preparing cylindrical plugs of powder at different particle sizes and moistures. Unconfined yield stress values were obtained as an index of cohesion for whole milk powder and skim milk powder. Dry... 

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.

Table 19.3 contains results of niacin determinations of some milk samples, again in MRM mode, including RM 8435 (whole milk powder) from NIST. These samples are not fortified and contain niacin at considerably lower levels than the samples in Table 19.2. Precision obtained for these samples is in the range 1-5% RSD. An example of an extracted ion chromatogram for commercial milk Brand F is shown in Figure 19.2. The USDA Nutrient Database for Standard Reference, Release 23 (US Department of Agriculture 2010) lists a value of 0.89 ppm niacin for milk, whole, 3.25% milkfat and a value of 0.84ppm niacin for milk, producer, fluid, 3.7% milkfat . We thus assume that expected values for niacin for whole milk samples are near 1 ppm. The levels...

Table 19.3 Results of niacin determinations for milk samples. Niacin determinations by liquid chromatography-isotope dilution mass spectrometry (LC-IDMS) are compared to expected values for four milk samples. Expected niacin levels for milk are roughly 1 ppm, according to the USDA Nutrient Database for Standard Reference (US Department of Agriculture 2010) and results obtained for two commercial milk samples (Brands F and G) are a little under 1 ppm. The result for sample NFY0409F6 is about 30% lower, but is consistent with results obtained for other milk samples from the same source. In addition, the niaein level for NFY0409F6 was estimated by a standard additions experiment, the result from which is in agreement with the estimate from the normal LC-IDMS procedure. The level obtained for the reference material (RM) RM 8435 whole milk powder, reported on a dry mass basis, is in agreement with the reference value. Data are from Goldschmidt and Wolf (2007), with permission from the publisher.

The specific heat of a substance is the amount of heat energy, in kJ, required to increase the temperature of 1 kg of the substance by 1 K. The specific heat of skim milk increases from 3.906 to 3.993 kJ kg-1 K-1 from 1 to 50°C. Values of 4.052 and 3.931 kJ kg-1 K-1 have been reported for skim and whole milks, respectively, at 80°C (Sherbon, 1988). The specific heat of milk is inversely related to its total solids content, although discontinuities have been observed around 70-80°C. Skim-milk powder usually has a specific heat in the range 1.172-1.340kJ kg-1 K-1 at 18-30°C. 

Solid phase microextraction coupled to gas chromatography-mass spectrometry (SPME-GC/MS) has been used as a sensitive method for measuring volatiles in the headspace of milk powders. Headspace measurements on two samples of infant milk powders gave values of hexanal initially of 466 and 1181 parts per billion (ppb), and 617 to 3430 after accelerated storage at 37°C for 1 to 4 weeks (Table 6.7). These levels are far above the hexanal perception thresholds of 4.5 ppb in water and 50 ppb in homogenized whole milk. 

Orotic acid as well as total creatinine and uric acid are suitable indicators for the determination of the proportion of milk in foods. The average values for whole-milk and skim-milk powder given in Table 10.21 can serve as reference values. 

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