Distribuce 65Zn umele pridaneho do mleka a mlecnych frakci.
1991
Mirchi R. | Kminkova M.
Milk was labelled with the Zn-65 radioisotope at a rate of 156 microgramme per litre. The content of Zn-65 was measured by the radiometrical method in the main milk fractions, indicated in the diagramme. Pasteurized nonhomogenized milk with an initial fat content of 3 per cent was centrifuged and 0.3 per cent fat remained in the skimmed milk. The skim milk contained 98.1 per cent of the zinc and the fat contained 1.9 per cent of it. The zinc levels measured during the washing of the fat (7.1 per cent) were included in the total level of 98.1 per cent. Further fractionation was carried out in industrially centrifuged milk containing 0.03 per cent fat and enriched again with the same amount of Zn-65 (156 microgramme per litre). The milk was subjected to acid coagulation with 1M HCl to the isoelectric point of casein fraction with 36.2 per cent of Zn-65 and whey with 62.0 per cent of the radioisotope. The casein was transferred to a solution to separate the coagulated salts, which contained 20.1 per cent Zn-65. After further coagulation, the casein contained 16.0 per cent of the radioisotope. Ultrafilration on PM 10 membrane separated the whey into retenate with 28.4 per cent Zn-65 together with high-molecular substances, and permeate with 33.4 per cent of the radioisotope. The same starting conditions were used in other trials from which it follows that pasteurized homogenized milk and pasteurized nonhomogenized milk with a starting fat content of 3.4 per cent have very different levels of radioisotope (1.6 and 9.6 per cent) in their fat phase after skimming under the same conditions to 0.15 per cent and 0.8 per cent of fat. Raw milk with a starting fat content of 4.3 per cent had an even greater content of radioisotope (11.6 per cent) after the skimming. The starting treatments (pasteurization and homogenization) have an influence on zinc content in the fat phase of the milk.
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