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Changes of Disc Gel Electrophoretic Patterns of Human Milk Protein with Duration and Temperature of Storage of the Milk

Central Research Laboratory, Morinaga Milk Industry Co., Ltd., Tokyo, Japan

ABSTRACT

Changes in pH, nitrogen distribution, and electrophoretic patterns of proteins in human milk during storage at 5 C were observed for eight days. The pH of human whole milk rapidly dropped to about 6.4 on the second day of storage, regardless of the presence or the absence of thimerosal. When whole milk was heated at 80 C for 20 min or defatted, a slight increase of pH was observed. In skimmed milk containing thimerosal, no significant change occurred in nitrogen distribution during storage. However, skimmed milk without thimerosal markedly increased in nonprotein nitrogen and decreased in casein nitrogen after the fourth day of storage. On disc gel electrophoretic patterns of human whey protein, the -lactalbumin band decreased in intensity during storage. In human casein, together with decreased intensity of the main bands, faster moving secondary bands appeared. When a casein solution prepared from human milk immediately after its collection was incubated at 37 C, the faster bands also appeared. However, in human casein solutions preheated at 80 C for 20 min, and in cow casein solutions, changes in the bands were not observed.