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Measurements and Counts of Large Protein Particles in Sterile Concentrated Skimmilk¹

Department of Food Science, University of Illinois, Urbana 61801

ABSTRACT

Large casein particles dissociated in NaCl solution (.9% w/v) used as electrolyte to count particles in the Coulter counter. Replacing 10% of the NaCl ions with CaCl₂ stopped dissociation and made possible Coulter counts of large protein particles in sterile concentrated skimmilks. Comparisons were made between direct microscopic counts, counts from photomicrographs taken immediately after processing, and Coulter counts of summer milk after 260 days storage. Counts of particles in winter milk were from photomicrographs taken immediately after processing and Coulter counts after 80 days storage. Particles in winter milk were smaller than those in the summer milk. This cannot be explained by the data available because other winter milks processed similarly have had particles as large as those in summer milk. The predominant size in volume was 3 µd for summer milk. Eleven and nine-tenths per cent of the particles in summer milk (3 µd) included 41.5% of the total volume. In winter milk 2-µd particles made up 41.9% of the total count and 66.3% of total volume. About 55% of total phosphate in large particles was inorganic. This suggests that calcium phosphate is the bond that holds large particles together.

¹ This work has been supported by a grant from the Department of Health Education and Welfare of the U.S. Public Health Service, Grant 5ROI FD 00126-04.