CASEIN VISCOSITY STUDIES.
1. Viscosity and pH curves of casein dissolved in NaOH, KOH, LiOH, and NH(4)OH are shown and it is found that a maximum viscosity occurs at about the same pH point with each alkali; i.e., 9.1 to 9.25. The magnitude of the viscosity is largest in ammonia solutions. 2. The maximum viscosity occurs in 8 to 10 per cent solutions of casein in alkalies when about 98 x 10(-5) gram equivalents of base are combined with 1 gram of casein. 3. A maximum viscosity occurs in the same region (pH 9.1 to 9.25) when casein is dissolved in Na(2)CO(3), Na(3)AsO(4), Na(2)SO(3), NaF, and Na(2)PO(3). 4. The maximum viscosity obtained with borax solutions of casein occurs at 8.15 to 8.2 pH. It is suggested that casein acts like mannitol, glycerol, etc., in increasing the dissociation of boric acid. 5. The flattening of the viscosity curves of casein solutions, following the decline from maximum, is shown to be due to alkaline hydrolysis whence casein no longer exists as such but is cleaved into a major protein containing no phosphorus or sulfur and less nitrogen. This cleavage commences at pH 10.0 to 10.5. 6. When casein is prepared from solutions that have been subjected to high temperatures (60 degrees C. and above) or has otherwise been heated during its preparation, it yields solutions in alkalies of high viscosity.
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Research Laboratories of the Dairy Division, Bureau of Animal Industry, United States Department of Agriculture, Washington.