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Influence of Phosphate and Other Factors on the Rennin Gel Obtained with Whole Casein and with -Casein in the Presence of Calcium Salts

Eastern Utilization Research and Development Division, Agricultural Research Service, USDA, Philadelphia, Pennsylvania 19118

ABSTRACT

Firm gels are obtained by the action of rennin on solutions of whole casein (0.5%) containing calcium chloride (0.010 m) and sodium phosphate (0.0030 m) ; without the phosphate, flocculent precipitates are obtained. -Casein acted on by rennin gives gels irrespective of the type of salts present. The phosphate effects gel formation with whole casein at molar ratios of phosphate to calcium chloride as little as 1:24. Glycerophosphate, substituted phosphate, is not effective in gel formation nor is the sulfate ion. Polyphosphate-hexameta (7) and imidazole prevent or lessen gel formation, presumably because micelle formation is decreased, judged by visual changes in turbidity. Reduction of gel formation by sodium chloride (0.05 it) is also indicated by reduction in micelle formation. It could only be concluded that the phosphate-calcium bond, presumably ionic, is no weaker than the calcium-casein bond. Exposure of casein solutions to HC1 vapors gives gels characterized by the low pH (1.0) of formation.

Addition of sodium chloride to whole casein solutions reduced viscosity; further addition of calcium chloride reduced viscosity more. The latter is a specific effect accompanying micelle formation. -Casein alone does not show this effect. Addition of phosphate to the whole casein calcium-containing system does not give the expected increase in viscosity but a slight decrease instead, supporting the theory that the surface of the casein micelle does not favor calcium-phosphate cross bonds but that the action of rennin leads to the appearance of a reactive surface.

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