The Effect of Rennin Upon Casein

Abstract

In a preceding investigation (1) upon certain properties of paracasein, we attempted to identify paracasein by physicochemical means.Paracaseins were prepared by coagulating milk by means of rennin or pepsin preparations, puri/ying the resulting paracasein in the same way as was done in the case of casein (2). Such preparations, free from any proteolytic enzyme, were then tested for their solubility in water and for their solubility in dilute NaOH solutions at two temperatures. It was found that although paracasein at about 6°C. dissolves in water to the same extent as casein, the capacity to bind base was distinctly different from that of casein. While casein at 21 to 37°C. dissolves in combination with base to the extent of about 2100 gm. per tool of NaOH added (2, 3), most of the paracasein preparations combined with NaOH in this temperature range with a combining weight of 1450 gm.The ratio of the equivalent combining weight of casein to the combining weight of paracasein is as 1 to 1.45. Solubility measurements at 5°C. indicated that the same relationship held true for these proteins at low temperature.In the present investigation, we have studied further some of the other properties of paracasein preparations, among which are the hydrogen ion activity in systems composed of paracasein and base, and the maximum base-binding capacity of certain paracaseins.