Rapid Determination of Casein in Milk

Abstract

MORE than half the total acidity of milk is due to casein. This casein, which occurs in the form of calcium caseinate, can be removed by curdling the milk with rennet. The amount of calcium bound to casein is related to the acidity of the milk; the higher the acidity, the lower the calcium content of the casein. We therefore conclude that the casein content can be determined on the basis of milk acidity and of acidity of whey obtained by rapid precipitation of the calcium caseinate with rennet; it will be proportional to the difference between total milk acidity and acidity of whey. Moreover, for a given milk in which the casein content does not change, this difference will be higher, the higher the milk acidity at the moment of adding rennet. Hence the coefficient used for multiplying the difference between milk and whey acidity for determining the casein content must be lower the higher the acidity of the milk under investigation. This determination should not be affected by the development of microflora in the milk (as is the case with the formol method), since amino- and carboxyl-groups are liberated equally.