Calcium Caseinate Agar, Granulated (Revised as Calcium M- Protein Agar, Granulated)

Principle And Interpretation

Protein hydrolysis by microorganisms in foods may produce a variety of odour and flavour defects. On the other hand, microbial proteolytic activity may be desirable in certain foods such as in the ripening of cheese, where it contributes to the development of flavour, body and texture. In some foods the level of proteolytic microorganisms may be of value to predict refrigerated storage life and to assess processing methods (1, 2). Calcium Caseinate Agar is a modification of the original formulation of Frazier and Rupp (3) and is used for the detection and enumeration of proteolytic microorganisms in foodstuffs and other materials. Peptic digest of animal tissue, casein enzymic hydrolysate, meat extract provides nitrogenous, carbonaceous nutrients along with vitamins and amino acids. Phosphates are added to buffer the medium. Sodium chloride maintains the osmotic equilibrium. Casein in the medium is degraded by the proteolytic organisms. This results in formation of clear zones around the proteolytic colonies, in the otherwise opaque medium. Agar acts as a solidifying agent.

The test sample can be directly surface inoculated or the inoculation can be carried out by the pour plate technique. After an incubation for 24-48 hours, proteolytic organisms, if present will form clear zones on the medium. For better visualization of the zones, the plates can be flooded with 5-10% acetic acid.