Question

List all possible the biochemical reactions of litmus milk broth? Explain why there is change of color or precipitation in each reaction. Provide a full details about this answer.

Answer 1

The litmus milk broth contains milk, litmus, lactose and casein. It differentiates between microorganisms according to their ability to metabolize these substances. The biochemical reactions that occur in this test include- lactose fermentation (with or without gas), litmus reduction, curd formation, proteolytic degradation. These are described below-

1. The lactose present in the medium can be fermented by the microorganism to obtain energy. When lactose fermentation occurs, lactic acid is formed, which is indicated by the litmus as it turns pink or red. Lactose fermentation can be accompanied with formation of gas. When gas formation takes place, cracks are observed in the medium.

2. Litmus present in the medium can get reduced by accepting hydrogen ion. The purple color of litmus is converted to white.

3. Casein protein can get coagulated. This leads to formation of curd and a precipitation is observed. Curd can be of two types- acid or rennet. Acid curd is formed due formation of calcium caseinate, in presence of lactic acid (hard curd). Rennet curd results due production of Rennin enzyme. In it's presence, casein changes to paracasein and calcium paracaseinate is formed (soft curd).

4. Hydrolysis of casein with the help of proteolytic enzymes. Ammonia is produced which is indicated as the litmus turns blue in the upper portion while the media turns brown (whey like).

5. Digestion of milk protein which leads to a clear medium.

None of the above results will be obtained if their is no change in the medium.