Question

Silver nitrate and Potassium chromate solutions are reagents used in the test meant for .............................

• A. Detection of mastitic milk
• B. Differentiating faecal and non faecal coliforms
• C. Assessing activity of starter cultures
• D. Differentiating Gram positive and Gram negative bacteria

Hint:

Remember the physiological changes in mastitis:
- Chloride and Sodium levels increase (leakage from blood).
- Potassium, Casein, and Lactose levels decrease.
Mohr's titration detects this increased chloride using silver nitrate and a chromate indicator.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Mastitis is an inflammatory disease of the mammary gland in dairy cows, usually caused by bacterial infection.
This inflammation damages the milk-secreting epithelial cells and increases the permeability of the blood-milk barrier.
This structural change allows blood constituents, particularly sodium and chloride ions, to enter the milk while suppressing the synthesis of lactose and casein.

Step 2: Detailed Explanation:
Normal bovine milk has a relatively low chloride content, typically ranging between 0.08% and 0.12%.
In contrast, mastitic milk exhibits a significantly elevated chloride concentration, often exceeding 0.14%.
This biochemical change is used in rapid chemical screening tests to detect mastitis, such as the chloride estimation test.
The quantitative or semi-quantitative estimation of chloride in milk is performed using Mohr's argentometric titration method.
In this test, Silver nitrate (\(\text{AgNO}_3\)) serves as the titrant, and Potassium chromate (\(\text{K}_2\text{CrO}_4\)) is used as the indicator.
When silver nitrate is added to the milk sample, silver ions react preferentially with the chloride ions present to form a white precipitate of silver chloride (\(\text{AgCl}\)):
\[ \text{Ag}^+ + \text{Cl}^- \rightarrow \text{AgCl}\downarrow \quad (\text{White precipitate}) \]
Once all chloride ions are precipitated, any excess silver ions react with the chromate indicator to form a reddish-brown precipitate of silver chromate (\(\text{Ag}_2\text{CrO}_4\)):
\[ 2\text{Ag}^+ + \text{CrO}_4^{2-} \rightarrow \text{Ag}_2\text{CrO}_4\downarrow \quad (\text{Reddish-brown precipitate}) \]
An elevated chloride level in mastitic milk requires a higher volume of silver nitrate to reach this color change, providing a clear diagnostic indicator of the infection.

Step 3: Final Answer:
Silver nitrate and potassium chromate are reagents used in the argentometric test for the detection of mastitic milk.