Question

Reichert-Meissl (RM) number is defined as......

• A. The number of mg of KOH required to completely neutralize free fatty acids present in one-gram fat or oil.
• B. The number of ml of 0.1 N KOH required to completely neutralize the soluble volatile fatty acids distilled from 5 g fat.
• C. mg of KOH required to hydrolyse one gram of fat or oil.
• D. grams of iodine absorbed by 100 g of fat or oil.

Hint:

Associate the Reichert-Meissl (RM) test with:
- 5 grams of fat sample
- 0.1 N alkali solution
- Detection of butyric acid to identify ghee adulteration.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The Reichert-Meissl (RM) number is a critical alytical parameter used in food quality laboratories to assess the purity of milk fat (ghee and butter).
Key Principle:
Butterfat is unique because it contains high concentrations of short-chain, water-soluble, volatile fatty acids, particularly butyric acid ($C_4$) and caproic acid ($C_6$).

Step 2: Detailed Explation:
The RM value is determined through a standardized chemical procedure:
1. A 5-gram sample of the fat is saponified using sodium hydroxide and glycerol to break down the triglycerides into free fatty acids and glycerol.
2. The mixture is acidified with dilute sulfuric acid to liberate the volatile fatty acids.
3. Steam distillation is performed to separate the volatile, water-soluble fatty acids from the non-volatile, insoluble fatty acids.
4. The distillate is filtered, and the soluble fraction is titrated against a standard 0.1 N alkaline solution (such as KOH or OH).
The Reichert-Meissl number is defined as the volume (in milliliters) of this 0.1 N alkali required to neutralize the soluble volatile fatty acids obtained from exactly 5 grams of fat.
Pure butterfat has a high RM value (typically between 26 and 30) due to its butyric acid content.
In contrast, vegetable oils and animal fats have RM values close to zero.
This difference makes the RM number an invaluable tool for detecting the adulteration of butter or ghee with cheap foreign fats.
Option (A) defines the Acid Value; Option (C) defines the Saponification Value; and Option (D) defines the Iodine Value.

Step 3: Fil Answer
The RM number is defined as the volume in mL of 0.1 N KOH needed to neutralize the soluble, volatile fatty acids distilled from 5 g of fat.