Question

The indicator used in estimation of Reichert-Meissel/Polenske value of ghee is

• A. Methyl red
• B. Methylene blue
• C. Starch
• D. Phenolphthalein

Hint:

Ghee Constants Indicators: RM Value & Polenske Value Titration uses PHENOLPHTHALEIN INDICATOR (Titrated against 0.1 N NaOH to pink endpoint).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Acid-base neutralization titration in fat constant analysis: Reichert-Meissl and Polenske values titrate steam-distilled volatile short-chain fatty acids against 0.1 N NaOH using phenolphthalein indicator (pH transition 8.2--10.0, colorless to faint persistent pink).
Key Formula or Approach:
\[ \text{Volatile Fatty Acids (Butyric, Caproic, Caprylic)} + \text{NaOH (0.1 N)} \xrightarrow{\mathbf{Phenolphthalein \text{ Indicator}}} \mathbf{Faint \text{ } Pink \text{ } Endpoint} \]

Step 2: Detailed Explanation:
In dairy lipid analysis and ghee purity constants (IS: 1479 IS: 3508 AOAC Method):
- Reichert-Meissl (RM) Value (number of mL of $0.1\text{ N NaOH}$ required to neutralize steam-volatile water-soluble fatty acids, principally butyric and caproic) and Polenske Value (PV) (steam-volatile water-insoluble fatty acids, caprylic and capric):
- Ghee is saponified with glycerol-NaOH, acidified with sulfuric acid, and steam-distilled in a standardized Polenske apparatus.
- The distilled volatile fatty acids are directly titrated against standard $0.1\text{ N Sodium Hydroxide (NaOH)$} using Phenolphthalein Indicator (D).
- The endpoint is reached upon the appearance of the first faint, persistent pink color lasting for 30 seconds (pH $8.3$).

Step 3: Final Answer:
Thus, the indicator used in RM/Polenske value estimation is Phenolphthalein, matching option (D).