RM Number (Reichert-Meissl Number)

The Reichert-Meissl (RM) number is a measure of the water-soluble, volatile fatty acids (mainly lower-chain fatty acids like butyric acid and caproic acid) present in fats and oils. It is commonly used for detecting adulteration in dairy fats, especially butter.

Formula & Definition:

The RM number is defined as:

“The number of milliliters (mL) of 0.1 N NaOH required to neutralize the volatile water-soluble fatty acids distilled from 5g of fat or oil.”

Significance:

• Higher RM number → Indicates higher volatile fatty acids, found in butter and animal fats.
• Lower RM number → Indicates adulteration with vegetable oils (which have negligible RM values).

Typical RM Numbers:

• Butter: 24–34
• Ghee: 21–28
• Coconut Oil: 6–8
• Vegetable Oils: ~0 (almost negligible)

Iodine Number (Iodine Value, IV)

The Iodine Number measures the degree of unsaturation in fats and oils, i.e., the presence of double bonds (C=C) in the fatty acid chains.

Formula & Definition:

“The amount of iodine (I₂) in grams that reacts with 100g of fat or oil.”

Significance:

• Higher Iodine Number → More unsaturated fatty acids (e.g., linseed oil, sunflower oil).
• Lower Iodine Number → More saturated fatty acids (e.g., coconut oil, butter).

Typical Iodine Numbers:

• Coconut Oil: 8–10
• Palm Oil: 50–55
• Groundnut Oil: 85–100
• Sunflower Oil: 120–140
• Linseed Oil: 170–190

Acid Value (Acid Number)

The Acid Value (AV) is a measure of the free fatty acids (FFA) present in fats and oils. It is an indicator of rancidity or the freshness of oils.

Formula & Definition:

“The number of milligrams (mg) of KOH (potassium hydroxide) required to neutralize the free fatty acids present in 1g of fat or oil.”

Significance:

• Higher Acid Value → Indicates oxidation, hydrolysis, or spoilage (poor quality oil).
• Lower Acid Value → Indicates fresher, better quality oil.

Typical Acid Values:

• Refined Edible Oils: <1
• Virgin Coconut Oil: 0.5–2
• Rancid Oils: >10 (Indicates significant deterioration)

Summary Table