Question

Which fatty acid produces characteristic off-flavour with hydrolytic rancidity of butter?

• A. Stearic acid
• B. Butyric acid
• C. Palmitic acid
• D. Linolenic acid

Hint:

Rancidity Types in Dairy:
HYDROLYTIC Rancidity = Release of free BUTYRIC ACID (C4:0) by Lipase.
OXIDATIVE Rancidity = Lipid peroxidation of unsaturated fats yielding Aldehydes (Hexanal, Octanal).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Lipolysis and hydrolytic rancidity in dairy products: milk lipoprotein lipase hydrolyzes milk fat triglycerides at the sn-3 position, releasing free volatile short-chain butyric acid (C4:0) with its pungent rancid/sweaty odor.
Key Formula or Approach:
\[ \text{Milk Fat Triglyceride} \xrightarrow{\text{Lipase (Lipolysis)}} \text{Diglycerides} + \mathbf{Butyric \text{ } Acid (\text{C}_4\text{H}_8\text{O}_2)} \implies \mathbf{Hydrolytic \text{ } Rancidity} \]

Step 2: Detailed Explanation:
In dairy chemistry and butter quality degradation:
- Hydrolytic Rancidity is caused by enzymatic cleavage of ester bonds in milk fat triglycerides by native milk lipoprotein lipase (LPL) or microbial lipases (from Pseudomonas).
- Milk fat is unique among dietary fats in containing high proportions of Butyric Acid (Butanoic acid, C4:0, $\approx 3 - 4\%$), which is esterified preferentially at the sn-3 position of the glycerol backbone where lipases act first.
- Free, unesterified Butyric Acid (B) (along with caproic C6 and caprylic C8 acids) is highly volatile and water-soluble with an extremely low sensory threshold, producing the sharp, acrid, pungent, vomity, and 'rancid' off-flavour of spoiled butter.

Step 3: Final Answer:
Thus, the fatty acid producing characteristic rancid off-flavour is Butyric acid, corresponding to option (B).