Question

n-Octanal is the product of autoxidation of______\

• A. Oleic acid
• B. Linoleic acid
• C. Alpha-linolenic acid
• D. Gamma-Linolenic acid

Hint:

Different fatty acids yield distinct major aldehydes upon oxidation: Oleic acid (monounsaturated) yields octanal and nonanal, while Linoleic acid (diunsaturated) yields hexanal.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Lipid oxidation (autoxidation) is a major cause of flavor deterioration in milk and dairy products.
Unsaturated fatty acids undergo free-radical reactions with oxygen to form unstable hydroperoxides.
These hydroperoxides subsequently decompose into a complex mixture of volatile secondary oxidation products, including aldehydes, ketones, and alcohols.
Specific fatty acids yield characteristic volatile aldehydes upon autoxidation.

Step 2: Detailed Explanation:
Oleic acid is a monounsaturated fatty acid with a single double bond at carbon 9 (C18:1, cis-9).
During autoxidation, hydrogen abstraction occurs primarily at the allylic carbons at positions 8 and
This results in the formation of four isomeric hydroperoxides at carbon positions 8, 9, 10, and
The subsequent cleavage of these hydroperoxides via homolytic $\beta$-scission yields volatile aldehydes.
Specifically, the cleavage of the 11-hydroperoxide of oleic acid yields n-octanal and 10-oxodecanoic acid.
The decomposition can be represented schematically as:
\[ \text{Oleic acid 11-hydroperoxide} \xrightarrow{\beta\text{-scission}} \text{n-Octanal} + \text{Alkyl radical product} \]
Autoxidation of polyunsaturated fatty acids like linoleic acid (C18:2) and linolenic acid (C18:3) yields different major compounds, such as hexanal and 2,4-decadienal, due to their multiple double bonds.
Thus, n-octanal is a specific indicator of oleic acid autoxidation.

Step 3: Final Answer
n-Octanal is a key volatile compound formed during the autoxidation of oleic acid.