Question

Antioxidants in foods function by -
(A) Inactivation of free radicals by donating hydrogen atoms
(B) Chelation of prooxidant metals
(C) Breakdown of hydroperoxides into non-flavourful substances
(D) Inactivation of lipolytic enzymes

• A. (B), (C) and (D) only.
• B. (B) and (C) only.
• C. (A), (B) and (C) only.
• D. (A), (C) and (D) only.

Hint:

Antioxidants are categorized into:
1. Primary (chain-breaking): Donate hydrogen to stabilize free radicals (A).
2. Secondary (preventive): Chelate metal catalysts (B) or decompose hydroperoxides (C).
They do not affect lipase enzymes.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Antioxidants are substances added to fat-containing foods to prevent or delay the onset of oxidative rancidity (autoxidation).
They function through different chemical mechanisms to interrupt the free radical chain reaction or prevent its initiation.

Step 2: Detailed Explanation:
Let us analyze the different antioxidant mechanisms:
- Inactivation of free radicals by donating hydrogen atoms (A): This is the primary mechanism of chain-breaking (or primary) antioxidants, such as BHA, BHT, propyl gallate, and natural tocopherols.
They donate a hydrogen atom to highly reactive lipid alkyl-peroxyl (\(\text{ROO}^\bullet\)) or alkoxyl (\(\text{RO}^\bullet\)) radicals, converting them into stable hydroperoxides and forming stable, low-energy antioxidant radicals that cannot propagate the oxidation chain.
- Chelation of pro-oxidant metals (B): This is the mechanism of secondary (or preventive) antioxidants, such as citric acid, EDTA, and phosphoric acid.
They bind divalent transition metal ions (like \(\text{Fe}^{2+}\) and \(\text{Cu}^{2+}\)) that catalyze the decomposition of hydroperoxides and the initiation of free radicals, rendering them inactive.
- Breakdown of hydroperoxides (C): Certain oxygen scavengers and reducing agents (such as ascorbic acid, sulfites, or specific enzymes) chemically reduce hydroperoxides into stable, non-radical, non-flavorful alcohols, preventing them from decomposing into volatile aldehydes and ketones.
- Inactivation of lipolytic enzymes (D): Lipolytic enzymes (lipases) catalyze hydrolytic rancidity, not oxidation.
These enzymes are inactivated by thermal processing (pasteurization), not by food antioxidants.

Step 3: Final Answer:
Antioxidants function through mechanisms (A), (B), and (C), which corresponds to (A), (B) and (C) only.