Question

Given below are two statements:
Statement (I): Diacetyl is formed by oxidative decarboxylation of alpha-acetolactate.
Statement (II): The process of diacetyl formation is a chemical process taking place in presence of lactic acid at low pH.

• A. Both Statement (I) and Statement (II) are true
• B. Both Statement (I) and Statement (II) are false
• C. Statement (I) is true but Statement (II) is false
• D. Statement (I) is false but Statement (II) is true

Hint:

Diacetyl production requires oxygen (for oxidation) and low pH (acidity). This is why incorporating air (oxygen) and allowing sufficient acid development (low pH) are crucial in industrial butter starter fermentations.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Diacetyl (2,3-butanedione) is the primary volatile flavor compound responsible for the characteristic buttery aroma in fermented dairy products like dahi, butter, and cultured buttermilk.
Detailed Explanation:
Let us evaluate both statements individually:
- Statement I: During citrate metabolism by aroma-producing lactic acid bacteria (such as Lactococcus lactis subsp. diacetylactis and Leuconostoc spp.), citrate is converted to pyruvate. Excess pyruvate condenses with active acetaldehyde to form \(\alpha\)-acetolactate. Under aerobic conditions, \(\alpha\)-acetolactate undergoes oxidative decarboxylation to produce diacetyl. Thus, Statement I is true.
- Statement II: Lactic acid bacteria do not possess an active enzyme to convert \(\alpha\)-acetolactate directly into diacetyl internally. Instead, \(\alpha\)-acetolactate is excreted from the bacterial cells into the surrounding milk. The non-enzymatic, chemical oxidative decarboxylation of \(\alpha\)-acetolactate to diacetyl takes place in the extracellular environment. This chemical conversion is highly favored and accelerated by low pH (acidity) generated by lactic acid production and the presence of dissolved oxygen. Thus, Statement II is true.
Since both Statement I and Statement II are correct, the correct option is (A).
Final Answer:
Both Statement (I) and Statement (II) are true. Hence, the correct option is (A).