Question

Which of the following statement is NOT true for lactanins

• A. Lactanins exhibit little activity under anaerobic conditions
• B. Addition of reducing substances reduces antimicrobial activity of lactanins in milk
• C. All the three lactanins (\(\text{L}_1, \text{L}_2\) and \(\text{L}_3\)) exhibit similar activity
• D. Lactanins are active against Streptococcus pyogenes

Hint:

Remember that natural milk preservatives like the lactoperoxidase system (lactenins) are oxygen-dependent and are easily inactivated by reducing agents or heat treatment.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Lactenins (historically spelled as lactanins) are naturally occurring, non-immunoglobulin antimicrobial substances found in raw milk.
They play a major role in the natural bacteriostatic properties of raw milk, protecting the newborn and inhibiting spoilage bacteria.
They primarily consist of different fractions, notably Lactenin 1 (\(\text{L}_1\)), Lactenin 2 (\(\text{L}_2\)), and Lactenin 3 (\(\text{L}_3\)).

Step 2: Detailed Explanation:
Let us analyze the physiological and chemical properties of these lactenins:
- Lactenins are highly active against various Gram-positive bacteria, particularly Streptococcus pyogenes and other lactic acid streptococci. This confirms that Statement (D) is true.
- The antimicrobial action of the lactenin system (specifically the lactoperoxidase-thiocyanate-hydrogen peroxide system) is highly dependent on oxidative processes.
- Under anaerobic conditions, the generation of inhibitory intermediate compounds is restricted, resulting in very little antimicrobial activity. This confirms that Statement (A) is true.
- The addition of reducing agents, such as cysteine, hydrogen sulfide, or sodium sulfite, inactivates or significantly reduces the antimicrobial efficacy of lactenins.
These reducing agents disrupt the essential disulfide bonds or consume the oxygen intermediates necessary for the enzymatic reaction. This confirms that Statement (B) is true.
- Regarding Statement (C), the three lactenin fractions do not exhibit similar activity.
\(\text{L}_1\) is predominantly found in colostrum and is highly sensitive to heat, whereas \(\text{L}_2\) is found in mature milk and has different stability characteristics.
\(\text{L}_3\) is another distinct fraction associated with specific agglutinins.
These fractions differ in their thermal stability, concentrations, target ranges, and synergistic interactions, meaning they do not exhibit similar individual activities.

Step 3: Final Answer:
The statement that is not true is that all three lactanins exhibit similar activity, making Option (C) the correct choice.