Question

Factors affecting the improved shelf life of fermented milk products is due to:
A. Reduced pH value
B. Low redox potential
C. High water activity
D. Growth inhibition of undesirable organisms by development of undissociated acids
E. Formation of metabolites such as \(\text{H}_2\text{O}_2\)
Select the correct answer from the given options

• A. A, B, D and E
• B. A and D
• C. A, D and E
• D. A, B, and E

Hint:

Remember that high water activity (\(a_w\)) always favors microbial growth and reduces shelf life. Excluding statement C easily guides you to the correct option.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Fermentation naturally preserves milk by creating an environment that inhibits the growth of spoilage and pathogenic microorganisms.

Step 2: Detailed Explanation:
Let us analyze each factor:

• A. Reduced pH value: Lactic acid production lowers the pH to around 4.0–4.6, which inhibits most spoilage bacteria. (Correct)

• B. Low redox potential: Fast microbial growth during fermentation depletes oxygen, creating a low redox potential that restricts aerobic spoilage organisms. (Correct)

• C. High water activity: High water activity (\(a_w\)) actually *promotes* microbial growth and spoilage. Reducing water activity improves shelf life, so this statement is incorrect. (Incorrect)

• D. Growth inhibition of undesirable organisms by undissociated acids: Weak organic acids (like lactic and acetic acids) are more effective at low pH because they remain undissociated, allowing them to penetrate bacterial cell membranes and disrupt cell function. (Correct)

• E. Formation of metabolites such as \(\text{H}_2\text{O}_2\): Starter cultures produce antimicrobial metabolites like hydrogen peroxide and bacteriocins (e.g., nisin) that inhibit competitors. (Correct)
Since statement C is incorrect, the correct combination is A, B, D, and E.

Step 3: Final Answer
The factors that improve the shelf life of fermented milk are A, B, D, and E.