Question Bank • QB_EXP_DFE_PKG_001 MCQ • 1 Mark

Section 7: Dairy and Food Engineering

Water Activity & Food Packaging

Subtopic: Absolute minimum water activity for microbial growth

Question Statement:

The absolute lower threshold of water activity ($a_w$) below which no known pathogenic or spoilage microorganism (including halophilic bacteria and xerophilic molds) can proliferate is approximately:

Options:

  • (A) $0.60$
  • (B) $0.85$
  • (C) $0.75$
  • (D) $0.91$

Answer Key:

A

Step-by-Step Solution & Explanation

Microbial growth boundaries: - Normal bacteria: $a_w > 0.91$ - Yeasts: $a_w > 0.88$ - Ordinary molds: $a_w > 0.80$ - Halophilic bacteria: $a_w > 0.75$ - Xerophilic molds / osmophilic yeasts: $a_w > 0.61$. Below $a_w = 0.60$, all microbial proliferation ceases completely.
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