Subtopic: Engineering Properties of Biological Materials
Question Statement:
In agricultural grain and food preservation, the critical water activity ($a_w$) below which all pathogenic and spoilage bacteria cease to grow is approximately:
Options:
(A) $0.85$ (with no bacterial proliferation below $0.60$ for halophilic/xerophilic microbes)
(B) $0.99$
(C) $0.20$
(D) $0.05$
Answer Key:
A
Step-by-Step Solution & Explanation
Most foodborne pathogenic bacteria require $a_w > 0.91$, while staphylococci grow down to $0.85$. Below $a_w = 0.60$, no microbial proliferation (including xerophilic molds and osmophilic yeasts) is possible.