Subtopic: Water activity, sorption and desorption isotherms
Question Statement:
Most pathogenic bacteria (including *Salmonella* and *Escherichia coli*) are completely inhibited from growing in foods when the water activity ($a_w$) is reduced below:
Options:
(A) 0.91
(B) 0.80
(C) 0.60
(D) 0.50
Answer Key:
A
Step-by-Step Solution & Explanation
The minimum water activity required for growth of most foodborne pathogenic bacteria is $a_w = 0.91$ (with *Staphylococcus aureus* growing aerobically down to $0.86$). Below $0.60$, no microbial growth (bacteria, yeast, or mold) can occur.