Subtopic: Preservation of food by cooling and freezing
Question Statement:
The microbial death kinetics for a food suspension follows the equation: log(N0/N) = 1 + (t−t_l)/D, where N0=initial microbial load, N=microbial load after time t, t_l=lag time, D=decimal reduction time. The correct statement for this equation is
Options:
(A) the time required to reduce 10% of the initial population is lag time.
(B) the time required to reduce the initial 90% of population is lag time
(C) time required to kill the first 90% population is lower than D value at the same temperature
(D) lag time approaches D value as N0 becomes smaller and temperature decreases.
Official Answer Key:
B
Step-by-Step Solution & Explanation
Find the time t at which the population is reduced by 90% (i.e., N=0.1N0, so N0/N=10, log(N0/N)=1). Substituting into the given equation: 1 = 1+(t−t_l)/D ⇒ (t−t_l)/D = 0 ⇒ t = t_l. This shows that, according to this equation, a 90% reduction in population is achieved exactly at t = t_l (the lag time) — i.e., “the time required to reduce the initial 90% of population IS the lag time.” This directly matches statement (B). Answer: (B).
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