Discussion
The microbial death kinetics for a food suspension follows the equation:
\[ log \frac{N_{0}}{N} = 1 + \frac{t - t_{l}}{D} \]
where No= initial microbial load, N = microbial load after time t, tl = lag time and D = decimal reduction time.
The correct statement for this equation is
Answer: B
The correct statement is that the time required to reduce the initial 90% of the population is the lag time.
Put \(t = t_{l}\) in the equation:
\[ \begin{aligned} log\frac{N_{0}}{N} &= 1 + 0 = 1 \\ \frac{N_{0}}{N} &= 10, \ N = 0.1N_{0} \end{aligned} \]
So at the end of the lag time one log cycle, 90% of the population, has already been destroyed. Thereafter each further D minutes removes another 90%.
Reducing only 10% of the population is a far smaller change than one log cycle, so the first option is wrong. The other two statements compare the lag time with D, but the equation treats them as independent constants: nothing in it makes the time for the first 90% shorter than D, or makes the lag time approach D as N0 and the temperature fall.
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