Objective:  To determine the specific thermal death rate of S. cerevisiae at different temperature in a batch cultivation.

Theory:  The killing of the microbial population by heat (elevated temperatures, dry / moist heat etc) is majorly applied in fermentation laboratories &/or industries. In all the above procedures the destruction or death of the microorganisms by heat features loss of viability, not destruction in physical sense. The physical entity (dead cells) of the microorganism will remain in the bioreactor and will still contribute in the optical density values of different samples from the bioreactor. The cell death rate by heat at a specific temperature follows a monomolecular rate of reaction as shown below:

Where "NV" is the number of viable cells

"kd" is the specific thermal death rate at temperature "T"

So, for a system where there only killing of the cells (no growth) at a particular temperature "T", then the slope of a plot between "loge Nv" vs "t" will give  "kd"  (the specific thermal death rate)
 

However, if the temperature is not high enough and it will feature growth as well death of the microorganisms. Assuming that µ is the specific growth rate at a temperature "T", then the net rate of growth of viable cells is given by.

The rate of increase in the total microbial population (NT) is given by

From equation (3) plot of "loge NV / NV0" vs "t" will give "(µ - kd)".

From equation (5) plot "(NT – NT0)" vs "(NV – NV0)", slope will give "µ / (µ - kd)".

Hence "kd" and "µ" can be simultaneously evaluated from the above plots.

From plug [1], [2] & [3] "µ" & "kd" can be determined.