Posted: April 2nd, 2015

The inactivation curve is done by plotting temperature against time

 

 

The inactivation curve is done by plotting temperature against time (Holger 2002, p. 47). The area under the curve is then determined using the

trapezoid rule. Afterwards the D – value of the thermal processes can be determined (Yoshihiro, Eugene and Ludwig 2002, 250).

For all the graphs, X axis are the plot for temperature whereas y axis represents time in seconds.

 

1. Inactivation Curves for each Set of Results

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2. Explanation for the shapes of the inactivation curves

For all the curves, the temperature increases as the time for inoculation increase at the

start. This is a clear indication that the bacteria survived the low temperatures. However, the situation changes after the temperature reaches 1 degree as the temperature increase but the time decrease for the Streptococcus faecalis and E.Coli while that of Staphylococcus aureus changes at 2 degree temperature.

This indicates that the bacteria became inactive and succumbed to the high temperatures.

 

 

3. Appropriate data to determine the D values* for each organism and reasons for the choice

The data selected for the three vegetative bacteria is from time 0 to time 5 minutes because using logarithm to base 10, the data becomes linear, and would be more representative of the inactivation process. The units for the inactivation rate are colony forming units per ml per minute.

 

 

 

4. Determination of D values* for each organism and comments

For Staphylococcus aureus the D values* are:

D values* at 5^oC

D values* at 20^oC = 1.0852

D values* at 35^oC = 1.1677

 

 

 

 

 

The D values* for Streptococcus feacalis are:

D values * at 5^oC

D values* at 20^oC = 1.2056

D values* at 35^oC = 1.1685

 

The D values* for E. coli are:

D values* at 5^oC

D values * at 20^oC = 1.1167

D values * at 35^oC = 1.1361

 

It can be concluded that for Staphylococcus aureus, the highest inactivation rate was 1.1677cfu/ml/minute at 35^oC, whereas the lowest was at 5^oC.

The highest inactivation rate for Streptococcus feacalis was 1.2056cfu/ml/minute at 20^oC and the lowest was at 5^oC.

The highest inactivation rate for E.coli was 1.1361cfu/ml/minute at 35^oC, and the lowest rate was at 5^oC.

Conclusion

In conclusion, as the temperature increased the rate of inactivation increased, and for Staphylococcus aureus and E.coli, 35^oC

was the optimum temperature for inactivation by thermal-chemical disinfection.