Welcome back.

I am going to explain how to do this bycalculating the slope of the thermal death curve for the organism you havestudied using an Excel function called "slope". The D-value is thenobtained by obtaining the negative reciprocal of the slope.

1. I presume that you have these valuesin an Excel spreadsheet? If not create a workbook with 3 columns, Time(minutes), Colony forming units/ml, and Log_{10 }colonyforming units/ml.

2. Convert your colony forming units (CFU)/mlvalues to their log_{10 }equivalents.

3. Excel 2010 has a useful slopefunction to calculate the slope of the linear regression line for x and yvalues and I will explain how to use this function.

4. Lets assume that your time values (xvalues) are in column A and range from A2 to say A15 and the corresponding log_{10 }colonyforming units/ml are in column C and range from C2 to C15. The slope can thenbe calculated using =slope(C2:C15, A2:A15).

5. The D-value is obtained by obtainingthe reciprocal of the slope and multpling this value by -1.

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Hi again!

Got table of time (mins) and nos of survivors at 200F. Pl can you tell how to calculate D at 200F?

Thanks.

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