Use this page to download an Excel workbook that simulates the logarithmic inactivation of a targeted microorganism during non-isothermal heat treatment. This version of the program simulates the inactivation of organisms whose isothermal survival curve follows the model LS(t) = If[Time<=t1 then -k1*Time else -k1*t1-k2*(Time-t1)]. The temperature dependence of the inactivation parameters t1(Temp), k1(Temp) and k2(Temp) obeys a logistic relationship.
For generating an inactivation curve with this version of the program, the user needs to generate a temperature profile first by selecting a temperature model and its parameters. The default model included here, Temp(time)=TempInit + time/(Tpar1 + Tpar2*time), has three parameters: TempInit, the initial temperature, Tpar1, a rate parameter and Tpar2, the inverse of the asymptotic temperature value.
CAUTION: Some combinations of temperature profile and survival parameters with the chosen time interval (dt) may create a very steep survival curve which will result in a program error.
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Note: The first version of the Excel file was dated October 27, 2006. The September 4, 2007 version updated the first reference. The February 4, 2008 version added compatibility with Windows Excel 2007 and made corrections to a few comment notes.
The Excel workbook (MicrobialBiphasicInactivation.xls) is available in the file format of Excel 97 through 2007 for Windows and Excel 98 through 2004 for MacOS. If you have a modern web browser you should be able to download the binary Excel file directly by clicking on the above link. If a compatible version of Excel is currently installed on your computer, double-click the icon for the .xls file that was downloaded to open the workbook file in Excel. Be sure to click the 'Enable Macros' button in the dialog box that appears. If you are using a recent version of Excel for Windows, you may need to first reduce the security level in Excel under Tools>Macro>Security to Medium, then close and reopen the file to enable the macros.
On the Excel worksheet, the Solve button executes a Visual Basic macro to automatically update any cells and charts in the worksheet that are affected by changes you make to the model parameter and chart setting cells in columns A and B. You must click on the 'Enable Macros' button in the dialog box that is displayed before the worksheet opens in Excel in order for the macro to be useable.