Thermal Processing

The app, shown below, was designed to aid in thermal processing calculations of foods (calculating F0 value) subjected to different time and temperature combinations. To be able to use the app, D- and z-value of the target enzyme or microorganisms should be known.

 

For the thermal processing we will use the following time-temperature profile:

Time (minutes) Temperature (°C)
2
1 30
2 55
3 76
4 50
5 25
6 2

 

Here, the usage of app will be demonstrated by creating a Food variable and subjecting that food variable to thermal processing. However, this step can be skipped.

 

Create a variable of type Food which can be done either using command-line or using the Food Database app. Here, command-line will be used.

>>milk=Food.new{water=88.13, protein=3.15, CHO=4.80, lipid=3.25, ash=0.67}

 

Once the app is run and the variable name is entered in the text box where it says "Variable:" and "Show Organisms" button is clicked, possible organisms in the food are listed, as shown in the following figure.

 

 

By using the Microorganism database (located in databases folder), organisms which can grow at the temperature, pH and water activity of the food, namely the variable milk, are listed. Due to D- and z-values of organisms being dependent on the food media as well, it can be noticed that in the list of "Possible Organisms in the Food" some of the organisms are listed more than once. Clicking on each of them will change the value in the "Food Media:" textbox and correspondingly the D- and z-values as well.

 

Please note that D(time), D(temperature) and z-values do not require a specific unit; however, these units must be consistent with the time-Temperature data. In the following figure, the “Thermal Process Calc” tab is shown:

 

Once calculate the data is selected and Calculate button is clicked, a report similar to the following will be prepared on a new worksheet.

t (min) T°C Lethality Rate D-value ∑ Log Reduction F-value
0 2 0.00 NR 0.00 0.00
1 30 0.00 NR 0.00 0.00
2 55 0.00 16.5 0.00 0.00
3 76 2.31 0.003 4.93 1.16
4 50 0.00 133.6 6.66 2.31
5 25 0.00 NR 6.66 2.31
6 2 0.00 NR 6.66 2.31

*NR: Not reported.