3 replies to this topic

[mrtipex]

I need the Z and D values for E. coli O157 in apple juice. The temperature I’m interested in ranges from 71 to 75 °C, and it’s for a pasteurization process. The pH could be around 2.5 to 3. Does anyone know where I can find these values or how to calculate them? Thanks in advance!

[Brothbro]

Your D/z values are going to be unique to your product formulation, the makeup of your particular juice will affect the thermal penetration. Linked here is a study that shows a variance in D/z values across a couple different apple juice brands: https://pmc.ncbi.nlm...cles/PMC106681/

 

To me this means you should be consulting a process authority to determine your thermal process. They can help you determine these D/z values, as well as the spec range for key product parameters that would affect your product's thermal conductivity.

[mrtipex]

Your D/z values are going to be unique to your product formulation, the makeup of your particular juice will affect the thermal penetration. Linked here is a study that shows a variance in D/z values across a couple different apple juice brands: https://pmc.ncbi.nlm...cles/PMC106681/

 

To me this means you should be consulting a process authority to determine your thermal process. They can help you determine these D/z values, as well as the spec range for key product parameters that would affect your product's thermal conductivity.

Hi, thanks for your reply.

 

I found this:

 

The heat treatment suggested by Mazzota(16) and recognized by the U.S. Food and Drug Adminis-tration for acidic juices is based on a D-value of 7 min at 56 °C, which exceeds the greatest D-value obtained in thisexperiment (D56 °C of 3.7 +/- 0.3 min), thus confirming thatthe heat treatment currently recommended of 3 s at 71.1 C(z ~ 5.3 C) is suitable to ensure a 5-log reduction of E. coliO157:H7 ATCC 43895 in apple juice.

 

 

So what I need is to adjust this D value to 56°C at my process temperature of 71°C. Is there a formula I can use for this case? I was thinking Arrhenius, but I don't know if it is valid for this case.

[Brothbro]

There is an FDA guidance document that references a NFPA study (which you have also mentioned) endorsing a thermal process of 3 seconds at 71.1C to achieve a 5-log reduction for E.Coli O157:H7. 

 

Study #1 Summary: A study done by the NFPA(7) has resulted in a recommended general thermal process of 3 seconds at 71.1 degrees C (160 degrees F), for achieving a 5-log reduction for E. coli O157:H7, Salmonella, and Listeria monocytogenes in fruit juices. The efficacy of this process was measured using single strength apple, orange, and white grape juices adjusted to a pH of 3.9. The authors noted that a pH in the range of 3.6 to 4.0 has been reported as a non-significant variable in the heat resistance of E. coli O157:H7. The authors also noted that the heat resistance of these vegetative bacterial pathogens might be considerably greater at pH values of 4.0 and higher. This process assumes that the pathogens will have increased thermal resistance due to their being acid-adapted.

...

FDA Comments/Recommendations: We believe that the process recommended in the NFPA study is adequate to ensure a 5-log reduction of the three stated vegetative bacterial pathogens, (E. coli O157:H7, Salmonella and Listeria monocytogenes) at juice pH values comparable to those in the study. However, other validation studies may be needed for juices that have pH values greater than 4.0.

 

So in this example, 71.1C for 3 seconds results in a 5-log reduction. The D-value would be considered a fifth of the total process time at this temperature (0.6s at 71.1C). The z-value is determined by plotting D-values at different temperatures and examining the slope between points (usually a line of best fit). This study actually lists their z-value as 5.3C, which you have mentioned.

 

Calculating the z-value based on two equivalent processes is possible, but I'm not personally very experienced with that. There is a calculator site that explains their math a bit that I've found, but it's difficult to encourage using results from sites like this in real-world applications. https://www.dairysci...alculation.html

 

You could use the equations/calculator in this site to try and determine a z-value mathematically between the 35min @ 56C process and the 3sec (0.05min) @ 71.1C process. Their calculator does indeed result in a z-value of 5.3, just like the study mentions. I also found the full pdf of the study you've mentioned, which I've attached. Beyond this I don't think I'll be of much help (if I've been of any at all!)

Attached Files

•  Thermal inactivation of stationary-phase and acid-adapted Escherichia coli O157H7, Salmonella, and Listeria monocytogenes in fruit juices.pdf   162.77KB   2 downloads