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D values for salmonellas-colis at 162F

Printed From: Dairy Science and Food Technology
Category: Thermal processing
Forum Name: Thermal processing
Forum Description: Effects of heat on food, enzymes and microorganisms
Printed Date: 25 Jan 2022 at 8:52pm
Software Version: Web Wiz Forums 12.03 -

Topic: D values for salmonellas-colis at 162F
Posted By: Guests
Subject: D values for salmonellas-colis at 162F
Date Posted: 20 Mar 2010 at 3:41pm
Appreciate info on the above pl. Anyone wish to share thoughts re meeting salmonella specs? Say you had to meet 0 in 25 g would you test multiple 25 g lots or multiple 250 g lots?

Posted By: Guests
Date Posted: 20 Mar 2010 at 3:42pm
Interesting re spec and testing. Anyone got a view re Enterobacter sakazakii and testing sme line as R2D? 0 in multiplles of spec weigt, 10 X spec weight etc?

BTW interesting website!

Posted By: Guests
Date Posted: 20 Mar 2010 at 3:42pm
r2d your Emails have been noted and I am responding through the forum. BTW sorry for delay in responding, I have been away for the last week or so.

Since I do not understand the context associated with both posts I am restricted in what I can say for legal and other reasons.

Firstly a few comments on the safety/legal aspects of salmonella or Enterobacter sakazakii in foods. These bacteria can kill and it would be prudent to regard the ingestion of even one of them in a food serving as having the potential to cause death or serious illness.

Companies using end product testing as the major instrument for clearing product for direct human consumption would be advised to study the salmonella incidents at Cadbury Schweppes. These have been well publicised and have led to costs estimated at £23 m to the company, including a £1 m fine. Among the many lessons from what went wrong is that companies must practice a zero tolerance policy for pathogens.

Future costs to companies and individuals doing otherwise are likely to be severe.

The limitations of end product sampling, even when dealing with homogeneous materials, and evenly distributed pathogens, are well known to microbiologists but perhaps less well understood by others. There are statistical and costs issues concerned with clearing product e.g. milk powder for babies for direct human consumption based on the absence of pathogens at whatever testing level is used. Hence the current legislative requirement to use a HACCP system with associated in-process monitoring of critical control points e.g. temperature in many countries.

D and Z values are easily assessable using Google Scholar for these bacteria. They are all very heat sensitive and HTST pasteurisation will reduce their numbers, which would be expected to be very low in most raw materials, by many log-cycles.

Posted By: Guests
Date Posted: 20 Mar 2010 at 3:42pm
Say the samonella has a 2 second D at 162F pl say how many log kills will happen after 15 s. Can you say in simple words what this means? Sorry for basic questions!

Posted By: Guests
Date Posted: 20 Mar 2010 at 3:43pm
With the exception of Salmonella senftenberg, D-value around 1.2 seconds at 72C, most salmonella have D-values at 72C of much less than 1 second so you are being cautious re the 2 second-D-value!

Lets take your 2 second value and assume that there are 100 salmonella/ml.

After 2 seconds at 72C there will be 10/ml- a 1 log cycle reduction.

After 4 seconds at 72C there will be 1/ml- a 2 log cycle reduction.

After 6 seconds at 72C there will be 0.1/ml- a 3 log cycle reduction.

After 8 seconds at 72C there will be 0.01/ml- a 4 log cycle reduction.

After 10 seconds at 72C there will be 0.001/ml- a 5 log cycle reduction.

After 12 seconds at 72C there will be 0.0001/ml- a 6 log cycle reduction.

After 14 seconds at 72C there will be 0.00001/ml- a 7 log cycle reduction.

So subjecting the salmonella of D-value 2 seconds to 72C for 15 seconds will result in the number of viable organisms being reduced by > 7 log cycles.

Note that the number of survivors never reaches 0/ ml!

Posted By: Guests
Date Posted: 20 Mar 2010 at 3:43pm
Does this mean that there are small nos of pathogens in foods beacuse tiny levels survive heating?

Posted By: Guests
Date Posted: 20 Mar 2010 at 3:43pm
Yes the statistics of thermal processing suggest that there is a probability of small numbers e.g. 1 CFU/200 L surviving a heat process. Note that we are talking about probabilities. However some of these organisms may have been damaged by the heat process and require special conditions before they can grow again.

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