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Unexpected bad challenge test results with normal chemical parameters.

listeria challengetest microbiologie fssp

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#1 Marloes

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Posted 10 May 2021 - 03:09 PM

Hi all, we have done challenge tests to validate our predictive modelling for Listeria. We just got the challenge test results from one of our products. One out of our three sample cashes badly and we cannot figure out why. I am hoping you guys have some input for a cause analysis. The product is an homogenised sausage made of organ meats (sounds delicious right? :giggle: ) which is sliced and MAP packaged. According to our original FSSP modelling this product should be <0,5log. The data used in FSSP is based on 3+ chemical analyses of the product. During our challenge test we also had chemical analysis performed on the different time intervals. The chemical analysis of the different batches don't show anything peculiar. If the info is put into FSSP these should a flatline (0,0log). For storage the first 7 days were kept at 7 degrees, the following 23 days were kept at 9 degrees (based on local law of industry and retail storage temperatures). The last three days of the shelf life the product packaging was openend to simulate consumer behaviour. We cannot figure out why the third batch crashed. It is an homogenised product, so deviants within the product batch are highly unlikely. The lab checked their procedures and did not find any deviations (temperature was normal, enting of the LM was fine, microleakage of the package was not detected). Does any of you have any idea where else we could be looking for a cause? I put our test results down below.

 

Day 0

 

18

 

27

 

30

 

 

 

 

CFU

Log

CFU

Log

CFU

Log

CFU

Log

 

Monster 1

10

 

100

 

60

1,778151

80

 

 

 

10

1

110

2

90

 

80

1,90309

(2-1)=1

 

20

 

100

 

40

 

90

 

 

 

Monster 2

10

 

100

 

370

2,568202

80

 

 

 

10

1

180

2,230449

280

 

170

2,230449

(2,57-1)= 1,56

40

 

170

 

510

 

200

 

 

 

Monster 3

40

 

2800

 

40

 

64000

 

 

60

1,778151

2900

3,447158

90

1,845098

69000

4,838849 

(4,83 - 1,78) 

3,058

90

 

2500

 

70

 

72000

 

 

 

             

 

 

Lactic acid

0,91

 

0,92

  0,88

 

0,89

 

 

 

Acetic acid

0,63

 

0,61

  0,68

 

0,62

 

 

 

NO2

10

               

 

Salt(Cl)

1,47

 

1,44

  1,44

 

     

 

Aw

0,95

 

0,974

  0,976

 

     

 

Moisture

58,1

               

 

Dry matter

41,9

               

 

pH

6,1

 

6,2

  6,15



#2 Scampi

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Posted 10 May 2021 - 04:40 PM

the lab is certain they didn't contaminate the samples upon opening????

 

Do you use MAP packaging? What is the gas concentration(s) if you are?


Please stop referring to me as Sir/sirs


#3 Charles.C

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Posted 10 May 2021 - 05:55 PM

Hi Marloes,

 

Sorry but to me yr post/data is unintelligible.

FSSP ???

<0,5 log ???

 

Nonetheless I do concur that (2-1) = 1

 

But (2,57-1 )= 1,56 is (a) not mathematical and (b) would (obviously) be incorrect even if it were.


Kind Regards,

 

Charles.C


#4 Marloes

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Posted 14 May 2021 - 07:35 AM

the lab is certain they didn't contaminate the samples upon opening????

 

Do you use MAP packaging? What is the gas concentration(s) if you are?

 

The lab re-checked their data since the outcome is soo strange. They assured us that all regular procedures are followed. And no contamination has taken place.

 

Hi Marloes,

 

Sorry but to me yr post/data is unintelligible.

FSSP ???

<0,5 log ???

 

Nonetheless I do concur that (2-1) = 1

 

But (2,57-1 )= 1,56 is (a) not mathematical and (b) would (obviously) be incorrect even if it were.

FSSP is a program which allows to model Listeria monocytogenes growth.

 



#5 Marloes

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Posted 14 May 2021 - 07:56 AM

I can also see that the intended formatting did not work out on the post.
Let me try again.

Monster 1
Day 0 (10cfu, 10cfu, 20cfu) = 1log
Day 18 (100cfu, 110cfu, 100cfu) = 2log
Day 27 (60cfu, 90 cfu, 40 cfu) = 1,778 log
Day 30 (80 cfu, 80 cfu, 90 cfu) = 1,90log
Results= (Highest growth - start growth) = 2log - 1 log =  1log

Monster 2
Day 0 (10cfu, 10cfu, 40cfu) = 1log
Day 18 (100cfu, 180cfu, 170cfu) = 2,23log
Day 27 (370cfu, 280 cfu, 510 cfu) = 2.56 log
Day 30 (80 cfu, 170 cfu, 200 cfu) = 2.23 log
Results= (Highest growth - start growth) = 2,57 log - 1 log =  1,57 log

 

Monster 3
Day 0 (40cfu, 60cfu, 90cfu) = 1,78 log
Day 18 (2800cfu, 2900cfu, 2500cfu) = 3,44 log
Day 27 (40cfu, 90 cfu, 70 cfu) = 1,85 log
Day 30 (64000 cfu, 69000 cfu, 72000 cfu) = 4,84 log
Results= (Highest growth - start growth) = 4,84 log - 1,78 log =  3,058log

 

Hope this is more clear!


Edited by Marloes, 14 May 2021 - 07:57 AM.






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