Unexpected bad challenge test results with normal chemical parameters.
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
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?
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.
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.
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!