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VALIDATION OF THE PROPERTIES ANTI-LISTERIA OF The AFS-LMC ( a new & light liquid smoke , developped
by Forest Flavour Int'l - Usa ) ( Study realized by VALUTEC / CITIA- France
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PHASE N°2, IN JUNE,
2001, SUMMARY |
1) Introduction :
This study follows upon a fast laboratory screening of the bacterio-static effect of the product supplied by AMCAN INGREDIENTS on strains of not pathogenic Listeria. ( See Part # 1 .)
This new study aims to carry out a quantitative measurement of the effect of the by-product of liquid smoke AFS-LMC when used over pathogenic strains of type Listeria monocytogenes. It will allow to determine the number of pathogenic germs found when AFS-LMC is used and not used during the manufacture of a typical product of cooked pork meats.
Attention: This study will not allow to draw the parallel with other products having similar or comparable action.
2 ) Progress :
The study consists of the manufacture of cooked pork meat products contaminated by pathogenic germs with and without a witness of AFS-LMC, the follow-up of the evolution of the microbiological load during time with break of the chain of cold and until the end of the shelf life, the follow-up of the pH and the aw.
- Type of product of cooked pork meats :
The study is made on lardons because this product presents several advantages (simplicity, wide-spread use in the world and the easily controllable voluntary contamination).
- Strains used for the contamination :
We use 1 representative pathogenic strain of the current
concerns of the food industry, namely: Listeria monocytogenes.
The Tests are made in 104 UFC / g.
- Preparation of the Tests :
Every production of lardons is made in an experimental
churn in which are added the inoculum and the additives.
They're then packaged in bags of 150g under semi-vacuum atmosphere.
The procedures of inoculation, decontamination and control
of neatness are validated by the Institute Pasteur of Lille.
All the microbiologic analysis are realized by the Institute Pasteur
of Lille.
To feign the real conditions of conservation, samples are kept 14 days at 4°C, then 26 days at 8°C. Follow-ups are made in: Day 0, D+7, D+15 , D+21, D+29, D+40. We chose these dates because they're particularly representative of the Shelf Life usually indicated in fresh products of the food industries. At each of these dates a double measure of population and pH are made.
3) Results :
A) Disinfection of premises and material :
The results of the detection of Listeria monocytogenes in the sampling of surface showed to be negative (absence in 25g by PCR). The disinfection is then considered as effective and can be validated.
B) Enumeration and Listeria's detection :
Checking of the raw material
The strains of Listeria spp and monocytogenes L. were isolated and identified by API galleries Listeria:
The raw material, although naturally contaminated with Listeria monocytogenes, is considered as acceptable for the realization of our tests, being given the weak number of pathogenic already present with regard to the rate of the artificial contamination.
Ø graphic Representations of the evolution of Listeria monocytogenes
in lardons of Day0 to D+41.
Graph 5: evolution of Listeria monocytogenes in the samples of lardons
T2 (Witness) and E2a and E2b (Tests)
Graph 6: follow-up of the evolution of Graph 7: histogram
of the log N / N0
L.monocytogenes in T2 ( Witness) and E2 according to the time of T2
( witness) and
( Average of the Tests of E2a and E2b) E2 (average of the attempts E2a
and E2b)
The graph 5 above shows that :
- The rate of Listeria monocytogenes, 104 UFC / g, obtained
by artificial contamination at
Day 0 increases 0,5 log in the Witness T2 to D+7 and remains constant
in the Test E2 at the same date.
THE AFS-LMC seems to have a bacteriostatic effect on Listeria
monocytogenes from D+7.
- The microbiological analysis made on D+15 after break of the chain of cold from +4°C to +8°C puts in evidence a continuance of the growth of Listeria monocytogenes in the Witness T2 and shows the beginning of the decrease in the Test E2. Then a difference of the rate of germs among decimal T2 and E2 of 0,8 logarithms is recorded.
- The counting of Listeria monocytogenes made from D+15 to D+41 show a stabilization of their number in the Witness T2 and a diminution in E2 of 8,2 - 8,7 103 UFC/g on D+15, to 1,68 - 3,95 103 UFC/g to D+41.
- On D+41, a 1 log of difference of the number of Listeria monocytogenes is obtained among the Witness T2 and the Test E2. This result let suppose again that the AFS-LMC has a bacteriostatic effect over the Listeria monocytogenes.
- The growth of this germ remains however limited since in the witness, from an initial contagion of 1,3 104 UFC / g, a maximum is reached on D+21 with 5,3 104 UFC/g to stabilize at the end of Shelf life on D+41 at 3,27 104 UFC/g. These results let suppose that the other factors such as the composition of the lardons, physico-chemical parameters or secondary flora intervene too in the behavior of Listeria monocytogenes.
The graph 6 shown above puts in evidence the same findings observed
in the graph 5. The evolution of Listeria monocytogenes in the Test
E2 corresponds to the average of E2a and E2b.
The graph 7 presenting the log N / NO according to time for the Witness T2 and the attempt E2 (average E2a and E2b) allows to put in evidence a growth or a diminution of the rate of Listeria monocytogenes. Here is confirmed a light growth in the Witness T2 from D0 to D+21, followed by a weak diminution until D+41, and a diminution in the Test E2 from Day0.25 to D+41 after addition of the AFS-LMC.
C) Counting of the total flora during the conservation of lardons
Products packaged in semi-vacuum bags presented a fast swelling in the beginning of conservation at +4°C (4 to 7 days).
So that, in order to estimate the total bacterian population of lardons
responsible for this phenomenon, a counting on gelose PCA (Plate Count
Agar) was made on D+30. It shows that the secondary flora is important,
of about 1,10 108 for the Witness T2 and of about 4,42 - 4,5 107 for
the Test E2. The important number of the secondary flora can explain
the
swelling of the bags notably if it consists of lactic flora.
D) Physico-chemical measure during the conservation of lardons
* Follow-up of the pH
Ø Graphic Representation of the evolution of Listeria monocytogenes in lardons according to the pH of Day 0 to D+41
Graph 8: evolution of Listeria monocytogenes in lardons during time
according to the pH
* Follow-up of the aw
The values of aw for the Witness and the Tests are comparatively identical (0,963 - 0,966). These measures vary only 0,002 unit of aw, what is unimportant with regard to the uncertainty of the method of measure of this parameter.
4) Conclusions
The Listeria monocytogenes 4b introduced artificially into lardons behave in a different way in the Witness and the Test until the end of the shelf life. The extract of smoke tested at 1,5 % presents a marked bacteriostatic effect on the pathogenic in these conditions of contamination. Indeed, a difference of 1 log decimal between the Witness and the Test is observed at the end of the shelf life. This result allows to consider that the tested AFS-LMC indeed acts on the diminution of Listeria monocytogenes present in lardons.
Considering the mode of action of lactates and AFS-LMC
which is rich in carbonyls and phenol compounds, the perspectives of
improvement of the searched inhibiting effect could maybe pass by the
research of a possible synergy between the AFS-LMC and lactates
by-products such as potassium or sodium or other agents?. Maybe Lactates
have the advantage of improving the efficiency of the smoke extract
by facilitating the membrane transfer into the Listeria and certainly
by facilitating the decontamination of the other florae...
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In view of these results, if you wish to improve significantly the sanitary quality of your finished products using our Liquid Smoke AFS-LMC, our commercial team is at your disposal to supply you with additional information as well as for the realization of industrial trials.
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File realized by Karine SERRANO, Engineer ENSIA
M.A.J. / August, 2001
Local food regulations should always be consulted with respect to specific applications and necessary declaration. Legislation may vary from country to country .Our products are sold subject to the understanding that prospective purchasers will conduct their own evaluation to determine the suitability of the products in their applications