Pathogen in ambient yoghurt

Hello ALL,

I've got a question regarding pathogen growth in ambient yoghurt. When i say ambient yoghurt is the regular yoghurt pasteurized after culturing and filling in ambient temp, as well as the storage condition. PH of the finish product is 4.3. Since there is no live LAB remained in the ambient yoghurt, it seems to be more sensitive to the micro contamination, esp pathogen. Cause some of pathogens are resistant to acid environment.

Do you guys have any experience on this specific category to be shared.

Thanks with regards

Hello ALL,

 

I've got a question regarding pathogen growth in ambient yoghurt. When i say ambient yoghurt is the regular yoghurt pasteurized after culturing and filling in ambient temp, as well as the storage condition. PH of the finish product is 4.3. Since there is no live LAB remained in the ambient yoghurt, it seems to be more sensitive to the micro contamination, esp pathogen. Cause some of pathogens are resistant to acid environment.

 

Do you guys have any experience on this specific category to be shared.

 

Thanks with regards

Hi smallyiyi,

Welcome to the Forum

Cause some of pathogens are resistant to acid environment.

 

Which pathogens are you thinking about ?

It's interesting that you pasteurize after culturing.  Is that normal for your area of the world?

I worked in a yogurt plant that pasteurized before culturing.

The major pathogens we looked for was E-Coli, Listeria, and Salmonella.  We also looked for Yeast and Mold.

I'm not sure what "no live LAB" stand for.  What is LAB?  Are you using that to denote lactobacillus?

The reason we pasteurized before culturing was so that there weren't competing bacteria in the milk that could suppress the culture's ability to grow.  If there are multiple microorganisms that are using up the fuel source you may have a slower growth rate of the culture.

Even if you pasteurize after culturing you have to be careful of contamination during the filling step.

We used to run rapid plates for E. Coli and Total Plate Count (yeast and mold).  We would hold samples at room temperature for checking yeast/mold growth (I believe they sat there for a week) and we sent out environmental swabs for Salmonella and Listeria.  We also did air sampling for mold.

TBH I can't remember every test we ran and I'm pretty sure we were testing for Salmonella but I can't be 100% sure.  I'm sure we tested for listeria.

Hi smallyiyi,

 

Welcome to the Forum

 

Which pathogens are you thinking about ?

Hello Charles,

As far as I know, BACILLUS CEREUS, SALMONELLA SPP .and PATHOGENIC STRAINS OF ESCHERICHIA COLI can be survived under PH 4. 3 or even less, means can be grown in high acid environment. 

It's interesting that you pasteurize after culturing.  Is that normal for your area of the world?

 

I worked in a yogurt plant that pasteurized before culturing.

 

The major pathogens we looked for was E-Coli, Listeria, and Salmonella.  We also looked for Yeast and Mold.

 

I'm not sure what "no live LAB" stand for.  What is LAB?  Are you using that to denote lactobacillus?

 

The reason we pasteurized before culturing was so that there weren't competing bacteria in the milk that could suppress the culture's ability to grow.  If there are multiple microorganisms that are using up the fuel source you may have a slower growth rate of the culture.

 

Even if you pasteurize after culturing you have to be careful of contamination during the filling step.

 

We used to run rapid plates for E. Coli and Total Plate Count (yeast and mold).  We would hold samples at room temperature for checking yeast/mold growth (I believe they sat there for a week) and we sent out environmental swabs for Salmonella and Listeria.  We also did air sampling for mold.

 

TBH I can't remember every test we ran and I'm pretty sure we were testing for Salmonella but I can't be 100% sure.  I'm sure we tested for listeria.

Hello Incognito,

Thanks for the reply. 

The LAB is an abbreviation of "lactic acid bacteria" .  The intention of pasteurizing the yoghurt after culturing is to extend the shelf life and available of storage under ambient environment. After pasteurizing, the LAB and other microorganism are killed, and then fill into aseptic paper pack with ambient temperature. It should be  theoretical an aseptic product, however we still need to evaluate the risk of micro contamination, esp the pathogen. 

Ah thank you.

I found a little information for you.  While listeria, on the chart, says the minimum growth pH is 4.4 unless you are constantly hitting 4.3 or lower every time I might be concerned about it.  Otherwise salmonella and Staphylococcus are listed as a possibility. 

http://www.fda.gov/d...n/UCM252447.pdf

Hi smallyiyi,

I enclose a few literature extracts on some bacterial pathogenic possibilities in conventional yoghurt (ie not further heat treated). I have later, briefly, added my own deductions for the heat-treated case since literature data seems limited.

Regarding conventional yoghurt –

The heat treatment of the yoghurt milk at 85-95 degC  is sufficient to kill the majority, if not all, of the vegetative cells of microorganisms associated with raw milk , but spore-formers and some heat-stable enzymes will remain. This reduced competition ensures that the heated milk will provide a  good  growth  medium  for  the  yoghurt  starter  culture,  but  nevertheless,  the bacteriological quality of the raw milk and any dry ingredients used in the milk base is of great importance.

Regarding B.cereus –

 

Spore germination and growth of  B. cereus in fermented milks are prevented by low pH. However, growth of  B. cereus has been shown in yoghurt milk at 31 °C, although, as the pH dropped, the growth rate declined, and it ceased at pH 5.7. Although  it  is  possible  that  high  levels  could  be  reached  when  initial  acid production is slow,  B. cereus is not normally considered a hazard in fermented milks.

 

Fermented  milks  have  a  good  safety  record  in  terms  of  foodborne  disease,  and there  are  very  few  recorded  incidents  of  food  poisoning  associated  with  these products.  Milk  used  in  fermentations  is  generally  subjected  to  a  severe  heat treatment sufficient to destroy vegetative pathogens.

 

Owing to its acidic nature, fermented milks limit the growth of pathogenic microorganisms. Especially, some pathogens including Listeria monocytogenes, Salmonella spp., coliforms, and Staphylococcus aureus are rarely present in yogurt and other fermented milks. These pathogens are rapidly inhibited within 24 h after the manufacture . The level of survivability of the pathogenic organisms in fermented milk depends on the severity of contamination and the pH of the product . Mild yogurts with pH values of >4.5 can allow the survival of salmonellae for up to 10 days.

Regarding pathogenic E.coli -

Postfermentation contamination of verotoxigenic Escherichia coli O157:H7 carries a high risk for consumers’ health . Although E. coli O157:H7 is negatively affected by high acidity, it can survive in yogurt during cold storage.

Experiments to determine the survival of foodborne pathogens in yoghurt and other fermented milks tend to produce quite variable results. Survival times can be  influenced  by  pH,  acidity  and  the  characteristics  of  the  starter  culture  used.

Regarding further stage of heat treatment to eliminate LAB, Y&M, other vegetative bacterial contaminants, enzymes and extend shelf-life –

I’m not familiar with the temp.-times used but I assume the major risk is again post-pasteurization contamination, ie dependent on hygiene for environment/personnel/equipment/packaging. I presume the pH is similar to initial level so most of previous pathogen-related comments unchanged.

 

 

Even if you pasteurize after culturing you have to be careful of contamination during the filling step.

 

 

I’m not familiar with the temp.-times used but I assume the major risk is again post-pasteurization contamination, ie dependent on hygiene for environment/personnel/equipment/packaging. I presume the pH is similar to initial level so most of previous pathogen-related comments unchanged.

Yup I said that.

Yup I said that.

Sorry, i thought you said it for non-further heat treated yoghurt.

Sorry, i thought you said it for non-further heat treated yoghurt.

No matter when it's heat treated there is always the possibility of further contaminating the product in any step before it's in the packaging (unless the packaging is contaminated of course).  Unless it was irradiated or some other way of rendering all pathogens inert after packaging.

Hi Mr Inc,

Pls refer to the OP

Hence the emphasis.

I've already responded to the OP I was just responding to you.  

I think he's received some good information on pathogens that may be appropriate to his operation.  However the risk of contamination after pasturization is his biggest risk that may happen on a regular basis, other than a CCP violation where other pathogens are not removed from the product.  And seeing as his pH is only .1 under the rating for Listeria I would advise him to consider swabbing for Listeria as well.  If the product is off just slightly on pH then there is a risk of it contaminating his product.  Which directly relates to the OP.

Have a good day Charles.

Hi Mr Inc.

I have no doubt that the OP is happy to receive all input.

Regarding L.monocytogenes, pls see my earlier post. However the reality is that we may both be correct. Such is the yoghurt world.

TBH, I'm not even sure that the extended heat treatment should be called pasteurization.

Cheers !

Hello ALL,

Thanks for the clarifications. Yes, the GMP implementation regarding environment hygiene during culturing has been taken into account, air quality monitoring and surface swabbing already in place, filling is accomplished in Tetra Pak system. This is a mature processing solution which's been validated by scientific method and historical data. 

However, FDA has got quite a lot concerns on the pathogen contamination in such PH lever at 4.3, and supposed to postpone certifying such process.  that was the really intention i wanna have your support here:)

regards, 

XuYi

Hello ALL,

 

Thanks for the clarifications. Yes, the GMP implementation regarding environment hygiene during culturing has been taken into account, air quality monitoring and surface swabbing already in place, filling is accomplished in Tetra Pak system. This is a mature processing solution which's been validated by scientific method and historical data. 

 

However, FDA has got quite a lot concerns on the pathogen contamination in such PH lever at 4.3, and supposed to postpone certifying such process.  that was the really intention i wanna have your support here:)

 

regards, 

 

XuYi

Hi smallyiyi,

I presume you mean the FDA in China.

If it involves a similar procedure to canning, such issues are typically a question of Process Validation by a (local) recognized authority.

Hello All,

The microbe test result of retention samples taken from last trail indicates positive on B. cereus which is finally confirmed. Quite funny as this is the first time ever we find pathogen in the product although it's produced in a R&D trail.

The other key point i wanna have your clarification is: Is it mandatory to apply over 100 degree. C  on eliminating B. cereus or can you provide your pasteurization parameters which's  been validated, cause i was just told R&D made some changes on the combination of parameter during the trail.

Thanks

XuYi

Is there an FDA in China?  Or are you exporting to the United States?

Pasteurization, of course, uses time and temperature for destruction of hazardous pathogens in milk products.

If you want a good source of information you can look at the PMO (Pasteurized Milk Ordinance) put out by the FDA (In the USA).  http://www.fda.gov/d...n/UCM209789.pdf

In the United States it's the guidelines put out that milk, yogurt, etc companies are required to follow for safe milk products.

I'm not a microbiologist so I can't tell you, without looking at the PMO and knowing your system, what time and temperature is appropriate for you.

I appologize that was the 2009 version.  Let me see if I can find one newer.

Currently this is the newest one I've found http://www.fda.gov/d...n/UCM291757.pdfit's the 2011 version

ok... here is a copy of the 2013 version.  I don't think there is one newer. http://www.idfa.org/...al.pdf?sfvrsn=0

Hi smallyiyi,

Do you know what level of B.cereus found ?

 Micro. limit for B.cereus in yr product specification ?

Many of the possible causes are presumably as per noted in previous Posts.

Also as per yr OP, I noticed –

B. cereus has been reported to be capable of growth at pH values between 4.3 and 9.3, under otherwise ideal conditions.

Fact sheet and  Interpretations of B.cereus problems for conventional pasteurized dairy products here –

 B.cereus,NZ, 2010,fact sheet.pdf   60.45KB   32 downloads

 B.cereus - Outbreak.pdf   55.73KB   25 downloads

I deduce yr elimination query relates primarily to spores.

Vegetative cells of  B. cereus are readily destroyed by pasteurisation or equivalent heat  treatments.  However, spores  can  survive quite severe heat  processes, but there is considerable variation between different strains. D(95) values of between 1.2  and  36  minutes  have  been  reported.  It  has  been  shown  that  strains commonly implicated in food poisoning are more heat-resistant than other strains, and are therefore more likely to survive a thermal process.

 

If  the thermal  process is to be accepted as an effective control measure, a detailed review of  databases  for  thermal death  data and validation of the chosen  process would  be necessary.

 

Other posters familiar with heat-treated yoghurt  may have more suggestions.