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Can Yeast & Mould count be higher than total aerobic count


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#1 elise

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Posted 29 September 2010 - 09:55 AM

I have come across this question when looking through some test results where the yeast & mould count is higher than TAC. As far as i am concern, TAC represents the total bacteria growth whereby it should be the highest count among the others.

According to the explanation that i obtained from a fellow colleagues, the YM count could possibly be higher than TAC if the sample are acidic. Is this true?

Please advice.

Thank you.



#2 Charles.C

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Posted 29 September 2010 - 11:22 AM

Dear elise,

Product = ?
procedure = ? (eg APC incub.temp / time = ?)
Results = ?
:smile:

Rgds / Charles.C


Kind Regards,

 

Charles.C


#3 Gao Yu Qing

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Posted 29 September 2010 - 02:56 PM

elise

It is completely possible that M&Y could be higher than TAC, especially if the product is acidic or contains something that supresses bacteria growth. Acidification is a standard part of making a media M&Y friendly and supressing bacteria.
Charles also mentioned incubation. Depending on time and temperature the counts could vary as well. We incubate bacteria at ranges between 30-37 C while we incubate M&Y at 25 because these ranges have been found to be ideal for the organisms we're trying to grow.



#4 AS NUR

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Posted 30 September 2010 - 01:10 AM

IMO in acidic product i.e Juice the most mcro problem is Y&M.. because Y&M more resistant then bacteria.. so if your product tend to acid (pH < 6), its possible Y&M count higher then bacteria..

rgds

AS Nur



#5 elise

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Posted 02 October 2010 - 11:15 AM

Dear elise,

Product = ?
procedure = ? (eg APC incub.temp / time = ?)
Results = ?
:smile:

Rgds / Charles.C


Dear Charles,

The product is food product, sush rice with scallop ( i think they boiled the scallop).
APC was conducted according to BS method and incubated @ 37 degrees for 48 hrs. While YM incubated for 4 - 5 days @ 25 degrees
The result for YM is 104 while APC is 103

#6 Charles.C

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Posted 02 October 2010 - 08:11 PM

Dear elise,

Thks yr data.

2.1.4 Yeasts and moulds
In non-acid, moist foods, yeasts and moulds grow more slowly than bacteria and
therefore seldom cause problems in such foods. However, in acid foods and foods of
low water activity, they outgrow bacteria and thus cause spoilage losses especially if
the products (e.g., fresh fruit and vegetables, frozen or dried foods) are improperly
stored. Additionally, there is also the potential hazard form production of mycotoxins
by moulds.
(taken from a SA interpretational micro.guideline for environment inspectors)


The above is only a general comment of course.

Any other items in the sushi ?? :smile:

Yeasts and molds not my speciality but it occurs to me that the two procedures you refer may not give numerically comparable data, eg, if the sushi contained raw seafood it is very likely that a plate count at 25degC will give significantly higher results than at 38degC due to the actual species present. There are also other relevant parameters such as the accuracy of the data and the condition of the material. I recall once having a sample of cooked shrimp with a S.aureus count of 100,000/g although the plate count was 10,000/g; clearly contaminated by S.aureus but I guess the procedure for APC is simply not designed to optimise growth of S.aureus, eg insufficient salt content.

The only obvious comment is that the APC you quote is apparently quite good since most sushi refs I saw gave typical APC limits in the 1M range, somewhat depending on content presumably. Didn’t see any specific limits quoted for yeast&mould.

Perhaps yeast-mould specialists here will know more. :smile:

Rgds / Charles.C

Kind Regards,

 

Charles.C


#7 elise

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Posted 09 October 2010 - 03:47 PM

Dear Charles,

Thank you so much for the explanation.

As far as i can remember, there wasn't any other ingredients, at least that was what i observe. And the sushi rice is freshly prepared. As for the topping i wasn;t so sure about that.

I agree with you that it is hard to find specifications for YM. I have went through quite a number of books and none of it really give me a clear picture. This leads to the second question, how we actually determine the allowable limit. I understand that different type of foods have different set of limitations.

Me and my colleague were questioned by clients before on the allowable limit. Even though it might be true that no matter what specification we provided to the client, in the end it will be depending on the individual's tolerance, some has higher tolerance some might be lower. But too bad, we can't tell that to the client.

Raw food is really a challenge for us because raw foods usually have higher count, fruits, juice, salad, these are some of the foods that we really scared of. Because in the end we are to answer.

Again, based on your explanation, it seems that no matter what matter you are using, there is no best method for the determination only most widely use by labs.



#8 Bets

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Posted 24 November 2010 - 06:21 AM

if you have molds that are anaerobic. than yes you will have higher counts. But typically you slightly can have a higher variation because the media for Y&M is more specific to the yeast or mold than the TAC media and therefore you will generally have a better recovery.






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