Sandwich Shelf life - micro results interpretation

Hi all,

 

We did a shelf life study for a mix of cheese sandwich. We did both sensory & micro evaluation. A fresh batch of  sandwiches were made each day & test was carried out on the 4th day, meaning starting sun-72hrs,mon-48hrs, tues-24hrs,wed-fresh batch.

 

For micro - the Total coliform count below (duplicates) & E.Coli - at 48 hrs-10,21 (cfu/g)

1100-Fresh 950-Fresh 2200-24hr 2700-24hr 1700-48hr 2800-48hr 1200-72hr 630-72hr

Why is there a fluctuation of the readings, particularly at 72hrs coliform is less & E.coli is <10? Can a competing flora dormant these species? We did APC, Total coliform, E.coli, B.cereus, Staph. aureus and salmonella.

Will be great if anyone has possible explanations or what different we could to repeat the tests to get more coherent results.

Hi all,

 

We did a shelf life study for a mix of cheese sandwich. We did both sensory & micro evaluation. A fresh batch of  sandwiches were made each day & test was carried out on the 4th day, meaning starting sun-72hrs,mon-48hrs, tues-24hrs,wed-fresh batch.

 

For micro - the Total coliform count below (duplicates) & E.Coli - at 48 hrs-10,21 (cfu/g)

1100-Fresh 950-Fresh 2200-24hr 2700-24hr 1700-48hr 2800-48hr 1200-72hr 630-72hr

Why is there a fluctuation of the readings, particularly at 72hrs coliform is less & E.coli is <10? Can a competing flora dormant these species? We did APC, Total coliform, E.coli, B.cereus, Staph. aureus and salmonella.

Will be great if anyone has possible explanations or what different we could to repeat the tests to get more coherent results.

Hi merlin,

 

 

I assume this is a RTE chilled storage product with a labelled shelf-life of 4 days..

 

afaik, shelf-llife in such cases is typically based on L.monocytogenes which you appear to have not monitored ?

 

Sorry but I found the listed data as presented not readily intelligible . A table might have been more easily comprehendable.

Dear Charles,

Thank you for your honest opinion. I have attached a sample report. I am aware we need to test for listeria, we have some issues with the testing and we will be repeating it with listeria by next week. But for the time being I was wondering what could be the cause for the increase & decrease in coliform counts.
What could be the possible reasons? we could be more careful when we do the repeat tests, if we could see what are the possible causes.

I have attached a report, is anyone able to see it? I don't see it with my posted reply

Hi Merl1in,

 

I do not see your attachment.
You can also try to edit your text to make it more readible.

Dear Charles,

Thank you for your honest opinion. I have attached a sample report. I am aware we need to test for listeria, we have some issues with the testing and we will be repeating it with listeria by next week. But for the time being I was wondering what could be the cause for the increase & decrease in coliform counts.
What could be the possible reasons? we could be more careful when we do the repeat tests, if we could see what are the possible causes.

I have attached a report, is anyone able to see it? I don't see it with my posted reply

Hi Mer1in,

 

To attach a document, you need to click the "More Reply Options" tab on the right-hand side and just below the Posting Box. This should generate a new page. Then follow the instructions under "Attach Files".

Please find attached report.

Hi Merlin. First of all, the APC (Aerobic) values for each product max out at 49,000 cfu/g which tells me the dilution used was incorrect for the amount of growth obtained. The APC test should be re-done with the correct dilution since you cannot tell how much growth actually occurred above 49,000 which could be important information to help explain your question. Additionally, the change in Coliform counts could be due to 1) Competing flora like you mention which is why accurate APC counts are important, 2) Chemical changes that occur to the product over the 4 day period (for example, if there is Lactic Acid bacteria in the product (which grow well in refrigerated products), this will start to lower the pH of the product over this 4 day period which could be undesirable to the Coliforms), 3) Since a "Fresh batch of sandwiches was made each day", variation in ingredients, cleanliness of the sandwich making area, personal hygiene of the person making the sandwiches, same ingredients/shelf life of ingredients, etc... could all potentially impact the differences you mention. Better controlling this "daily process" is very important to obtaining accurate micro data. Hope this helps. 

Please find attached report.

Hi mer1in,

 

Thks for the report.

 

Based on experiences in various disputes over micro. results, it is "risky" to interpret data such as in yr report without knowing how the data was obtained/calculated. Nonetheless I have offered a few general comments below.

 

Is cheese the only food ingredient  in the sandwich ?

 

I'm not a cheese expert but APC measurements are apparently not applicable to certain cheeses, eg cheddar, stilton, brie.

 

Some of the micro. results, eg APC, look so odd that the methodology(s) used seem questionable. More information is needed regarding procedures involved.

 

Just for example, -

 

(1) Getting an identical positive value of APC for so many different samples (and replicates) is highly improbable unless some peculiar calculation or Procedure was performed.

(2) I deduce a plate count method was used for Coliform. IMEX this can give unreliable results for certain types of product. IMO MPN methods are preferable.

(3) It seems a plate count method was also used for (generic) E.coli. This is usually evaluated via MPN due to the low values typically involved.

(4) For S.aureus, a similar comment as given for E.coli in (3) also applies.

 

Yr location is unknown however, offhand, I would consider looking for another lab to compare results using a known procedure..