Food micro (long-ish)

BioSage m.j.grossman at
Sun Jan 2 14:40:31 EST 2005

I agree with with the reponse that if you are going to do this than
make sure it is validated, but, it would seem that going to a less
labor intensive and higher throughput system is perhaps a better way to

Systems with greater ability for signal amplification, e.g. nucleic
acid approaches come to mind.

Matthew Grossman, Ph.D.

The Sceptical Chymist wrote:
> Hello everybody.
> I would appreciate any comments on the following:
> We are a company that makes frozen dough products, some of which
> cured meat in the filling. We're having a problem with one of our
> a major food multinational, and I would like to hear the opinions of
> The situation is as follows:
> Two of our products contain boiled ham and bacon, which are placed in
> open dough base (they're exposed). The cooking instructions state
> that the product should be baked at 180 deg C for15-20 min. However
> customer believes that the end-user might let the product thaw rather
> take it straight from the freezer to the oven and additionally might
> and eat the ham or bacon. For that reason they treat those two
> as ready-to-eat and ask for an "absence of Salmonella spp in 375g"
> We're using a Biomerieux Minividas instrument, and the protocol
asks for:
> 1. Homogenising 25g of sample in 225 ml of buffered peptone water
> 2. Incubating the resulting 250ml of homogenate at 37 °C for 16-20
> 3. Subculturing 0.1 ml of homogenate in 10 ml of Rappaport
Vassiliadis (RV)
> broth.
> 4. Incubating the RV broth at 41.5 °C for 6-8 hrs.
> 5. Subculturing of 1 ml from the RV broth in 10 ml of M-broth.
> 6. Incubating the M broth for 16-20 hrs at 41.5 °C.
> 7. Heating 1 ml of M broth at 100 °C for 15 min.
> 8.  Adding 0.5 ml of heated M broth to the Vidas SLM test strip and
> the results in 45 minutes.
> Positive results are followed by confirmation by a reference method
> involves plating the selective broth and running biochemical (API
> and/or serological (agglutination) tests.
> If we were to follow the protocol to the letter we would have to test
15 25g
> samples (the instruments can only run 12 samples at a time) with all
> reagents, incubator space, staff and time requirements that would
> What we do instead is pool the 15 samples of 25g to 4 samples of 100g
> makes 400 rather than 375g). We dilute those 1:10 with BPP and
> ending up with four homogenates of 1000 ml. These we incubate at 37
°C for
> 16-20 hrs and then draw 0.1ml and subculture it in RV broth. From
that point
> onwards we follow the rest of the protocol to the letter.
> The probability of the 400g sample carrying Salmonella remains the
same as
> long as the sample is representative and drawn from different points.
> does change is the probability that 0.1 ml drawn from 1000 ml of
> homogenate carry Salmonella. There's a better chance of detecting
it if
> 0.1ml is drawn from 250 ml as the protocol requires. However we
believe that
> after incubating the homogenate at 37 °C for 16-20 hrs in BPP, if
> is present it will multiply to such levels that this difference is
> insignificant.
> I'm interested in other people's opinion on the matter, so I
would like to
> hear from you.
> I will be posting this to more than one food list/newsgroup, so
apologies to
> anyone who reads it more than once.
> Sincerely
> Kostas Polyzonis
> QA Manager
> Michael Arabatzis AVEE - Hellenic Dough
> To reply by private e-mail type replace invalid with gr

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