You can also use filter-sterilized Isopropyl Myristate in combination with
membrane filtration. You must use a polyvinylidene fluoride (PVDF) filter.
This will allow you to physically separate the "bad critters" from the oil
material. Hopefully, you pretreatment of the material will have removed
enough particulate material as not to clog the filter membrane pores.
Depending on how you set up the assay, you could immerse the filter in a
broth enrichment and subsequent streaking onto selective media for the
organisms of interest. Whatever you decide to do, make sure you validate
the ability of the experimental setup to recover the organisms of interest.
This can be done by "spiking" a known number of organisms, e.g., <100 cfu
(using Quanticult) onto the filter, etc.....
As far as "free or available" water goes, it probably is much too low to
allow any pathogens to multiply in the material. You can have the material
sent out for water activity measurement (using a water activity instrument)
to support this. However, this doesn't necessarily mean that they are
absent. It will tell you whether there is enough free water to support
propagation.
References:
Robertson, J.H. "Sterility testing of ophthalmic ointments using isopropyl
myristate", Bull Parenter Drug Assoc. 1974 Nov-Dec;28(6):288-94.
Friedel, R.R. (1999) "The Application of Water Activity Measurement to the
Microbiological Attributes Testing of Raw Materials Used in the Manufacture
of Nonsterile Pharmaceutical Products," Pharmacopeial Forum, Vol. 25, No. 5,
pp. 8974-8981.
Bob Friedel
Quality Assurance Manager
Perritt Laboratories
http://www.perritt.comrfriedel at perrittlab.com
Michel Desbiens <mdesbien at agr.gouv.qc.ca> wrote in message
news:01C0128C.94A90480.mdesbien at agr.gouv.qc.ca...
> A processor of seal oil (these adult mammalian are very abundant in
Canada)
> wants to export his product to Asia as a food supplement. He was asked by
> the Asian custom authorities to perform routine microbiological analyses
> (coliforms, Salmonella). The processor asked to our lab to help him to
> perform these analyses.
>> As the process includes centrifugation to remove residual solid particles
> and all the water content (less than 0,2 % in the final product), we don't
> see the use of such microbiological testing, but the requirements have to
> be met anyway. So, we wonder what kind of method to use to test the oil.
> Most of the methods are adequate for aqueous phase, and we strongly
presume
> that official methods using plating or MPN cannot give satisfactory
results
> due to the immiscibility of fat with water. Can somebody suggest a
> methodology ?
>> Thank you very much,
>> M. Desbiens
>>> ---
