139 Determination of Fungus Germ Count (Plate Count Method)

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Methods Type: Generic Methods
Key data
Number: 139
Analyte: Fungus Germ Count (Plate Count Method)
Matrix: Cereals, cereal products, bread and baked goods, pasta
Year of Approval: 1986
Scope: Cereals, cereal products, bread and baked goods, pasta.
Principle: 
  • Since a direct count of the microbial germs present in and/or on the products listed above (2) is impossible, an indirect method has to be used.
  • The product under investigation is treated with a sterile physiological solution by which the germs are separated out and suspended (8.1.), if necessary after grinding of the product by means of a homogeniser acc. to 5.2.1. or 5.2.2.
  • A decimal dilution series (8.2.) is prepared from the initial suspension.
  • Aliquots of the dilution stages are transferred into Petri dishes (8.3.) and mixed with a culture medium (8.4.), which, at this stage, is still liquid.
  • Once the agar has solidified, the individual germs and colony-forming entities are fixed in their places, where they can multiply and form colonies during incubation (8.5.).
  • After the end of incubation the number of colonies is determined (9.1.) and designated as the "number of fungal (mould, yeast) germs per gramme of sample" (9.2.).
  • The accuracy of the method depends on the extent to which it proves possible to separate the microbial germs from the substrate, to avoid damage to the germs during the necessary handling, and to obtain a good, even distribution of the germs in the culture medium. Accuracy will also be enhanced, if the microbial count is carried out on several (two to three) sub-samples.

Definition

The fungus germ count is the number of such aerobic mesophilic colony-forming germs as become visible as colonies (9.1.) after transfer of an aliquot of a suspension of the product under investigation into a fungal culture medium acc. to 6.2. and subsequent incubation at 25 °C for 120 hours.

 

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