134 Determination of the Fungus Germ Count (Plate Count Method) in Cereals, Cereal Products, and Animal Feed

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Methods Type: Generic Methods
Key data
Number: 134
Analyte: Fungus Germ (Plate Count Method)
Matrix: Cereals, Cereal Products, and Animal Feed
Year of Approval: 1980
Scope: Feedstuffs and cereals or cereal products for making feedstuffs.
Principle: It is not possible to carry out a direct count of the microbial organisms present in or on the product to be examined. Therefore an indirect method must be applied to detect them. To do this the product to be examined is first mixed with a sterile physiological dilution fluid (5.1.) to separate and suspend the organisms (8.1.), if necessary after grinding the product with grinding apparatus according to 6.9.1. or 6.9.2. A series of tenfold dilutions is made from this initial suspension (8.2.). Aliquot parts of these dilution stages are transferred to petri dishes (8.3.) and mixed with a nutrient medium which is still molten at first (8.4.). When the agar has solidified the individual cells are fixed and they can multiply and form colonies in these positions during incubation (8.5.). The number of colonies is determined (9.1.) and described as "number of moulds and yeasts per g sample" (9.2.). The accuracy of the method depends on how far one is successful in completely separating all the microbial organisms from the substrate, in avoiding damage to the cells during the necessary manipulations and obtaining an even distribution of cells in the culture medium. Greater accuracy is obtained if the count is determined on several subsamples (three, preferably five).

Definitions

Mould or yeast count means the number of those aerobic mesophilic colony-forming units which become visible as colonies when an aliquot of a suspension of the product to be examined has been transferred to a fungal nutrient medium according to 5.2. and incubated aerobically at 25 °C for 5 days (9.1.).

 

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