144 Enumeration of Spores of Mesophilic Bacteria

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Methods Type: Generic Methods
Key data
Number: 144
Analyte: Spores of Mesophilic Bacteria
Matrix: Cereals, Cereal Products, Bread and Baked Goods, Pasta
Year of Approval: 1992
Scope: Cereals, Cereal Products, Bread and Baked Goods, Pasta
Principle: 
  • Since direct counting of the Bacillus spores contained in or on the product under investigation is impossible, an indirect method has to be used.
  • The product under investigation is first mixed with a sterile physiological solution (6.1) in order to separate and suspend the microorganisms (8.1), where necessary, after grinding the product by means of blending equipment according to 5.2.1, 5.2.2 or 5.2.3.
  • A tenfold dilution series is made from this initial suspension (8.2).
  • Aliquots of the dilution stages are subjected to heat treatment to inactivate the vegetative cells.
  • The pasteurized diluents are transferred into sterile Petri dishes and mixed with the culture substrate.
  • In the course of incubation the spores may germinate and form colonies on and under the surface of the culture substrate.
  • After the end of incubation the "number of spores of mesophilic bacteria per gram of sample" is calculated from the number of colonies present on and under the surface of selected plates of the culture substrate (9.1).

Definition

The standard plate count of the spores of mesophilic bacteria is the number of those aerobic mesophilic bacteria that form colonies (9.1) on or under the surface of the culture substrate after any vegetative cells present have been killed, after heat activation of Bacillus spores, transfer of a certain part of a suspension of the product under investigation into a caseine peptone-glucose-yeast extract-agar and subsequent incubation (30 °C for 72 hours).

 

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