Horizontal method for the enumeration of yeasts and moulds - Part 1: Colony count technique in products with water activity greater than 0,95
ISO 21527-1 (2008) method: Yeasts and moulds
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1 Quantitative process control with CRM-PAU
- Use a quantitative reference material (CRM-PAU) with a known number of Penicillium aurantiogriseum.
- Defrost the material at room temperature for 30 minutes.
- Mix well before use and dilute the material so countable numbers are inoculated on the media (DRBC) by spread plate method.
- Best results are obtained when a practicable range of 80 cfu to 120 cfu per plate with a minimum number of 50 cfu per plate is used.
- Incubate at (25 ± 1) °C for 5 days.
- Count the colony forming units and register in a control chart.
- The characteristic reaction is: Characteristic colony/propagules according to each species.
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2 Quantitative process control with RM-PAUYL
- Use a quantitative reference material (RM-PAUYL) with a known number of Microorganisms.
- Defrost the material at room temperature for 30 minutes.
- Mix well before use and dilute the material so countable numbers are inoculated on the media (DRBC) by spread plate method.
- Best results are obtained when a practicable range of 80 cfu to 120 cfu per plate with a minimum number of 50 cfu per plate is used.
- Incubate at (25 ± 1) °C for 5 days.
- Count the colony forming units and register in a control chart.
- The characteristic reaction is: Characteristic colony/propagules according to each species.
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3 Quantitative process control with RM-YL
- Use a quantitative reference material (RM-YL) with a known number of Yarrowia lipolytica.
- Defrost the material at room temperature for 30 minutes.
- Mix well before use and dilute the material so countable numbers are inoculated on the media (DRBC) by spread plate method.
- Best results are obtained when a practicable range of 80 cfu to 120 cfu per plate with a minimum number of 50 cfu per plate is used.
- Incubate at (25 ± 1) °C for 5 days.
- Count the colony forming units and register in a control chart.
- The characteristic reaction is: Characteristic colony/propagules according to each species.

Best Practice
The single strain CRM-PAU, contains a mould, is used for the enumeration of Yeasts and moulds
Kind of reference material | Biosisto product for this control method | Control Strain | |||
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Single-strain reference material | Penicillium aurantiogriseum | ||||
The Biosisto reference material in this table is used in the best practice for Quantitative process control according ISO 17025. |

Best Practice
The multi strain RM-PAUYL, contains a mould and a yeast, is used for the enumeration of Yeasts and moulds. The material can be used simultaneously as process control for ISO 21527-1 enumeration of yeasts and moulds.
Kind of reference material | Biosisto product for this control method | Control Strain | CBS number | ||
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Multi-strain reference material | Penicillium aurantiogriseum | 792.95 | |||
Yarrowia lipolytica | 11385 | ||||
The Biosisto reference material in this table is used in the best practice for Quantitative process control according ISO 17025. |

Best Practice
The single strain RM-YL, contains a yeast, is used for the enumeration of Yeasts and moulds