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The use of reference materials in quality assurance programmes in food microbiology laboratories
1National Institute of Public Health and the Environment, Microbiological Laboratory for Health Protection, Bilthoven, The Netherlands.
Abstract:
Nine different reference materials (RMs) for use in food and water microbiology have been developed with the support of the European Commission (EC). The production process of RMs is based on spray drying bacteria suspended in milk. The highly contaminated milk powder (HCMP) obtained is mixed with sterile milk powder to achieve the desired level of contamination and is subsequently filled into gelatine capsules. The HCMP may need to be stabilised by storage for more than a year before a stable RM can be prepared. The HCMP are mixed with sterile milk powder using a pestle and mortar in order to produce homogeneous RMs. For routine use of RMs Shewhart control charts can be produced. Based on log10 transformed counts, control limits are calculated. Rules for the interpretation of results facilitate the detection of out of control situations. Besides RMs there are also CRMs (Certified Reference Materials) that are certified by the EC Community Bureau of Reference (BCR) and are intended for occasional use. Based on the BCR certificate, user tables are produced presenting the 95% confidence limits for the number of capsules likely to be examined in practice. Also power analysis is made to indicate the minimum difference between the certified value and the observed geometric mean value in relation to the number of capsules examined.
Insights
Nine new reference materials (RMs) for food and water microbiology were developed using spray-dried bacteria in milk. These RMs ensure accurate microbial testing through controlled contamination levels and statistical process control.
Area of Science:
- Food Microbiology
- Water Microbiology
- Reference Materials Development
Background:
- Development of standardized methods is crucial for reliable food and water microbiology testing.
- Existing methods may lack consistency, necessitating the creation of robust reference materials.
- European Commission support facilitated the creation of novel reference materials.
Purpose of the Study:
- To develop and characterize nine different reference materials (RMs) for food and water microbiology.
- To establish production protocols for stable and homogeneous microbial reference materials.
- To provide tools for quality control and validation in microbiological analysis.
Main Methods:
- Bacteria were spray-dried in milk to create highly contaminated milk powder (HCMP).
- HCMP was stabilized through storage and then mixed with sterile milk powder for homogeneity.
- Shewhart control charts and statistical analysis were employed for routine use and quality control.
Main Results:
- Nine distinct RMs were successfully produced, offering varying levels of microbial contamination.
- Protocols for stabilization and homogeneous mixing of HCMP were established.
- Methods for routine use, including Shewhart control charts and interpretation rules, were detailed.
Conclusions:
- The developed RMs provide a reliable standard for food and water microbiology.
- Statistical process control methods ensure the consistent quality and usability of the RMs.
- Certified Reference Materials (CRMs) are also available for specific validation needs.