Flow cytometry, a cell-counting method for assessing the quality of cultures by determining the proportion of active cells, has met with a degree of skepticism.
Now, a new ISO standard rubber-stamps the validity of this method, speeding up quality control and facilitating trade.
ISO 19344 (IDF 232) provides a method for the quantification of lactic acid bacteria (LAB) by flow cytometry in fermented products, starter cultures and probiotics used in dairy products. This publication is the result of the joint work of ISO and the International Dairy Federation (IDF).
Advantages of flow cytometry
Quantification of LAB is important in assessing the quality of starter cultures, probiotics and fermented milk products. Examination of LAB in these products can be carried out with different methods, with plate count techniques being the most traditional and widely used.
Newer techniques include flow cytometry, which is able to determine the proportion of active cells and/or total units.
Dr. Sandra Casani, IDF/ISO project leader, said: “Advantages of the use of flow cytometry include low variation, reduction of testing time, differentiation between active and total cells and the possibility of high-throughput analysis.
“Furthermore, quantification of the fraction of active cells per total cells is a key feature of flow cytometry. This is of special relevance for certain applications, such as optimization of production processes and stability assessment during shelf life.”
Industry and academia collaboration
The project relied on the participation of producers and users of LAB as well as experts and users of flow cytometry from both industry and academia. The ISO says that this reflects the need and support for such a standard, which the ISO says is crucial for obtaining general acceptance by the industry and for getting the recognition of this methodology by regulatory bodies.
Harrie van den Bijgaart, chair of the ISO technical committee on milk and milk products (ISO/TC 34/SC 5) and chair of the IDF Methods Standards Steering Group, added: “Joint standards such as this one are important to avoid duplication of work and ensure optimal and harmonized procedures in analysis and sampling of milk and milk products around the globe.
“They also provide safeguards to the equivalence of testing results, whereas the availability of these well-respected joint standards also limits the required in-house validation efforts of the instrument users. The collaboration between IDF and ISO is key in achieving this.”