FDBusiness.com

A new ISO standard (ISO 19344 (IDF 232)) describes a method for the quantification of lactic acid bacteria by flow cytometry in fermented products, starter cultures and probiotics used in dairy products. The publication is the result of the joint work of ISO and the International Dairy Federation (IDF).

Lactobacillus and bifidobacterium, present in yogurt and other dairy products, are well-known medical foods used as probiotics, or “friendly bacteria”, to maintain a healthy digestive tract. 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 scepticism. The new ISO standard is claimed to rubber-stamp the validity of this method, speeding up quality control and facilitating trade.

The standard provides quantification of lactic acid bacteria (LAB) and is important in assessing the quality of starter cultures, probiotics and fermented milk products. Examination of LAB in these products can be carried out following 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.

“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,” said Dr. Sandra Casani, IDF/ISO Project Leader. “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.”

This ISO/IDF 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. This reflects the need and support for such a standard, which is crucial for obtaining general acceptance by the industry and for getting the recognition of this methodology by regulatory bodies.

“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,” said 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. “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.”

An international collaborative study of ISO 19344 (IDF 232) was conducted to determine precision figures, which validated that the method is fit for purpose.