BS ISO 19344:2015 pdf download

BS ISO 19344:2015 pdf download.Milk and milk products — Starter cultures, probiotics and fermented products — Quantification of lactic acid bacteria by flow cytometry
1 Scope
This International Standard specifies a standardized method for the quantification of active and/or total lactic acid bacteria and probiotic strains in starter cultures used in dairy products by means of f low cytometry. The method is also applicable to probiotics used in dairy products and to fermented milk products such as yogurts containing primarily lactic acid bacteria. This International Standard does not apply to taxonomical differentiation of bacteria. Due to its non- specificity, the method may quantify other bacteria than those within the scope of this International Standard, when present in the sample. This may lead to overestimation of the counts. The minimum bacterial cell concentration in the sample before applying this standardized method depends on the dilution rates used in the individual protocols. Typically 10 6 cells per gram or ml are considered within the minimum range.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 6887-1:1999, Microbiology of food and animal feeding stuffs — Preparation of test samples, initial suspension and decimal dilutions for microbiological examination — Part 1: General rules for the preparation of the initial suspension and decimal dilutions
ISO 6887-5:2010, Microbiology of food and animal feeding stuffs — Preparation of test samples, initial suspension and decimal dilutions for microbiological examination — Part 5: Specific rules for the preparation of milk and milk products
ISO 7218, Microbiology of food and animal feeding stuffs — General requirements and guidance for microbiological examinations
ISO 7889 IDF 117, Yogurt — Enumeration of characteristic microorganisms — Colony-count technique at 37 °C
ISO 15214, Microbiology of food and animal feeding stuffs — Horizontal method for the enumeration of mesophilic lactic acid bacteria — Colony-count technique at 30 °C
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
4.3 The stained samples are analysed by means of a flow cytometer using a combination of light scattering (LS) and detection of emitted fluorescent light. As cells pass into the flow cytometer, each cell is counted and the fluorescence is recorded.
4.4 Gating is conducted to separate cells from noise and to differentiate AFUs and n-AFUs.
4.5 Calculation of the concentration in the original sample is a multiplication of AFUs (or TFUs) per volume of analysed sample and the dilution factors employed in the sample preparation.