ISO 29981:2010

Overview

ISO 29981:2010 (IDF 220:2010) defines a standardized microbiological method for the enumeration of presumptive bifidobacteria in milk products. The method uses a colony count technique at 37 °C under anaerobic conditions on a selective TOS‑MUP culture medium (transgalactosylated oligosaccharides with mupirocin). It is intended for fermented and non‑fermented milks, milk powders, infant formulae and starter cultures where bifidobacteria are present and viable, and often co‑occur with other lactic acid bacteria.

Key topics and technical requirements

• Selective medium: Use of TOS‑MUP medium (TOS promotes bifidobacterial growth; mupirocin inhibits many other lactic acid bacteria).
• Sample preparation: Follow ISO guidance for test portion, primary suspension and decimal dilutions (e.g., ISO 6887 series); use appropriate diluent such as quarter‑strength Ringer’s solution.
• Inoculation method: Pour‑plate technique with appropriate decimal dilutions to obtain countable plates.
• Incubation conditions: Anaerobic incubation at 37 °C (optimum growth 37–41 °C) for the specified period (standard indicates 72 h).
• Colony identification and counting: Presumptive bifidobacteria form characteristic lenticular/whitish colonies on TOS‑MUP; count colonies to calculate CFU per gram. Optional confirmation tests (e.g., F6PPK assay) can be used on selected isolates.
• Quality and precision: The standard addresses precision (repeatability, reproducibility) and requires laboratory quality control and media validation (TOS‑MUP is heat sensitive and batch performance should be verified).
• Documentation: Test report format and interpretation rules for CFU enumeration are specified.

Applications and users

ISO 29981:2010 is used by:

• Dairy microbiology and quality control laboratories performing routine counts of probiotic or starter bifidobacteria.
• Dairy product manufacturers (yogurt, fermented milks, infant formula producers) for product specification and shelf‑life studies.
• Starter culture producers for validation and release testing.
• Regulatory and certification bodies assessing compliance with microbiological criteria. Practical uses include validating probiotic content claims, monitoring production hygiene, and characterizing starter culture viability.

Related standards (select)

• ISO 6887‑1, ISO 6887‑5 - sample and dilution preparation
• ISO 7218 - general microbiological examination requirements
• ISO 7889|IDF 117 - yogurt colony‑count technique at 37 °C
• ISO/TS 11133‑1 - culture media production and QA
• ISO 14461‑1 / ‑2 - quality control and analyst performance for colony counts

Keywords: ISO 29981:2010, bifidobacteria enumeration, TOS‑MUP medium, colony count technique, anaerobic incubation, milk products, CFU, dairy microbiology.