Overview
ISO/TS 19046-1:2017 | IDF/RM 233-1:2017 specifies a laboratory method for the determination of propionic acid in cheese using gas chromatography (GC). The Technical Specification defines sample preparation, extraction, chromatographic separation and quantification using an internal standard (valeric acid). Results are reported as mass fraction (mg/100 g cheese). This method supports quality control, regulatory testing and research in dairy laboratories.
Key topics and technical requirements
- Scope and principle
- Determines propionic acid level in cheese by converting volatile fatty acids to their sodium salts (soaps), extracting, and analyzing by GC with an internal standard.
- Sample preparation
- Homogenization after addition of internal standard and sulfuric acid; removal of rind/mould recommended where appropriate.
- Extraction
- Continuous liquid–liquid extraction (Soxhlet-type) with a mixed solvent (diethyl ether + petroleum ether); typical extraction time is 6 hours (see Annex A example).
- Soap preparation and derivatization
- Neutralization to obtain soaps, drying and dissolution in trifluoroacetic acid in ethanol prior to GC injection.
- Gas chromatography conditions
- Semi-capillary column (30 m × 0.53 mm, 2 µm film) with a polar FFAP-type stationary phase; carrier gas purity ≥ 99.9997%;
- Example oven program: 80 °C (0.5 min), ramp 20 °C/min to 170 °C, hold 6.5 min;
- Flame ionization detector (FID) and on-column injector at 250 °C.
- Calibration and calculation
- Use of calibration solution (propionic and valeric acids) to calculate response factors and quantify propionic acid (Clauses 9 and 10).
- Performance and reporting
- Precision data: interlaboratory test and repeatability details included (Clause 11 and Annex C).
- Safety and reagent quality
- Use analytical-grade reagents and observe solvent flammability and laboratory safety warnings.
Applications and users
- Who uses it
- Dairy industry QC/analytical labs, food control authorities, contract testing laboratories, university research groups studying cheese chemistry.
- Practical applications
- Monitoring propionic acid levels in Swiss-type and other cheeses where Propionibacterium activity or added propionates affects flavor, shelf life and regulatory compliance.
- Routine QC, formulation verification, shelf-life studies and investigational analysis following production changes.
Related standards
- ISO 707 | IDF 50 - recommended sampling procedure for cheese (sampling not part of this method).
- ISO/TS 19046 series - other parts may cover alternative chromatography methods or complementary procedures (see ISO website for full list).
Keywords: ISO/TS 19046-1:2017, propionic acid, cheese analysis, gas chromatography, GC method, dairy lab, cheese QC, propionate determination.