Overview
ISO/TS 22113:2012 (IDF/RM 204:2012) specifies a routine laboratory method for determining the titratable acidity of milk fat. Known as the BDI method, it applies to milk fat extracted from raw milk, heat‑treated milk, reconstituted milk from powder and diluted cream (4–6% fat). The method is not suitable for fermented milk or milk damaged by bacterial/enzymatic activity. It is aimed at analytical laboratories processing from small batches (≈5 samples) up to several hundred test portions per day.
Key topics and technical requirements
- Principle: Mix sample with a sodium tetraphosphate + surfactant reagent (BDI reagent), heat to separate fat, extract a measured fat portion into an organic solvent and titrate with alcoholic alkali to determine acidity.
- Reagents: Includes BDI reagent (sodium tetraphosphate + octylphenylpoly(ethyleneglycol)), thymol blue indicator, fat solvent (thymol blue + light petroleum), tetra‑n‑butylammonium hydroxide titrant (non‑aqueous standardised solution), and potassium hydrogen phthalate for titrant standardisation.
- Apparatus: Fat separation tubes or butyrometers, calibrated syringes/positive displacement pipettes, water and boiling water baths, microburette, titration vessel with stirring, nitrogen supply and gas washbottle, and optional colorimeter with dip‑probe for endpoint detection.
- Sample preparation:
- Milk/cream stored at 0–4 °C and analysed within 36 h (or preserved with H2O2 for short extension).
- Cream must be diluted to 4–6% fat (note: dilution in water may require correction for free fatty acid results).
- Reconstituted milk powder procedure (example given: ~13 g powder made up to 100 ml with staged mixing).
- Quality control: Use pilot fat and prepared reference fat samples (spiked with palmitic acid) to check accuracy and reproducibility; procedures and regression checks detailed in annexes.
- Throughput & precision: Designed for routine daily analysis; precision and interlaboratory trial data are provided in the specification.
Applications and users
- Who uses it: Dairy quality control and analytical laboratories, milk processors, cream manufacturers, regulatory testing labs and R&D units in the dairy industry.
- Practical uses:
- Monitoring free fatty acid levels in milk fat for quality, storage and processing assessments.
- Routine production control of milk, cream and reconstituted dairy products.
- Supporting shelf‑life studies, process optimisation and supplier/product verification.
Related standards
- ISO 707 | IDF 50 - recommended sampling for milk (referenced).
- ISO 3432 | IDF 221 - butyrometers mentioned as alternative fat separation devices.
- Annexes in ISO/TS 22113 provide device models, titration setups, reference fat preparation and interlaboratory trial guidance.
Keywords: ISO/TS 22113, titratable acidity, milk fat, BDI method, dairy laboratory, titration, tetra‑n‑butylammonium hydroxide, thymol blue, fat separation, milk testing.