Overview
ISO 5546:2010 (also published as FIL 115:2010) specifies a reference method for determination of pH of all types of caseins (acid and rennet caseins) and caseinates. The method defines sample preparation, instrumentation, calibration and reporting so laboratories can obtain comparable, traceable pH values for dairy protein ingredients used in food, pharmaceuticals and industrial applications.
Key topics and technical requirements
- Scope: pH measurement of aqueous extracts of caseins and aqueous solutions of caseinates at 20 °C.
- Principle: electrometric determination using a calibrated pH‑meter with a glass measuring electrode and a reference electrode (e.g., calomel).
- Reagents: analytical grade reagents; distilled water protected from CO2 absorption; buffer solutions for calibration with known pH at 20 °C (examples: phthalate ≈ pH 4, phosphate ≈ pH 7, borax ≈ pH 9).
- Apparatus: balance (0.1 g), pH‑meter with sensitivity ≥ 0.05 pH unit, thermometer (±0.5 °C), 100 ml conical flask, 250 ml mixing beaker and mixer, 500 µm sieve (ISO 3310‑1).
- Sample preparation:
- Caseins: weigh 5.0 g (±0.1 g) into 100 ml conical flask, add 30 ml water at 20 °C (alternative: 7.0 g + 42 ml), shake 10 s and rest 20 min at ~20 °C.
- Caseinates: dissolve 5.0 g in 95 ml water in mixer, blend 30 s, then rest 20 min at ~20 °C.
- Measurement: decant or withdraw aliquot and measure pH immediately after rinsing electrode. Calibrate pH‑meter at 20 °C and verify calibration every 30 min for sample series.
- Results & precision:
- Report casein extract pH to at least one decimal; caseinate solution pH to at least two decimals.
- Repeatability: ≤ 0.1 pH unit (caseins), ≤ 0.05 pH unit (caseinates).
- Reproducibility: ≤ 0.3 pH unit (caseins), ≤ 0.15 pH unit (caseinates).
Applications and users
ISO 5546:2010 is intended for:
- Dairy testing and QC laboratories measuring pH of casein/caseinate ingredients.
- Food formulators and ingredient suppliers monitoring product consistency.
- Regulatory and certification bodies requiring standardized test methods.
- R&D groups assessing functional and processing properties influenced by protein pH (e.g., solubility, gelation, emulsifying behavior).
Using this reference method ensures consistent, comparable pH data for quality control, specification compliance and product development of dairy proteins.
Related standards
- ISO 707 | FIL 50 - Guidelines for sampling milk and milk products (referenced).
- ISO 3310‑1 - Test sieves - technical requirements (referenced for sieve).
Keywords: ISO 5546:2010, caseins, caseinates, pH determination, reference method, pH meter, dairy analysis, food testing.
