Overview
ISO 11814:2002 (IDF 162:2002) specifies a standardized HPLC method for assessing the heat treatment intensity applied during processing of skim milk powder. The procedure quantifies undenatured whey proteins after isoelectric precipitation to help differentiate extra‑low‑heat from low‑heat skim milk powder. The standard is intended for analytical and quality‑control use in dairy laboratories and by producers and regulators involved in milk powder characterization.
Key topics and technical requirements
- Scope: HPLC determination of undenatured whey proteins after precipitation of casein and denatured whey proteins at pH 4.6. No absolute r‑limits are given; classification depends on national legislation.
- Sample prep: Dissolve 2 g test portion in 40 ml water (40 °C), adjust to pH 4.6 with HCl, stand 15 min, filter and discard first filtrate.
- HPLC conditions (typical):
- Column: Zorbax Bio GF‑250 (25 cm × 0.94 cm) or equivalent with precolumn.
- Eluent: phosphate/sulfate buffer, pH 6.0; flow 1.0 ml/min.
- Column oven: 30 °C; eluent reservoir heated to 85 °C to degas and prevent bacterial growth.
- Injection: 20 µl; detector: UV 280 nm.
- Integration: peak areas measured by perpendicular drop method; baseline must be stable.
- Calculations: Compute relative ratio r from peak areas of immunoglobulin (Ig) + bovine serum albumin (BSA) normalized to β‑lactoglobulin (β‑Lg) and corrected by a reference sample factor f (NILAC or equivalent).
- Precision: Interlaboratory study provides performance data. Repeatability: in 95% of cases differences ≤ 5 (relative sample ratio r_t). Reproducibility: in 95% of cases differences ≤ 17.
- Reporting: Include sample ID, sampling method, method reference (ISO 11814:2002), operational details and final results (r and r_t to one decimal place; peak ratios to three decimals).
Applications and users
- Quality control and classification of skim milk powder (extra‑low‑heat vs low‑heat).
- Routine testing in dairy industry laboratories, contract analytical labs and regulatory bodies for dried milk specifications.
- Product development and process validation teams monitoring protein denaturation during spray‑drying and thermal processing.
- Used where accurate measurement of undenatured whey proteins and assessment of heat damage is required.
Related standards and references
- ISO 707 - Sampling of milk powder (recommended sampling practice).
- ISO 5725‑1 / ISO 5725‑2 - Precision of measurement methods (interlaboratory testing).
- IDF 135 - Guidance for interlaboratory tests on methods for milk products.
- Note: ISO 11814:2002 may reference commercial columns (e.g., Zorbax) as examples; users should select equivalent HPLC packing and follow national classification limits for r.
Open preview (PDF)Dried milk — Assessment of heat treatment intensity — Method using high-performance liquid chromatography