Overview
ISO 11868:2007 (IDF 147:2007) defines a standardized laboratory method for the determination of lactulose in heat-treated milk using high-performance liquid chromatography (HPLC). The method applies to skimmed, partially skimmed and whole milks and is specifically intended to distinguish ultra‑heat treated (UHT) milk from in‑bottle sterilized milk. The procedure has been validated over a lactulose concentration range of 200 mg/L to 1 500 mg/L and is intended for use in formal dispute resolution and quality verification.
Key topics and technical requirements
- Scope: Quantitative lactulose analysis for all heat‑treated milks (skimmed to whole).
- Principle: Remove fat and protein, filter the sample, then measure lactulose in the filtrate by HPLC against calibrated standard samples.
- Reagents: Analytical‑grade chemicals; a specified sample pretreatment solution containing zinc acetate dihydrate and phosphotungstic acid; lactulose standard (≥99 % purity); HPLC‑grade water as eluent.
- Calibration: Use lactulose‑free pasteurized skim milk spiked to produce calibration levels (approx. 250, 500, 750 and 1 000 mg/L).
- HPLC system: Column equivalent to Bio‑Rad HPX‑87 P (polystyrene divinylbenzene resin, sulfonic ion exchanger in lead form) with a de‑ashing precolumn; thermostatted column oven (~75 °C); pump flow typically 0.3–0.6 mL/min; refractive index (RI) detector with low noise and stable baseline.
- Sample preparation: Controlled dilution, addition of pretreatment reagent, 1 hour standing, filtration through 0.45 μm membrane; degassing of filtrate before injection.
- Performance and reporting: The standard includes instructions for calculation, repeatability/reproducibility assessment and the format of test reports. The method is designated for cases of dispute.
Applications and users
- Quality control in dairy processing: Verification that pasteurization/sterilization processes meet product specifications and labeling claims (e.g., UHT vs in‑bottle sterilized).
- Regulatory and enforcement laboratories: Official testing where provenance of heat treatment is contested.
- Contract testing and certification bodies: Routine lactulose monitoring and comparative product testing.
- Research laboratories: Studies of heat‑induced changes in milk chemistry and process optimization.
Primary users: dairy chemists, analytical labs, food safety authorities, quality assurance managers, and forensic food analysts.
Related standards
- ISO 707 | IDF 50 - Recommended sampling methods for milk (referenced for representative sampling).
- ISO/IDF joint standards for milk analysis and heat‑treatment characterization.
Keywords: ISO 11868:2007, lactulose determination, HPLC, heat‑treated milk, UHT detection, dairy testing, milk analysis, refractive index detector.
Open preview (PDF)Heat-treated milk — Determination of lactulose content — Method using high-performance liquid chromatography
