ISO 3356:2009 PDF

Overview

ISO 3356:2009 / IDF 63:2009 specifies a standardized laboratory method for the determination of alkaline phosphatase (ALP) activity in milk. The procedure quantifies ALP activity as the mass of phenol liberated (µg phenol per ml) and is applicable to raw and processed milk, milk powder, buttermilk and powders, whey and whey powder. The method covers activities not less than 1 µg phenol/ml and includes sample preparation, reagent recipes, measurement steps and reporting requirements.

Key topics and technical requirements

• Analytical principle: ALP in the sample hydrolyzes disodium phenylphosphate at pH 10.6 and 37 °C (1 h), releasing phenol which reacts with 2,6-dibromoquinonechloroimide (Gibbs reagent, BQC) to form a blue dye (dibromoindophenol) measured photometrically at 610 nm.
• Reagents and buffers: Detailed formulations provided for barium borate–hydroxide buffer, colour development buffers, disodium phenylphosphate substrate, zinc–copper precipitant, BQC (Gibbs reagent) and phenol standards.
• Apparatus: Photometer (610 nm), thermostatted water bath (37 ± 1 °C), boiling water bath, volumetric glassware, pipettes and filtration equipment.
• Sample preparation: Homogenize milk samples; reconstitute powders (10 g in 90 ml water, ≤35 °C); neutralize acidic samples (pH