Overview
ISO 5506:2018 specifies a laboratory method for the determination of urease activity in soya bean products. The standard provides a reproducible urease assay to detect inadequate cooking or heat treatment of soy-derived foods and ingredients. Results are reported as milligrams of nitrogen released per gram of product (mg N/g) under defined test conditions.
Key topics and requirements
- Scope: Applicable to products with urease activity < 1 mg N/g as received; for more active samples reduce the test portion (see clause 9.1). The method detects residual urease activity indicative of underprocessing.
- Principle: Ground sample is mixed with a buffered urea solution (pH 6.9–7.0), incubated at 30 °C for 30 minutes to allow enzymatic conversion to ammonia, neutralized with excess HCl and the liberated ammonia quantified by back-titration with 0.1 mol/L NaOH to pH 4.70.
- Reagents: Buffered urea solution, 0.1 mol/L hydrochloric acid, and titrated 0.1 mol/L sodium hydroxide. Analytical-grade reagents and distilled (or equivalent) water are required.
- Apparatus: 200 µm sieve, grinding device (avoid heating), thermostatic water bath (30 ± 0.5 °C), potentiometric titrator or pH meter (±0.02 pH unit), analytical balance, pipettes, test tubes.
- Sampling and sample prep: Follow ISO 5500 (sampling) and ISO 5502 (sample preparation). Typical test portion ~0.2 g (can be reduced to 0.05 g); cold degreasing recommended for samples with >10% fat.
- Quality control: Perform two determinations per sample. Repeatability requirement: the difference between the paired values must not exceed 10% of their mean. Results are averaged and expressed with two decimal places. Dry-matter correction can be applied using ISO 771 moisture results.
Applications and who uses it
- Food manufacturers and soybean processors: routine quality control to verify adequate heat treatment and deactivate urease in soy flours, meal, textured soy protein, and other derivatives.
- Food testing laboratories: standardized urease assay for conformity testing, process validation, and troubleshooting undercooking or enzyme residuals.
- Regulatory authorities and certifiers: objective measure to support safety, labelling, and processing standards compliance.
- R&D and process engineering teams: optimize blanching/thermal processes and monitor enzyme inactivation during product development.
Practical benefits include early detection of underprocessing that can affect flavor, nutritional properties and downstream processing behavior, delivering reliable data for food safety and quality control decisions.
Related standards
- ISO 5500 - Oilseed meals - Sampling
- ISO 5502 - Oilseed meals - Preparation of test samples
- ISO 771 - Determination of moisture and volatile matter (for dry-matter corrections)
