GB 5009.183-2025

National Food Safety Standard Determination of Urease in Food (English Version)

Standard No.

GB 5009.183-2025

Language

Chinese, Available in English version

Release Date

2025

Published By

General Administration of Quality Supervision, Inspection and Quarantine of the People‘s Republic of China

Latest

GB 5009.183-2025

Introduction

Background of Standard Revision and Technological Evolution

This standard integrates 5 existing test methods (GB5413.31-2013, GB/T5009.183-2003, etc.). The main technological breakthroughs are:

• Expanding the scope of application to 8 categories of food (including the addition of special medical purpose formula foods)
• Establishing a dual-method system: qualitative detection (Nessler's reagent method) and quantitative detection (titration method)
• Optimizing reagent storage conditions (e.g., extending the storage period of urea solution at 2-8℃ to 2 weeks)

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Comparison of core test methods

Dimensions	Method 1 (Nessler's reagent colorimetric method)	Method 2 (Titration)
Method Type	Qualitative determination	Quantitative determination
Applicable Samples	Liquid/semi-solid foods	Solids such as soy protein powder
Detection Limit	0.005 U/g	0.02 U/g
Key Equipment	Constant Temperature Water Bath, Colorimetric Tube	Acidity Meter, Titration Apparatus

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Technical Analysis of Nessler's Reagent Method

Reaction Principle

Urease catalyzes urea → ammonium carbonate → ammonium hydroxide → reacts with Nessler's reagent to generate dimercuric ammonium iodide (brown compound)

Critical Control Points

Case: When testing soy milk beverages, if the sample has pigment interference, it is necessary to use a graphitized carbon black solid phase extraction cartridge for purification, and collect 2mL of the middle section of the effluent

Color determination: brick red (strong positive) → orange red (second strongest positive) → yellow (weak positive)

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Key Points of Titration

1. Reaction conditions: 30 minutes in a water bath at 30±0.5℃ (precise timing of ±10 seconds is required)
2. Endpoint determination:
   • Instrumental method: pH 4.70 (acidity meter)
   • Indicator method: methyl red-bromocresol green turns blue-green
3. Calculation formula:

   X=(14×c×(V₀-V))/(30×m)

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Implementation recommendations

Laboratory preparation

• Establish a reagent validity monitoring table (e.g., 1 month for Nessler's reagent)
• Regularly calibrate the temperature deviation of the constant temperature water bath (±1℃)

Method selection guide

Select the method based on the sample type: Method 1 is recommended for infant formula, and Method 2 is preferred for soy protein isolate.