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GB 5009.238-2016 PDF English

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GB 5009.238-2016: National standard for food safety - Determination of water activity in foods
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GB 5009.238-2016: National standard for food safety - Determination of water activity in foods

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GB NATIONAL STANDARD OF THE PEOPLE’S REPUBLIC OF CHINA National standard for food safety - Determination of water activity in foods Issued on. AUGUST 31, 2016 Implemented on. MARCH 1, 2017 Issued by. National Health and Family Planning Commission of the People’s Republic of China.

Table of Contents

Foreword... 3 1 Scope... 4 Method I Conway’s Dish Diffusion Method... 4 2 Principle... 4 3 Reagents and materials... 4 4 Instruments and equipment... 7 5 Analytical procedures... 8 6 Expression of the analysis results... 10 7 Precision... 11 Method II Water Activity Meter Diffusion Method... 11 8 Principle... 11 9 Reagents and materials... 11 10 Instruments and equipment... 11 11 Analytical procedures... 11 12 Expression of the analysis results... 12 13 Precision... 12 Annex A Two-dimensional straight-line graphs for reference of water activity 13

Foreword

This Standard replaces the GB/T 23490-2009 Determination of water activity in foods and SN 0180-1992 Method for determination of water activity of food. Compared with GB/T 23490-2009 and SN 0180-1992, the major changes in this Standard are as follows. — CHANGE the standard name into “National standard for food safety - Determination of water activity in foods”; and — This Standard integrates the methods for determination of water activity in GB/T 23490-2009 and SN 0180-1992. National standard for food safety - Determination of water activity in foods

1 Scope

This Standard specifies the Conway’s dish diffusion method and the water activity meter diffusion method for determination of water activity in foods. This Standard is applicable to the determination of water activity in pre- packaged cereal products, meat products, aquatic products, bee products, potato products, fruit products, vegetable products, milk powder and solid drinks. This Standard is not applicable to the frozen foods and foods containing volatile ingredients. Method I (Conway’s dish diffusion method) of this Standard applies to the water activity in foods with a range of 0.00 to 0.98; while Method II (water activity meter diffusion method) applies to the water activity in foods with a range of 0.60 to 0.90. Method I Conway’s Dish Diffusion Method

2 Principle

In a sealed Conway’s dish at constant temperature, there is inter-diffusion between free water in the sample and standard saturated solution with a higher and lower water activity (Aw). After the equilibrium is reached, the water activity in the sample is determined according to the variation of the sample mass.

3 Reagents and materials

3.1 Reagents Unless otherwise stated, the reagents used in this method are of analytical grade, and water is the tertiary water specified in GB/T 6682. 3.1.1 Lithium bromide (LiBr · 2H2O). 3.1.2 Lithium chloride (LiCl · H2O). 3.1.7 Cobalt chloride (CoCl2 · 6H2O). 3.1.8 Strontium chloride (SrCl2 · 6H2O). 3.1.9 Sodium nitrate (NaNO3). 3.1.10 Sodium chloride (NaCl). 3.1.11 Potassium bromide (KBr). 3.1.12 Ammonium sulfate [(NH4)2SO4]. 3.1.16 Potassium nitrate (KNO3). 3.1.17 Potassium sulfate (K2SO4). 3.2 Preparation of reagents 3.2.1 Saturated lithium bromide solution (water activity of 0.064, 25°C). Accurately WEIGH 500g of lithium bromide at a readily soluble temperature. ADD 200mL of hot water. COOL to form saturated solution of solid-liquid two- phase. STORE saturated solution in a brown reagent bottle. PLACE at room temperature for one week before use. 3.2.4 Saturated potassium carbonate solution (water activity of 0.432, 25°C). Accurately WEIGH 300g of potassium carbonate at a readily soluble temperature. ADD 200mL of hot water. COOL to form saturated solution of solid- liquid two-phase. STORE saturated solution in a brown reagent bottle. PLACE at room temperature for one week before use. 3.2.7 Saturated cobalt oxide solution (water activity of 0.649, 25°C). Accurately WEIGH 160g of cobalt oxide at a readily soluble temperature. ADD 200mL of hot water. COOL to form saturated solution of solid-liquid two-phase. STORE saturated solution in a brown reagent bottle. PLACE at room temperature for one week before use. 3.2.8 Saturated strontium oxide solution (water activity of 0.709, 25°C). Accurately WEIGH 200g of strontium oxide at a readily soluble temperature. ADD 200mL of hot water. COOL to form saturated solution of solid-liquid two- phase. STORE saturated solution in a brown reagent bottle. PLACE at room temperature for one week before use. 3.2.9 Saturated sodium nitrate solution (water activity of 0.743, 25°C). Accurately WEIGH 260g of sodium nitrate at a readily soluble temperature. ADD 200mL of hot water. COOL to form saturated solution of solid-liquid two- phase. STORE saturated solution in a brown reagent bottle. PLACE at room temperature for one week before use. 3.2.12 Saturated ammonium sulfate solution (water activity of 0.810, 25°C). Accurately WEIGH 210g of ammonium sulfate at a readily soluble temperature. ADD 200mL of hot water. COOL to form saturated solution of solid-liquid two- phase. STORE saturated solution in a brown reagent bottle. PLACE at room temperature for one week before use. 3.2.13 Saturated potassium chloride solution (water activity of 0.843, 25°C). Accurately WEIGH 100g of potassium chloride at a readily soluble temperature. ADD 200mL of hot water. COOL to form saturated solution of solid-liquid two- phase. STORE saturated solution in a brown reagent bottle. PLACE at room temperature for one week before use. 3.2.16 Saturated potassium nitrate solution (water activity of 0.936, 25°C). Accurately WEIGH 120g of potassium nitrate at a readily soluble temperature. ADD 200mL of hot water. COOL to form saturated solution of solid-liquid two- phase. STORE saturated solution in a brown reagent bottle. PLACE at room temperature for one week before use.

4 Instruments and equipment

4.1 Conway’s dish (with frosted glass cover). SEE Figure 1. 4.3 Balance. with the sensitivity of 0.000 1g and 0.1g. 4.4 Constant temperature incubator. with an accuracy of ± 1°C. 4.5 Electro-thermostatic blast oven.

5 Analytical procedures

5.1 Preparation of samples 5.1.1 Powdery solid, granular solid and pasty samples TAKE at least 200g of representative sample. MIX evenly. PLACE in an airtight glass container. 5.1.4 Mixed samples of various masses TAKE a representative sample that has been mixed evenly. 5.1.5 Liquid or flowing sauce samples Directly TAKE a homogeneous sample for weighing. 5.2 Pre-determination of samples 5.2.1 Pre-processing PLACE a sealed container, a Conway’s dish and a weighing dish containing the samples in a constant temperature incubator. MAINTAIN constant temperature at 25°C ± 1°C. USE and DETERMINE immediately after removal. 5.2.2 Pre-determination Respectively ADD 12.0mL of saturated lithium bromide solution, saturated magnesium chloride solution, saturated cobalt chloride solution and saturated potassium sulfate solution to the outer chambers of 4 Conway’s dishes. 5.2.3 Calculation of pre-determination results 5.2.3.1 The increment or decrement of sample mass shall be calculated in accordance with the Formula (1). 5.2.3.2 DRAW a two-dimensional straight-line graph. DRAW a two- dimensional straight-line graph, by taking the numerical values of the water activity (Aw) in selected saturated salt solution (25°C) as the x-coordinates, and the mass increment or decrement of the sample of corresponding standard saturated salt solution as the y-coordinates. TAKE the intercept value of the x- coordinates, that is, the predicted value of water activity in this sample. REFER to Figure A.1. 5.3 Determination of samples According to the pre-determination results in Subclause 5.2.3, SELECT 3 kinds of saturated salt solution with the water activity values of greater than and less than the predicated value of the sample, respectively, each taking 12.0mL.

6 Expression of the analysis results

Same as Subclause 5.2.3. TAKE the intercept value of the x-coordinates, that is, the water activity value of this sample.

7 Precision

The absolute difference between the two independent determinations obtained under repeatability conditions shall not exceed 10% of the arithmetic mean value.

8 Principle

In a sealed measuring chamber of the water activity meter at constant temperature, the water in the sample achieves diffusive equilibrium.

9 Reagents and materials

Same as Subclauses 3.1 and 3.2.

10 Instruments and equipment

10.1 Water activity meter. 10.3 Sample dish.

11 Analytical procedures

11.1 Preparation of samples Same as Subclause 5.1. 11.2 Determination of samples 11.2.1 USE saturated salt solution to calibrate the water activity meter at a room temperature of 18°C to 25°C and a humidity of 50% to 80%.

12 Expression of the analysis results

When the requirements specified in the precision are met, the arithmetic mean value of the two parallel determinations is taken as the result.

13 Precision

The absolute difference between the two independent determinations obtained under repeatability conditions shall not exceed 5% of the arithmetic mean value. ......
Source: Above contents are excerpted from the full-copy PDF -- translated/reviewed by: www.ChineseStandard.net / Wayne Zheng et al.
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