GB/T 8622-2006Determination of urease activity in soya bean products for feeds (English PDF)

Foreword

This standard is the revised edition of GB/T 8622-1988 "Determination of urease activity in soya bean products for feeds".

The main differences between this standard and GB/T 8622-1988 are as follows.

- CHANGE the consumption of phosphate in the urea buffer;

- DEFINE the timing steps in the measurement process;

- CHANGE the volume of distilled water, which is used to rinse the contents of the test tubes;

- ADD the judgment of using the indicator as the end point;

- ADD the number of reserved digits for the test results, setting to two decimal places.

- INCREASE the allowable difference between two tests of samples <= 0.2 activity unit; the relative difference is <= 20%. This standard replace GB/T 8622-1988, from the date of implementation.

1 Scope

This standard specifies the determination of urease activity in soybean products and their by-products.

This standard applies to the determination of urease activity in soybeans, soybean products, and by-products. By this method, it can understand the degree of moist heat treatment of soybean products.

2 Normative references

The provisions in following documents become the provisions of this Standard through reference in this Standard. For the dated references, the subsequent amendments (excluding corrections) or revisions do not apply to this Standard; however, parties who reach an agreement based on this Standard are encouraged to study if the latest versions of these documents are applicable. For undated references, the latest edition of the referenced document applies.

GB/T 601 Chemical reagent - Preparations of standard volumetric solutions

3 Terms and definitions

The following terms and definitions apply to this standard.

4 Principles

Mix crushed soybean products with neutral urea buffer solution. Precisely incubate at 30 °C ± 0.5 °C for 30 minutes. Urease catalyzes the hydrolysis of urea, to produce ammonia.

5 Instruments and equipment

5.1 Pulverizer. There shall be no strong heat during pulverization.

5.2 Sample sieve. Pore size 200 µm.

5.6 Acidity meter. Accuracy 0.02, with magnetic stirrer and titration device.

5.7 Glass instruments commonly used in laboratories.

6 Reagents and solutions

The reagents are of analytical pure. The water shall meet the requirements of GB/T 6682.

7 Preparation of specimens

Use a pulverizer (5.1), to pulverize a representative sample, so that it all passes through the sample sieve (5.2).

8 Measurement steps

Weigh about 0.2 g of the prepared specimen (Chapter 7), accurate to 0.1 mg, into a glass test tube (if the activity is very high, it can weight 0.05 g of specimen). Add 10 mL of urea buffer (6.1). Immediately cover the test tube cap and shake vigorously.

9 Calculation of results

9.1 The urease activity X in soybean products is expressed in urease activity unit per gram (U/g), which is calculated according to formula (1). If the specimen is pre-dried before crushing, it can be calculated according to formula (2).

9.2 Repeatability. When the same analyst uses the same analytical method to make measurement, simultaneously or two consecutive times, the difference between the results is not more than 20% of the average value, if the activity is <= 0.2; the difference between the results is not more than 10% of the average value, if the activity is > 0.2. […]