This standard is applicable to the determination of urease activity in products and by-products made from soybeans. This method can confirm the degree of heat and humidity treatment of soybean products. GB/T 8622-1988 Determination of urease activity in soybean products GB/T8622-1988 Standard download decompression password: www.bzxz.net

1 Scope of application
National Standard of the People's Republic of China
Method for the determination of urease activity in soya bean products GB/T8622—88
This standard is applicable to the determination of urease activity in products and by-products made from soybeans. This method can confirm the degree of wet heat treatment of soybean products.
2 Definition
The urease activity referred to in this standard is defined as follows: the number of milligrams of ammonia nitrogen released by the decomposition of urea per gram of soybean products per minute under the conditions of 30±0.5℃ and pH7. 3 Principle
Mix the crushed soybean products with a neutral urea buffer solution and keep it at 30℃ for 30 minutes. Urease catalyzes the hydrolysis of urea to produce ammonia. Use excess hydrochloric acid to neutralize the generated ammonia, and then use sodium hydroxide standard solution to back titrate. 4 Instruments and equipment
4.1 Sample sieve: pore size 200um;Www.bzxZ.net
4.2 Acidity meter: accuracy 0.02pH, with magnetic stirrer and titration device;4.3 Constant temperature water bath: controllable temperature 30±0.5℃:4.4 Test tube: diameter 18mm, length 150mm, with ground stopper;4.5 Precision timer;
4.6 Pulverizer: no strong heat should be generated during pulverization (such as ball mill);4.7 Analytical balance: sensitivity 0.1mg:
4.8 Pipette: 10mL.
5 Reagents and solutions
5.1 Urea (GB696-77): analytical grade
5.2 Disodium hydrogen phosphate (GB1263-77): analytical grade; 5.3 Potassium dihydrogen phosphate (GB1274-77): analytical grade; 5.4 Urea buffer solution (pH 6.9 to 7.0): 4.45g disodium hydrogen phosphate (5.2) and 3.40g potassium dihydrogen phosphate (5.3) are dissolved in water and diluted to 1000mL, and then 30g urea (5.1) is dissolved in this buffer solution, which can be stored for 1 month. 5.5 Hydrochloric acid (GB622-77): analytical grade, 0.1M solution; 5.6 Sodium hydroxide (GB629-77): analytical grade, 0.1M standard solution, prepared according to the provisions of the preparation method of standard solution in GB601.
6 Preparation of sample
Use a pulverizer (4.6) to grind 10g of sample so that it can all pass through the sample sieve (4.1). Special samples (products with high moisture or volatile content that cannot be crushed) should be pre-dried at laboratory temperature before being crushed. When calculating the results, the drying loss should be included.
Measurement steps
Weigh about 0.2g of the crushed sample, weigh to 0.1mg, transfer to a test tube (4.4) (if the activity is very high, only weigh 0.05g of the sample), transfer 10mL of urea buffer solution (5.4), immediately cover the test tube and shake it vigorously, and immediately place it in a constant temperature water bath (4.3) at 30±0.5℃, accurately time it and keep it for 30min. Immediately transfer 10mL of hydrochloric acid solution (5.5) and quickly cool it to 20℃. Transfer all the contents of the test tube into a beaker, rinse the test tube twice with 5 mL of water, and immediately titrate to pH 4.70 with sodium hydroxide standard solution (5.3). Take another test tube for a blank test. Transfer 10 mL of urea buffer (5.4) and 10 mL of hydrochloric acid solution (5.5). Weigh a sample equivalent to the above sample, also weigh to 0.1 mg, and quickly add it to this test tube. Immediately cover the test tube and shake it vigorously. Place the test tube in a constant temperature water bath at 30±0.5℃, and keep it for 30 minutes to cool to 20℃. Transfer all the contents of the test tube into a beaker, rinse the test tube twice with 5mL of water, and titrate to pH 4.70 with a sodium hydroxide standard solution (5.3). 8 Calculation of the test results
8.1 Calculation method
The urease activity U expressed as milligrams of nitrogen released per gram of soybean product per minute is calculated according to the following formula: 14×c(V0-V)
Where: C is the molar concentration of the sodium hydroxide standard solution, mol/L; - the volume of sodium hydroxide solution consumed in the blank test, mL; VO
V—the volume of sodium hydroxide solution consumed by the test sample, mL; m is the mass of the sample, g.
Note: If the sample is pre-dried before crushing, then 14×C(V0-V)
Where: S is the percentage of weight loss of the sample during pre-drying. 8.2 Repeatability
×(1 -S)
The difference between two simultaneous or consecutive determinations by the same analyst using the same method shall not exceed 10% of the average value, and the result shall be reported as its arithmetic mean.
Additional Notes:
This standard was drafted by the China Veterinary Drug Supervision Institute. Approved by the Ministry of Agriculture, Animal Husbandry and Fisheries of the People's Republic of China on August 20, 1987 and implemented on August 1, 1988
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