This standard specifies the qualitative test method for urease. This standard is applicable to the qualitative test of urease in infant formula and milk powder. GB/T 5413.31-1997 Qualitative test of urease in infant formula and milk powder GB/T5413.31-1997 Standard download decompression password: www.bzxz.net

GB/T5413.31--1997
This standard provides a qualitative determination method for urease, which is fast and accurate. This series of standards will replace GB5413-85 from the date of implementation. This standard is proposed by the China Light Industry General Association.
This standard is under the jurisdiction of the National Dairy Standardization Center. The responsible drafting unit of this standard is the National Dairy Quality Supervision and Inspection Center. The participating drafting units of this standard are: Food Hygiene Supervision and Inspection Institute of the Ministry of Health, Zhejiang Light Industry Research Institute, Harbin Morinaga Dairy Co., Ltd., and Nestlé (China) Investment Services Co., Ltd. The main drafters of this standard are: Wang Yun, Yin Xiaohong, Fang Yuguo, and Wang Kexin. 352
National Standard of the People's Republic of China
Infant formula foods and milk powder
Qualitative detection of urease
Milk powder and formula foods for infant and young children-Qualitative detection of urease1Scope
This standard specifies the qualitative detection method for urease. This standard applies to the qualitative test of ammonium iodide in infant formula and milk powder. 2 Principle of the methodWww.bzxZ.net
GB/T 5413.31—1997
Replaces GB5413--85
Ammonium iodide catalyzes the conversion of urea into ammonium carbonate under appropriate pH and temperature. Ammonium carbonate forms ammonium hydroxide under alkaline conditions, which reacts with potassium mercuric iodide in sodium reagent to form brown ammonium iodide. NH.CONH,+ 2H,O (NH,),CO
(NH)2CO:+ 2OH-—→ CO-+ 2NH,OHK,[Hgl] + KOH + NH---- NH,Hg2I + KI →+ H,O Yellow-brown precipitate
3 Reagents
3.1 Urea solution: 10g/L.
3.2 Sodium tungstate solution: 100g/L.
3.3 Potassium sodium tartrate solution: 20g/L.
3.4 ​​Sulfuric acid: volume fraction 5%
3.5 Neutral buffer solution
Take 611mL of disodium hydrogen phosphate solution and 389mL of potassium dihydrogen phosphate solution, and mix the two solutions evenly. 3.5.1 Disodium hydrogen phosphate solution
Weigh 9.47g of anhydrous disodium hydrogen phosphate and dissolve it in 1000mL of distilled water. 3.5.2 Potassium dihydrogen phosphate solution
Weigh 9.07g of potassium dihydrogen phosphate and dissolve it in 1000mL of distilled water. 3.6 Na's reagent
Weigh 55g of red mercuric iodide (Hglz) and 41.25g of potassium iodide and dissolve them in 250mL of distilled water. After dissolution, pour into a 1000mL volumetric flask. Weigh 144g of sodium hydroxide and dissolve it in 500mL of water. After dissolving and cooling, slowly pour it into the above 1000mL volumetric flask, add it to the mark, shake it well, pour it into the reagent bottle and let it stand, then use the supernatant. 4 Operation steps
4.1 Take two 10mL colorimetric tubes A and B, add 0.1g of sample and 1mL of distilled water to each. Shake for 0.5min (about 100 times). Then add 1mL of neutral buffer solution (3.5) to each tube.
GB/T5413.31--1997
4.2 Add 1mL of urea solution (3.1) to tube A (sample tube). Then add 1mL of distilled water to tube B (blank control tube). After shaking the two tubes well, place them in a 40℃ water bath for 20min. 4.3 After taking out the two tubes from the water bath, add 4mL of distilled water to each tube, shake well, then add 1mL of sodium tungstate solution (3.2), shake well, add 1mL of sulfuric acid solution (3.4), shake well, filter and set aside,
4.4 Take 2mL of the above filtrate and inject it into two 25mL stoppered colorimetric tubes respectively. Add 15mL of water, 1mL of potassium sodium tartrate solution (3.3), 2mL of sodium reagent (3.6) to each tube, and finally dilute to 25mL with distilled water and shake well. Observe the results. 5 Expression of analysis results
The analysis results are judged according to Table 1.
Table 1 Judgment of results
Qualitative analysis of adenosine
Strongly positive
Sub-strongly positive
Weakly positive
Symbol
Display
Brick red turbid or clear liquid
Orange-red clear liquid
Dark golden yellow or yellow clear liquid
Light yellow or slightly yellow clear liquid
The sample tube is the same color as the blank control tube or lighter
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