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Express analysis of full-fat soya extrudate to determine the activity of urease


I. The initial components for preparation of the indicator

  • Phenol red indicator
  • Chemically pure urea
  • The standard titer NaOH
  • Distilled water
  • Standard titer H2SO4


II. Preparation of the indicator 

1) Preparation of 0.1-normal solution of NaOH.

To do this, 1 ampoule standard titer NaOH is flown out in flask 1 liter, than the flask is "scrubbed " with distilled water and the volume of the solution is being brought to 1 liter. 


2) 210 g of urea dissolved in 370 ml of distilled water, into this solution is flown out 70 ml of 0.1-normal solution of NaOH, also add 1.4 g of phenol red indicator and then fill with 3 liters of distilled water.

Solution turns bright red colour. 


3)Preparation of 0.1-normal solution of H2SO4.

To do this, 1 ampoule of standard titer H2SO4 flown out into a flask 1l, than the flack is "scrubbed" with distilled water and the volume of the solution is being brought to 1 liter.

4) 0.1-normal solution of H2SO4 is being flown out into burette. 


5) Fill the 25 ml of ready phenol solution in a beaker and titratу 0.1-normal solution of H2SO4 from the burette to the straw-yellow color of the solution.



III. Determination of urease activity 

Into Petri dish throw 11 g of soya extrudate and fill with the previously prepared solution of straw-yellow color.


Keep for 5 minutes until appear bright red dots:

  • separate dots - the activity of urease 0,05 pH 
  • the dots are of 25% - urease activity 0,1 pH
  • dots of 50% - urease activity 0,1 - 0,15 pH
  • dots of 75% - urease activity 0,2 - 0,3 pH




Regulatory activity of urease pH = 0,05...0,20 

Shelf life of phenol solution - 15 days