I. Initial components for the preparation of the indicator
- The indicator is phenol-red.
- Urea is chemically pure.
- Standard titer of NaOH.
- Distilled water.
- Standard titer H2SO4
II. Indicator production
- A 0.1-normal NaOH solution is prepared. For this, 1 ampoule of the standard titer of NaOH is poured into a flask with a capacity of 1 liter, the flask is \ "washed \" with distilled water and the volume is adjusted to 1 liter.
- 210 g of urea is dissolved in 370 ml of distilled water. 70 ml of a 0.1-normal NaOH solution are poured into this solution, here we add 1.4 g of a phenol-red indicator and add 3 l of distilled water. It turns out a solution of bright red color.
- Preparing a 0.1-normal solution of H2SO4. For this, 1 ampoule of the standard titer of H2SO4 is poured into a flask with a capacity of 1 liter, the flask is \ "washed \" with distilled water and the volume is adjusted to 1 liter.
- A 0.1-normal solution of H2SO4 is poured into the burette.
- Pour 25 ml of the prepared phenolic solution into a glass and titrate with a 0.1-normal solution of H2SO4 from the burette until the solution turns straw yellow.
III. Determination of urease activity
In a Petri dish, add 11 g of the finished soybean extrudate and fill with a previously prepared straw-yellow solution. We stand on the hourglass for 5 minutes.
Bright red dots appear:
- individual points - urease activity of 0.05 pH;
- points are 25% - urease activity 0.1 pH;
- points are 50% - urease activity 0.1 - 0.15 pH;
- points are 75% - urease activity 0.2 - 0.3 pH.
The standard activity of urease is 0.10-0.20 pH.
The shelf life of the phenolic solution is 15 days.