Detection of pepsin in the gastric juice.
5 ml of milk-acetate mixture are poured into a test tube. Then this mixture is placed into a thermostat at a temperature of 25°С. After the test tube heats up to the given temperature they add 0,1 ml of the gastric juice to it and mix. They watch the moment of the first casein clots appearance on the sides of the test tube. This moment testifies the completion of the reaction of soluble caseinogen conversion into dissoluble casein under the influence of proteolitic enzyme pepsin.
3. Hydrolysis of starch by α-amylase.
A mouth is rinsed 2–3 times with water to remove the scraps of food. 50 ml of distilled water are measured and the mouth is being rinsed for 3-5 minutes for several times. The collected liquid is filtered through cotton wool. And the filtrate is used for working.
Table 1. The results of hydrolysis of starch.
| № | The contents of the test tube | temperature, °С | Time, min. | Color in reaction with iodine | the presence of hydrolysis |
| 3 ml. of starch solution + 2 ml. of 10% H2SO4 | … | ||||
| 3 ml. of starch solution + 2 ml. of 10% H2SO4 | … | ||||
| 3 ml. of starch solution + 3 ml. of amylase solution | … | ||||
| 3 ml. of starch solution + 3 ml. of amylase solution + 1 ml. 2 n. НС1 | … | ||||
| 3 ml. of starch solution + 3 ml. of the boiled amylase solution | … |
2 water baths with a temperature of 37-40 and 100°С are prepared. They pour the solutions into the test tubes according to the table. The enumerated test tubes are placed into the water baths. Every 2 minutes they place a drop of Lugol’s solution on the glass plate with a glass stick. And then а drop of the solution from the test tube is placed with a clean stick. As a result the mixture of the two drops gives coloring. The experiment lasts for 10-15 minutes. The results of the experiment and the conclusions of hydrolysis passing (full, partial or does not pass) are given in the table (table 1).
The scheme of hydrolysis of starch by α-amylase:
| (С6Н10О5)n starch | 
| (С6Н10О5)m amylodextrines |
|
| (С6Н10О5)k erythrodextrines |
|
| (С6Н10О5)l achrodextrines |
| (С6Н10О5)x maltodextrines |
|
| С12Н22О22 maltose |
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