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EXPERIMENTS WITH PROTEIN

 

Protein is the most important ingredient of a food is the basis of all life, the building blocks of every organism. Thousands of researchers worldwide are working with protein, study its properties. Of course, in our experiments we will not discover anything new. But, they say, would only be the beginning...

First experience - qualitative reaction on the protein, i.e. this reaction, which will allow us to judge protein before us or not. Such reactions a few. The one we have, called biuret. For it we will need the solutions of washing soda (or sodium hydroxide) and copper sulphate.

Prepare several solutions, which, as you might expect, contain protein. Let it be meat or fish broth (preferably filtered through cheesecloth), the decoction any vegetables or mushrooms and other Solutions pour into a test tube about half. Then add a little of the solution of alkali is caustic soda or washing soda (soda solution preferably boiled and cooled). Finally, add a blue solution of copper sulphate. If test-broth really is the egg white, then the color will immediately become purple. Such reactions say that they are typical. They only go in if the solution really is protein. For control, put a experience with lemonade or mineral water.

Everyone knows that when heated, the protein is folded and transformed into an insoluble form - raw egg becomes steep. This phenomenon is referred to as denaturation of the protein. Every woman knows that in order to cook a delicious broth, one chopped put the meat in cold water. And when I want to cook boiled meat, large pieces were immersed in the boiling water. Is there a chemical sense? We will try to understand.

Pour and a test tube of cold water, put a bit of raw minced meat and heat. As heat generated (in large numbers) gray flakes. This coiled protein foam, which is removed with a slotted spoon to not spoil the look and taste of the broth. With further heating, water-soluble substances are gradually moving from the meat in the solution. These substances are referred to as extractive, because they are extracted from the meat during its extraction boiling water (in other words, when the cooking broth). They, in the first place, and give the soup its characteristic taste. And the meat deprived of these substances becomes less tasty.

In another tube water boil in advance and put raw meat already in the boiling water. Once the meat comes in contact with water, it will instantly become gray, but the flakes produced very little. The protein that was found on the surface, under the action of high temperature immediately curled up and corked numerous pores which penetrate the meat. Extractives and proteins including, can not go into solution. So they remain inside the meat, giving it a good taste and aroma. And the broth, of course, gets slightly worse.

Protein denaturised (folded) not only when heated. Pour into test tube a little bit of fresh milk and drip one or two drops of vinegar or citric acid solution. Milk immediately turn sour, forming white flakes. It coagulates milk protein. By the way, without such a reaction is not to cook the curd, and not by accident cheese so useful - it goes almost the whole milk protein.

When milk is left in a warm place, then it folded protein too, but for another reason - it is the work of the lactic acid bacteria. They know a lot, and they all produce lactic acid even if you don't eat milk, but, for example, cabbage juice. Strain a little sour milk and add to the serum a few drops of some self-made indicator. The colour of the indicator will show that the solution is acid. This acid - milk, it also can be found in cabbage, and cucumber brine,

Some protein molecules include, in addition to carbon, hydrogen, oxygen and nitrogen, and even sulfur. You can confirm this from experience. A little egg whites and place in a test tube with a solution of caustic soda or washing soda and heating a test tube, add a little of the solution of basic lead acetate Pb(CH3COO)2 * 3H2O - lead lotions that are sold in pharmacies. If the contents of the tube will turn black, then sulfur is formed of lead sulfide, PbS, a black substance.

And finally prepare this protein glue - casein, which is used to this day, despite the abundance of synthetic adhesives. Casein is the basis of cheese, and if so, what glue are we going to do from milk, more precisely, of its protein substances,

Filter the milk from the whey. What is left on the filter, rinse several times with water to remove soluble impurities, and dry. Then rinse the mass of gasoline and dry again; this is necessary in order to get rid of milk fat (it dissolves in gasoline). When the mass becomes quite dry, grind it in a mortar - and you'll have casein powder.

To make him the glue is very easy to mix powder with liquid ammonia and water in the ratio of 1:1:3. Of course, you'll want to try the glue. Try to glue them some wooden or ceramic objects, because these materials casein glue is particularly good.

O. Holguín. "Experiments without explosions"
M., "Chemistry", 1986

 

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