The good reproducibility and is suitable for determining

The process of digestion is nothing more than a chemical breakdown of food into three main components: proteins, fats and carbohydrates. Whether we eat an apple, a piece of bread or meat, during digestion, the food is split into these components and water. Further, proteins break down into amino acids, fats into fatty acids, and carbohydrates into simple sugars. Digestion occurs in the mouth, stomach and in the small intestine. After the food is ground and dissolved by enzymes, it is absorbed from the intestine into the bloodstream.

This is the basis of life and all biological processes. From proteins our body is constructed, they transfer various substances inside the body, work as hormones and signaling devices. In fact, proteins perform the bulk of the work in the body. Proteins as a component of food are very complex substances: the molecules of some of them are the largest molecules in nature in general.

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Contained in: meat, fish, cottage cheese, nuts, cereals, legumes.

Proteins are formed from amino acids that are structural chemical units or “building blocks.” There are about 28 amino acids in the human body, many of which are synthesized in the liver, but 8 amino acids cannot be synthesized in the body and must be supplied with food.Most animal proteins contain in sufficient quantities all 8 essential amino acids and are called high-grade proteins. Plant proteins are inferior because none of them contains a kit with the right amount of essential amino acids. Therefore, vegetarians should mix groups of plants and seeds in their diet.

Determination of protein by biuret reaction is by far the most common method of protein determination. The method is relatively cheap, simple, has good reproducibility and is suitable for determining all types of protein.

Principle of reaction

The proteins react in an alkaline medium with copper sulfate to form complex compounds colored in violet.

Main source of energy, receptor function, osmoregulation.
Contain in bread, potatoes, cereals, confectionery, sweet fruit, honey.

Carbohydrates, in terms of nutritional value, can be divided into two categories, depending on their level of glycemic index (GI):- Mono and Disaccharides – simple sugars, soluble in water. They have high GI (quickly absorbed into the blood, sharply increasing the level of insulin in the blood). This sugar, honey, sweet fruit, fruit juices, sweet fizzy drinks, confectionery, milk sugar (lactose), chocolate.

 The reaction of Benedict is one of the simplest and most indicative for determining carbohydrates in a sample. Its action is based on the oxidation-reduction reaction between aldehyde groups of sugars and Cu2 + ions in an alkaline medium. In this case, copper is reduced to copper oxide (I) Cu2O, which drops out of the solution as a red precipitate.


Source of energy, participation in metabolism, protective and thermo-isolating functions.

Contained in butter and vegetable oils, lard, yolk.

Lipids are divided into two main types:

– Saturated lipids -: all animals and milk fats, margarine, as well as palm and coconut oil.

– Unsaturated lipids – sunflower, corn, soy, olive, linseed oil.

To maintain the health of the cardiovascular system, preference should be given to the use of unsaturated fats.

A common property of lipids is their insolubility in water, but good solubility in organic solvents for example in ethyl alcohol. On this property, almost all methods of quantitative determination of fat are based.


Starches – complex carbohydrates insoluble in water. They have polysaccharides and oligosaccharides low GI (slowly absorbed into the blood, gradually supplying the body with energy). This potato, cereals, bread, legumes, pasta from durum wheat, muesli.

In nowadays widely recognized that the basis of a healthy diet – at least half – should be slowly digestible carbohydrates. And consumption of carbohydrates with high GI should be reduced, as they contribute to obesity.

Starch is used as an energy source. Although excess starch can lead to obesity, its absence disrupts protein metabolism: it forces the body to use proteins coming from food as a source of energy, which can lead to muscle atrophy.

One of the properties of starch is the ability to give a blue colour when interacting with iodine.

With the help of iodine, you can open the most insignificant amounts of starch.

iodine + starch => dark blue compound

 I2 + (C6H10O5) n => I2 * (C6H10O5) n

(yellow) (transparent) (blue)