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Concept
Protide
Résumé
Proteins are essential nutrients for the human body. They are one of the building blocks of body tissue and can also serve as a fuel source. As a fuel, proteins provide as much energy density as carbohydrates: 4 kcal (17 kJ) per gram; in contrast, lipids provide 9 kcal (37 kJ) per gram. The most important aspect and defining characteristic of protein from a nutritional standpoint is its amino acid composition.
Proteins are polymer chains made of amino acids linked together by peptide bonds. During human digestion, proteins are broken down in the stomach to smaller polypeptide chains via hydrochloric acid and protease actions. This is crucial for the absorption of the essential amino acids that cannot be biosynthesized by the body.
There are nine essential amino acids which humans must obtain from their diet in order to prevent protein-energy malnutrition and resulting death. They are phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine. There has been debate as to whether there are 8 or 9 essential amino acids. The consensus seems to lean towards 9 since histidine is not synthesized in adults. There are five amino acids which humans are able to synthesize in the body. These five are alanine, aspartic acid, asparagine, glutamic acid and serine. There are six conditionally essential amino acids whose synthesis can be limited under special pathophysiological conditions, such as prematurity in the infant or individuals in severe catabolic distress. These six are arginine, cysteine, glycine, glutamine, proline and tyrosine. Dietary sources of protein include grains, legumes, nuts, seeds, meats, dairy products, fish, eggs, edible insects, and seaweeds.
Protein is a nutrient needed by the human body for growth and maintenance. Aside from water, proteins are the most abundant kind of molecules in the body. Protein can be found in all cells of the body and is the major structural component of all cells in the body, especially muscle. This also includes body organs, hair and skin.
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Concepts associés (19)
Orge commune
L’orge commune (Hordeum vulgare) est une céréale à paille, plante herbacée annuelle de la famille des Poaceae, sous-famille des Pooideae. Elle fait partie des plus anciennes céréales cultivées. Bien adaptée au climat méditerranéen du fait de sa rusticité, elle constituait ainsi la principale céréale cultivée dans l'Antiquité grecque et était consommée sous forme de galette ou de bouillie (maza). L'orge pousse aussi bien sous les tropiques qu’à d’altitude au Tibet. Le mot orge est féminin, mais les termes orge mondé et orge perlé sont masculins.
Cottage cheese
Cottage cheese is a curdled milk product with a mild flavor and a creamy, heterogenous, soupy texture. It is made from skimmed milk by draining curds but retaining some of the whey and keeping the curds loose. An essential step in the manufacturing process distinguishing cottage cheese from other fresh cheeses is the addition of a "dressing" to the curd grains, usually cream, which is mainly responsible for the taste of the product. Cottage cheese is not aged.
Méthode de Kjeldahl
La méthode de Kjeldahl est une technique de détermination du taux d'azote dans un échantillon. Elle est applicable pour le dosage de l’azote de différents composés azotés tels les amines et les sels d’ammonium quaternaires. Elle ne permet pas le dosage direct des nitrates, nitrites, nitrosyles, cyanures qui doivent d’abord être réduits en ammoniac. Quand l’azote est sous forme organique, on procède d'abord à la minéralisation du composé pour passer à de l’azote minéral.