Proteins are:  Very huge molecules.  Are the union of smaller molecules called amino- acids.  There are 22 aminoacids and the number of combinations between they is enormous.  Elements in protein: Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, Sulphur.

 Growth.  Maintenance.  Repair  Energy  Body secretions / enzymes / antibodies / hormones  The proteins also provide energy but it is not their main function.

 10 of these aminoacids are essential, indispensables for growth and repair in children.  8 are indispensables for repair and mainteinance in adults.  Essential means that they must be obtained from foods in the diet, as they cannot be made in the body.

 High biological value proteins are those which contain all the indispensable amino- acids (IAA) in sufficient quantity. Also are called complete proteins.  They are found mainly in animal foods: Milk, cheese, eggs, fish and meat.

LBV PROTEINS:  Proteins that lack one or more of the IAA are said to be of Low Biological Value (LBV) or incomplete proteins.  LBV proteins are found mainly in plant foods: cereals (rice, wheat, oat) or pulses (peas, beans, lentils), some nuts, and the mycoprotein called Quorn.  There are two exceptions to this:  Soya beans (plant) contain HBV and gelatine (animal) contains LBV  LBV proteins are not inferior to HBV protein foods.

Indeed, if a combination of LBV foods is eaten together, e.g. beans on toast (wheat), or lentil soup with bread, then the IAAs which are limited in one is provided by the other. In this way proteins complement each other to provide a complete protein. Cereals + pulses = complete protein. Animal protein foods are expensive to produce and there have been attempts to manufacture alternative protein-rich foods from soya beans.

 In the stomach: hydrochloric acid creates a suitable medium for the digestion of protein to begin. There are two enzymes in the stomach.  Pepsin converts protein to peptones / peptides / polypeptides and rennin clots milk so the pepsin can act more efficiently.

 In the duodenum: the enzyme trypsin, produced by the pancreas continues to convert protein to peptones / peptides / polypeptides.  In the ileum: the enzyme erepsin, from intestinal juice, completes the breakdown of protein to amino acids.

 Absorption takes place in the ileum. Finger-like projections, known as villi, provide a large surface area. The end products of protein digestion are absorbed into blood capillaries.  They dissolve in blood and are carried around the body.

Nombre de Las proteínas.

 Everyone needs some proteins in their daily diet, but at certain times these needs increase. For example:  Babies and children: require a lot of protein as they are growing rapidly.  Adolescents: require protein for their rapid spurt of growth.  Pregnant women: require more than normal to cater for the growing baby.  Nursing mothers: require more than normal for milk production during breast-feeding (lactation).

RNIs for protein Age Grams per day Children 0-3 months months months months years years years28.3 Males years years years years53.3 Females years years years years46.5 Pregnant 51.0 Lactating 56.0

EFFECT OF HEAT  When proteins are heated, their chemical structure is denature (change).  This is a permanent alteration and cannot be reversed.  As heating continues, proeins coagulate (set), and generally become less soluble. If overheated, they become less digestible.

MECHANICAL AGITATION  The denature of the proteins also can be done through mechanical agitation. An example of this is when the whites are whipped and the ovoalbumine partially separate out.

 The change of pH also denature proteins. Examples: add acid or alcohol.  A meat that was marinate for several hours coagulate the casein in the same way that occurs in the stomach.

Uses of coagulate proteins: Thickening (espesante)The sauces can be thicker by adding egg or being heated. Binding (ligante) Complete eggs added to a mixture provide moisture an keep it together. The same occurs if the mixture is heated and the egg coagulates. Coating (cobertura) The whipped egg (whipping the white and then adding the yolk) can make a layer of protection that insulate the food during the heat exposure. Cheese production The enzyme called rennin is added to milk to produce a coagulation (curds and whey) denominated cheese. Yogurt productionMilk can be coagulated and acidified because of the production of lactic acid from innocuous bacteria.

 Protein has to be deaminated: in liver, the nitrogen is removed to form ammonia and then converted to urea.  This urea is carried to kidneys and excreted as urine.  Remainder proteins is used for energy and stored as fat under skin (adipose tissue or around internal organs) may lead to obesity or CHD Cholesterol of high density, etc.