Carbohydrates Liceo Banfi

• Carbohydrates are molecules, consisting of carbon, hydrogen and oxygen, which give the flavour, texture and variety to foods.

• We can distinguish between simple carbohydrates (monosaccharides and disaccharides, indicated by the generic term sugars) and complex carbohydrates (polysaccharides).

• These definitions are also those used in the tables of nutritional food labels

• (eg. "Carbohydrates 10.7 g, of which sugars 10.7 g").

• Carbohydrates are the main source of energy in our body and therefore occupy a prominent place in the human diet; their presence should represent 60-70% of total daily calories.

• Carbohydrates are also many structural components of cells

Classification• Carbohydrates are classified according to the number of molecules that contain into:• monosaccharides e.g. glucose, fructose• disaccharides e.g. sucrose, lactose• polisaccharides e.g. cellulose, starch

Monosaccharides• The monosaccharides are formed by a single molecule, and

represent the monomers which constitute the basis of more complex carbohydrates

• The sugars that have 5 carbon atoms,are called pentoses ribose, deoxyribose

• The sugars that have six carbon atomsThe sugars that have six carbon atoms are called are called hexoseshexoses glucose, fructose glucose, fructose

Cn(H20)n

Glycosidic bond• A monosaccharide can be chemically bonded to another

monosaccharide following the bond that is formed between a carbon atom of one of the two monosaccharides and the hydroxyl group of the other.

• During the reaction, which is called condensation, for each pair of monosaccharides that joins, a water molecule is eliminated.

Glucose• The monosaccharide glucose is the most important one

for vertebrate species.• The glucose is contained in a wide range of foods, such

as honey, fruit and vegetable.• Glucose is obtained by hydrolysis of many

carbohydrates, including sucrose, maltose, cellulose, starch and glycogen.

• Glucose through the blood system reaches all body cells

Fructose• Fructose is present, together with glucose, in

fruits and all the elements derived from it: juices, nectars, jams, etc..

• Fructose is used more slowly by the body compared to glucose.

Disaccharides • Disaccharides are sugars formed from two molecules

of monosaccharide linked together by a glycosidic bond. Included in this group are:Lactose (glucose + galactose)Sucrose (glucose + fructose)Maltose (glucose + glucose)

Sucrose • Sucrose is common table sugar.• The sucrose is present in various plants, in

particular in sugar beet and sugar cane, from which it is extracted.

• Sucrose consists of one molecule of glucose and one molecule of fructose, linked by a glycosidic bond between the C-1 of glucose and C-2 of fructose.

Polysaccharides• The polysaccharides are composed of long chains of monosaccharides linked together by glycosidic bonds.• The polysaccharides can be classified according to the

function in polysaccharides reserve and polysaccharides support.

• The polysaccharides are remarkably widespread in plants and shortly in animals.

• Included in this group are:starchglycogencellulose chitin

Starch • Starch is composed of organic type carbohydrate (or carbohydrate

polysaccharide), commonly contained in foods such as bread , pasta, rice, potatoes, characterized by a large number of units of (+) -glucose polymerized joined together by binding α - bond glycosidic and consists of 4/5 and amylopectin from 1/5 amylose .

• Its rough formula is:(C6H12O6) n - (n-1) H20

where n is a number ranging from about a hundred up to several thousand, and from this the various types of starches found in nature (es. rice starch, corn starch, etc.)

• In ancient times, the starch was typically obtained by macerating the advanced and unground wheat in the mill, which is why it is called so (gr. mylos a-, a- mylon, lat. Amydos = no mill) .

• Together with glycogen and cellulose it is one of the most well-known polysaccharide found in plants , which naturally synthesize from glucose. One gram of starch makes about 4.2 kcal .

Carbohydrates feeding 1/2• In the human body the carbohydrates represent only 1 % of the weight, but

have considerable nutritional importance having to be in a normal diet , 60-70 % of total calories.

• They are also the nutrients more accessible from the economic point of view as the main constituents of cereals, legumes , fruits and many other plant products.

• In the diet there is a higher contribution of carbohydrates in the form of starch (bread, pasta, rice, etc. ), followed by a considerably lower amount of lactose (milk ), sucrose ( table sugar), and finally the glucose and fructose (fruits).

YES NO

Carbohydrates feeding 2/2• In order to follow a balanced diet, a diet based on complex carbohydrates

is preferable to one based on simple sugars such as main nourishing energy .

• In industrialized countries, starting from the '60s, the consumption of complex carbohydrates has gradually been decreasing while simple sugars, especially sucrose have been increasing. Reasons could be :flavour and status symbol (because in the past the consumption of confectionery was not accessible to everyone).This has led to deleterious consequences for health (obesity, atherosclerosis, etc. ). Only since the '80s there was a return to the previous eating habits thanks to the spread of food and the revaluation of the Mediterranean diet .

YES NO

The Mediterranean diet• The Mediterranean diet is a nutritional model inspired by the

traditional dietary patterns of Italy, Greece, Spain and Morocco. It provides a high consumption of bread, fruit, herbs, vegetables, cereals, olive oil, fish and wine (in moderation).

• People who live in the Mediterranean countries consume relatively large amounts of fat but despite this, they have lower rates of cardiovascular diseases than the U.S. population, whose diet contains similar levels of animal fat.

The explanation is the large amount of olive oil

used in Mediterranean cuisine: olive oil seems to

lower cholesterol levels in the blood.

Moreover Mediterranean diet says it is better

to drink at least 6 glasses of water a day.

The importance of fiber• The intake of carbohydrates from the diet also includes a

quote of nutrients that fiber has (cellulose, hemicellulose, pectin, lignin of plant cell walls and gums, mucilages and other vegetable secretions)

• It is characterized by glycosidic bonds that the enzymes produced by human body are not able to cleave: it nevertheless has considerable importance for the mechanical action that takes place at the intestinal level by promoting the peristalsis and the movement of chyme through the intestine.

Functions of carbohydrates• Energy: glucose is oxidized to derive all the energy

incorporated into the molecule.• Energy reserves: glycogen in animal cells; starch in plant

cells.• Structural: cellulose constitutes the cell walls of plants;

complex polysaccharides constitute the receptors membrane.

Rice 1/2

• The chemical composition of rice varies depending on its degree of refining, therefore, it is distinguished between white rice and brown rice.

• The protein content is generally between 7% and 9% and is located mainly in the outer layers of the kernel and therefore a significant portion is lost with the refining.

• The proteins of the brown rice are better utilized by the body. The amount of proteins is equal to 70% compared to 50% of the polished rice.

• The lipids present in rice are: oleic acid, linoleic acid, palmitic acid, linolenic acid and stearic acid.

• The content of carbohydrates is very high, even more than 80%, while the raw fiber which is the 1,5% is absent in polished rice.

• The most important minerals are: potassium, calcium, sodium, silicon, iron and manganese, the refining results in the loss equal to 40/75% of the salt content.

Rice Rice 2/22/2

Flour vs Rice

• Flour Energy 353 Kcal -1476 Kjoule 100% -Water 10,8 g - Carbohydrates 79,9 g - Lipid 1,4 g Protein 10,9 g - Fiber 2,7 g.

• Rice Energy 332 Kcal - 1389 Kjoule 100% - Water 12,0 g - Carbohydrates 80,4 g - Lipid 0,4 g -

Protein 6,7 g - Fiber 1,0 g.

• Flour has a caloric content slightly higher, it is richer in lipids, proteins and fiber while it is poorer in water and carbohydrates.

• Rice is also more digestible because the rice starch is composed of granules of smaller size and is poor in amylose (only requires 1 or 2 hours of gastric activity against the 3 or 4 hours of the dough) . Rice has a protein content lower than pasta.

• Its weight increases considerably during cooking just think that 1 pound of uncooked rice will get about 320 grams of cooked rice. For this reason it has a satiety index higher than pasta .

Flour vs Rice Flour vs Rice 2/32/3

• Parboiled rice as well as the integral one retain much of the vitamins contained in the bean.

• Finally, rice can also be used by coeliacs, because it contains little prolammina, a substance that participates in the formation gluten.

Flour vs Rice Flour vs Rice 3/33/3

Experience in laboratoryExperience in laboratory

Identification of sugars, starches and proteins

Target: identify the presence of glucose or starch in food.

Used material: •Distilled water•Starch, sucrose, glucose, milk, potato starch, bread, cheese, albumen or other food•Boiling water for water bath•Benedict's reagent, Lugol's reactive and Fehling's reagent A•Pasteur pipettes, test tubes

Safety instructions: use gloves to avoid contact with the reagents

Procedure:•Prepare three series of test tubes numbered according to the number of substance to test•Place a small amount of distilled water and minced food in the test tubes with the same number of copies•Place few drops of Lugol's reagent in the first series of test tubes and observe•Place few drops of Benedict's reagent in the second series and heat in water bath•Place 1ml of hydroxide solution in the third series and heat in water bath, after about 1 minute remove it, add Fehling's reagent A and leave it to rest a few minutes•Observe the variation of colour and write down the results

Final considerations:

Analyze the results and invite students to fill in a table, and associate the colour change with the presence of

starch, glucose or protein.