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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 atoms
are called hexoses  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.
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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:
starch
glycogen
cellulose
chitin
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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) .
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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
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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 , 6070 % 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
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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.
Rice
2/2
• 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.
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 vs Rice
2/3
• 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
3/3
• 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.
Experience in laboratory
Identification of sugars, starches and proteins
Target:
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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
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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.