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TOPIC 1
THE BASIC COMPOSITION OF FOODS
Vegetable and animal food products are composed by two groups of substances:
inorganics and organics.
The organic substances represent the mainly component of the foods. They can be biosynthesised by plants from inorganic substances through photosynthesis and chemosynthesis. The
animals take the organic substances from food and they are able to transform the absorbed
substances in own organic substances. Thus, from monosaccharides absorbed from food the
animals can biosynthesise glycogen, which is stored as spare substance in liver, muscles and other
organs.
Saccharides
Saccharides (carbohydrates) are natural organic substances that contain carbon, hydrogen
and oxygen, in the same proportion as in water. That’s why they were called “carbohydrates” or
hydrates of carbon. Saccharides are the richest organic compounds from earth. They include the
structural parts of plants as cellulose and their deposits as starch and sugar that became food
sources for human.
They are the result of photosynthesis realised by the plants` chlorophyll which synthesise
saccharides from carbon dioxide taken from the air or the water from soil, using the solar power.
Classification of carbohydrates
After their origin:
 Saccharides of plant origin (fructose, saccharose, starch, etc.)
 Saccharides of animal origin (lactose, glycogen)
After their energetic value:
 Energetic Saccharides (glucose – is the most important energy donor, lactose, etc.)
 Not energetic Saccharides (cellulose, pectin, starch, etc.)
After their chemical structure:

monosaccharides – consists of one molecule. Example: glucose, fructose, galactose.

disaccharides – consists of two molecules. Example: saccharose (consisting of glucose
+ fructose), lactose (glucose + galactose), maltose (glucose + glucose).
 polisaccharides - have branched structure and may contain tens, hundreds or thousands
of scraps of monosaccharides. Examples: cellulose, hemicellulose, pectin substances,
starch, glycogen.
The role of saccharides in the human body:
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 Energy supplier role, is the most important source of energy in the human body due to its
ability to be metabolized by anaerobic and aerobic pathways. Carbohydrates should cover 50-60%
of the daily caloric needs. By burning 1 g carbohydrate 4.1 kcal are produced.
 Plastic role, because they enter in the cell and tissue structure.
 Physiologic role, have the glucides known as food fibers (cellulose, hemicelluloses, pectin
substances). These have the role to gather the remains of digestion and remove them (laxative
and detoxifier).
 Role in maintaining a constant level of glycogen in the liver and the blood sugar.
The human body can only store limited amounts of carbohydrates in the liver and muscles
as glycogen. Due to the limited storage capacity, all carbohydrates consumed over the energy
needs of the body are converted into fat and stored in the adipose tissue.
The body needs 4-5 g / kg body weight per day carbohydrates. This amount depends on
the energy consumed by the body, depending on the physical effort.
The carbohydrate metabolism is closely linked to the metabolism of proteins and lipids.
Dietary sources of glucides
 Vegetable s and fruits (food fibre, glucose, fructose, saccharose, starch);
 Grains and grain products (cellulose, starch, maltose) ;
 Sugar and sugar products (saccharose) ;
 Milk (lactose) ;
 Meat, liver (glycogen).
Proteins
From the nutritional point of view, proteins are a group of chemical substances that provide
to the human body aminoacids. Proteins are present in all alive cells, in vegetal cells, animal,
fungal or bacterial ones.
By their structure and properties, proteins represent the material
base of living beings and their specific manifestations. The protein intake induces the growth and
development of the body, and also its function and integration in the environment.
The nutritional quality of proteins is given by their composition in aminoacids. The human
body can synthesise some of them (not essential aminoacids), other ones cannot be synthesized.
These had to be provided by food intake in corresponding amounts and in certain proportions
(essential aminoacids).
Classification of proteins
Proteins can be classified by their chemical structure in two groups: simple proteins and
complex ones.
 The simple proteins (holoproteins) have their molecules formed only of polipeptidic
threads. By hydrolyses holoproteins set free only amminoacids. Here belong proteins that realize
important biochemical and physiological functions like serum α, β and γ-globulins, antibodies,
histones, fibrinogen, myosin, actins, collagen, keratins, etc.
 The complex proteins (named also conjugated ones, or heteroproteins) contain in their
molecule a protein compound and a not protein compound named prosthetic grouping.
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Heteroproteins can be divided in many groups according the chemical nature of their prosthetic
groups, like glycoprotein, phosfprotein, metalloproteinase, lipoprotein, flavonoprotein.
The role of proteins in the human body
 Structural or plastic role because thei enter in the structure of all cells.
 Catalytic role, because they enter in the structure of enzymes.
 Regulation role because they enter in the structure of hormones.
 Imunostimulation role because they interfere in the defence process of the body, and
participate to the formation of antibody.
 Balancing role because they interfere in maintaining the osmotic balance in the cells.
 Energetic role because they provide energy to the body. By ignition they provide 4,1
Kcal/g proteins.
Sources of dietary protein
 Animal food products: eggs, milk, cheese, meat (20% proteins), organs (liver, kidney,
heart spleen) fish
 Leguminous plants (beans (20-25%), peas, soya beans (35%).
 Cereals: wheat corn rice
 Nuts, peanuts, potatoes, mushrooms
Lipids
Lipids are natural organic compounds that are present in the body of living beings. They
are principal compound of the cell membrane and are also the energetic reserve of the body. They
participate in the transmission of the nervous impulses, in the formation of some waterproof and
thermo-insulating covers, etc.
They have the property to dissolve in organic solvents (ether, chloroform) and to be water
proof.
Most lipids are substances formed of two compounds: one being represented by the fatty
acids and the other by glycerin or other alcohols. From the fatty acids, some of the unsaturated
ones are essential for the human body because they cannot be synthesized by the organism.
Classification of lipids
Alter their biological role lipids can be divided in:
 reserve lipids that are accumulated by human in the adipose tissue, and in plants in
different organs, most in some seeds or fruits.
 constitution lipids, that enter in the cells structure contributing to the formation of
the nucleus, the cell membrane and the mitochondria.
After their chemical composition, lipids can be divided in:
 simple lipids (neutral) formed only of C, H and O.
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
Complex lipids (polar) hat contain in their molecule in addition to C, H, O also N,P, S
etc.
After the nature of the alcohol, the simple lipids are classified in:
 glicerids – esters of glycerol with fatty acids
 sterids – esters of the sterols with fatty acids
 cerids – esters of the superior mono-alcohols with fatty acids

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

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The role of lipids in the human body
Energetic role - lipids are more efficient energy providers than proteins and glucids. They
are kept in the body most in the adipose tissue from where they are mobilised for
energetic needs if food intake doesn’t provide enough calories. They provide to the body
9,3 Kcal/g lipid.
Structural role (plastic) – they are in the composition of the cell membrane in the wall of
some cellular organelles, in some hormones and in the nervous cell
They are starting compounds for the synthesis of some indispensable substances for the
body like phosphatides, sterids, unsaturated fatty acids, tocopherols, etc.
They are solvents and carrier for the fat-soluble vitamins (A, D, E, K).
Sources of dietary lipids
saturated fatty acids – are in meat, sausages, eggs, and whole dairy products
mono-unsaturated fatty acids – are most in olive oil, goose and duck fat, goose pie
poli-unsaturated fatty acids – in this category are the liquid fats at room temperature
(sunflower oil, olive oil, rape oil) and the fish fat.
Vitamins
Vitamins represent a class of natural organic substances with a relative low molecular
mass, with very different chemical structures, that are absolutely necessary to the human body.
Vitamins are vital compounds necessary to balance food intake. In comparison with the
other food compounds, vitamins are necessary in smaller amounts. They have catalytic functions
in the body.
Classification of vitamins
Vitamins are classified in two groups:
 vitamins soluble in water (hydro-soluble vitamins) - vitamin C, vitamins of the B group
(B1, B2, B6, B12), vitamin PP, etc.
 vitamins soluble in fat (lypo-soluble) – A, D, E, K
The role of vitamins in the human body
 The hydro-soluble vitamins interfere especially in the reactions that release energy.
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 The vitamins soluble in fat participate in the use of the food substances and metabolic
assimilation processes and in the cell and tissue growing and restoration processes of
the body.
 Vitamins enter in the composition of enzymes that are present in the cells and tissues
and act as co-enzymes.
Sources of dietary vitamins
 Vitaimn A is present in the animal food products, ussualy in association with lipids (Exp. In
dietary food products and liver). The precursors of vitamin A (carotenoids) are present in the
colored plants (yellow and red fruits and vegetables like carrots, tomatoes, etc.).
 Vitamin D can be found in the oil from code liver, fatty fish (mackerel herring salmon
sardines), brewer's yeast. Different amounts are present in butter, liver, eggs, human and cow
milk.
 Vitamin E. The plant oil are the most important poli-unsaturated fatty acid sources and so
even of vitamin E. Important amounts of this is also in nuts, grains, fish, meat, green vegetables
(broccoli, spinach).
 Vitamin K. The most important dietary source are the green leguminous plants, Smaller
amounts are present in milk and dairy products, meat, eggs, grains, vegetables and fruits.

Vitamin B1 is large spread in food. The most important amount is in porc meat. High
amount are present in whole grains, potatoes, brewer's yeast.

Vitamin B2 is present most in dairy products, meat, organs, fish, eggs, whole grains,
brewer’s yeast.

Vitamin B6 is large spread in food. High amounts are in meat, viscera, whole grains.

Vitamin B12 is present exclusively in animal food products like liver, kidney, lean meat,
eggs, milk and cheese.
 Vitamin C is present in plant food products. The most important dietary sources are fruits
(cedrate fruits, currant, blueberry, apple), vegetables (parsley, pepper, cabbage, etc)
Minerals
Minerals are absolutely necessary compounds for the life. They contribute to the normal
vital activities and the development of the body. They are anorganic substances with a simple
structure (that cannot be splited). The human body had to take them from food intake because
they cannot be synthesized.
Classification of minerals
 macro-elements, that are in the body in high amounts (Ca,F, Mg, S, Cl, Na, K).
 micro-element-se, that are in small or very small amounts (Fe, I, F, Zn, Mn, Cr, St).
Role of minerals
 Plastic role contributing to the structure of the bone system and other tissues.
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 Functional role in the metabolism, because they activate many enzymatic or
physico-chemical systems by pH control, the electrical neutrality and the gradient of
the electro-chemical potential.
 Physiologic role because they enter in the constitution of some compounds with
physiological role (hydrochloric acid in the gastric secretion, iodine in the thyroid
hormones, iron in hemoglobine from blood)
Sources of dietary minerals
 Calcium is present in large amounts in milk and dairy products, but also in
vegetables with green leaves, fish with small bones (sardines, canned salmon), clams and oysters
 Phosphorus is present in chicken, fish, red meat and eggs. Milk and dairy products,
nuts, leguminous plants, whole grains are also good phosphorus sources.
 Magnesium is present in many food products like some seeds (most sun flower),
unprocessed grain, sprouted wheat and meadow wheat, nuts, leguminous plants, green
vegetables, tea, cacao.
 Sodium comes most from food products that contain sodium chloride. In general,
the natural content of sodium is in food products rich in proteins (milk, cheese, eggs, meat, fish).
Small amount are in vegetable and grains. Fruits contain small amount or none sodium.
 Potassium is spread in food products like fruits, vegetables, fresh meat, dairy
products.
 Iron is taken by the body most from eggs, lean meat, vegetables, nuts, dry fruits,
grains and green plants.
 Iodine is present especially in food sources of marine origin and in those cultivated
in soil rich in iodine.
 Zinc come most from fish, meat from home birds, milk and dairy products. Liver,
cheese, grains, dry beans, soya products and nuts are other rich zinc dietary sources.
 Cooper is large distributed in food products. The riches sources are liver, sea food
(in particular, oysters), nuts and seeds. Small amount are in grains and vegetables.
 Fluorine is present in general in smaller amounts in the most food sources.
Exception is made by the fluorinated water, tea and marine fish. Even it is present in most fruits
and vegetables, the amount find here are very small.
 Chromium is present most in brewer's yeast, black pepper, meat products, dairy
products, eggs, dry prunes, raisins, nuts, asparagus, beer and wine.
Bibliography
1. Segal Rodica. Principiile Nutriţiei. Alimentele şi Sănătatea. Editura Academica, Galaţi 2002.
2. Florea Traian. Chimia Alimentelor. Editura Academica, Galaţi 2002.
3.Cîmpeanu Ghiorghe şi alţi. Biochimie Vegetala. Editura Didactică şi Pedagogică, Bucureşti
4. http://www.ms.ro/documente/3%20vitamine%20si%20minerale_8319_6028.pdf- Vitamine
şi minerale. Societatea de Nutriţie din România
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PRACTICAL ACTIVITIES
The basic composition of foods
General objective of the work: Highlighting of nutrients (protein, fat, carbohydrates, vitamins) in
food.
Premises:
Proteins are a primary constituent of living things. Each protein is linear polymers built of amino
acids. Proteins are also nutrient sources for organisms. They function as catalysts, they transport
and store other molecules such as oxygen, they provide mechanical support and immune
protection, they generate movement, they transmit nerve impulses, and they control growth and
differentiation.
High protein foods include meat, fish, cheese, tofu, beans, lentils, yogurt, nuts, and seeds, egg,
milk.
Vegetable proteins: soybean protein, potato protein, corn gluten, wheat gluten,
Lipids are the group of biological macromolecules that have a major hydrocarbon component and
are mostly nonpolar and hydrophobic.
Functionally, lipids are important in cell membrane structure and in energy production.
Both plant and animal sources contain different types of lipids that can provide beneficial and
damaging health effects, depending on the type of lipid and the levels within the body.
Sources of fats include: soybean oil, corn oil, olive oil, sunflower oil, nuts, avocado, milk, egg.
Carbohydrates are the most abundant class of organic compounds found in living organisms.
It is made up of carbon, hydrogen and oxygen and has a configuration of (CH2O)n. It is significant
as an energy source, storage, structure and as a precursor molecule. Carbohydrates can be
categorized under different types of sugars such as mono, di, oligo and polysaccharides and can
contain an aldehyde or ketone group.
Healthy high carbohydrate foods include vegetables, legumes (beans), whole grains, fruits, nuts,
and yogurt.
Sugars that contain aldehyde groups that are oxidised to carboxylic acids are classified as reducing
sugars. Reducing sugars include glucose, glyceraldehyde, lactose, arabinose and maltose.
Vitamin C is a water-soluble vitamin that is necessary for normal growth and repair of tissues in all
parts of your body. Vitamin C is one of many antioxidants. Antioxidants are nutrients that block
some of the damage caused by free radicals.
The body is not able to make vitamin C on its own, and it does not store vitamin C. It is therefore
important to include plenty of vitamin C-containing foods in your daily diet.
All fruits and vegetables contain some amount of vitamin C.
Fruits with the highest sources of vitamin C include: Citrus fruits and juices, such as orange and
grapefruit, Kiwi fruit, Pineapple, raspberries, blueberries.
Vegetables with the highest sources of vitamin C include: Broccoli, Brussels sprouts, cauliflower,
Green and red peppers, Spinach, cabbage, turnip greens, and other leafy greens
Tomatoes and tomato juice.
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Lets investigate:
 Identifying the proteins in food
 Identifying the lipids in food
 Identifying the carbohydrates in food
 Identifying the vitamins in food
IDENTIFICATION OF PROTEIN
BIURET TEST
Biuret solution is used to identify the presence of protein. Biuret reagent is a blue
solution that, when it reacts with protein, will change color to pink-purple.
Equipment and materials:
•
Reactiv biuret: CuSO4 1%, NaOH 20-30%
 Pipettes
 Tubes
 Protein solution (egg white, milk)
Procedure:
 Add 1 ml of sodium hydroxide solution to 2 ml of sample shake well.
 Add 1% copper sulfat solution, drop by drop, gently shaking after each drop.
 Record obtained color
Colour change
Remains blue →proteins absent
Blue to violet → proteins present
Test for proteins (Biuret test)
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IDENTIFICATION OF OIL AND FAT
Equipment and materials:
 Pipettes
 Tubes
 Ethanol
 Oil
Procedure
 Place about 1 cm3 of ethanol in a test tube.
 Add a few drops of oil and mix by shaking.
 Add an equal amount of water and shake again.
Obsevation:
Positive result: A cloudy emulsion forms
Negative results: Liquid remains clear
 Note
o Food with solid fats can be tested by crushing them in ethanol.
Test for oil/Fats (Ethanol/Alcohol Emulsion Test)
IDENTIFICATION OF REDUCING SUGAR
Reducing Sugars
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aldehyde
carboxylate
red precipitate
Fehling’s Test
Equipment and materials:
 Fehling 1
 Fehling 2
 Pipettes
 Tubes
 Alcohol burner (gas burner)
 Fruit Juice (test solution)
Procedure
 1 mL Fehling 1 + 1 ml Fehling 2 + few drops fruit juice (test solution)→ heat the mixture ( 5
min) and observe a colour change.
 The production of yellow 'or brownish-red precipitate of cuprous oxide indicates the
presence of reducing sugars in the given sample.
IDENTIFICATION OF VITAMIN C (ACID ASCORBIC)
Equipment and materials:
 Blue methylene
•
•
•
•
Pipettes
Tubes
Berzelius
Fruit or vegetable juice
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Bibliography
Segal Rodica. Principiile nutritiei. Alimentele si sanatatea. Editura Academica, Galati 2002.
Nancy A. Rice. Face the Fats: The Biochemistry of Lipids.
https://en.wikipedia.org/wiki/Biuret_test
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http://www.sciencecompany.com/Food-Chemistry-Experiments.aspx
http://www.watt.ro/docs/utilitare/vitaminele.pdf
http://www.nlm.nih.gov/. MedlinePlus. Vitamin C
http://www.slideshare.net/msjacklynkong/nutrients-2012- Nutrients
This project has been funded with support from the European Commission. This presentation
(communication) reflects the views only of the author(s), and the National Agency and
Commission cannot be held responsible for any use which may be made of the information
contained therein.
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