EATING WELLEATING WELL““THE CHEMISTRY OF FOODTHE CHEMISTRY OF FOOD””

If you eat a balanced diet,you are already well on the way to good health.

A healthy balanced diet can be a achieved by eating sufficent amounts of each

of the following types of food: carbohydrates, fats, proteins, fibre, vitamins,

minerals and water, ideally in as pleasant form as possible.

Progetto Progetto ““SCIENCE SPEAKS ENGLISHSCIENCE SPEAKS ENGLISH”” Classe 5B a.s. 2007/2008 Classe 5B a.s. 2007/2008

THE FOOD GUIDE PYRAMIDTHE FOOD GUIDE PYRAMID

The Food Guide Pyramid suggest

optimal nutrution guidelines for each

food category, per day, using a

mnemonic graphic of a pyramid with

horizontal dividing lines, to represent

suggested percentages of the daily

diet for each food group.

The Food Groups, according to the

Food Guide Pyramid, are:

-Bread, Cereals, Rice and Pasta

-Vegetable group

-Fruit group

-Milk, Yogurt and Cheese group

-Meat, Poultry, Fish, Dry Beats,

Eggs and Nuts group

They contain the elements Crabon, Hdrogen and Oxygen; they are

included in organic compounds because they contain Carbon.

They have general molecular formula Cx(H2O)x.

Carbohydrates are produced from CO2 and H2O during photosynthesis

and are therefore the end products of the process by which plants

capture energy in sunlight.

Carbohydrates, especially starches, provide the bulk of the calories

(4kcal/g) in most diets.

CARBOHYDRATESCARBOHYDRATES

Carbohydrates include:

•Monosaccharides

•Disaccharides

•Polysaccharides

MonosaccharidesMonosaccharides

Also known as “single” sugars or “simple” sugars, they are soluble and easily digested.

Monosaccharides have the general molecular formula CnH2nOn or Cn(H2O)n.

Ribose (C5H10O5) is the sugar in RNA and deoxyribose (C5H10O4)is the sugar in DNA.

Three common sugars share the same molecular formula: C6H12O6. They are:

Glucose, which is carried around the body in blood and is used by our cells and tissues

as a source of energy;

Galactose, a sugar in the disaccharide lactose;

Fructose, a sugar found in fruits, honey and others.

Ribose Deoxyribose Glucose Galactose Fructose

DisaccharidesDisaccharides

They consist of two monosaccharides linked together: they are turned in monosaccharides

by the digestive system.

The three most common disaccharides are:

•sucrose, or cane sugar = α-glucose + β-fructose

•lactose (the main sugar in milk) = β-galactose + α-glucose

•maltose, a product of starch digestion = α-glucose + α-glucose

PolysaccharidesPolysaccharidesMonosaccharides may be bonded together to form long chains called polysaccharides.

Polysaccharides are the most abundant compounds in the biosphere. They include:

•Starches (long chains of a- glucose): they are insoluble in water and serve as energy

storage molecules in plants, particularly in seeds, tubers, etc. Rice, bread, wheat, corn

and others are the major sources of starch in the human diet. Before starches can enter

(or leave) cells, they must be digested. The hydrolysis of starch is done by amylase.

•Glycogen (chains of α-glucose): it is only in animal cell. Animals store extra

carbohydrates in glycogen in the liver and muscles.

•Cellulose ( a long chain of β-glucose): is the main structural component of plant cell

walls and is the most abundant carbohydrate on earth. Cellulose serves as a source of

dietary fibre since humans do not have the intestinal enzymes necessary to digest it.

amylopectine amylose

LIPIDS or FATSLIPIDS or FATSFats and their compounds are known as lipids.

Amongst the various foods, fats provide the body with maximum

energy (9kcal/g), approximately twice that for an equal amount of

protein or carbohydrates. That is why the human body stores fat as an

energy source. When it needs extra fuel, our body breaks down the fat

and uses the energy.

They are compounds that are generally insoluble in water but soluble

in organic solvents (except for phospholipids).

Major roles of lipids:Major roles of lipids:

They are concentrated source of energy

� They are structural component of cell membranes (phospholipids)

� They cushion internal organs

� They transport fat-soluble vitamins A, D, E and K through the body

� They play a role as messengers (hormones)

� They make food taste nicer

� They contain essential fatty acids, which have a positive effect on the

health of the heart and the immune system

� triglycerides

� phospholipids

� steroids

� waxes

DifferentDifferent kindskinds of of lipidslipids are:are:

TriglyceridesTriglyceridesA triglyceride is made up of a molecule known as GLYCEROL which is connected to one,

two, or three FATTY ACIDS, that are long chains of carbon atoms connected to each other.

There are two kinds of triglycerides: saturated and unsaturated.

Unsaturated triglycerides have at least one double bond in one of the fatty acids.

They are usually liquid at room temperature and generally come from vegetable sources.

They are healthier alternatives to saturated fats and can be found in vegetable oils such

as sesame, sunflower, soya and olive; oily fish, such as sardines and salmon, and soft

margarine.

Saturated triglycerides have no double bonds.

They are generally solid at room temperature ans are usually from animal sources.

They can be found in lard, butter, cheese, whole milk, eggs and any thing that contains

these ingredients, such as cakes, chocolate, biscuits, pies and pastries. It is also the

white fat that can be seen on red meat.

The less saturated fat you eat, the better, since a high intake has been linked with an

increased blood level of cholesterol and an increased risk of coronary heart disease.

SteroidsSteroids -- WaxesWaxes

Steroids are used in animals in hormones. The basis of

a steroid molecule is a four ring structure, one with five

carbons and three with six carbons in the ring.

Waxes are used to coat and protect things in nature.

Bees make wax.

Plant leaves even have wax on outside. Plants use wax

to stop evaporation of water from their leaves.

PROTEINSPROTEINS

Proteins are needed regularly by the body for

growth, and also for the repair and

replacement of cells; what’s more, proteins

play many important functions in our body. The

main sources of dietary proteins are meat, fish,

eggs, milk, cheese, pulses, etc.

Proteins contain Carbon, Hydrogen, Oxygen,

Nitrogen and sometimes sulphur. Proteins

consist of smaller units called amino-acids,

which link together to form chains.

Some amino-acid are created by our body, but

those called essential amino-acids must come

from our diet.

Although all animal and plant cells contain

some protein, the amount and the quality of

the proteins varies a lot.

The The functionsfunctions of of proteinsproteins

Proteins are truly the physical basis of life, since every function in the

living cell depends on them:

� the structure of cells and tissues is largely made of protein

� the catalysis of all biochemical reactions is done by enzymes, which are

proteins

� the transport of materials in body fluids depends on proteins

� proteins are important in motion and locomotion of cells and organisms

� the receptors for hormones and other signalling molecules are proteins

� proteins, such as antibodies, play an important role in defending our

body

StructruresStructrures of the body of the body formedformed fromfrom proteinsproteins

Hair and nails are made of keratins which are long

protein chains containing a high percentage (15-17 %)

of the amino-acid cysteine.

Collagen is the most common protein in the body and

comprises approximately 20-30% of all body proteins.

It is found in tendons, ligaments, and many tissues

that serve structural or mechanical functions.

Collagen consists of amino-acid sequences that coil

into a triple helical structure to form very strong fibres.

Tooth enamel and bones consist of protein matrix

(mostly collagen) with dispersed crystals of minerals

such as phosphate of calcium.

Muscle tissue consists of approximately 65% actin and

myosin, which are the contractile proteins that enable

muscle movement.

ENZYMESENZYMESEnzymes are sometimes called biological catalysts because they speed up

reactions, and only small amounts are required.

Digestive enzymes speed up the breakdown of complex food substances into simpler

subunits. The breakdown of food in digestion is actually caused by water chemically

splitting the complex food molecules, a process called hydrolysis. Digestive enzymes

do not break down foods into the elements they are made of, and they do not release

any energy from the food. This happens when the simpler food substances are

respired in the individual cells.

Enzymes names usually end in the letters –ase, as in amylase, protease and lipase.

The enzyme amylase is in the saliva, and is released as soon as we put food into our

mouths. Amylase digests starch molecules (long chains), cutting them up into the

shorter molecules of maltose. Another group of enzymes breaks disaccharides down,

turning them into simple sugars. Protease digests proteins cutting them up into

smaller chains of amino-acids and eventually into individual amino-acids; lipase

digests lipids (it cuts triglycerides up into fatty acid molecules and glycerol).

amylasestarch maltose

maltasemaltose glucose + glucose

sucrasesucrose glucose + fructose

lactaselactose galactose + glucose

There are two main types of enzymes. Digestive enzymes are extra-cellular

enzymes: they control reactions that take place outside cells. Those enzymes

which control reactions inside cells are called intracellular enzymes.

Enzymes intervene in chemical reactions by locking onto one of the reactants

and speeding up the reaction. The chemical which the enzymes locks onto is

called the substrate, and enzyme has a kind of chemical sensor, called

active site, which helps it to recognise the substrate. Just like a key fits into a

specific lock, each enzyme has its own specific substrate. Once the reaction

is completed and the required product has been produced, the enzyme

releases itself and moves on to the next reaction.

VITAMINSVITAMINSVitamins are organic substances found in plants and animals. Most of them

can not be made by our body, so they must be taken from our diet.

Nutritionists have divided vitamins into two groups: fat-soluble and water-

soluble.

The fat-soluble vitamins - A, D, E and K - are transported through the body

by fat. They can also be stored in fat and liver cells for a limited period of time.

The water-soluble vitamins - B and C – are absorbed by and and trasported

through our body in water. They need to be eaten every day, as they can not

be stored for any length of time.

A A fatfat--solublesoluble vitaminvitamin::

The vitamin D helps our body absorb calcium,

needed to ensure strong bones and teeth.

The most important source is the sun, but it’s also

found in tiny amounts in dairy products, cod liver oil

and oily fish.

A A waterwater--solublesoluble vitaminvitamin::

The vitamin C helps our body produce

collagen and absorb iron.

We can found it in a wide variety of

vegetables and fruit, including spinach,

broccoli, tomatoes, strawberries, citrus

fruit and potatoes.

MINERALSMINERALSMinerals have an important role to play in our good health.

They are inorganic substances, since they are found in the rocks and soil.

Vegetables absorbe mineral goodness as they grow, while animals digest it

through their diet.

Like vitamins, minerals can also be divided into two groups: those that are

needed in minute quantities and those that are needed in larger quantities.

The latter are the major minerals and include calcium, magnesium,

sodium, potassium and phosphorus.

The former are called trace minerals; this group include iron, zinc, iodine,

selenium and copper.

The The importanceimportance of of calciumcalcium

Calcium is a mineral that strengthens bones and

teeth and makes sure that everything runs smoothly

with muscles and nerves.

It’s especially important for growth because it can

continue to add to the strength of our bones until

you reach the age of 30-45, when peak bone mass

is reached. After this point, as a natural part of the

ageing process, your bones lose their density and

grow weaker. If people have not had enough

calcium in their diet prior to this, there is an

increased risk that bones will not be strong enough

to cope with any weakening, which can result in

osteoporosis.

Health professionals estimate that one in three

women and one in ten men suffer from

osteoporosis, and there is concern that the diets of

teenage girls and young women, in particular, are

not high enough in calcium.