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Food science
6 groups of nutrients:
1. Carbohydrates: provide energy and dietary fibre
2. Fats and oils: provide energy
3. Proteins: used for the growth and replacement of tissue, may also provide energy
4. Vitamins: regulate body process
5. Minerals: replacement of tissue
6. Water: essential for body process
Poor diet leads to malnutriation – “bad nutrion”
May be caused by a lack of 1 ore more of the essential nutrients
Consumption of too little or too much food
Insufficient food leads to starvation, later death
Excess and deficiencies of some components of the diet are associated with
certain “diseases of affluence”
Measurement:
SI units (International System of Units)
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6 basic SI units
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length: m
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mass kg
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time s
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electric current A
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thermodynamic temperature K
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luminous intensity cd
Non-SI units
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energy J
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customary temperature ‘C
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area m2
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volume m3
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density kgm-3
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force N
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pressure Pa
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volume l
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derived units, allowed in conjunction with SI
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Use of prefixes
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1 kJ=1000J
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1 mm=0,001m
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1microg=0,000001 g
Length: metres, mm, micrometers, nanometers
Area: length x breadth
Volume: is derived from the measurement of length
Volume= length x breadth x height
Density: weight/Volume
Relative density (RD) of a substance is the number of times a substance is heavier than
an equal volume of water
Relative density = density of substance / density of water
If a substance is dissolved in water to form a solution, the density is altered.
The density varies directly with the concentration of the solution.
Measuring instrument: hydrometer
Relative density of milk: 1,030
Energy: energy value of a food can be assessed by burning the food in oxygen and measuring
the amount of heat energy produced (Joule, Calorie)
Temperature: degree celsius
Melting point of ice is 0 Celsius, boiling point of water is 100 Celsius
On Fahrenheit scale: melting point of ice is 32 Celsius, boiling point of water is 212
Celsius (5 celsius degrees = 9 Fahrenheit degrees)
1. Carbohydrates
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are a group of nutrients important in the diet as a source of energy; contain carbon,
hydrogen, oxygen, are produced in plants by the process of photosynthesis.
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6CO2 + 6H2O = C6H12O6 + 6O2
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Calorophill is a green pigment which absorbs energy from sunlight and enables
plant to build up carbohydrates from carbon dioxide and water.
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Monosaccharides (sugars) in food containing 6 carbon atoms and its equation:
C6H12O6
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Glucose: found in fruits and vegetables
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Fructose: laevulose: chemically similar to glucose the arrangement of the atoms
within the molecule is different . Fructose is found together with glucose in fruits
and honey.
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Galactose: chemically similar to glucose. It doesn’t exist as such in foods but is
produced when lactose – a dissacharide is broken down during digestion
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Dissacharides: sugars have the general formula C12H22O11. They are formed when
2 monosacharides molecules combine with the elimination of a water molecule.
C6H12O6 + C6H12O6 = C12H22O11 + H2O
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sucrose: ordinary household sugar produced in plants by condensation of glucose
and fructose. Can be found in many fruits and vegetables.
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Lactose: by condensation of glucose and galactose. Found only in milk (where it is
the sole carbohydrate).
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Maltose: by condensation of 2 glucose molecules. During germination of barley,
starch is formed into maltose.
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Formation: glucose + fructose = sucrose + water
Glucose + galactose = lactose + water
Glucose + glucose = maltose + water
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properties of sugars: white, crystalline compounds, soluble in water
invert sugar: mixture of glucose and fructose
when it is heated, it caramelized
sucrose act as reducing agent – reducing sugars – to reduce oxidizing
agent; sucrose is non-reducing sugar.
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Polysaccharides: condensation polymers of monosaccharides and made up of
many monosaccharides molecules with the elimination of 1 water molecule at each
link. C6H10O5
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Starch: mixture of amylase and amylpectin. Amylose contains 50-100 glucose
units joined in a straight chain. Amylopectin consists 100.000 glucose units joined
in a branch chain. Contains 80% amylopectin and 20% amylose. Occures as small
granules. White, non-crystalline powder , insoluble in cold water. Do not have
sweet taste. Hydrolisis: action of an acid or an enzyme. When starch is heated up
with an acid it is broken down into successively smaller molecules – the final
product is glucose. (C6H10O5)n + n H2O = nC6H12O6. First large starch molecules
are broken down into shorter chains of glucose units: dextrines. Secondly dextrins
further broken down into maltose (2 glucose units). Thirdly maltose is broken
down into glucose. Gelatinisation (with water): as the size of the granules
increases the mixture is viscous. At 80% the granules breaks up and the contents
become dispersed throughout the water. Long-chain molecules begin to unfold and
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starch-water mixture becomes more viscous. On cooling starch molecules form a
network with the water, producing a gel. = gelitanisation of starch – more starch,
stronger gel. Retrogradiation: amylase molecules tend to unwind and the gel
becomes opaque and like a pulpy sponge. Dextrinisation (dry heat): on heat
dextrines polymerise to form brown-coloured compounds: pyrodextrins.
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Cellulose: polysaccharide, containing long-chains of glucose units. Acts as a
structural material in plants, found in cell walls, where it gives rigidity.
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Glycogen: carbohydrate, found only in animals, in muscles and liver. When it is
required it is converted into glucose and it is broken down to provide energy.
Branched chain in glucose units.
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Pectin: complex mixture of polysaccharides found in fruits and root vegetables.
Jelling agent: jam making – sugar is needed in about 65%, pH also effects the gel,
optimum pH level: 3.0-3.5. Unwanted pectin can be removed by pectolytic
enzymes.
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Gums, alginates, agar: gums: tragaxanth, Arabic, guar are produced by plants.
Agar is used in microbiological media.
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Functions: Energy: glucose oxidized in the cells, is broken down in a series of
reactions. 1g carbohydrates = 16kJ. Storage: glucose can be converted into
glycogen (in liver, muscles), into fat (all over in the body in the fatty cells). We
have 400g stored glycogen and about 12kg of stored fat. Protein sparing: provide
material for growth, repair of tissue. Dietary fibre: unavailable carbohydrate
provide dietary fibre.
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Sources of carbohydrate in the diet: cereal and cereal foods (all cereal contain high
percentage of starch, they account for 49% of the total carbohydrate content of the
av. British diet), refined sugar (sucrose, account of the 18% of the diet), vegetables
(contain starch and sugar, most important is potato, pulse vegetables contain
significant amount of carbohydrate, but root and green contain less, account for
15% of the diet), fruits: (fruits ripen – form into sugar, contains 5-10% sugars,
banana contains starch and sugar when ripen), milk (contains lactose, cheese and
butter do not contain, cottage cheese contain a small amount, 8% of the diet)
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Health: sugars and starch: in Britain sugars provide 15% of the total energy, fats:
42%. Present sugar consumption is about 100g/day. 1/3 is household sugar. Tooth
decay is caused by acids produced by oral bacteria which break down sugars in the
paleque in teeth. Sugars provide “empty calories” , it is a source of energy but
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contain no other essential nutrients. Intake should be reduced to 55g/day. Dietary
fibre: is the material in plant food, which is resistant to break down by enzymes in
the alimentary canal. Consist of cellulose, homocellulose, pectin, guns, noncarbohydrate lignin. Acts by binding water, increasing “bulk” of the material
passing through the large intestine, aiding the voiding of faeces (sugar, white flour,
white bread). Diverticular disease, cancer of the colon and haemorrhoids. Lowers
blood cholesterol level and the risk of coronary heart disease and the risk of
diabetes. Intake is about 20g/day, should be 30g/day.
2. Fats and oils
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known as lipids, contain carbon, hydrogen, oxygen, esters of glycerol and fatty
acids. Glycerol is a trihydric alcohol (3 –OH groups), general formula of fatty
acids (alkanoic acid) is R.COOH (R is the hydrocarbon chain).
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Are mixture of triglycerides: consist of 1 molecule of glycerol combined with 3
fatty acids molecules
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Diglycerides consist of glycerol combined with 2 molecules of fatty acids
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Monoglycerides: only 1 fatty acid molecule
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Diglycerides and monoglycerides are used as emulsifiers
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About 40 different fatty acids found in foods
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Saturated fatty acids: hydrocarbon chain is saturated with hydrogen.
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Unsaturated fatty acids: hydrocarbon chain is not saturated with hydrogen – has 1
or more double bonds. Can be monosaturated (1 double bond – oleic acid) and
polyunsaturated (more than 1 double bond – linoleic acid) and can be cis fatty
acids (2 hydrogen atoms on the same side of the double bonds) and trans fatty
acids (hydrogen atoms on the geometrically opposite sides of the double-bonds).
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Have generally the same chemical structure; fats commonly refers to the mixture
of triglycerides, which are solid at room temperature. Oil refers to those which are
liquid at the same temperature.
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Difference between them is the prescence of different fatty acids.
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Fats contain large proportion of saturated fatty acids distributed among the
triglycerides.
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Oils: large proportion of unsaturated fatty acids.
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In general: fats are from animal, oils are from vegetable sources
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The contain a small amount of non-triglyceride
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Degree of unsaturation can be measured in terms of its iodine value. A molecule of
iodine (I2) will react with each double bond and so with unsaturated oils and have
higher iodine value than saturated fats. Vegetable oils should not be confused with
mineral or essential oils. Mineral oils are from crude oil and are mixtures of
hydrocarbons. Essential oils are in plants but are not triglycerides. Eugenor is
responsible for the flavour of cloves.
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Hydrogenation: is the addition of hydrogen across a double bond: unsaturated
fatty acid turns into saturated one.
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Properties: Solubility: fats and oils are insoluble in water. Emulsifying agent is
used to form a stable mixture of fat and water. Emulsion can be fat-in-water (milk)
and water-in-fat (butter). Fats and oils are soluble in organic solvents (petrol, ethor,
carbon tetrachloride). Effect of heat: melting point (fats melt when heated, fats do
not have distinct melting point but melt over a range of temperature. The
temperature at which melting starts is called slip point. Fats between 30-40C. For
oils the melting point is below the normal air temperature. The more double bonds,
the lower the melting point.). Smoke point: (when fat/oils heated up to a certain
temperature it starts to decompose , producing a blue haze or smoke and a
characteristic acrid smell. Most fats and oils start to smoke at about 200C. For lard
it is 185C, for corn oil it is 232C. Vegetable oil has a higher smoke point than
animal fats. Decomposition of the triglycerides produces small quantities of
glycerol and fatty acids. The glycerol decomposes acrolein. This decomposition is
irreversible, during deep-frying we should keep the temperature below the smoke
point. Repeated heating reduces the smoke point and produces oxidative and
hydrolytic changes.). Flash point: (fat is heated to a high enough temperature, the
vapour given off will spontaneously ignite. This is the flash point. Corn oil: 360C.
Fat fire should never be put out with water. ) Plasticity: substances will change
their shape under pressure but will remain in their final shape when pressure is
removed. They do not return to their original shape. Fats contain small chrystalls –
which are produced by rapid cooling of the fat during manufacture – will be more
plastic. Plastic range of the fat is the range temperature over plastic behaviour of
fats. Most animal fats have a narrow plastic range and are hard and different to
spread.) Rancidity: (spoilage of fats and oils. There are 2 types of rancidity:
oxidative rancidity: result of the reaction between unsaturated triglycerides and
oxygen from the air. O2 molecules join across the double bonds of the triglyceride
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molecule and a variety of compounds are formed including aldehydes and ketones
which give rise to an unpleasant rancid taste. Reaction is accelerated by heat, light,
traces of metal. The second type is hydrolytic rancidity: enzymes – lipases –
hydrolyse fats, breaking them down into glycerol and fatty acids: fat and water –
lipase – glycerol and fatty acids. Lipids can be inactivated by heat treatment and
can be produced by microorganism in fatty foods. The free fatty acids can give fats
an unpleasant taste and smell. Rancidity can be reduced by storing fats and oils in
a cool, dark place in a non-metal container. Antioxidants (BMT – butylated
hydroxytoluene) are added commercially to fats to reduce rancidity. Vegetable oils
contain natural antioxidants (vitamin E): it is destroyed by heat treatment.)
Saponification: triglycerides react with alkalis forming a soap and glycerol.
Sodium-hydroxid and potassium-hydroxid are used. Soap is a mixture of sodium
salts of different fatty acids.)
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Use of fats and oils: frying, shortening effects of fat (fat coats the starch and gluten
molecules, so breaks up the structure), creaming and aerating effect.
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Production of oils and fats: vegetable oils (70%): oils are obtained from nuts, seeds
of plants (corn, ground nut, soya, olive, sunflower). Soya, sunflower and corn oils
are high in polyunsaturated fatty acids (PUFAs). Olive oils are high in
monounsaturated, coconut and palm oils in saturated fatty acids. Erucic acid is a
fatty acid which have been associated with heart disease. Oils are extracted by
crushing and by the use of solvent extraction. Neutralization with sodiumhydroxide removes the free fatty acids. Oils is than bleached with Fuller’s earth
(absorbs the coloured matter). Finally the oil is deodrorised by heating under
vacuum and injecting steam – removes the volatile substances responsible for
odour. Margarine: emulsion of water-in-fat. Hydrogenation is carried out by
heating the oil in large sealed vessels under pressure. Hydrogen is bubbled into the
oil and finely divided nickel – which is removed by filtration – is required as
catalyst. Artifical colouring, salt, vitamin A and D are needed. Emulsion is formed
in a machine: votator – mixing and cooling occur together. Hard margarines are
more hydrogenated. Must contain 80% fat. Low fat spreads: fat content: 40%,
water content: 60%. Less fat, lower energy. Cooking fats and shortenings: are pure
fat products rather than emulsions. Is a blend of veg. and fish oil and animal fats.
Oils are partially hydrogenated. Fat blend is cooled, air is incorporated into the
product to improve texture. Some fats have an emulsifying agent added. Lard:
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extracted from pigs. Almost 100% pure fat. Butter: made by churning pasteurized
cream. Cream becomes viscous than mass of solid butter. Butter-milk liquid byproduct is removed. Salt and colouring matter can be added. Churning reverses
emulsion. It is water-in-fat emulsion.
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Function of fat in the diet: energy: fat is broken down by process of oxidation and
energy is released. 1g fat = 38kJ. Fat has more than twice calorific value of
carbohydrates. Formation of adipose tissue has 3 functions: energy reserve,
forming under the skin an insulating layer to prevent heat loss from the body and
to protect organs from physical damages. Essential fatty acids can not be
synthetised in the body (linoleic, linolenic, arachidonic). Linoleic is the only real
essential acid since the other 2 can be formed in the body from it. Linoleic is
needed for the formation of the cell membranes. Arachidonic form hormone-like
substances. Fat soluble vitamins: D, E, A, K.
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Sources of fat in the diet: meat and fish (meat 25%, fish 20% of needed fat), butter
and margarine (butter 10%, margarine 14%), milk, cream and cheese (milk: 3-4%,
cream 15%, cheese 5%), baked goods (9%)
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Coronary heart disease
3. protein
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found in the cytoplasm of all living cells (animals, plants)
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organic substance, resemble fats and carbohydrates in that they contain the
elements of carbon, hydrogen, oxygen, nitrogen (sulphur, phosphorus)
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plants are able to synthetise protein from inorganic materials. Carbon dioxide from
air, water from soil, compounds (nitrates, nitrites). Legumes are able to utilize
nitrogen from the air with the aid of bacteria.
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The structure of protein: protein molecules are large and consist of long-chains of
amino acids chemically bound.
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There are about 20 different amino acids: each amino acid molecule contains at
least 1 amino group (-NH2) and at least 1 acidic group (-COOH). Amino acids said
to be amphoteric. A protein molecule contains about 500 amino acids joined
together by peptide links. A peptide link is formed when the amino group of 1
amino acid reacts with the acidic group of an adjacent amino acid (a molecule of
water is eliminated during the formation) = condensation polymerization. Two
amino acids form a dipeptide and COHNatoms = peptide link. Longer chains of
amino acids are called polypeptides. Protein contains all 20 amino acids in any
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arrangement. The order of amino acids in the protein molecule is called primary
protein structure. Cross links also can be found. One of the most important type of
cross-linkage is the disulphide bridge. Amino acid cysteine contains an –SH group,
when 2 cysteine units are adjancent, a disulphide bridge: -S-S- may be formed by
the oxidation of the –SH groups. Cross links can be produced by the formation of
hydrogen bonds. Cross-linking determines the secondary structure of protein.
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There are 2 groups of protein according to their shape: globular proteins: rounded
in shape but not necessarily spherical. Molecules are not closely packed, there is
no organized arrangement. Easy to disperse in water and in salt solutions to form
colloids (hemoglobin, myoglobin). Fibrous proteins: molecules of it are straighter.
May be completely straight (inelastic, extended) or coiled in spiral. Molecules are
closely packed together and there is an organized arrangement. There are crosslinks between adjacent amino acid chains and difference for water molecules to
penetrate structure – not soluble in water. Gluten is an elastic protein. Collagen is
an extended protein.
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Properties: fibrous proteins are not greatly affected by acids, alcaids and moderate
heat. Globular proteins form colloidal solutions and are affected by acids, alkaids
and heat.
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Denaturation and coagulation: denaturation: proteins’ secondary structure is
altered but their primary structure is unchanged. Molecules unfolds and changes
shape but the sequence of amino acids remains the same. Involves the breaking of
cross-linkage(which maintains the shape of the molecules). Proteins become less
soluble and more viscous. This result in the hardening is called coagulations (1.
Action of heat: many protein coagulates when heated. 2. Prescence oh heating:
lactic acid. 3. Addition of salt: sodium chloride. 4. Addition of rennin: rennin is an
enzyme. 5. Mechanical action: protein molecules unfold and form a reinforcing
network round the air bubbles – stabilizes the foam).
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Maillard reaction (non-enzymetic browning): reaction takes place between amino
group of a free amino acid on a protein chain. There is some loss of nutritional
value of proteins; reaction can cause discoloration of foods during storage.
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Functions in the body: growth and maintenance: proteins are the main constituents
of cells of body (in membranes, in cells, within cells). Protein is necessary to form
enzymes, antibodies and some hormones. Energy: excess protein used for energy.
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Deaminated molecules contain carbon, hydrogen, oxygen. Glucose is oxidized in
the cells to supply energy. 1g protein = 17kJ.
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Essential amino acids and protein quality: from 20 amino acids 8 are essential in
the diet, they can not be synthetised in the body. Tho non-essential amino acids
can by syntethised in the body by converting 1 amino acid into the other in the
cells. Methionine and cysteine are sulphur containing amino acids. Proteins are
hydrolised during digestion to produce amino acids. Biological value of protein is
used to measure protein quality. BV is the percentage of absorbed protein which is
converted into body protein. When 2 different proteins are mixed, the resulting
mixture has a higher BV than the average BV of the components. Net protein
utilization is the percentage of the dietary protein which is converted into body
protein. NPU=BVxDigestibility.
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Sources in the diet: meat and fish ( meat, muscle, liver, kidney, sweetbreads, 31%
of necessary protein intake; fish: 5%), bread and cereals (bread: 15%, cereal foods,
rice: 8%), milk (10%), cheese (6%), eggs (4%), vegetables (4% potato), nuts
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Protein requirements: depends on the rate of growth and body weight.
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Protein deficiency: causes a disease: kwashiorkor (wasting of muscles, retarded
growth, distended abdomen caused by oedema), causes anaemia (lack of formation
of red blood cells).
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Energy output is a measure of energy value of the food obtained. Energy input:
energy required to grow crops or rear animals. Energy output: energy input ratio of
various foods (wheat, bread, egg, chicken). If a ratio is less than 1: more energy is
used in producing the food than by its consumption.
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Novel sources: new type: single cell protein produced by microorganism: 1.
Textured vegetables proteins: proteins from certain oil seeds can be used to make
textured products which can be used to replace meat. Soya bean meal can use to
manufacture a product with a meat-like texture (TVP). 2. Single cell protein:
microorganisms are valuable source of protein. 3. Protein rich preparation:
incaparia is fortified with calcium and vitamins.
4. Vitamins
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group of organic compounds required in small quantities by the body for the
maintenance of health. They are not synthetised in the body so are essential in the
diet. Vitamins are not chemically similar to each other. Each vitamin has a specific
chemical structure and a specific function in the body.
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Fat-soluble vitamins: vitamins A and D are not soluble in water and are stored in
the liver. Hypervitaminosis.
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Water-soluble vitamins: vitamins of group B and C not soluble in fats. They are
not stored in the body. B vitamin: thiamin, riboflavin, nicotinic acid.
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Vitamin A (retinol): pale, yellow solid, soluble in fats, only in animal foods, but
fruits contain carotenes (a group of orange pigments), which can be converted into
retinol in the body (most important pigment: β-carotene). 1 µg retinol equivalent =
1 µg retinol = 6µg carotene. Sources: liver, fish, liver oil, butter, milk, cheese, egg,
oily fish, margarine, heart. Sources of carotene: vegetable, dark green vegetable,
carrot, yellow-coloured fruits (peach, apricot), 2/3 retinol, 1/3 carotene. Functions:
essential for growth and metabolism of all body cells, formation of rhodopsin
(pigment found in retina, a membrane at the lack of eyes), maintenance of healthy
skin. Deficiency: reduces rate of growth, body is unable to synthetise rhodopsin,
causing night blindness, xeropthalmia: membranes at the front of the eye become
dry and inflamed, blindeness. Excess: large doses of vitamin A is harmful.
Recommended intake: 750µg/day., for pregnant women: 1200µg/day. Losses on
cooking and storage: during frying, oxidation.
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Vitamin B: Thiamin (B1): white solid, soluble in water. Sources: cereal grains,
germ and bran of the grain, whole-wheat flour, brown rice, bacon, pork, potatoes,
peas, beans, nuts, milk, Brewer’s yeast (Beer), bread. Function: release energy.
Deficiency: cracks at the corner of the mouth, tongue becomes red, hard swollen.
Recommended intake: 1,3-1,6mg/day. Cooking losses: very small. Effects of
sunlight: robiflavin is sensitive to light. Milk looses 10% of riboflavin/hour.
Nicotinic acid (niacin): white, crystalline, water-soluble solid. Nicotinamide can
be formed in the body by amino acid: tryphtophan. 1 mg nicotinic acid equivalent
= 1 mg available nicotinic acid = 60 mg tryphtophan. Sources: yeast, meat (offal,
fish, cheese, pulse vegetables, cereals). Much in wheat is lost during milling, milk,
egg, potato, beer, bread. Function: forms part of enzyme system concerned in the
oxidation of glucose and release energy in body cells. Deficiency: pellagra
(symptoms: diarrhea, dermatitis, dementina – mental disorders). Recommended
intake: 18 mg for men, 15 mg for women. Losses on cooking: nicotinic soluble in
water, only small amount is lost. Folic acid (folate): name used to cover several
related compounds. Sources: liver, green leafy vegetables, kidney, pulse, nuts,
flour, cereal foods. Function: synthetis of nucleic acid, formation of red blood
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cells. Deficiency: anaemia (iron tablets needed). Recommended intake: 300µg,
during pregnancy: 500µg. cooking losses: destroyed by heat in the pressure of
oxygen and alkalis, green vegetables are boiled: 90%. Other B vitamins:
cyanocobolamyn (B12): involved more than 1 enzym system, needed for red blood
cell formation; contains element cobalt; in foods of animal origin, yeast, liver,
milk, meat, fish, egg; deficiency causes pernicious anaemia. Pyridoxine (B6): meat,
liver, fish, some, vegetables; functions: in many enzyme system (mainly in protein
synthesis); deficiency is rare; large dose can be harmful. Biotin: release energy
from fats; egg-yolk, liver, yeast; can be synthetised by bacteria in the intestine.
Panthotenic acid: in plants and animal foods; no danger of deficiency, essential
constituent of enzyme system, release energy from fats and carbohydrates.
Choline, PABA (para aminobenzoic acid), inositol.
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Vitamin C (ascorbic acid)white, crystalline substance, very soluble in water.
Sources: vegetable, fresh fruits, raw liver, kidney, raw milk. Functions: formation
of collagen, main protein of connective tissue (packaging material). Deficiency:
scurvy. Recommended intake: 30mg, 60mg for pregnant women. Losses on
cooking and storage: readily destroyed during cooking (very soluble in water),
readily oxidized. Ascorbic acid oxidize is an enzyme. Fruits looses less vitamin C
than vegetables. Average loss of vitamin C due to cooking fruits is only 10%.
Preserved foods: 50% loss during canning, greater during drying. Frozen foods
retain most of their ascorbic acid. Frozen vegetables has more ascorbic acid than
fresh ones. Gradual loss during storing.
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Vitamin D (cholecalciferol): white, crystalline compound, soluble in oils and fats.
Cholecalciferol (D3): natural form of vitamin. Under the skin by sunlight (ultraviolet radiation). Ergocalciferol (D2): synthetic form, has the same activity as D3.
produced by ultra-violet radiation of ergosterol. Sources: in relatively few foods,
fish-liver oil, oily fish, eggs, butter, liver, cheese, sunlight. Functions: for growth,
maintenance of bones and teeth. Deficiency: rickets (softening of bones),
osteomalacia (bones become soft, week, painful). Excess: much vitamin D –
kidney damage. Recommended intake: 10µg. no effect of cooking.
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Vitamin E (tocopherols)natural antioxidant, protect vitamin C against oxidation.
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Vitamin K: essential for normal clotting of blood, sythetised by bacteria.
5. mineral elements and water
a) Mineral element: chemical element required by the body
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are present in foods in form of inorganic salts, in organic compounds
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account for 4% body weight
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calcium and phosphorus are present in large amount and called major minerals or
macrominerals; others occur in very small quantities called trace elements
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have 3 main function in the body: 1. Calcium, phosphorus and magnesium are
constituents of bones and teeth. 2. Control the composition of body fluids. 3. Trace
elements are concerned in enzyme-system in the body.
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Calcium: sources: milk, cheese, yoghurt, flour, small fish eaten with bones, fruits,
vegetables, bread, cereals. Functions: formation and development of bones and
teeth, essential factor for clotting of blood, normal functioning of muscles and
nerves in the body. Absorption: 1/3 from the intestine. Deficiency: vitamin D is
essential for calcium absorption so deficiency of calcium is the deficiency of
vitamin D. Rickets in children, osteomalacia in adults, oseoporosis. Recommended
intake: 600-1200mg. little effect of cooking.
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Iron: sources: liver, kidney, egg-yolk, cereals, white flour, potato, pulse vegetables,
black pudding, cocoa, black treacle, shell fish, curry powder, bread. Function:
body contains 4 g of iron (in hemoglobin) and in myoglobin. Absorption: only 520%. Deficiency: anaemia: number of red blood corpuscles reduced – lack of
energy and feeling of lethargy, headache, dizziness. Recommended intake: 10-15g.
effect of cooking: small in cooking, sideroses.
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Sodium (and chlorine): sources: common salt, production of bacon, smoked fish,
bread, butter, cheese, cereals. Sodium-hydrogen carbonate used as raising agent;
monosodium glutamate as flavour enhancer, sodium nitrate as meat preservative.
70% of diet comes from food, 30% is added during cooking. Function: essential in
regulation of the water-content of the body. 3g salt/day. Deficiency results
muscular cramps. Excess: maintain an equivalent excess of water. Oedema. High
salt intake: raised blood pressure.
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Potassium: ionized form inside the body cells. Regulation of the fluid-content of
the cells. Can be found in fruits and vegetables.
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Phosphorus: with calcium is an essential constituents of bones and teeth. Release
of energy. Formation of nucleic acids, DNA, RNA. No dietary deficiency.
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Iodine: sources: cereals, vegetables, milk, sea fish. Functions: trace elements
thyroid gland for the formation of hormones, involved in the regulation of the rate
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of oxidation of nutrients in the body cells. Deficiency: goiter (enlargement of the
thyroid gland).
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Fluorine: main source is drinking-water. Protect against tooth decay.
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Zink: meat, milk, bread, cereals. 40% of zink in the diet is absorbed. Involved in
large number of enzyme-systems. Essential for growth and development.
Deficiency: delayed sexual maturity.
b) Water: all living organism contain water. Human body is 65% water.
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adult men: 40L
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provides medium in which nutrient, enzymes, other chemical substances can be
dispersed and in which chemical reactions necessary for body. Blood plasma: 90%
water.
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Water balance: water cannot be stored in the body – regular intake is essential.
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100g glucose produces 60ml water
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hard water: water, which contains dissolved mineral salts. 1. Temporary hardness:
hardness can be removed by boiling, contains calcium, magnesium hydrogen
carbonates. In stalk and limestone regions: H2O + CO2 = H2CO3; H2CO3 + CaCO3
= Ca(HCO3)2. 2. permanent hardness: contains calcium, magnesium sulphates,
dissolved as rainwater, cannot be removed by boiling. Disadvantages of hard
water: soap won’t lather easily, will form a scum. When water is heated up or
boiled, insoluble calcium and magnesium carbonates are formed.
Ca(HCO3)2 --- CaCO3 + H2O + CO2
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affects the colour and texture of vegetables. Advantages of hard water: dietary
intake of calcium more suitable in certain industries, safer in conjunction.
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How to remove hardness from water:
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Addition of washing soda: washing soda reacts with calcium and magnesium salts,
forming soluble sodium salts and insoluble calcium and magnesium salts.
CaSO4 + Na2CO3 –-- CaCO3 + Na2SO4
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ion exchange process: calcium and magnesium ion are exchanged for sodium ions
in the resins.
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Use of sequestering agents (calgon: sodium hexametaphosphate) added to hard
water, encloses calcium and magnesium ions in stable complexes which are
soluble but do not react with soap.
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Mineral waters: carbon dioxide can be added.
6. Enzymes and digestion
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a) Enzymes: are substances, which control all the chemical reactions in the living
organism
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they are proteins produced by living cells and are often called organic catalysts as
they spread up reactions which would accure very slowly.
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Release energy
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The function of a cell is determined by the nature of the enzymes present in it.
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Name of enzymes: giving “ase” to the end of the word indicating the nature of the
substrate or the name of the type of type of the chemical reactions which the
enzyme catalysis.
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Mode of action: factors affecting enzyme action: affected by temperature and pH
and co-factors.
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Effect of temperature: for animal enzymes the optimal temperature is between 3540C. above 50C enzymes are inactivated, above 100C all enzymes are destroyed.
At very low temperature they are not destroyed but their activity is reduced.
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Effect of pH: for each enzyme there is an optimum pH: pH 5-9, most active at 7.
pepsin: optimum pH: 2
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Presence of co-factors: need of an other substance to function effectively. Coenzymes are non-protein compounds, aiding enzyme-activity (vitamins, vitaminderivatives). Certain mineral ions are enzyme-activators (zink, iron, magnesium)
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Enzyme-inhibitors (cyanide) result death.
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Enzymes in dread-making: flour contains amylases which in the prescence of
water converts starch into maltose. The enzyme maltase continue the breakdown
by splitting maltose into glucose. Glucose is fermented by zymase. The products
are carbon-dioxids, which aerate the dough and ethanol (alcohol) which is driven
offduring baking. Proteases present in flour and yeast.
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Production of alcoholic drinks: fermentation of glucose by yeast enzymes, alcohol
is retained, carbon-dioxide is allowed to escape. Enzymes remove cloudiness in
wines.
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Cheese production: rennet – which enzyme is rennin – coagulate protein in milk
and form curd.
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Meat tenderizing enzymes: protein-splitting enzymes, papain – obtained from
papaya plant and bromelin – from pine-apple juice.
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Tea production: PPO
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Undesirable effects of enzymes in foods: Autolysis: distruction of plant and animal
cells by their own enzymes – food spoilage. Microbial spoilage: produce
unpleasant end products. Enzymic-browning: enzymes are destroyed by heat.
Oxidation of ascorbic acid: vitamin C oxidaze enzyme is responsible for oxidation
of vitamin C.
b) Digestion: is the breakdown of complex nutrient molecules into molecules
small enough to be absorbed through the linig of the intestine; is a chemical
process of hydrolysis: dis- and polysaccharides form to monosaccharides, fats
and oils to fatty acids and glycerol; proteins to amino acids.
- Alimentary canal: continuous tube, 8 m long, open at both sides (upper mouth,
lower: anus). Mouth: mastication: food is broken down into small pieces; saliva is
composed of water together with 1. mucin (slimy protein substance, makes easier to
swallow) 2. salivary amylase(initiates the breakdown of starch into maltose). After
swallow food is carried down into small oesophagus by peristalsys (rithmic contractions
of muscles, in the wall of it. Stomach: acts as reservoir site of some digestion, cells
produce gastric juice (contains: pepsine, an enzyme breaks down proteins into
polypeptides, hydrochloric acid; activates pepsin and kills bacteria, rennin – an enzyme
coagulates milk protein, intrinsic factor – a substance needed for absorption of vitamin
B12). Food and gastric juice is the chime. Small intestine: chime enters the duodenum:
pancreatic juice produced in prancreas and contains trypsin, chymotripsin (enzyme
continue digestion of proteins, pancreatic amylase – enzyme breaks down starch into
maltose; lipase – enzyme hydrolysis lipids into fatty acids and glycerol.) Bile: yellowbrown fluid produced in liver and stored in gall-bladder; contain bile-salts. Intestinal juice:
secreted by cells, containes: peptidases – group of enzymes completing breakdown of
protein; disaccharides – splitting enzymes: maltase, sucrase, lactase (hydrolysis maltose,
sucrose and lactose into their respective monosaccharides. Digestion later in jejunum,
ileum, small intestine. Large intestine to remove water from fluid mixture – undigested
food leaves the body in semi-solid state.
- Absorption: mainly in small intestine (6 m long, finger-like projection, called villi) –
20m2
- Digestibility: weight of food or nutrient digested and absorbed (weight of food eaten
x 100); carbohydrates: 95%, proteins, fats: 90%
7. Commodities:
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a) Meat: structure: is flesh or muscle of animals. Fibres are held together by connective tissue
to form bundles. The whole muscle is surrounded by connective tissue. Fatty deposits –
marbling – and blood vessels are found between boundless and fibres.
Composition: fat content varies from 10% to 50% depended on the animal and the part of the
animal. Meat with high fat content has lower water content. Meat proteins: muscle fibres:
contain 2 soluble vitamins: actin and myosin which are responsible for the construction of
muscles. Connective tissues contain collagen, elastin and reticulin. Collagen can be found in
skin; during cooking it is converted into gelatin. Elastin is a though, insoluble protein in blood
vessel walls and ligaments. Reticulin is fibrous and found between muscle fibres. Elastins are
known as gristles. Fat: marbling found in connective tissues and between boundless of fibres;
stored under skin and around certain organs. Keeps meat moist during cooking. Yellow fat:
old animal, yellowness is due to the deposition of carotene.
Food value: meat is valuable protein food and source of B-vitamin, iron but poor in calcium.
Liver and kidney contain A and D vitamins but the meat itself does not. There is no difference
between fresh and frozen meat. Canned meats contain less thiamin than cooked or fresh meat.
Tenderness: depends on: 1. size of muscle fibres (meat composed of small, narrow fibres is
more tender). 2. amount of connective tissue (older the animal, greater the amount of
connective tissue). 3. activity of animal before death: animals must be rested before slaughter.
4. length of hanging: meat is hung for several days to make it tender, pH falls from 7.4 to 5.5,
enzyme action causes breakdown of protein, increasing tenderness. Further tenderizers:
physically and chemically (acid marinades, enzymes breaking down of proteins). Colour: red
colour of fresh meat by myoglobyn (purplish – red pigment, similar to hemoglobin), when
meat is cut and surface is exposed to air, bright-red oxymyoglobyn is formed. During storage
myoglobyn is formed into brownish-red metmyoglobyn. When meat is cooked myoglobyn is
converted (above 60C) into a brown compound: hemichrome. Nitrites converts myoglobyn
into pink-coloured nitrosomyoglobyn. Effect of cooking: cooked to increase palatability and
tenderness, kills most food-poisening organism. It causes changes: meat shrinks, loss of
juices, collagen is converted into gelatin – makes meat more tender, certain nutrients are lost
(B vitamin).
b) Offal
liver: iron, riboflavin, nicotinic acid, folic acid, vitamin A and D, thiamin.
c)Poultry, game and fish: fresh water, sea water. Structure: fish muscles consists of blocks of
short fibres called myotomes (separated by their sheets of connective tissue). Composition:
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oily fish: 10-20% unsaturated oils. White fish less than 2% oil. Food value: oily fish: vitamin
A, B, D. all fish: B, small ones: calcium.
d)eggs: structure: 60g, made up shell, white and yolk. Colur does not indicate the quality of
egg. Porous shell is composed mainly of calcium carbonate. Inside the shell 2 thin membranes
separate the shell from white. White is divided into regions of thick and thin white: 60% of
total weight of egg. Yolk is suspended in the white and held in position by strands of protein
called chalazal. Composition: white is a colloidal solution of protein in water with small
quantities of vitamins and mineral salts. Food value: iron, vitamin A, B and D, riboflavin,
saturated fat, cholesterol. Changes during storage: 1. air-space increases in size. 2. yolk
becomes enlarged. 3. thick white is converted into thin white. 4. pH increases. 5. bacterial
spoilage occurs. Effect of cooking: during heating, proteins in white and yolk coagulate: egg
white protein: 60%, yolk protein 66%. Rate of coagulation increases by salt and acids. Iron
sulphide is formed in cooked eggs. Loss: 5-15% of thiamin and riboflavin. Uses of eggs in
cooking: 1. thickening and binding. 2. emulsifying. 3. foaming.
e)milk: composition: colloidal system is complex and is a fat-in-water emulsion. Min. 3%
butterfat, 8,5% solids-not-fat. Proteins: corseinogens, lactalbumin, lactoglonulin. Fat,
carbohydrate: disaccharides – lactose. Food value: protein, riboflavin, calcium, vitamin A and
B. 586ml milk provides 680mg calcium, provides ½ riboflavin, ¼ protein and vitamin A
recommended. Effect of cooking: heating causes skin (skin holds steam – “overboiling”);
prolonged cooking cause caramelisation of lactose: some of thiamin and vitamin C is
destroyed: effect of processing: milk is ideal medium for bacterial growth, so to make it safe
and improve its keeping quality, it is normally processed before being sold. 60% of milk
produced is sold as liquid milk; 95% of this is heat treated and the remaining 40% is used to
manufacture milk products, such as evaporated milk, dried milk, cheese and butter. During
processing there is a loss of heat sensitive vitamins (thiamin and vitamin C). the greater the
severity of heat treatment the greater the loss of vitamins. Pasteurization is a mild heat
treatment compared with sterilization. Condensed milk does not require the same degree of
heat treatment as evaporated milk because of its higher sugar content. Dried skimmed milk
contains only a trace of fat and so lacks vitamin A and D. it should not be used for feeding
baby, though it is a useful protein supplement since it is 37% protein. It also has a high
calcium and riboflavin content.
f)Cream: is a fat-in-water emulsion. It is separated from milk by centrifugation, a process
which involves spinning milk in centrifuge, so the heavier particles are forced to the outside
and the lighter particles, which make up the milk, remain nearer the centre. Composition:
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cream contains all the fat and a proportion of the protein and lactose in milk. Single cream
must have a minimum fat content of 18%, double cream of 48%. Single cream will not whip,
since only a cream with fat content greater than 30% will whip. Cream which is sold as
whipping cream contains 35% to 40% fat. Clotted cream has a very high fat content (at least
55%, as much as 70%) and produced by heating milk in special pans and skimming off the
cream. Food value: all cream contain useful quantities of vitamin A and D. Double cream has
a higher energy value than single cream, as it contains more fat.
g)Butter: is made by churning cream. It is a water-in-fat emulsion. Composition: it must
contain at least 80% milk fat. Food value: butter and margarine are valuable of sources of
vitamin A and D. vitamin content is lower in winter months. Butter provides 7% of vitamin A
and 3% of vitamin D in the diet. Margarine contains 10x as much vitamin D as butter.
Margarine provides 10% of vitamin A and 45% of vitamin D. They all have high fat content
so high energy value. 100g = 3041kJ. Low fat spreads are healthier alternative to butter,
containing only about 40% fat.
h)Yoghurt:
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