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COLOUR
Cemre Ünal 12-C
Food Colour

The color of food is due to the ability of
substances in the food to absorb light in
the visible region of the electromagnetic
spectrum.

The substances that cause food to be
colored may be natural (pigments) or
synthetic (dyes).
PIGMENTS

Anthocyanins

Carotenoids

Chlorophyll

Haem
Anthocyanins
Most widely occuring in pigmets in
PLANTS.
 Responsible for pink, red, purple and
blue colors in fruits and vegetables.

Carotenoids
Most widespread pigments in nature
(mostly produced by algae)
 Acts as a precursor for VITAMIN A
synthesis
 Colors range from yellow-red/orange.


Red astaxanthin (complexed to a protein)
is responsible for the blue green color of
live crabs and pink color on salmon.
Chlorophyll

Major pigmets necessary for
photosynthesis found in green plants.
Haem
Myoglobin is responsible for the purple-red
color of fresh meat.
Synthetic Colorants (DYES)

They are the artificial ingredients that
provide color and flavour.

Any artificial dyes used in the past have
been shown to be potentially
carcinogenic.
Analyzing Color From Spectra

In a visible spectrometer the amount of
light absorbed is measured again the
wavelength of the light passing through
the sample to provide an absorption
spectrum.

This can be illustrated with the visible
spectro of chlorophyll.
Spectrum of Chlorophyll a and
Chlorophyll b
Factors Affecting the Color
Stability of Pigments

Any factor which will change the
structure of the molecule will affect the
color as this will affect the precise
wavelength of visible light that pigment
absorbs.
Oxidation
 pH Change

Temperature Change
Presence of Metal Ions
ANTHOCYANINS
Anthocyanins exist in different forms.
 In aqueous solution these different forms
are in equilibrium with each other.


Changing the pH and the temperature
affects the position of equilibrium.

They are most highly colored at low
temperatures and low pH (acidic
solutions)
ANTHOCYANINS

When exposed to heat the equilibrium
moves to right and the compounds are
less thermodynamically stable. This
causes loss of color and browning.

Anthocynanins also form complexes
with metal ions such as aluminium ions,
and iron (III) ions.
ANTHOCYANINS

They contain the flavonoid skeleton
It is the conjugation of pi electrons contained in
this structure which accounts for the color of
anthocyanins.
The more extensive the conjugation, the lower
energy of the light absorbed.
This can be explained by using cyanidin.
In acidic solution it forms a positive ion and there is less
conjugation than in alkaline solution where pi electrons
in the extra bond between the carbon and oxygen are
also delocalized.
Structure of Cyanidin in acidic
solution.
Structure of cyanidin in alkaline
solution
Less Conjugation so absorbs bluegreen region and transmits red light.
More conjugation so absorbs in the
orange region of the spectrum and
transmits blue light.

Other anthocyanins differ in the number
and types of other groups such as
hydroxyl or methoxy groups which affects
the precise wavelength of the light.

The basic flavonoid is essentially nonpolar. As more polar hydroxyl groups are
added the potential for them to form
hydrogen bonds with water molecules
increases and many anthocyanins are
soluble in water.
CAROTENOIDS
They contain many alternate C-C , or
C═C bonds.
 Because of unsaturation due to the C═C
bonds caretenoids susceptible to
oxidation.
 Oxidation process can be catalyzed by
light, metals and hyroperoxides.
 This changes the type of bonding and
results in the bleaching of color.

Carotenoids are stable up to 50˚C and in a pH range of 2-7.
When heated the naturally occuring tran-isomer rearreanges to the cisisomer.
In carotenoids the conjuction is mainly due to a long
hydrocarbon chain (as opposed to anthocyanins)
consisting of alternate single and double C-C bonds.
The majority are derivered from a (poly)ene chain
containing forty carbon atoms which may be
terminatedby cyclic end groups and may also be
complemented with oxygen containing functional
groups.
Alfa, Beta-carotene and vitamin A are all fat soluble and
not water soluble.
CHLOROPHYLL

Different forms of chlorophyll contain
different groups attached in the Rposition

Chlorophyll contains a group with four
nitrogen atoms which is called a
porphin.

The porphin ring forms a very stable
complex with a magnesium ion with the
non-bonding electrons on the nitrogen
atoms.

In a basic solution with a pH of 9 it is
thermodynamically stable but in acidic
solution with a pH of 3 is unstable.

When heated, the cell membrane of the
plant deteriorates releasing acids which
decrease the pH. At this lower pH
magnesium ion is replaced by two
hydrogen ionsresulting in the formation
of an olive-brown pheophytin complex
HAEM (HEME)
The haem group also contains a porphin
ring but it is complexed to an iron ion.
 During oxidation, oxygen binds to pruplered oxyoglobin(Mb) and red oxymyoglobin
forms.
 In both the iron group is in the form of iron
(II).
 Through auto-oxidation of Mb and red
oxymyoglobin the oxidation state of ıron is
changed into iron (III). This state is called
metmyoglobin.


In order to minimize the rate of auto-oxidation
meat can be stored free of oxygen.
Chlorophyll and Haem

They both contain a planar heterocyclic
unit with the general name of porphin.

Porphins contain a cyclic system in
which all the carbon atoms are in sp2
hybridized. This results in a planar
structure with extensive pi conjugation.
Porphin groups have 1-8
different positions.
In chlorophyll the porphin
complex with the original
double bond between
positions 7 and 8 is now
saturated.
In chlorophyll a the –R group
is methyl group and in
chlorophyll b the r group is an
aldehyde group.
HAEM
Heamoglobin is the
oxygen carrier in the
blood of mammals and
myoglobin is the primary
pigment in muscle tissue
and is a complex of
protein, globin, together
with a haem group
which is porphin ring
containing iron (II) as a
central atom.
The haem group is present both
in myoglobin and heamoglobin.
NON ENZYMATIC BROWNING
OF FOOD

Food high in carbohydrate content, esp.
Sucrose and reducing sugars, lacking
nitrogen-containing compounds can be
caramelized.

Both molecules sucrose and glucose
when caramelized form many different
products, sweet and bitter derivatives of
acids.
CARAMELIZATION
Factors that increase the rate of
caramelization include the pH
change and the temperature.
For acids lower than pH < 3
and for bases pH > 9.
Temperature above 120
celcius degrees is required.
MAILLARD REACTION
For foods contain nitrogen Maillard Rxn
occurs.
 This involves the reaction of a
carbohydrate, either a free sugar or one
bound up in starch, with the amine
group on an amino acid, which may also
be a part of a protein chain.

MAILLARD RXN

Basicly it involves a condensation rxn
between the carbonyl group on the
reducing sugar and the amine group.

The presence of amino acid lysine
results in the most browning color and
cytesine the least.

Some of the foods contain lysine readily.
Moisture lowers the
temperature, in order to
make a good stew it is
sensible to brown the meat.