F.4.1 Distinguish between a
dye and a pigment.
F.4.2 Explain the occurrence
of colour in naturally
occurring pigments.
F.4.3 Describe the range of
colors and sources of
naturally occurring
pigments.
F.4.5 Describe the factors
that affect the color stability
of anthocyanins, heme,
carotenoids & chlorophyll
F.4.5 Discuss the safety
issues associated with the
use of colorants in food.
F.4.6 Compare the
processes of non enzymatic
browning and
caramelisation.
F4 Colour
Dye versus Pigment
Dye
  A food grade
synthetic
water soluble
colorant that
can be added
to food to
enhance or
change its
natural color .
Pigment
  A naturally occurring
colorant found in the
cells of plants and
animals.
  Chemical families:
porphyrins,
carotenoids, flavonoids,
chlorophyll, heme and
myoglobin.
What causes Colour?
  Dyes and Pigment molecules with
conjugated (alternating single and
double) carbon-carbon bonds.
  The π electrons of the double bond are
delocalized and spread out along the
adjacent molecules.
  Colorless organic molecules do not have
conjugated carbon-carbon bonds.
  The delocalized electrons absorb visible light when the energy of the
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incoming light photon matches the energy difference between the
electrons ground state and excited state.
The electron becomes excited and transition from a lower-energy or
ground electron configuration to a higher-energy electron
configuration.
When the electrons drops back down to its ground state it releases/
reflects/transmits visible light with a complementary wavelength.
The color we see has a complementary relationship with the
color of the visible light absorbed.
Molecules that do not absorb light in the
400-700nm visible light range are colorless.
  Pigment molecules differ in color due
to differences in the amount of
conjugation.
  There is a positive relationship between
the amount of conjugation and the
wavelength of visible light absorbed.
  As the amount of conjugation
increases, the wavelength of light
absorbed increases changing the
complementary color reflected.
Activity 1
  When hydrogen is added across the double bond of
lycopene (the yellow/orange) pigment found in tomatoes,
the number of C=C double bonds decreases. Predict and
explain the color change that would be observed in the
tomato.
Activity 2
1. The color of Cherry
Kool-Aid is the result of
added an artificial dye.
Explain why makes cherry
Kool-Aid, appear red to
your eye?
2. Using structures on Pages
37-38 of the Data Booklet
predict whether β-carotene
and lutein would appear
orange or red.
Anthocyanins
  Sub-class of flavonoids
  Orange-red, red-blue colors
  Foods: strawberries, berries
(blueberries, cherries,
blackberries), grapes and some
vegetables, such as egg-plant and
avocado.
  Water soluble – form hydrogen
bonds with water due to the
presence of multiple hydroxyl
groups.
  Three phenol groups (benzene
ring) with conjugated carboncarbon bonds and varying
numbers of hydroxyl groups.
  Glucose molecules bond to the
oxygen atom on the second phenol
group. Anthocyanins are found in
foods high in sugar content.
Anthocyanin Stability
  Unstable with pH, temperature, in the presence of UV light and Fe3+
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& Al3+ ions. Most stable at low pH (acid) and low temperature.
Equilibrium exists between four different forms. Position of
equilibrium affected by adding acid or alkali or by changing the
temperature causing different colored forms to predominate.
Page 35 of the Data Booklet shows the equilibrium relationship
between the four different colored structures at 25°C and pH.
At high temperature during cooking anthocyanins decompose. The
position of equilibrium moves to the right, resulting in a loss of color
due to the predominance of the colorless structure.
- Blue quinonoidal base (A), stable at pH 6-7
- Red flavylium cation (AH+), stable at pH 1-2
- Colorless carbinol psuedobase (B), stable at pH 4-5
- Colorless chalcone (C), stable at pH > 7
Make good natural acid-base indicators. E.g red cabbage is red in acid
and blue and purple in base.
Activity 3
1.  What color are
anthocyanins at pH 0-6
and pH 7-14.
2.  Using Bronsted-Lowry
theory and the equation
on page 35 of the Data
Booklet explain how that
addition of ethanoic acid
and sodium bicarbonate
changes the color of red
cabbage. Account for the
purple color.
Carotenoids
  Color: Yellow to orange-red
pigments
  Food sources: carrots, oranges,
salmon, tomatoes, lobster, yellow
peppers
  Solubility: Fat soluble and
insoluble in water. Long conjugated
hydrocarbon chain which outweighs
the small number of polar hydroxyl
groups.
  Functions: Acts as antioxidants.
Can be converted/precursor to
Vitamin A (retinol) in the body and
so is considered a nutrient. Vitamin
A needed for good vision (production
of light sensitive cells in the retina)
and to hydrate skin cells. Carotenes
contribute 30-100% of our Vitamin A
requirement.
Color Stability in Carotenoids
  Stable in pH 2-7. At low pH color will change from red-
orange to orange-yellow due to the formation of alternate
structure.
  Stable up to 50°C and therefore color is not degraded by
most forms of food processing.
  C=C double bonds mean that they are easily oxidized by
oxygen in the air causing discoloration, loss of Vitamin A
and off odors.
  Metals from knives and cutting surfaces and UV light
also catalyze the oxidation.
  Food need to be kept wrapped, kept away from light and
metal and kept in the refrigerator.
Activity 4
  α and β-carotene absorb
visible light in the
430-490nm range and
reflect/transmit yelloworange light.
  The carotenoid found in
lobster shell is called
astaxanthin (page 38 of
Data Booklet). Suggest
a reason why lobsters
are blue-green when
live and orange-red
when cooked.
Activity 5
  Astaxanthin is responsible for
the natural pink color of
shrimp. It contains C: 80.54%,
H: 8.72%, and O: 10.74% by
mass.
1.  Distinguish between a
pigment and a dye
2.  Calculate the empirical
formula for Astaxanthin
3.  Given that the Molar Mass of
Astaxanthin was found to be
620.00 gmol-1 determine the
molecular formula.
4.  How are the empirical and
molecular formula related?
Chlorophyll
  Color: Green to olive green
  Sources: green leafy plants
(spinach), algae
  Function: Photosynthesis (food
production) in Plants.
  Solubility: Fat soluble in pure
form due to lack of hydroxyl group
to hydrogen bond with water.
  Structure: A mixture of
molecules each with a different R
group. Ring structure called a
porphyrin coordinately bonds 4
nitrogen atoms to a central Mg2+
ion. Square planar shape.
Attached to ring IV is a phytol
group (C20H39 carbon chain)
Structure page 36 of Data Booklet
Activity 6
  A UV-Visible spectrometer/
spectrophotometer measures
the amount of visible light
absorbed by a colored
pigment. This can be read as
Absorbance versus
wavelength.
  Maximum absorbance
corresponds to the
wavelength of light absorbed.
  The color seen / reflected is
its complementary color.
  Beer’s Law can be used to
determine the concentration.
The absorbance spectrum of chlorophyll-a
taken from a spectrophotometer is shown
alongside.
1.
Determine λmax .What does it
represent?
2.
Explain why chlorophyll appears green.
Activity 7
  Normally metal ions form ionic compounds with
non-metal ions. Complex ions are an exception to
this rule. Chlorophyll is a complex ion because each
of the N atoms on the four rings of the porphyrin
donates its lone pair of electrons to the central Mg2+
ion forming a coordinate covalent bond. The
porphyrin rings are called ligands.
1.  Define a coordinate bond and ligand.
2.  Name another molecule with this structure.
Colour Stability in
Chlorophyll
  Unstable - affected by heat,
oxygen gas (in air), UV light
and pH.
  Fresh foods containing
chlorophyll should be stored
away from heat, light and air
so color changes do not
occur.
  Canning and preserving in
jars will change color of
chlorophyll because
processing requires heating
to boiling to kill microorganisms.
Olive-brown
Pheophytin-a
Bright green chlorophyll-a
  When green leafy plants are exposed to heat, the cell wall
deteriorates releasing H+ ions, lowering the pH. H+ ions displace
the Mg2+ ion replacing it with two H atoms forming the olivebrown pheophytin-a pigment. This coloration often occurs in
canned and preserved vegetables like peas and beans.
  Chlorophyll also reacts with OH- ions (source NaOH) to give the
bright green chlorophyllin pigment.
Oxygen Transport
  The O2 we breath in is not very
soluble in the blood. and can only
provide about 1% of the oxygen
our cells need.
  O2 transport in humans is effective
when it is carried through the
blood to the tissues by a protein
molecules called hemoglobin
(Hb).
  When the Hb-O2 complex reaches
the tissue, the O2 molecules are
transferred to another protein
myoglobin (Mb) which
transports the oxygen to the
individual cells that will use it to
make energy during cellular
respiration.
  Both molecules have a heme group
Heme
Heme molecule
Function: transport of oxygen for
cellular respiration.
Structure:
  Central Fe (II) ion which bonds to 6
other groups (called coordination
sites)
  4 of the 6 coordination sites
occupied by nitrogen atoms from a
porphyrin ring.
  5th coordination site occupied by the
nitrogen atom from a protein
molecule.
  6th site is available to bind an O2
molecule.
Hemoglobin vs. Myoglobin
Hemoglobin
Myoglobin
  Structure: Four protein
  Structure: Single protein
chains and four heme
groups that carry
oxygen from the lungs
to the tissues.
  Source: red blood cells
  Function: Carries
oxygen in the blood to
tissue
chain and one heme
group that transports
oxygen in tissue - muscle
cells (page 35 of Data
Booklet)
  Source: Muscle tissue
  Function: Carries oxygen
in the tissues
Myoglobin
One protein chain and one
heme group.
Hemoglobin
Four protein chains and four
heme groups
Colour Stability in Myoglobin
  When animal tissue comes in contact with oxygen in the air
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the myoglobin exits in three different structures.
Myoglobin (Mb) is purple-red with Fe(II) oxidation state. On
exposure to oxygen in the air it forms bright red oxymyoglobin
(MbO2), also Fe(II). This is the color of freshly cut meat.
Mb-Fe2+ + O2  Mb-Fe2+-O2
With extended exposure to oxygen the Fe2+ ion is autooxidized (loses an electron) to form Fe3+ - the metamyoglobin
(MMb) structure. MMb has an undesirable brown in color.
Mb-Fe2+  Mb-Fe3+
Choose bright red colored meat – it is the freshest. To keep
meat from forming metamyoglobin store in an oxygen
reduced atmosphere – low gas permeability film, vacuum
packed or replace oxygen with an inert gas.
Fe2+ more stable than Fe3+.
Activity 8
1.  Compare the structural features of chlorophyll and
heme.
2.  Deduce and explain their solubility in water.
Synthetic Colorants in Food
  Use of synthetic food colorings/dyes in food is not
regulated by international standards, so countries have
their own regulations concerning their use.
  In the US FD&C numbers are given to approved synthetic
food dyes that do not exist in nature. In the European
Union, E numbers are used for all additives, both synthetic
and natural. Other countries have their own numbering
system.
  The Codex Alimentarius Commission (FAO and WHO)
sets food standards, and codes of practice that can be used
by international governmental and non-governmental
organizations (NGO).
  Some synthetic food dyes have been linked to health
problems – hyperactivity in children. Research into the
health effects is still in its infancy.
Natural food dyes, commercially produced and allowed in food in the
US include:
  Caramel coloring (E150),used in cola products. Green dye made from chlorella
algae (chlorophyll, E140). Cochineal (E120), a red dye derived from the cochineal
insect. Betanin extracted from beets. Turmeric (curcuminoids, E100). Saffron
(carotenoids, E160a). Paprika (E160c)
  Often provided in highly purified form, for increased
stability.
Artificial coloring approved in the US:
  FD&C Blue No. 1 – Brilliant Blue, E133 (Blue)
  FD&C Blue No. 2 – Indigotine, E132 (Dark Blue)
  FD&C Green No. 3 – Fast Green, E143 (Blue-green)
  FD&C Red No. 40 – Allura Red AC, E129 (Red)
  FD&C Red No. 3 – Erythrosine, E127 (Pink)
  FD&C Yellow No. 5 – Tartrazine, E102 (Yellow)
  FD&C Yellow No. 6 – Sunset Yellow, E110 (Orange)
Also a list of delisted artificial coloring, no longer permitted.
(FD&C Blue No. 1, Red No. 40, Yellow No. 5 and Yellow No. 6 used
to color Starbursts)
Activity 9
  Erythrosine is a cherry-pink/
red synthetic dye used to
color foods like cherries,
candy bars, and baked goods.
It has been linked to
hyperactive behavioral
disorders in children, thyroid
cancer in rats. Banned in in
Norway. Identified using the
following coding.
* FD&C Red No. 3
* E127 (Food Red 14)
* Indian Standards No. 1697
  Outline some of the issues
related to the use of this dye.
Browning of Food
Enzymatic Browning
Non-Enymatic Browning
  Chemical reaction
  Browning of food
which occurs in foods
containing the enzyme
polyphenoloxidase,
  Results in the
production of brown
colored pigments.
without enzymes
  via the Maillard
reaction and
caramelization.
Maillard Reaction
  Food Composition: Food containing protein and carbohydrates (specifically a
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reducing sugar).
Complex reaction mechanism. The first step involves a condensation reaction
between an amino acid and a reducing sugar (glucose, fructose, sucrose, lactose)
followed by a series of dehydration, fragmentation and condensation reactions to
form brown pigmented products called melanoidins. Also causes flavor and smell
changes.
Factors effecting rate of browning: pH (4-7 optimum), type of amino acid
(lysine most & cysteine least brown), type of reducing sugar, temperature (wide
range), time, presence of oxygen and water.
E.g. boiling milk, frying meat and foods that involve cooking sugar and protein
(often from milk) like fudge, caramel toffee, milk chocolate, baking bread.
Features of the Product: Desirable brown color, flavor and smell. Reduces
nutritional value of food as amino acids and sugar is lost during reaction.
Food affected: Frying meat. Heating sugar and milk to make fudge, caramel
toffee, and milk chocolate. Brown crust on baked bread, roasted coffee beans.
Browning meat
http://www.bbc.co.uk/food/get_cooking/techniques/003001.shtml
What is a Reducing Sugar?
  Sugars exist in solution as an equilibrium
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mixture of open/straight-chain and closedring (cyclic) structures.
In the straight chain form, the C1 atom
contains the C=O bond (carbonyl group)
either as a ketone or aldehyde. In the ring
(cyclic) structure, the carbonyl carbon, C1
is the one which is attached to the O of the
ring and an OH group.
Straight chained sugars that have an
aldehyde or ketone group can act as a
reducing agent in a chemical reaction.
Reducing agent – means the sugar is
oxidized – gains oxygen atoms & loses
electrons in a chemical reaction.
Reducing sugars are: glucose, fructose,
lactose, maltose (not sucrose)
First Step in Maillard Browning
  Condensation of a reducing sugar and the amino group on
an amino acid. One molecule of water formed.
  Forms an amadori structure that exists in three structural
isomers (same molecular formula but different structural
formula).
Caramelization
  Food Composition: During dry heating and roasting of food
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high in sugar and without proteins/amino acids.
Complex reaction mechanism. At its most simple the process
involves melting sugar at a temperature > 120°C in order to
dehydrate (remove water)
Factors the increase rate of browning: pH <3 & >9,
temperature >120°C, type of sugar (fructose best).
Feature of product: desirable brown color, caramel/
butterscotch smell and flavor. Undesirable effects – burned
sugar smell and taste, and black color. Occurs when heated for
too long at high temperatures causing all the water is removed
from the sugar producing carbon.
CnH2nOm  nC + mH2O
Foods affected: roasted vegetables, color and flavor of cola
beverages, topping on baked egg dishes.
Activity 10
1.
2.
3.
4.
Write an equation to show the
condensation reaction that
occurs between glucose and
cysteine. Give the structure of
the three possible amadori
compounds formed.
Distinguish between the type
of browning that occurs in
bread and bananas. Explain
each process.
Compare the Maillard
browning and caramelization
in terms of the chemical
composition of the food and
the products formed.
Write an equation for the
burning of sucrose during
caramelization.
Activity 11
Deduce with a reason the type of browning:
1.
Caramel candy or milk candy is a made by
boiling milk, sugar, butter, vanilla essence,
water, and glucose or corn syrup. It is
heated in a pot up to 120 °C.
2.  Many cultures have a baked egg desert
made with cream, eggs and sugar (crème
brulee, crème caramel, flan, egg tarts).
Typically sugar is sprinkled on the top &
heated to a high
temperature
until it browns.
Bibliography
  Brown, Catrin and Mike Ford. Standard Level Chemistry developed
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specifically for the IB diploma. Heinemann Baccalaureate, 2008.
Derry, Lanna, et al. Chemistry for use with the IB Diploma Options:
Standard and Higher Levels. Melbourne: Pearson Heinemann,
2009.
Neuss, Geoffrey. IB Diploma Programme Chemistry Course
Companion. Oxford: Oxford University Press, 2007.
—. IB Study Guides, Chemistry for the IB Diploma. Oxford: Oxford
University Press, 2007.
Organisation, International Baccalaureate.
—. "Chemistry Data Booklet." International Baccalaureate
Organisation, March 2007.
—. "Chemistry Guide." International Baccalaureate Organisation,
March 2007.
—. "IB Chemistry Examination Papers ." Cardiff: International
Baccalaureate Organisation, 1999-2009.
Useful Sources
  http://www.dartmouth.edu/~chemlab/chem6/dyes/full_text/
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chemistry.html
Using a spectrometer
http://www.dartmouth.edu/~chemlab/techniques/
spectrometerD.html
Color
http://www.chemguide.co.uk/inorganic/complexions/colour.html
Chlorophyll
http://chestofbooks.com/food/science/Experimental-Cookery/PlantPigments.html
Heme
http://www.elmhurst.edu/~chm/vchembook/568globularprotein.html
Synthetic Dyes http://www.codexalimentarius.net/web/index_en.jsp
Maillard browning http://www.food-info.net/uk/colour/browning.htm
Food coloring http://www.answers.com/topic/food-coloring
Images
  http://farm1.static.flickr.com/
230/509313477_e00b368ad5.jpg
  http://www.lastnightsdinner.net/2007/05/22/
orrecchiette-with-peas-and-chives/
  http://asweknowit.net/MIDDLE_SCH/DWA 5
organ systems.htm
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