1. OPTION F:FOOD CHEMISTRY
F4 COLOUR

2. F.4.1: DISTINGUISH BETWEEN A DYE
AND A PIGMENT
• Dye: Synthetic compounds which are added to
food to enhance its appearance.
• Pigment: defined as naturally occurring
colours found in the cells of animal and plants.

3. DYE PIGMENT
• Dye are soluble in water. Insoluble in water
• Composed of organic Composed of inorganic
substances. substances

4. F4.2 EXPLAIN THE OCCURRENCE OF COLOUR
IN NATURALLY OCCURRING PIGMENTS
Role of pigments in reflecting colour of foods into our
eyes.
• A pigment is a naturally occurring colour found in the
cells of plants and animals
• The pigments have colour because of their ability to
reflect or emit different quantities of energy at
wavelengths able to stimulate the retina in the eye.
• They absorb light in the visible region of the
electromagnetic spectrum and transmit the remaining
light in the visible spectrum which has not been
absorbed

5. Examples of the common naturally occurring
pigments
• Poriphyrins (Chlorophyll and Haem)
• Carotenoids
• Anthocyanins

6. F4.3 DESCRIBES THE RANGE OF COLOURS AND SOURCES OF
THE NATURALLY OCCURRING PIGMENTS ANTHOCYANINS,
CAROTENOIDS, CHLOROPHYLL AND HEME.

7. Anthocyanins Carotenoids Chlorophyll Haem
Most widely Most widespread pigments in Plants, algae, and Fresh meat
occurring pigments in nature (the large majority are cyanobacteria
1) Source plants produced by algae)
Yellow to red orange Green Red (myoglobin
Red astaxanthin responsible for the
(complexed to a protein) colour of fresh meat)
is responsible for the
1) Colour blue or green colour of
range live lobster and crabs,
and pink colour of
salmon and flamingo
Fruits and vegetables Banana, carrots, tomatoes, Green plants Meat of adult
(cranberries, watermelon, peppers, and mammals
blueberries, saffron. (cows, sheeps,
1) Examples strawberries, and horses)
raspberries

8. F4.4
DESCRIBE
THE FACTORS THAT AFFECT
THE COLOUR STABILITY OF
ANTHOCYANINS,CAROTENOIDS,
CHLOROPHYLL AND HEME

9. THE FACTORS THAT AFFECT THE
COLOUR STABILITY OF ANTHOCYANINS
• The structure and colour of anthocyanins
changes with pH.
• The flavylium cation is bright red in acidic. In
basic solution, H+ removed from the OH group
on the left ring to form a quinoidal base which
is blue. As the colour of anthocyanins is pH
dependent, they can be used as acid-base
indicator.

10. • In aqueous solution, anthocyanins can exist in four
possible structural forms depending on the pH and
temperature.

11. (A) (AH⁺) (B) (C)
quinonoid flavyium carbinol base chalcone
(blue) (red) (colourless ) (colourless)
Very high pH Low pH Neutral pH
• At low pH, the AH⁺ predominates and the
mixture is red, at neutral pH values there is
sufficient concentration of OH ions for this to
hydrolyse and the solution becomes
colourless as it is converted to B and C. At
greater pHs the AH⁺ in eqm with this is
converted to A and the solution turns to blue
and form this product

12. • As the stability of anthocyanins is also affected by
the temperature, the colour of anthocyanins can vary
significantly during the cooking process.
• The anthocyanins is most stable and most highly
coloured at low pH and low temperature.
• When exposed to heat the eqm moves to the right
and the compounds are less thermodynamically
stable. This causes a loss of colour and browning.
• The anthocyanins also form deeply coloured
coordination complexes with Fe3+ and Al3+ ions
that are present in metal cans and this lead to
discolouration in canned fruit.

13. THE FACTORS THAT AFFECT THE
COLOUR STABILITY OF CAROTENOIDS
• Carotenoids are highly unsaturated molecule and
the presence of carbon-carbon double bonds
makes them susceptible to chemical attack.
• Degradation pathways include
isomerization, oxidation and decomposition of
the carotenoids molecule.
• Light, enzymes and reaction with hydroperoxides
(from the oxidation of lipids) causes oxidation
that will results in the bleaching of
colour, unpleasant off odours and loss of vitamin
A activity

14. • Carotenoids are stable up to 50°C and in the
pH range 2 – 7 and therefore not degraded by
most forms of food processing. When heated
the naturally occurring trans- isomer
rearranges to the cis- isomer.

15. THE FACTORS THAT AFFECT THE
COLOUR STABILITY OF CHLOROPHYLL
Chlorophyll contains a group with 4
nitrogen atoms which is called a
porphin.
The porphin ring forms a very stable
complex with Mg ion.
The stability of chlorophyll towards
heat depends on the pH.
In a basic solution with a pH of 9 it is
thermodynamically stable but in acidic
solution with a pH of 3 is unstable.

16. • When heated, the cell membrane of the plant
deteriorates releasing acids which decrease
the pH.
• At this lower pH, the 2 H ions will displaces Mg
ion resulting in formation of an olive-brown
pheophytin complex.
• The breakdown of the cell during heating also
increases the susceptibility of chlorophyll to
decomposition by light (photo-degradation).

17. THE FACTORS THAT AFFECT THE
COLOUR STABILITY OF HEME
• In muscles, heme is associated with the purple –
red protein myoglobin molecule, which binds to
oxygen molecules to form the red oxymyoglobin
molecule.
• The Fe2+ is more stable than Fe3+ in the non-polar
environment provided by the side chain in the
complex.
• The red oxymyoglobin undergo a slow auto-
oxidation reaction to form the complex of the
Fe3+ known as metmyoglobin (brown red).

18. • To reduce this happen, meat are packed in
plastic films with low gas permeability and
stored in an atmosphere of carbon dioxide.
MbO2(red,Fe2+) Mb(purple-red,Fe2+) MMb(brown,Fe3+)
Oxymyoglobin myoglobin metmyoglobin

19. ANTHCYANINS CAROTENOIDS CHLOROPHYLL HEME
Oxidation Affects position of Unsaturated carbon bonds Oxygen binds to purple-red
equilibrium allow for oxidation catalyzed myglobin (Mb), forming red
by light, metals and oxymyoglobin (MbO2)
hydroperoxides =LOSS of *Fe2+ in MbO2 and Mb
color (bleached) Auto-oxidation of MbO2 and
Mb = Fe2+ → Fe3+
(metmyoglobin, MMb)
*Loss of Vit. A activity = = brown-red color
stinky
Temperature Higher temperatures = Stable up to 50°C Stability depends on pH
equilibrium shifts to the Therefore, 50°C+ = LOSS of High pH (basic) – about pH 9 =
right =LOSS of color color thermodynamically stable
Increase heat = trans- isomer Low pH (acidic) – about pH 3 =
rearranges tocis-isomer thermodynamically unstable (LOSS)
Increase heat = deterioration of cell
membrane = decreases pH =
chlorophyll decomposition by light
pH levels Low pH levels = greater Stable in range of pH 2 – pH7
color Therefore, pH < 2 and pH > 7 Refer to temperature
= LOSS of color
Presence of Can form complexes Structure of chlorophyll contains Porphin ring forms complex
metal ions with Al3+ and Fe3+ (in porphin ring (group with 4 nitrogen with Fe ion.
tin cans) = LOSS of color atoms) which forms complex with a Mg Fe2+ in MbO2 and Mb
of canned foods ion
Low pH = Mg ion displaced by 2 H ions
=olive-brown pheophytin color

20. F.4.5: Discuss the safety issues
associated with the use of synthetic
colorants in food.

21. Concerns:
• Synthetic dyes are biochemically active
– Can negatively impact health
• toxicity is easy to prove
• chronic health effects are difficult to determine
• Special concern about carcinogenic effects
– Standards vary from country to country
• Malachite green and sudan red are generally banned

22. • Synthetic colorants = dyes
International Numbering System (INS) or E numbers = food additive identifiers
Artificial dyes are potentially carcinogenic (any substance, radionuclide, or
radiation that is an agent directly involved in causing cancer) so these particular
carcinogens are banned in certain countries.
Therefore in most countries, all ingredients are required to be on packaging labels.
International Food Concerns:
Some dyes banned in certain countries but not others. Now with lots of
international trade, it has become a concern with the use of these particular dyes.
Possible solution: international legislation on colorant legislation
Example of International Food/Colorant Concern: Sunset Yellow in M&M's
Banned in Finland and Norway
• Potential carcinogen
• Allergic reaction in people with aspirin intolerance

23. F.4.6: COMPARE THE PROCESSES OF NON-
ENZYMATIC BROWNING AND CARAMELIZATION
What is enzymatic browning process?
A chemical process which occurs in fruits and
vegetables containing the enzyme
polyphenoloxidase and produce brown
pigments.

24. MAILLARD REACTION
• Is a type of non-enzymatic browning which consist of a complex
series of reactions between amino acids and carbohydrate.
• Responsible for the smell and colour change of common cooking
processes.
• the first step in Maillard browning is condensation reaction of the
aldehyde group in the reducing sugars with the free amino group of
an amino acid.
• leads to the replacement of a C=O bond in the aldehyde group by
C=N-R bond and the formation of water.
• Reducing sugar + amino acid → initial condensation product + water
• Condition: Occur at a faster rate when the temperature is high, siza
of sugar.

25. CARAMELIZATION
• process which involve the oxidation of with high
carbohydrate concentration, (sugar) and it is used
extensively in cooking which result for the product to be
brown in colour and have nutty flavour.
• This process occurs when sugar are heated at high
temperature.
• The compound are dehydrated and double bonds are
introduced into the structure.
• The small sugar molecules react together to form polymers
with conjugate bonds which absorb light and thus
producing the brown colour.
• Equation: Cn (H2O)n → n C + n H2O
• Conditions: extreme pH value, type of sugar used.

27. • Genetic engineering is important especially to food
scientists to alter the properties and processing conditions
of foods.
• Genetic engineering involves the alteration of the DNA.
• In the past, to improve the quality of genes, cross breeding
was done. But this method is inaccurate and time
consuming.

28. • GM corn produce a poisonous compound
to reduce the dependency on pesticides
and herbicides.
• GM hens produce eggs containing human
interferone
• GM cow produce milk rich in nutrients.