color in foods

1. Pigments and colour in foods
• Flavonoids
– These are phenolic compounds with at least 3
phenyl groups and a sugar residue
– Anthocyanins
– Anthoxanthins

2. Pigments and colour in foods
– Anthocyanins
• These are flavonoids which contribute to several colours:
Red, purple, violet, and deep blue .
• Examples of food whose colours are due to anthocyanins
include strawberries, grapes, egg plants, peach skin,
plums, radish, apple etc
• Anthocyanins have three phenyl rings designated as A, B
& C rings
• They have a sugar residue attached to carbon 3 of the A
ring.
• The sugar can be glucose or arabinose, rhamnose

3. • Have a characteristic C6C3C6 carbon skeleton –
the basic structure of the flavonoids.
• The structure of all anthocyanins is based on
the flavan structure.

4. Flavan – Flavylium cation.
O
Flavan nucleus
A
B
1
2
3
4
5
6
7
8 1'
2'
3'
4'
5'
6'
+
O
General structure of anthocyanidins
The flavylium cation (at low pH)
A
B
5
7
3'
4'
5'
HO
OH
OH
R'
OH
R''
3
R` and R`` = H, OH
or OCH3

5. • The are:
R` R``
pelargonidin H H
cyanidin OH H
peonidin OCH3 H
delphinidin OH OH
petunidin OCH3 OH
malvidin OCH3 OCH3
Anthocyanins commonly found in
foods

6. Pigments and colour in foods
• Characteristics of anthocyanins
– They are water soluble
– They undergo colour change due to change in pH
• pH 7- Purple
• <pH 7 (acidic) – Red
• > pH 7 (alkaline) – Navy blue
– Colour intensity is reduced by
• Phenolase which removes the sugar
• Oxidation

7. • Meat colour from oxidation state of myoglobin,
ligands bound and state of the globin protein.
• Oxidation – the Fe in the haem can exist as the
reduced Fe2+ (Mb) or oxidised Fe3+ (MMb).
• Oxygenation – binding of molecular oxygen to
the sixth ligand site on the Fe2+.
• Both Mb and Hb transport oxygen bound to this
sixth ligand site – oxymyoglobin (MbO2)
Myoglobin

8. • Myoglobin (deoxymyoglobin) is purplish-red
• Binding O2 to oxymyoglobin gives the
customary bright red of meat.
• Both Mb and MbO2 can have oxidation, the Fe2+
being oxidised to Fe3+ - undesirable brownish
red in colour.
• Conditions in muscle determine the ratios of
Mb, MMb and MbO2. Inter-conversion of these
occurs readily in muscle not in meat.
Myoglobin

9. • Heat denatures myoglobin.
• Myoglobin decreases rate of haem oxidation –
so denaturation leads to easier oxidation of
Mb to MMb.
• Also easier oxidation at lower pH.
• In cured meats have stable pink colour – due
to reaction with nitrite compounds at 6th co-
ordination site.
Myoglobin

10. General structure of myoglobin:

11. Pigments and colour in foods
• Myoglobin
– This is the pigment responsible for the colour of muscle.
– Myoglobin is composed of a heme unit and globin protein
molecule
– The colour of myoglobin depends on
• The presence of oxygen: Red vs purplish red
• Heat: Denatured, brown colour
• Presence of oxidising agents: brownish
• Spoilage: Greenish colour due to the presence of sulfur

12. Meat color – chemical state of myoglobin:

14. Browning reactions in foods,
and acrylamide formation: