Anthocyanins are water-soluble pigments that contribute various colors like red, purple, and blue to foods. They are flavonoids that contain three phenyl rings and a sugar residue. Common anthocyanins found in foods include pelargonidin, cyanidin, and malvidin. Anthocyanin color changes from red to blue depending on pH. Myoglobin is the pigment that gives meat its color. Its color depends on the oxidation state of the iron in its heme group and whether oxygen is bound. Oxymyoglobin is bright red while deoxymyoglobin is purplish-red. Heat and oxidation cause myoglobin to turn brown.

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: