Explain Animal sources of Novel Sources of Natural Colourants  

The most common animal pigments of use as food colourants are those based on the haem structure. In nature, haem is combined with proteins and occurs mainly as haemoglobin and myoglobin. Although the appearance of these two components is attractive when they are oxygenated (bright  red), the colour produced on heating is typically brown (e.g. cooked meat) and removal of oxygen in the native state gives rise to the blue/purplish colour of venous blood. The  colour changes are due to the oxidation state of the central iron atom in the haem portion of the molecule and the nature of ligands surrounding the iron atom. The bright red colour of freshly cut meat is due to oxygen binding as a ligand to the iron atom which is in the ferrous state. However, oxygen does not bind very strongly and it is known that other ligands bind more strongly, stabilizing the molecule and preserving the red colour.