Water Soluble Plant Pigments
Flavonoids: This group includes red and yellow colour pigments which are water soluble substances present in vacuoles of cell sap of plants, glycosides, non-sugar portion accounts for colour.
Chemical Nature of Flavonoids: Flavonoids are phenolic compounds having C6, – C3- Cs, skeleton.
a) Anthocyanin: They occur as glycosides involving sugars such as glucose, rhamnose, occasionally pentose. Anthocyanin hydrolysis sugar + Non sugar (Anthocyanidin). They show different colours at different pH solution.
1. Acid pH Red colour
2. Alkali pH Blue colour
3. Neutral pH Violet /Purple.
Chemical Nature of Anthocyanin:
1. Anthocyanin is glycosides of benzopynylium nucleus
2. It also consists of sugar rhamnose, arabinose and glucose
3. Anthocyanin nucleus consists of one pyrone ring and two benzene rings
4. Non-sugary residue of anthocyanin is called anthocyanidin – derivatives of 2-phenylbenzopyrylium salts or derivatives of polyhydroxy flavylium.
1. It is yellow colour pigment, found in flowers, fruits, leaves, bark, roots
2. It specially consists of rhamnose and glucose, freely soluble in cell sap
3. It is always associated with anthocyanin.
Chemical Nature of Anthoxanthins:
1. Anthoxanthins nucleus consists of 2-phenyl benzo pyrone rings, include flavone and flavonol pigments, gycoside.
2. Non sugar residue of Anthoxanthins is called as anthoxanthedin. Basic unit: of aglycone portion or Anthoxanthins is the gamma-pyrone.
Examples of Anthoxanthins:
a. Flavone Apigenin from the ivory white snapdragon
b. Xanthone Gentisin from gentian root
c. Favonol Quercetrin from bark of oak
d. Flavanones Hesperidin from oranges.
e. Flavin Riboflavin (vit B2) distributed in plants and animals.
Physiological Role of Water Soluble Pigments:
1. Flavonoids attract the insects for pollination
2. Anthocyanin absorbs the heat and it increases the transpiration in cell.
3. Anthocyanin increases osmotic pressure in the cell.
4. Contribute to the food flavours a colours.