Wide distribution in plant tissues; in fruits, vege and flowers.

Include flavonoids and related compounds Classes of flavonoids

i. Anthocyanins (in syllabus)ii. Flavones & Flavonolsiii. Flavanalsiv. Flavanones

Water soluble pigments

Flavonoids have a C6C3C6 skeleton- consist of 2 benzene rings and a 3C chain that

together with oxygen, forms part of the central ring.

Structure

Anthocyanin structure

6 common anthocyanidins Cyanidin- strawberries Delphinidin- plums, peaches, apple skins,

figs Pelargonidin- grapes, pomegranates,

eggplant Peonidin Malvidin methyl derivatives petunidin

Red, blue and purple coloured pigments Exist as glycosides (> stable). Usually 1 or 2

sugars are present. Commonest sugars; glucose Others; galactose, rhamnose or pentose sugar Common position for sugars: C3 or C5

Anthocyanins with sugars = Glycones Anthocyanin without sugars = Aglycones/

anthocyanidins

ANTHOCYANINS

1. Leaching Pigments can leach into processing fluid (eg.

Canning fluid due to breakdown of cell wall & their water soluble nature

~use < mature fruits for processing

2. Enzymatic degradation Anthocyanin sugar + aglycone

anthocyanase (slow)

chalcone (pale yellow)

Stability of pigments during processing

3. Colour changes due to pH of processing/ cooking water.

Red cabbage bluish coloured cabbage

soft water +H (eg lime juice or vinegar) pH ~7

reddish cabbage At pH 8 or >8 = greyish colour At high pH = green colour

4. Contact with metal Anthocyanin form greenish, blue, purplish and slate

grey pigments with metals

Colour depends not only on particular anthocyanin but also metal ions

Anthocyanin anhydro bases form coloured compounds with metal like Fe and Al. The complexes form sometimes are very stable

Because of this, food contain anthocyanin processed in enamel-lines (lacquering inside metal can) rather than thin plate as it can degrade colour af anthocyanin