Turmeric (curcuma longa) is a rhizomatous
herbaceous perennial plant of the ginger family, (zingiberaceae). Turmeric
contains up to 5% essential oils and up to 5% curcumin, a polyphenol.
Curcumin is the active substance of turmeric and curcumin is known as C.I.
75300, or Natural Yellow . The systematic chemical name is
It can exist at least in two tautomeric forms, keto and enol. The keto form
is preferred in solid phase and the enol form in solution. Curcumin is a pH
indicator. In acidic solutions (pH <7.4) it turns yellow, whereas in basic
(pH > 8.6) solutions it turns bright red.
The rhizomes are boiled and then dried, leaving a yellow powder. The colour
comes from pigments called curcuminoids. It is native to tropical south Asia
and needs temperature between 20 °C and 30 °C and a considerable amount of
annual rainfall to thrive.