Hydroxycitric acid
Also written (−)-hydroxycitric acid, HCA
Quick answer
The acid of kokum and kudampuli: the main organic acid of the dried rind of both Garcinia fruits, found there together with its lactone, a ring-closed form of the same molecule.
What it does
Hydroxycitric acid is the main acid of the two Garcinia rinds used for souring. An analysis of kokum by liquid chromatography found it to be the major organic acid of the rind, at 10.3 to 12.7 per cent, with its lactone and citric acid beside it in minor quantities. A later study of dried rinds bought in the markets of southern India, measured by NMR, found less of the free acid and more of the lactone: 1.7 to 7.6 per cent acid and 3.5 to 11.7 per cent lactone in six samples of kokum, and 3.9 to 10.3 per cent acid and 7.4 to 19.1 per cent lactone in eighteen of kudampuli. The two analyses disagree about how much is lactone, and the later authors say the balance between the two forms in the fruit is not known. Neither study tasted anything. That this acid is what makes the rinds sour follows from its being the acid present in the largest amount; how its sourness compares with that of citric or tartaric acid was not measured in anything read for this profile.
How it behaves when cooked
Four properties of the molecule, and what they mean at the stove.
- Volatility
- low
- Fat solubility
- low
- Water solubility
- high
- Heat stability
- moderate
The acid dissolves in water. The study that measured it drew it out of the powdered rind with hot water alone, and its authors class it among the water-soluble constituents of the fruit, as against fat-soluble ones such as garcinol; the reference record gives it a strong computed preference for water over fat. So the acid goes wherever the liquid of a dish goes, which fits how both rinds are used: steeped or simmered in the pot and then left in or lifted out. The other levels shown here are not measurements. That the acid does not evaporate and stays out of fat is the ordinary behaviour of a solid fruit acid. Heat stability is given as moderate, not high, for one reason: the acid and its lactone are two forms of one molecule, the study read could not say how they balance in the fruit, and nothing read followed either form through cooking.
Spices that carry it
Recorded on the compound rather than on each spice, so the two cannot disagree.
- KokumPrincipal component
The major acid of the rind in one analysis, at 10.3 to 12.7 per cent. Six market samples measured later held 1.7 to 7.6 per cent, with more of the lactone than of the acid.
- KudampuliPrincipal component
In eighteen market samples of the dried rind, 3.9 to 10.3 per cent acid and 7.4 to 19.1 per cent of its lactone: on average more of both than in the kokum measured beside it.
Not to be confused with
Compounds a reader is likely to take for this one, and why they differ.
Citric acid
Hydroxycitric acid is citric acid with one more hydroxyl group, and the two are different compounds. Citric acid is the acid of citrus and of most dried souring spices; in kokum it was found only in minor quantities beside hydroxycitric acid.
Hydroxycitric acid lactone
The ring-closed form of the same molecule, found beside the acid in every rind measured and, in the market samples, in the larger amount. Those measurements give the two separately and as a total, because how one turns into the other in the fruit is not known.
Garcinia cambogia extract
A concentrated extract of kudampuli rind, sold as a food supplement and labelled by its hydroxycitric acid content. It is a different product from a piece of rind in a curry. SpiceHQ makes no claim about it and does not assess it.