Hibiscus acid
Quick answer
The acid found in the largest amount in the dried calyx of roselle: about a tenth to a seventh of its dry weight in one set of measurements. A review describes it as a lactone, a ring-closed relative of the acid of the Garcinia rinds.
What it does
Hibiscus acid was the main compound in hot-water extracts of dried roselle calyces from sixteen places in India, measured by NMR: 9.8 to 15.5 g per 100 g of dry powder, depending on the lot and on how it had been dried. The same study found succinic and acetic acids at under a fifth of a gram per 100 g each, and did not list citric or malic acid among the compounds it assigned, though the handbook accounts put citric acid at about 4 per cent of the calyx and call the calyx high in citric and malic acids. A review of the acids of the calyx names hibiscus acid with citric and malic acid as the main ones and attributes the sour taste to the organic acids together. Nobody tasted hibiscus acid on its own in anything read for this profile. That it accounts for much of the sourness is an inference from its being the acid present in the largest amount.
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
It goes into the water. The study that measured it poured boiling water over the powdered calyx, left it for five minutes, and found hibiscus acid at about 0.6 to 0.7 per cent of the liquid. That is how the calyx is used: boiled or steeped, then strained out. So the sourness of a roselle drink or sauce is drawn out quickly and stays in the liquid once the calyces are removed. 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 and not high because nothing read followed the acid through long cooking. Calyces dried slowly in the shade held about 15 per cent less of it than calyces dried quickly in a heated tray, a loss the authors put down to possible fermentation in the damp calyces and not to heat.
Spices that carry it
Recorded on the compound rather than on each spice, so the two cannot disagree.
- RoselleMajor component
The main compound in hot-water extracts of dried calyces from sixteen places in India: 9.8 to 13.2 g per 100 g of dry powder in shade-dried calyces and 12.4 to 15.5 g in tray-dried ones.
What cooking and processing were measured to do to it
Findings from studies in which this compound was followed through heat, fat, water, drying or storage. Each belongs to its study and its conditions.
Drying · Depends on conditions Hibiscus acid, glucose, fructose, γ-aminobutyric acid, fumaric acid, moisture
Calyces from sixteen places were each dried two ways. The shade-dried lots averaged 10.5 per cent water and the tray-dried 7.9 per cent. Hibiscus acid was the main compound in a hot-water extract of every lot: 9.8 to 13.2 g per 100 g of dry powder after shade drying and 12.4 to 15.5 g after tray drying, about 12 g and 14 g on average, which the authors put as a loss of almost 15 per cent in the shade. Glucose and fructose were lower in most shade-dried lots too, at about 1.5 to 2.3 g per 100 g each against 2.0 to 2.7 g, while γ-aminobutyric acid and fumaric acid were higher. The authors suggest why: calyces that dry slowly stay damp and warm for days and may begin to ferment. Four of the sixteen shade-dried lots did not show the pattern, which the authors put down to how the drying went and not to where the plants grew.
Conditions: in air · 26–28 °C in the shade; 60 °C in the tray drier · Four days in the shade; six hours in the tray drier · About 50 g of fresh red calyces from each of sixteen places, fifteen in the Garo Hills of Meghalaya and one at Noida
It does not overturn the handbook’s advice for Africa, which is to dry in the shade because full sun lowers quality. The handbook sets shade against sun; this study set shade against a heated tray at 60 °C, above the 43 °C the handbook gives as the limit for heated dryers, and measured acids and sugars, not colour.
What this does not show: One study, on about 50 g of calyces per lot. The compounds were measured in a five-minute hot-water extract brought to neutral pH, not in the calyx itself, and citric and malic acids were not among those the study assigned. Colour and anthocyanins were not measured. The abstract says all sixteen lots came from Meghalaya; the table of locations places one at Noida, in Uttar Pradesh.
Measured on the spice
Not to be confused with
Compounds a reader is likely to take for this one, and why they differ.
Hydroxycitric acid
The acid of kokum and kudampuli. A review describes hibiscus acid as a lactone and as a diastereomer of garcinia acid, the lactone found in the Garcinia fruits: the same atoms joined in the same order and arranged differently in space. The two are related and are not the same compound.
Citric acid
Named beside hibiscus acid in the handbooks and in a review as an acid of the calyx. A study that measured the acids of the calyx by NMR reported hibiscus acid and did not report citric acid. Another, which measured citric acid by liquid chromatography in three Mexican varieties, found 4 to 29 mg per 100 g of dry calyx and did not measure hibiscus acid. No study read measured both.