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Issue 5

The Good Oil on Kurrajong 

Or why bushfood sometimes gives you the Sterks.

John Wrench 

Kurrajong  Genus Brachychiton
Family Sterculiaceae 30 Australian species.

Photo - John Wrench

The books about bushfoods, fast becoming too numerous to recall accurately, are all interesting, often beguiling, and sometimes downright frustrating. I do not mean so much that you cannot lay hands on the stuff, rather that the tricky bits are glossed over, or that the essential scientific explanations are not even broached. Doubtless, that is why some of us are driven to run courses and workshops in which we can tackle some of the issues at length. It is my view, in teaching, that the information which appears sometimes to be over the head is not always out of reach, given that human minds can make quantum leaps when challenged. 

The Brachychitons are worth regarding seriously as food, considering the nutrient value of the seeds alone - carbohydrate (starch) 15%, protein 18g%, fat 25% (+) fibre 33%, very high levels of potassium, magnesium and calcium, as well as iron and zinc, and just over 5% of water. 

Various species of Brachychiton occur across the country from coast to inland, differing in nutrient levels and the uses to which the original Bush Tucker people put them. Unfortunately, the handsome bottle trees have less significant flowers and fruits, but the others produce beautiful flowers and sizeable follicles packed with seeds smaller than a peanut, surrounded by golden, stellate hairs. 

Traditionally, there are two major problems in obtaining the benefits of Kurrajong nutrients - the irritant, stellate hairs surrounding the seeds and Sterculic acid (+) in the seed oil which causes gut irritation, gastroenteritis, etc. Let us deal with the sterculic acid first. There is no proof that the sterculic acid is confined to a particular portion of the seed, despite the suggestion that the membranous outer yellow coat is especially toxic. Traditional treatment involves roasting and eating the whole seed. Again, tradition claims that gut irritation and diarrhoea follow the ingestion of untreated seed. Like most edible seed oils, the Kurrajong lipids contain the glycerides of several fatty acids of purely nutritional importance. 

Index: 5
From the Editor...
Peak National Body
Research & Development News
The Desert Raisin (Akadjura) - Solanum centrale
Purely Pepper (Tamannia spp) 
Three Bucket Garden
Black fella, white fella
The Good oil on Kurrajongs
CSIRO report - Acacia
Christmas in the bush
Bushfires and bushtucker
Northern Exposure
The bee that 'fishes' for pollen
Fruiting times (N NSW)
Common names
From the papers



CH3 - [CH2]7 - C==C - [ CH2] n - C

                           \          /                    \

                          CH                         OH

n=6  Malvic acid   n = 7 Sterculic acid 



HC = C - [CH2]7 - C == C -[CH2] 6 - C

                                 \       /       \      

                                   CH         OH

Sterculynic acid

The presence of several different fatty acids, however, establishes the basis of toxicity; these are malvilic and sterculic acids. They resemble a number of harmless medium chain, except for the presence of a three member ring system arising in the middle of the straight chain of carbon molecules, straddling a double bond. This gives rise to the term 'cyclopropenoid'. As a matter of interest, a member of a related genus, Sterculia alata, contains in its oil 8% of sterculynic acid, a cyclopropenoid with a triple bond between the first two carbons. In case some of you may be interested, the molecular structure of these three fatty acids are represented above. 

All very interesting and a change from recipes and farm gate prices, but where does it lead? S. L. Everist, in 'Poisonous Plants of Australia' (Angus and Robertson, 1973), offers two clues: he lists cyclopropenoid fatty acids as a specific class of animal toxins; and he refers to cases of livestock poisoning attributed to the presence of cyclopropenoids in fodder obtained by lopping fruit-bearing Brachychiton foliage. There are three relevant points: the victims were ruminants, so that direct parallels to human response are not totally valid; the fodder was used in emergency, so that admixture with (much) other material did not occur; the wretched beasts did not have a camp cook to heat up their tucker. Some reference exists to locomotor effects, but the principal symptoms were of gastroenteritis and scouring, the very same effects produced in humans who ingest untreated Brachychiton seeds. 

By observation of Aboriginal practices in preparing Kurrajong seeds by roasting prior to ingestion, non indigenous people have managed to avoid adverse effects. How might it work? It relates to the oxidative changes in the cyclopropenoids during heating, at the least stable points in the molecules, that is, where the unsaturated bonds occur Depending on the circumstances, any number of breakdown products may be formed, but the important thing is that the cyclopropenoid ring is broken, with fragmentation of the long chain. As simple as that. In the absence of other irritant or toxic components, it is reasonable to assume that the cyclopropenoid moiety is entirely responsible for the gut problems. Most people with normal gut and liver/gall bladder function can cope with a wide range of edible plant seed lipids taken in reasonable quantities, with the exception of variants, such as ricinoleic acid in Castor seeds and some of the highly unsaturated oils. 

Which leaves sterculic acid (et al) in the dock. By the way, if the roasted seeds are converted to a seed meal by some kind of blender or coffee grinder, the interface with the air is greatly increased, exposing the various components to further risk of oxidation and rancidity, carrying as they do the catalysts formed during heating. Storage in a sealed container in a freezer or refrigerator is essential. The process of roasting (any seed) produces embrittlement which facilitates disintegration. The temperature and duration of roasting, however, are determined by the end usage. Seed meal or flour requires about 150c for 15 minutes or so, whereas a coffee substitute requires about 80c for only as long as it takes to darken sufficiently. 

But WATCH IT! For fun, the seeds can be treated like popcorn by roasting briefly in the lid of a Bedourie oven on hot coals, or in some civilised manner! The other problem with Kurrajong seeds is probably more obvious the matrix of stellate hairs in which the seeds are nested in the follicle or pod. The traditional, careful strategies of the Aborigines, and the consistent cautions of the various authors, all point to the need to avoid personal contamination during the removal and cleaning of the seeds. The physical structure of the stellate hairs is impressive - fine, long; sharp spikes, lignified and therefore tough, but light enough to remain airborne. Delicate human tissues, even tough skin, but especially eyes, mouth, and respiratory tract are readily perforated by the hairs, giving rise to irritation, pain and infection. Lodgment of the hairs in the eye can lead to inflammation, ulceration of the cornea and infection, to say nothing of intense pain and lacrymation. 

The several references to blindness in the literature, while not authenticated, are a warning. However, there are no sinister chemical agents involved - only devilish cunning spikes. It hardly matters what method is used to extract the seeds from the follicles, (all the authors have a favourite) provided that the generation of airborne hairs is minimised and personal protective measures are taken. It certainly helps to top and tail each follicle by secateurs, facilitating the opening of the two lips of the naturally split pod. Rubbing the seeds between leather gloves or on a coarse sieve is useful, but if you are worried, wash and rinse the seeds, allowing them to dry on a sieve. 

Now you know why it is practically impossible to buy Kurrajong flour. In conclusion, I should like to thank several people who gave kind help towards preparation of this article. Professor Trevor Clifford sent me copies of some extracts of overviews by Professor R. Hegnauer, University of Leiden, Holland - Chemotaxonomie der Pflanzen VoL 3, 1964 and Vol. 6, 1973 (Birkhauer Vertag, Basel and Stuttgart). One C. J. Wrench, lecturer, Griffith University, Queensland Conservatorium of Music, was pressed to translate the texts over dinner. Associate Professor John Bourke (University of Queensland Dept. Physiol. & Pharmacol.) obligingly discussed the gut issues, and the effects of heat on the seeds. Dr. Gordon Guymer, Queensland herbarium discussed the nature of the stellate hairs. It is worth remembering that the name of the family 'Sterculiaceae' is derived from Sterculius, the Roman god of dung heaps and privies. 

Happy days.

 John Wrench 14 Ennerdale Street Chermside West 4032, 

Ph:  07 3256 3310


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