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PeterHardwick
Dinkum Sheila
Joined: 17 Jun 2006
Posts: 158
Location: Nightcap Ranges, NSW
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 Posted: Mon May 04, 2009 2:49 pm Post subject: Watch-out for dangerous information on DVD's |
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Just to let everyone know to be on the look-out for amateur made DVD's and textbooks that have been coming out over the last few years which have some serious mistakes on advice on what can be eaten as far as bushfoods and edible weeds.
It recently came home to me how serious this problem is when I heard from a bushfoody friend that children were sucking the nectar straight from potentially dangerous Grevillea flowers.
Here are some of the gross toxicological mistakes that I've spotted, including inaccurate edible weeds claims:
- Grevillea nectar should NOT be drunk directly from the flower, especially as there is the risk of confusion for children eating the flower. Some Grevillea flowers are known to contain a plant toxin that breaks down to poisonous hydrogen cyanide. Grevillea’s are also known to contain unidentified irritant compounds. Also, hybrid Grevillea's have unknown toxicology and some hybrid parents are known to have toxins.
- Not all wattle seeds are known to be edible, and of those edible Acacia species, many need to be extensively processed to be safe.
- Not all species of grass are edible. Some grass species contain toxic compounds which can be potentially poisonous to humans. We recommend that people do not eat grass unless they know that the specific grass species in question is safe.
- Not all hibiscuses are edible. Some native Hibiscus species are suspected of containing toxic levels of oxalates in their leaves.
- Clover can contain toxic compounds and should be avoided as a wild vegetable for human consumption.
- The introduced white flowering “Wandering Jew” Tradescantia albiflora is likely to be toxic, especially uncooked.
- Gota cola, Centella asiatica, a small-leafed herb, is primarily used as medicine, and no more than two leaves should be eaten in one day. It should not be eaten in larger quantities.
Child safety with regards to wild food plants is paramount because children have a lower body weight, and it takes a less poison to make them ill. Parents need to clarify the above wild food safety issues with children if they know that children may have been influenced by potentially dodgy wild food documentaries.
I have been in dialogue with the producers of these DVD's, and they say they will edit future batches, but they are still releasing the current batch with a printed caveat on their DVD covers. Which I think is woefully inadequate.
Anyway, just watch-out for these DVD's - because they are also in public libraries as well.
It's a real problem, because on one hand it's good to encourage people to get involved and promote wild foods - but at the same time there is no place for people who don't have the skill to be giving out advice on wild foods on a public level. It's just dangerous. |
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Thomas B
Dinkum Sheila
Joined: 04 Jan 2009
Posts: 159
Location: Canberra
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| Posted: Mon May 04, 2009 8:23 pm Post subject: |
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Can you provide references for the possibility of grevilleas having poisonous nectar. The only member of the Proteaceae that I am aware of having toxic nectar is Lomatia silaifolia, but other plants include Oxylobium spp. I thought the issue with the hybrid Grevillea was that it was allergenic unlike the parent plant, and once individuals were sensitised, the allergy spread to cover other spp of Grevillea.
Also, while many wattle species have not yet been determined to be edible, those containing the main toxic agent in the poisonous species, monofluoroacetate, are well known for their toxicity. I am not aware of any coastal species yet identified as toxic.
The hibiscus claim likely arose from Tim Low's book, which said that no Hibiscus species were known to be poisonous, and any that tasted acceptable were likely to be safe to eat. Oxalates are in high concentrations in many food crops, such as spinach, but are mostly removed by cooking. Oxalate is such an irritating substance that unless someone was trying to poison themselves, they would not suffer any ill effects other than a stinging mouth and possibly vomiting. Only one death, in exceptional circumstances (the plant was the victims only source of green vegetables) has occurred from the consumption of the plant after which the substance is named, Oxalis. This really demonstrates that in most circumstances oxalate is generally unlikely to present a danger of poisoning. |
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JumpedAngel
Dinkum Sheila
Joined: 26 Oct 2005
Posts: 185
Location: Melb
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| Posted: Mon May 04, 2009 10:20 pm Post subject: |
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I agree Peter, I have to say that each time I go out I try to sample a few 'known' bush foods and am often put off by the flavour alone, this last November while out in the desert I tried the flowers of the bush pear which were absolutely scrumptuous and some mulga apples which were a definite mistake, as well as one or two other things.
I might have made an error with the i.d. of the acacia but although I took an image of the plant I havn't back tracked yet to be sure if it was the wrong acacia, the point is, beware of acacia apples, I am now certain that not all are edible, I was cautious so all I got out of it was a very strong acrid flavour in my mouth which lasted a few days but it might have been a lot worse if I hadn't spat it out immediately or if I had swallowed some.
Since then I have noticed apples on many different acacia and have considered how easy it is for someone with little bush food experience to assume that they see dinner on a plate.
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one shot, two shot, three shot, floor |
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PeterHardwick
Dinkum Sheila
Joined: 17 Jun 2006
Posts: 158
Location: Nightcap Ranges, NSW
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| Posted: Tue May 05, 2009 11:43 am Post subject: |
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| Thomas B wrote: |
| Can you provide references for the possibility of grevilleas having poisonous nectar. |
No worries Thomas B. Reference to cyanogenetic glycosides in Grevillea banksii and Grevillea robusta is in: Everist, S.L., “Poisonous Plants of Australia”, Angus and Robertson, 1974.
Of course, G.banksii is also a parent species in many of the modern hybrid Grevillea varieties.
Also concerning is the unknown allergenic compound in Grevillea hybrids, similar reactions have been also noted in wild species. Given this, there is a potential scenario of a child getting a reaction from drinking Grevillea nectar where the child's throat closes due to an allergenic reaction. This could be a consequence of popularizing Grevillea nectar drinking.
| Thomas B wrote: |
| I am not aware of any coastal species yet identified as toxic. |
Acacia's have ample nitrogen available to produce alkaloids, and of course they do. Some are very potent. No one in their right mind would ever say that ALL wattles are safe - even if we don't know their individual toxicity profiles.
| Thomas B wrote: |
| The hibiscus claim likely arose from Tim Low's book, which said that no Hibiscus species were known to be poisonous, and any that tasted acceptable were likely to be safe to eat. Oxalates are in high concentrations in many food crops, such as spinach, but are mostly removed by cooking. Oxalate is such an irritating substance that unless someone was trying to poison themselves, they would not suffer any ill effects other than a stinging mouth and possibly vomiting. Only one death, in exceptional circumstances (the plant was the victims only source of green vegetables) has occurred from the consumption of the plant after which the substance is named, Oxalis. This really demonstrates that in most circumstances oxalate is generally unlikely to present a danger of poisoning. |
Aboriginal elders from the Mid-North Coast of NSW have told me they only used Hibiscus heterophyllus sparingly as a medicine - because it was considered toxic.
I'd previously found this out the hard way, after I had the personal experience of getting what I interpret (from symptoms) as probable oxalic acid poisoning when I was doing a dose related feeding trial (using myself) when I was doing bushfood assessment for commercial use.
The symptoms were severe kidney pains for over a week - consistent, but not definitive as oxalic poisoning. But a reasonable assumption given the conformation of oxalic acid since. (But it always possible that there maybe another toxin also present in H. heterophyllus) Also, keep in mind that rhubarb leaves have been known to cause oxalic acid poisoning - so it's not a minor issue by any stretch.
Also, while Tim Low and Cribb & Cribb are excellent reference documents, they are out-of-date as definitive bushfood references and should not be used as an absolute. Besides, anybody mainstreaming wild food knowledge should be obliged to independently check the safety of wild foods.
Also, mainstreaming wild food knowledge via DVD's takes it to another level where people are more exposed to potentially dangerous information. Whereas, Cribb & Cribb and Low's 'mistakes' are at least somewhat 'buried' in a reference text. Film is a much more powerful medium - and in the hands of someone who is ill-informed on bushfoods - can be very dangerous to say the least.
Mainstreaming wild food knowledge involves as much responsibility as putting it on a restaurant plate.
There is little margin for error. |
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Thomas B
Dinkum Sheila
Joined: 04 Jan 2009
Posts: 159
Location: Canberra
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| Posted: Tue May 05, 2009 7:25 pm Post subject: |
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Just for reference, the incidence of poisoning from rhubarb leaves are inconsistent with oxalate toxicity. Some other toxic principle is indicated. |
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PeterHardwick
Dinkum Sheila
Joined: 17 Jun 2006
Posts: 158
Location: Nightcap Ranges, NSW
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| Posted: Wed May 06, 2009 4:28 pm Post subject: |
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| Thomas B wrote: |
| Just for reference, the incidence of poisoning from rhubarb leaves are inconsistent with oxalate toxicity. Some other toxic principle is indicated. |
What reference are you using for that? Everist suggests oxalates as a culprit. This reference suggests oxalates as also playing a primary role.
http://www.rhubarbinfo.com/rhubarb-poison.html |
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Thomas B
Dinkum Sheila
Joined: 04 Jan 2009
Posts: 159
Location: Canberra
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| Posted: Wed May 06, 2009 10:09 pm Post subject: |
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"Wild Herbs of Australia and New Zealand" by Tim Low. |
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PeterHardwick
Dinkum Sheila
Joined: 17 Jun 2006
Posts: 158
Location: Nightcap Ranges, NSW
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| Posted: Fri May 08, 2009 2:12 pm Post subject: |
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Thomas B, I think Tim Low stuck his neck out in playing down oxalates, and it might be a reason why he seems to have got it wrong on Hibiscus safety in general, and H.heterophyllus specifically. (NB That was 20 years ago when he wrote about Hibiscus being probabaly safe)
Also, the anthraquinones may play a role in rhubarb posioning, but that's far from certain. Whereas it is well known that soluble oxalates are poisionous. And certainly some rhubarb symptoms don't look inconsistent with oxalic acid poisoning:
http://www.drugs.com/enc/rhubarb-leaves-poisoning.html
Also, Selwyn Everist, who wrote the definitive text on Australian plant toxins puts acute oxalic acid posioning like this:
"Symptoms are usually dullness, twitching and trembling of body muscles, frothing at the mouth, collapse on the brisket and coma prior to death which takes place about 10 hours after the plant is eaten."
It's not insignificant.
Also, oxalic acid poisoning is a well known medical cause of nephritis.
But back to H. heterophylus: The symptoms of kidney pain that I experienced after consuming moderate amounts of H. heterophyllus is consistent with oxalate poisioning. And this also parallels an experience of someone else I know who was advised to go on a raw spinach fast back in the 1970s, and as a result they subsequently experienced severe kidney pains - again consistant with oxalate poisoning. And of cause spinach is well known to have oxalates - but not normally a problem at normal doses.
Also, we now have it confirmed that there is oxalic acid in H. heterophyllus.
Where I think Tim Low made his mistakes on down playing the significance of plant oxalate toxicity - with all respect, because Tim's wild food contribution has been great - is that he seems to have brushed over the difference between soluble and insoluble oxalates (barely mentions the difference - which is critical because the soluble oxalates are more poisonous); and also seems to assume that there may not be much of a problem with oxalate poisoning from plants because there had not been many recent recorded cases in humans. Also, I note that he didn't point out that the acidic taste of the non-toxic rhubarb stems is primarily from malic acid and other acids - not so much from oxalic acid. Whereas rhubarb leaves have the oxalic acid.
The thing is, Tim's wild food research was some of the best at the time - 20 years ago - but now we know a bit more. And oxalates are an issue. |
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eataust
Jillaroo
Joined: 11 Sep 2005
Posts: 999
Location: Tarago, NSW
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| Posted: Fri May 08, 2009 5:53 pm Post subject: |
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Oxalates are present in warrigal greens (Tetragonia tetragoniodes), and apparently are what cause the sort of "fuzzy" feeling in the mouth when eating raw.
The usual recommendation is to blanch in boiling water and to throw out the subsequent green-tinted water. I presume this means they've got the "soluble" version of oxalates - the same as spinach and other dark leafy greens? (One of my aims in growing warrigal greens is to see if it's possible to select for lower oxalate content, eventually arriving at a variety that doesn't require the pre-blanching).
I was slightly concerned recently to see the ABC's "Cook and the Chef", which has been brilliant in promoting bushfoods, use warrigal greens without blanching first. They were being cooked, but from my understanding that would simply mean the oxalates would move from the greens into the rest of the food.
Is there cause for concern for using them in this way? I did write into the show immediately, but I haven't seen anything come back from it.
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eat australia: grow it, find it, eat it: http://blog.eataustralia.info
Bushfood books - see my "website". |
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PeterHardwick
Dinkum Sheila
Joined: 17 Jun 2006
Posts: 158
Location: Nightcap Ranges, NSW
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| Posted: Sat May 09, 2009 2:42 pm Post subject: |
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This post is actually written by eataust, but somehow the gremlins mis-ascribed it to me (Peter). The quotes are actually from me. P.
| Quote: |
| Hi eataust, long time between threads. |
Hello!! This has been a fun thread - glad you're in here with your info 
| Quote: |
| You are right eataust, chefs should not be encouraging the eating of raw warrigal greens. Certainly research indicates that soluble oxalates are present in Tetragonia tetragonides, and it should be blanched before eating. |
OK, cool ... I'll bear that in mind and maybe write in a little more firmly.
I've been educated into "pouring boiling water over them and letting it sit is adequate" - true blanching is "actively boiling in water for one minute". Definitely it seems to remove the odd things.
| Quote: |
But, I also think it's questionable that the "fuzzy" feeling you describe is from oxalic acid. There's the saponic and other compounds present in T.tetragonoides as well.
Oxalic acid is more sharp and tangy in flavour going on Hibiscus, sheep sorrel, French sorrel, Oxalis, swamp dock etc... |
Ahhhhhh. Thank you!! That does make sense when you realise the name of clover - oxalis
I love the sharp sour flavour of those things - sorrel in particular - so this probably explains my love for the greens.
| Quote: |
| The flavour in raw warrigal greens is more acrid, soapy and beany - more in keeping with the saponic compunds. |
Are they good things, or bad? Are they removed during blanching? Should I start a new thread to ask these questions?? (And should I talk to RIRDC for funding to investigate all this???).
| Quote: |
Interestingly, during the 1970s when Australia was doing research into how to get rid of T. tetragonoides as a weed in wheat paddocks, Japan was doing research into T.tetragonides phytochemistry because it's used there as a folk remedy for treating stomach cancer.
One could speculate (and emphasis on speculate) as to why T.tetragonoides gets rid of stomach cancer - wonder if the large saponic compounds that usually can't cross the gut lining, are able to cross directly into cancer cells in the stomach via a kind of internal topical application. Just a thought. |
_Definitely_ room for investigation ...
| Quote: |
| It would be good to get some phytochemical clarification on T.tetragonoides from the Japanese - including on the possible medicinal uses. |
I'll add that into my little business plan then ...
| Quote: |
Warrigal greens is a strong food. It's not the sort of thing that I would eat big quantities of every day. |
I eat it like spinach - blanched and then added to stir-fries, or drizzled with olive oil, or so on. This is mostly because I have better luck growing tetragon than I do spinach - it needs a lot less water and TLC, and likes the cool shady spots the spinach doesn't appreciate as much.
So it's not a daily food, but it's definitely a regular one. My parents are converts (given their scepticism toward bush tucker when I first started this obsession, this makes me incredibly proud) and request it whenever they visit. They've got their own plant now, carefully dug out and given the 6 weeks of TLC required to establish a transplanted tetragon, so they can do their own. I'll ensure they always blanch it.
Sorry to divert the conversation, but the oxalites in the greens have always been of interest to me in terms of relative toxicity ...
Last edited by PeterHardwick on Tue Jul 27, 2010 3:35 pm; edited 1 time in total |
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PeterHardwick
Dinkum Sheila
Joined: 17 Jun 2006
Posts: 158
Location: Nightcap Ranges, NSW
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| Posted: Sat May 09, 2009 2:59 pm Post subject: |
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Just a clarification with regards to Grevillea flowers. If you refer to my original post, I'm primarily expressing concern about the flowers being poisonous, not so much the nectar - but there's a big question around the allergy potential of Grevillea nectar (and pollen?) as well.
When it comes to children it's too confusing to be placing poisonous flowers into their mouths.
Like I say, it only takes one toddler to get confused and eat the flower itself. Let's not go there. |
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Thomas B
Dinkum Sheila
Joined: 04 Jan 2009
Posts: 159
Location: Canberra
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| Posted: Sun May 10, 2009 3:40 pm Post subject: |
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Do you know if the same toxicity is true for close relatives like banksias? |
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Thomas B
Dinkum Sheila
Joined: 04 Jan 2009
Posts: 159
Location: Canberra
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| Posted: Sun May 10, 2009 3:59 pm Post subject: |
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With insoluble oxalates, as far as I know, their danger arises from the crystals they form (raphides), which puncture the oral lining, allowing the coatings of other toxins to enter (Cunjevoi/Alocasia, Colocasia, Amorphophallus, Typhonium).
How can an insoluble substance be absorbed into the bloodstream in order for a toxic effect to occur? Incidentally, the insolubility of calcium oxalates is actually how the soluble oxalates kill, removing calcium from the bloodstream.
With soluble oxalates present in Warrigal Greens and Native Rosella, couldn't these be removed by blanching or sauteeing with a calcium rich substance, like milk or cheese? |
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PeterHardwick
Dinkum Sheila
Joined: 17 Jun 2006
Posts: 158
Location: Nightcap Ranges, NSW
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| Posted: Sun May 10, 2009 6:41 pm Post subject: |
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Thomas B thanks for your response. It's great to have someone draw-out the issues.
| Thomas B wrote: |
| With insoluble oxalates, as far as I know, their danger arises from the crystals they form (raphides), which puncture the oral lining, allowing the coatings of other toxins to enter (Cunjevoi/Alocasia, Colocasia, Amorphophallus, Typhonium). |
These oxalate crystals are another thing. It's like swallowing a pack of needles I believe! A bit like eating slightly unripe Monsterio magnified by a hundred fold - all the way down the oesophagagus if one is unfortunate enough to swallow. Ouch!
The big issue seems to be especially with toddlers. I was rung-up once by a friend whose two year had swallowed some cunjevoi, Alocasia brisbanensis (syn. A. macrorrhiza), leaf that was growing near their back door.
The concern was that the oxalate crystals in the cunjevoi may cause a reaction that could close off the airways in the childs throat. So the child was kept in the hospital until the percieved danger period had passed.
Just another point to remember, many of these plants you mentioned are also known to have other plant toxins in them, as well as the oxalate crystals.
| Thomas B wrote: |
| How can an insoluble substance be absorbed into the bloodstream in order for a toxic effect to occur? |
This is exactly my point. The insoluble oxalates are excreted harmlessly out of the body - very different to the soluble oxalates which go into the bloodstream.
The problem is that there's too much over-generalization about oxalates - and often no differentiation on whether they are soluble or insoluble oxalates. For example, look at the table on oxalate content in Tim Low's book "Wild Herbs of Australia and New Zealand". There's no differentiation between soluble and insoluble oxalates in the table - it's just gross oxalate content.
The dangerous soluble oxalates are sodium, potassium and ammonium oxlalates.
The safe execreted insoluble oxalates (except the large crystals of course)are calcium and iron oxlates.
Just to confuse things, it's likely that many plants have various portions of insoluble and soluble oxalates.
| Thomas B wrote: |
| Incidentally, the insolubility of calcium oxalates is actually how the soluble oxalates kill, removing calcium from the bloodstream.? |
Actually, calcium oxalates are safe as its an insoluble oxalate. but the soluble oxalates in the blood precipatate calcium from the blood stream, and most deaths are from loss of calcium ions in the body.
But when the calcium levels in the blood are high enough to protect from this effect, calcium oxalate crystals preciptate out in the tubules of the kidney - hence kidney stones and nephritis.
| Thomas B wrote: |
| With soluble oxalates present in Warrigal Greens and Native Rosella, couldn't these be removed by blanching or sauteeing with a calcium rich substance, like milk or cheese? |
When we blanch spinach or warrigal greens, and then use it in say a spinach triangle with feta cheese - the soluble oxalates are leached out into the water during the blanching and then if we bake with the feta any remaining soluble oxalates have a high chance of being bound into safe insoluble form by combining with the calcium in the cheese. Perfect!
But the problem is with something that seems to have a very high level of soluble oxalates - which can be occaisionally used raw (witness Eatuast's example of the "Cook and the Chef" and use of raw warrigal greens) or imagine a scenario with use in soup or tea for example - where the soluble oxalates are in solution and even more available. With spinach and silverbeet we get away with it in normal doses, but when levels of soluble oxalates are high, as they seem to be in Hibiscus heterophyllus and rhubarb leaf, there seems little margin for error in preperation. Also, it could be complicated by other compounds that may be potentising the effects of oxalates in some cases.
So we don't go there with Hibiscus heterophyllus in popular culture use. Keep it simple.
Last edited by PeterHardwick on Sun May 10, 2009 7:18 pm; edited 5 times in total |
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PeterHardwick
Dinkum Sheila
Joined: 17 Jun 2006
Posts: 158
Location: Nightcap Ranges, NSW
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| Posted: Sun May 10, 2009 6:53 pm Post subject: |
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By the way. These been a bit of confusion with one of the earlier postings on this thread - where I'm quoted as writing a post (which was actually written by Eataust), supposedly quoting Thomas B (actually quoting me). And my original thread disappeared.
Gremlin's got into the thread. Hopefully it will get sorted soon
Cheers, Pete. |
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