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I often buy frozen vegetables, defrost and eat them.

Recently, I came across an article that says Lima Beans contain Cyanide, should be thoroughly cooked and then eaten.

Do frozen Lima Beans come precooked or are they supposed to be cooked before consuming them?


Location: Canada
If you need product information, please do let me know.

  • Apples contain cyanide, too. Of course, it's in the seeds. (but lots of apple juice has it, because of how they extract the juice) – Joe Mar 21 '16 at 20:41
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Raw lima beans do contain a compound, a cyanogenic glycoside, which would release cyanide if ingested raw.

(1) http://www.atsdr.cdc.gov/toxprofiles/tp8-c1.pdf

(2) http://www.foodsafety.govt.nz/elibrary/industry/Cyanogenic_Glycosides-Toxin_Which.pdf

(3) http://www.ncbi.nlm.nih.gov/pubmed/24863488

(4) http://article.sciencepublishinggroup.com/pdf/10.11648.j.jfns.20140204.21.pdf

Frozen lima beans are typically uncooked. The usual stories about cooking many varieties of lima beans quote boiling for at least 15 minutes and discarding the cooking water.


Now trying to unwind the folklore....

(A) What is the toxicity of cyanide?

Cyanide in the body is an anion, which has a negative charge. In order to balance the charge a cation, a positive charged ion must be present too. Since beans would be eaten let's look at the toxicity of sodium cyanide.

The dose of sodium cyanide which would kill 50% of the subjects (LD-50) is about 15 mg/kg of body weight for mammals. But by weight sodium cyanide is 47% sodium and 53% cyanide. So the lethal dose for cyanide itself would be about 7mg/kg.

So a 154 pound person weighs 70 kg (2.2 lbs per kg). 70*7 is approximately 500 mg or 0.5 grams.

(B) Does the cyanide content of lima beans vary?

Yes. Supposedly the varieties of lima beans consumed in the US (and presumably Canada) are specifically chosen to be low in cyanide.

Cyanide in "lima beans [varies] between 15 and 500 mg HCN/kg fresh weight (Bickerstaff, 2003)" quoted from:

(5) http://members.ecetoc.org/Documents/Document/JACC%20053%20Vol%20I.pdf

But I can find the original source by Bickerstaff in the article.

(C) How much does cooking reduce the cyanide?

There is a paper which notes that in other foods the cyanogenic glycosides are 100% destroyed by cooking.

(6) http://www.onlineresearchjournals.org/JBFSR/pdf/2013/jan/Onyeike%20et%20al..pdf

(D) How does the bean produce cyanide?

The cyanide in lima beans is present as "pure" cyanide, but a cyanide compound called a cyanogenic glycoside. Lima beans contain two such compounds, linamarin and lotaustralin

Linamarin

enter image description here

Lotaustralin

enter image description here

I'll quote Dr. G. Speijers of the National Institute of Public Health and Environmental Protection, Laboratory for Toxicology, Bilthoven, The Netherlands

(7) http://www.inchem.org/documents/jecfa/jecmono/v30je18.htm

The first aspect is the processing of plant products containing cyanogenic glycosides. When the edible parts of the plants are macerated, the catabolic intracellular enzyme ß-glucosidase can be released, coming into contact with the glycosides. This enzyme hydrolyzes the cyanogenic glycosides to produce hydrogen cyanide and glucose and ketones or benzaldehyde.

It seems that the human gut also has bacteria which are capable of hydrolyzing the cyanogenic glycosides to produce hydrogen cyanide.

  • For reference, the bag in my freezer says to boil 12-15 minutes ("until tender") but says you can steam them just 6-8 minutes, so even the manufacturers seem to be a bit fuzzy about exactly how much cooking is necessary. – Cascabel Mar 22 '16 at 5:03
  • I like southern cooking. I cook them until soft, drain off water and mash a few to make sort of a sauce with a bit of water. Add butter, some salt and black pepper. – MaxW Mar 22 '16 at 5:05
  • @Jefromi Yes, you're right. The bag in my freezer says the same. – Dumbledore Mar 22 '16 at 13:11
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Lima beans contains Cyanide in small quantity [1].

I am not certain, nor do I want to make an uneducated guess as what quantity per/day/year one needs to eat in order to be sick (fatally or not)

They need to be cooked to let the cyanide evaporate as a gas; so cook'em up.

[...]Cooking the beans uncovered allows the poison to escape as a gas. To be perfectly safe, drain the cooking water.[...]

http://www.npr.org/templates/story/story.php?storyId=11861532

[1] http://www.atsdr.cdc.gov/toxprofiles/tp8-c1.pdf

  • Many frozen vegetables are precooked. Are you saying that's not the case with lima beans? – Cascabel Mar 21 '16 at 18:49
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    Thanks for your answer. However, I need to know whether frozen lima beans needs to be cooked or not? – Dumbledore Mar 21 '16 at 19:11
  • Check what brand you have, most of the frozen beans I've used were raw. (YMMV) – Max Mar 22 '16 at 1:10

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