Does cooking or ripening reduce the concentration of solanine in nightshade?

Question

I recall a story from one of my Botany professors where he encountered a woman picking Solanum dulcamara (nightshade) berries. When he asked her what she was doing with them, she responded that her husband had her make a pie from them every year.

As her husband was presumably still alive, and since I regard this particular professor as reliable, what would have removed enough solanine from the berries to avoid ill effects? Does the concentration decrease upon ripening, or would cooking destroy the toxin? Would that also be why we fry green tomatoes?

(As a disclaimer, no-one should eat plants that are known to be poisonous. Even though some people don't react to poison ivy, it is still a bad idea to rub it all over your body.)

Answer 1

If you ask Dr. Duke's phytochemical database, by far the most solanine is found in green potatoe fruits (their skin), with much less in leaves and tissues. Similar values are seen in green tomatoes, with dozens of mg per 100g fruit. There is no value for Solanum dulcamara (doesn't mean there is nothing in it) but it appears to have small quantities of atropine. Furthermore, Wikipedia gives for solanine a minimum toxically effective dose for humans of 200 mg---that's where dizzyness and dispnoe starts---, and gives for children a lethal amount of S. dulcamara of 30-40 unripe berries or less. The amount of solanine increases (in potato) when temperature goes up, because it is produced by plants as an antifungal against rot. Ripening in S. dulcamara and, as we know all ourselves, potato and tomato, destroys solanine, so fully ripe berries seem to be okay. Solanine does not degrade when cooked but is lost with the cooking water. For an account of solanine poisoning from potatoes see e.g. this free paper. Newer potato varieties have much less solanine than those from former times.

http://www.ars-grin.gov/duke/

http://de.wikipedia.org/wiki/Solanin

Know your databases!

Answer 2

First of all there is no solanine in green tomato, there wasn't, and there never will be.

Steroidal glycoalkaloids (SGAs) extracted from tomato leaves and berries (Lycopersicon esculentum Mill.) were separated and identified using optimized reversed-phase liquid chromatography with electrospray ionization (ESI) and ion trap mass spectrometry (ITMS). The ESI source polarity and chromatographic conditions were evaluated. The ESI spectra contain valuable information, which includes the mass of SGAs, the mass of the aglycones, and several characteristic fragment ions. Cleavage at the interglycosidic bonds proximal to the aglycones is the most prominent process in the ESI process. A protonated molecule, [M+H]+, accompanied by a mixed adduct ion, [M+H+Na]2+, was observed for α-tomatine (i.e., m/z 1034.7 and 528.9) and dehydrotomatine (i.e., m/z 1032.6 and 527.9) in positive ion mode spectra. The structures of these tomato glycoalkaloids were confirmed using tandem mass spectrometry. The identification of a new α-tomatine isomer glycoalkaloid, named filotomatine (MW 1033), which shares a common tetrasaccharide structure (i.e., lycotretraose) with α-tomatine and dehydrotomatine, and soladulcidine as an aglycone, is described for the first time. It occurs in significant amounts in the extracts of wild tomato foliage. Multistage mass spectrometry both of the protonated molecules and of the doubly charged ions was used for detailed structural elucidation of SGAs. Key fragmentations and regularities in fragmentation pathways are described and the fragmentation mechanisms involved are proposed.

• 2005 - Analysis of tomato glycoalkaloids by liquid chromatography coupled with electrospray ionization tandem mass spectrometry

Your bitter nightshade really has solanine content:

Alkaloids are well known for their antimicrobial activity. Though all natural alkaloids come from plants, not all plants produce alkaloids. Plants of the Solanaceae family are known for their high alkaloid content. Alkaloids are found in all plant parts like roots, stems, leaves, flowers, fruits and seeds. In the present study, those plant parts of Solanum dulcamara were selected which have been reported to produce a high content of a specific alkaloid: solanine (from unripe fruits), solasodine (from flowers) and β-solamarine (from roots). These alkaloids were extracted from various parts of S. dulcamara by well-established methods and were screened for their antibacterial activity. Human pathogenic bacteria, viz., Enterobacter aerogenes, Escherichia coli, Staphylococcus aureus, were selected for the study. All three alkaloids inhibited the growth of E. coli and S. aureus. However, no significant activity was observed against E. aerogenes. Minimum inhibitory concentration and minimum bactericidal concentration were also evaluated.

• 2009 - Biological activity of alkaloids from Solanum dulcamara L.

The glycoalkaloid content usually decrease by ripening, so that the animals can eat them safely and deliver the seeds. At least that's my observation. So there is a good chance that the ripe fruits are edible...

If they are not, it is hard to get rid of the solanine. Solanine is heat stable it decomposes over 200°C (about 240-260°C afaik) and it is not (poorly) water soluble. So cooking in hot water does not help.

Reduction in concentration of α-chaconine (CHA) and α-solanine (SOL), toxic glycoalkaloids in potatoes, during cooking by 3 procedures was investigated. Raw or cooked potato samples (2 g) were extracted twice with 5% acetic acid solution. The extract was purified on Sep-Pak C18 and CHA and SOL contents were determined by HPLC. Recoveries of CHA and SOL from raw potatoes were 96.5 and 98.2%, respectively, vs. 96.2 and 96.7% from cooked potatoes. >93.9% of CHA and 95.9% of SOL remained in potatoes after boiling. Contents of both were reduced by 15% on microwave treatment. On deep-frying alkaloid contents varied according to temperature. At 157°C, both alkaloids were unaffected; at 170°, potatoes showed a large variation in residual alkaloids. At 210°, alkaloids were partially decomposed; after 10 min heating, 64.9% of CHA and 59.7% of SOL remained. It is suggested that the critical temperature for decomposition of both alkaloids in potatoes may be around 170°. Results confirmed the relatively high stability of CHA and SOL in potatoes under normal home cooking conditions.

• 1990 - Effect of cooking on contents of α-chaconine and α-solanine in potatoes.

Deep frying over 200 °C might help, because it degrades the glycoalkaloids and probably moves them from the fruits to the oil, but be aware that this is an old article... Teflon will burn over 270°C afaik, and you should check the smoke point of the oil, because most of them have in a range of 150°C to 250°C. I guess there are other methods which I don't know of, but I think you don't want to eat that pie... ;-)