Cucurbitacins

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The basic body of all cucurbitacins is cucurbitan .
Small fat leaf ( Bacopa monnieri )
Cucurbitacin E (Elaterin)

Cucurbitacins are bitter substances that mainly occur in the cucurbit and figwort family ( e.g. Bacopa monnieri ). The group is derived from Cucurbitan , a tetracyclic triterpene and steroid . There are around 40 known cucurbitacins. With the exception of the representatives cucurbitacin A, cucurbitacin C and cucurbitacin F, they occur mainly as glycosides .

Occurrence

Cucurbitacins are mainly found in cucumbers ( Cucumis ) and cucurbitaceae (Cucurbitaceae), some cruciferous vegetables (Brassicaceae) and in the Japanese mushroom (Basidiomycetes) Hebeloma vinosophyllum .

There are numerous cultivars among cucumbers , which differ in the presence or absence of cucurbitacin C. This could already be traced back to a single diallelic gene locus (= gene location with two different alleles ) in early studies . The allele Bi (for “bitter”) leads to cucumber plants that become bitter under stress conditions and accumulate around 300 mg / kg fresh weight. This applies both to the fruit, i.e. the cucumber, and to the entire plant. Therefore, the ability to synthesize cucurbitacin C can already be determined in the cotyledon stage . The allele bi (for “not bitter”) prevents this accumulation. Since this discovery at the end of the 1950s until today, the entire - at least Central European - market has been determined by non-bitter cucumbers.

structure

From a chemical point of view, cucurbitacins belong to the group of tri- terpenoids with four ring closures (tetracyclic triterpenes), based on the basic structure of the gonan or cucurbitan. All cucurbitacins are unsaturated derivatives of cucurbitan that carry several hydroxyl and keto groups (an 11-oxo group is characteristic ) and are partially acetylated .

The 40 naturally occurring representatives as well as other synthetically modified ones are divided into 12 different classes, among other things depending on their oxygenation. The cucurbitacins A to S, the norcucurbitacins and the cardiotoxic elaterinid (synonymous with gratiotoxin , colocynthin , alpha-elaterin-2-D-glucopyranoside , curcurbitacin-E-beta-glucoside , coloside A ) are known. Cucurbitacins can be glycosylated .

properties

The cucurbitacins are heat-resistant and hardly soluble in water; their content is therefore preserved when cooking vegetables. Environmental stress, i.e. heat, temperature fluctuations, damp-dry fluctuations, fungal infection of moist plants, as well as overripe and incorrect storage can lead to an increased content of cucurbitacins in pumpkin , zucchini, melon and cucumber in addition to backcrossing .

The bitter taste of the cucurbitacins is still perceptible in very low concentrations (the taste threshold is 10 −6 mol / L). They also have strong laxative, diuretic, antihypertensive and anti-rheumatic effects. In addition, the effect of cucurbitacin as an attractant from the kairomone group has been proven for some species of beetles such as Diabrotica .

toxicity

All cucurbitacins are toxic and also have an insecticidal and fungicidal effect. The cytotoxic effect has been tested experimentally as a chemotherapeutic agent in cancer therapy .

Ornamental and wild pumpkins pose a particular risk of poisoning. By back- mutations or uncontrolled return crossing cultivated pumpkins, also isolated from garden zucchini , with wild pumpkins the cucurbitacins can also severe, fatal in rare cases, food poisoning cause.

The following cases of poisoning were reported:

  • 1981/1982 in Australia,
  • 1984 in Alabama and California,
  • 2001 in New Zealand,
  • 2010 in India
  • and - probably due to the particularly hot weather in July / August 2015 - in Germany.

The LD 50 for cucurbitacin-B in the mouse animal model is 5 mg per kg of body weight after oral ingestion, from which a lethal dose of around 300 mg in humans can be concluded. The strongly bitter taste usually prevents the intake of dangerously high doses. There are no legal norms that determine the maximum level of cucurbitacins in food. However, the plants of the Cucurbita family are listed in 2009 by the European Food Safety Authority (EFSA) in the Compendium of botanicals that have been reported to contain toxic, addictive, psychotropic or other substances of concern .

See also

literature

  • P. Bhandari et al .: Cucurbitacins from Bacopa monnieri . In: Phytochemistry . tape 68 , no. 9 , 2007, p. 1248-1254 , PMID 17442350 .

Web links

Individual evidence

  1. ↑ a b c d Entry on Cucurbitacine. In: Römpp Online . Georg Thieme Verlag, accessed on August 21, 2015.
  2. ↑ JM Andeweg, JW De Bruyn: Breeding of non-bitter cucumbers. In: Euphytica. 8, 1959, p. 13, doi : 10.1007 / BF00022084 .
  3. ↑ Wolfgang Blaschek, Rudolf Hänsel, Konstantin Keller, Jürgen Reichling, Horst Rimpler, Georg Schneider (eds.): Hager's Handbook of Pharmaceutical Practice: Volume 2: Drugs AK. 5th edition, Springer-Verlag, 2013. ISBN 978-3-642-58928-7 . Pp. 809-810. limited preview in Google Book search
  4. ↑ An overview of occurrences and effects in: JC Chen, MH Chiu u. a .: Cucurbitacins and cucurbitane glycosides: structures and biological activities . In: Natural Product Reports . Volume 22, Number 3, June 2005, pp. 386-399, doi : 10.1039 / b418841c , PMID 16010347 (review).
  5. ^ RL Metcalf, RA Metcalf, AM Rhodes: Cucurbitacins as kairomones for diabroticite beetles. In: PNAS . Volume 77, Number 7, July 1980, pp. 3769-3772, PMID 16592849 , PMC 349707 (free full text).
  6. ↑ MS van Kester, JJ Out-Luiting a. a .: Cucurbitacin I inhibits Stat3 and induces apoptosis in Sézary cells. In: Journal of Investigative Dermatology . Volume 128, Number 7, July 2008, pp. 1691-1695, doi : 10.1038 / sj.jid.5701246 , PMID 18200050 .
  7. ↑ T. Liu, M. Zhang et al. a .: Inhibitory effects of cucurbitacin B on laryngeal squamous cell carcinoma. In: European archives of oto-rhino-laryngology. Volume 265, Number 10, October 2008, pp. 1225-1232, doi : 10.1007 / s00405-008-0625-9 , PMID 18309509 .
  8. ↑ a b c Erwin Bachmann: Man after zucchini meal in intensive care unit. In: Heidenheimer Zeitung , August 14, 2015.
  9. ↑ Matthias Karl Bernhard et al .: Cucurbitacin poisoning by pumpkins - a case report ( memento of the original from September 24, 2015 in the Internet Archive ) Info: The @1@ 2Template: Webachiv / IABot / www.schattauer.de archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . Pediatric and Adolescent Medicine 5 (2003).
  10. ↑ Bitterness in Cucumber & Zucchini. UNL Extension: Hort Update, University of Nebraska-Lincoln. Retrieved August 21, 2015.
  11. ^ Richard Lawley, Laurie Curtis, Judy Davi: The Food Safety Hazard Guidebook. Royal Society of Chemistry, 2012, ISBN 978-1-84973-381-6 , p. 264 ( limited preview in Google book search).
  12. ^ The Times (of India), July 10, 2010, accessed August 21, 2015.
  13. ↑ orf.at: D: Man dies of poisoning from homemade zucchini. August 20, 2015, accessed August 21, 2015.
  14. ↑ EFSA Compendium of botanicals that have been reported to contain toxic, addictive, psychotropic or other substances of concern. ( Memento of the original from September 24, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. In: EFSA Journal Volume 7, Number 9, 2009, p. 34. (PDF file)  @1@ 2Template: Webachiv / IABot / www.efsa.europa.eu