Natural Toxins in Food Plants

Toxic Food Components of Plant origin

-> low-molecular-weight endogenous toxins

-> products of secondary metabolism
- species specific and give the plant its particular characteristics
- plant pigments, flavours, and compounds that serve to protect
- impart toxicity to individual when taken orally
- toxins: growth inhibitors, neurotoxins, carcinogens, and teratogens

-> Products of primary metabolism
- energy metabolism (photosymthesis, growth, reproduction)
- they form macronutrients and micronutrients in plants

ALKALOIDS -> glycoalkaloids

Common example:
Solanine, an alkaloid present in small amounts in potatoes while tomatine found in tomatoes

Glycoalkaloids

- ingestion of greened, damaged or sprouted potatoes -> consequence of high levels of glycoalkaloids

- Acute toxicity syndromes in humans have been observed at glycoalkaloid levels of more than 2.8 mg/kg body weight

CYANOGENIC GLYCOSIDES

- taxiphyllin in bamboo shoots, linamarin in cassava,
flaxseeds, and seeds of stone fruits (apricot and peach), seeds of peas and beans such as lima beans, and shell of soya beans, ground almonds powder or paste, marzipan

-clinical signs of acute cyanide intoxication can include: rapid respiration, drop in blood pressure, rapid pulse, dizziness, headache, stomach pains, vomiting, diarrhoea, mental confusion, stupor, cyanosis with twitching and convulsions followed by terminal coma

- acute lethal dose of hydrogen cyanide for humans is reported to be 0.5-3.5 mg/kg bw. Approximately 50-60 mg of free cyanide constitutes a lethal dose for an adult man

LECTINS

- green beans, red kidney beans and white kidney beans

- acute toxicity include severe stomachache, vomiting and diarrhoea

- Lectins can destroy the epithelia of the gastrointestinal
tract, interfere with cell mitosis, cause local haemorrhages, damage kidney, liver
and heart and agglutinate red blood cells

- moist heat to reduce toxicity of lecitin

World Health Organization (WHO). Pyrrolizidine Alkaloids, Environmental
Health Criteria 80. Geneva: WHO; 1988. Available from URL:
http://www.inchem.org/documents/ehc/ehc/ehc080.htm

Australia New Zealand Food Authority. Pyrrolizidine Alkaloids in Food. A
toxicological review and risk assessment. Technical Report Series No.2. ANZFA;
2001. November. Available from URL:
www.foodstandards.gov.au/_srcfiles/TR2.pdf

World Health Organization (WHO). Cyanogenic Glycosides. Toxicological
evaluation of certain food additives and naturally occurring toxicants. WHO Food
Additive Series 30. Geneva: WHO; 1993. Available from URL:
http://www.inchem.org/documents/jecfa/jecmono/v30je18.htm