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Food Matters

Spud's Down to Earth Advice on...

CHEMICAL (FOOD) POISONING - POISONOUS PLANTS AND FUNGI

Food poisoning is not just caused by bacteria such as Campylobacter or Salmonella. It can also be caused by the consumption of (familiar) food plants or parts of food plants, poisonous fungi or certain poisonous seeds/berries that might be eaten accidentally.

FAMILIAR FOODS
Some familiar food plants can be poisonous under certain circumstances e.g. rhubarb, potatoes and red kidney beans. All people preparing such foods should be aware of the hazards and necessary precautions in order to ensure food safety.

Rhubarb
Although cooked rhubarb stalks are edible, rhubarb leaves and buds are toxic. It is likely that this toxicity is attributable to the very high levels of oxalic acid, a substance that can interfere with iron and calcium absorption, in rhubarb leaves. There is some evidence that anthraquinone glycosides, which are also present, may be involved in the poisoning mechanism.

Symptoms
The main gastrointestinal symptoms are:

abdominal pain
nausea
vomiting
diarrhoea

Other symptoms may include:

general weakness
burning in the mouth/throat
difficulty in breathing
convulsions, coma and death from cardiovascular collapse in extreme cases

Precautions/Control
Never eat the leaves or buds of rhubarb plants.

Potatoes
Potatoes naturally produce solanine and chaconine, chemicals known as glycoalkaloids, as a defence mechanism against insects, disease, and predators. Potato leaves and stems are naturally high in glycoalkaloids. When potato tubers are exposed to light, they turn green and increase glycoalkaloid production to help prevent the uncovered tuber from being eaten. The green colour is from chlorophyll, and is itself harmless. However, it is an indication that increased level of solanine and chaconine may be present.
Consumption of greened potatoes therefore poses a risk due to elevated levels of solanine, which can cause toxic symptoms.

Symptoms
Solanine poisoning results in symptoms that include:

nausea
diarrhoea
vomiting
stomach cramps
burning of the throat
headaches
dizziness
hallucinations, loss of sensation, and paralysis, fever, jaundice, dilated pupils and hypothermia have been reported in more severe cases.

Symptoms usually occur 8 to 12 hours after ingestion, but may occur as rapidly as 30 minutes after eating high-solanine foods.

Precautions/Control

The safest approach of all is to not to buy or use potatoes that are noticeably spoiled by greening.
As most solanine occurs in the skin or just under the skin of potatoes, if they are well peeled one can reduce the amount of any solanine present by 30-80%. However, as solanine is water soluble it will dissolve into surrounding boiling water. Although this may make the potatoes safer to eat, the chemical is not actually destroyed and therefore the water should not subsequently be consumed or used in making stock or gravy.
The greatest risk arises from the use of green or sprouting potatoes as jacket potatoes (baked in their skins) because the solanine may not be destroyed or adequately reduced.
Deep-frying potatoes at 170^oC is effective at lowering glycoalkaloid levels, but boiling is ineffective and microwaving only somewhat effective.

Red Kidney Beans
Red kidney bean poisoning is usually caused by the ingestion of raw, soaked kidney beans, either alone or in salads or casseroles. Just a few beans can trigger symptoms.

The toxic agent that causes this poisoning is a heat labile (changed by heat) protein called phytohaemagglutinin. This toxin is found in many species of beans, but it is in highest concentration in red kidney beans. The unit of toxin measure is the haemagglutinating unit (hau). Raw kidney beans contain from 20,000 to 70,000 hau, while fully cooked beans contain from 200 to 400 hau.

Symptoms
The onset of symptoms varies from between 1 to 3 hours and is usually marked by extreme nausea, followed by vomiting, which may be very severe. Diarrhoea develops somewhat later (from one to a few hours), and some may report abdominal pain. Although recovery is usually rapid (3 - 4 hours<

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Thursday 9 September 2010