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Food Safety Focus (149th Issue, December 2018) – Incident in Focus

The Ginkgo – A Living Fossil with Poisonous Seeds

Reported by Mr. Johnny CHU, Scientific Officer,
Risk Assessment Section, Centre for Food Safety

In November, 2018, the Centre for Health Protection of the Department of Health announced a case of ginkgo seed poisoning.  The case involved a 38-year-old woman who developed dizziness, nausea, tremor, headache and abdominal pain after consuming around 50 to 60 fried ginkgo seeds purchased from a street hawker.

Ginkgo biloba

Ginkgo biloba, commonly known as ginkgo, the maidenhair tree, and Yín Xing, is famous for having witnessed dinosaurs roaming the earth as well as their sudden disappearance from the earth.  Once thought to be extinct by some researchers in the West, the ginkgo is native to China and now has made its way around the world.  Ginkgo is often called a living fossil because it has remained essentially unchanged for 200 million years and can be found in the fossil record at the same time as the dinosaurs.

(a)Ginkgo seeds consumed as food

(a)Ginkgo seeds consumed as food

Ginkgo Seeds as Food

The ginkgo seeds (Bai Guo in Chinese) are commonly consumed as food in Asia (especially China, Japan and Korea); they are used as an ingredient in congee, soups, dinner dishes and desserts.  It is also not uncommon to see food premises serving Japanese-style grilled ginkgo seeds and street hawkers selling fried/roasted seeds.

(b)Ginkgo seeds

(b)Ginkgo seeds

Toxins in Ginkgo Seeds

Natural toxins are present in a wide variety of plants (Table below), some of which are commonly consumed as food, including ginkgo seeds.  Ginkgo seeds have poisoning effects due to the presence of toxins such as 4'-methoxypyridoxine (MPN) and cyanogenic glycosides; and MPN is believed to be the incriminated chemical in food poisoning cases.

MPN is found in the food storage tissue of the ginkgo seeds.  It has an antivitamin B6 activity and inhibits the formation of 4-aminobutyric acid (GABA) from glutamate.  GABA and glutamate play a role in transmitting nerve signals from one nerve cell to another.  The dual effect of a decrease in GABA and an increase in glutamate is believed to induce seizures and convulsions.  Cooking cannot inactivate MPN; however, it can reduce the toxicity of the seeds, probably by inactivating heat-labile toxins such as cyanogenic glycosides.  It is worth noting that immature and uncooked ginkgo seeds are more toxic. 

Examples of food poisoning cases caused by plant and mushroom toxins in Hong Kong from 2008 to 2018.

Plants

Toxins

Symptoms

Preventive measures/
remarks

Ginkgo seeds

4'-methoxypyridoxine and cyanogenic glycosides

Nausea, vomiting, diarrhoea, abdominal pain, confusion and convulsions

  • Cook ginkgo seeds.
  • Limit intake to a few seeds per day.

Wild taro

Calcium oxalate raphide

Numbness of the tongue and swelling of lips

  • Do not pick and consume wild plants.

(1)  Wild mushrooms

(2)  Edible mushrooms mixed with poisonous mushrooms

Mushroom toxins

Nausea, vomiting, abdominal pain, profuse sweating, hallucination, coma or other neurological symptoms

  • Do not pick wild mushrooms.
  • Do not buy mushroom products which are doubted to be mixed with unknown species.

Fresh Jin Zhen

Colchicine

 

Vomiting, nausea, abdominal pain and diarrhoea

  • Soak well in water and cook thoroughly.
  • Commercially processed Jin Zhen and dried Jin Zhen are safe to eat.

Raw bitter apricot seeds

Cyanogenic glycosides

Constriction of the throat, nausea, vomiting and headache

  • Soak and cook thoroughly in boiling water (e.g. soup) for a longer period.

Narcissus bulbs

Toxic alkaloids

Nausea, vomiting, diarrhoea and dizziness

  • Do not eat narcissus bulbs.

Wild fruits

Plant toxins

Abdominal pain, vomiting, diarrhoea and burning sensation of the throat

  • Do not collect and eat wild fruits from parks or the countryside.

Public Health Significance

Acute toxicity is the main concern of ginkgo seed poisoning. Nausea, vomiting, diarrhoea, abdominal pain, confusion and convulsions are the classic symptoms which usually begin 1 to 12 hours after ingestion.  Children are especially susceptible to this type of food poisoning.  In severe cases where large amounts have been taken or in susceptible individuals, loss of consciousness and deaths may occur.  It has been reported that ingestion of 10 to 50 cooked seeds at one time can cause acute poisoning.

Action Taken and Preventive Measures

Regarding the case of ginkgo seed poisoning, a press release and a message on Facebook were issued by the Department of Health and the Centre for Food Safety respectively on 5 November 2018 to remind the public not to consume uncooked ginkgo seeds and to limit the daily intake of ginkgo seeds. Particular attention should be given to children, the elderly and individuals with poor health conditions.

Key Points to Note:

  1. Natural toxins are present in ginkgo seeds.
  2. Cooking can reduce but cannot eliminate the toxicity of the seeds.
  3. Ingestion of 10 to 50 cooked seeds at one time can cause acute poisoning.

Advice to the Trade

Advice to the Public