Food Safety Focus (204th Issue, July 2023) – Article 2
Ginkgo Seed Poisoning
Reported by Dr John LUM, Scientific Officer,
Risk Assessment Section,
Centre for Food Safety
In June 2023, the Centre for Health Protection announced a suspected case of ginkgo seed poisoning. The case involved a 57-year-old man who developed dizziness, nausea, vomiting, malaise, headache and rapid heartbeats after consuming about 50 ginkgo seeds, given from a relative, in a soup. This article will give a brief introduction on ginkgo seed poisoning.
Ginkgo biloba and Ginkgo Seed Poisoning
Ginkgo biloba is one of the world's oldest living tree species and has become popular as an ornamental tree in many countries. Eating excessive amounts of ginkgo seeds in one go can cause food poisoning due to the natural toxins present in the seeds. Ginkgo seed poisoning has been reported in mainland China, Korea and Japan, where the seeds are commonly used in different dishes (Figure 1).
Figure 1. Ginkgo seeds are consumed in different cuisines
Toxins in Ginkgo Seeds
Ginkgo seeds contain a number of natural toxins, such as ginkgotoxin (4'-methoxypyridoxine (MPN)), MPN glucoside and cyanogenic glycosides. Among these toxins, MPN is believed to be the major implicated toxin in ginkgo seed poisoning cases.
MPN is found in the food storage tissues of ginkgo seeds. It is chemically similar to vitamin B6 and interferes with its biosynthesis, metabolism and function, including the formation of gamma-aminobutyric acid (GABA) from glutamate, a process that requires vitamin B6. Both GABA and glutamate play a role in transmitting nerve signals from one nerve cell to another. The dual effects of a decrease in GABA and an increase in glutamate are thought to cause seizures in the victims of ginkgo seed poisoning.
Figure 2. The neurotoxic ginkgotoxin (4'-methoxypyridoxine) found in Ginkgo biloba seeds is structurally similar to vitamin B6 and interferes with its biosynthesis, metabolism and function
Clinical Presentation of Ginkgo Seed Poisoning
Acute toxicity is the main concern of ginkgo seed poisoning. Nausea, vomiting, diarrhoea, abdominal pain, confusion and convulsions are common symptoms in ginkgo seed poisoning which usually begin 1 to 12 hours after ingestion.
Children are especially susceptible to ginkgo seed poisoning. In severe cases where large amounts of ginkgo seeds have been eaten, loss of consciousness and deaths may occur. There is no antidote for ginkgo seed poisoning. Treatment mainly centre on alleviating various symptoms, depending on the manifestation of each poisoning case.
Can Cooking Destroy Ginkgo Seeds Toxins?
Cooking cannot completely destroy toxins in ginkgo seeds because MPN is relatively heat-stable. Nevertheless, cooking may reduce the toxicity by inactivating some other heat-labile toxins in the seed such as cyanogenic glycosides. It is worth noting that unripe and uncooked ginkgo seeds are reported to be more toxic, and should not be consumed.
Any Limits on Ginkgo Seeds Consumption?
Ginkgotoxin has not been evaluated by food safety authorities authorities including the Joint FAO/WHO Expert Committee on Food Additives (JECFA), and health-based guidance value has not been established for risk assessment. There is no relevant food safety standard established by Codex. Nevertheless, it has been reported that the ingestion of as few as 10 cooked ginkgo seeds at one time may cause acute poisoning in humans. As such, consumers should limit the intake to a few cooked ginkgo seeds per day, especially for children.
Key Points to Note
- Various natural toxins are present in ginkgo seeds.
- Cooking can reduce but not eliminate the toxicity of ginkgo seeds.
- Ingestion of as few as 10 cooked ginkgo seeds at one time may cause acute poisoning.
Advice to Consumes
- Limit intake to a few ginkgo seeds per day, especially for children, the elderly and individuals with poor health conditions.
- Cook ginkgo seeds before consumption to reduce toxicity, but cooking cannot completely eliminate all toxins.
- Anyone who feels ill after eating ginkgo seeds should seek medical attention immediately.
Advice to Trade
- Provide food safety advice to consumers such as reminding customers not to consume more than a few ginkgo seeds per day especially whe selling in bulk.