Is it true that seeds of biwa (Japanese medlar or loquat) contain harmful matters?

The seeds of Rosaceae (family of roses) including biwa contain a substance called “amygdalin”, which may cause poisoning symptoms if large amounts are consumed.

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<What is amygdalin?>

• A substance naturally contained in seeds and immature fruits of Rosaceae, including biwa, apricots, plums, and peaches.
• If amygdalin is ingested by a human, it changes inside the body to a highly poisonous hydrogen cyanide (hydrocyanic acid).  Ingestion of large amounts of it may cause poisoning symptoms including headache, dizziness, nausea, and vomiting.

< It is wrong to believe that “amygdalin is good for health”.>

• Amygdalin was once called “Vitamin B17” by some people.  As a matter of fact, however, it is never a nutrient essential for human metabolism and no case of deficiency diseases has been reported.  Therefore in recent times amygdalin is not defined as a vitamin.
• Additionally, some alleged anti-cancer properties of amygdalin were negated by the US National Cancer Institute based on their clinical research.
• In overseas countries, health hazards and deaths due to ingestion of large amounts of amygdalin have been reported.

< Amygdalin detected from some foods at high concentrations>

• The Tokyo Metropolitan Government investigated into foods possibly containing amygdalin.
• As a result of the research, amygdaline was detected at a high value from powder of biwa seeds.  (Maximum values: 7,200 ug/g of amygdaline and 980 ug/g of total cyan)
• The Ministry of Agriculture, Forestry and Fisheries based on their research, recommends not to ingest powder of biwa seeds on their website and cautions against cooking recipes using biwa seeds.
• The Ministry of Health, Labor and Welfare notified local governments that, “Biwa seed powder shall in principle be treated as falling within the definition of Paragraph 2 in Article 6 of the Food Sanitation Act (Prohibition of sales of foods containing hazardous substances) if the cyanides (total cyan) detected therefrom exceed 10 ppm (10 ug/g)”.
• Special attention should be paid to food products in forms by which large amount can be consumed at once, such as processed foods from dried and powdered biwa seeds.

< Mature fruit pulp is safe.>

• Because amygdalin is decomposed as the fruits ripen, mature fruit pulp can be safely consumed.
• It is known that amygdalin contained in immature, green ume fruits (Japanese apricots) can be reduced when processed into such foods as ume liquor and umeboshi (pickled ume).