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Blowfish Ovaries Pickled in Rice-bran Paste

How can the poison be removed?

Production processes for making blowfish ovaries pickled in rice-bran paste and changes in amount of poison

There are individual differences in the blowfish ovaries that are brought to the processing plant, but they contain 400-1,000 MU/g of tetrodotoxin. After one year of pickling in salt, that amount is reduced to about one tenth of what it was initially—30~50 MU/g. It is surmised that during that time, when the moisture seeps out of the ovaries, most of the tetrodotoxin seeps out with it.
After that, the ovaries are pickled in rice bran for a year and a half to two years or more, tested for toxicity and shipped. According to the standard set by Ishikawa Prefecture, a toxicity level of 10 MU/g or lower is safe, and the ovaries are edible.
It is thought that the tetrodotoxin seeps out of the ovaries along with the moisture, during the process of pickling in rice bran. However, if it only seeped out, there would be a lot of tetrodotoxin left in the salt water and the rice bran. However, if you look at the overall toxicity in the chart below, the toxicity is reduced to one tenth of what it was before processing after one year of pickling in rice bran. It seems that there is some kind of mechanism at work.
A lot of expectation is being placed on the microorganism lactobacillus. It is thought that fermentation caused by this bacterium breaks down the tetrodotoxin that remains in the rice-bran pickles, thus reducing the amount of poison they contain. There is also speculation that non-biological structural changes in tetrodotoxin might reduce the amount of poison.

Changes in Toxicity of Blowfish Ovaries Pickled in Salt and Rice Bran
Time Number of samples Toxicity(MU*/g) Total toxicity**(MU)
Average ±S.D Min Max
Before pickling in salt 35 443±279 15 1050 1.20×106
After pickling in salt 　 　 　 　
1 month after 12 281±69 194 404 1.40
2 months after 34 379±94 163 759 1.40×105
7 months after 33 90±15 65 116 3.14×105
After pickling in rice bran 　 　 　 　 　
1 year after 32 28±5 17 38 1.16×105
2 years afte 12 14±2 11 18 　

*Mouse units
** Total toxicity of ovaries, exudate and rice bran
 -Reference: Chieko Ozawa "Science and Living Things" 25.222 (1987)

However, at the present time there is no scientific proof of how the amount of tetrodotoxin decreases. Further research is anticipated.
The mystery of why the poison disappears remains. That is why it is not possible to change the method of production of blowfish ovaries pickled in rice-bran paste. Poison remaining in the ovaries because of a change in the production process would be a serious problem. By stubbornly preserving traditional production methods that have been used for a long time without causing any accidents, we can continue to enjoy the sophisticated flavor of a miraculous food that is unique in the world.
 -Reference: Chieko Ozawa "Science and Living Things" 25.222 (1987)