This is karei a flounder white fish that has started to appear in season and this is referred to as kobujime because it has been marinated with kombu and it has a very long taste of umami.
The difference in the levels of glutamate found in the two kinds of fluke sashimi can be explained when we consider that 100g of kombu (makombu) is known to contain 3000mg (3g) of glutamate. When the fluke is placed between sheets of kombu during the time of kobu-jime, this glutamate penetrates thoroughly the flesh of the fish.
Analysis shows that 100g of untreated fluke sashimi contains 12mg of glutamate, compared this with 100g of fluke sashimi treated with kobu-jime, which contains 320mg of glutamate. The kobu-jime treated fluke also contains greater levels of asparagine, the amino acid contained in kombu.