Japanese researchers say they have determined how long people should wait to eat chilled tuna sashimi after thawing.

It is known that some amino acids in fresh fish that bring out savory flavors increase during chilled storage. But if the fish is chilled for a prolonged time, the risk of decay increases.

A group of researchers at the Riken institute and Hiroshima University conducted a study to identify when chilled fish is good to eat.

With a focus on texture and firmness, they used a special microscope to study how fish muscles degrade during chilled storage.

The researchers thawed frozen tuna fillets and stored them at a low temperature to observe changes in muscle structure.

They found there are roughly three degradation processes. There were few changes in 12 hours after thawing, some degradation followed by stabilization from 24 to 48 hours, and only a few muscle fibers left 48 to 72 hours after thawing.

The researchers say they know the best time to eat thawed fish differs among people.

They recommend that people who prefer firm texture eat chilled tuna within 12 hours after thawing.

For those who want to enjoy a good balance of soft texture and flavor, they recommend waiting 24 to 48 hours.

Watanabe Tomonobu, who heads the research team, says the practice of eating raw fish is spreading around the world, but that there are few techniques to evaluate fish freshness outside Japan.

He says that as Japanese scientists, they want to introduce such methods to the world.