Photo/Illutration A portable measurement instrument that evaluates the freshness of seafood using odors (Provided by the National Institute of Advanced Industrial Science and Technology)

An odor-sniffing machine that shows the freshness of fish is expected to further the popularity of sushi and sashimi overseas.

The portable device detects a smell associated with early decomposition. The aroma is a subtle one, and not the stinky ammonia that rotten fish is known for.

The project aims to establish technology to “measure freshness quickly, on site, and in a non-destructive manner,” said Toshio Ito, a senior researcher at the National Institute of Advanced Industrial Science and Technology, better known as AIST.

The device was created by scientists from AIST and the Hokkaido Industrial Technology Center.

Chilled marine products are exported from Japan worldwide by air. The fresher they are, the higher the price tag.

But because few dealers overseas can accurately assess the condition of fish, the marine products have a restricted market. Often they end up at restaurants with Japanese affiliation or similar businesses.

If non-specialists were to have a simple method to determine the state of a fish, seafood could become more accessible to consumers.

One objective indicator of fish freshness is its K value. It is a measure of the decay of adenosine triphosphate, an energy store better known as ATP, which is present in living muscle.

However, assessing the K value directly requires the fish’s flesh to be sampled. Proper equipment, technique and time are needed to do this accurately.

To determine freshness more easily and quickly without sampling fish meat, the researchers decided to rely on smell.

The team first analyzed the odor of freshly farmed yellowtail. Then they collected data from fish that could still be eaten raw. 

They also surveyed yellowtail that must be cooked for consumption. Finally, they took data from a rotten sample.

An analysis of these results led the team to artificially produce indicator gases that simulate the odor of each freshness level. A portable measuring instrument developed by AIST learned those indicator gases as training data.

Then the trials began. Initially, the sensing device was poor at determining freshness. It identified samples correctly only 60 percent of the time.

Improvements were made, and the embedded sensor eventually hit a 95 percent success rate.

The scientists now plan to test their method on other variants of fish.

Meanwhile, another system is also being considered as part of efforts to predict the K value solely by smell.

And Ito believes the system could have applications far beyond raw fish.

“Being able to determine how mature seafood is based on odors will also allow us to decide the best timing for consumption for dried marine products and other articles,” he said.

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