Achieving Fish Without Bones Through X-Ray Inspection

The worldwide fish and seafood market, worth $624.20 billion in 2023, is expected to grow at a compound annual growth rate (CAGR) of 6.9 percent between this year and 2028. Enhanced processing, refrigeration, ice production and transportation methods have significantly broadened the commercialization and distribution of fish in diverse product forms over recent decades.

However, a prominent obstacle remains for many consumers — the existence of fish bones. Not only are they an unpleasant interruption in a meal, but they can also lead to serious health issues if swallowed and lodged in the throat. That’s why fish without bones are becoming a top priority for processors, grocery stores and consumers alike.

Deboning machines are automated solutions that deal with the majority of this issue for processors. Yet, even the most efficient machines occasionally miss a bone. Most of these machines function by carving out a V-shaped portion of the filet, striving to minimize the section removed. Furthermore, it typically extracts a piece of the bone, leaving a smaller segment behind, which makes it more difficult to spot. Then there are the “floating bones” — bones that shift during the processing stages.

Especially for high-value fish and products like sushi, boosting the customer’s assurance that they are receiving a piece of fish without bones is vital. Supermarkets are quite conscious of the distaste many customers have for fish bones and are thus encouraging processors to deliver a product that can be labeled “guaranteed bone-free.” This is where the latest X-ray inspection technology proves helpful.

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X-ray inspection functions by transmitting low-energy X-rays through a product. The resulting images display metal, glass and bone darker than the fish due to their different absorption levels. Despite its prevalent use in the broader food industry, fish bone detection still poses a challenge because fish bones have low density, contain minimal minerals and are incredibly thin, making them difficult to find.

Traditional end-of-line X-ray inspection equipment employs a 0.4 mm or 0.8 mm resolution sensor to identify contaminants; however, it’s inadequate to detect pin bones and other sub-mm diameter bones. For detecting such minute bones, a 0.05 mm (50 micron) resolution area sensor is needed, a kind usually seen in medical or electronics industries. The combination of this superior resolution and low-energy X-ray generators produces images capable of revealing even the smallest of bones.

Upon creating a high-resolution image of the fish — possibly including bones — it is processed through an automatic inspection software that doesn’t require human intervention. The software must be able to differentiate between the darker features of the bones and the lighter features caused by the natural texture, which is complicated by freezing, defrosting or excessive processing, which can lead to false rejections.

If bones are detected, manufacturers have two options: either reject the products containing bones or put in place additional control procedures. This might entail notifying the operator to adjust the deboning machine or pinpointing which area of the fish still contains bones. Furthermore, the area can be classified into high-risk (where no bones can be tolerated) or low-risk (where bones are likely to dissolve during cooking).

Historically, the main reason for installing X-ray equipment was metal contaminant detection. But, the ability to detect ever smaller bones is now a crucial factor in the ongoing struggle to enhance product quality. X-ray inspection technology from companies like Sapphire, Marcel and TDI PACKSYS, for example,  provides suppliers a fresh perspective in meeting the public’s demand for fish without bones.