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Seafood Processing Technical Talk



How Technology Could Make Bone-free Fish a Reality

By David Bosworth, a senior programme manager at X-ray equipment specialist Cheyney Design

Fish is an important part of a healthy diet and today we enjoy a greater variety of fish products than ever before, thanks to major improvements in processing, refrigeration, ice making and transportation.

But for many people there remains one big drawback – the presence of fish bones. Usually long and thin, these sharp bones are at best a frustration and at worse can cause serious health problems if they are swallowed and get stuck in the throat. Supermarkets are very aware of the aversion many of their customers have to fish bones – and, as a result, are pushing processors to make a product that can be “guaranteed bone free”.

How Technology Could Make Bone-free Fish a Reality

X-ray image of a salmon fillet showing a number of bones still present

Automatic deboners swiftly and efficiently take care of most of the problem – but even the very best machines inevitably let the odd bone through. Often the deboner will lift the bone and remove most of it but leave a small section behind – making it even more challenging to detect. That’s when X-ray inspection can often come to the rescue.

X-ray inspection works by passing low-energy X-rays through a product. Different elements absorb different amounts of X-ray, so in the resulting images metals, glass and bone appear darker than the surrounding product. That works fine for many food production lines – but it doesn’t solve the problem of detecting fish bones. The bones are low density, with low mineral contents and are very thin, making them difficult to detect.

Standard end-of-line X-ray inspection equipment uses a 0.4 mm or 0.8 mm resolution sensor to detect contaminants. However, this is insufficient to detect pin bones and other sub-mm diameter bones. To detect such tiny bones requires a 0.05 mm (50 micron) resolution area sensor more typically seen in the medical or electronics industries. This unparalleled level of resolution, combined with low-energy X-ray generators, gives rise to images which can reliably show even the smallest of bones in fish.

These high-quality images are then processed via automatic inspection software that looks for dark features that follow a straight line – taking into account the natural muscle patterns in fish, which would otherwise lead to false rejects.

The production line can be programmed to reject any products where bones over a certain size have been identified. It’s also possible to count the number of bones and so allow through a certain number of small bones that pose little risk to health. This information can also be used to grade fish – sending truly bone-free fish along lane one, for example, while products containing a low number of bones go to lane two, leaving fish with a large number of bones to go to lane three and be reworked.

If fish is reworked, the X-ray image can be provided to a rework station so that operators can see the location of the bone – speeding up the process, as well as satisfying public demand for bone-free fish.