Conductivity and fish freshness - or a new take on fish and chips

Monday, 25 November, 2013

Consumers and retailers could ascertain the freshness of the fish without opening the packaging if an RFID chip that measures freshness is included in the packaging. Consumers could then read the chip with their smartphones before deciding whether or not to buy.

Water temperature, the sex of the fish and the type of food a fish has recently eaten can all influence the speed at which the meat decays and so determining fish freshness is not always straightforward. Even the catch from a single fishing boat can contain fish with very different shelf lives.

To try to make fish selection less risky for consumers, Wageningen University PhD candidate Jenneke Heising is looking at three different ways of measuring the freshness of packaged fish without disturbing the packaging.

Heising decided to look at acidity, conductivity and ammonia as measures of freshness. All three metrics can be measured by including a sensor in the pack.

As the fish decays, various substances are released into the air inside the packaging and they subsequently dissolve in water in the sensor. The ammonia sensor does not appear to be very useful because the substance is only released once the fish is almost ‘off’. Acidity is unreliable because temperature appears to have too much influence on the readings. However, conductivity looks promising, Heising says.

Various substances released from the fish cause water to conduct electricity more easily. At differing temperatures, Heising investigated whether the sensor readings represented how fresh the fish was. “We can see an effect very rapidly and that is just what we need. It seems we’ve found a good method. To confirm that, we’d also like to know in more detail which substances cause that effect. That’s what we’re investigating at the moment.”

Jenneke Heising’s research into three ways of measuring the freshness of packaged fish has been published in the Journal of Food Engineering.


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