“The fish stinks from the head” it is not just a proverb that indicates how the blame for problems in a group of any type can always be traced back to those in charge and not to subordinates: it is also a wise phrase, very useful (at the market, for example) to understand if a fish is still fresh or is starting to rot.
It is on the head, in fact, that the first signs of loss of freshness appear, and it is on this basis that a new sensor, developed by an Australian team, works, which is able to evaluate this important parameter in less than two minutes. Its operation is explained in a study published in the journal ACS Sensors.
On the hunt for hypoxanthine. The signs that a fish is starting to go bad are actually concentrated in the head: blurry eyes, bruised gills, bad smells… However, these are signs that can take hours if not days to appear, distorting the evaluation. On the contrary, there are chemical compounds that begin to form immediately after the death of the fish; one of these is called hypoxanthine and is a product of the degradation of nucleic acids: it can therefore be used as a more precise indicator of the freshness of a specimen, or even of a simple fillet.
Degree of freshness. The sensor developed by the Australian team is based precisely on hypoxanthine, and on the use of micro-needles (whose dimensions vary from 25μm to 2000μm) to inject an enzyme into the meat to be analyzed that “disassembles” this molecule. This process changes the electrical potential of the fish, in a way that can be measured by the sensor itself: the results allow us to establish the degree of freshness of the analyzed sample.
Freshness in real time. The sensor was put to the test with a series of salmon meat samples, which were left to rot at room temperature for different periods of time, from a few minutes up to 48 hours. Its performance was satisfactory, as it managed to identify with extreme precision how fresh the fish was, and produced results within around 100 seconds.
From the sensor to the portable kit. The performance of the sensor was finally compared with that of similar, but bulkier and more expensive instruments, which are usually only used in the laboratory: the results have decreed that the new sensor can be put on the market, after fine-tuning.
So it will soon be able to be “packaged” in a portable kit, useful for evaluating in real time the quality of the fish you are about to buy.
