A considerable amount of fish and seafood is wasted, accounting for approximately 30 % of the total production, according to the Food and Agriculture Organization of the United Nations (FAO).

For animal-derived products, such as fish, typically more than half of the food waste occurs at the end of the value chain in developed countries, including supermarkets, restaurants and consumer households, partly due to over-cautious expiry dates.

In cooperation with the University of Southern Denmark, Danish Technological Institute, Copenhagen University, Fraunhofer Institute for Silicon Technology in Germany as well as industrial partners in Denmark, researchers from the Department of Food Science at Aarhus University have evaluated a new biosensor technology as a real time tool to handle the challenge of food waste by evaluating the freshness and remaining shelf-life potential of fresh marketed fish products.

The biosensor can measure a biogenic marker in the headspace of the fresh fish products and according to the evaluation study it can detect shelf life changes in chilled tuna corresponding to the methods commonly used to define the expiry dates of fresh fish.

But what separates the new biosensor technology from the existing methods in the fish industry?

Professor Derek V. Byrne from the Department of Food Science explains:

- Currently, in industry and retail contexts, the shelf life and expiry date of fresh fish is mainly determined by estimations based on generic shelf life curves or limited data, due to sampling limitations. This results in conservative expiry dates to ensure safety and quality upon consumption.

Accurate methods for estimation of freshness and expiry of fresh fish products do exist, especially the Quality Index Method (QIM) - a well-accepted sensory evaluation of freshness performed by trained assessors, and microbial analysis indicating the microbial load and safety of products. However, these are expensive, time-consuming and invasive methods, limiting their real time application in everyday industrial scenarios.

- Non-invasive and cost-efficient tools, such as biosensors calibrated based on these standard measurements, can allow for increased and real time sampling, creating therefore an effective alternative to set expiry dates and avoid unnecessary food waste, Derek V. Byrne states.

Revealing quality and shelf life with biomarkers

In cooperation with researchers from the University of Southern Denmark, the Danish company AmiNIC ApS, has developed the prototype biosensor technology for measuring the levels of a biogenic amines, which are produced by bacterial activity on amino acids existing in food.

Due to the relation of the production of biogenic amines to microbial activity and implications of those for the safety of food products, they have been highlighted by existing research as potential spoilage biomarkers, especially for scombroid fish such as tuna.

The prototype biosensor was specifically developed to bind cadaverine, since this biogenic amine is present in the gas phase under normal conditions, allowing therefore non-invasive sampling through the air surrounding a food product.

- Our evaluation with key involvement of Aarhus University was carried out by comparing the cadaverine levels measured by the prototype biosensor to the freshness states and expiry date as determined by validated methods - QIM and microbial analyses - performed on the same tuna loins, Derek V. Byrne says.

Imitating an industrial and retail scenario

Taking into account that the cadaverine production may differ across fish species, but even within the same species pending on the supply chain conditions (e.g. processing, packaging, storage, temperature), the potential of cadaverine as a biomarker and prototype biosensor were evaluated in a very specific and controlled context, imitating the import of vacuum packed yellowfin tuna loins for Danish sushi restaurants (sashimi).

After capture and pre-processing, the skinless tuna loins were vacuum-packed and imported to a Danish commercial distributor who delivered them to the Department of Food Science where they were filleted in steaks. During transportation, storage and handling, the loins and steaks remained in chill temperatures (between 0 and 2 °C), following the realistic conditions of this supply chain.

The variance in packaging, beginning with vacuum-packed tuna loins and ending with steaks stored in limited oxygen atmosphere (1-2 °C), was decided in consultation with sushi restaurants to resemble the realistic retail conditions.

Comparing new technology to existing methods

Beyond the biosensor measurements, the cadaverine levels in tuna steak undergoing chilled storage were additionally validated by the liquid chromatography-tandem mass spectrometry (LC-MS/MS) method that gives a very precise measure of the tissue concentration.

Postdoc Niki Alexi from the Department of Food Science was responsible for designing the experimental trials conducted across the different institutes.

- We have determined the freshness and expiry of tuna steaks undergoing chilled storage by validated sensory -QIM- and microbial methodologies. Then we have compared the cadaverine biosensor responses of tuna stored under the same conditions to the validated LC-MS/MS concentrations - and finally compared the sensor responses to the QIM and microbial loads measured during the shelf life experiment.

- The results of this 3 step validation indicate that the biosensor does allow an estimation of freshness and expiry, comparable to other methods such as LC-MS/MS determination of cadaverine, QIM and determination of microbiological counts - and this can be good news for reducing unnecessary waste produced within the fish supply chains.

Taking into account the variability existing among fish species, retail storage temperatures and packaging among others, which in turn may affect the formation of cadaverine, more studies are required to validate the use of the cadaverine sensor for other fish species and supply chain contexts.

- However, the literature existing on cadaverine production for other fish species under different storage conditions gives promising indications for the potential of the cadaverine biosensor as a unified tool for freshness assessment and expiry date allocation for fresh fish products undergoing storage, Niki Alexi concludes.