Storage boxes that can detect spoiled food: Using smart gas sensors to prevent food wastage

Die beiden Forscher stehen vor einem geöffneten Kühlschrank und halten eine Vorratsdose und verschiedene Früchte in die Kamera.
© Iris MaurerForschung gegen Lebensmittelverschwendung; Professor Andreas Schütze (l.) und Christian Bur von der Universität des Saarlandes arbeiten mit europäischen Partnern aus Wissenschaft und Industrie an praxistauglichen Verfahren, um die Qualität von Lebensmitteln zu überwachen. Ziel ist, dass weniger Lebensmittel weggeworfen werden, obwohl sie noch gut sind.

Food storage containers that can tell you how long their contents can still be eaten and hand-held food spoilage analysers that can predict how long supermarket fruit and vegetables will remain fresh. These are the goals that the Saarbrücken sensor specialists Andreas Schütze and Christian Bur and their research team at Saarland University are hoping to achieve in an EU-funded project that they are conducting together with partners from academia and industry.

The project, whose overall objective is to reduce levels of food waste, is funded through the EU's Horizon Europe framework programme and offers exciting research opportunities for early career researchers.  

Is that soup from the weekend still safe to eat? What about that piece of ham that has passed its best-before date? And the raspberries? Are they mouldy or still okay? Questions like this come up millions of times a day around the world. As the consequences of eating spoilt food are potentially highly unpleasant, huge quantities of food are simply thrown out every day. It's a similar story in supermarkets, where mountains of fruit and vegetables are regularly chucked. Of course, this sort of wastage could be avoided if we always had access to an expert advisor who could carry out immediate on-site checks to determine how long a particular food is still edible. While that might sound totally unrealistic, a team of scientists across Europe is working to make this a reality.

'We are currently developing practical methods of monitoring food quality. Specifically, we're working on an intelligent storage container that can monitor its contents and on a portable food quality analyser for supermarkets. Simply holding the instrument over crates of unpackaged fruit and vegetables will provide a precise indication of how long the food will remain fresh,' explained Professor Andreas Schütze of Saarland University – an expert in the field of sensor and measuring technology. This would help ensure that less food ends up in the bin. The storage container would indicate whether the contents are safe to eat. This sort of technology would also make it easier for supermarkets to plan their sales strategy. They would, for instance, know the best time to reduce the price of salad vegetables or berries that are nearing the end of their shelf life.

The 'Serenade' project is a collaborative undertaking involving experts across a variety of disciplines in science and industry. The project consortium of ten partner institutions in Belgium, Germany, Italy and Spain includes the universities of Padua, Zaragoza, Leuven and Saarland, the Belgian research institute VITO and five companies. The project members are developing smart tools ranging from the novel sensor system to the sustainable, dishwasher-safe materials they need to be made from. The Saarbrücken research team, led by Andreas Schütze and Christian Bur, a PhD engineer from Schütze's team, are working on the gas sensor system and the associated AI-based analysis model. The scientists in Saarbrücken are specialists at developing highly sensitive gas sensors and at training their technology to draw accurate conclusions about what the sensor detects.

When food ages, we know that it changes its appearance and its taste, but above all it changes its smell. That's why we instinctively smell food that we're unsure about. If something has a sickly sweet or an earthy smell, our desire to eat it disappears fast. When food goes bad, it ferments, turns acidic or becomes rancid. The unpleasant odour we detect is caused by volatile molecules such as ammonia, hydrogen sulphide, ethylene or acetic acid that are released into the air when microorganisms, like bacteria, yeasts or moulds, feed on and decompose the organic substances in our food.

Humans are able to detect these molecules thanks to the millions of olfactory cells in our noses. When these volatile, odorant molecules attach to the olfactory cells, the latter send information to the brain, which then begins to interpret what is going on. The highly sensitive artificial sensory organs that have been developed by Andreas Schütze's research team in Saarbrücken can reliably detect individual odorant molecules from among billions of air molecules. They are able to fish out the few molecules that matter from a vast ocean of gaseous atoms and molecules. In fact, theses sensors are more sensitive than the human nose. 'Our sensors can detect molecules such as ethylene or carbon dioxide, which people are unable to smell,' explained Andreas Schütze.  The sensor system is able to determine the identity and concentration of these trace volatiles. This involves collecting the molecules over a certain period of time and then measuring the amount harvested. 'Our sensor systems make use of the metal-oxide semiconductor (MOS) gas sensors now being developed and refined by our industrial partners. Over the course of many previous research projects, we have refined the systems and the signal processing and analysis used,' said Professor Schütze.

The technology that Schütze and his coworkers have developed makes it possible to track spoilage by identifying the different volatiles released during different stages of the food's storage and shelf life –from the unproblematic initial ripening of the fruit to the point where the composition of the volatile molecules being detected indicates that the food is no longer safe to eat. 'We don't simply measure the concentration of the individual volatile substances, but rather their concentration ratio in air. That's important because it means that we get meaningful results irrespective of the quantity of volatile molecules detected. Put another way, it means that we get reliable measurements even at larger distances between the sensor and the food,' explained Andreas Schütze.

'As odours are often a cocktail of different concentrations of volatile components, they leave their own particular chemical 'fingerprint' in the air. We use these odour fingerprints, or 'smellprints' as they are often known, to determine the condition or spoilage state of the food. We essentially assign individual smellprints to the different spoilage states,' added Christian Bur. Using this approach, the research team is able to train the technology to assess the spoilage state of particular foodstuffs and to predict the spoilage process using artificial intelligence models. The AI-based analyser categorizes and assesses the incoming sensor data, draws relevant conclusions and initiates appropriate actions, such as showing the message 'still fresh for five days' on a display. 'Our approach involves combining microsensors, microelectronics, analytical components and machine learning methods,' said Christian Bur.

The research partners are collaborating closely to ensure that the smart food storage containers and hand-held analysers will be ready for series production at the end of the project. 'The work being undertaken covers a wide range of scientific and technical activities, from assessing the actual state of food spoilage, predicting future spoilage using artificial intelligence, designing and installing the innovative miniaturized gas chromatographs that separate the air intake stream into its components before it reaches the sensors, and developing materials suitable for use in real-life retail environments,' explained Dr. Bur. According to Professor Andreas Schütze: 'The project is international and the problems we're working on are interdisciplinary in nature, making Serenade an ideal environment for young graduate researchers. The project consortium offers a platform for training doctoral students at the exciting interface of food management, sensor and materials technologies, with some conducting research in a university environment and others doing research in an industrial setting.'

The Serenade project has been allocated €1.8m in funding through the MSCA Doctoral Networks programme, which is part of the EU's key funding framework Horizon Europe.

Consortium members: In addition to the team led by Andreas Schütze and Christian Bur at Saarland University, the German participants in the Serenade project are BOSCH Sensortec and the Saarbrücken-based 3S GmbH. Italy is represented by the University of Padua and the company Sirmax S.p.a. The Spanish members are the University of Zaragoza and the company BSH Electrodomésticos España. Participants from Belgium are the University of Leuven, the Flemish Institute for Technological Research VITO and the company Galloo.
Sensors and Eco-fRiendly food-grade matErials for a sustaiNable and smArt fooD storagE and quality monitoring (Serenade)
doi: 10.3030/101072846

Questions can be addressed to:
Prof. Dr. Andreas Schütze
: Tel.: +49 (0)681 302-4663, Email: schuetze@lmt.uni-saarland.de
Dr. Christian Bur: Tel.: +49 (0)681 302-2256, Email: c.bur@lmt.uni-saarland.de
Further information: www.lmt.uni-saarland.de

Press photographs:
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