Compostable, edible, made from apples: the label that reduces the environmental impact of food packaging

Some objects are so small that they seem marginal. A sticker on the skin of an apple, for example. We peel it off absent-mindedly, or it ends up in the organic waste bag, or it remains attached to the fruit until the moment of consumption. And yet, behind that fragment of packaging lie some of the major challenges of sustainability in the agri-food sector: reducing plastic, avoiding contamination in organic waste, improving composting, ensuring food safety, protecting product authenticity and communicating traceability.

This need gave rise to APPEAL - Agrifood Protected by Printable Edible Authenticating Label, the project coordinated by Politecnico di Milano and funded by the Italian Fund for Applied Sciences (FISA) of the Ministry of University and Research. Led by Carlo Spartaco Casari, Professor of Physics of Matter at the Department of Energy, APPEAL involved seven scientific and industrial organisations, including Consorzio Melinda, the University of Ferrara, Consorzio Innovazione Frutta and Enigma, a startup and spin-off of Politecnico di Milano co-founded and led by Alessandro Vidale and Sonia Peggiani. In the laboratory, the research work also saw Andrea Macrelli, Margherita Orazi and Anna Facibeni playing a leading role in the development of the materials and formulations.

The result is a label for fruit and vegetable products that is not only an alternative to plastic, but is edible, compostable and traceable. One of its most innovative aspects is that the label can also be obtained from by-products of apple processing: a material designed to withstand the supply chain, adhere to the surface of the fruit, be printed with readable information and, if accidentally ingested, be safe.

We met Carlo Spartaco Casari, Andrea Macrelli and Alessandro Vidale in the laboratory, where this complexity takes concrete shape: among materials to be formulated, surfaces to be tested, inks to be made compatible with food and prototypes to be brought closer to industry needs. The strength of APPEAL perhaps lies precisely here: in showing that even a simple object from our everyday experience can become a laboratory of innovation.

CC: The starting point was very concrete: finding an alternative to plastic labels applied to fruit and vegetable products, in compliance with the new European PPWR regulation. It is an issue that concerns the entire supply chain, but for a company like Melinda it was particularly urgent, because the sticker on apples has to work under far from simple conditions: damp, waxy surfaces, different from one variety to another, passages through water, cold, handling and storage times. Compostable alternatives already existed, but they were not designed to meet all these requirements. APPEAL therefore stems from a very precise industrial request: to develop a sustainable label that was not only compostable, but also suitable for real use on fruit.

AV: The meeting with Melinda happened almost by chance, during a trade fair in 2022. Sonia and I were presenting a technological solution for anti-counterfeiting labels: for the ink we used special materials, carbon nanostructures, which can act as markers for creating unique codes. This solution can have numerous applications, especially for documents such as passports. Melinda was also interested in this functionality for its own labels; from that meeting, the industrial need linked to the European regulation Carlo mentioned also emerged.

CC: This project was born in a different way from many lines of academic research. Not from a fundamental discovery for which possible applications are then sought, but from an urgent industrial problem, which we tried to transform into applied research. It was almost the opposite path compared with other projects: here, a company need gave us a very precise objective, and that objective guided choices, experiments and priorities from the very beginning.

AM: The European regulatory requirement on packaging set a very clear constraint: reducing the use of plastic materials and making certain packaging elements, including food labels, compatible with composting. That is where we started. But with APPEAL we wanted to take one more step: not limiting ourselves to developing a compostable sticker, but designing an edible label, that is, one made of materials compatible with food and with the entire food supply chain. In this way, the sticker is no longer just something to be disposed of better, but becomes part of a new idea of packaging: more sustainable, safer and more functional.

AM: Using the apple itself to produce the label was something we initially had not even imagined. The project constraint was to create a label made only of materials of plant origin; this requirement is already challenging in itself, because some materials well suited to this use derive from crustaceans or beeswax.

Together with Margherita and Anna, who have a background in chemistry, we worked on plant-based food formulations; from this research came the idea of using apple pomace, which is what remains after juice extraction: a mixture of peel, pulp, seeds and stems. It is not exactly “waste”, because it retains potential value, but rather a by-product that the company still has to manage. In the laboratory, we dried it, ground it, sieved it and turned it into a fine powder, which was then mixed with other food ingredients — plasticisers, thickeners, emulsifiers — until a continuous film was obtained.

We can therefore speak of upcycling: the residue is not only reused, but acquires a higher value.

CC: The apple returns to the apple, in the form of a label. The line developed with the by-product in fact retains a visually natural appearance, with a slight roughness and its own colour. It does not imitate plastic: even at first glance, it declares itself to be another material.

In parallel, we developed a second line, more transparent and similar in consistency to a flexible plastic, but obtained from commercially available food products. We wanted to pursue both directions because the first line has a strongly identity-based appearance, since it is also made of apple, while with the second we wanted to create a product that could also open the way to different applications, in other sectors or with other products.

CC: The apple returns to the apple, in the form of a label. The line developed with the by-product in fact retains a visually natural appearance, with a slight roughness and its own colour. It does not imitate plastic: even at first glance, it declares itself to be another material.

In parallel, we developed a second line, more transparent and similar in consistency to a flexible plastic, but obtained from commercially available food products. We wanted to pursue both directions because the first line has a strongly identity-based appearance, since it is also made of apple, while with the second we wanted to create a product that could also open the way to different applications, in other sectors or with other products.

AM: In the laboratory, the apparent simplicity of the sticker proved to be a formulation challenge. The material had to be flexible but not fragile, continuous but thin, printable with food-grade inks, resistant to humidity, cold and the various stages of the supply chain. At the same time, we could not introduce components incompatible with food consumption.

At the beginning we had materials that broke as soon as we touched them, others that seemed to work but then deteriorated with the glue, or did not behave as we hoped in the climatic chamber. Even small variations in ingredients, temperature or volume completely changed the result. The glue, also edible and compostable, was a further challenge: finding the right balance between film, adhesive and printing required about two hundred formulations and many subsequent tests.

The material’s testing ground was not only the laboratory: APPEAL had to pass real trials. Seven apple varieties were tested, under different temperature and humidity cycles.

AM: Since each component was selected from food-grade ingredients, we were starting from a good safety basis. But for an application of this kind, that is not enough. The University of Ferrara and Consorzio Innovazione Frutta, which were involved in the project, carried out biocompatibility and food safety tests.

The final formulations, including colourants and markers, passed the safety checks for consumption and food contact. At the time of the interview, compostability tests are still ongoing: a long procedure, taking several months, which assesses the disintegration of the material and the absence of ecotoxic effects on the soil and on plant growth.

The project also involved consumers. In two focus groups, different versions of the label were presented, with different colours, shapes and QR codes. The reactions were positive and brought out valuable insights and observations because they bring the research back into contact with the everyday gesture of those who buy and consume.

AV: The sticker can integrate different levels of information and security. The first, most immediate one is the QR code: readable with a smartphone, it can link to the producer’s website, the lot, the origin or other information about the supply chain. Looking ahead, it can become a tool for communicating the product transparently, but also for activating connected digital services.

A second level concerns authenticity: some labels incorporate a fluorophore, that is, a molecule which, when illuminated with UV light, emits a visible response that leads to a colour change. A partner company in the project has also developed an application capable of comparing the image of the sticker in normal light and in UV light, recognising shape and colour variation through an artificial intelligence algorithm and therefore confirming the authenticity of the labelled product.

Finally, there is a more specialised level, designed for internal company controls, for which we drew on our research experience with security markers and inks. In this case the challenge was even more delicate: adapting know-how developed for anti-counterfeiting applications to a food context, replacing non-edible materials with molecules compatible with the project’s requirements.

CC: APPEAL is an applied research project, not yet a commercial product. The next step concerns scale-up: moving from the production of sheets in the laboratory to quantities, rhythms and processes compatible with industry. Making one hundred millilitres of semi-finished product is one thing; making litres, or kilos of material, is another: times, temperatures, viscosity and mixing methods all change.

We have already started trials with a company specialised in food printing and pastry supplies, because it uses processes close to those tested in the laboratory. Many aspects remain to be defined: production of the film, application of the adhesive, integration with labelling machines, costs, partnerships and the commercial model.

AV: One encouraging element is the willingness of industrial counterparts to consider modifications to labelling machines as well, if necessary. In terms of valorisation, the patent application for the label was filed by Enigma S.r.l., a startup and spin-off of Politecnico di Milano. The search report was positive: an important step towards protecting the technology and its possible transfer to the market.

CC: Preparing the apple by-product in quantity also requires dedicated tools and procedures. At the beginning, we did everything by hand: from grinding to sieving. But even the machinery we later purchased is suited to laboratory production and would need to be scaled up to industrial techniques.

AM: We have already carried out some tests with other fruit and vegetable products: kiwis, peppers, oranges, fennel. But each supply chain has its own conditions. An apple can be handled in water tanks and then labelled while damp; an avocado can travel refrigerated or frozen; a citrus fruit has a completely different surface and handling process. For this reason, extension to other products will require specific tests.

There is also the possibility of using by-products from other plant-based supply chains that have residues with high potential value, such as citrus fruits, tomatoes, artichokes and many others. But not all materials behave in the same way, and not every waste product can become a film. The idea is nevertheless very compelling: imagining labels and packaging that arise from the residue of the same product or the same supply chain.

AV: Trade fairs have opened up further scenarios; there we had the opportunity to meet many different organisations. From bakery to pastry, from catering to haute cuisine, the material could be used to personalise food products, dishes, desserts, pizza bases or hot drinks, always after specific tests on temperature, humidity, freezing and melting. In some applications, such as haute cuisine, for example, the adhesive might not even be necessary: the label would become a decorative, informative or identity-related element, directly in contact with the food.

CC: This experience shows a possible “third way” for young researchers: not only an academic career or direct entry into a company, but also entrepreneurial paths born from research. Andrea, Margherita, Anna, Alessandro and Sonia brought different and complementary skills. People really do make the difference. Funding, tools and machinery are needed, but without the right team you do not achieve this kind of result. APPEAL required scientific and technical expertise, but also the ability to listen to a company, accept marketing constraints, change priorities, seek compromises and transform a prototype into something that can engage with the market.

AV: A startup is a radical change of perspective: in the world of research, you focus on the properties of materials and on scientific questions; in a startup, you have to arrive at a product. And around that product there is everything else: patents, contracts, financial and legal management, consultancy, safety, commercial relations. It is stimulating to deal with many different things, but it also requires great mental flexibility.

AM: For me too, APPEAL meant changing the object of study; previously, during my PhD, I worked on materials for batteries. The most fascinating part of the project was getting hands-on with the materials and seeing, step by step, an apple by-product turn into a sticker with real functionalities. At the beginning, we found ourselves facing a mountain of literature to study and an enormous quantity of powders, ingredients and many tests to carry out. Now we have in our hands the result of all our research, and seeing that it passes the tests and arouses great interest gives me great satisfaction.

CC: I would really like to see it on the market. It would be a concrete example of a project that starts from basic research, meets an industrial need and becomes an everyday application, something that can be seen and touched with one’s own hands. Or, in this case, even tasted.