An abundant and undervalued agri-food residue, onion peel may play a relevant role in the transition towards more sustainable packaging. Research conducted at the University of Aveiro (UA) demonstrates that ground onion peel can be directly incorporated into bioplastics, yielding materials with improved functional performance and reduced environmental impact, without the need for complex extraction or purification processes.

The investigation carried out at CICECO – Aveiro Institute of Materials, one of UA’s research units, is based on the incorporation of ground onion peel into matrices derived from starch recovered from industrial residues, namely sludge generated during potato processing. This approach enabled the development of bioplastics with enhanced mechanical properties, increased water resistance, improved gas barrier performance, and antioxidant activity—key requirements for applications in the functional packaging sector.

Beyond technical performance, the concept aligns with two central principles of the circular economy: the full valorisation of residues and the replacement of fossil-based or food-grade raw materials with non-edible by-products. In this way, it contributes simultaneously to reducing environmental impact and alleviating pressure on primary resources.

The work was developed by researchers Mariana Vallejo, Beatriz Esteves, Pedro Carvalho, Manuel Coimbra, Martinho Oliveira, Paula Ferreira and Idalina Gonçalves. In addition to CICECO, the study involved collaboration with the Laboratório Associado para a Química Verde (LAQV) of the Rede de Química e Tecnologia (REQUIMTE), and was carried out within the Department of Materials and Ceramic Engineering, the Department of Chemistry, and the Escola Superior Aveiro-Norte.

A Residue with High Valorisation Potential

Although no systematic public statistics are available regarding the quantity of onion peels sent annually to landfill in Portugal, global figures provide context. Worldwide onion production exceeds 98 million tonnes per year, and it is estimated that approximately 5 percent corresponds to peels—representing around 550 thousand tonnes of residues annually at global level.

Given the relevance of the agri-food and vegetable processing industries in Portugal, the researchers consider it plausible that several thousand tonnes of onion peel are generated each year nationally, particularly by peeling, processing and ready-meal industries. This study demonstrates that, rather than representing an environmental and economic burden, this residue can become a high value-added functional raw material.

Patented Technology with Industrial Potential

A particularly relevant aspect, beyond the published scientific results, is that this technology is already protected by patent, highlighting its potential for industrial transfer. The patent describes the production of active and biodegradable thermoplastics from non-purified starch recovered from industrial residues and onion peel, using conventional processing technologies such as extrusion or compression moulding.

The developed materials exhibit thermal stability, antioxidant activity and adjustable barrier properties. They may be applied not only in active packaging for food preservation or other products, but also in medical devices. According to the researchers, these characteristics reinforce the technological maturity of the solution and its feasibility at industrial scale.

Translated from UA: link.