Agri-food by-product valorisation and safety in sustainable food systems: Hidden hazards, risk–benefit trade-offs, challenges and opportunities

The transformation of agri-food by-products into value-added food components is central to circular economy strategies and sustainable food production. Upcycled materials, including fruit peels, seed cakes, cereal brans, pomace and animal trimmings, ca offer proteins, fibres, lipids, antioxidants, and other bioactive compounds that can be used to enhance nutritional and techno-functional properties of foods. However, these by-products may also carry undesirable substances of chemical and microbiological nature, such as pesticide residues, metals and metalloids, mycotoxins, acrylamide, polycyclic aromatic hydrocarbons and pathogenic bacteria, which may persist or be altered through processing. This review critically maps these food safety hazards across diverse by-product sources, exploring interrelationships and highlighting gaps in detection, characterization, and mitigation approaches. Actionable guidance is proposed, including validation of advanced analytical methods (e.g., matrix-adapted multi-residue analysis and high-resolution mass spectrometry) and risk assessment approaches (e.g., exposure-based evaluation), advancement of green processing technologies (e.g., membrane filtration), and targeted contamination management strategies (e.g., prevention of microbial hazards through controlled processing). By providing an evidence-based framework, this work supports safe, sustainable, and responsible valorisation practices, contributing to advancing food system innovation while safeguarding public health.