Winery By-Products as Sustainable Sources of Proteins and Bioactive Peptides: Characterisation, Extraction and Potential Applications Under the EU Regulatory Framework

The global wine industry generates approximately 20 million tonnes of organic residues annually, representing a significant environmental and management challenge. While phenolic compounds from winery by-products have been extensively studied, protein and peptide fractions remain underutilised. This review provides a systematic overview of proteins derived from major winery side streams, including grapevine leaves, stems, pomace, seeds, and wine lees, with emphasis on their characterisation and recovery. Conventional and emerging extraction strategies are evaluated, with particular attention to green technologies such as ultrasound-assisted extraction (UAE), pulsed electric fields (PEF), and natural deep eutectic solvents (NADES) in the context of sustainable and resource-efficient processing. Enzymatic hydrolysis is discussed as a key approach for converting complex proteins into bioactive peptides with antioxidant, antimicrobial, and antihypertensive properties. Potential applications in agriculture, plant protection, animal nutrition, and food systems are considered, together with the implications of the EU circular economy regulatory framework. Overall, winery by-products are highlighted as promising nitrogen-rich secondary resources, and the review outlines valorisation pathways supporting nutrient recycling, waste reduction, and the development of a more sustainable agricultural bioeconomy.