Exploring the chemical potential of ‘Vinhão’ grape stalks for circular economy applications

The Portuguese wine industry produces tons of waste annually, during processing, this waste accumulates, leading to problems such as attracting pests and unpleasant odors. This waste is burned in the open, releasing greenhouse gases and heat into the atmosphere, causing damage to the environment. Among the various residues generated in the production of wine, the grape stalks stand out, the structure of the bunch removed before the winemaking process.The study explores the chemical characterization of grape stalks (G.S.) from Portuguese ‘Vinhão’ red grapes, aiming to upcycle wine industry residues in a circular bioeconomy framework. The analyses performed for this raw material (G.S.) were proximal composition, total phenolics, antioxidant activity, colorimetry, Fourier Transform Infrared Spectroscopy with Attenuated Total Reflectance (FTIR-ATR), fatty acid and mineral profile. Dried and milled stalks were analyzed for moisture (5.31 %), ash (7.67 %), lipids (0.60 %), protein (3.28 %), and insoluble fiber (55.00 %). With the results of the antioxidant activity, the extract obtained from grape stems, about the DPPH (0.64 mmol Trolox. g⁻¹) and ABTS (0.39 mmol Trolox. g⁻¹) radicals, resulted in an expressive capacity to neutralize free radicals, providing a significant antioxidant potential. These findings suggest that the compounds present in the extract may contribute to the reduction of oxidative stress, making it a promising alternative for applications in the food and pharmaceutical industries. FTIR confirmed lignin, polysaccharides, and polyphenolics. Fatty acid profiling revealed that linoleic acid (PUFA, 34.80 %) and oleic acid (MUFA, 14.48 %) were major components. Mineral analysis showed high levels of Mn, Fe, and Mg, surpassing recommended daily intakes. These findings highlight the potential of ‘Vinhão’ stalks as sustainable food and feed supplements, reducing waste and enhancing wine industry circularity.