The global wine industry generates millions of tonnes of by-products annually, including grape stems, pomace, and skins. These sidestreams, like those of other fruits and vegetables – often discarded or underutilized, are rich in bioactive compounds such as phenolic acids, flavonoids, anthocyanins, selenium, and tryptophan.
Recent research highlights the potential of upcycling these by-products into nutraceutical ingredients, offering a sustainable solution to reduce waste, promote circular economy principles, and address food loss in the agri-food chain. The key findings from a 2025 study published in Food Chemistry (Fernandes et al., 2025), to follow.
The challenge: wine industry by-products
The wine industry is a significant contributor to agricultural waste, with approximately 52% of the 73 million tonnes of grapes produced annually being processed into wine. This generates substantial amounts of by-products, including grape stems, which are often discarded or used in low-value applications such as animal feed or fertilizer.
The disposal of these by-products poses environmental challenges, including landfill accumulation and greenhouse gas emissions. However, these sidestreams are a treasure trove of bioactive compounds with potential health benefits, making their valorization a promising avenue for sustainable development.
Bioactive compounds in grape stems
A 2025 study by Fernandes et al. analyzed grape stems from four red grape varieties (Tinta Amarela, Sousão, Touriga Franca, and Touriga Nacional) in Portugal’s Douro Demarcated Region. The research identified high levels of bioactive compounds, including:
– phenolic compounds. Grape stems are rich in phenolic acids, flavonols, anthocyanins, and proanthocyanidins, which exhibit strong antioxidant properties.These compounds play a crucial role in neutralizing free radicals, reducing inflammation, and protecting against oxidative stress-related diseases such as cancer and neurodegenerative disorders.
Proanthocyanidins and catechin derivatives were the most abundant phenolic compounds, with concentrations ranging from 2943.32 to 5788.39 mg/g dry weight. Touriga Nacional stood out with the highest phenolic content (60.12 mg gallic acid equivalents/g dry weight) and antioxidant capacity (0.78 mmol Trolox/g);
– tryptophan. An essential amino acid and precursor to serotonin and melatonin, tryptophan was found in significant amounts in grape stems. Tryptophan’s role in mood regulation, sleep, and cognitive function makes it a valuable ingredient for nutraceuticals targeting mental health and well-being. Tinta Amarela and Touriga Nacional exhibited the highest tryptophan levels (356.98 mg/kg and 316.06 mg/kg, respectively).
Selenium was also detected in grape stems, albeit in lower concentrations. Touriga Nacional had the highest selenium content (0.22 µg/kg dry weight). While natural selenium levels in grape stems are low, biofortification strategies could enhance their selenium content, addressing global selenium deficiencies. This mineral is indeed essential for antioxidant enzyme function and immune health.
Health benefits and nutraceutical potential
The bioactive compounds in grape stems offer a wide range of health benefits, including:
– antioxidant activity. Phenolic compounds scavenge free radicals, reducing oxidative stress and inflammation;
– cognitive and mood support. Tryptophan’s conversion to serotonin and melatonin supports brain health, mood regulation, and sleep quality;
– protein and enzyme synthesis. Selenium and tryptophan are essential for protein biosynthesis and enzymatic functions.
These properties make grape stems a promising source of nutraceutical ingredients for functional foods, dietary supplements, and pharmaceuticals. Consumer information on these properties in European Union remains linked to the implementation of the Nutrition and Health Claims Regulation, which continues to pose significant challenges.
Circular economy and sustainability
The valorization of grape stems aligns with the principles of a circular economy, where food loss and waste (FLW) is transformed into valuable resources. By upcycling wine sidestreams, the wine industry can:
– reduce food loss. Minimize the environmental impact of grape processing by repurposing by-products;
– generate revenue. Create new income streams through the production of high-value nutraceuticals;
– promote sustainability. Support the United Nations Sustainable Development Goals (SDGs), particularly Goal 12 (Responsible Consumption and Production) and Goal 13 (Climate Action).
Future directions and applications
To fully realize the potential of grape stems as nutraceutical ingredients, further research is needed to:
– optimize extraction methods. Develop efficient and sustainable techniques for extracting bioactive compounds from grape stems;
– enhance bioavailability. Study the bioavailability and bioaccessibility of phenolic compounds, selenium, and tryptophan in human models;
– explore biofortification. Investigate biofortification strategies to increase selenium content in grape stems;
– develop functional foods. Create innovative nutraceutical products, such as supplements, beverages, and snacks, enriched with grape stem extracts.
Provisional conclusions
The upcycling of wine sidestreams into nutraceutical ingredients represents a win-win solution for the wine industry, the environment, and human health. By transforming grape stems into valuable bioactive compounds, we can reduce waste, promote sustainability, and address global health challenges.
This innovative approach not only supports the circular economy – in addition to precedent studies on pomace upcycling– but also paves the way for a more sustainable and resilient agri-food chain. The #Wasteless research project aims to collect these solutions in an online toolbox, for the benefit of all stakeholders.
Dario Dongo
References
(1) Fernandes, R., Medrano-Padial, C., Dias-Costa, R., Domínguez-Perles, R., Botelho, C., Fernandes, R., & Barros, A. N. (2025). Grape stems as sources of tryptophan and selenium: Functional properties and antioxidant potential. Food Chemistry: X, 26, 102260. https://doi.org/10.1016/j.fochx.2025.102260
(2) Baenas, N., García-Viguera, C., Domínguez-Perles, R., & Medina, S. (2023). Winery by-products as sources of bioactive tryptophan, serotonin, and melatonin: Contributions to the antioxidant power. Foods, 12(8), 1871. https://doi.org/10.3390/foods12081571
(3) Barros, A., et al. (2014). Evaluation of grape (Vitis vinifera L.) stems from Portuguese varieties as a resource of (poly)phenolic compounds: A comparative study. Food Research International, 65, 375–384. https://doi.org/10.1016/j.foodres.2014.07.021
(4) Costa-Pérez, A., Medina, S., Sánchez-Bravo, P., Domínguez-Perles, R., & García-Viguera, C. (2023). The (poly)phenolic profile of separate winery by-products reveals potential antioxidant synergies. Molecules, 28(5), 2081. https://doi.org/10.3390/molecules28052081
(5) United Nations. (2015). Sustainable Development Goals. Retrieved from https://sdgs.un.org/goals.
(6) Leal, C., et al. (2020). Potential application of grape (Vitis vinifera L.) stem extracts in the cosmetic and pharmaceutical industries: Valorization of a by-product. Industrial Crops and Products, 154, 112675. https://doi.org/10.1016/j.indcrop.2020.112675
(7) Niculescu, V. C., & Ionete, R. E. (2023). An overview on management and valorisation of winery wastes. Applied Sciences, 13(8), 5085. https://doi.org/10.3390/app13085063
Dario Dongo, lawyer and journalist, PhD in international food law, founder of WIISE (FARE - GIFT - Food Times) and Égalité.
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