The wine industry generates vast amounts of by-products, and grape stems are often discarded as waste. However, a recent study titled “Grape stems as sources of tryptophan and selenium: Functional properties and antioxidant potential” shed light on the untapped potential of these by-products. Conducted by researchers examining grape stems from the renowned Douro Demarcated Region in Portugal, the study reveals that these overlooked materials are rich in bioactive compounds with potential applications in nutrition, health, and sustainability.
From Waste to Wellness: Bioactive Compounds in Grape Stems
Traditionally seen as a by-product of wine production, grape stems are now emerging as valuable sources of key nutrients. This study analyzed four red grape stem varieties—Tinta Amarela, Sousão, Touriga Franca, and Touriga Nacional—and discovered that these stems contain significant levels of selenium, tryptophan, and various phenolic compounds. Among these, Touriga Nacional stood out for its exceptionally high levels of selenium and polyphenols and antioxidant capacity, while both Tinta Amarela and Touriga Nacional exhibited elevated tryptophan levels.
Grape and stem morphology and composition. Adapted from (Blackford et al., 2021).
A Rich Source of Health-Boosting Compounds
Grape stems contain a variety of phenolic compounds, including proanthocyanidins, phenolic acids, flavonols, and anthocyanins. These compounds are known for their antioxidant properties, which help combat oxidative stress, an underlying factor in aging and many chronic diseases. The strong correlation between the polyphenolic content and antioxidant capacity, particularly in Touriga Nacional, underscores the potential health benefits of incorporating grape stem-derived compounds into dietary supplements and functional foods. Moreover, the presence of tryptophan, an essential amino acid, suggests its potential applications in cognitive health and mood regulation. Tryptophan is a precursor of serotonin and melatonin, which play crucial roles in mental well-being, sleep regulation, and protein synthesis.
Beyond the health benefits, this study supports the valorization of grape stems as a means of reducing waste, creating new revenue streams, and promoting a circular economy in the wine industry. By repurposing grape stems, wineries can enhance sustainability, while simultaneously exploring innovative applications in nutraceuticals and food science. This approach aligns with the broader goals of reducing the environmental impact and maximizing the use of agricultural resources.
Scientific Rigor Behind the Findings
To quantify selenium and tryptophan content, researchers employed precise analytical methods:
- Selenium Determination: A fluorometric reaction with 2,3-diaminonaphthalene (DAN) following nitric acid/hydrogen peroxide digestion allowed accurate quantification.
Selenium content in four grape stems from the Douro Demarcated Region (μg/kg dw) (n = 3 for each sample). Bars with different letters correspond to significant differences between varieties (p < 0.05), according to the analysis of variance (ANOVA) followed by a post hoc Tukey’s test. dw: Dry weight, Se: Selenium.
- Tryptophan Quantification: Ultra-high performance liquid chromatography coupled with mass spectrometry (UHPLC-ESI-QqQ-MS/MS) was used to extract, derivatize, and analyze free amino acids, ensuring precise measurement. These methodologies ensure the reliability of the study’s findings and lay the groundwork for future research on the bioavailability and health impacts of these compounds.
Tryptophan content in four grape stems from the Douro Demarcated Region (mg/kg dw) (n = 3 for each sample). Bars with different letters correspond to significant differences between varieties (p < 0.05), according to the analysis of variance (ANOVA) followed by a post hoc Tukey’s test. dw: Dry weight, Trp: Tryptophan.
Challenges and Future Research Directions
Although the potential of grape stems is promising, several challenges must be addressed for their widespread use. Extraction and Processing: Efficient and cost-effective methods for extracting bioactive compounds on an industrial scale need to be developed.
- Regulatory Approval: Ensuring compliance with food safety and pharmaceutical regulations is essential before introducing commercial products.
- Market Acceptance: Consumer education is needed to overcome skepticism about products derived from wine industry waste.
- Scalability: Further research is required to determine how bioactive compound levels vary across grape varieties and growth conditions.
- Competitive Positioning: Grape stem-derived products must compete with the existing sources of antioxidants and amino acids in the nutraceutical market.
Moving Forward: A Vision for the Future
- To capitalize on these findings, wineries and researchers should focus on:
- Product Development: Integrating grape stem extracts into functional foods, dietary supplements, and cosmetics.
- Collaboration: Partnering with health professionals and food scientists to validate and promote the benefits of grape stem-derived compounds.
- Consumer Education: Communicating the sustainability and health advantages of these products through storytelling and transparency.
- Investment in Innovation: Supporting research on the bioavailability and long-term health effects of grape stem compounds.
This study marks a significant step toward transforming grape stems from waste into a valuable resource for human health and environmental sustainability. By harnessing the bioactive potential of grape stems, the wine industry can play a pioneering role in sustainable agriculture, circular economic initiatives, and the development of novel functional foods. As research continues to unveil the benefits of these compounds, we may soon see grape stem-derived products making their way into mainstream health and wellness markets.
Read all at: 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, 102260.https://doi.org/10.1016/j.fochx.2025.102260