Stability of phenolic compounds in grape stem extracts

Grape stem is rich in phenolic compounds, especially stilbenes. These antioxidants can be degraded during the storage of grape stem extracts for long periods of time. The aim of this work was to analyze the stability of Mazuelo stem extracts during storage at 25 and 40◦C, in two different light conditions (amber and transparent vials). The stability of the antioxidants was studied after 2, 4 and 6 months of conservation. Gallic acid and the quercetin derivative concentration were stable throughout the storage period. In contrast, catechin disappeared from all the extracts in just two months of storage. Anthocyanins were significantly affected by temperature, and light enhanced their degradation when the extracts were kept at 40◦C. Resveratrol and viniferin showed a similar behavior. Their concentration decreased from the beginning of storage, and in both cases, they were significantly affected by both temperature and light.This research was funded by the Government of Navarra, grant numbers VARASVI PI022 and PI038.This research was funded by the GOVERNMENT OF NAVARRA, grant numbers VARASVI PI022 and PI038

Reducing SO₂ doses in red wines by using grape stem extracts as antioxidants

SO₂ is a very important wine preservative. However, there are several drawbacks associated with the use of SO₂ in wine. The aim of this work is to evaluate the effect of the partial substitution of SO₂ in the Tempranillo wine by a Mazuelo grape stem extract and by a commercial vine wood extract (Vinetan®). The results were compared with a control sample (with no addition of any extract). After 12 months of storage in a bottle, total anthocyanin content, together with total polyphenol and flavonoid content were slightly higher for control wines than for those treated with extracts. These differences were of little relevance, as no differences in antioxidant activity were found between any of the wines at the end of the study. The sensory analysis revealed that the use of both extracts as partial substitutes of SO₂ could lead to wines with good organoleptic properties, similar or even better to the control ones.This research was funded by the Government of Navarra, grant numbers VARASVI PI022 and PI038.This research was funded by the Government of Navarra, grant numbers VARASVI PI022 and PI038