Grape pomaces from Spanish minority Vitis vinifera L. varieties as a valuable source of phenolic compounds

Abstract

The recovery and characterization of Spanish minority Vitis vinifera L. varieties has gained increasing relevance in enology, since it can contribute to wine diversity and typicity and may enhance resilience to climate change through differences in phenology, adaptability, and stress tolerance. On the other hand, grape pomace represents the main solid by-product of winemaking and constitutes an abundant source of bioactive compounds with technological and functional potential. Its valorization is essential within current circular economy strategies in the wine sector and key to reduce the environmental impact of wine production [1]. In this context, this work aimed at characterizing, by HPLC-DAD-MSn [2], the detailed phenolic composition (including phenolic acids, flavanol, flavonol and anthocyanins) of grape pomaces obtained as by-products in the winemaking of 8 different red and white V. vinifera grape varieties (Tempranillo, Rufete, Juan García, Mandón, Gajo Arroba, Bruñal, Verdejo and Puesta en Cruz). In addition, color intensity (I), shade (N), total polyphenol index (IPT), and Folin–Ciocalteu index were determined using the OIV methodologies but optimized for their application to grape pomaces. The technofunctional potential of the grape pomace extracts was also assessed through tristimulus colorimetry in the CIELAB space and by evaluating antioxidant capacity using FRAP and ABTS assays. The results revealed marked varietal differences in the phenolic composition among the studied varieties. Moreover, the proportions of coumaroyl-derived anthocyanins detected in grape pomaces were significantly higher than those usually observed in fresh grapes. This feature could be of special interest due to the enhanced chemical stability and distinctive chromatic properties associated with this type of pigments. Indeed, the extracts exhibited differentiated color characteristics, pointing out their potential as natural colorants that could be used, for instance, in the food industry. Furthermore, significant variability in antioxidant capacity was observed among varieties, closely related to the differences observed in their phenolic profiles. Overall, grape pomaces from Spanish minority varieties emerge as valuable sources of phenolic extracts with diverse technofunctional properties depending on varietal origin. Thus, their potential use as natural colorants or antioxidant additives may revalorize this important enological by-product.

References

1. Karastergiou, A.; Gancel, A.-L-; Jourdes, M.; Teissedre, P.-L. (2025). Transforming winemaking waste: grape pomace as a sustainable source of bioactive compounds. OENO One, 59(2).
2. Alcalde-Eon, C.; Ferreras-Charro, R.; Ferrer-Gallego, R.; Rivero, F.J.; Heredia, F.J.; Escribano-Bailón, M.T. (2019) Monitoring the effects and side-effects on wine colour and flavonoid composition of the combined post-fermentative additions of seeds and mannoproteins. Food Res. Int., 126, 108650.