Content and bioavailability of trace elements and nutrients in grape pomace

BACKGROUND: The possible agricultural use of grape pomace could be limited by the content and mobility of metals. This is influenced by many factors. In this study, the abundance and availability of heavy metals and essential nutrientswere evaluated comprehensively in different grape pomace residues from winemaking of five white and red grape varieties, before and after the distillation process. RESULTS: The total metal content found in grape pomace skins and seeds confirmed that there was greater metal accumulation in skins than in the corresponding seeds, with the exception of Ca and Mg. The enrichment of all metals (except K) during the distillation stagewas confirmed bymeans of a significant correlation (R = 0.996, P<0.001) between themetal content obtained in distilled and undistilled samples. Regarding availability, multivariate statistical analysis showed different behavior among elements, but a great similarity for metalmobility in both distilled and undistilled grape pomace samples and in both skins and seeds, except forMn, Zn andMg. CONCLUSION: The results obtained in this study suggest the potential application of these grape residues as organic fertilizers for agricultural soils, without limitations resulting fromheavy metal contamination.