The wine industry produces large amounts of residues, which has an impact on the environment and whose management is a problem. These residues possesses high content of polyphenolic antioxidant and antimicrobial compounds, which can be used for inhibiting the growth of pathogenic microorganisms. This would result in an added value of these by-products.

The objective of this work was to study the antioxidant and the antimicrobial activities of extracts of the main vinification by-products: grape pomace, seeds and stems, from Vitis vinifera L., Tempranillo variety, obtained by two different methods of extraction: accelerated solvent extraction (ASE) and ultrasound assisted extraction (UAE), both methods using green solvents.

Determination of the total polyphenol content was performed by the Folin-Ciocalteu and the antioxidant capacity was evaluated by the method of capturing free radicals using the DPPH radical (2,2-diphenyl-1-picrylhydrazyl) and by the method of the inhibitory activity of the ABTS radical cation (2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid). Inhibition of microbial growth by the extracts was determined by the microtiter dilution method, using serial double dilutions of the antimicrobial agents, with concentrations varying from 0.06 to 30.0 g/L.

Bacterial growth was determined by optical density at 630 nm. MIC₅₀ and MIC₉₀ were defined as the minimal inhibitory concentration that inhibited 50% and 90%, respectively, of the tested microorganisms. Both extraction techniques showed to be very efficient in the recovery of polyphenol compounds with antioxidant activity from winery residues.

All the extracts showed moderate antimicrobial activity, against the three bacterial strains tested, with values of MIC₅₀ comprised between 0.47 g/L and 15 g/L, and values of MIC₉₀ between 0.06 and 30 g/L. It was observed a higher antimicrobial activity for extracts obtained by UAE as compared to ASE extracts. This study points out the potential of these by-products for being used as natural preservatives in foods.