| Περίληψη: | Phenols are compounds with high antioxidant activity. They are common in nature, mainly found in plants, where they may act as pigments or part of defense mechanisms against herbivores. Due to their positive effects on human health, their isolation from agricultural byproducts for the production of cosmetic products and food supplements is of great interest. In this thesis, four plant materials or byproducts were examined, rich in phenolic compounds, for the separation of their phenolic content and its concentration through physicochemical methods like solid-liquid extraction, membrane filtration, resin adsorption/desorption and vacuum evaporation. The materials examined were olive mill wastewater, cocoa powder, grape marc and olive leaves. For the solid materials (cocoa powder, grape marc and olive leaves), initially, optimization of the extraction of their phenolic content was carried out, with the use of hydro-ethanolic mixtures, regarding solvent composition, extraction duration and solid/solvent ratio. Then, the extracts and olive mill wastewater were filtrated through ultrafiltration, nanofiltration and reverse osmosis in line, for the separation of their content according to molecular weight. For the removal of non-polar compounds with similar molecular weight with phenols from the most suitable fraction occurring from membrane filtration, resin adsorption/desorption was applied. The resin processes consisted of three stages in line, adsorption, desorption of carbohydrates with the use of water and finally desorption of phenols with the use of ethanol, with the final products being ethanol solutions, rich in phenolic compounds. Finally, ethanol was recycled through vacuum evaporation. The final concentrate of olive mill wastewater contained 378 g/L phenols in gallic acid equivalents and 84.8 g/L hydroxytyrosol, the final concentrate of grape marc contained 190 g/L phenols in gallic acid equivalents and 4.7 g/L catechin and the final concentrate of olive leaf extract contained 98 g/L phenols in gallic acid equivalents.
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