Antimicrobial activity of phenolic extracts from olive leaves and grape skins and seeds - impact of encapsulation

Olive leaves and grape skin with seeds produced as by-products in olive oil and wine production constitute a cheap source of plant material with certain amount of bio-active substances. Antioxidant, antimicrobial, anti-inflammatory and anticancer properties of the phenolic extracts were reported. The efficiency of extracts depends also on the ability to preserve their biological activity. Encapsulation of the extracts can improve stability, biological availability, hydrophobic/hydrophilic character and unpleasant taste for potential use in food preservation. Antimicrobial activity was first screened by broth microdilution method for minimal inhibitory concentrations (MICs) of phenolic extracts from olive leaves (Olea europaea, cv. ―Leccino‖) and grape skins and seeds (Vitis vinifera L., cv. ―Zelen‖) against 14 strains of Candida, Pichia and Ogataea sp., which were isolated from spoiled olive oil, and Dekkera bruxellensis from spoiled grape must. The kinetics of antifungal activity was followed by the yeast inhibition curves in YPD medium with phenolic extracts added in MICs. Finally, the impact of extract encapsulation into ß-cyclodextrin and liposomes on antifungal activity was tested. Phenolic extracts from olive leaves and grape skins with seeds expressed high efficiency against most isolates of spoilage yeasts. Encapsulated olive leaves extracts showed the same or better efficiency than non-encapsulated extracts in broth microdilution screening test and during yeast growth inhibition in liquid medium. The encapsulation into ß-cyclodextrin was more efficient than encapsulation into liposomes. Grape skins and seeds and olive leaves as plant waste materials have been proven to be a rich source of phenolic compounds with antimicrobial activity against spoilage yeasts.