Grape stalks as a source of antioxidant and antimicrobial substances and their potential application

This research project aimed to analyse the biological potential of aqueous, ethanolic, methanolic, and ethyl acetate extracts of red grape stalks, as well as lyophilised red grape stalks from Krnjevo (Serbia). The concentration of the total phenols and flavonoids, as well as the antioxidant activity of the stalk extracts were measured by means of the spectrophotometric method. In vitro antimicrobial activity of 23 selected species of microorganisms (13 species of bacteria and 10 species of fungi) was evaluated by determining the minimum inhibitory concentration (MIC) and the minimum microbicidal concentration (MMC). The results indicated that the highest concentration of total phenols was measured in the ethyl acetate extract (60.08 mg GAE/g of extract), while the highest total flavonoid concentration was observed in the acetone extract (34.24 mg RUE/g of extract). The tested extracts showed poor antioxidant activity compared to chlorogenic acid. The acetone extract probably showed the strongest antimicrobial activity due to the high concentrations of phenols and flavonoids. The tested extracts showed a better effect on Gram-positive bacteria than on Gram-negative bacteria. Although grape stalks are a by-product in the wine industry, they are a potential source of natural compounds which can be used for a variety of purposes in many fields ranging from the food industry to medicine.