The polyphenol composition of purified extracts obtained from plum pomace gathered from production lines of a modern fruit transformation plant was characterized. The extraction of polyphenols from pomaces was performed using water. These water extracts were purified on an Amberlite polymer bed and freeze-dried. The resulting preparations were characterized by high polyphenol contents (up to 50 g/100 g) determined using spectrophotometric method with Folin–Ciocalteu reagent. The selected plum preparations were characterized by high flavanol contents (up to 10 g/100 g) and high antioxidant capacities. Additionally, significant amounts of hydroxycinnamic acids and flavonols were detected in the plum preparations. The bacteriostatic effects of the extracts were observed against Salmonella, Listeria and E. coli O157:H7. Two of the extracts had high bactericidal effects against Listeria. This research showed that plum pomaces are a good raw material for the production of highly-concentrated polyphenol preparations with potential biological properties.