Phenolic Composition and Antimicrobial and Antiquorum Sensing Activity of an Ethanolic Extract of Peels from the Apple Cultivar Annurca

This study investigated the phenolic composition and antioxidant capacity of an ethanolic extract from the peel of the Annurca (Malus domestica var. Annurca), which is widespread in the Campania region of southern Italy. The antimicrobial effect of the extract on different pathogens was also examined. The potential antiquorum sensing activity of the extract was tested by using the microorganism Chromobacterium violaceum. Ultra-performance liquid chromatography revealed that rutin, epicatechin, dicaffeoylquinic acid, and caffeic acid were the most abundant phenolic compounds in the extract; these compounds constituted 27.43%, 24.93%, 16.14%, and 15.3% of the total phenols, respectively. The test for 2,2-diphenyl-1-picryl-hydrazyl free radical-scavenging activity showed that the extract possessed an impressive antioxidant capacity (50% effective concentration of 2.50 mu g/g of product). Furthermore, the extract clearly exhibited antimicrobial activity against Bacillus cereus (11- to 14-mm diameter of inhibition halo, depending on the strain) and Escherichia coli serotype O157:H7 (10-mm diameter of inhibition halo). No activity was observed against the probiotic lactobacilli tested or against Staphylococcus aureus. Antiquorum sensing activity was reported for the first time for apple extracts. In conclusion, these results indicate the potential of this extract for treating some microbial infections through cell growth inhibition or quorum sensing antagonism, thereby validating the health benefits of apples.