Bioassay-guided evaluation of antimicrobial properties and profile of bioactive compounds from leaf, peel and mesocarp of four apple cultivars (Malus domestica Borkh.) grown in Serbia: Application of HPTLC-EDA and UHPLC Q-ToF MS techniques

The aim of this study was to evaluate the antimicrobial properties and profile of bioactive compounds from mesocarp, peel and leaves of four autochthonous apple cultivars against human pathogens, Escherichia coli, Staphylococcus aureus and Bacillus subtilis and the apple pathogen Erwinia amylovora by direct detection on HPTLC plates and subsequent chemometric analysis. UHPLC Q-ToF MS was used for detailed characterization of the bioactive compounds with antimicrobial properties. Leaf extracts showed the highest antibacterial activity against all bacterial strains, followed by peel extracts, while the mesocarp extracts showed only weak and selective inhibition zones for E. coli and B. subtillis. The apple cultivars, 'Kadumana' and 'Kopaoničanka' showed the best antimicrobial properties. The active compounds were triterpenoids, coumaroylquinic acid and caffeoylquinic acid isomers and methyl derivatives, naringenin, kaempferol and quercetin aglycones and glycosides, phloretin and its glycosides and acylated derivatives that detected for the first time in the apple leaves and fruits.