Antimicrobial effect of polyphenols from apple skins on human bacterial pathogens

Apples possess many beneficial properties for the human health related with their high content in phenolic compounds. The antimicrobial effect of these compounds from the skin of two apple varieties, Royal Gala and Granny Smith, against human pathogens was examined. The phenolic compounds were extracted with the following solvents: A, acetone: water: acetic acid; B, ethyl acetate: methanol: water and C, ethanol: water. Total phenolic, flavonoid and non-flavonoid contents were analyzed in the extracts. The antimicrobial effect was determined using the agar diffusion method. The highest inhibitory effect of both apple varieties corresponded to extract A, which contained a high phenolic content. The Granny Smith extracts with higher phenolic content presented a superior antimicrobial effect against the selected microorganisms: Escherichia coli, Escherichia coli ATCC 25922, Escherichia coli ATCC 35218, Staphylococcus aureus ATCC 25923, Staphylococcus aureus ATCC 29213, Pseudomonas aeruginosa ATCC 27853, Enterococcus faecalis ATCC 29212 and Listeria monocytogenes. The most sensitive microorganisms were Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853 and Staphylococcus aureus ATCC 29213, whereas the most resistant strains were Escherichia coli ATCC 35218 and Escherichia coli. The results obtained demonstrate a direct relationship between the phenolic content of the extracts and the antimicrobial effect.