Antioxidant and antilisterial activity of olive oil, cocoa and rosemary extract polyphenols

Antibacterial and antioxidant activity of polyphenols from olive oil, cocoa, and rosemary extract was tested. Antimicrobial activity against Listeria strains was assessed using broth dilution and time-kill curve methods. The 2,2-diphenyl-2-picrylhydracyl hydrate (DPPH) radical scavenging method, Folin–Ciocalteu method, and high performance liquid chromatography (HPLC) were used for phenolics identification and determination of antioxidants level. Antibacterial and antioxidant activity of main pure phenolic compounds, such as hydroxytyrosol in olive oil, epicatechin in cocoa and carnosic acid in rosemary was each compared with their extracts.Rosemary extract showed strong, while olive oil and particularly cocoa phenolic extract showed lower antilisterial activity. The overall relative antioxidant capacities of the samples were as follows in decreasing order: rosemary > cocoa > olive oil. These results indicate that rosemary, olive oil, and cocoa polyphenols could be potentially used as alternative food additives for the prevention of food spoilage, and contamination with Listeria monocytogenes.

Research highlights
► Rosemary extract shows strong antilisterial activity.
► Olive oil and cocoa phenolic extracts show lower antilisterial activity.
► Antilisterial effect of extracts is superior to the effect of their main phenolics.
► The antioxidant capacities are as follows: rosemary > cocoa > olive oil.
► Additive/synergistic effect could exist between polyphenols present in extracts.