Total phenolic and flavonoid contents, antioxidant and antibacterial activities of selected honeys against human pathogenic bacteria

Abstract

The study analyzed color intensity, the total phenolic and flavonoid contents, as well as antioxidant and antibacterial activities of honeys from Serbia. All the tested honeys contained considerable levels of phenolics. The highest phenolic content was obtained in forest honey ñ 1389.71 mg gallic acid equivalents/kg. High levels of phenolics and flavonoids were also determined in honeydew, meadow and oregano honeys. The radical scavenging activity measured by DPPH method in linden and forest honey was 0.45 and 2.75 mmol Trolox equivalents/kg, respectively. The ferric reducing potential was the greatest in forest honey ñ 6.04 mmol Fe2+/kg. Darker honeys had greater phenolic content and antioxidant activity. The antimicrobial activity of honeys against six bacterial strains isolated from human material was studied using a microwell dilution assay. The minimal inhibitory concentration of honeys ranged from 6.25% w/w (for oregano honey against Enterococcus faecalis and honeydew honey against Streptococcus pneumoniae) to > 50% w/w (meadow honey against Staphylococcus aureus). The minimal bactericidal concentration ranged from 12.5% w/w (honeydew and bee pollen enriched honey against E. faecalis) to > 50% w/w. Higher values of antimicrobial activities were found in honeydew, oregano, and forest honeys, while meadow honey showed the lowest antimicrobial activity. Analyzed honeys exhibited a strong antioxidant and broad-spectrum antibacterial activity against multidrug-resistant pathogenic bacteria. Phenolic compounds, especially in dark amber forest and honeydew honey, as well as in amber oregano honey, may contribute to their efficacy in therapeutic administration.