In vitro antibacterial phenolic extracts from 'sugarbag' pot-honeys of Australian stingless bees (Tetragonula carbonaria)
J Agric Food Chem. 2014 Nov 25. [Epub ahead of print]
Australian stingless bee honeys have shown to exert antioxidant and in vitro antimicrobial properties; however their bioactive factors remained unidentified. This study investigated the antibacterial properties of phenolic extracts from Tetragonula carbonaria honeys. Honeys were harvested from beehives in three sites of South East Australia. Liquid-liquid extractions yielded the phenolic concentrates, for analyses by liquid and gas chromatography mass spectrometry. Antibacterial assays were conducted against Staphylococcus aureus and Klebsiella pneumoniae by in vitro agar diffusion and broth dilution assays. The phenolic extracts averaged to 5.87 mg/100 g of honeys, and constituents were 3-phenyllactic acid, lumichrome, di-glycosil flavonoids, norisoprenoids. The honeys did not contain methylglyoxal, dihydroxyacetone or phenolics characteristic of Leptospermum nectars. Hydrogen peroxide content amounted up to 155.8 µM in honeys. Beyond the bactericidal effects of hydrogen peroxide at 760 µM, other antibacterial factors were the phenolic extracts of 'sugarbag' honeys that were active at minimum bactericidal concentrations of 1.2 - 1.8 mg/mL.