Antimicrobial and antioxidant activities of different solvent extracts from fermented and green honeybush (Cyclopia intermedia) plant material

Abstract

Ethnopharmacological relevance: Cyclopia intermedia is indigenous to South Africa and used to prepare honeybush herbal tea. This aromatic herbal tea has been associated with numerous health benefits, mostly based on anecdotal evidence and with very few studies reporting on the antimicrobial activities. Aim: The inhibitory effect on the growth of important nosocomialmicroorganisms and possible association with the antioxidant capacity/content of various solvent extracts of green/unfermented and fermented honeybush plant material were determined in the current study. Materials andmethods: The agar disk diffusion assaywas used as a screening assay for the antimicrobial activity of the various honeybush extracts,while the minimal inhibitory concentration (MIC) values, using the brothmicrodilution method, were determined against Streptococcus pyogenes, Staphylococcus aureus and Candida albicans. Active antimicrobial compounds were then shown using thin layer chromatography bioautography. Total antioxidant capacities and -content were also determined for each extract, while the main phenolic compounds were quantified using HPLC. Results: Six of the eight solvent extracts of honeybush showed antimicrobial activity, with the fermented and greenmethanol extracts being most effective against S. aureus and C. albicans respectively,whilst the green chloroform extract was most potent against S. pyogenes. Thin layer chromatography-bioautography acknowledged the existence of active antimicrobial fractions within these different solvent honeybush extracts. Regardless of the assay, the green honeybush extracts generally exhibited the highest antioxidant capacity when compared to the fermented honeybush. The total polyphenols were also observed to be highest in green extracts when using water and methanol as solvents. In general the mangiferin and hesperidin contents were higher in the green than the fermented extracts of honeybush plant material. Conclusions: The inhibitory activity of the various extracts against specific microorganisms was observed to be linearly proportional to the extract concentration. Although the different solvent extracts can only be considered weak antimicrobial agents, three compounds showed specific activity and should be further elucidated in future. It appears the antioxidant capacity of the various solvent herbal extracts did not relate to the antimicrobial activities; however, further work will be required to ascertain this observation. The current data also suggested that the various extracts of honeybush can be considered a good source of a unique blend of natural phytochemical antioxidants and antimicrobial compounds and should be further elucidated.