South African food and medicinal plant extracts as potential antimicrobial food agents

Abstract

Abstract Many South African plants are used as both foods and traditional medicines for the treatment of diarrhoea and dysentery. A survey of edible plants for natural preservative/ functional food potential was undertaken on native South African plants with a history of medicinal usage. Sixty six extracts from 29 plant species were investigated for the ability to inhibit the growth of bacteria and fungi associated with food spoilage and food poisoning. Of these, 27 of the 29 plant species tested (93.1 %) inhibited the growth of at least one of the Gram-negative bacteria tested, compared with 23 of the 29 (79.3 %) plants tested inhibiting the growth of at least one Gram-positive bacterium, and seven of the 29 (24.1 %) plants tested inhibiting the growth of at least one fungal species. In general, the methanol plant extracts were better antimicrobial agents than the water extracts, as determined by the disc diffusion minimum inhibitory concentration (MIC) method. Syzygium cordatum, Terminalia pruinoides and Terminalia sericea extracts were particularly effective, with broadspectrum antimicrobial activity and MIC values generally significantly below 1000 姯ml. Extracts of these plants were generally more potent antimicrobial agents than the control antibiotics, with significantly lower MIC values. All extracts exhibiting bacterial and fungal inhibitory activity were also shown to be non-toxic, or of low toxicity in the Artemia nauplii bioassay. The low toxicity of these extracts and their inhibitory bioactivity against bacteria and fungi associated with food spoilage/poisoning indicate their potential as natural food preservatives.