The Potential of Bunya Nut Extracts as Antibacterial Functional Food Agents

Abstract

Introduction: A.bidwillii is an endemic Australian plant traditionally used by Australian Aborigines as a food. Its nuts are known to keep well, raising the possibility that they may contain antimicrobial compounds and therefore may have value as a functional food to retard spoilage and prevent food poisoning, as well as potential medicinal antibiotic uses. Methods: A.bidwillii solvent extracts were tested for antimicrobial activity against a panel of bacteria (Aeromonas hydrophila, Alcaligenes feacalis, Bacillus cereus, Citrobacter freundii, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Pseudomonas fluorescens, Salmonella newport, Serratia marcescens, Shigella sonnei, Staphylococcus aureus, Staphylococcus epidermidis and Streptococcus pyogenes) and toxicity in vitro. Results: All extracts displayed antibacterial activity in the disc diffusion assay. The methanol extract proved to have the broadest specificity, inhibiting the growth of 8 of the 14 bacteria tested (57.1 %). The water, ethyl acetate, chloroform and hexane extracts inhibited the growth of 5 (35.7 %), 6 (42.9 %), 7 (50.0 %) and 6 (42.9 %) of the 14 bacteria tested respectively. All extracts were more effective at inhibiting the growth of Gram-negative bacteria than Gram-positive bacteria. Indeed, only the methanol extract was capable of inhibiting the growth of any of the Gram- positive bacteria, inhibiting the growth of only 1 (B. cereus) of the 4 Gram-positive bacteria tested (25%). All A. bidwillii extracts were non-toxic in the Artemia franciscana bioassay with no significant increase in mortality above that of the negative control induced by any extract at 24, 48 and 72 h. Conclusions: The lack of toxicity of the A. bidwillii extracts and their antibacterial bioactivity against a broad range of bacteria demonstrate their potential as food additives to inhibit bacterial spoilage and food borne illnesses without the need for chemical preservative addivives. Furthermore, A. bidwillii extracts also have promise as antimicrobial agents for medicinal purposes.