An examination of the anti-bacterial, anti-fungal and anti-Giardial properties of macadamia nut

Abstract

Macadamia integriflora (family Proteaceae) is an endemic Australian plant that has been used for thousands of years as a food. Its nuts are known to store well, raising the possibility that they may contain antimicrobial compounds and therefore may have value as a functional food, able retard food spoilage and prevent food poisoning and other food-borne diseases. M. integriflora extracts were investigated for their ability to inhibit the growth of a panel of bacteria and fungi of importance to food spoilage and food poisoning, as well as the gastro-intestinal protozoal parasite Giardia duodenalis. All extracts displayed broad spectrum antimicrobial activity, each inhibiting the growth of 7 of the 18 bacterial species tested (39%). In contrast, none of the fungal species were inhibited by these extracts. Strong inhibitory activity was detected with minimum inhibitory concentration (MIC) values as low as 8.0 µg mL-1 against some bacteria, although most measured MICs were generally several orders of magnitude higher. All extracts inhibited 54% of the Gram negative bacteria tested and none of the Gram positive bacteria. All extracts were also effective in inhibiting the gastrointestinal protozoal parasite G. duodenalis, yet were non-toxic in the Artemia franciscana bioassay. The inhibitory bioactivity against a range of microbes as well as the lack of toxicity indicates the potential for macadamia nuts in the discovery and development of new natural food preservatives and pharmaceuticals.