12th Government Food Analysts’ Conference (GFAC)

Theme: Food Microbiology

Antimicrobial films from Kakadu plum

Morgan Brossier1, Andrew Cusack2, David Edwards2, Michael Kelly3and Yasmina Sultanbawa4*

1Agrocampus Ouest 35000 Rennes, France ()

2Agri-Science Queensland, Department of Employment, Economic Development and Innovation, Coopers Plains, QLD 4108, Australia (, );3CSIRO, Food and Nutritional Sciences () 4Queensland Alliance for Agriculture and Food Innovation (QAAFI), The University of Queensland, Coopers Plains, QLD 4108, Australia (), *Corresponding author

Abstract

An area that is gaining importance in food safety is the development of films containing plant antimicrobials as a potential treatment to extend product storage life and reduce risk of pathogen and food spoilage organism growth on contaminated food surfaces.An extensive range of native foods is available in Australia that possesses significant health promoting and other functional properties.Kakadu plum (Terminalia ferdinandiana) is one of the native fruits indentified for its health properties. The objective of this study was to understand the potential of using Kakadu plum as a natural antimicrobial, to develop an antimicrobial filmand evaluate the antimicrobial andmechanical properties of the film. Ethanol extracts ofkakadu plum were screened for antimicrobial activity against Staphylococcus aureus and Escherichia coli using a microtitre assay. The film forming solution comprised of freeze dried Kakadu plum with caroboxymethylcelluslose (CMC) as the thickener and glycerol as the plasticizer. Batch cast films were produced using a glass plate and a 1.5 mm spacer. The tensile strength, elongation and thickness of the film were measured.Zones of inhibition in the agar diffusion test was used to determine the antimicrobial effect of Kakadu plum films against nine microorganismsnamely Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), Listeria monocytogenes, Bacillus cereus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii and Geotrichum candidum.The diffusion of the antimicrobial compounds across the agar plate was determined by High Pressure Liquid Chromatography method. Microtitre assay revealed the complete inhibition of Staphylococcus aureus and Escherichia coliat a concentration of 3.9 mg /Gallic acid equivalents(GAE) /g in the ethanol extract. Kakadu plum powder at 3%(w/w), CMC 1.5% (w/w) and glycerol 2%(w/w) were selected as the most suitable combination to be used as a wrap for food products. Antimicrobial activityof the film was most effective against Gram positive bacteria in comparison to Gram negative bacteria and had no effect on the fungus Geotrichum candidum. Out of the Gram positive bacteria Staphylococcus aureus and MRSA had the largest zones of inhibition of 23 mm and 18 mm respectively. HPLC results revealed gallic acid as one of the compounds responsible for antimicrobial activity in Kakadu plum.

This preliminary study indicates the potential of using Kakadu plum as an edible film which can be used to inhibit the growth of food related bacteria. Further studiesneed to be done to evaluate its potential as an antimicrobial edible film to extend the storage life of food products.

GFAC- Brossier et al 1