ARS | Publication request: Novel approach to inhibit the growth of Aspergilus flavus and aflatoxin production by essential oil edible film

Submitted to: American Society for Microbiology General Meeting
Publication Type: Abstract Only
Publication Acceptance Date: February 28, 2011
Publication Date: N/A

Technical Abstract: The use of edible films as carriers of natural antimicrobials constitutes an approach for external protection of almonds. The films can reduce surface microbial populations and enhance oxygen-barrier in stored almonds. The first phase of this project is to screen for edible films which can inhibit the growth of Aspergillus flavus and its ability to produce aflatoxin. Methods: Edible films containing 3% of oregano oil, allspice oil, thyme oil or cinnamon oil were fabricated by using apple or tomato purees. The nor mutant of A. flavus, which produces red-orange colored colonies, was used as an indicator strain for scoring aflatoxin production. Potato dextrose agar (PDA) plate was inoculated with 50 'l of nor spores (105/ ml) using a Spiral Biotech Autoplate 4000 system. A 15 mm film disk was placed in the center of each agar plate. After incubation at 280C for 4 days, clear zones of fungal growth were measured using a digital caliper. The color of the colony at the bottom was visualized and recorded using a scanner. Results: The nor fungal colony expanded to the edge of PDA plate (100 x15 mm) and was orange-red color at the bottom. Growth of nor in the presence of cinnamon oil had a clear zone of 25mm. The surviving fungal colony was red-orange. Oregano oil inhibited the growth of nor and showed a clear zone of 10 mm but the surviving colony was colorless. Microscopic observation of the aerial part of fungal colony indicated the conidial heads were much less dense than the control colony. Allspice oil and thyme oil had similar inhibitory effect on A. flavus as described for oregano oil. Conclusion: A visual screening method for anti-fungal activity of essential oil edible films was developed. Oreganol oil was shown to inhibit both the growth and aflatoxin production of A. flavus.