Influence of abiotic factors and their interactions on aflatoxin B1 and cyclopiazonic acid co-production by strains of Aspergillus flavus isolated from corn

ASTORECA, A.; VAAMONDE, G.; DALCERO, A.; MARIN, S.; RAMOS, A.

Mendoza

Conferencia; ISM 2011 Conference: Strategies to reduce the impact of mycotoxins in Latin America in a global context'; 2011

Universidad Nacional de Río Cuarto

Influence Of Abiotic Factors And Their Interactions On Aflatoxin B1 And Cyclopiazonic Acid Co-Production By Strains Of Aspergillus flavus Isolated From Corn   Andrea L. ASTORECA*1, Graciela VAAMONDE1, Ana M. DALCERO2, Sonia S. MARIN3, Antonio J. RAMOS3.   1 Food Microbiology Laboratory, Department of Organic Chemistry, Faculty of Natural Sciences, Buenos Aires University, Campus, Buenos Aires, Argentine. 2 Mycology Laboratory, Department of Microbiology and Immunology, Faculty of Sciences, Physical Chemical and Natural, Río Cuarto National University, Argentine. 3 Food Technology Department, Lleida University, UTPV-CeRTA-CRA Rovira Roure 191, Lleida, Spain.   The objectives of this study were i) to determine the effects of the interactions of water activity (aW), temperature, incubation time and media on the co-production of aflatoxin B1 (AFB1) and cyclopiazonic acid (CPA) by strains of A. flavus with different profiles of mycotoxin production and ii) to identify the aW and temperature limiting conditions for the production of both mycotoxins. Fungi used in this study were isolated from corn used for poultry feed elaboration and selected because they belong to different chemotypes (Vaamonde et al., 2003): chemotype I (AFB1+/CPA+), III (AFB1+/CPA-) and IV (AFB1-/CPA+), respectively. Three strains (A, chemotype I; B, chemotype III and C, chemotype IV) were grown in two culture media, Czapek Yeast Extract Agar (CYA) and Corn Extract Medium (CEM), at different temperatures (10-40ºC) and aW levels (0.83-0.98). The media for each treatment were centrally needle-inoculated and sealed in polyethylene bags. AFB1 and CPA production was analyzed after 7, 14, 21 and 28 days of incubation according to the extraction methodology proposed by Bragulat et al. (2001). AFB1 and CPA determinations were performed by HPLC following the methodologies proposed by AOAC International (1995) and Da Motta & Valente Soares (2000), respectively. Significant differences were observed with respect to mycotoxin production depending on the media evaluated. The AFB1 production occurred more favourably on CYA while the highest CPA concentrations were recorded on CEM. None of the assayed mycotoxins was produced at 10 or 40ºC throughout the range of aW tested. At 15ºC and only at aW ≥0.94, low amounts of both mycotoxins were produced. Within the range of aW evaluated in this study, 0.83 was the limiting factor for both toxins production. The optimum conditions for AFB1 production occurred at 0.96 aW and 30°C after 21 days of incubation, regardless the media and isolate. The maximum CPA amounts were registered after 28 days of incubation on CEM at 0.96 aW/35°C for the strains A and C. Although different amounts of toxins were produced in each medium, the limiting and optimum conditions for their production were similar in both. No differences in the response of the three strains to the abiotic factors discussed were observed despite belonging to different chemotypes. The determination of the thresholds of mycotoxins tested co-production, especially in the case of data obtained with the corn extract medium can be useful to design control strategies of these mycotoxins in corn.   Acknowledgements: The authors are grateful to CYTED (Action 109AC0371) and Buenos Aires University for their financial support.   References: AOAC International. (1995b). Natural toxins. Official methods of analysis of AOAC international, section 990.33. Gaithersburg: AOAC International. Bragulat M.R., Abarca M.L., Cabañes F.J. (2001). Int J Food Microbiol 71:139-144. Da Motta S. & Valente Soares L.M.( 2000). Food Chem 71: 111-116. Vaamonde G., Patriarca A., Fernández Pinto V., Comerio R., Degrossi C. (2003). Int J Food Microbiol 88: 79-84.